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A Report of the Workshop entitled “Recent Biogeochemical Changes in the
Biogeochemistry of the Great Lakes System (BOGLS)”
Contributions of the BOGLS Steering Committee along with participants of
the Workshop and Community Forums at IAGLR and Goldschmidt2013.
Edited by:
Mark Baskaran, Department of Geology, Wayne State University, Detroit, MI-48202; and
John Bratton, Great Lakes Environmental Research Laboratory, NOAA, Ann Arbor, MI-48108
Steering Committee:
James Bauer (Ohio State), Ruth Blake (Yale U), Robert Hecky (U. Minnesota-Duluth), Norman
Grannemann (USGS), J. Val Klump (U. Wisconsin-Milwaukee), Lawrence Lemke (Wayne
State), Nathaniel Ostrom (Michigan State) and Thomas Johnson (U. Illinois, Urbana-
Champaign)
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Final Report
Executive Summary:
The pelagic and benthic food webs and associated elemental cycles in the Laurentian
Great Lakes have undergone major perturbation over the past 30 years due to factors such as
nutrient abatement and introduction of invasive species (zebra and quagga mussels). Such
human-induced alterations (directly or indirectly) provide a unique opportunity to document how
this natural system has responded and would respond to other such large-scale alterations in the
ecosystem. Thus, the Great Lakes System (GLS) could serve as a ‘model laboratory’ to quantify
biogeochemical changes caused by humans. The changes in the terrestrial ecosystem and
bordering wetlands influence the fundamental biogeochemical processes that take place in the
lakes where complex interactions between the adjoining terrestrial environments with that in the
aquatic system are integrated. Approximately 37 million people live in the Great Lakes basin
with 26 million people relying on the Great Lakes for their drinking water. The water quality has
direct impact not only on human health but also on jobs in agriculture, fisheries, manufacturing,
shipping, and tourism. In order to assess the scientific needs for process-oriented research in the
changes caused by the directly or indirectly human-induced perturbations, a three-day (March
11-13, 2013) workshop was held at Wayne State University, Detroit, Michigan. Sixty scientists
mostly from across the Great Lakes states representing 17 universities, five federal agencies,
among others, with expertise spanning a spectrum of research areas including nutrients and
carbon cycling, key trace elements and isotopes as biogeochemical tracers, geo- and
radiochemistry, ecology, hydrogeology, physical oceanography, modeling, remote sensing, and
climate change, gathered and discussed the state of the Great Lakes system.
The community identified a number of major changes that have taken place recently in
the Laurentian Great Lakes that are remarkable in their scope and speed. The community
recognized the urgent need for a long-term process-oriented study coupled with modeling to
evaluate ecosystem changes in the Great Lakes system. Food webs in the lower lakes have
undergone drastic changes from the expansion of dreissenid mussels, a process that occurred in <
30 years and accelerated greatly in the last 10-15 years. The reengineered ecosystem caused by
the dreissenid mussels has resulted in a ‘benthification’ of the system at the apparent expense of
pelagic food chains. Drastic decline in the abundance of diatoms, zooplankton, benthic
amphipods, forage fish and top piscivorous population have been reported, including ~95%
population decrease of benthic amphipod Diporiea. Filtration of water by dreissenids had
resulted in water clarity exceeding 20 m secchi depths in Lakes Huron and Michigan, which in
turn has resulted in the triggering of resurgence of the submerged macrophyte, Cladophora, in
the near-shore causing fouling of beaches throughout the lakes by decaying algal mats. The
pelagic primary production in Lake Michigan has decreased by ~70% and other winter and
spring blooms have largely disappeared.
The lakes are highly sensitive to climate change, particularly their hydrology (water
levels), radiation budgets, stratification and atmospheric forcing. Decrease in areal extent,
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thickness and duration of the ice cover, increase in water temperature and the increase in
frequency of extreme weather events (resulting in changes in the riverine loading of key macro-
and micro-nutrients) have been reported. Summertime thermal stratification is predicted to
increase in duration by several weeks, exacerbating issues of hypoxia, benthic metabolism and
diagenesis, thermal habitat changes, and the timing of long standing ecological phenomena.
Climate change is expected to have a significant impact on regional climate such as changes in
‘lake effect’ precipitation. The recent climate change is felt faster in L. Superior than in many
coastal ocean areas.
The concentrations and stoichiometric ratios of key nutrients have been considerably
altered during the past century. For example, there has been a net accumulation of nitrate over
the past hundred years in Lake Superior which is reported to have an imbalance in NO3-/PO4
3-
ratios (as high as ~10,000). The factors and processes that lead to these alterations in
stoichiometric ratios in different lakes of the Great Lakes system are not fully understood. While
the chemical reactions (nitrification, denitrification and anammox) are expected to be slower in
Lake Superior due to cooler waters compared to Lakes Michigan, Huron, Erie, and Ontario, other
factors that control N, C and P cycling, N assimilation, and microbial community structure are
not well studied in all the Great Lakes. The degree to which changes result from increases in
external sources discharged to the lakes (rivers/streams, atmospheric deposition, submarine
groundwater discharge), or active in-lake processes (such as nitrification/denitrification,
anammox) is not understood. Despite active removal of PO43-
, Ca2+
, and key bio-limited
elements in the lower lakes and Lake Michigan by dreissenids, answers to questions such as how
the NO3-/PO4
3- ratios have changed the cycling of organic carbon and other micro-nutrients in
lakes that are severely impacted remains unknown.
The inland freshwater seas are similar to marine systems in several respects and are
unique as well. Many of the dominant physical processes are large scale, such as circulation
(affected by the Earth’s rotation), atmospheric forcing mechanisms, upwelling/downwelling,
seiches and internal motions, etc. Ecologically they are young (~10 kyr) with relatively simple
food webs and low biodiversity. This produces an extreme susceptibility to invasion and
perturbation by non-native species.
Lake-wide simultaneous measurements of primary production (PP) and grazing rates in
most lakes are lacking; thus, gaps in our understanding of the cycling of N, P, and Si and their
link to other key micro-nutrients exist. Lack of data during the cooler periods and deeper waters
fuels the uncertainty in PP and grazing estimates. Estimates of PP and respiration rates due to
scaling factors are less reliable due to limited data (or lack of data) during winter months and
from deeper waters.
The key micronutrients such as Fe play a critical role in nitrate utilization by plankton
and thus, the cycling of Fe, Cu, Zn, Cd, Se, V, Mo, Ni, Co are important. Newly-emerging
modern isotope tools could serve as powerful tools in quantifying the sources, pathways and
transport of these micronutrients. The horizontal and vertical transport of key macro- and micro
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nutrients can be investigated using a set of radioactive tracers. Sinkhole vents in some of the
lakes offer a unique opportunity to probe how novel microbial communities adapt and thrive in
extreme environments.
A concerted and focused research effort will provide new knowledge and improve our
fundamental understanding of the processes and yield answers to several key questions. Much of
the historical understanding of the ecology and biogeochemistry of the lakes, while relevant and
informative, is often no longer operative or has been altered in significant ways. At the same
time, the lakes have been the subject of improved physical modeling and forecasting systems and
expanding observing platforms under U.S. Integrated Ocean Observing System (IOOS). The
breadth of our collective knowledge of these closed systems provides a significant baseline on
which to build improved ecological and biogeochemical process models. Both their similarities
and their differences provide opportunities to study fundamental ecological/biogeochemical
dynamics across time and space scales that are relevant to many aquatic systems, from coastal
bays and gulfs, to semi-enclosed seas and estuaries. New and novel approaches, tools, and
analytical techniques are also now available that are ideal for process-oriented research on these
scales.
This report summarizes number of driving questions, gaps and opportunities for future
inquiry that would substantially improve our understanding and ability to sustainably manage
these and similar aquatic systems.
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1. Introduction to the Great Lakes and their Recent History:
1.1 Introduction to the Great Lakes System:
The largest freshwater seas of the world (244,000 km2), the Laurentian Great Lakes
System, has undergone major biogeochemical changes over the past 3 decades due to
anthropogenic activities such as nutrient abatement, introduction of invasive species and human-
induced climate change. Approximately 37 million (11.8% of US population) people live in the
Great Lakes basin of which about 8% of the United States total population relies on the Great
Lakes for their drinking water. The water quality has direct impact not only on humans but also
the economic activity and vitality of the 8 states that adjoin these lakes.
