Interaction of Climate Change and Eutrophication - Climate Change Impacts on Freshwater Ecosystems - page 123

Figure 6.2 Experimental set-up showing (a) submerged and (b) free-floating artificial
plant beds. During summer 2005, four replicate plant beds of each type were introduced
to 10 lakes in Uruguay and 10 similar lakes in Denmark.
direction. With fewer large-sized Daphnia and a lower average size of zooplankton,
grazing on phytoplankton is likely to decline.
Further evidence comes from subtropical lakes. Here, the typical cladoceran
community comprises small-bodied genera (Meerhoff et al . 2007a; Iglesias et al .
2007), and experimental studies have shown that high fish predation is the key
factor for the observed patterns in the structure of the littoral zooplankton
communities (Iglesias et al . 2008). Comparative experimental studies with
artificial plants in lakes in Uruguay (warm temperate to subtropical) and Denmark
(temperate), described below, provide further evidence of lower grazer control of
algae in warm lakes compared with otherwise similar temperate lakes (Meerhoff
et al . 2007a, b).
Field experiments in Uruguay and Denmark
To test the hypotheses that in a warmer climate (i) fish impact the littoral trophic
structure more strongly; (ii) trophic cascades are more truncated; and (iii) the key
role of submerged plants in maintaining clear water may be negatively affected,
we carried out experiments in subtropical Uruguay (30-35°S) and temperate
Denmark (55-57°N). We introduced artificial plastic plant beds mimicking
submerged and free-floating macrophytes (Fig. 6.2) to 10 shallow lakes, paired
in terms of size, nutrient concentrations and water turbidity (Secchi depth), and
compared the structure of the communities associated with the plant beds.