DILUTION OF NONPOINT-SOURCE NITRATE IN GROUNDWATER

Nonpoint-source pollution from agriculture can cause the degradation o f groundwater and surface water. Some studies conducted in Coastal Pla in aquifers have shown NO3- removal from groundwater due to assimilati on by vegetation or dentification before discharge to a stream is sign ificant; relatively few have been conducted on other physiographic and geological regions within the Chesapeake Bay watershed. This study wa s conducted at the boundary of the Valley and Ridge and Appalachian Pl ateau physiographic provinces to understand how the hydrological and g eochemical conditions in this region effect the transport and removal of NO3-. The groundwater dow system at the farm studied, located at th e base of a valley, is influenced by one groundwater flow component pa rallel to the axis of the valley and a second flowing perpendicular to the axis having been recharged from topographic highs along the sides of the valley. The axis-perpendicular component is transporting NO3- and Cl- applied as fertilizers and manure on an upgradient held and al so Cl- from salting of an adjacent road to the study site. The relativ ely nutrient-free water from the axis-parallel component dilutes NO3- and Cl- concentrations at the site from seasonal averages of 11 mg N/L and 90 mg CI/L to levels <0.4 mg N/L and 1 mg CI/L, respectively. Som e evidence exists for NO3- removal from groundwater <3 m belowground; however, it is difficult to confirm the removal process with dilution dominating the system.