The Great Lake system is similar to oceans in terms of large scale water mass circulation
pattern, discrete coastal zones, shelf breaks and deep basins, yet this system is bounded
physically with constrainable inputs and outputs in the mass balance of micro- and macro
nutrients, carbon and other radionuclides and tracers. In terms of size, these lakes are
intermediate in scale between common lakes and oceans and are complex integrators of
watershed changes, biology, biogeochemistry and regional environmental and climate change
making these systems unique and attractive for tracking how changes, many anthropogenically
induced, reverberate through the system. Relative to more saline waters or ocean basins, the
forces controlling the mixing of water masses are, in some cases, weak or absent (e.g. tidal
currents), and in some cases stronger (e.g. isothermal mixing). Nutrient concentrations range
from hyper-oligotrophic (the P concentrations in Lake Superior are lower than the central North
Pacific gyre) to hyper-eutrophic and nutrient limitation is both complex and varied (Sterner et al.,
2004; Duhamel et al., 2011). This wide range of conditions is embedded within a system that is
logistically accessible to analysis at the appropriate density, geochemically and geologically
similar, but not uniform. Important internal differences, e.g. in residence times, physical
chemistry, loadings, etc. are known and changes are occurring with a speed which is easily
measurable on a scale of years. Thus, the diversity of water depths, differences in the
hydrological residence times, temperature differences and diversity in biota in these five
freshwater inland seas provide an unparalleled opportunity for focused research on the
responsiveness of biogeochemical cycles to human-induced perturbations in ecosystem
properties in semi-enclosed systems (Table 1).
1.2 Recent Rapid Changes in the
Biogeochemistry of the Great Lakes
System:
Historically, changes in the
biogeochemistry of the Great Lakes have
Figure 1: Long-term trends of major ions for
the Great Lakes (Chapra et al., 2012)
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responded rapidly to external stress. The first
acceleration in biogeochemical changes in the
Great Lakes was observed in changes in the
concentrations of major ions in the early to middle
part of the 20th
century (Beeton, 1965) (Figure 1).
The common stressors among great lakes (and many
small lakes as well) include: i) eutrophication, ii)
fisheries exploitation; iii) exotic species; iv)
contaminants; and v) climate change. The major
milestones in the alterations of major nutrients to the
Great Lakes system included: 1950s to 1970:
increases in P loading to the lakes; 1972 to 1990:
mandated P reductions resulting in water quality
improvements (lower P, Chl and fewer algal blooms); 1988-1997: dreissenid mussels invasion
and colonization of all lakes (except Lake Superior), first zebra mussels in shallow regions and
then quagga mussels in deeper water; and 2000-2010: quagga mussel populations explode in
profundal regions of all lakes, except Lake Superior; 1980-present: a warmer, wetter climate.
Excessive nutrients loading from pulse events (e.g., excessive rains over a short period of
time discharging a large amount of nutrients) from the watershed have resulted in eutrophication
in some of the lakes. The implementation of the Clean Water Act
resulted in significant reduction in loading of nutrients that
generated improvements in water quality in tributaries and open
waters throughout the lower lakes, in particular. Yet,
eutrophication remains an issue with some of the most extensive
algal blooms ever observed in some of the lakes. For example, in
2011, ~10% of the surface area of Lake Erie (~2.5 x 103 km
2) was
covered with bloom concentrations, a historical record. This
occurrence is hypothesized to be the consequence of a complex
interactions among climate, invasive species, and changing land
use practices (Figure 2), and is indicative of how quickly the system can revert to an apparently
“previous state” under entirely new conditions.
The rapid, extensive colonization and reengineering of the lower Great Lakes by
dreissenid mussels in the last 20-30 years fundamentally altered the cycling of biogeochemically
important materials with a speed and magnitude which is remarkable even for the Great Lakes
that has resulted arguably in the largest biogeochemical shift in the lakes in recent history
(Hecky et al., 2004), despite the long history with nearly 200 non-native invaders (Figures 3, 4).
This directly and indirectly human-induced large-scale perturbation is an example of an
opportunity to investigate the response of a large land-margin ecosystem which integrates
complex interactions among terrestrial, atmospheric and aquatic components.
Table 1: Ratio of terrestrial catchment (CA) to lake area (LA), mean depth, hydrologic residence time (WRT) and mean nitrate concentration in major lakes in the world (Bootsma and Hecky, 2003; Weiss, 1991) Lake CA/LA Mean
Depth (m)
WRT (y)
NO3-
(mol/L)
Superior 1.6 148 191 20
Michigan 1.6 84 99 12
Huron 2.1 61 22 20
Ontario 3.4 86 6 16
Erie 2.3 18 2.6 18
Baikal 12.1 730 327 7
Great Bear
5 72 131 10
Victoria 2.8 40 123 < 0.5
Figure 2: The largest algal
bloom ever recorded in Lake
Erie was observed in 2011
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1.3 Contrasts in the Biogeochemistry Between all
Five Lakes:
The highly varying inputs of nutrients
among the five lakes, contrasting regeneration of
macro- and micro nutrients due to highly differing
mean
water
depths, hydrological residence times (Quinn, 1992),
and mean annual surface temperatures make each of these lakes unique resulting in differences in
the biogeochemical cycling of nutrients within these five lakes. Influence of internal recycling in
lakes generally is a function of hydrological residence time both on scale of whole lakes as well as locally
within lakes while influence of external loading is associated with the ratio of catchment area to lake area
(CA/LA). The values of CA/LA ratios are given for all five lakes in Table 1, Fig. 5. The annual
mixing of nutrients from the deep water, which is the primary source of nutrients supporting new
production for the deep waters in the lake, can vary substantially from lake to lake and from year
to year due to differences in the vertical mixing of waters (Dymond et al., 1996; Hecky et al.,
1996). The hydrodynamical regimes of the five lakes are not the same. There are striking
contrasts, in terms of ecological status, between the five lakes in the Great Lakes system. A
large and predictable hypoxic zone in Lake Erie, differences in the trophic states from ultra-
oligotrophic (Superior) to hyper-eutrophic (Sandusky Bay, Lake Erie), eutropic to oligotrophic
conditions in Lake Erie, and marked differences in the response to recent climate change in
different lakes (e.g., such as Lake Superior warming at twice the rate of the atmosphere), are
some of the special features of the Great Lakes system. Due to the size of the lakes, the changes
caused by changing climate will be expressed sooner and can be more easily quantified in the
Great Lakes than in the oceans and they may be harbingers of climate change impacts, but not an
indicator of the direction of those changes in the oceans.
Figure 3: Temporal evolution of aquatic
non-native species in the Great Lakes
over 150 years.
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Pre-mussel:
The input of
Figure 4: Changes in the P loading in lakes that are reengineered by zebra mussels. The differences in the
thickness of the arrows indicate the changes taken from pre-mussel to post-mussel periods (From Hecky
et al., 2004).
Post-mussel:
Figure 5: Depths of Lakes and major rivers in the Great Lakes
system
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anthropogenically induced external loading of nutrients to the lake primarily depends on the
population density in the watershed surrounding the lake. The population density in the
watershed surrounding Lake Superior is the lowest and thus, the input of nutrients from sources
such as sewage and fertilizer are relatively minor. Lake Superior is reported to have a century-
long buildup of NO3- such that nitrate is far in excess of P, with a NO
3/PO4
3- molar ratio in deep-
water of 10,000, more than 600 times the mean requirement ratio for primary producers (Sterner
et al., 2007), but the temporal variations for other lakes are less known. The low rates of primary
production coupled with low watershed inputs of organic C input and low OC burial rates to
sediments limit rates of nitrate removal by denitrification in Lake Superior (Johnson et al., 1982;
2012; Finlay et al., 2007). Rates of N cycling processes in the Great Lakes, however, are nearly
lacking thus while changes in nitrate are apparent, the precise causes remain elusive. The
concentrations of dissolved organic carbon vary widely, from about 100 M in Lake Superior to
about ~400 M in Huron, Michigan, Erie and Ontario (Waples et al., 2008). The primary
productivity is the lowest in Lake Superior (12-25 mmol C m-2
d-1
) and highest in Lake Erie (73-
84 mmol C m-2
d-1
; Kumar et al., 2008; Sterner, 2010).
2. Rapid and Unexpected Recent Changes in the Large Lake System:
The major drivers of ecosystem change are changes in the flow of macro- and micro-
nutrients. The overall loadings of phosphorus to the Great Lakes have decreased due to a
combination of regulations to reduce point source loadings and improved agricultural practices to
reduce nonpoint source loadings (e.g., Bertram, 1993; DePinto et al., 1986). For example,
between 1970 and 1990, the total loading of phosphorus to Lake Michigan from point and non-
point sources (such as streams/rivers/tributaries, atmospheric and point sources) decreased by
50% (Miller et al., 2000) and such reductions in the loading of phosphorus have resulted in the
decrease in the turbidity and algal blooms in the lake’s water column and increases in the clarity,
light penetration, and dissolved oxygen, while the introduction of invasive species in late 1980s
(such as zebra and quagga mussels) have bioengineered this ecosystem. The patterns of turbidity
in Lake Erie during 1980s and early 2000s were reported to have been altered with near-shore
waters often clearer than offshore waters whereas in the western and central basin of the lake
there were increases during this period (Cha et al., 2011). Such an increase in clarity has resulted
in deepening of euphotic zone which allows biota to have better access to the nutrient-rich
deeper water in stratified season (Barbiero and Tuchman, 2004). Earlier studies have
documented large changes in productivity and diatom abundance at two stations in Lake Erie,
although lake-wide data is not available (Saxton et al., 2012).
