Table 3.

Source apportionment using the PIT source apportionment spreadsheet (as P)

Class of sourceSource of phosphatePercentage contribution by HOST class
1* (%)5* (%)10 (%)18 (%)24 (%)
Catchment total P loading (kg ha−1)0.510.561.11.62.7
Predicted dissolved phosphate (mg P l−1) in River Nar0.110.120.350.420.76
AgriculturalTotal manure-P19.3418.925.059.0638.03
Total fertilizer-P18.7418.3087.5057.3437.63
Non-agriculturalOlsen-P§15.9216.241.718.846.42
Particulate-P34.8636.430.5121.1715.77
Direct delivery0.280.2900.170.13
Urban areas9.898.954.753.121.85
Septic tanks0.960.870.460.300.18
Total100100100100100
  • * Less surface flow containing dissolved P, free draining, weakly consolidated with no or little bypass flow.

  • More clayey Till over Chalk causing runoff, creating more dissolved P in runoff.

  • Calculated by subtracting predicted concentrations for particulate P from total P.

  • §Olsen-P represents the extractable P content of neutral and calcareous soils (Horta & Torrent 2007).