Submitted to: American Water Resources Association Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 4, 2000
Publication Date: N/A
Interpretive Summary: Riparian forest buffer strips along streams can remove agricultural nitrogen from water and improve the quality of rivers, lakes, and coastal waters. Use of buffer strips is an important part of best management practices for improving water quality in the Chesapeake Bay watershed. The Natural Resources Conservation Service (NRCS) has initiated a program to develop two million miles of buffers along our nation's rivers and streams Routine monitoring of buffers for effectiveness in mitigating agricultural nitrogen from groundwater is difficult because direct measurement methods do not exist. A relatively simple and precise method based on the measurement of dissolved gas concentrations in groundwater was developed. This method is capable of accurately measuring nitrogen gas concentrations. It can also be utilized for assessing seasonal and spatial variation of nitrogen concentrations in groundwater.
Technical Abstract: Dissolved gas analysis permits direct detection of groundwater denitrification and was used in this study to assess nitrogen fate in a riparian wetland. Dissolved argon and dinitrogen were measured in transects of nested piezometers installed at different depths within upwelling regions of the riparian wetland. The method used argon content in the water ras a natural inert tracer for assessing background N2 content caused by a previous air-water equilibrium. Assessment of nitrate loss and Ar in groundwater within the upwelling zone indicated that the shallow piezometers had significant dinitrogen loss through degassing. Most of the total measured nitrate-nitrogen loss in the groundwater could be accounted for by dinitrogen produced from dinitrification. Oxygen concentrations in these samples increased from anoxic with less than 10 uM to oxic in piezometers close to the aquifer layer indicating upwelling of oxic groundwater. This relatively simple and sensitive technique for analysis o dissolved gases in groundwater can be applied to detect small changes in nitrogen gas concentration and aids in assessing nitrate fate along the groundwater flow path.