Embed Size (px)
Citation preview
Using nitrate δ15N and δ18O values to iden6fy poten6al sources of nutrient inputs to a highly impacted inlet in South Puget Sound, Washington
Yvonne Wetzig1, Jackie Perkins2, Liz Roepke2, Kena Fox-‐Dobbs2 1University of Puget Sound, Chemistry Department, Tacoma, WA USA 2University of Puget Sound, Geology Department, Tacoma, WA USA
Research QuesLons Q1: Do surface and deep inlet marine water samples have different NO3 concentraLons, δ15NNO3
values, and δ18ONO3 values? Do NO3 concentraLons and isotopic values change with distance into the inlet?
Q2: Can we detect anthropogenic nitrogen sources in freshwater sources around the inlet? Q3: Do the δ15NNO3 and δ18ONO3 values of inlet samples provide insight into water quality issues?
References CascioW KL, Sigman DM, Galanter HasLngs M, Bahlke JK, Hilkert A. 2002. Measurement of the oxygen isotopic composiLon of nitrate in seawater and freshwater using the denitrifier method.
Analy'cal Chemistry 74: 4905-‐4912. DeGasperi C. 2008. EPA Grant ApplicaLon: Targeted Watershed Grants 2008 Puget Sound IniLaLve -‐ Quartermaster Harbor Nitrogen Management Study. HasLngs MG, CascioW KL, Elliod, EM. 2013. Stable isotopes as tracers of anthropogenic nitrogen sources, deposiLon, and impacts. Elements 9: 339-‐344. Kendall C, Elliod EM, and Wankel SD. 2007. Tracing anthropogenic inputs of nitrogen to ecosystems, Chapter 12, In: R.H. Michener and K. Lajtha (Eds.), Stable Isotopes in Ecology and
Environmental Science, 2nd ediLon, Blackwell Publishing, p. 375-‐449. King County. 2014. Quartermaster Harbor Nitrogen Management Study: Final Study Report. Prepared by C. DeGasperi, Water and Land Resources Division. Seadle, Washington. Sigman DM, CascioW KL, Andreani M, Barford C, Galanter M, Bahlke JK. 2001. A bacterial method for the nitrogen isotopic analysis of nitrate in seawater and freshwater. Analy'cal Chemistry
73: 4145-‐4153. 1867 U.S. Coast Survey Chart or Map of Puget Sound, Washington -‐ Geographicus -‐ PugetSound-‐uscs-‐1867" by United States Coast Survey -‐ Report of the Superintendent of the United States
Coast Survey, (Washington) Licensed under Public domain via Wikimedia Commons.
Judd Creek
Buoy #52
Buoy #53
Buoy #54
Buoy #55
Buoy #56
Mileta Creek
Backbay Creek Well
Acknowledgements Our greatest thanks must be given to: our professor, Kena Fox-‐Dobbs, for her guidance throughout our project; Anne Fetrow, for her feedback on this poster; the IsoLab at the University of Washington for all analyLcal work; Joel Elliot and the UPS Biology department for providing a boat for sample collecLon; the kind resident who allowed us to sample their well water; and the kind resident who allowed us to sample creek water on their property. This work was supported by the UPS Geology Department McMillin Fund, and UPS University Enrichment Commidee Conference Travel Grants to JW and KFD.
*Note: The NO3 concentra'ons of the two samples taken from Backbay Creek are indis'nguishable from a blank standard, so their isotopic data were omiGed.
Study Area • Quartermaster Harbor (QMH) is a hydrologically restricted inlet on Vashon Island in Puget Sound surrounded by residenLal, agricultural, and open spaces
• The inlet depth ranges from 5 meters (inner QMH) to 45 meters (outer QMH)
• Nutrient loading and limited circulaLon in the inlet is related to environmental issues including poor water quality and annual toxic algal blooms, which contribute to fish kills and shellfish contaminaLon.
Sampling and Analysis • 15 samples collected from 3 creeks, 5 buoys in the inlet, and 1 well. • Creek water samples from outlets of Judd, Mileta, and Backbay Creeks.
• Two inlet water samples from each buoy, one at depth (just above
Figure 4: CollecLng a creek sample.
