Exploring causes of increasing nitrate concentrations in ......and J.J. McDonnell, eds., Isotope...
Transcript of Exploring causes of increasing nitrate concentrations in ......and J.J. McDonnell, eds., Isotope...
Exploring causes of increasing Exploring causes of increasing nitrate concentrations in the nitrate concentrations in the
Lower St. Croix RiverLower St. Croix River
Brenda Moraska Lafrancois, Byron Karns, Brenda Moraska Lafrancois, Byron Karns, Wade Miller, Brian Schuetz, Elizabeth Wade Miller, Brian Schuetz, Elizabeth
Peterson, and Will DanielsPeterson, and Will Daniels
K. Heideman
Why N?Why N?
•• Like P, N can be a Like P, N can be a limiting nutrientlimiting nutrient
•• Excess N (or changes Excess N (or changes in N:P) can lead to in N:P) can lead to nuisance bloomsnuisance blooms
Coastal Dead ZonesCoastal Dead Zones• Spread exponentially since 1960s• 400 ecosystems• Result of coastal eutrophication• Fertilizer runoff • Serious ecological consequences
Diaz and Rosenberg. 2008. Science 321:926-929.
Gulf of Mexico HypoxiaGulf of Mexico Hypoxia•• Noticed since 1950s, Noticed since 1950s,
monitored since 1970smonitored since 1970s•• Driven by increases in Driven by increases in
nitrate (NOnitrate (NO33--N) N) –– fertilizer fertilizer •• 56% of nitrate from Upper 56% of nitrate from Upper
MississippiMississippi•• 30% reduction in N 30% reduction in N
loading requiredloading required
Goolsby (2000) Eos. Rabalais et al. (2002) BioScience.
Lake St. Croix NitrateLake St. Croix Nitrate
D. Morrison, MPCA
0.645 mg/l
1.590 mg/l
Median values for SC 0.3 and MR 796.9, 2000-2004.
Lake St. Croix NitrateLake St. Croix Nitrate
1.0
0.8
0.6
0.4
0.2
0.0
19751980
19851990
19952000
Seasonal Kendall TestPrescott (1976-2002)p < 0.05
Nitr
ate-
N (m
g/l) Median (1990-1999)
0
0.2
0.4
0.6
EPA Reference
(Rivers)Prescott
Stillwater
Nitr
ate-
N (m
g/l)
Potential CausesPotential Causes•• Increases in fertilizer useIncreases in fertilizer use•• Changes in wastewater Changes in wastewater
treatment (NHtreatment (NH33→→NONO33))•• Atmospheric depositionAtmospheric deposition•• Changes in soil Changes in soil
denitrification processesdenitrification processes
Stable Isotope AnalysisStable Isotope Analysis
•• What are stable isotopes?What are stable isotopes?–– Different forms of the same element Different forms of the same element –– Not radioactiveNot radioactive–– Common ones = C, N, O, S, HCommon ones = C, N, O, S, H
•• Relative proportions used to infer things about Relative proportions used to infer things about ecosystem structure and processecosystem structure and process
•• Isotopes of N and O useful for tracking nitrateIsotopes of N and O useful for tracking nitrate–– 1414NN and and 1515NN–– 1616OO, , 1717O, and O, and 1818OO
Nitrate Stable IsotopesNitrate Stable Isotopes
C. Kendall. 1998. Tracing nitrogen sources and cycling in catchmC. Kendall. 1998. Tracing nitrogen sources and cycling in catchments. Chapter 16 ents. Chapter 16 inin C. Kendall C. Kendall and J.J. McDonnell, eds., Isotope tracers in catchment hydrologyand J.J. McDonnell, eds., Isotope tracers in catchment hydrology. Elsevier Science B.V.. Elsevier Science B.V.
