Reactive interfaces in agroecosystems: quantifying coupled biogeochemical dynamics across scales using a comprehensive lab-field-modeling approach

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Sustaining agricultural production is critical to food security and economic development but also leads to environmental degradation, in large part due to the loss of nutrient elements, including carbon (C), nitrogen (N), phosphorus (P) and sulphur (S), from agricultural soils to waterways where they have adverse ecological effects, foremost excessive algal growth. Best management practices (BMPs) aim at creating or enhancing conditions that reduce the export of nutrient elements from agricultural fields. The design of BMPs should therefore optimize the natural biogeochemical processes that immobilize or eliminate nutrients before they enter the receiving waterways. In natural landscapes, these processes tend to be concentrated in relatively small zones known as 'reactive interfaces' (RIs). Despite widespread recognition of the importance of RIs for watershed-scale nutrient processing, their systematic, science-based incorporation in agricultural BMPs remains underutilized. A key barrier is our limited understanding of how RIs affect the coupled fate and transport of C, N, P, and S in agroecosystems. The focus of the proposed work will therefore be to advance the predictive modeling of RIs in agroecosystems, using a combination of data synthesis, field, laboratory, and computational approaches. We will specifically focus on three RIs, the capillary fringe, riparian areas and the hyporheic zone. Four PhD students, one post-doctoral researcher and 12 undergraduate students will be trained through this proposal. Students will work in the laboratory and at four agricultural field sites located across soil type and landscape gradients in Ontario. The empirical understanding will be encoded into process models of individual RIs and their hydrological and biogeochemical connectivity at the field and watershed scales. The process models will inform the practical implementation of BMPs to maximize their effectiveness. This work is significant as it provides insight into the mechanisms of nutrient retention and elimination at critical RIs in agroecosystems. This will advance our ability to track and predict nutrient fluxes in the landscape and make improved, evidence-based recommendations to reduce nutrient losses in agricultural systems across Canada.****