Simulation of flow and eutrophication in the central Salem River, New Jersey

First posted May 18, 2023 For additional information, contact: Director, New Jersey Water Science CenterU.S. Geological Survey3450 Princeton Pike, Suite 110Lawrenceville, NJ 08648 The central Salem River in is subject to periods of water-quality impairment, marked by elevated concentrations phosphorus and chlorophyll-a, low large diurnal swings dissolved oxygen. These seasonal eutrophic conditions are controlling factors for water quality lower reaches, where the river more lacustrine than upper as a result downstream damming. This biological productivity supported nutrient wash-off from agricultural areas surrounding watershed. To investigate this flow measurement sampling were conducted during 2007–08 support development one-dimensional surface-water-quality model that simulates cycling transformation processes.The U.S. Survey, cooperation with Department Environmental Protection, used Protection Agency Quality Analysis Simulation Program (WASP) develop receiving-water-quality between Woodstown Deepwater, Jersey, April 2007 October 2008. main-stem largest tributary simulated. In model, kinematic wave simulate reaches ponded weir reaches. makes use mass-balance equation fate transport nutrients, phytoplankton oxygen, oxygen demands (an indicator rather substance) river. Model input included channel characteristics, boundary quality, environmental parameters, vertical dispersion coefficients, settling rates, kinetic constants. Inputs estimated field data lacking, notably flows loads.The was calibrated observed variables nutrients at locations, emphasis on growing-season conditions. Calibration achieved through graphical statistical comparison simulated results data. Sensitivity analyses performed, limitations applicability evaluated. Simulated closely matched most cases, although some overpredicted slightly. important causes overprediction watershed loads model. dissolved-oxygen closer, predicted variations consistent high algal photosynthesis/respiration, lack continuous precluded verifying these predictions. A similar caveat applies chlorophyll-a. growth those based indicated main limiting nutrient, except certain when nitrogen limiting.Two management scenarios assess effect point- nonpoint-source reductions Scenarios involved (1) return land predevelopment natural (2) an extreme reduction input. Although extreme-nutrient-reduction scenario yielded improvements natural-conditions minimal violations standards or thresholds. However, years may be needed attain full benefit accumulation organic carbon riverbed sediments study indicate will improve if policies mitigate effects nutrient-loading practices watershed, particularly related agriculture, implemented.