Abstract
Currently, California has no methods in evaluating the amount of geological and other forms of phosphorus that enters reservoirs or the chlorophyll-a concentrations that result. Excess phosphorus plays a vital role in ecosystems and studies have shown that a surplus of phosphorus loaded into a system can have undesirable affects such as aquatic life dying off due to eutrophication and reduced drinking water quality and clarity. This study has shown use of the SPARROW (Spatially Referenced Regressions On Watershed attributes) model to predict riverine Total phosphorus (TP) loads entering a reservoir used in combination with the Vollenweider model that outputs a Normalized phosphorus concentration (PLN), prediction of chlorophyll-a levels can then be extrapolated. Results from this study are inconclusive due to all sampled reservoirs plotting in the eutrophic zone. However, trophic state based on lake productivity (chlorophyll-a) show all five reservoirs as oligotrophic. Furthermore, a sensitivity test was executed and a possible discrepancy as to why reservoirs are plotting eutrophic was the calculation for the Total Phosphorus output. The chosen sampling year of 2017 may not have been an “average year” meaning drought conditions could have affected the phosphorus calculation. Calibration for TP sampling was beyond the scope of this study. Additionally, when comparing chl-a against secchi depth reading the results of the trophic state correlation does not exist meaning, chlorophyll levels measured at oligotrophic but secchi disk readings were shallow and measured at the mesotrophic – eutrophic boundary. One reason could be boaters wave action that created highly turbid waters in some reservoirs but does not clearly explain why some of the less turbid waters, such as Camp Far West still show low chlorophyll-a. During sampling events there were various and many different types of watercrafts, and efforts were made to sample as far from recreational activities as possible. Most importantly Rast & Lee, 1978 and Vollenweider, 1979 state that trophic state permissible and excessive boundaries are not strict but flexible as the water quality gradually shifts from one state to the next. In addition, reservoirs that plot right at the excessive loading boundary tend to plot as higher in the eutrophic zone while reservoirs closer to the permissible boundary will end up oligotrophic or mesotrophic. However, Vollenweider states the trophic state of a reservoir or lake is ultimately up to the lake managers discretion.
Other findings include Lake Englebright acting more as a river due to such high outflows, and a very low hydraulic residence time. For 2017, Englebright had an outflow of over 240 million cubic meters per year, and a hydraulic residence time of 14.4 weeks; all other reservoirs act as expected.