The spread of invasive mussels has led concomitantly to alterations in nutrient ratios
(e.g., C/N and P/N ratios), increased water clarity, and hardening of formerly soft substrates over
large areas, all with implications for shifts in the biogeochemical cycling of both major and
minor elements (Fig. 1). These changes have resulted in the alterations of pelagic and benthic
food webs and associated elemental cycles. In the near-shore areas of Lakes Huron, Erie, and
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Ontario, significant decreases in the
concentrations of P, phytoplankton,
and chlorophyll and Chl-a/P ratios
coincided with the establishment of
dreissenid zebra mussels and later
quagga mussels (e.g., Fahnenstiel et
al., 1995; Nicholls et al., 2002). For
example, less dissolved P in the
water column, either from the
abatement of P loading to lakes or
removal of particulate P from the
near-shore water column by filter-feeding mussels, led to decreased pelagic productivity,
increased benthic macroalgal productivity in littoral waters, less organic material ultimately
settling to the bottom and thus less available materials and energy for benthic communities
(Eberts and George, 2001; Nalepa et al., 2007). Diatoms, once a dominant component of the
spring bloom during the isothermal mixing period, have been significantly reduced in abundance,
resulting in disappearance of the spring phytoplankton bloom in Lake Michigan and dramatic
decreases in some zooplankton species (Figure 6, Vanderploeg et al., 2010, Kerfoot et al., 2010).
Chlorophyll a, phytoplankton carbon biomass, and water column primary production decreased
66%, 87%, and 70%, respectively, in Lake Michigan during 2007-08 as compared to 1995-98
(Fahnenstiel et al., 2010). These changes have affected the annual biogeochemical cycling of
nutrients and carbon as well (Mida et al., 2010). Prior to this shift, dissolved silica uptake during
the spring bloom lowered silica concentrations to near zero (a few molar). Subsequent diatom
settling, dissolution and silica regeneration resulted in an annual cycle of depletion and
regeneration. Annually about 20% of the silica deposited was ultimately buried, with the
remainder recycled back into the overlying water during isothermal conditions. Today, silica
concentrations drop by less than half of their winter seasonal maximum, i.e. dissolved silica
uptake has been significantly reduced in a shift that has been termed “incidental
oligotrophication” (Evans et al., 2011). Gradual increases in spring silica concentration in all
basins of Lakes Michigan and Huron between 1983 and 2008 have been recently reported
(Barbiero et al., 2006; Evans et al., 2011). This shift has transferred nutrients and energy from
the pelagic system to the benthic system in the form of an expanding population of quagga
mussels throughout the lake. The consequences of these changes on the nutrient and energy flow
for benthic carbon metabolism are unknown, but likely dramatic. Since Si is required by
diatoms, the depletion of Si can be used as a measure of diatom and phytoplankton production.
The silica drawdown in lakes Michigan, Huron and Superior is compared in Figure 9. It has been
reported that after the invasion of quagga mussels, there was much less consumption of silica
Year
75 80 85 90 95
Pri
mar
y P
rodu
ctio
n (m
g/m
2/d)
0
200
400
600
800
1000
1200
Saginaw Bay Primary Producers After Zebra Mussels
Zebra Mussels
Benthic Algae (450 mg/m2/d)
Phytoplankton
Figure 6: Drastic decrease in the primary productivity after the
invasion of zebra mussels in Lake Superior
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during winter-spring. A widespread observed decline of Ca in lake waters and was attributed to
the reduction in the
exchangeable Ca
concentration in
catchment soils (Jeziorski
et al., 2008). Such
reduction is caused by a
number of factors that
include acidic deposition,
reduction in atmospheric
deposition of Ca, Ca loss
from forest biomass
harvesting (Jeziorski et
al., 2008). It has been shown that the dreissenids have caused decreases in Ca and
lower lakes due to calcification in producing shells (Chapra et al., 2012). It is estimated that
alkalinity concentrations in decline in Ca due to mussels would reduce soluble reactive
0
0.2
0.4
0.6
1980 1990 2000 2010
Silic
a u
tiliz
atio
n
(mg
/l)
Figure 7: closed symbols, northern basin; Open symbols: southern basin
(data from EPA_GLNPO).
Figure 8: Total P loading reductions exceeded the target. The standard errors vary from 1.5 to 19% of the total lake
load depending on the lake and the year. Lake Superior typically has larger standard errors (9.1% of the load, on
average), while Lake Erie has some of the smallest estimates (3.5% of the average load).
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phosphorus (SRP) in the waters by approximately 3 mg/L (Arnott and Vanni, 1996; Chapra et
al., 2012). Thus, it appears that mussel shells are a major sink of P and Ca in the lakes where the
mussel shells have dominated. In Lake Ontario, Ca and alkalinity concentrations have fallen and
summer ‘whitings’ are reduced in frequency and in some cases no longer appear (Barbiero et al.,
2006).
3. Long-Term Nutrient Concentration Variations in the Great Lakes:
The concentrations of some of the nutrients have varied widely. The total P loading has
decreased considerably due to management decisions. The total P loading reductions have
exceeded targets in all the 5 lakes and the loading and its variability is now dominated by non-
point sources, mainly runoff, which responds to precipitation (Figure 7). From a large database
of nitrate concentrations from samples collected spanning over a century for Lake Superior,
Sterner et al. (2007) reported a continuous, century-long increase in nitrate whereas phosphate
remains at very low levels (Fig. 8). The NO3- concentration in Lake Ontario increased by more
than a factor of 2 during the last 40 years (Figure 9a,b,c), similar to Lake Superior. There seems
no historical P or Si data going back to a century. The cycling of carbon, nitrogen, silica, calcium
and other key micro-nutrient trace metals (e.g., Zn, Co, Fe, V) in all five lakes have been
affected (Fig. 10). These micro-nutrients play a significant role on the structure of the freshwater
ecosystems and their biological activity which are key factors in regulating the carbon cycle. It is
not known how the dissolved trace element concentrations have changed over the past 30 years
as reliable data based on ultra-clean trace metal sampling are limited. The changes in
biogeochemical cycling of nutrients have resulted in the changes of benthic fauna diversity and
biomass as well flora (e.g., increased abundance of sea grasses, red macroalgae; Figure 5, Hecky
et al., 2004).
3.1 Stoichiometric challenge:
One of the most important differences between freshwater and salt water is stoichiometric
paradigm in that C:N:P ratios of different components of the oceanic ecosystem exhibit little
temporal and spatial variation (Redfield, 1934; Falkowski, 2000). However, the variations of
SRP in lakes are quite large (e.g., Hecky et al., 1993; Elser et al., 2000). The limited spatial and
temporal data on the primary productivity (PP) and respiration rates (RR) adds a large
uncertainty on the controls of stoichiometric ratios, and data on the seasonal and deep water PP
and RR are generally lacking. For example, the elemental ratios of C:P in seston varies
dramatically on a multi-year time scale (100-150 in 1996-1997 to 300-350 in 2000, Sterner et al.,
2007). Such a change has major consequence on the entire food web, species abundance,
secondary production, autotrophy/heterotrophy relationships, etc. (e.g., Elser et al., 2000).
Furthermore, decreased pelagic productivity and lower amounts of organic carbon in benthic
sediments have been driven by alterations in the sources, pathways and cycling of nutrients in the
littoral regions of the Great Lakes system.
