Stacked conservation practices reduce nitrogen loss: A paired watershed study.

Area of Science:

• Environmental Science
• Water Quality Management
• Agricultural Hydrology

Background:

• Nutrient reduction goals in the Mississippi/Atchafalaya River Basin (MARB) necessitate combined best management practices (BMPs).
• Field data on stacked BMP adoption is vital for encouraging widespread implementation.
• Understanding the influence of BMPs, precipitation, and seasonality on nitrogen export is critical for effective watershed management.

Purpose of the Study:

• To assess the impact of varying BMP coverage on nitrogen (N) export at a catchment scale.
• To evaluate the influence of precipitation patterns and seasonality on N export.
• To quantify the effectiveness of stacked BMPs in reducing nitrate (NO₃-N) and total nitrogen (TN) loads.

Main Methods:

• A paired catchment-scale study was conducted from 2015-2018.
• Flow-weighted water samples were collected and analyzed for total ammonia nitrogen (TAN), NO₃-N, and TN.
• Catchments with differing BMP areal coverage (Low-BMP 11: 27.6%, High-BMP 12: 87.6%) were compared.

Main Results:

• No significant difference in TAN concentrations was observed between catchments.
• Significantly higher NO₃-N and TN concentrations were found in the Low-BMP catchment compared to the High-BMP catchment.
• Stacked BMPs in High-BMP 12 effectively lowered NO₃-N and TN loads by 60.3% and 59.1%, respectively, compared to Low-BMP 11.
• Precipitation patterns, including post-drought flushing and early-season rainfall, significantly affected N export.
• The highest flow percentiles (50th-90th) were responsible for the majority of NO₃-N export.

Conclusions:

• Stacked BMP application is highly effective in reducing nitrogen loads and improving water quality in the MARB.
• Precipitation patterns and seasonality are key factors influencing nitrogen export dynamics.
• Collaborative landowner efforts within a watershed are essential for achieving downstream water quality objectives.