The Effects of Particulate Organic Carbon Quantity and Quality on Denitrification of Groundwater Nitrate

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Project Number:

WR11R006

Other Project Number:

2011WI297O

Funding Year:

2011

Contract Period:

7/1/2011 - 6/30/2013

Funding Source:

UWS

Investigator(s):
PIs:
  • Robert Stelzer, UW-Oshkosh
  • J. Thad Scott, Other
  • Lynn Bartsch, Other
Abstract:

Groundwater nitrate concentrations are elevated and rising in many aquifers throughout the world, including those in Wisconsin. High nitrate concentration in groundwater can lead to human health problems and can contribute to eutrophication in ecosystems. Many comparative studies have shown that denitrification rates are positively related to organic carbon quantity. However, there have been few manipulative studies in field settings that have addressed how carbon quantity affects groundwater nitrate removal. Even less is known about how carbon quality, especially particulate organic carbon (POC) quality, regulates denitrification of groundwater nitrate. The overall objective of the proposed research project is to determine how POC quantity and quality influence groundwater nitrate removal and retention in stream sediments. We propose to use field experiments to test the following hypotheses: 1) POC supply (quantity) limits denitrification rate and nitrate retention in stream sediments with high concentrations of groundwater nitrate; 2) Denitrification rate and nitrate retention in stream sediments will increase with POC quality. POC quantity and quality will be manipulated in Emmons Creek, a high-nitrate groundwater-fed stream in the Central Sand Ridges Ecoregion of Wisconsin. In Year 1, POC of different quantities will be buried in sandy sediments within open-ended mesocosms deployed in Emmons Creek. In Year 2, POC of varying quality, at identical quantities, will be buried in sandy sediments in the mesocosms. Response variables in both years will include denitrification rate (based on acetylene block assays using sediment slurries and measurements of in situ N2 concentrations in the field), net nitrate and ammonium retention along groundwater flow paths, and groundwater dissolved oxygen profiles. The project will be one of the first studies to use manipulative experiments to test how organic carbon quantity and quality affect removal of groundwater nitrate.

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