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Dove, 2009
http://www.on.ec.gc.ca/solec/nearshore-water/paper/part5.html
Long-term trend of increasing nitrate: other Great Lakes
Rising NO3- evident in all of the Great Lakes
But not likely to be for the same reasons
NO
3-m
g/L
Lake Ontario 1970-2008
Lake Ontario 1970-2008
Eutrophic
Mesotrophic
0.02
Oligotrophic
0.01
PO
43
-m
g/L
0.03
0.04
0
0.2
0.3
Lake Erie (central basin)
http://www.on.ec.gc.ca/solec/nearshore-water/paper/part5.html
NO
3-m
g/L
Figure 9b: Nitrate concentration in Lake
Superior
Figure 9c: Concentrations of NO3- in L. Superior Figure
8b: NO3- + NO2
- and total Mo in L. Ontario (Sterner et al.,
2007) & Mo-unpublished data (Twiss, 2013)
Figure 9a: Temporal variations of nitrate and phosphate in Lake Ontario over the past ~40
years and nitrate concentrations in the Great Lakes system
14
T
he
concentrations of nitrate in Lake
Superior have been reported to have
increased steadily over the past
century, from ~5 to ~30 mol L-1
(Sterner et al., 2007). While the
phosphate concentrations in Lake
Superior have decreased over the past
4 decades, the atmospheric deposition
of nitrate has remained constant. This has resulted in the present-day severe stoichiometric
imbalance in Lake Superior, with the (NO3-/PO
3-4) ratio of ~10,000 (molar ratio) in the deeper
waters of Lake Superior (Sterner et al., 2007). Continuous gradual increase of spring silica
concentration in some of the lakes (e.g., Lakes Michigan and Huron) from 1983 to 2008 has
altered the N:P:Si stoichiometric ratios. These changes in the cycling of key macro-nutrient
elements in the Great Lakes system have likely altered key micro-nutrient stoichiometry as well
which needs further investigation.
4. Fluxes and Processes of Key Major and Minor Nutrient Elements in the Great Lakes
System:
4.1. Atmospheric deposition of key macro- and micronutrients:
Long-term records of atmospheric deposition of N or P or Si emissions in the airshed of
the Great Lakes are very limited. The relative percentages of the reduction of the nutrients are
different for different nutrients. For example, phosphorus concentrations in precipitation have
decreased from an average of 57 mg as P L-1
in 1976 to an average of 6.4 mg as P L-1
for 1994-
1995 while the volume-weighted mean concentration of NO3- in Lake Michigan did not change
between 1983 (2.0-2.5 mg as NO3-) and 1994-1995 (1.9 mg as NO3
-) (Voldner and Alvo, 1989;
Miller et al., 2000), thus altering the PO43-
/NO3- stoichiometric ratio of the atmospheric input to
Lake Michigan (Miller et al., 2000). The atmospheric emissions of nitrate from U.S. and Canada
over a period of 20 yrs (1980-2000) have been reported to be constant, although temporal
increases were reported between 1940 and 1980 (EPA, 2000; Chen et al., 2000). Simultaneous
year-long measurements of major nutrient elements along with their isotopic ratios are needed in
different air sheds in the Great Lakes system.
4.2 Inputs of micro- and macro nutrients through groundwater discharge studies
Figure 10: Variations in the concentrations of Ca
and alkalinity in all five lakes.
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Over the past 250 years, the geochemistry of the Great Lakes groundwater and surface
water systems has been altered by regional land use changes including deforestation, wetland
drainage, agriculture, industrialization, and urbanization. Further changes stemming from the
“green revolution” in agricultural practices and accelerating climate change beginning in the
latter half of the twentieth century are anticipated, but not well constrained. The volume,
location, and quality of direct groundwater discharge to the Great Lakes are poorly understood.
Coastal areas, where groundwater discharge is expected to be greatest, are largely ungaged.
Therefore, the amount and chemistry of groundwater discharging to the Great Lakes are not well
known.
Some of the groundwater flow systems in an aquifer system provide base flow to the
streams in response to recharge from the precipitation events. Submarine groundwater discharge
could be one of the significant sources of nutrients and key trace elements to the lakes. The
groundwater component of stream flow (for 195 selected streams in the US part of the Great
Lakes Basin) ranges from 25 to 97%, with an average value of ~67%. Although there is no
estimate on the total amount of direct groundwater discharge to Lake Huron, Superior, Erie and
Ontario, there is an estimate for Lake Michigan. The total groundwater discharge to Lake
Michigan was estimated to be ~2.7 x 103 ft
3 s
-1 (~76.5 m
3/yr; Grannemann and Weaver, 1998).
Highest rates of groundwater discharge were calculated for the northeastern shore of Lake
Michigan. Numerical groundwater flow and transport models are therefore needed, in
conjunction with field measurement (seepage meter covering several locations around the lakes)
and tracer studies (e.g., 234
U/238
U, 223,224,226,228
Ra, 222
Rn, 87
Sr/86
Sr in aquifers and lakes), to
investigate processes controlling nutrient and solute flux across an appropriate range of spatial
and temporal scales. Groundwater flow paths vary from local to regional with travel times
ranging from days to decades to centuries. Regional flow paths through carbonate, siliciclastic,
and crystalline bedrock will likely have different equilibrium chemistries and spatial variability
in both the volume and chemistry of submarine discharge to the Great Lakes is expected.
Consequently, models will enhance our ability to predict: i) flow paths and discharge regions; ii)
estimate geochemical signals; iii) quantify nutrient and solute fluxes; and iv) detect and confirm
anomalous regions. Hence, they will contribute to a greater understanding of the role of
groundwater and surface water hydrology in the biogeochemical cycling of phosphorous,
nitrogen, and micronutrient cycling within Great Lakes ecosystems.
In about 37% of the monitor-well samples in the Lake Erie and Lake St. Clair drainages,
the nitrate concentrations indicated evidences of human influence such as fertilizer, manure or
septic systems and thus, the contribution of nitrate to base-flow in riverine systems is expected to
be significant. Phosphate concentrations in groundwater depend on the bedrock, with siliciclastic
bedrock groundwater exhibiting lower concentrations (0.017-0.020 mg/L) compared to carbonate
rocks (< 0.1 mg/L). Many of the shallow groundwater aquifers is hydraulically connected to the
land surface, based on the presence of tritium in ~83% of the waters from monitor wells which
were recharged after 1953 and 53% of the wells contained a pesticide or elevated nitrate
16
concentration (Myers et al., 2000). However, there is no estimate on the fluxes of N, P, Si or C or
any of the micro-nutrients to the Great Lakes through groundwater discharge.
Recently, three sinkhole vents were discovered in cyanobacterial mats that are similar to
extreme and exotic ecosystems. These cynaobacterial mats thrive in low-O2, conduct both
oxygenic and anoxygenic photosynthesis and these organisms could serve as sentinels of
environmental change (Voorhies et al., 2012). The waters that are discharged in these vents are
anoxic, with high concentrations of sulfate and chloride and low concentrations of nitrate and
oxygen. It remains unknown if there are more sinkhole vents in other areas of Lake Huron and
other lakes in the Great Lakes system, at large. Stable (18
O and H) and radioactive isotope
studies (226
Ra, 228
Ra) in water samples collected near the sediment-water interface at few
kilometers from the sinkhole vents indicate that there several effusive fluxes where highly anoxic
waters are leaking (Baskaran et al., 2014 – in review). These sinkhole vents can serve as analogs
for life in extreme environments.
4.3. Inputs of macro- and micro nutrients from sediments:
The sediment accumulation rates in lacustrine systems are generally higher than the shelf
and deep oceans and the degree of bioturbation that causes the loss of temporal resolution of
sedimentary record is low and hence usually lacustrine sedimentary records are better candidates
for paleo reconstruction studies. There are some sporadic attempts to quantify the transport and
burial rates of organic carbon. Quantitative assessment and numerical models of sediment
dynamics have been conducted in a limited area (e.g., Edgington and Robbins, 1990). The nature
of the bathymetry in the coastal areas in the Great Lakes makes the storm-generated episodic
resuspension and horizontal advection of nutrients, carbon, sediments and other
biogeochemically key material to be significant, although the trapping of the nutrients,
particulate matter containing key elements and isotopes, attenuation and sequestration of key
material fluxes are not investigated. Sediment burial of C seems to be more important in the
shallower lakes, although the data is very limited in the Great Lakes system. Earlier studies on 14
C in POC indicate presence of resuspended material to be the major source of particulate
matter. Data on well-constrained benthic flux estimates of C, N and P are also needed for a
better understanding of the biogeochemical cycling of key macro-nutrients in the lacustrine
system.
4.4. Internal Cycling and regeneration studies:
The internal cycles of macro- and micro nutrients (both dissolved, particulate and
colloidal forms) in the inland sea waters are influenced by a complex set of removal, transport
and transformation processes that include removal by invasive species, atmospheric deposition
from the industrial belt in the Midwestern states, agricultural industry, etc. The hydraulic
residence times of these waters (Table 1) are much lower than the global ocean circulation times
of ~2000 yrs and hence the uniform mixing of the water takes place much quickly compared to
the oceans (Fee et al., 1996). Some of the trace metals (e.g., Fe) has been found to serve both as
17
a limiting factor in the growth of phytoplankton in high-nutrient low chlorophyll regions and for
its regulation of nitrogen fixation.
