Abstract
Reducing excessive reactive nitrogen (N) in agricultural waterways is a major challenge for freshwater managers and landowners. Effective solutions require the use of multiple and combined N attenuation tools, targeted along small ditches and streams. We present a visual framework to guide novel applications of ‘tool stacking’ that include edge-of-field and waterway-based options targeting N delivery pathways, timing, and impacts in the receiving environment (i.e., changes in concentration or load). Implementing tools at multiple locations and scales using a ‘toolbox’ approach will better leverage key hydrological and biogeochemical processes for N attenuation (e.g., water retention, infiltration and filtering, contact with organic soils and microbes, and denitrification), in addition to enhancing ecological benefits to waterways. Our framework applies primarily to temperate or warmer climates, since cold temperatures and freeze–thaw-related processes limit biologically mediated N attenuation in cold climates. Moreover, we encourage scientists and managers to codevelop N attenuation toolboxes with farmers, since implementation will require tailored fits to local hydrological, social, and productive landscapes. Generating further knowledge around N attenuation tool stacking in different climates and landscape contexts will advance management actions to attenuate agricultural catchment N. Understanding how different tools can be best combined to target key contaminant transport pathways and create activated zones of attenuation along and within small agricultural waterways will be essential.
Highlights
Nutrient pollution from agricultural land use has degraded water quality and aquatic ecosystem health, creating significant management challenges for aquatic ecosystems around the world [1,2].Excess reactive nitrogen (N) and phosphorus (P) inputs can cause eutrophication, toxic algal blooms, anoxic dead zones, altered food webs in receiving freshwater and estuarine environments, and nitrate toxicity in groundwater [2,3,4]
We suggest the suitability of N attenuation tools be evaluated based on the attenuation outcome for the receiving environment, and the delivery pathway and timing of N export
By combining multiple tools to target a range of N loading locations and hydrological variability that limit the ability of waterways to attenuate nutrients, small agricultural waterways impacted by multiple stressors can behave more like linear wetlands [139], potentially providing greater ecosystem benefits than channelized ditches primarily intended to drain water from the landscape
Summary
Nutrient pollution from agricultural land use has degraded water quality and aquatic ecosystem health, creating significant management challenges for aquatic ecosystems around the world [1,2]. Despite promising modeled N export reductions by combining in-stream options with land-based N management and attenuation [15], ‘tool stacking’ from the edge-of-field to in-stream has not yet been evaluated in situ at the catchment scale. We evaluate the challenges and opportunities for codeveloping tool stacking approaches to attenuate excess N from edge-of-field to in-stream environments along small, agricultural waterways. Managing small waterways to elicit effective change in the receiving environment, targeting local N export dynamics and underlying hydrological variability from agricultural land to waterways, and overcoming factors limiting N attenuation with suites of edge-of-field to waterway-based tools at multiple scales and locations. We emphasize the need to encourage codevelopment of novel, effective, multiple-tool, multiple-scale waterway N attenuation approaches by scientists, practitioners, and farming communities to overcome the technical and practical challenges to managing N in agricultural landscapes
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