Kc. Stone et al., NITRATE-N DISTRIBUTION AND TRENDS IN SHALLOW GROUNDWATER ON AN EASTERN COASTAL PLAINS WATERSHED, Transactions of the ASAE, 41(1), 1998, pp. 59-64
Nonpoint source pollution from agriculture has been a major concern, p
articularly where intensive agricultural operations exist near environ
mentally sensitive waters. To address these nonpoint source pollution
concerns, a Water Quality Demonstration Project (WQDP) was initiated o
n the Herrings Marsh Run (HMR) watershed in Duplin County North Caroli
na. The WQDP was implemented to determine water quality benefits from
voluntary adoption of improved management practices. In the WQDP, 84 g
roundwater monitoring well sites were established on 21 farms selected
to represent the major farming practices on the watershed. On the HMR
watershed nitrate-N contamination of groundwater was not a wide sprea
d problem. Seventy-four percent of the groundwater monitoring sites ha
d nitrate-N less than the drinking water standard of 10 mg/L. Mean nit
rate-N concentrations were below 10 mg/L on 16 of the 21 farms. Of the
four farms with nitrate-N exceeding 10 mg/L, one farm had mean nitrat
e-N that exceeded 20 mg/L. This farm had an undersized and overloaded
swine wastewater spray field. After the spray field was expanded and a
pplication rates were reduced, groundwater nitrate-N concentrations de
clined; but they continued to exceed 20 mg/L. Other farms with swine w
aste spray fields had mean groundwater nitrate-hr concentrations <20 m
g/L throughout the study period. Groundwater nitrate-N concentrations
under row crops were <10 mg/L on all but two farms. Three of the four
farms with nitrate-IV concentrations exceeding 10 mg/L were in a subwa
tershed of the HMR that had the highest concentration of animal waste
application and excess nitrogen applied. Of the 21 farms, three farms
had a significant increasing trend in groundwater nitrate-N while four
farms had a significant decreasing trend. The overloaded swine wastew
ater spray field had a significant decreasing nitrate-N trend. Most fa
rms with concentrations less than 10 mg/L had no detectable trend in n
itrate-N concentration during the study. These findings indicate that
nitrate-N contamination of groundwater is not a widespread problem on
the HMR watershed even though it is intensively farmed.