Regional synthesis of algal community change in the lakes and tarns of the Windermere catchment, Lake District, UK, since the 19th century
Moorhouse, Heather Louise (2016) Regional synthesis of algal community change in the lakes and tarns of the Windermere catchment, Lake District, UK, since the 19th century. PhD thesis, University of Nottingham.
The rural Windermere catchment, English Lake District, UK comprises 11 upland and lowland lakes which feed into Windermere, England’s largest lake. Palaeolimnological algal records, alongside long-term climate and catchment land use monitoring data from all basins in the catchment were used to quantify the relative importance of regional and local-scale drivers of algal community change. Like many temperate lakes, Mann-Kendall trends showed increased concentrations of total algal production and cyanobacteria accompanied by declines in C/N ratios across the Windermere catchment over the last few centuries. Regression tree analyses suggest that nutrient enrichment has an overarching effect, with temperature playing a secondary role. Synchrony and breakpoint analyses suggested that local forcings led to catchment-wide asynchrony of algal communities after the 1950s. In the lowlands (<100 m.a.s.l), 20th century wastewater treatment installation explained the greatest changes in the algal communities, overriding agricultural intensification, but at sites without point sources, correlations to variables that indirectly explain sewage expansion such as resident catchment human populations were apparent. In contrast, algal community change in upland lakes was more responsive to atmospheric pollutants which caused acidification in the late 19th and early 20th century, alongside climatic variables notably temperature. Evidence for upland atmospheric nitrogen deposition in the 20th century was suggested by decreasing stable δ15Norg isotope values, concurrent with increased concentrations of Chlorophyll a (from all algae) but no clear response was found in algal compositional changes. Higher algal community change occurred in lakes with longer residence times overlaying sedimentary geologies typically in the lowlands. However, algal community change was also high in lowland lakes with lower residence times that had point sources, suggesting centennial-scale fertilisation had reduced the ability of local lake characteristics to attenuate environmental change. This work demonstrates that lakes within a few kilometres of one another respond uniquely to environmental change depending on physical characteristics and landscape position. Management measures should focus on reducing nutrients from waste water effluent and develop local stewardship programmes to increase environmental awareness in the region.
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