Year of Award

2021

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

Dr. H. Maurice Valett

Commitee Members

Dr. Robert Hall Dr. Matthew Church Dr. Michael DeGrandpre

Subject Categories

Environmental Sciences | Water Resource Management

Abstract

Studies relating ecosystem energetics to nutrient uptake in streams have generally found respiration to be a more dominant control on nutrient dynamics relative to primary production due to light limitation in most low-order systems. In this study, I measured biomass, hydrology, metabolism, and dissolved solutes in an open-canopy mid-order river located in western MT. Daily stream metabolism was modeled using a modified single-station, open-channel method, and measures of dissolved solutes were evaluated at both local and reach scales to examine how point-measures and those integrated through space represent biogeochemical behavior. Metabolic rates and standing stocks of benthic organic matter were greater at Site 2 despite greater nutrients loads delivered to Site 1. Benthic organic matter ranged from 1.11-60.4 g OM m-2 and chlorophyll a from 40.9-150.9 mg Chl a m-2 between sites. GPP ranged from 1.89 to 11.14 g O2 m-2 and ER from -0.93 to -8.66 g O2 m-2 d -1 with greater rates observed at Site 2. The fraction of GPP consumed as autotrophic respiration (ARf) was high at both sites, 76 and 66% for Sites 1 and 2, respectively. Mean loads for NO3-N at Site 1 (61.29 ± 4.92 kg N d-1 ) were greater than loads delivered to Site 2 (27.02 ± 3.36 kg N d-1 ), and an effective solute flux (Ueff) calculated from mass-balance that the reach between sites is a biological sink for NO3-N. Compared to hydrologic losses, biological uptake (Ueff-bio) accounted for nearly 90% of the reduction in material loads. Correlation between Ueff-bio-NO3 and NEP (r2 = 0.22, p < 0.01), as well as calculated autotrophic N demand (Udem) derived from NPP (r2 = 0.29, p < 0.01), suggests that autotrophic assimilation is a major control on changes in material load. Average Udem (147.7 ± 6.06 mg N m-2 d -1 ), however, was nearly triple the mean value for Ueff-bio-NO3, suggesting unmeasured sources of DIN linked to autotrophic assimilation via other processes such as Nfixation, nitrification, and N mineralization.

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© Copyright 2021 Jacob Anthony Prater