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Evaluating Colloidal Phosphorus Delivery to Surface Waters from Diffuse Agricultural Sources

^a The Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK
^b Institute of Grassland and Environmental Research, North Wyke, Okehampton, EX20 2SB, UK
^c Environment Agency, Burghill Road, Westbury on Trym, Bristol, BS10 6BF, UK

View larger version (21K): [in a new window]   Fig. 1. Linear regression of the relationship between water-extractable supernatant turbidity (formazin turbidity units, FTU) and colloidal P release across the particle-size range 2 to 0.0003 µm for different soils.

View larger version (23K): [in a new window]   Fig. 2. Variation in the concentration of total phosphorus (TP) and reactive phosphorus (RP) for different particle-size fractions in near-surface flow to 30 cm from untreated 30-m2 plots for three consecutive sampling periods: (a) 2 Mar. 1999, (b) 4 Mar. 1999, and (c) 10 Mar. 1999. The data are means of six replicate plots; the error bars represent 1 SE. The variation in TP and RP for different particle-size fractions is significant (p = 0.05).

View larger version (21K): [in a new window]   Fig. 3. Variation in the concentration of total phosphorus (TP) for different size fractions collected in near-surface flow to 30 cm from 30-m2 replicated plots for each of four treatments: (i) untreated plots (zero P), and treated plots receiving (ii) the equivalent of 38 kg P ha–1 in the form of triple superphosphate (TSP), (iii) TSP + dairy manure slurry, and (iv) dairy manure slurry, for a single storm on 14 Apr. 1999. The data are means of six replicated plots; the error bars represent 1 SE. The difference in TP in runoff for zero-P vs. P-treated plots is significant (p = 0.05) but only for the >0.45-µm particle-size fractions. There was no significant difference in TP concentration between the P-treated plots (p = 0.05).

View larger version (22K): [in a new window]   Fig. 4. Variation in the concentration of reactive phosphorus (RP) for different size fractions collected in near-surface flow to 30 cm from 30-m2 replicated plots for each of four treatments: (i) untreated plots (zero P), and treated plots receiving (ii) the equivalent of 38 kg P ha–1 in the form of triple superphosphate (TSP), (iii) TSP + dairy manure slurry, and (iv) dairy manure slurry, for a single storm on 14 Apr. 1999. The data are means of six replicated plots; the error bars represent 1 SE. There is no significant difference (p = 0.05) in the concentration of RP in runoff between the different P-treated plots or between the P-treated plots and the zero-P plots.