Typical seasonal cycles in Schmidt stability, Secchi disk depth (SDD), and anoxic ratio (anoxic sediment area:surface area) under variable reservoir storage conditions. Development of stability and anoxia follow a Jan–Dec cycle, whereas SDD increases during stratification (Mar–Nov) and decreases during mixed conditions (Nov–Mar). The data shown are for Sutherland Reservoir from Jan 1992–Apr 1994.
SPONSOR: Water Resources Institute, California State University, San Bernardino
PROJECT DURATION: 1 September 2011 to 30 April 2014
PRINCIPAL INVESTIGATORS: Raymond Lee, Trent Biggs
PROJECT SUMMARY: Reservoir water quality can be compromised by algal production and anoxia, which in turn are impacted by hydrodynamic stability and water temperature. We developed a conceptual model to quantify the dominant controls on stability, anoxia, and transparency using statistical analysis of a longterm (1990–2011) data set for four reservoirs in San Diego, California, each receiving runoff from a watershed with a different level of urban and agricultural land use. We hypothesized that water depth, not air temperature, controlled stability and that anoxia, after correcting for stability, increased and transparency decreased with increasing land use. Depth fluctuated widely interannually and was the dominant control on stability, which in turn controlled transparency in shallow reservoirs. Shallow depth and low stability correlated with low transparency. Transparency decreased with increasing development in the watershed. Water quality deteriorated over time in the reservoirs with the most and, contrary to our hypothesis, least developed watersheds. Deterioration of water quality in the pristine watershed coincided with the introduction of forage fish, which can suppress zooplankton density and translocate phosphorus to the photic zone. The interaction of land use, climate, water level management, basin morphology, and aquatic food webs can deteriorate water quality, even in reservoirs receiving runoff from pristine watersheds.
Lee, R. M. and T. W. Biggs. (2015) Impacts of land use, climate variability, and management on thermal structure, anoxia, and transparency in hypereutrophic urban water supply reservoirs. Hydrobiologia 745: 263–284. [link][pdf]