Effect of riparian buffers and controlled drainage on shallow groundwater quality in the North Carolina middle coastal plain.

摘要

Degradation of water quality in the streams and estuaries of North Carolina in recent years has resulted in regulations to reduce the introduction of numerous types of contaminants to this system. In the Neuse and Tar-Pamlico River Basins, excessive amounts of nitrogen have been identified as causing increased algal growth, low dissolved oxygen concentrations, and have been linked to increased growth of toxic microorganisms such as Pfiesteria piscicida. There are numerous sources of nitrogen to the basins; however, agricultural nonpoint sources have been identified as the largest contributor of nitrogen. Riparian buffers, controlled drainage, and nutrient management have been identified as effective BMPs for reducing nitrogen transport to streams under many landscape conditions. As a result, a combination of nutrient management, controlled drainage, and riparian buffer best management practices have been mandated in the Neuse River Basin to reduce the loss of agricultural nonpoint source pollution.; Based on this research, several recommendations for further study are presented. Monitoring of riparian buffer vegetation plots should continue with the expectation that vegetation may have a significant impact over time as the vegetation types become established. Eventually the vegetation in the buffer will reach a steady state with respect to nitrogen in the buffer; however, this may take many years. Quantification of the relative proportion of dilution and denitrification for a given nitrate concentration decrease beneath the buffers should be investigated. One approach would be installation of redox probes at the deep well depth to give an indication if conditions are favorable (i.e. reducing) for denitrification. Also, the deep groundwater (i.e. below the impermeable layer) chemistry should be compared to the shallow groundwater chemistry to determine the relative proportions of constituents such as calcium and magnesium. This analysis would give an indication if dilution of the shallow groundwater were occurring as a result of deep groundwater upwelling. The REMM simulations may be improved by measuring groundwater velocity into the riparian buffer, improving the estimates of surface water runoff into the riparian buffers, and by modifying the model to simulate a single buffer zone rather than three. (Abstract shortened by UMI.)