Impacts of flow alteration on stream ecosystems

Arias Font, Raquel ORCID: 0000-0002-2093-1924 (2023). Impacts of flow alteration on stream ecosystems. University of Birmingham. Ph.D.

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Abstract

Worldwide, more than two-thirds of rivers are affected by channelization, damming, hydropower and/or water abstraction creating highly modified river flow regimes that potentially have profound impacts on their ecological integrity. Climate change is expected to further exacerbate these effects as extreme events, such as drought, increases in frequency and duration. Our knowledge of flow-ecology relationships is increasing but our current understanding of flow regulation is often confounded by additional stressors generated by dams, regional factors and human activities and thus experiments are required to disentangle these drivers. The research presented in the thesis used manipulative experiments in mesocosms mimicking headwater streams to investigate how flow regulation generated by irrigation (reversal of flow seasonality), flow homogenisation (no flow variability) and drought (reduced flow magnitude and dewatering) affect stream ecosystem structure and functioning (water quality, biofilm and macroinvertebrates). The different flow regimes had markedly different effects on benthic communities and their function. Flow homogenisation generated a stable and persistent flow with ecosystem functioning similar to the natural control, but promoted the occurrence of lentic macroinvertebrate communities. By contrast, reversal of the timing of high and low flows (flow ‘reversal’) increased stochasticity in biofilm growth, which generated two alternative states, and altered the taxonomic and functional trait composition of the macroinvertebrate assemblage. Specifically promoting survival strategies such as drift resistance, promoting big body size and reducing macroinvertebrates abundances. Drought reduced the functioning of the biofilm by constraining its growth and processing rates, but resilience and resistant strategies were present in the biofilm (temporal adaptation to wet and dry phases) and benthic macroinvertebrate assemblages (resource partitioning and persistence on refugia). A second mesocosm experiment investigated how biofilm functioning in streams was modified as a consequence of future climate change (low flow and heatwaves). Findings revealed that under low flow conditions, heatwaves increased heterotrophic processes more than autotrophic ones, with decomposition rates of recalcitrant fraction especially affected. New environmental flow strategies to mitigate the effects of flow regulation on stream ecosystems are need to preserve freshwater biodiversity and ecosystem services. Further research is required to identify the impacts on higher trophic levels and meta-community dynamics; and the potential for interactive effects with additional stressors.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):