Photoautotrophic productivity in eutrophic ecosystems

Abstract

Enhanced photoautotrophic productivity of lakes, reservoirs, rivers and streams is a consequence of prolific nutrient loading from the catchment known as eutrophication. In most cases, it is a syndrome of ecosystem responses to human activities in the watershed. Primary production is strongly influenced by latitude, insolation and nutrient availability, but also depends on lake size, the size of the catchment, the type of water body and lake depth. The outcome is therefore highly variable for specific continental waters. Nevertheless, autotrophic production is perhaps the best parameter to define the trophic level of waters. The complex techniques and frequent measurements necessary to estimate production accurately hampered the application, however. Recent improvements in methods and new developments in monitoring strategies have revived interest in primary production as an index to define trophy. Important relationships of production to environmental variables are analysed. Then, development of boundary criteria are discussed, production indices compared and trophic boundary classifications compiled from different authors. Maximum and global production is emphasised. The impact of a warmer world as a consequence of climate change on continental waters is highlighted and future perspectives of photoautotrophic production summarised.