EUTROPHICATION AND HARMFUL ALGAL BLOOMS (HABs)

Intent of this lecture?

• Link our discussions of terrestrial N & P dynamics with its influences on receiving water bodies

• How the relative amounts of N & P and other factors can influence eutrophication and the growth of harmful algal blooms (HABs)

• Making the connection between chemical pollution and biological problems

Lecture notes based on multiple sources:

• Val H. Smith – Cultural eutrophication of inland, estuarine, and coastal waters. In Successes, Limitations and Frontiers in Ecosystem Science. M. L. Pace & P. M. Groffman (Editors), Springer Verlag, NY. 1998. Pgs 7-49.

• Aquatic Pollution – Edward Laws• Anderson et al. 2002 – Harmful Algal Blooms and Eutrophication• Heisler et. al., 2008 – Eutrophication and harmful algal blooms: A scientific consensus• Conley et al., 2009. Controlling eutrophication: nitrogen and phosphorus. Science, vol 123: 1014-

1015.

Red Tides

Lecture Outline:

• Background and definition of Eutrophication• Nitrogen & Phosphorus as limiting nutrients• Redfield ratio• Factors controlling eutrophication• Mixing of water bodies due to temperature and salinity gradients• HABs – definition• Types of HABs• HAB occurrence and nutrient and environmental factors• Management of HABs

Natural versus Cultural Eutrophication• Natural – slow, takes decades/centuries• Cultural – accelerated by anthropogenic activities

HistoryProductivity of water bodies – research initiated in Europe – work of Einar Naumann (Sweden) and August Theinemann (Germany)

Naumann developed the Trophic State Concept –

• Phytoplankton production determined by concentrations of nitrogen and phosphorus

• Productivity of lakes varied with the geological characteristics of the watersheds

Naumann also developed the terms that we use to categorize lakes based on their productivity and nutrient supplies

1. OLIGOTROPHIC2. MESOTROPHIC3. EUTROPHIC4. HYPEREUTROPHIC

Condition Total P(µg L-1)

Chlorophyll a

(µg L-1)

Secchi disk

depth (m)Ultra-Oligotrophic <4 <1 >12

Oligotrophic <10 <2.5 >6Mesotrophic 10-35 2.5-8 6-3

Eutrophic 35-100 8-25 3-1.5Hypereutrophic >100 >25 <1.5

Mean values for the trophic classification system

Crater Lake, Oregon

Murderkill Pond, Delaware

Eutrophication studies began in the 1940s and published work peaked in the 1980/ 90s.

These studies were conducted via –

• Comparative analyses of different water bodies over time and space, and • Experimentation at three different scales –

1. small-scale flask experiments such as bio-assays2. medium-scale experiments such as mesocosms3. whole-system manipulations (whole-lake experiments)

3 Important Developments that promoted Eutrophication Research

Nitrogen & Phosphorus as limiting nutrients

First important development in eutrophication research – identification of N & P

Driven by Leibig’s Law of the Minimum(1855)–

The yield of a given species should be limited by the nutrient that was present in the least quantity in the environment relative to its demands for growth

Nitrogen & Phosphorus as limiting nutrients

Key variables for eutrophication –• Sunlight• Silica• N• P

Leibig’s law – resulted in the concept of nutrient limitation for algal growth –

1. A single nutrient should be the primary limiting factor for algal growth

2. Observed algal growth should be proportional to the supply of the limiting nutrient

3. Practical control of the growth of algae can be accomplished via restricting the supply of the nutrient.

N & P were identified as the primary limiting nutrients -- this recognition was arrived at primarily by using bioassays.

Alfred Redfield (1958) proposed that the nutrient (N, P) content of living algal cells can be given by a –

• 7:1 by mass for N:P, or• elemental ratio of 16:1 for N:P

referred to as the Redfield ratio

Given mass ratio, how would you compute the elemental ratio?

This concept was extended to determine N & P controls

If N:P supply > Redfield ratio – P limitingIf N:P supply < Redfield ratio – N limiting

Alfred Redfield

However later work – showed that algae are composed of many species with varying N:P ratio (3 – 30)– and thus a single ratio was not very effective in determining N or P limitation

• when TN:TP < 10:1 – N limitation• when TN:TP > 17:1 – P limiting• between 10:1 17:1 – either N or P

Nutrient Loading Models (2nd important development)

Development of mass budgets for N & P for water bodies and the linkage of input/outputs with waterbody concentrations –

• Initially received with considerable skepticism; Thienemann remarked – that the concept “had nothing to do with limnology”.

