Lake management gets harder as the climate changes

Posted on March 26, 2022

Excessive inflows of nutrients, especially phosphorus in fertilisers, pesticides and sewage, reduce water quality in lakes and reservoirs and can encourage toxic algal blooms, often with serious implications for public health, food security and biodiversity.  Increases in nutrient inputs are partly due to increased rainfall associated with  climate change.  And the availability and residence times of incoming nutrients are affected by landform features and the size of receiving water bodies: for example, phosphorus concentrations tend to be relatively low in deep lakes.   These considerations make it likely that interactions between nutrients, climate change and landform are important influences on water quality in lake ecosystems.  However, although many researchers have explored possible predictors of lake eutrophication and algal blooms, there have been almost no studies on the relative importance of nutrients, climate and landform features.  This prompted a group of Canadian and U.S. -based scientists to analyse a large lake database with the aim of identifying key predictors of chlorophyll a, which was used as an indicator of eutrophic conditions.  The database included information on 2561 lakes in seven countries, and the data for climate and landform covered eleven predictor variables.  Multivariate analysis established that the predictor variables together explained 60% of the variation in lake chlorophyll.   Of that, the most important variable was total phosphorus, which explained 42% of the variation. Climate variables (summer and spring air temperatures, solar radiation, precipitation, and cloud cover) together explained 38% of the variation, and landform (especially lake depth and watershed area) accounted for 20%.   The most striking finding was that climate influenced water quality almost as much as nutrient pollution: rising water temperatures caused by climate change will increase algal growth rates and encourage bloom development.  Although lake management plans have tended to focus mainly on nutrient reductions, the results of this study suggest that they  may not be sufficient to address the problem of deteriorating water quality, and equal attention should be given to examining the implications of climate change.

Reference:   Shuvo, A. et al.  2021.  Total phosphorus and climate are equally important predictors of water quality in lakes.  Aquatic Sciences 83:16.