System Wide Eutrophication Model – History

The System Wide Eutrophication Model or SWEM is the fourth in a sequence of water quality models developed as tools to assist Long Island Sound’s water quality and natural resource managers in improving water quality in Long Island Sound. Work on the initial model (LIS 1.0) was initiated by HydroQual in 1987 and resulted in the development of a 2-dimensional steady-state water quality model of the Sound. HydroQual then developed LIS 2.0, which was 2-dimensional and time-variable. The LIS 3.0 model incorporated a 3-dimensional time-variable hydrodynamic model (ECOM), which was applied and calibrated to Long Island Sound by NOAA, and HydroQual implemented a 3-dimensional time-variable water quality model. This model was used to develop the nitrogen TMDL for Long Island Sound.

The spatial extent of the LIS 3.0 model was increased, with funding provided by the New York City Department of Environmental Protection (NYCDEP), to include the New York/New Jersey Harbor complex and the Mid-Atlantic Bight. There were two reasons for expanding the spatial domain of the LIS 3.0 model. First, it was concluded during peer-review of LIS 3.0 that the western and eastern boundaries of the LIS 3.0 model, which were located at mouth of the East River (where it converges with the Hudson River) on the west and Block Island Sound on the east were being impacted by internal loads and therefore it was difficult to determine how management actions or nutrient waste load reductions by wastewater treatment plants or other management actions might affect nutrient boundary concentrations. Secondly, the NYCDEP wished to understand what the effects of waste load relocation from its East River treatment plants would be on water quality in lower New York Harbor and Raritan Bay, as well as Long Island Sound. Therefore, NYCDEP provided funding to support the expansion of the LIS 3.0 model into a “system wide” modeling tool, as well as funding to collect water quality data to support the calibration of the SWEM model.

The resulting model, which was calibrated against an extensive field data collection effort conducted between September 1994 and September 1995, was completed in 2001. Since that time, SWEM has been used in the re-evaluation of the Long Island Sound nitrogen TMDL, as well as by NYCDEP for facility planning studies and by the Connecticut Department of Environmental Protection to assist in its nitrogen trading program.
In 2010 UConn performed an evaluation of the sensitivity of SWEM to the water quality model parameter choices and also examined the sensitivity of the model predictions to the particular meteorological conditions of the calibration and evaluation years. This project identified that the vertical mixing rates in the model were much lower than they should be and suggested that the community respiration and production in SWEM were also too low. To address these limitations the formulation of the primary production and the nutrient cycles in the model were further examined in this project.