• Mass balance approaches since then have become a cornerstone of ecosystem science research

• Models are based on the hydraulic characteristics of the water body –depth, flow rate, length, etc. – factors that determine the residence time or turnover time of the waterbody

• P models have received most of the attention. Example of P model –

TP – in lake P concentration (mg/m3)82.0

155.1

+=

w

in

tPTP

where Pin is the mean annual P concentration in inflow, and tw is the residence time (yrs)

• Compared to N, P models have also been easier to formulate –why?

Effects of nutrients on aquatic systems

3rd important development –Linking nutrient concentrations to – water quality variables of concern – e.g., algal biomass, water clarity, etc.

Factors controlling Eutrophication in fresh and marine waters

• Important differences between fresh waters and marine waters

• The controls that N and P have for eutrophication also varies with these waters

• Early work by Schindler in 1970 in Experimental Lakes Area (ELA) of Canada indicated that - freshwater lakes and reservoirs are limited by P

David Schindler ELA, Canada

P controls on phytoplankton –• hyperbolic relationship with P, with decreasing algal yields beyond TP > 100

mg/m3

• shifts in limiting nutrient (becomes N limited) as P concentration increases

Not surprisingly then, when P reductions in terms of reduction of phosphate detergents and wastewater treatment were instituted in the 70-80s, Lake Erie water quality improved tremendously.

In contrast to freshwaters, in marine systems the phytoplankton biomass is more tied to the N concentrations – suggesting that these systems are N-limited

Why?

Why? Likely reasons –

1. Strong P sequestration by Fe and Al oxides in freshwater systems. In contrast, Fe concentrations very low in marine systems to sequester P. P not recycled effectively in deep marine systems.

2. Sufficient Fe and Mo availability for N-fixing bacteria in freshwater systems – thus N is available. Fe and Mo are very low in marine waters and thus limit N fixation

3. High losses of N due to denitrification in marine waters

However, some studies (Hecky & Kilham, 1988) have shown that N-limitation in marine systems may not be applicable always.

For Estuarine systems, nutrient controls could be somewhere between freshwater and marine systems.- P limitation in upper portions and N limitation in lower portions?

Other important factors that could influence eutrophication:

• Bioavailabity of organic forms of N and P – most work has focused on inorganic forms

• Other macronutrients – Ca, Mg, K, S.• Micronutrients – Si, Fe, Mo, Cu, Zn, Mn, Cl, Co, Na, B, and V.• Light • Exudates, animal wastes, and other stimulations• Salinity• Water and nutrient mixing regime as a function of stratification• Dissolved oxygen • Type of algae• Community of grazers

Stratification of the lake because of the water temperature gradients during seasons

Stratification occurs because of the variation in the density of water with temperature

- water most dense at 4 degree C- less dense above and below 4 degree C

Mixing is limited to specific zones

Surface mixing occurs in the epilimnion –maybe 1m deep in summer or as much as 100 m under destabilized conditions.

Epilimnion water will not mix with the hypolimnion when stratification is in place.

After summer - When surface water temperatures cool up – reach 4 degree C – the surface water sinks – causes mixing and overturning! --- Fall Overturn

If surface temps drop below 4C, again stratification will take place

In spring when surface waters warm up and go beyond 4C – you will have the spring overturn!

Two overturning periods – dimicticOne overturning period – monomictic

Two important functions of overturning:• oxygenation of the hypolimnion by sinking surface

waters• nutrient enrichment of the epilimnion by rising

bottom waters

Susceptibility of water bodies to O2 depletion:

Deep oligotrophic systems do NOT suffer depletion –

• Low productivity in epilimnion – respiratory rates not high enough• The large depth of hypolimnion provides more than enough O2 to meet

any likely demands

Shallow eutrophic systems – do not develop seasonal depletion –

• because the mixing layer extends to the bottom• But – shallow eutrophic systems may develop – low O2 conditions

overnight under no wind or calm weather conditions (when the mixing mechanism is shut off) --- example – the shallow western basin of Lake Erie

Eutrophic systems with intermediate depths – most likely to be seasonally depleted by O2

- hypolimnion is small in depth - high production in the epilimnion- e.g., - central basin of Lake Erie.

Seasonal depletions of O2 – do not cause mass die off’s of fish and aquatic species – it’s the overnight O2 depressions that do!

Salinity gradients can also affect mixing/stratification

In the Chesapeake Bay –increased inflows of freshwater – make the O2 depletion condition worse.

