Simple relationships between residence time and annual nutrient retention, export, and loading for estuaries

Simple mathematical models are derived from mass balances for water and transported substance to provide insight into the relationships between import, export, transport, internal removal nonconservative substances in an estuary. Extending previous work, our explicitly include inputs ocean expressed terms of timescales (i.e., mean residence time timescale net removal). Steady-state, timescale-based expressions ratios export retention loading, as well loading annually averaged concentration, provided. The export:loading model explains underlying mechanisms a well-known empirical relationship fractional by other authors. Although simplified first-order approximations, relative importance physical biochemical processes influencing or can be assessed using removal. Assumptions employed deriving (e.g., well-mixed, dynamic steady state) may not met real estuaries. However, application Chesapeake Bay 1985–2012 demonstrates that interannual variations total nitrogen (TN) evaluated, annual nutrient loadings estimated numerically modeled time-varying time, observation-based freshwater inflow, appropriately timescale. Our shows TN ranges 0.3 0.5 over 28-yr period. bodies if assumptions applicable.