A September 8th article – “Green gunk bad sign for Lake Erie" – in the Windsor Star describes the algal blooms that have been plaguing Lake Erie. Reporter Craig Pearson explains that excessive nutrients – especially the increasing levels of phosphorus – are most likely feeding the cyanobacteria (called blue-green algae) blooms that are impacting recreation and the overall health of the lake.
While the article paints a very vivid picture of the recurring phenomenon, it lacks details on the lake's main sources of phosphorus and does not mention that individuals can make a difference in this water quality problem. Phosphorus is found naturally in soils and rocks, but human activities can increase the nutrient's levels in lakes and rivers, as they have in Lake Erie's not too distant past.
Pearson draws excellent parallels between the current blooms and the buildup of nutrients in Lake Erie during the 1960s and 1970s. High phosphorus levels in those decades caused excessive algae and plant growth. When the algae and plants died and decomposed, low or no oxygen in parts of the lake led to fish kills.
Laws were passed to reduce phosphorus from going into the Great Lakes, mainly by restricting its levels in factory effluent and household detergents. This led to a recovery of Lake Erie's ecosystem in the 1980s and early 1990s.
However, as Pearson mentions in his article, phosphorus levels in the lake are on the rise again. Why they are increasing – and which of the known sources is contributing the most – is not exactly clear.
Today, the nutrient still enters Lake Erie and its tributary streams from both industry and household sources. Commercial production of fertilizers and pesticides is one source. Home laundry detergents is another, even though levels in the products are lower than they once were. Many other cleaning products – including automatic dishwashing detergents – contribute phosphorus, too.
Advanced (tertiary) municipal wastewater treatment can remove up to 95 percent of the phosphorus in sewage. Yet,
municipal wastewater is still one of the biggest sources of this nutrient to surface waters in Ontario, contributing more than one ton per year, according to Environment Canada.
Untreated sources are also a problem. These can include sewage from combined sewer overflows, sewage from septic fields and runoff from farm fields.
Synthetic fertilizers or manure applied to farm fields can contain phosphorus that can be carried into the lake with rain and snow runoff. Although it is not clear how much phosphorus enters the lake from farming, a number of recent federal government programs in Canada have focused on understanding nutrient inputs and and reducing them through changes in agricultural practices.
The recent increases in phosphorus in Lake Erie remain a mystery. The bright side of the story is that when nutrient levels are reduced, lakes can and do recover from the excessive nutrient inputs.
By explaining the major sources of phosphorus in Lake Erie, Pearson could have helped readers better understand where it comes from and how they as individuals could help reduce its levels.
