Source apportionment of nutrients in Chichester Harbour
You asked for more information about our view of the source apportionment of nitrogen into Chichester Harbour.
- 55% of nitrogen arise from background levels within the Solent and coastal background (offshore) – these enter the Harbour on each tide from the sea
- 29% comes from agricultural runoff in the catchment
- The remaining 16% is split between urban diffuse pollution and point source discharges from waste water treatment works
Apart from the Solent and coastal background nitrogen, the main source of nitrogen in Chichester Harbour is from rural diffuse nitrogen from agriculture in the catchment that enters harbour mainly via rivers.
Most of the rivers in the Chichester catchment are fed by groundwater. The groundwater has a high nitrate content as a legacy of historic farming practices. Nitrate leached from the soil can be ‘held-up’ in the groundwater system for decades before it enters rivers.
Sources of nitrogen from sewage treatment works in Chichester Harbour are much smaller and contribute 10% of the nitrogen sources.