Not much P needed to foul up a river

6 December 2012

Research has shown that the ecological functioning of streams starts to occur when the level of dissolved phosphorus in the water starts to exceed 20 microgrammes per liter.  This is a very low level and approximate the concentration present in rainfall in many areas.  A just-published study by the US Geological Society (USGS) has shown that the impacts of urban development on streams occurs very early on.

The loss of sensitive species in streams begins to occur at the initial stages of urban development, according to a new study by the USGS. The study found that streams are more sensitive to development than previously understood.  Contaminants, habitat destruction, and increasing streamflow flashiness resulting from urban development can degrade stream ecosystems and cause degradation downstream with adverse effects on biological communities and on economically valuable resources, such as fisheries and tourism.  For example, by the time urban development had approached 20 percent in watersheds in the New England area, the aquatic invertebrate community had undergone a change in species composition of about 25 percent.

In Australia, the target management concentration for P in rivers appears to be 6o microgrammes per liter – a number that would be exceeded easily by many, many rivers in South Africa.  Australia has just held what they call P-week – during which they test the phosphate levels in their waterways – and many spots along the Hunter River did not make the grade (although some were pretty close!):

According to the results, samples at Hillsborough (0.10mg/L), Melville Ford (0.13mg/L), the Belmore Bridge (0.22mg/L) and Morpeth boat ramp (0.10mg/L) measured well above the 0.06mg/L guideline.  “Phosphorous is a major contributor to water quality problems in the form of phosphate and can lead to outbreaks of the toxic blue-green algae across the Hunter-Central Rivers region,” Hunter-Central Rivers Waterwatch catchment officer Ingrid Berthold said.

Phosphate is an essential plant and animal nutrient that occurs naturally in low concentrations in Australian soil and water.

What is important to take note of here is that countries like the US and Australia are taking the issue of eutrophication very seriously.  For example, the very problematical Lake Chautauqua will soon benefit from a TMDL management programme.  See this report for the range of measures to be implemented in the Grand Lake catchment in Ohio.

In New Zealand, an algal bloom in the Waimea River is causing a bit of a panic:

The Tasman District Council has now put up warning signs and is advising everyone to avoid contact with the water in the river.  This follows the death of a dog and other cases of dogs becoming ill with vomiting and diarrhoea [sic .The blue-green algae, or cyanobacteria, forms thick, dark-brown mats in the river.  Cawthron research scientist Susie Wood went to look at the algae in the river up from the Appleby bridge and said: “It’s the worst I have seen.”





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