Year of Award

2010

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Forestry

Department or School/College

College of Forestry and Conservation

Committee Co-chair

Tom DeLuca, Steve Running

Commitee Members

Joel Harper

Keywords

climate change, discharge trends, Northern Rockies, streamflow trends

Abstract

This thesis is composed of two potential professional papers written to be independent of each other. Both papers were written to explore changes in late summer discharge patterns across the Northern Rockies (NR). Water in the interior western United States is a vital resource and the demand for this resource has increased. Watersheds in the NR are mainly snowmelt dominated in that they depend on the seasonal flux of snow-melt during dry periods. During the summer months August is a critical time for aquatic ecosystems due to typical low discharge and warm air temperatures. During this period water temperatures can become elevated stressing aquatic biota. The first chapter addresses historic August discharge trends across the NR and examines the frequency of low discharge over time. Using historic discharge data from United States Geologic Survey’s national water information system web interface, we analyzed data for trends of 40-59 years. Combining these records with aerial photos (<10m resolution) and water rights records we selected gaging sites based on the length and continuity of discharge records and categorized each site based on the amount of diversion and location of water storage devices. Local significance was examined using the Mann-Kendall non-parametric test and regional significance was obtained using a bootstrap procedure in combination with the Mann-Kendall test. Our analyses indicate that watersheds throughout the NR are experiencing substantial declines in stream discharge and we have found that 75% of all stations exhibit a declining slope. Bootstrap analysis indicates that the NR is experiencing a significant (á = 0.10) decline in discharge from 1951-2008. The second chapter takes a subset of the original 153 sites, deemed pristine sites, and examined the relationship of August discharge to climatic parameters for each watershed. By using stations with no identifiable diversion and minimal land use change we were able to analyze precipitation and air temperature records for correlations with discharge trends. Bootstrap methods were used to determine field significance of the region. Long term discharge analyses demonstrate that eight of the fifteen watersheds throughout the NR are experiencing significant declines in stream discharge over the last half century and all stations have a negative slope. Additionally, the region as a whole appears to have a significant decrease in discharge over the period 1951-2008. Correlations results show a weak to moderate negative relationship between air temperatures and discharge and these results coupled with increasing air temperature trends pose serious concern for aquatic ecosystems in NR.

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© Copyright 2010 Jason Christopher Leppi