Integrating and managing nitrogen and phosphorus dynamics in agriculturally impacted inland waters via a stoichiometric nutrient management framework

Agricultural nutrient management tends to treat nitrogen (N) and phosphorus (P) in surface waters as separate entities, potentially overlooking their strong interactions in biogeochemical cycles. This study proposes a unifying approach by integrating these nutrients through a stoichiometric nutrient management framework. This framework suggests two paradigm shifts in inland-water nutrient management: 1. It improves catchment and ecosystem-level understanding of N and P sources and effects via N : P ratio assessments of sources, transport and ecological effects, such as eutrophication. 2. It proposes that provision of organic carbon (OC) can increase the retention of N and P in agriculturally impacted inland waters, which can be assessed using C : N : P ratios. Provision of OC to modify C : N : P ratios may be reached through restoring natural OC sources. This can be done by focusing on areas such as wetlands, riparian forests, and bogs at catchment scale. Here, stoichiometric rules are utilized to assess the responses of key microbial processes, which includes examining how nutrients are assimilated by microbial primary producers and heterotrophs, as well as the process of denitrification. Understanding the secondary effects of wetted area development through the stoichiometric nutrient management framework will also support decision making for flood and drought protection based on such wetted areas. With these aspects, the stoichiometric nutrient management framework provides comprehensive understanding of nutrient dynamics, retention, and their ecological impacts in inland water catchments and ecosystems. In the presentation, we will present evidence supporting the comprehensiveness of the stoichiometric nutrient management framework. This evidence is based on a series of studies we conducted, including conceptual modeling, statistical modeling, ratio-based monitoring, and targeted proof-of-concept microcosm experiments. We conclude that the stoichiometric nutrient management framework could provide crucial strategies to mitigate current nutrient pollution issues in agriculturally-impacted inland waters, thereby aligning with the Water Framework Directive’s objectives for improving water quality.