Diffuse Pollution, Degraded Waters: emerging policy solutions.
After decades of regulation and investment to reduce point source water pollution, OECD countries still face water quality challenges (e.g. eutrophication) from diffuse agricultural and urban sources of pollution, that is disperse pollution from surface runoff, soil filtration and atmospheric deposition.
The relative lack of progress reflects the complexities of controlling multiple pollutants from multiple sources, their high spatial and temporal variability, associated transactions costs, and limited political acceptability of regulatory measures.
This report outlines the water quality challenges facing OECD countries today, presents a range of policy instruments and innovative case studies of diffuse pollution control, and concludes with an integrated policy framework to tackle diffuse water pollution.
An optimal approach will likely entail a mix of policy interventions reflecting the basic OECD principles of water quality management – pollution prevention, treatment at source, the polluter pays and beneficiary pays principles, equity, and policy coherence.
This book belongs to the OECD Report Series.

Top soil removal reduces water pollution from phosphorus and dissolved organic matter and lowers methane emissions from rewetted peatlands.
However, long-term drainage and intensive agricultural use make it unlikely that the original sink functions for nutrients and carbon (C) as well as low-nutrient conditions can be re-established within a human time perspective.
2.We hypothesised that the removal of the upper degraded peat layer can be a suitable measure to avoid the negative implications of excess mobilisation of P and C after rewetting.
To evaluate the effect of top soil removal (TSR) we performed lab and field experiments in six inundated peatlands in northern Germany without TSR compared to six inundated sites with TSR.
Although highly decomposed peat released more or less no methane, dissolved organic matter (DOM) mobilisation was highest in this substrate while less decomposed peat was characterized in general by lowest rates of mobilisation.
In conclusion, top soil removal (TSR) prior to rewetting can be a suitable method to avoid the negative consequences of the excess release of phosphorus (P) and carbon post-rewetting.
We developed a simple decision–support schematic to assist the peatland restoration process and to understand better the implications of TSR.
Despite the potential benefits TSR should not be declared as a universal method, as it requires detailed consideration prior to application.
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Tool for a cleaner Long Island Sound.
There are 116 rivers, estuaries, harbors, and bays along Long Island Sound, and the amount of nitrogen runoff varies enormously from one to another.
They spent four years collecting data on where the nitrogen comes from in each of the 116 estuaries, rivers, and harbors, because while people may only care a little about Long Island Sound in the abstract, they care a lot about their own specific place.
"[The model] is a tool for citizens and managers to explore the impact of different actions," says Vaudrey, an assistant research professor in marine sciences.
There’s also a page called ‘interesting results’ that shows the 27 places with the highest load of nitrogen per water area.
With this information, decision-makers can identify the most significant sources of nitrogen pollution and use proven solutions — such as upgrading and modernizing septic systems or reducing fertilizer use — to sustain clean water," says Holly Drinkuth, director of outreach and watershed projects at The Nature Conservancy in Connecticut.
Vaudrey hopes to work with organizations adept at outreach, such as The Nature Conservancy, Save the Sound, and the Long Island Sound Study, to better inform management decisions at the local level.
She is also starting work on a second model, one that looks at what happens in the coastal waters once nitrogen is introduced.
"Tool for a cleaner Long Island Sound: Model could help citizens manage nitrogen pollution in their local waterways."
"Tool for a cleaner Long Island Sound: Model could help citizens manage nitrogen pollution in their local waterways."