Effect of Riparian Buffer Width and Vegetation Type on Shallow Groundwater Quality in the Middle Coastal Plain of North Carolina

The effect of riparian buffer width and vegetation type on shallow groundwater quality has not been evaluatedin the Middle Coastal Plain of North Carolina. Four riparian buffer vegetation types and nobuffer (notill corn and ryerotation or pasture) were established at 8 and 15 m widths as follows: cool season grass (fescue), deeprooted grass (switchgrass), forest (pine and mixed hardwood), and native vegetation. Nested groundwater monitoring wells were installed at thefield/buffer edge and the stream edge in the middle of each riparian buffer plot at three depths. Most deep, middepth, andshallow wells were 3.0 m, 1.8 m, and 0.6 m deep from the ground surface to the top of the 0.6 m perforated section, respectively.Wells were sampled for 23 months beginning July 1998. Although the ditch well nitratenitrogen concentrations at the middlewell depth were significantly lower in the 15 m wide plots compared to the 8 m plots over half the monitoring period, extremeflooding as a result of a hurricane in the middle of the study confounded the results. The effect of vegetation was not significantat any time, including the nobuffer cropped and fertilized plots. The effect of vegetation was minimized because at the earlystage in the buffer vegetation establishment, vegetative cover and root mass were not fully developed, the hurricaneinducedflooding forced the reestablishment of several vegetation types (forest and fescue), and there was likely some mixing ofgroundwater flowing toward the vegetation plots. Establishment of buffers along streams where groundwater flowed awayfrom the stream did not result in lower groundwater nitrate levels.