Search for: All records

Abstract Estuarine exchange flow controls the salt balance and regulates biogeochemistry in an estuary. The Albemarle‐Pamlico estuarine system (APES) is the largest coastal lagoon in the U.S. and historically susceptible to a series of environmental issues including salt water intrusion and eutrophication, yet its estuarine exchange flow is poorly understood. Here, we investigate the estuarine exchange flow in the APES, its tributary estuaries (Pamlico and Neuse), and sub‐basin Albemarle Sound using the total exchange flow analysis framework based on results from a deterministic numerical model. We find the following: (a) Dynamics controlling estuarine exchange flow in the APES vary spatially and depend on timescales considered. At inlets, estuarine exchange flows respond to both tidal prism and residual water levels at weather‐to‐spring/neap timescales. At a long quasi‐steady timescale represented as annual means, estuarine exchange flow is dominated by barotropic flow. Within the tributary estuaries, estuarine exchange flows at timescales of wind periods are controlled by wind‐induced straining, whereas the quasi‐steady state condition is dominated by gravitational circulation. At Albemarle Sound, exchange flow is dominated by the residual water levels at weather‐to‐spring/neap timescales, while at quasi‐steady state it is controlled by barotropic flow. (b) At the quasi‐steady annual timescale, the salt content decreases with river discharge. At the weather‐to‐spring/neap timescales, salt content is insensitive to variations in estuarine exchange flow, except for within Albemarle Sound. (c) Estuarine exchange flow likely influences the biogeochemistry of the APES by playing a key role in regulating the flushing efficiency and material exchange, a role that has been previously overlooked. 

Excessive nitrate loading from agricultural runoff leads to substantial environmental and economic harm, and although hydrological models are used to mitigate these effects, the influence of various satellite precipitation products (SPPs) on nitrate load simulations is often overlooked. This study addresses this research gap by evaluating the impacts of using different satellite precipitation products—ERA5, IMERG, and gridMET—on flow and nitrate load simulations with the Soil and Water Assessment Tool Plus (SWAT+), using the Tar-Pamlico watershed as a case study. Although agricultural activities are higher in the summer, this study found the lowest nitrate load during this season due to reduced runoff. In contrast, the nitrate load was higher in the winter because of increased runoff, highlighting the dominance of water flow in driving riverine nitrate load. This study found that although IMERG predicts the highest annual average flow (120 m3/s in Pamlico Sound), it unexpectedly results in the lowest annual average nitrate load (1750 metric tons/year). In contrast, gridMET estimates significantly higher annual average nitrate loads (3850 metric tons/year). This discrepancy underscores the crucial impact of rainfall datasets on nitrate transport predictions and highlights how the choice of dataset can significantly influence nitrate load simulations.