Lake fertility: effects of latitude

Posted on May 26, 2009

When nutrient inputs are high, dense growths of plant plankton and periphyton (small surface-attached algae and bacteria) can shade out higher plants (macrophytes) in lakes.  However, in  principle macrophytes should do better in warmer climates because higher temperatures, greater light intensities and longer growing seasons will allow them to colonise deeper water and increase their surface cover.  Higher rates of evaporation in warm conditions should have the effect of reducing water levels, increasing light intensities at the bottom of lakes and assisting macrophyte growth.  Macrophytes also benefit by harbouring grazing animals that help to limit algal populations.

In mesososm (enclosed environment) experiments in a number of shallow European lakes, when nutrients were added the biomass of periphyton increased and the biomass of higher plants declined.  However, plants managed to survive better towards the lower end of a north-south gradient (Spain) than towards the northern end (Finland).  It seemed that macrophyte growth was helped by higher light intensities and evaporation-driven drops in water level in the southern lakes.  In a year when the temperature gradient was less clear, the effect of latititude disappeared.

Reference:  Becares, E. et al. 2008.  Effects of nutrients and fish on periphyton and plant biomass across a European latitudinal gradient.  Aquatic Ecology, 42,561–574.