Interaction of Climate Change and Eutrophication - Climate Change Impacts on Freshwater Ecosystems - page 146

be used as indicators of warming effects as the changes typically will be larger than
expected from those of eutrophication alone. The results of controlled experiments
can separate distinct effects in relatively simple though not necessarily unrealistic
systems, but in more complex real ecosystems, many pressures not only act
simultaneously but also interact, so that demonstration of the individual effects of
possibly reduced nutrient loading and anthropogenic CO 2 emissions in the future will
continue to be challenging and only give very general answers, even when advanced
statistical approaches are used in the analysis of trends.
Are there lessons to be learnt from the past that can help
to understand future problems better?
Our answer to the question whether useful lessons for the future can be learnt
from the past is yes, particularly if several approaches are employed in concert to
analyse past situations and make predictions. If we extend our records sufficiently
far back in time and consider change over long timescales, we reach a situation
where climate change was an important driver of ecosystem change while
anthropogenic effects such as eutrophication were less pronounced or even
negligible (cf. Chapter 2). Information from the past may therefore provide a
clearer picture of ecosystem change driven largely by climate and can help us to
extract a climate signal from contemporary data sets. Palaeolimnology holds
great potential to achieve this goal.
In several lakes, there is evidence of ecological response to changes in both
nutrient levels and climate, although in most cases, the eutrophication signal tends
to eclipse the climate signal. Nonetheless, in Lago Maggiore of Northern Italy, for
example, there is evidence of increased temporal variation in zooplankton
communities following exceptional meteorological events and changes in fish
predation, which might be partly attributable to increased temperatures (Manca
et al . 2007). Furthermore, several data sets indicate that climate change is likely to
have a confounding effect on recovery from eutrophication (Jeppesen et al . 2009),
suggesting that lake responses to nutrient reduction may be somewhat slower under
warmer and wetter conditions than originally envisaged based on current climate.
Can we mitigate negative effects of climate change on ecosystems
in terms of enhanced eutrophication?
There is much scope for combating eutrophication symptoms that will be
aggravated by global warming by taking measures to reduce external nutrient
loading to freshwaters beyond those already implemented or planned. These
include (i) less intensive land use in catchments with sensitive freshwaters to
reduce diffuse nutrient inputs; (ii) re-establishment of riparian vegetation to
buffer nutrient transfers to streams and rivers and improve in-channel structures
to increase the retention of organic matter and nutrients; (iii) improved land
management to reduce sediment and nutrient export from catchments; (iv)
improved design of sewage works to cope with the consequences of flood events
and low flows in receiving waters; and (v) more effective reduction of nutrient
loading from point sources and, for N, from the atmosphere.