Interaction of Climate Change and Eutrophication - Climate Change Impacts on Freshwater Ecosystems - page 119

6
Interaction of Climate Change
and Eutrophication
Erik Jeppesen, Brian Moss, Helen Bennion, Laurence Carvalho,
Luc DeMeester, Heidrun Feuchtmayr, Nikolai Friberg, Mark O.
Gessner, Mariet Hefting, Torben L. Lauridsen, Lone Liboriussen,
Hilmar J. Malmquist, Linda May, Mariana Meerhoff, Jon S.
Olafsson, Merel B. Soons and Jos T.A. Verhoeven
Introduction
The conversion of much of the earth's land surface to agriculture or urban land
has had major effects on nutrient flows from the local to the global scales. Natural
ecosystems generally conserve nutrients and store organic matter effectively. In
all agricultural systems, such conservation mechanisms are weakened, and
management increases nutrient inputs over natural levels. These altered features
of ecosystems together result in massive leakage of nutrients into waterways.
Humans also concentrate nutrients from food and release excreta that generate
immense nutrient flows in areas of high population density, even where modern
sewage treatment technology is applied. The consequent eutrophication of many
of the world's waters has become a widespread and expensive problem for water
supply, human health and amenity, as well as for nature conservation.
Eutrophication profoundly affects aquatic ecosystems by altering biodiversity,
trophic structure and biogeochemical cycling.
Biological processes are temperature sensitive. Increasing temperature,
expected under future climate change, might (i) change growth and respiration
of organisms, potentially leading to lower net primary production, (ii) enhance
oxygen consumption (and, as warm water holds less oxygen, the risk of oxygen
depletion increases with problems for sensitive species) and increase nutrient
release from sediments; (iii) affect life history in the direction of shorter lifespans
and earlier reproduction; and (iv) change phenology and trophic dynamics,
which potentially may result in a mismatch between consumer demand and their
prey availability. Such temperature-induced changes are expected to interact
strongly with existing increased nutrient flows and create new problems for