Year of Award

2019

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Systems Ecology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

H. Maurice Valett

Committee Co-chair

Marc Peipoch

Commitee Members

Benjamin P. Colman

Keywords

nutrient process domains, biogeochemistry, linked ecosystems, wetland-streams, mass-balance

Subject Categories

Applied Statistics | Biogeochemistry | Biology | Environmental Monitoring | Hydrology | Longitudinal Data Analysis and Time Series | Natural Resources Management and Policy | Systems Biology | Water Resource Management

Abstract

Studies of aquatic ecosystems often segregate streams from the influential ponds, lakes, and wetland zones that act as important transitions between terrestrial and fluvial systems. Across the aquatic landscape, these zones interact to form linked ecosystems that function as discrete nutrient processing domains, shifting biogeochemical signals due to spatial and temporal variability in hydrologic and biologic controls. Using a mass-balance approach, we profiled nutrient dynamics along a 23-km wetland-stream sequence over three seasons. Hydrologic, morphologic, and biologic conditions, as well as landscape attributes, were quantified to determine potential controls on biogeochemical cycling in a tributary of the Upper Clark Fork River (UCFR), MT that is known for contributing disproportionate nutrient loads. Results identified a geomorphic and hydrologic sequence of wetland-stream interactions that generated discrete zones of nutrient production, transformation, and uptake. Zones of production resulted in five-to seven-fold increases in nitrate loads. Across all four stream reaches, nutrient dynamics were driven primarily by net groundwater exchange, which explained up to 30% (P = 0.0064) of the change in nitrate load. Nitrogen transformation of ammonium-rich groundwater inputs resulted in mean nitrification rates of 248.49 mg N m-2 d-1; on par with engineered surface-flow constructed treatment wetlands. Abnormally high C loss rates(up to -54.9 g C m-2 d-1) calculated from changes in the dissolved organic carbon (DOC) load between ground-and surface water compartments suggest DOC removal pathways other than heterotrophic respiration –i.e., adsorption to the extensive carbonate precipitates which coat benthic and hyporheic substrates. During the study period,water flowing through this sequence of aquatic systems exhibited an average increase in nitrate load of 461% and a doubling of ammonium, soluble reactive phosphate, and DOC loads with a mere 32% increase in discharge.

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© Copyright 2019 Patrick E. Hurley