Increasing urbanization (impervious surfaces) are expected to increase flows.

Harmful Algae or Harmful Algal Blooms (HABs)

• Definition is operational and not technical – due to diversity of HAB types and effects

• Toxic HABs – those that produce toxins or metabolites harmful to humans or animals

• Nuisance HABs – no toxins, but high biomass

Red tides Cyanobacteria

Types of Harmful Algal Blooms (HABs)

• Diatoms• Most are not toxic• Most common organisms associated with “spring blooms”• Require silica• Toxic form - Pseudonitzschia spp. • produce domoic acid that is responsible for the human illness called

amnesic shellfish poisoning (ASP) - neurotoxin• Loss of memory in animals and humans

Types of Harmful Algal Blooms (HABs)

• Dinoflagellates• Slower growth rates than diatoms• produce toxins that can kill fish directly or that intoxicate seafood with

toxins that can be passed onto human consumers. • Karenia brevis - large blooms along the coast of the Gulf of Mexico.

• produces a neurotoxin, brevetoxin, that is responsible for the human illness called neurotoxic shellfish poisoning

Karina brevis

Types of Harmful Algal Blooms (HABs)

• Dinoflagellates• Pfiesteria piscicida, P shumwayae, …• Neuse river estuary• Chesapeake Bay

Types of Harmful Algal Blooms (HABs)

• Cyanobacteria• The most common toxins – hepatotoxins (damages liver), such as

microcystin, nodularin, and cylindrospermopsin

• neurotoxins, such as anatoxin and saxitoxin

• Could include both N fixing and non N-fixing bacteria

• Nodularia, Anabaena, Aphanizomenon, MicrocystisMicrocystis

Life stages of a Toxic Bloom

Environmental SignificanceMicrocystis bloom in Aug 2014 led to shut down of drinking water in Toledo, Ohio - nearly half a million people were told not to use water for drinking, cooking, or bathing.

http://news.nationalgeographic.com/news/2014/08/140804-harmful-algal-bloom-lake-erie-climate-change-science/

Harmful Algal Blooms (HABs) and relationship with nutrients:

• Amount of nutrients

• Increasing nutrients = increasing chance of HABs

Florida Red Tide

Image – NOAA web site.

Harmful Algal Blooms (HABs) and relationship with nutrients:

• Nutrient stoichiometry –

• Low N:P ratios could favor N-fixing cyanobacteria and dinoflagellate species that could outcompete other species

Karenia brevis toxic bloom off of Florida

Harmful Algal Blooms (HABs) and relationship with nutrients:

• Composition of nutrients:

• Many HAB forms can use organic forms of N and P; posses the enzymes needed to breakdown the organic nutrients

• Type of fertilizers – like urea tend to increase HAB occurrence

• Many flagellate species are – mixotrophic and can consume particulate forms of nutrients, algal prey, ….

• Human and animal wastes may stimulate some HABs

Harmful Algal Blooms (HABs) and relationship with nutrients:

• Other nutrients –

• Diatoms require Si whereas some dinoflagellate require high P, thus decrease in Si:P ratios could move the community towards dinoflagellates.

Harmful Algal Blooms (HABs) and relationship with nutrients:

• HAB physiology, mobility –

• Microcystis (cyanobacteria) can vertically migrate – can consume excess P at the sediment water interface and then rise to the surface to form blooms• Non N-fixer

Harmful Algal Blooms (HABs) and relationship with nutrients:

• Mixing conditions of the water body –

• Stagnant water conditions, poor flushing, may also favor some HABs –e.g., toxic pfiesteria

Lake Erie Cladophora

Harmful Algal Blooms (HABs) and relationship with nutrients:

• Seasonal supply variation in nutrients

• During spring – N loadings are typically high and Si and P may be limiting.

• During summer – anoxic conditions in sediments may result in internal release of P which may stimulate the production of N-fixing HABs.

• A situation that has been observed in Chesapeake Bay.

Management Implications for HABs:

• Should not focus on one single nutrient or management practices that reduce a nutrient

• Control practices in headwaters should not alter the N:P balance downstream – e.g., the case of Neuse River in NC.

• Need to control both N and P• Stoichiometry should be maintained in favor of desirable species• N-fixing cyanobacteria not observed in estuaries and coastal seas (where

salinity 8-10 ppm; ocean salinity ~ 35ppm)• Sorbed P can be released under saline conditions of estuaries – internal

source