River metabolism and carbon cycling in a heavily impacted agricultural watershed
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Date
2024
Authors
Janvier, Ilyanna K.
University of Lethbridge. Faculty of Arts and Science
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Publisher
Lethbridge, Alta. : University of Lethbridge, Dept. of Biological Sciences
Abstract
Rivers support people in many ways, including for agriculture and irrigation, drinking water, and recreational and cultural uses. Streams and rivers also play an important role in the global carbon (C) cycle as they not only transport C and nutrients to the ocean, but they also store, emit, and transform different sources of C. Consequently, rivers contribute large quantities of carbon dioxide (CO2) to the atmosphere. Human activities can modify food web metabolism and the cycling of C in rivers in complex ways that are hard to predict. For streams and rivers in southern Alberta, one of Canada’s most heavily impacted agricultural landscapes, riverine metabolism and C cycling are not well quantified. Here, I explore these issues in the Little Bow River (LBR) and Mosquito Creek (MCR). I used a combination of methods including both low and high frequency measurements to calculate CO2 flux, microbial incubations to measure C consumption, and whole-river metabolism. My research revealed that concentrations of CO2 were low compared to the global average, and as a result, emissions were also generally low in the river network. I found that modelled rates of metabolism in the river network, on average, were higher for gross primary production (GPP) but lower for ecosystem respiration (ER) than median rates reported for global rivers, and the network was generally on the low side for metabolic rates compared to streams in other agricultural regions. I document a shift in C cycling patterns from headwaters to the lower river, by showing increased coupling of GPP and ER, decreased bioavailability of DOC, and ultimately, elevated pH and lower CO2 emissions downstream. Human controls on flow regimes appeared to be the driving factor for differences between sites throughout the network. My research presents new network-scale patterns of river C cycling in drought-stressed agricultural landscapes.
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Keywords
river metabolism , carbon cycling