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The effect of riparian buffer width and vegetation type on shallow groundwater quality has not been evaluated in the Middle Coastal Plain of North Carolina. Four riparian buffer vegetation types and no–buffer (no–till corn and rye rotation or pasture) were established at 8 and 15 m widths as follows: cool season grass (fescue), deep–rooted grass (switch grass), forest (pine and mixed hardwood), and native vegetation. Nested groundwater monitoring wells were installed at the field/buffer edge and the stream edge in the middle of each riparian buffer plot at three depths. Most deep, mid–depth, and shallow 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 nitrate–nitrogen concentrations at the middle well depth were significantly lower in the 15 m wide plots compared to the 8 m plots over half the monitoring period, extreme flooding as a result of a hurricane in the middle of the study confounded the results. The effect of vegetation was not significant at any time, including the no–buffer cropped and fertilized plots. The effect of vegetation was minimized because at the early stage in the buffer vegetation establishment, vegetative cover and root mass were not fully developed, the hurricane–induced flooding forced the re–establishment of several vegetation types (forest and fescue), and there was likely some mixing of groundwater flowing toward the vegetation plots. Establishment of buffers along streams where groundwater flowed away from the stream did not result in lower groundwater nitrate levels. |
