Effects of Riparian Buffer Vegetation and Width: A 12-Year Longitudinal Study

Area of Science:

• Environmental Science
• Water Resource Management
• Agricultural Science

Background:

• Agricultural nitrogen runoff is a major water quality concern.
• Riparian buffer zones are implemented to mitigate groundwater nitrate pollution.
• Optimal riparian buffer design and long-term effectiveness require further investigation.

Purpose of the Study:

• To evaluate the long-term (12-year) effectiveness of different riparian buffer types and widths on groundwater nitrate (NO) and dissolved organic carbon (DOC) reduction.
• To determine the influence of buffer width and vegetation on nitrate removal efficiency over time.
• To assess the impact of riparian buffers on water quality in the North Carolina coastal plain.

Main Methods:

• A 12-year field study was conducted using various buffer types (trees, switchgrass, fescue, native, control) and widths (8m, 15m).
• Groundwater nitrate-nitrogen (NO-N) and dissolved organic carbon (DOC) concentrations were monitored over time.
• Statistical analysis was used to assess the significance of buffer type, width, and time on NO-N and DOC trends.

Main Results:

• Wider buffers (15m) showed 2.5 times greater NO-N reduction (46%) compared to narrower buffers (16%) at intermediate groundwater depths.
• Buffer effectiveness for NO-N removal increased by 0.62% per year, regardless of width.
• Vegetative type did not have a statistically significant impact on NO-N removal. Deep groundwater showed no time-dependent NO-N removal, but wide buffers with specific vegetation types had high removal rates (19-82%).
• Dissolved organic carbon (DOC) concentrations remained low (≤5.0 mg/L) and increased slightly over time. Higher DOC did not enhance NO-N removal, suggesting potential limitations from intermittent reduced soil conditions.

Conclusions:

• Riparian buffer width is a more critical factor than vegetation type for groundwater nitrate removal in newly established buffers in the North Carolina coastal plain.
• Long-term monitoring indicates a continuous improvement in nitrate removal efficiency with time, particularly in wider buffers.
• Understanding the interplay between buffer design, hydrology, and soil conditions is essential for optimizing riparian buffer functions in agricultural watersheds.