The Eutrophication Discontinuity

11 January 2011

Over time there have been two big changes in the movement of nutrients from human waste or activities into the aquatic environment.  The first was in the late 1800s when the discovery of guano replaced the use of nightsoil as a fertilizer.  The second, demonstrated by water quality measurements, occurred in the 1950s as post-war development and movement to cities saw a marked increase in sewage generation and disposal – evident as a sudden and massive increase in surface water P-levels.

P-discontinuity for Hartbeespoort Dam

A group of researchers from Canada have produced elegant and similar results using diatoms!  Diatoms can be used to historically infer a lot of things, including what the prevailing concentrations of phosphorus were (=diatom-inferred total phosphorus, DI-TP).  An important conclusion from their work is that  lakes situated in catchments that have had a long history of agriculture or elevated population densities may not be able to fully recover from excessive nutrient loading. Research to understand when lakes cross this ‘point of no return’ will be an important next step to managing eutrophication and restoring eutrophic lakes.

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