Interaction of Climate Change and Eutrophication - Climate Change Impacts on Freshwater Ecosystems - page 141

0.8
Coefficients for water temperature lag 1
0.6
0.4
0.2
0
-0.2
-0.4
J FMAMJ J ASOND
Month
Figure 6.13 Calculated correlation coefficients for the relationship between water
temperature and Daphnia population density at Loch Leven (the United Kingdom) over
the year. Shaded region identifies ± 2 standard errors, indicating a significant positive
relationship during winter and spring months, but no significant effect from May to
November.
Daphnia numbers have also increased in winter and spring (Ferguson et al . 2007,
2009) (Fig. 6.13). Higher temperatures have direct physiological effects (e.g.
increased growth rates) on plankton. However, the negative relationship at Loch
Leven between chlorophyll a and water temperature in spring suggests an indirect
response to higher spring temperatures, probably related to greater zooplankton
production and grazing.
The phytoplankton community model PROTECH (Phytoplankton Responses
To Environmental Change; Reynolds et al . 2001) was used to investigate the
impacts of changing water temperature and nutrient loading upon the
phytoplankton in Loch Leven (Elliott & May 2008). A range of water temperature
and nutrient loading scenarios was run to examine the effect of changes in these
variables on chlorophyll a concentration, phytoplankton species diversity and
cyanobacterial abundance. Change in water temperature had relatively little
effect on phytoplankton biomass and species diversity in comparison with
changes in nutrient loading. However, phytoplankton varied according to the way
in which nutrient loading changed. For example, increasing P load alone caused
a large increase in total chlorophyll a concentration and in Anabaena
(cyanobacteria) abundance. In contrast, simultaneously increasing the loads of
phosphate and nitrate resulted in higher Anabaena densities at lower nutrient
concentrations. A likely explanation for this observation is that Anabaena , which
is a nitrogen fixer, is able to exploit the available P better than other phytoplankton
species when nitrogen levels are low.
Sediment cores provide an alternative way of examining relationships over
long periods. A sediment core from Loch Leven, representing the period
1940-2005, showed that changes in diatom composition and abundance were