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Ecological Engineering Practices for the Reduction of Excess Nitrogen in Human-Influenced Landscapes: A Guide for Watershed Managers

Passeport, Elodie, Vidon, Philippe, Forshay, Kenneth J., Harris, Lora, Kaushal, Sujay S., Kellogg, Dorothy Q., Lazar, Julia, Mayer, Paul, Stander, Emilie K.
Environmental management 2013 v.51 no.2 pp. 392-413
anaerobic conditions, carbon, climate change, coasts, decision support systems, denitrification, ecosystems, engineering, estuaries, groundwater, lakes, land use, landscapes, leaching, managers, nitrogen, pollution, riparian buffers, septic systems, watersheds, wetlands
Excess nitrogen (N) in freshwater systems, estuaries, and coastal areas has well-documented deleterious effects on ecosystems. Ecological engineering practices (EEPs) may be effective at decreasing nonpoint source N leaching to surface and groundwater. However, few studies have synthesized current knowledge about the functioning principles, performance, and cost of common EEPs used to mitigate N pollution at the watershed scale. Our review describes seven EEPs known to decrease N to help watershed managers select the most effective techniques from among the following approaches: advanced-treatment septic systems, low-impact development (LID) structures, permeable reactive barriers, treatment wetlands, riparian buffers, artificial lakes and reservoirs, and stream restoration. Our results show a broad range of N-removal effectiveness but suggest that all techniques could be optimized for N removal by promoting and sustaining conditions conducive to biological transformations (e.g., denitrification). Generally, N-removal efficiency is particularly affected by hydraulic residence time, organic carbon availability, and establishment of anaerobic conditions. There remains a critical need for systematic empirical studies documenting N-removal efficiency among EEPs and potential environmental and economic tradeoffs associated with the widespread use of these techniques. Under current trajectories of N inputs, land use, and climate change, ecological engineering alone may be insufficient to manage N in many watersheds, suggesting that N-pollution source prevention remains a critical need. Improved understanding of N-removal effectiveness and modeling efforts will be critical in building decision support tools to help guide the selection and application of best EEPs for N management.