THE SIMULATION OF DISSOLVED OXYGEN AND ORTHOPHOSPHATE FOR LARGE SCALE WATERSHEDS USING WASP7.1 WITH NUTRIENT LUXURY UPTAKE
Abstract:Phosphorus is often listed as a parameter causing impairment of rivers and streams throughout the nation. Excess available phosphorus may increase primary productivity in the stream and cause eutrophication. When periphyton is the main type of organism responsible for primary productivity, the total phosphorus uptake can be significant for the analysis of the overall system. Orthophosphate is absorbed and stored by periphyton and macrophytes during times of excess concentrations in the stream, and it can be used to support productivity during times of low phosphorus concentrations. This phenomenon is called nutrient luxury uptake. Although the importance of nutrient luxury uptake has been known for many years, it hasn't been systematically adopted for large scale studies. One of the reasons for omitting this important component of the nutrient cycling in the stream is that watershed models do not incorporate nutrient luxury uptake algorithms due to its relative complexity. Recently, the Water Quality Analysis Program (WASP) version 7.1 was updated to include the nutrient luxury uptake for periphyton. The objective of this paper is to demonstrate the importance of using the nutrient luxury uptake algorithm for dynamic water quality models when periphyton is the main type of organism responsible for primary productivity. An application of the new WASP7.1 model with the nutrient luxury uptake algorithms was developed for a large scale and diverse watershed in New Jersey. The application consists of simulating dissolved oxygen and orthophosphate at selected water quality monitoring stations representing different flows and nutrient availability conditions. Water quality parameters affecting the transport and fate of phosphorus were calibrated in order to capture the uptake of phosphorus by periphyton. This is likely the first application of the nutrient luxury uptake within the WASP7.1 water quality modeling framework to a large scale and diverse watershed. The model results show the importance of using the nutrient luxury uptake when periphyton is the main type of organism responsible for primary productivity and dissolved orthophosphate is scarce. The observed and predicted data show a good representation of dissolved oxygen and orthophosphate for the selected stations. During times of phosphorus depletion in the water column, the periphyton productivity did not cease; this is consistent with data obtained from field sampling. These results would not be obtained without implementing the nutrient luxury uptake for periphyton.
Document Type: Research Article
Publication date: January 1, 2007
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