It has been estimated that the external loading of nutrients is sufficient to meet the algal
demand on a daily basis, while internal cycling meets the overall needs. The influence of internal
cycling/recycling on lakes generally is a function of water residence time, both at the scale of
whole lakes as well as factors and processes that operate locally within lakes while the influence
external loading is associated with the terrestrial catchment to lake area (Table 1). The vertical
distribution of a micro- or macro nutrient results from a combination of processes such as
physical transport, chemical control, and biological activity. The external loading of nutrients
can be relatively easily characterized and quantified, while the internal loading and cycling is
difficult, as it involves quantification of several biogeochemical processes that are not well
understood in the Great Lakes system. Internal loading estimate would require an estimate of
benthic fluxes, rates of particle-recycling of N, P and C, and extent of remineralization of POC,
PON and POP. There are very little data on the benthic fluxes of macro- and micro nutrients for
the Great Lakes system. Furthermore, data on the remineralization term for POC, PON and POP
in the water column from sinking particulate matter are very limited and is confined to a limited
area.
To investigate the cycling and transport of N, P, Si, and OC, some of the U-Th series
radionuclides (e.g., 234
Th, 210
Pb, 210
Po, 210
Bi), cosmogenic radionuclides (e.g., 7Be) and
anthropogenic radionuclides (e.g., 90
Y/90
Sr) have been utilized (e.g., Coale and Bruland, 1985;
Murray et al., 1989; Buesseler et al., 1992; Baskaran et al., 2003; Moran et al., 2003; Cochran
and Masque, 2003; Murray et al., 2005; Waples et al., 2006; Rutgers van der Loeff and Geibert,
2008). Variations in the nature of particulate matter (biogenic versus lithogenic) due to the
presence of dreissenids can be investigated using tracers that trace biogenic particulate matter
(e.g., 210
Po) and terrigenous particulate matter (e.g., 210
Pb). They also can be used to constrain
rates of scavenging and biological uptake by particles and to quantify processes that regulate the
internal cycling and eventual removal of key nutrient elements. Radium isotopes can be used as a
tracer of other alkaline elements such as Ca, Ba, Sr, etc. The abundances of Ca and Ba are
considerably altered in the many of the lakes due to dreissenids and it is likely that Ra is also
altered from the water column. Quantification of sediment resuspension rates using particle-
reactive radionuclides (210
Pb and 7Be) in freshwater system has been conducted (e.g., Jweda et
al., 2008), and amount of release of organic C, N and P from sediments can be quantified from
the sediment resuspension rates.
4.5. Impacts on nutrient cycling due to climate changes:
The major impact of global climate change (or regional climate change) caused by human
perturbation will affect the hydrological cycle the most having the most immediate impact on
future human welfare of those who twelve in the Great Lakes region. The global climate change
has resulted in increasing annual surface air temperature as well changes in the amount and
frequency of precipitation in the Great Lakes region. The climate change will affect the
18
hydrologic balance, biological productivity, and ecosystem structure and water quality.
Continued rise of atmospheric CO2, both from measurements and predicted GCMs will have
significant impacts on the ecosystem of the Great Lake system. Model-predicted global warming
is expected to affect the length of the stratified period in the Great Lakes (by as much as 90 days;
Weiss and Sousounis, 1999). Such elongated period of stratification will result in extended
isolation of warmer hypolimnion from the atmosphere and could result in lower dissolved
oxygen (DO) levels and such lower DO potentially will have enormous impacts on nearly all
segments of the lake ecosystem, including nutrient cycling, benthic metabolism and fisheries
(SOFIS Report, 2003). Changes in the frequency and amount of precipitation could result in the
water level fluctuations, changes in river runoff and lake water evaporation. Changes in the
hydrological cycle expected to accompany global warming will likely have an impact on the
delivery of lithogenic and nutrient elements to the Great Lakes through several processes that
include increased watershed erosion and runoff in several areas. Changes in the wind field
resulting from regional climate change, as a result of global climate change, can alter the water
and nutrient exchange between semi-enclosed bays and the open lake water. For example,
changes in the wind field over the Great lakes basin since 1980 has resulted in a reduced amount
of water exchange between Green Bay and Lake Michigan which has led to the formation of
intensified bottom water hypoxia, increased benthic metabolism within the bay, and warmer
bottom water temperature (Waples and Klump, 2002). Over the last 30 years, the surface water
temperatures in Lake Superior have risen twice as fast as air temperatures (Austin and Coleman
2007). In Lakes Michigan and Huron evaporation has increased significantly, equivalent to a
nearly 4 meter drop in lake level, but this has been offset by increases in precipitation and runoff
(Hanrahan et al. 2010). Decreases in the water levels in Great Lakes and their connecting
channels are of major concern not only for recreation industry but also for other sectors including
transportation industry.
5. Tools for Biogeochemical Cycling Studies:
5.1 Particle-reactive and stable isotopes:
19
A major understanding of the biogeochemical cycles of many elements in aqueous system is
linked to the understanding of the cycling of particle-reactive radionuclides. Several key
biogeochemical processes in the water column including formation, aggregation/disaggregation,
dissolution, and scavenging of biogenic particulate matter, exchange of particle-reactive species
between particles and solution, and export of particulate organic carbon, nitrogen and other
particle-reactive organic matter (e.g., PCBs, PAHs) relies heavily on the natural radioactive
clocks provided by the U-Th series radionuclides along with a set of cosmogenic and
anthropogenic radionuclides
(Ivanovich and Harmon, 1992;
Bourdon et al.,2003;
Krishnaswami and Cochran,
2008; Hong et al., 2011; Kaste
and Baskaran, 2011). While a
large body of data exist utilizing
U-Th series radionuclides as
POC, PON export tracers
(234
Th/238
U and 210
Po/210
Pb) in
the marine systems (Buesseler,
1998; Moran et al., 2003; Waples
et al., 2006), virtually no data
exist in the freshwater system.
Although the 238
U concentration
in freshwater system is very low (~5% of open ocean value) in the Great Lakes (limiting 234
Th/238
U pair for export studies), the 210
Pb concentrations in surface waters are expected to be
significantly higher than that of most other deep ocean basins (210
Po/210
Pb pair can be utilized
export studies) due to differences in the sources of air masses. The half-lives of these nuclides
are short (e.g., 234
Th: 24.1 d; 210
Po: 138.4 d; 210
Bi: 5.1 d) to make these nuclides sensitive to
short-term changes that occur (e.g., POC flux integrated over a week to a few months) in upper
water column. The deficiencies of these nuclides are created by the scavenging of these onto
20
biogenic particulate matter and the sinking of such particulate matter out of the euphotic zone. It
has been documented that 210
Po traces much more efficiently the biogenic organic matter than Th
and hence Po is likely a better tracer for POC and PON export studies (Figure 11,12; Friedrich
and Rutgers van der Loeff, 2002; Verdeny et al., 2007). The lone study in Lake Superior (Chai
and Urban, 2004) that reported similar residence time for 210
Po and 210
Pb is in contrast with
much longer time of 210
Po compared to 210
Pb in the upper 150 m, due to remineralization of
particulate 210
Po in marine system (e.g., Sarin et al., 1999). No other data exists from any of the
other lakes in the Great Lake system to compare with. Using 210
Po-234
Th and 210
Po-210
Pb as
coupled tracers, Friedrich and Rutgers van der Loeff
(2012) estimated the sinking velocities of biogenic Si
and POC. Particle formation and dynamics can be
investigated using the disequilibrium between 210
Po-210
Bi-210
Pb pair, similar to aerosol removal in the
atmosphere. There are limited attempts to quantify
the lateral export suspended particulate matter using radioactive tracers (234
Th, 137
Cs, 7Be) in the
Great Lakes system. For example, the Keweenaw Interdisciplinary Transport Experiment in
Lake Superior (KITES) focused on a region dominated by a strong coastal jet, and the sister
project in Lake Michigan, Episodic Events—Great Lakes Experiment (EEGLE), concentrated on
the biogeochemical effects of a major plume of resuspended sediment that occurs annually in the
southern portion of the lake (Eadie et al. 2008; see JGR special issue, 2004:
http://www.agu.org/journals/ss/EEGLE1/). These studies were limited to one area and had
limited scope in terms of using key micro and macro-nutrients study.
The understanding of nitrogen cycle in the Great Lakes system is very limited, although
the N/P stoichiometry ratios in many of the lakes have drastically changed, mainly due to
increase in N rather than
drastic decrease in P values.
We have currently a better
understanding of N cycle in a
small lake in Switzerland
compared to the Great Lakes.
Although historical data on
the nitrification-
denitrification at the
sediment-water interface and
sediment cores are limited, it
has been shown that the
vertical distribution of 15
N
and 13
C of a dated core from
Figure 11: Parallels between N and Po cycles.
