Modelling the effects on phytoplankton communities of changing mixed depth and background extinction coefficient on three contrasting lakes in the English Lake District

Abstract

1. The process-based phytoplankton community model, PROTECH, was used to model the response of algal biomass to a range of mixed layer depths and extinction coefficients for three contrasting lakes: Blelham Tarn (eutrophic), Bassenthwaite Lake (mesotrophic) and Ullswater (oligotrophic). 2. As expected, in most cases biomass and diversity decreased with decreasing light availability caused by increasing the mixed depth and background extinction coefficient. The communities were generally dominated by phytoplankton tolerant of low light. Further, more novel, factors were identified, however. 3. In Blelham Tarn in the second half of the year, biomass and diversity did not generally decline with deeper mixing and the community was dominated by nitrogen-fixing phytoplankton because that nutrient was limiting to growth. 4. In Bassenthwaite Lake, changing mixed depth influenced the retention time so that, as the mixed depth declined, the flushing rate in the mixed layer increased to the point that only fast-growing phytoplankton could dominate. 5. In the oligotrophic Ullswater, changing the mixed depth had a greater effect through nutrient supply rather than light availability. This effect was observed when the mixed layer was relatively shallow (<5.5 m) and the driver for this was that the inflowing nutrients were added to a smaller volume of water, thus increasing nutrient concentrations and algal growth. 6. Therefore, whilst changes in mixed depth generally affect the phytoplankton via commonly recognized factors (light availability, sedimentation rate), it also affected phytoplankton growth and community composition through other important factors such as retention time and nutrient supply.

Water quality in four reservoirs of the metropolitan region of São Paulo, Brazil

“…According to Schindler (2006), the rate of water renewal is an important modifier of nutrients concentrations in aquatic ecosystems. Other authors also pointed that fluctuations in water level and residence time in reservoirs can strongly affect the phytoplankton community, acting directly upon the maintenance of these organisms in the water column (Reynolds, 2006;Bernhardt et al, 2008). Besides, short residence time causes biomass loss due to hydraulic washing and mechanical shock between phytoplankton cells (Kimmel et al, 1990;Straskraba et al, 1993).…”

Phytoplankton biomass is mainly controlled by hydrology and phosphorus concentrations in tropical hydroelectric reservoirs

“…The importance of water residence time for nutrient dynamics in aquatic systems has been also recognized previously, since the rate of water renewal is an important modifier of nutrient loading (Schindler, 2006). Hydrology, besides controlling light and nutrients, also acts directly upon the maintenance or non-maintenance of phytoplankton in the water column (Kalff, 2002;Reynolds, 2006;Bernhardt et al, 2008). Residence time is also a driving force for the zooplankton community.…”

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

“…The PROTECH model has had its key growth parameters verified (Elliott et al 1999b), tested for sensitivity (Elliott et al 1999a) and been validated at numerous sites (Elliott et al, 2000;Lewis et al, 2002;Elliott & Thackeray, 2004; Bernhardt et al, 2008). Also, it has been successfully used to simulate Bassenthwaite Lake in a previous study (Elliott et al, 2006).…”