Study Area
0
75
150
225
300
375
450
525
600
675
750
Judd Mileta Backbay, upstream Backbay, downstream Well water (85' deep)
[NO
3] (µ
M)
0.0
5.0
10.0
15.0
20.0
25.0
0 2000 4000 6000 8000 10000
[NO
3] (µ
M)
Distance into Inlet (m)
Buoy 52 shallow
Buoy 52 deep
Buoy 53 shallow
Buoy 53 deep
Buoy 54 shallow
Buoy 54 deep
Buoy 55 shallow
Buoy 55 deep
Buoy 56 shallow
Buoy 56 deep
[Deep sample trend]
0.0
2.0
4.0
6.0
8.0
10.0
0 2000 4000 6000 8000 10000
δ15 N
NO3 ‰
Distance into Inlet (m)
Buoy 52 shallow
Buoy 52 deep
Buoy 53 shallow
Buoy 53 deep
Buoy 54 shallow
Buoy 54 deep
Buoy 55 shallow
Buoy 55 deep
Buoy 56 shallow
Buoy 56 deep
[Deep sample trend]
4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
-‐5 0 5 10 15 20
δ18 O
NO3 ‰
(VS
MOW)
δ15NNO3 ‰ (air N2)
Buoy 52 shallow
Buoy 52 deep
Buoy 53 shallow
Buoy 53 deep
Buoy 54 shallow
Buoy 54 deep
Buoy 55 shallow
Buoy 55 deep
Buoy 56 shallow
Buoy 56 deep
Well Water
Mileta Creek
Judd Creek
PotenLal sepLc contribuLon to well water
Shallow marine samples from the the innermost inlet buoys.
Streams have similar NO3
-‐ source
SepLc Soil/Marine Terrestrial
Marine/FerLlizer
Q2: Mileta Creek, which has high [NO3], is isotopically very similar to Judd Creek. Neither creek have isotopic values that suggest an anthropogenic NO3 source. The well water has moderate [NO3] and isotopic values that may reflect sepLc leakage.
Q1: The larger difference in [NO3] and δ15NNO3 values of deep and shallow samples at inner vs. outer inlet buoys reflects differences in biological use and sources of NO3.
The consistent δ15NNO3 values of deep inlet samples may be due to relaLvely constant groundwater recharge or marine contribuLon.
The correlaLon between between shallow [NO3] and δ15NNO3 values and distance into the harbor suggests linear change in nutrient condiLons (vs. stepwise or threshold)
Q3: All deep and some shallow marine samples have similar NO3 source(s). The two shallow marine samples furthest into the harbor likely reflect the influence of anthropogenic source(s).
EPA Maximum Contaminant Level
Background • Manure, ferLlizers, sepLc waste, atmosphere, and nitrogen fixing plants are all possible
major sources of nitrate in this inlet and surrounding freshwater sources. • Nitrogen and oxygen stable isotope analysis of nitrate can be used to idenLfy
anthropogenic and natural sources, via the systems’ unique isotopic signatures. • Nitrate can enter the inlet through mulLple freshwater sources, Figure 8. Nitrate concentraLons in fresh water samples (streams and well), and the EPA’s
limit of water considered safe for drinking.
Figure 9. Isotopic data ploded relaLve to esLmated values of possible nitrate sources�.
Figure 6. Nitrate concentraLon in marine samples ploded vs. distance into inlet.
Figure 7. δ15NNO3 values of marine samples ploded vs. distance into inlet.
Figure 2. Sign posted at Dockton Park on the waterfront of Quartermaster Harbor.
some of which provide drinking __.water for local residents. • The unique bathymetry of the
inlet inhibits water circulaLon between the inner and outer regions, allowing a greater residency of pollutants.
• EPA has set the maximum contaminant level for nitrate in drinking water to be 10mg/L (~160µM).
Figure 3. SchemaLc representaLon of nitrate inputs into Quartermaster Harbor, including groundwater seepage, surface stream runoff, sepLc system leakage, and natural and syntheLc ferLlizer runoff, and marine influx.
Figure 5: Sample locaLons in the study area (inset of fig. 1 map).
sediment interface) and one at the water surface. • Well water from an organic farm next to Backbay Creek.
• Samples were frozen and analyzed at the University of Washington IsoLab for [NO3], δ15NNO3 and δ18ONO3 values via the bacterial denitrifier method.
Findings and InterpretaLons
Figure 1 . Map of western Washington and study area.
