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Ramirez, Samantha Zeane

University of British Columbia

Streams are subject to a variety of impacts as a consequence of human development which disrupt ecosystem processes and can lead to habitat change and species loss (Dos Reis Oliveira et al., 2019; Marques et al., 2019). Associated negative impacts include nutrient enrichment, increased light availability and water temperatures, and the alteration of channel structure and stream flow (Zhi et al., 2023; Mueller et al., 2005). Water quality is a good indicator of stream health, and was measured using various parameters, including nitrogen and phosphorus concentration, and DO concentrations. To understand the effects of nutrient enrichment (eutrophication) on stream metabolism and fish habitat, I measured key water quality parameters every month from May to August at 37 lower Fraser Valley stream sites. Overall patterns of water quality across the summer low-flow recession indicate increasing hypoxia associated with declining flow and water surface turbulence, high algal production and respiration associated with nutrient enrichment, and lack of canopy cover. One novel insight of this study is the limiting effect of hypoxia on aquatic plant and algal production; moderate increases in total P appear to stimulate plant and algal growth until moderate to severely hypoxic conditions occur (DO < 2 mg/L), causing total P to switch from a stimulating to inhibitory effect on algal and heterotroph production. Results showed that the likelihood of hypoxia is greater than 50% when total P exceeds ~0.06 mg/L, when discharge is less than ~0.05 m³·sec⁻¹, when mean K is less than 4 (m d⁻¹), when total N is greater than 1 mg/L, and when water column depth exceeds 0.7 m. Conserving water quality is a particularly important issue in streams where Species at Risk and other sensitive species occur (i.e., salmonid species, and listed taxa like Salish Sucker (Catostomus sp. cf. catostomus), and Nooksack Dace (Rhinichthys cataractae )). It is necessary to better understand the interaction between human impacts and water quality to minimize further fish and fish habitat loss in a changing environment. The widespread hypoxia observed in lower Fraser Valley streams indicates a failure by responsible agencies to address this pivotal conservation issue.

Text

2023-11-23

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/86662

Oceans and Fisheries

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/