Study GoalsStudy Goals
1.1. Characterize patterns in nitrate Characterize patterns in nitrate concentration concentration •• Mainstem Lake St. CroixMainstem Lake St. Croix•• TributariesTributaries•• Wastewater Treatment PlantsWastewater Treatment Plants
2.2. Identify nitrate sourcesIdentify nitrate sources3.3. Evaluate usefulness of biological proxiesEvaluate usefulness of biological proxies
HypothesesHypotheses
•• NONO33--N concentrations are highest in N concentrations are highest in downstream tributaries and WWTPsdownstream tributaries and WWTPs
•• δδ1515N and N and δδ1818O suggest wastewater O suggest wastewater influence at upstream sites, fertilizer influence at upstream sites, fertilizer downstreamdownstream
•• δδ1515N is more stable in zebra mussels than N is more stable in zebra mussels than in water or phytoplankton over seasonin water or phytoplankton over season
DesignDesign•• 14 sites14 sites
–– 7 mainstem7 mainstem–– 5 tributaries5 tributaries–– 2 wastewater plants2 wastewater plants
•• 5 sampling events5 sampling events•• 3 components3 components
–– Water (nitrate)Water (nitrate)–– PhytoplanktonPhytoplankton–– Zebra musselsZebra mussels
Stillwater
Bayport
Afton
Mississippi River
Valley Creek
Trout Brook
Willow River
Hudson
Prescott
Bayport
Afton
Mississippi River
Valley Creek
Trout Brook
Willow River
KinnickinnicRiver
Hudson
Prescott
2
3
4
5
6
7
1Brown’s Creek
Stillwater
Bayport
Afton
Mississippi River
Valley Creek
Trout Brook
Willow River
Hudson
Prescott
Bayport
Afton
Mississippi River
Valley Creek
Trout Brook
Willow River
KinnickinnicRiver
Hudson
Prescott
2
3
4
5
6
7
1Brown’s Creek
Stillwater
Bayport
Afton
Mississippi River
Valley Creek
Trout Brook
Willow River
Hudson
Prescott
Bayport
Afton
Mississippi River
Valley Creek
Trout Brook
Willow River
KinnickinnicRiver
Hudson
Prescott
2
3
4
5
6
7
1Brown’s Creek
Stillwater
Bayport
Afton
Mississippi River
Valley Creek
Trout Brook
Willow River
Hudson
Prescott
Bayport
Afton
Mississippi River
Valley Creek
Trout Brook
Willow River
KinnickinnicRiver
Hudson
Prescott
2
3
4
5
6
7
1Brown’s Creek
MethodsMethods
Phytoplankton
Water – NO3-N Zebra Mussels
MethodsMethods
•• Water analyzed for Water analyzed for nitrate concentration nitrate concentration and stable isotopes of N and stable isotopes of N and Oand O
–– Diffusion technique (Diffusion technique (δδ1515N) N) –– Denitrifier method (Denitrifier method (δδ1515N N
and and δδ1818O)O)
•• Phytoplankton and Phytoplankton and zebra mussel tissue zebra mussel tissue analyzed for analyzed for δδ1515N (N (δδ1313C) C)
Mainstem ConcentrationsMainstem Concentrations
Means and StDevs, May-Aug 2008Note: detection limit = 0.2 mg/l
0.00
0.10
0.20
0.30
0.40
0.50
SC1 SC2 SC3 SC4 SC5 SC6 SC7
Nitr
ate-
N (m
g/l)
High Bridge Prescott
Tribs and WWTPsTribs and WWTPs
Means and StDevs, May-Aug 2008
0
4
8
12
16
Browns
MallalieuTrout
KinnickValley
Hudson WWTP
St. Croix Valley WWTP
Nitr
ate-
N (m
g/l)
Stable Isotope ResultsStable Isotope Results(Hypothetical)(Hypothetical)
Measured Measured St. Croix sitesSt. Croix sites
δδ1515NN W
aste
Was
te
Ferti
lizer
Ferti
lizer
ExpectedExpectedSource SignalsSource Signals
Preliminary FindingsPreliminary Findings
•• Nitrate increases Nitrate increases systematicallysystematically–– Largest increases Largest increases
downstreamdownstream–– Lake St. Croix Lake St. Croix
tributaries and tributaries and tributary land use tributary land use importantimportant
AcknowledgementsAcknowledgements•• U.S. Army Corps of U.S. Army Corps of
EngineersEngineers•• National Park ServiceNational Park Service•• SCWRSSCWRS•• Metropolitan CouncilMetropolitan Council•• Colorado Plateau Stable Colorado Plateau Stable
Isotope LabIsotope Lab•• Dennis Lindeke, Jim Dennis Lindeke, Jim
SchreiberSchreiber•• David VanderMeulen David VanderMeulen •• Toben Lafrancois and the Toben Lafrancois and the
Youth River Action Youth River Action ProgramProgram
Seasonal PatternsSeasonal Patterns
Long-term means (1976-2002)
Jan FebMar
AprMay
Jun JulAug
Sep Oct NovDec
0
0.3
0.6
0.9
1.2
1.5
Nitr
ate-
N (
mg/
l)
HydrographStillwaterPrescott
0
4000
8000
12000
16000
20000
Dis
char
ge (c
fs)
Seasonal PatternsSeasonal Patterns
Means and StDevs, May-Aug 2008
0.00
0.10
0.20
0.30
0.40
May June July Aug
Nitr
ate-
N (m
g/l)
Mainstem St. Croix Sites