Total production = New production + recycled
production. Magnitude of POC export is
estimated based on mass balances in the
euphotic zone. New production is the supply of
‘new’ nutrients via upwelling and this is
balanced by the export of POC
Figure 12: The nutrient loadings (nitrogen) are easiest to measure in
outflow, and most difficult in internal loading. On a daily basis, most
algal demand is met by recycling. Concentrations are expected to be
in balance of internal and external loading.
21
Lake Ontario varied by ~2‰ over the past 140 years while 15
N values change by ~5-6‰ and it
was attributed to active denitrification at the sediment-water interface (Hodell and Schelske,
1998). The classical view that nitrogen cycle is dominated by nitrification and denitrification is
changing, and ANaerobic AMMonium OXidation (Anammox: NO3- + NH4
+ → N2) and
Dissimilartory Nitrate Reduction to Ammonium (DNRA: NO3- → NH4
+) are increasingly being
recognized as important processes that regulate the nitrogen cycling (Figure 13).
Very limited data is available on denitrification and on DNRA in the Great Lake systems and no
nitrification rate data seem to be available from Lake Huron and Ontario.
5.2 New and Newly Emerging Tools:
Key major nutrients (P, N and
Si) and some of the essential micro-
nutrient trace elements (e.g., Fe, Zn, Co,
V, Mo, and Cu) play important roles in
the biochemical activity in organisms
(e.g., Morel et al., 2003; Morel and
Price, 2003). High precision
measurements of the isotopes of these
micronutrients are available only in the last ~15 years
and there is limited data on their distributions in the Great Lakes system. For example, there are
vertical profiles of Si isotopes (29
Si) for Lake Tanganyika (Figure 14). The d29
Si isotopic ratio
could be useful in studying environmental changes and particularly recent changes in the diatom
utilization (Alleman et al. 2005). Lack of such information prevents the scientific community to
get a good handle on the sources, transport and cycling of these essential elements across the
lakes.
A large number of isotopes are utilized as a set of powerful tools to map the food webs in
terms of the major carbon flows and trophic relationships (Hecky and Hesslein, 1995). For
example, the distribution of phosphate and Cd are similar in marine system (Elderfield and
Rickaby, 2000) and thus, isotopes of Cd can be used to trace the pathways of P because both
species are likely removed from the freshwater sea by biological activity. Zinc which is an
an essential micronutrient
could serve as a tracer for
another macro-nutrient, Si, in
aqueous system (Ellwood and
Hunter, 2000; GEOTRACES
Science Plan, 2006). There is
very limited data on the
Figure 13: Schematic diagram of nitrogen cycling in
an aqueous system (Francis et al., 2007)
Figure 14: Dissolved Si concentration (dashed line) and δ29Si
(bold line) profiles at station TKI (northern basin), TK5 and
TK8 (southern basin) collected in July 2002.
22
isotopic fractionation of nutrient elements as well as micro-nutrient elements and thus, some of
the isotopic tools could serve as powerful tools in assessing nutrient utilization. Isotopes of
nitrogen and oxygen in nitrate are used to quantify the sources and dynamics of nitrate, both
15
N (15
N-NO3) and 18
O (18
O-NO3). It has been shown that the 15
N values of NO3- sources
often overlap and thus combined use of N and O isotopes are powerful (Kendall, 1998; Burns
and Kendall, 2002; Hastings et al., 2003). The 18
O-NO3 from nitrification is largely determined
by the 18
O in water in the ecosystems while 18
O-NO3 values in precipitation is the result of
isotopic fractionation taking place during interactions between oxides of nitrogen and O3 in the
atmosphere (Hastings et al., 2003; Michalski et al., 2011). Oxygen isotopes in phosphate are
used to trace the pathways of phosphate (Jaisi et al., 2011; Paytan and McLaughlin, 2011).
6. Missing Gaps in Knowledge and Key Questions:
A mass balance of C, N, P and Si in the lakes require good estimates on the primary
production, grazing, DOC inputs/outputs from rivers/streams and carbon burial rates. Attempts
for OC budget have been attempted for L. Superior (Urban et al., 2005). Lake-wide studies on
the production and grazing in most lakes are lacking and thus, there are gaps in our
understanding of the N, P, and Si cycling and its link to other key macro- and micro nutrients.
Earlier PP studies are primarily from certain seasons of the year and lack of data during the
colder periods and deeper waters fuels the uncertainty in the C estimate. The uncertainty in the
primary production rate for Lake Superior is mainly due to the scaling-up factors used on the
vertical temperature and chlorophyll data at measured at depths. The chemical reactions
(nitrification, denitrification and anammox) are expected to be slower in Lake Superior due to
cooler waters compared to other lakes (Michigan, Huron, Erie, and Ontario); other factors that
control the N, C and P cycling and N assimilation and microbial community structure are not
studied in all the Great Lakes, whether it is due to increase in external sources discharged to the
lakes (rivers/streams, atmospheric deposition, submarine groundwater discharge), or active in-
lake processes (such as nitrification/denitrification, anammox).
The first step in the transfer of nutrients and C to food chains is the grazing. In eutrophic
environments, the transfer by grazing is less efficient that that observed in oligotrophic waters
and hence the settling of nutrients to deeper waters is primarily controlled by grazing. Thus, the
relative importance of grazing compared to the export of particulate C, N, and P. During vertical
transport of POC, PON, POP, particles undergo remineralization contributing to the dissolved C,
N, and P in the water column. Thus, grazing data using some commonly used protocol (e.g.,
dilution gradient method, Landry and Hassett, 1982) is needed. The small consumers such as
picoplankton (<10 um) could play an important role as dominant consumers relative to the whole
food web. Lake-wide primary production rates from time-series, vertical profiles, and day/night
studies are needed to limit the range of variations on the primary production estimate, using
widely accepted method(s), such as 14
C methodology. Similarly, an estimate on the grazing on
planktons for the whole lake needs to be assessed. It is also essential to measure vertical profiles
of production and establish an empirical relation between production, light and temperature.
23
Establishing such a relationship at different seasons (summer, winter and spring) will help to
constrain the estimate on production. Lake-wide efforts on the simultaneous measurements of
primary productivity and respiration rate with special emphasis on seasonality, year-around
measurements and surface and deep-water measurements of these parameters are important
(including under-ice measurements of production and respiration to quantify autotrophic-
heterotrophic balance). Sporadic and sparse measurements of primary production and respiration
rates most likely have missed the important spatial and temporal variations of the biological
activity and thus, it is urgently needed to quantify these rates.
Recent studies in Lake Erie showed that Fe is required for the stimulation of NO3- draw
down and required for NO3- assimilation (Twiss et al., 2005; Havens et al., 2012). Several other
trace elements such as Co, Zn, Ni, Mn, Cu, also serve as essential micronutrients, and their
distribution, sources, pathways and eventual sinks remain unknown. The biogeochemical cycling
of Fe in the Great Lakes system remains poorly characterized. A potential relationship between
micro-nutrients and macro-nutrients (e.g., PO4-Cd; Si-Zn) could help in identifying and
quantifying processes in the freshwater systems. The trace metal enrichment is likely to play a
significant role on the nutrient assimilation in picoplanktons (Twiss et al., 2005). Low
availability of Fe and other micronutrients could also constrain the primary productivity in the
Great Lakes system. The concentrations of the micronutrients in the lacustrine system are
expected to be very low and large-volume of samples may be required.
With the present understanding of the Great Lakes system, there are several knowledge gaps.
A systematic process-oriented study is expected to answer the questions listed below:
i) How does the onshore-offshore coupling along with the presence of invasive species
affect the coastal trapping, attenuation and sequestration of nutrients, suspended
particulate matter, POC and other key micro-nutrients?
ii) How does the vertical and horizontal transport of nutrients due to episodic events
affect the lacustrine productivity on different temporal and spatial scales?
iii) How does the cycling and internal of loading of nutrients have impacted the
concurrent coastal eutrophication and pelagic oligotrophication in some of the lakes
in the Great Lakes system?
iv) In what time scales the stoichiometric ratios vary in different lakes in the Great Lakes
system? How does this ratio vary in seston in different Great Lakes system? How do
the stoichiometry ratios of nutrients from atmospheric loading compare with that of
terrestrial runoff year around in all the lakes?
v) How did the NO3-/PO4
3- ratios vary over the past 30 years in areas that are severely
impacted by invasive species (zebra and quagga mussels), due to active removal of
PO43-
, Ca, and key bio-limited elements and their isotopes in the lower lakes?
24
vi) How does the seasonal variations of the rates of primary productivity and respiration
and at deeper waters compare with the other decay of organic matter such as CO2
production from heterotrophic processes in different spatial and temporal scales?
vii) How we can quantify the horizontal and vertical transport of key macro- and micro
nutrients using a suite of newly emerging isotopes of Fe, Cu, Zn, Cd, Se,V, Mo, Ni,
Co in conjunction with a suite of particle-reactive radionuclide tracers.
viii) How do the sink terms of P, N, Si, and C vary across the five lakes as a result of
varying extent of denitrification due to varying supply terms of labile organic carbon
to the lake bottom resulting in nitrate build up.
ix) What factors and processes limit the nutrient utilization in the Great Lakes system?
