Testing the Sensitivity of Phytoplankton Communities to Changes in Water Temperature and Nutrient Load, in a Temperate Lake

Abstract

Freshwater lakes are biologically sensitive to changes in the surrounding environment and the impacts that such changes have on their water quality are of considerable ecological, recreational and economic importance. In this study the phytoplankton community model, PROTECH, was used to experiment with the effects of elevated temperatures and increased nutrient load on phytoplankton succession and productivity. The response of a phytoplankton community to combined incremental changes in these drivers was analysed, in order to elucidate the resulting ecological changes. Annual mean phytoplankton biomass increased with increases in temperature and nutrient loading, although the latter had the larger effect. The phenology of the dominant phytoplankton taxa changed with increasing water temperature; the three spring blooming species all peaked earlier in the year. The simulated summer bloom of Anabaena became earlier in the year and the Chlorella bloom later. The increased phytoplankton biomass was largely dominated by the cyanobacterium Anabaena, which was especially prevalent during the summer bloom. This resulted in a progressive loss of phytoplankton biodiversity with increasing water temperature and nutrient supply. Model experimentation showed that whilst both factors greatly affected the community, the changes to nutrient loading generally had the greater effect and that at low nutrient levels the effect of water temperature change was reduced considerably. Finally, the model predicted that cyanobacteria have the potential to dominate the phytoplankton community, with clear consequences for water quality, and that this dominance was at its greatest when high water temperatures were combined with high nutrient loads.

The importance of nutrient source in determining the influence of retention time on phytoplankton: an explorative modelling study of a naturally well-flushed lake

“…It is relatively shallow, with a mean depth of 5.3 m and a maximum depth of 19.0 m (Ramsbottom, 1976). Thermal stratification is episodic and readily broken down, and the average annual retention time is short, c. 19 days (Thackeray et al, 2006). Based on the annual average concentration of phytoplankton chlorophyll-a (13.4 mg m -3 , Thackeray et al, 2006), Bassenthwaite Lake may be considered eutrophic (OECD, 1982).…”

“…Thermal stratification is episodic and readily broken down, and the average annual retention time is short, c. 19 days (Thackeray et al, 2006). Based on the annual average concentration of phytoplankton chlorophyll-a (13.4 mg m -3 , Thackeray et al, 2006), Bassenthwaite Lake may be considered eutrophic (OECD, 1982). Estimates of the relative importance of the sources for nutrients entering the lake suggest that approximately 60% of the total annual load comes from anthropogenic sources (treated sewage waste) with the rest derived from the catchment (Thackeray et al, 2006).…”

“…Based on the annual average concentration of phytoplankton chlorophyll-a (13.4 mg m -3 , Thackeray et al, 2006), Bassenthwaite Lake may be considered eutrophic (OECD, 1982). Estimates of the relative importance of the sources for nutrients entering the lake suggest that approximately 60% of the total annual load comes from anthropogenic sources (treated sewage waste) with the rest derived from the catchment (Thackeray et al, 2006). In the UK, for example, this split can range from anywhere between 100% point source to virtually 0% (Anthony & Lyons, 2007).…”

“…Daily outflow discharges were available and the inflows were assumed to be the same as these values. Previous analysis (see Elliott et al, 2006) had identified that 1996 was the year during this study period with the longest annual retention time (c. 28.25 days), therefore this year was chosen for the subsequent sensitivity analysis in order to provide the widest range of retention times, and its corresponding observed discharge …”

Mathematical modeling of Microcystis aeruginosa growth and [D-Leu1] microcystin-LR production in culture media at different temperatures

“…Direct effects, such as rising temperatures, and indirect effects, such as intensified stratification, favor cyanobacterial blooms. Increased water temperature is expected to give cyanobacteria a selective advantage over competing phytoplankton because of the high optimal growth temperature of cyanobacterial species (Elliott et al, 2006;Jöhnk et al, 2008). Laboratory studies on Microcystis aeruginosa have demonstrated increasing growth rates with increasing temperatures from 20 to 32 C (van der Westhuizen and Eloff, 1985;Watanabe and Oishi, 1985;Imai et al, 2009).…”