Date of Award

Summer 2019

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geosciences

Committee Chair

Alysia Cox

First Advisor

Katie Hailer

Second Advisor

Robert Pal

Abstract

Throughout Silver Bow Creek’s history, consideration of the photosynthetic communities that make heterotrophic life possible have often been overlooked since macroinvertebrates made up a majority of ecosystem health assessments. Silver Bow Creek has had minimal biological research outside of macroinvertebrate surveys, especially as it pertains to photosynthetic organisms. This study assessed the photosynthetic communities of Silver Bow Creek and their limitations by limiting available light and comparing uptake of nutrients during a 23-day incubation experiment conducted at four sites along the flow of Silver Bow Creek and Blacktail Creek. At each site, nine one-liter microcosms, filled with creek water and divided evenly into three acrylic boxes, remained in the creek for 23 days. One of the boxes allowed 100% transmittance of visible light. The other two boxes restricted visible light to 54% transmittance and 6% transmittance. The boxes incubated in the creek for 23 days with samples withdrawn periodically to monitor for extracted chlorophyll a. Analysis of major anions and cations at the beginning and end of the experiment showed typical nutrient uptake. Despite anticipated light limitations, nutrient limitations, specifically phosphorus, had a stronger impact on total photosynthetic growth. Light did not limit total chlorophyll growth, instead light limited the chlorophyll growth rate. Together light and phosphorus created a biochemically dependent colimitation. At Slag Canyon, severe light limitation prevented oxygenation of microcosms and chemoautotrophic metabolisms took over reducing nitrate and sulfate. This experiment concluded that in Sliver Bow and Blacktail Creeks, light limited the primary production growth rate and phosphorus limited total possible photosynthesis.

Comments

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Geoscience: Geochemistry Option

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