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Katie Fisher

Abstract

This study was conducted to assess the applicability of the River Continuum and Serial Discontinuity Concepts to the Little Bear River, using chlorophyll a values along the gradient of the river and within Hyrum Reservoir. Periphyton was analyzed from seven sites and phytoplankton from nine sites (including Hyrum Reservoir) in September 2012. The lower parts of the Little Bear River is heavily influenced by agricultural and anthropogenic sources of nutrients and other pollution, creating poor water quality in its lower reaches. Periphyton levels in the river increased along the gradient, peaking just below Hyrum reservoir, and then decreased with distance downstream. Phytoplankton chlorophyll a concentrations increased significantly with distance downstream, with concentrations near 1.5 μg L-1 in the headwaters and 5 μg L-1 in the slow-moving valley sections. On an aerial basis, chlorophyll in the periphyton community overwhelmingly dominated (>98 percent) the total chlorophyll levels. Within the phytoplankton continuum, there was, however, a drop below Hyrum Reservoir. Furthermore, there was a significant positive relationship between the total phosphorous concentrations and phytoplankton levels. Periphyton levels, however, were not correlated with phosphorus concentrations. The chlorophyll a levels found suggest that high levels of phosphorus contribute to higher levels of algal chlorophyll a. Although these levels were not indicative of poor water quality, mitigation of nutrient sources in the valley would likely create more uniform chlorophyll a levels down the gradient of the LBR.

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