Does it vary from lake to lake? If most lakes are limited by N and P, are there any key
micronutrients, such as Fe, that is limiting the nutrient utilization?
x) How have the quantity and quality of groundwater and surface water discharged to
the Great Lakes been influenced by deforestation, wetland drainage, farming,
industrialization, and urbanization in the Great Lakes watershed? How have these
changes contributed to alteration of biogeochemical cycling of nitrogen, phosphorous,
and other micronutrients in the Great Lakes?
xi) What is the impact of sinkhole vents in the biogeochemical cycling of nutrients in
Lake Huron and other lakes, if they also have sinkhole vents?
xii) How does the filtering activity of dreissenids affect the inorganic nutrient forms of N
and P and the organic forms versus particulate forms of C, N and P.
xiii) How do the anthropogenic alterations on nutrients affect the ecological and
evolutionary trajectories? How the dreissenid mussel invasion has altered the CO2
emissions from freshwater system? and
xiv) How does the trace metal speciation and bioavailability of trace metals in freshwater
seas vary in different lakes
7. Field Sampling, Remote Sensing and Synergies Among Other Federal Agencies:
In field expeditions, it is essential to collect data of standard hydrographic parameters (e.g.,
temperature, oxygen, salinity) in all stations and the data quality is should to be comparable to
that of WOCE and GEOTRACES. Major nutrients (nitrate, phosphate, silicic acid) should also
be measured, again similar to the WOCE and GEOTRACES quality. The field sampling should
focus on areas of prominent sources (river/stream discharges), submarine sinkhole vents, etc.
From a review of the existing data and monitoring stations, sections should be selected to include
major biogeographic regions and gradients of biological productivity. The field sampling should
be coordinated with other federal agencies that have interest in the Great Lakes (EPA, NOAA
Vessels – NASA remote sensing data) and researchers in Canada.
25
From the Great Lakes Workshop 2010 conducted by NASA GRC, it was recognized that
there are significant opportunities for NASA to improve the understanding of the hydrology and
physical limnology of the Great Lakes (e.g., ice, temperature, precipitation, wind velocity,
currents, etc.). NASA current interest includes water cycle (quantity, quality, and availability and
future changes), limnology, climate, ecology and human effect modeling, and remote sensing.
Coastal processes in the Great Lakes are important for Great Lakes, yet often not considered
in national scope. The current interests of NASA include reflectance, surface radiometry, benthic
optical characterization and other atmosphere and water column correction factors relevant to
remote sensing. NOAA has conducted long-term sediment trap studies to investigate sediment
transport along cross and along-shore, benthic nepheloid layers and resuspension. GLNPO/EPA
monitors 11-18 stations in offshore regions in lakes Michigan, Huron and Superior collecting a
suite of limnological parameters.
The satellite remote sensing provides a synoptic view for the whole Great Lakes region of
several parameters of interest that include surface temperature, color, chlorophyll concentration,
colored dissolved organic matter, atmospheric aerosol loading, wind speed and direction.
Moorings with current meters in several sites have been deployed in Lake Superior from ~2007
to present. Current profilers (ADCPs) and thermisters at a range of depths also have been
deployed. The Muskegon Lake Observatory buoy is investigating the metabolism in Lake
Michigan and is being compared to the estimate obtained from bottles (McNair et al., 2013).
Remote sensing using satellites of optically-sensitive compounds (e.g., colored dissolved organic
matter, CDOM) provide valuable information on their sources, fate and transport in lacustrine
systems.
8. Link to the Major Ongoing Oceanographic Research:
The biogeochemical changes that have recently taken place in the estuarine and marine
coastal environments are useful in informing the key biogeochemical changes that have taken
place in inland seas, and vice versa. The distribution of these key macro and micronutrients are
being measured as a part of the GEOTRACES project in major ocean basins (North Atlantic:
2010 and 2011; East Pacific: October-December, 2013). During the first phase of the
GEOTRACES project two cruises (Atlantic inter-calibration cruise: 2008 and Pacific inter-
calibration cruise: 2009) were dedicated to establish the best practices of sampling (particulate
and dissolved), storage and analytical protocols for the contamination-prone elements and
radionuclides (http://www.obs-vlfr.fr/GEOTRACES/science/intercalibration/222-sampling-and-
sample-handling-protocols-for-geotraces-cruises) and thus the best practices of sampling,
storage, and analyses are established for the work in the Great Lakes.
9. Broader Impacts:
The water quality has direct impact on human health of about 8% of the US population.
These set of lakes in the Great Lakes system have different temperatures, water depths,
hydrological residence times, and varying amounts of anthropogenic impacts of macro- and
26
micro nutrients in the watershed and investigations on the sources, fate and transport of micro-
and macro nutrients will yield a dramatically improved knowledge of the nutrient cycles in the
world’s largest lake system. The biogeochemical processes as modified by human impact in the
Great Lakes system vary considerably due to the differences in the land use between their
watersheds. The major human induced perturbations of the nitrogen cycle in the Great Lakes and
their present and continuously growing impacts on the aquatic system, such as eutrophication,
hypoxia in lakes and streams can provide the changes that are taking place. Investigations in the
Great Lakes system provide tools to validate some of the existing models of nutrient transport
and cycling. Similar future perturbations in other large lakes worldwide (e.g., East African rift
lakes, Lake Baikal, Lake Tanganyika, and the Canadian interior great lakes (Great Bear, Great
Slave, Winnipeg, and Athabasca) are likely to happen and hence this study has broader
implications for lacustrine systems around the world. Since the extent of inter-watershed human
perturbations on the watershed varies, documenting the impact of such changes on these lakes
would provide baseline data which can be compared to the future studies, as continued
alterations by humans take place.
Acknowledgments: This Report is a product of the Workshop which was financially supported
by NSF (OCE-1253310), NOAA, NASA, Wayne State University, CILER, Michigan State
University, University of Illinois-Urbana Champaign, University of Minnesota-Duluth, Ohio
State University, University of Wisconsin-Milwaukee, Yale University, Sea-Grant-Wisconsin
and Sea-Grant-New York. Inputs from participants at the International Association of Great
Lakes Research Annual Meeting at West Lafayette, IN, Geochemical Society Meeting at
Florence, Italy, and American Geophysical Union Fall-2013 meeting are deeply appreciated.
Enclosed Appendix: A) BOGLS Workshop (11-13 March 2013) Agenda; B: List of Participants
at the BOGLS Workshop; C: List of participants at the IAGLR Annual Meeting (June 2013),
Geochemical Society Meeting (August 2013) and Fall AGU Meeting (December 2013).
27
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34
Recent Changes in the Biogeochemistry of
the Great Lakes System Workshop
McGregor Conference Center
March 11-13, 2013
Agenda
Monday March 11, 2013
07:30 – all day Lobby Registration
07:30 – 08:30 B/C Continental Breakfast
08:30 - 09:15 F/G/H Technical Session 1
Chair, Mark Baskaran
Welcome, Introductions, Workshop Overview
09:15 – 10:30 F/G/H Plenary Session: Disrupted Biogeochemical Cycles in the
Great Lakes: Challenges and Opportunities for Aquatic Science.
R.E. Hecky, University of Minnesota-Duluth
Presentation: Micronutrient Dynamics in Lakes and Their
Investigation Using New Isotopic Tools. T.M. Johnson, University
of Illinois at Urbana-Champaign
10:30 – 10:45 B/C Refreshment Break
10:45 - 12:30 F/G/H Technical Session 2
Chair, Val Klump
Presentation: Recent Advances in Understanding the Roles and
Reactions of P in Aquatic Systems. R.E. Blake, Yale University
Presentation: The Enigmatic Great Lakes Nitrogen Cycle: Review
and Insights from Isotopic Records. N.E. Ostrom, Michigan State
University
Presentation: Tracing the Biogeochemical Cycling of Key Micro-
and Macro- Nutrients in the Great Lakes System Using a Suite of
35
Particle-Reactive Radionuclides. M. Baskaran, Wayne State
University and V. Klump, University of Wisconsin-Milwaukee
12:00 – 12:30 F/G/H Questions and Discussion: Technical Sessions 1 and 2
Moderated by V. Klump
12:30 – 01:45 B/C Lunch (boxed lunch provided)
01:45 – 03:00 F/G/H Technical Session 3
Chair, Tom Johnson
Plenary Session: Recent Changes in Primary Productivity and
Phytoplankton Dynamics in the Great Lakes.
