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OBJECTIVES: Reduction of nitrogen, phosphorus, and suspended sediment load has been a principal focus of Chesapeake Bay Watershed management for decades. It is thus important to evaluate the progress of historical management plans and propose adaptive refinement options for future management plans. In the Chesapeake Bay Watershed, the Susquehanna River is the largest tributary in terms of both freshwater and nutrient inputs. In this context, the first objective of this project is to apply the most up-to-date loading estimation method, called the "weighted regression on time, discharge, and season", to reconstruct the long-term seasonal trends of nitrogen, phosphorus, and suspended sediment at various monitoring sites in the Susquehanna River Basin. Using such load estimates, the second major objective is to quantitatively examine the source apportionment, spatial budget, and in-stream cycling of these species in the Susquehanna River Basin, as well as impacts of stormflows on these processes. METHODOLOGY: We will estimates the seasonal loads and trends of various nutrient and sediment species at all long-term monitoring sites in the Susquehanna River Basin using the most up-to-date loading estimation method. This method can produce (a) true-condition estimates that can help understand the real history of nutrient (or sediment) and downstream ecological impact, and (b) flow-normalized estimates that can greatly remove the dramatic influence of random variations in streamflow and reveal more clear interannual trend. Using such load estimates, we will proceed to investigate the source apportionment, spatial budget, and in-stream cycling of these species. Specifically, we will (1) use load apportionment method to distinguish point and non-point contributions, (2) develop load budget for each species to separate the input from each sub-basin, and identify the critical source areas under stormflow conditions, and (3) examine the temporal and spatial variations of dissolved and particulate nitrogen and phosphorus species, and the impacts of stormflows on the speciation of nitrogen and phosphorus. RATIONALE: This project will reveal the long-term seasonal trends of nutrient and sediment species in the Susquehanna River using the most-up-to-date estimation method. The estimated loadings and trends can be shared with target audiences, including federal and state regulatory agencies, groups impacted by total maximum daily load allocation, and the broader scientific community. In addition, this project will help understand the source apportionment, spatial budget, and in-stream cycling of nutrient and sediment species, as well as impacts of stormflow on these processes. Overall, these findings can facilitate managers to adaptively refine the management plan by making "science-based decisions" that "consider how and when conservation and restoration efforts can be most effective" _ as acknowledged by "Focus Area 1: Resilient Ecosystem Processes and Responses" of the Maryland Sea Grant Strategic Plan. Finally yet importantly, this project will create benefits by serving as an exemplary prototype for follow-up work on the other tributaries of Chesapeake Bay.
Zhang, Q; Ball, WP; Moyer, DL. 2016. Decadal-scale export of nitrogen, phosphorus, and sediment from the Susquehanna River basin, USA: Analysis and synthesis of temporal and spatial patterns. Science of the Total Environment563:1016 -1029. doi:10.1016/j.scitotenv.2016.03.104. UM-SG-RS-2016-12.
Zhang, Q; Brady, DC; Boynton, WR; Ball, WP. 2015. Long-Term Trends of Nutrients and Sediment from the Nontidal Chesapeake Watershed: An Assessment of Progress by River and Season. Journal of the American Water Resources Association51(6):1534 -1555. doi:10.1111/1752-1688.12327. UM-SG-RS-2015-16.
Zhang, Q; Brady, DC; Ball, WP. 2013. Long-term seasonal trends of nitrogen, phosphorus, and suspended sediment load from the non-tidal Susquehanna River Basin to Chesapeake Bay. Science of the Total Environment452:208 -221. doi:10.1016/j.scitotenv.2013.02.012. UM-SG-RS-2013-18.