Biodiversity and functional responses to flow regulation in UK upland rivers

Worldwide many rivers are now impounded by dams or reservoirs due to rising human water demands. River damming is regarded as a major threat to riverine ecosystems, affecting sediment transport, natural flow and thermal regimes, subsequently impacting freshwater biota. In recent decades, the use of environmental flows has gained prominence as a promising strategy to mitigate the ecological impacts of dams. Nonetheless, there is currently a lack of understanding of the impacts of river regulation and environmental flow implementation in regulated rivers. More specifically, less work has been carried out to understand the functional responses to flow change compared to structural responses. As such this thesis explores how ecosystem structure and functional processes respond to flow regulation and environmental flow implementation in UK upland rivers. This PhD thesis consisted of four data chapters: i) applicability of a database-driven technique for food web characterisation in regulated river systems across the UK upland streams; ii) quantification of ecosystem functioning processes (microbial-driven decomposition of leaf litter; total microbial decomposition and invertebrate consumption of leaf litter; biofilm accrual on benthic substrata) in response to innovative real-world experimental flow releases (Seasonal compensation flows (SCFs)) downstream of two Yorkshire Water-managed reservoirs, using a Before-After-Control-Impact (BACI) design in the UK uplands; iii) quantification of sediment bacteria community responses to flow regulation and environmental flow implementation (SCFS) using the Next Generation Sequencing techniques (NGS) across 28 sites in the UK upland rivers; and iv) quantification of biodiversity of sediment fungi in regulated upland rivers. Overall, this thesis revealed that ecosystem structure and food webs were largely invariant to both flow regulation or e-flows (SFCs), resulting in only minor changes in ecosystem functioning in UK upland river systems. Nonetheless, this thesis shone a light onto the remarkable levels of biodiversity found in benthic biofilms in Pennine rivers, with species numbers more than two orders of magnitude higher than the most commonly used bioindicators (fish and invertebrates). As these species of bacteria and fungi are of central importance to ecosystem services such as water quality regulation, nutrient cycling to higher trophic levels, and greenhouse gas uptake/emissions, their spatial and temporal ecological dynamics should be investigated further as a priority in regulated rivers to understand whole ecosystem implications of environmental flow management.