Abstract
Climate change is likely to have large impacts on freshwater biodiversity and ecosystem function, especially in cold-water streams. Ecosystem metabolism is affected by water temperature and discharge, both of which are expected to be affected by climate change and, thus, require long-term monitoring to assess alterations in stream function. This study examined ecosystem metabolism in two branches of a trout stream in Minnesota, USA over 3 years. One branch was warmer, allowing the examination of elevated temperature on metabolism. Dissolved oxygen levels were assessed every 10 min from spring through fall in 2017–2019. Gross primary production (GPP) was higher in the colder branch in all years. GPP in both branches was highest before leaf-out in the spring. Ecosystem respiration (ER) was greater in the warmer stream in two of three years. Both streams were heterotrophic in all years (net ecosystem production—NEP < 0). There were significant effects of temperature and light on GPP, ER, and NEP. Stream discharge had a significant impact on all GPP, ER, and NEP in the colder stream, but only on ER and NEP in the warmer stream. This study indicated that the impacts of temperature, light, and discharge differ among years, and, at least at the local scale, may not follow expected patterns.
Highlights
It was expected that higher discharge might influence ecosystem respiration bringing in more allochthonous material to be decomposed
Since seasonal and interannual variability in ecosystem metabolism could be due to differences in temperature, PAR, and discharge, we examined the correlations between these factors and Gross primary production (GPP), Ecosystem respiration (ER), and net ecosystem production (NEP)
Within our streams, increasing temperature was correlated with increased GPP, as predicted
Summary
The major impacts of climate change on stream systems are likely to cause alterations in water temperature, light regime due to shifting phenological patterns in watersheds, and hydrological function because of changing precipitation patterns [5]. These changes are projected to have impacts on water quality [6–8] and are expected to influence individual organisms, populations, and communities [9], substantially impacting food webs [10]. Since their value in providing ecosystem services (such as nutrient cycling, water purification, carbon sequestration, and recreational opportunities) and the impacts that climate change may have on these resources, there must be long-term monitoring of these systems [11]
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