Different responses to land use

Posted on December 9, 2010

 Although it’s clear that the water quality of lakes can be affected by the run-off of nutrients and contaminants from the surrounding catchment,  little work has been done to compare the impacts of land use on lakes with different types of mixing patterns.  Deep lakes tend to stratify into near-surface and bottom layers, which restricts the recirculation of lake-bed nutrients into the upper productive zone, but in shallow lakes biological production and water quality are much more likely to be affected by the wind-induced mixing of nutrients.  This means that in shallow lakes productivity is more unpredictable and strategies for nutrient management, which are derived mainly from work on deep lakes, are less successful.   In a Canadian study, surface-water phosphorus concentrations in deep lakes, but not shallow lakes, were significantly related to the percentage of agricultural land in the catchment.  Sediment cores provided evidence that midge communities in deep lakes had changed in response to increases in land use, nutrient loads and oxygen stress following European settlement.  In contrast, shallow lakes were relatively unresponsive to changes in land use because their internal nutrient load was high, and this masked the effect of external loading from the catchment. 

Reference:  Taranu, Z.E., Koster, D., Hall, R.I., Charette, T., Forrest, F., Cwynar, L.C., Gregory-Eaves, I.  2010.  Contrasting responses of dimictic and polymictic lakes to environmental change: a spatial and temporal study.  Aquatic Sciences 72, 97–115.