Abstract
Utah Lake is highly eutrophic with large phosphorous inflows and a large internal phosphorous reservoir in the sediment. There are debates over whether this phosphorous is from geologic or more recent anthropologic sources. This study characterizes total phosphorous in geologic and current lake sediments to attempt to address that question. The average total phosphorous concentrations in the lake sediment were 666 ppm, with most samples in the 600 to 800 ppm range with a few larger values. Concentrations in historic geologic sediments were not statistically different from lake sediments. A spatial analysis showed that phosphorous distributions appeared continuous from the lake to the shore and that high and low values could be attributed to areas of seeps and springs (low) or feed lots and waste water discharge (high). These results indicate that geologic sediments without anthropogenic impacts are not statistically different than current lake sediments. The high values indicate that internal natural phosphorous loadings could be significant and the impaired state may be relatively insensitive to external anthropogenic loadings. If this is the case, then mitigation efforts to address anthropogenic sources may have minimal impacts. This case study presents an impaired water body where non-anthropogenic nutrient sources are significant and shows that reservoir management decisions should consider these non-anthropogenic phosphorous sources relative to anthropogenic sources. This study can serve as a template for evaluating the importance of geologic phosphorous sources for management decisions.
Highlights
The Utah Division of Water Quality has determined that phosphorous inflows, in the form of phosphate, significantly contributes to the impairment of Utah Lake [1,2] and are considering a number of mitigation efforts, all of which carry significant costs in both monetary and resource terms
We present evidence that internal natural phosphorous loadings could be a significant factor, and that the impaired state of the lake may be relatively insensitive to external anthropogenic loadings
The sampling results show that Utah Lake sediments have large concentrations of total phosphorus with an average total phosphorous concentration of 666 ppm
Summary
The Utah Division of Water Quality has determined that phosphorous inflows, in the form of phosphate, significantly contributes to the impairment of Utah Lake [1,2] and are considering a number of mitigation efforts, all of which carry significant costs in both monetary and resource terms. These mitigation efforts assume that external phosphorus loading, mainly from anthropogenic sources, significantly contribute to Utah Lake’s impaired state. 150,000–200,000 people visit Utah Lake each year for its shoreline recreation, fishing, and water activities It supports agriculture uses as it is used to irrigate about 50,000 acres (202.3 km2 ) yearly
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