Strategic management of non-point source pollution from sewage sludge.

In the UK, the recycling of sewage sludge to land is expected to double by 2006 but the security of this route is threatened by environmental concerns and health scares. Strategic investment is needed to ensure sustainable and secure sludge recycling outlets. At present, the security of this landbank for sludge recycling is determined by legislation relating to nutrient rather than potentially toxic elements (PTEs) applications to land--especially the environmental risk linked to soil phosphorus (P) saturation. We believe that not all land has an equal risk of contributing nutrients derived from applications to land to receiving waters. We are currently investigating whether it is possible to minimise nutrient loss by applying sludge to land outside Critical Source Areas (CSAs) regardless of soil P Index status. Research is underway to develop a predictive and spatially-sensitive, semi-distributed model of critical thresholds for sludge application that goes beyond traditional "end-of-pipe" or "edge-of-field" modelling, to include hydrological flow paths and delivery mechanisms to receiving waters from non-point sources at the catchment scale.

Rapid incidental phosphorus transfers from grassland.

In Britain, frequent rainfall means that there is a high potential for rapid, direct (incidental) losses of phosphorus (P) to occur after fertilizer or manure application. However, despite the known contribution of P to the eutrophication of water bodies in Britain, such incidental transfers have received little experimental attention. To rectify this, we used lysimeter plots (each 3 x 10 m) to investigate incidental transfers in a composite of overland and lateral subsurface flow (0-27 cm) following the application of different P sources. The treatments used were triple super phosphate (TSP), dairy slurry (Slurry), an equal mix of TSP plus slurry (TSP + Slurry), and no P (Zero P). The treatments were applied to wet soil at a rate of 29 kg ha(-1). In the following 169 h, 48.8 mm rainfall (intensity < or =3 mm h(-1)) resulted in total phosphorus (TP) exports between 1.8 and 2.3 kg ha(-1). A single 4-h period (with overland flow) accounted for 33 to 46% of overall loads from the P-amended treatments. Concentrations in discharge from TSP + Slurry and TSP peaked at 11000 microg TP L(-1) (67-68% as reactive P < 0.45 microm (RP<0.45). Slurry peaked at 7000 microg TP L(-1), 66% as particulate TP (>0.45 microm) and 20% as RP<0.45. Even in subsurface flow, concentrations exceeded 3000 microg TP L(-1) for all P-amended treatments. Incidental TP concentrations in plot discharge were up to 110-fold higher than those considered eutrophic in inland waters. We suggest that targeting short-term management decisions for P applications is the most immediately viable method to mitigate P loss and benefit the environment.