Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Watershed Sciences

Committee Chair(s)

Janice Brahney


Janice Brahney


Sarah Null


Bethany Neilson


Max Bothwell


Climate change is causing rapid glacial recession and earlier snowmelt, which alter the physical and chemical properties of rivers. As a result, organisms at the base of the food web are responding in unforeseen ways. We use the nuisance algae D. geminata (Didymo) as a case study for how climate induced shifts in the timing of glacial and snowmelt runoff are affecting river ecosystems. We evaluated how shifts in the timing of nutrient concentrations and light availability affect nuisance blooms of Didymo in three complementary ways. These are, field studies across streams in various stages of glacial recession, weekly measurements at one section of river, and experimental studies. We used a range of streams in different stages of glacial recession as a proxy for decadal scale climate change to evaluate the relationship between chemical and physical stream characteristics and nuisance blooms. Blooms were found in streams with low nutrient and high light, and with less glacial cover. We sampled the snowfed Logan River, in Utah weekly from May to December of 2019 and found that blooms were triggered under similar circumstances, specifically at the juncture of clear water and low phosphorous concentrations at a time of year when day length was near its maximum. Finally, we used experimental flumes to investigate only the role of light on blooms. We found the highest algal growth with the high light treatments. Our results show that environmental conditions linked to glacial recession and earlier snowmelt are driving the formation of Didymo blooms through shifts in the timing of high nutrient, turbid water, occurring earlier in the year when light availability is lower. Didymo serves as a case study for how climate change alters the timing of important environmental conditions resulting in unforeseen effects to stream ecosystems. This study exemplifies the need to study how altered glacial and snowmelt timing will change stream ecosystems.