7/1/2001 - 6/30/2003
- Bryant Browne, UW-Stevens Point
Nitrate concentrations in groundwater-fed streams are frequently lower than concentrations in groundwater beneath adjacent agricultural recharge areas. The cause of this discrepancy, and similar discrepancies for other chemicals, poses a key question for understanding how agricultural practices affect water quality in many river systems. Unfortunately, conventional stream monitoring approaches are insufficient to address this question. Two factors that contribute to differences in groundwater nitrate concentrations between recharge areas and stream discharge points are: 1) the transformation of nitrate to gaseous forms (nitrous oxide, nitrogen gas) by denitrifying bacteria and 2) the amount of time it takes groundwater to move through the landscape from recharge areas to discharge points (lag time). To predict how these factors affect the baseflow water quality, a better understanding of the spatial and temporal scales of groundwater/surface water interactions is needed. The objectives of this study are to characterize the spatial and temporal scales of groundwater discharge to a 4th order stream within an agricultural basin and to quantify the influence of groundwater denitrification on baseflow Nitrate concentrations.