Frame, Jessica Laura (2010)
Ph.D. thesis, University of Birmingham.
This study investigates the current impact of acid deposition on the structure and function of benthic communities in streams of contrasting pH in mid-Wales, UK, and examines barriers to biological recovery across the sites. The results of field surveys across 30 streams revealed sustained effects of acid stress on macroinvertebrate assemblages. Acid streams supported fewer grazers and filter-feeders than circumneutral waters but other functional groups were less affected by low pH. Field experiments tested the effects of acidification on two key processes in stream ecosystems, benthic algal grazing and leaf decomposition. Grazer impacts on algal abundance were generally feeble and largely unaffected by acid stress. Leaf litter decomposition was impaired by acidification, due largely to reduced microbial breakdown. Prospects for biological recovery in chemically restored streams are discussed, and field experiments were undertaken to test two hypotheses (biotic resistance and resource limitation) proposed to explain the observed delays in faunal recolonisation. A resident-colonist competition experiment revealed no evidence in support of biotic resistance as mediated through interspecific competition, whereas growth experiments revealed that the quality or palatability of algal resources in chemically ‘restored’ streams limits growth and survival of colonist mayfly nymphs (Baetis).
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