Groundwater nitrate reductions within upstream and downstream sections of riparian buffers

Riparian buffer systems have been found to effectively decrease groundwater nitrate through denitrification. However, the ability to reduce nitrate has been variable and does not always work as effectively as desired. Defining ideal buffer placements that maximize denitrification could protect more stream miles, improving overall water quality. Over the past five years a detailed evaluation of the hydrology and attenuation of groundwater nitrate was conducted on two buffer sections along the same stream enrolled In the North Carolina Conservation Reserve Enhancement Program. These sections had two distinct widths and topographic locations. The objective of the study was to compare the differences between these buffer sections and provide a clear illustration of the necessity of preliminary evaluations prior to buffer installation. The average buffer widths were 60 m (Section 1, upstream) and 45 m (Section 2, downstream). Three transects of groundwater monitoring well nests with shallow (1.5-2.3 m) and deep (2.7-3.6 m) depths were installed within each buffer zone. Groundwater nitrate levels significantly decreased through the buffer sections (α=0.05). Water table measurements, nitrate to chloride ratios, deep well water quality analyses, topography, and redox measurements indicated denitrification as the predominant nitrate reduction mechanism and both sections were suitable for denitrification to proceed at high rates. However, groundwater contributing areas significantly influenced the overall efficiency of nitrate reduction in Section 1 due to nitrate limitations (α=0.05). Findings from this project provide an advanced understanding of factors that could lead to design recommendations that will enhance pollutant reductions in riparian buffers.