G. Fahnenstiel, Michigan Technological University
Presentation: Spatio-temporal Variability and Potential Long-Term
Trends in Great Lakes Carbon Cycling. G.A. McKinley, University
of Wisconsin-Madison
Presentation: Carbon Cycling in the Laurentian Great Lakes:
What’s Known? Unknown? Changing? E. Austin-Minor,
University of Minnesota-Duluth
03:00 – 03:30 F/G/H Questions and Discussion: Technical Session 3
Moderated by T. Johnson
03:30 – 03:45 B/C Refreshment Break
03:45 – 05:00 F/G/H Technical Session 4
Chair, Norm Grannemann
Presentation: Gaps in Understanding of the Role of Groundwater in
Great Lakes Biogeochemical Processes. J. Bratton, GLERL-
NOAA, N. Grannemann, USGS, L. Lemke, Wayne State
Presentation: Inertial Oscillations as a Primary Ecosystem Driver.
J. Austin, University of Minnesota-Duluth
05:00 – 05:30 F/G/H Questions and Discussion: Technical Sessions 1-4
Moderated by N. Grannemann
05:30 – 06:00 Lobby Social Break
05:30 – 06:00 A Steering Committee Meeting: Formative Workshop Assessment
06:00 – 07:30 B/C Catered Dinner
36
Recent Changes in the Biogeochemistry of
the Great Lakes System Workshop
McGregor Conference Center
March 11-13, 2013
Agenda
Tuesday March 12, 2013
07:30 – all day Lobby Registration
07:30 – 08:30 B/C Continental Breakfast
08:30 – 08:40 F/G/H Technical Session 5
Chair, Larry Lemke
Goals and objectives for today’s sessions
M. Baskaran, Wayne State University
J. Bratton, GLERL-NOAA
Guidelines for advocacy presentations
L. Lemke, Wayne State University
08:40- 10:30 F/G/H 15-Minute Introductory Talks
Dreissenid Mussels Have Reengineered the Biogeochemistry of the
Great Lakes
H.A. Vanderploeg, GLERL-NOAA
Sediment Trap Studies in the Great Lakes
N. Hawley, NOAA Federal GLERL
5-Minute Advocacy Talks
Important Negative Impacts on the Nitrogen Cycle are Ignored in
the Debate About Managing Eutrophication. D. Bade, Kent State
University
37
Microbiogeochemical Ecophysiological Time Series Analysis in
Lake Michigan: Key to Distinguishing Between Episodic and
Progressive Perturbations. R. L. Cuhel, University of Wisconsin-
Milwaukee
A modeling Approach to identify Factors Driving Increased
Dissolve Reactive Phosphorous Loss from Agricultural Fields in the
Maumee Basin. S. Y. Gerbremariam, Ohio State University
The Effect of Bain Scale Meteorological Events and the Persistence
of Major Invasive Species on Biogeochemical Cycling and
Ecosystem Function in Lake Michigan. C. Aguilar, University of
Wisconsin-Milwaukee
Potential Impacts of Changes in Major Ion Composition on Trace
Metal Interactions with Phytoplankton: the Lake Ontario Example.
M. Twiss, Clarkston University
The Importance of Iron and Sulfur Cycling in the Great Lakes
System. L. Kinsman-Costello, University of Michigan
Great Lakes Traces: A program to Study the Biogeochemical
Cycling of Trace Elements and Their Isotopes in the Great Lakes.
A. Chappez, Central Michigan University
Measuring Particle Flux in the Nearshore: What Are Short-Lived
Radiotracers Telling Us? J.T. Waples, University of Wisconsin-
Milwaukee
10:30-10:50 B/C Refreshment Break
10:50 – 12:30 F/G/H Technical Session 6
Chair, Ruth Blake
5-Minute Advocacy Talks
Carbon Dynamics in Response to Environmental Change?. L. Guo,
University of Wisconsin-Milwaukee
Using Observations to track Lake Metabolism and Their Role in the
Global Carbon Cycle. L. Gereaux, Grand Valley State University
Sediment Biogeochemistry of Great Lakes Sediment. G. Matisoff,
Case Western Reserve University
Unique Cyanobacterial Mats in Lake Huron Sinkholes: Sentinels of
Environmental Change? G. J. Dick, University of Michigan
38
Is Climate Change Tuning the Invisible Engine of the Great Lakes?
V. Denef, University of Michigan
Direct Measurements of Heat, Moisture and Carbon Fluxes on the
Great Lakes. J. Lenters, Limno Tech
Variability of Satellite-Derived Chlorophyll Concentrations and
Colored Dissolved Organic Matter in Lake Superior. C. Mouw,
Michigan Tech University
The Importance of Biogeochemical Water Quality Monitoring.
M.D. Rowe, NOAA/GLERL
Climate Change Impact on Reservoir Thermal Structure and
Turbidity Transport and Some Aspects of Ice Cover Modeling in
New York City Drinking Water Reservoir. N. R. Samal, New York
City Government
` Simulating the 1998 Spring Bloom in Lake Michigan using
FVCOM-Ecosystem Model. J. Wang, University of Michigan
CILER
Pollutant Loads Generated from Lake St. Clair Metroparks during
Dynamic Stormwater Runoff Events. S.P. McElmurry, Wayne
State University
Ballast Water Verification and Early Detection of Invasive Species
J.L. Ram, Wayne State University
A Landscape Ecology Vision for the Great Lakes. M.A. Evans, U.S.
Geological Survey, Great Lakes Science Center
12:30-01:30 B/C Buffet Lunch
01:30 – 02:30 F/G/H Technical Session 7
Chair, Mark Baskaran
Funding Agency Perspectives
NSF- Tele Conference with Don Rice
Larry Liou, NASA
Norm Grannemann, USGS
John Bratton, NOAA
39
Goals and Expectations for Breakout Sessions
M. Baskaran, Wayne State University
02:30 -04:00 J Breakout Session 1A – Micro- and macro-nutrient and carbon
cycling and tracer studies – field studies
I Breakout Session 1B – Modeling, environmental/climate change
and physical oceanography and how these affect the carbon and
nutrient cycling
E Breakout Session 1C – Exchange of water and nutrients between
reservoirs; field and modeling studies; tracer studies
04:00 – 04:15 B/C Refreshment Break
04:15 -05:30 Technical Session 8
Chair, Nathanial Ostrom
J Breakout Session 2A – Nearshore, shallow water dynamics and
processes
I Breakout Session 2B – Offshore, deep water and cross margin
processes
E Breakout Session 2C – Land margin interface and terrestrial
aquatic coupling, atmospheric interactions
0:530 – 0:600 A Steering Committee Meeting: Formative Workshop Assessment
05:30 – 06:30 Lobby Posters
In Situ Approaches to Assess Sediment Contamination. Allen
Burton, Anna Harrison, et al., University of Michigan
40
The importance of winter plankton assemblages in Lake Erie.
Hunter Carrick, Central Michigan University
Surface ground Water Exchange. Lynn Katrib, Wayne State
University
The Dynamics of Hypoxia in Green Bay, Lake Michigan. Val
Klump, University of Wisconsin-Milwaukee
Comparative Effects of Climate on Green Bay Stratification. Shelby
LaBuhn, University of Wisconsin-Milwaukee
Sediment Loading Budgets in the Great Lakes Watershed. Carol
Miller, Wayne State University
Ecosystem Metabolism and Microbial Sources of N2O in Muskegon
Lake, a Eutrophic Area of Concern. Kateri Salk, Michigan State
University
Relative Contribution of Hypoxia and Natural Gas Drilling to
Atmospheric Methane Emissions From Lake Erie. Amy Townsend
Small, University of Cincinnati
Radiocarbon Distributions in Lake Superior, the World’s Largest
Freshwater Lake. Paul Zigah, University of Minnesota-Duluth
41
Appendix-A
Recent Changes in the Biogeochemistry of
the Great Lakes System Workshop
McGregor Conference Center
March 11-13, 2013
Agenda
Wednesday March 13, 2013
07:30 – 08:30 B/C Continental Breakfast
08:30 – 10:30 F/G/H Technical Session 9
Chairs, Jim Bauer/Mark Baskaran
Presentation of Breakout Group Session Summaries
Discussion of Breakout Group Sessions
10:30-10:50 B/C Refreshment Break
10:50-12:00 F/G/H Technical Session 10
Chair, John Bratton
Sensors and Monitoring Networks
Logistics for Field Sampling
Ship Capabilities and Ongoing Efforts. Russell Kreis, USEPA
Blue Heron
University of Minnesota – Duluth
Final Session and Summary of the Workshops
12:00 B/C Boxed lunch
BOGLS Workshop Ends
12:00 A Steering Committee Meeting: Summative Workshop Assessment