Interaction of Climate Change and Eutrophication - Climate Change Impacts on Freshwater Ecosystems - page 120

freshwater biota or exacerbate existing ones (Mooij et al . 2005; Blenckner et al .
2006; Jeppesen et al . 2007a, 2009).
Attempts to adapt to or mitigate the effects of climate change as well as to cope
with a rapidly increasing world population needing to be fed are likely to lead to
intensified crop production in the temperate zone and, for reasons of water
scarcity, less intensive production in the Mediterranean (Olesen & Bindi 2002;
Alcamo et al . 2007). Intensification of agriculture in the temperate zone will
probably cause increased nutrient export from land to water as a result of
increased run-off (Olesen & Bindi 2002), now that the P and N cycles have been
massively accelerated by human activities (Galloway et al . 2008; Smil 2000),
unless additional nutrient retention measures are applied. However, the control
of diffuse losses of nutrients from land has proven very difficult, not least because
nitrate is extremely mobile and cultivation inevitably leads to erosion and
downslope transport of soil particles containing phosphorus. Changes in
temperature and rainfall will also lead to alterations in agricultural practices,
including changes in soil cultivation and in the rates and timing of fertilization.
These changes will, in turn, have cascading effects on nutrient flows (IPCC 2007).
Extreme rainfall events and periodic droughts (through aeration, mineralization
and subsequent washout of mineralized nutrients) will also enhance the risk of
nutrient losses from catchments to freshwaters.
At the higher temperatures of Southern Europe, the predicted decrease in
precipitation and higher evaporation will result in less run-off and, as a result,
possibly lower nutrient loading to freshwaters (Jeppesen et al . 2009; Özen et al .
2010). However, this reduction is not expected to compensate for the negative
consequences of water deficits that will lead to a concentration of nutrients from
point sources and a reinforcement of eutrophication symptoms in aquatic
ecosystems (Beklioglu et al . 2007; Beklioglu & Tan 2008; Özen et al . 2010).
Moreover, in Southern Europe, drought and reduced discharge into inland waters
will result in greater salinization exacerbated by increased evaporation and
greater use of water for irrigation (Zalidis et al . 2002). For example, a decrease
in hydraulic loading has been found to lead to a threefold increase in salinity in
two shallow Mediterranean lakes (Beklioglu & Tan 2008; Beklioglu & Özen
2008). Salinities of a few parts per thousand, which are not uncommon in such
inland basins, lead to reduced species richness (Williams 2001; Barker et al .
2008; Brucet et al . 2009), community shifts and a higher risk of clear water
switching to a phytoplankton-dominated turbid state (Jeppesen et al . 2007b).
There is a substantial body of literature on inland water eutrophication, which
has been summarized in several reviews (e.g. Carpenter et al . 1998; Smith 2003;
Schindler 2006; Dodds 2007). It is perhaps the most widespread problem in
freshwater ecosystems now that aerial deposition of nitrogen fertilizes ecosystems
at the global scale (e.g. Galloway et al . 2008). Similarly, the anticipated effects of
global warming on freshwater ecosystems have been repeatedly reviewed (e.g. Firth
& Fisher 1992; Mooij 2005; Jeppesen et al . 2009). In this chapter, we will describe
new results on the interaction between eutrophication and climate change based on
studies carried out as part of the Euro-limpacs project during the period 2004-8.
Studies of climate-nutrient interactions in lakes, streams and wetlands in the
Euro-limpacs project and elsewhere have shown that warming is likely to