Productivity of freshwater ecosystems and climate change

Global climate change is altering freshwater production by changing the global area of these ecosystems, increasing their temperature, altering stratification regimes, increasing pulsed nutrient supplies, and increasing solute concentrations. Although average air temperatures are likely to increase slightly more at high northern latitudes than elsewhere, day- and season-length differences mean that rates of increase in annual average surface water temperature over the next century will be 0.1-1° toward the poles but up to 10 °C in the tropics. The production of algae, plants, benthos, zooplankton, and fish will increase substantially. Primary production will more than double at low latitudes, but lake benthos, stream benthos, zooplankton, and fish will increase their secondary production by about 5 %, 2.5 %, 4.7 %, and 2 %, respectively, per degree of water temperature change. Global climate change will yield increased runoff due to storms across the globe but especially at high latitudes. Increased runoff will exacerbate global eutrophication problems. Stratification will weaken substantially at low latitudes, leading to increased mobilization of sediment nutrients, but will strengthen somewhat at higher latitudes due to temperature effects on water density. Intense heating of surface waters between 30° N and S, coupled with the high heat of vaporization of water, will lead to increased salinity of inland waters at low latitudes and loss of productivity of key organisms. Shifts in world patterns of temperature will favor Cyanobacteria blooms across much of the Earth and alter the production of economically important freshwater organisms.