Publication Date

5-2016

Date of Final Oral Examination (Defense)

12-11-2015

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Hydrologic Sciences

Department

Geosciences

Supervisory Committee Chair

Shawn Benner, Ph.D.

Supervisory Committee Member

Kevin Feris, Ph.D.

Supervisory Committee Member

James P. McNamara, Ph.D.

Abstract

Nitrate and phosphate concentrations in the Lower Boise River become increasingly elevated with distance downstream. While there is correlative evidence that there is algal growth from elevated nutrients, no one has formally evaluated the algal growth response from nutrient loading. We quantified algal biomass in response to increased nutrient concentrations by sampling benthic algal biomass from natural substrata (rocks) and artificial substrata that also assessed nutrient limitation along a 64 mile reach from near Diversion Dam to the city of Parma that exhibited an increase of nitrate (0.01 mg/L to 3.40 mg/L) and phosphate (below detection to 0.56 mg/L). Samples were collected from August to October of 2013. We observed low values for algal biomass accrual rate on the unamended artificial substrata in the upper section of the Boise (above Lander Street, Mile 12) of 1.41 – 1.60 mg chlorophyll a/m2/day, accrual rate values increased to 7.03 – 9.88 mg chlorophyll a/m2/day near Caldwell (Mile 41), then declined to 6.42 mg chlorophyll a/m2/day at the confluence with the Snake River. Trends in nutrient limitation were similar for both August and October, showing lack of algal biomass response to nutrient additions (nutrient limitation) downstream of the Lander wastewater treatment plant discharge (Mile 12). This observation corresponds to higher algal biomass growth downstream. The increased algal biomass growth in the lower Boise is interpreted to be in response to nutrient loading, primarily from wastewater discharge. In the lowermost portion of the Boise River (below Mile 55) a decline in algal biomass is observed, presumably due to light limitation by turbid water in the lower portion of the river. Reductions in nutrients in this section of the river may not reduce algal biomass. Above Lander wastewater treatment plant (Mile 12), nitrate limitation is observed. This suggests that declines in phosphorus loading alone in the lower Boise River may not reduce algal biomass levels to those observed above the Lander wastewater treatment plant.

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