Abstract
We used coupled watershed and reservoir models to evaluate the impacts of deforestation and l Niño Southern Oscillation (ENSO) phase on drinking water quality. Source water total organic carbon (TOC) is especially important due to the potential for production of carcinogenic disinfection byproducts (DBPs). The Environmental Fluid Dynamics Code (EFDC) reservoir model is used to evaluate the difference between daily pre- and post- urbanization nutrients and TOC concentration. Post-disturbance (future) reservoir total nitrogen (TN), total phosphorus (TP), TOC and chlorophyll-a concentrations were found to be higher than pre-urbanization (base) concentrations (p < 0.05). Predicted future median TOC concentration was 1.1 mg·L−1 (41% higher than base TOC concentration) at the source water intake. Simulations show that prior to urbanization, additional water treatment was necessary on 47% of the days between May and October. However, following simulated urbanization, additional drinking water treatment might be continuously necessary between May and October. One of six ENSO indices is weakly negatively correlated with the measured reservoir TOC indicating there may be higher TOC concentrations in times of lower streamflow (La Niña). There is a positive significant correlation between simulated TN and TP concentrations with ENSO suggesting higher concentrations during El Niño.
Highlights
Forested watersheds provide essential ecosystem services such as the provision of high quality water
Measured data provided the basis for partitioning watershed model total nitrogen (TN) concentrations into TON, nitrate and ammonium values based upon the following relationship; TN is the sum of inorganic N
We report the change in overall median (1992 to 2005) and median monthly TN, total phosphorus (TP) and total organic carbon (TOC)
Summary
Forested watersheds provide essential ecosystem services such as the provision of high quality water. We assess the impact of forest to urban land conversion on reservoir TOC concentrations at Converse Reservoir, which supplies the drinking water for the City of Mobile, Alabama through the Mobile Area Water and Sewer Systems (MAWSS). To evaluate the impact of forest to urban land conversion and ENSO phase on reservoir water quality, linked watershed [24] and reservoir [25] models were used. The objectives of this study were to (1) utilize linked watershed and reservoir models to test the hypothesis that watershed nutrient loads during future scenarios will lead to increased TOC concentrations and algae growth at the source water intake when compared with base scenarios;. Regional and national urbanization studies concur that the study area will likely experience significant urbanization in the coming decades [8,10,11,31]
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