Relation between turbidity and suspended material at different soils, scales and phosphorus levels

Abstract: Losses of phosphorous (P) from agricultural soil may cause eutrophication of receiving water bodies. Beside surface runoff, leaching has recently been considered an important P transport pathway. P losses in runoff are associated with eroded clay particles where the highest P accumulation occurs.This study investigated the use of turbidity measurement as a surrogate method for suspended solids (SS), particulate P (PP) and total P (TP) concentration in leachate water.Water samples were collected at lysimeter, plot and field scale from the Uppsala lysimeter station and Lanna/Bornsjön experimental field, over a period between January and April 2011. Turbidity and SS were measured on samples from six soils with different soil properties from central and south of Sweden. Total P (TP), dissolved reactive P (DRP) and PP concentration of water samples were measured. Turbidity, SS, PP and TP values obtained were then studied considering the different scales.The highest values of turbidity and SS were found in a soil with a significant clay content (59%), the correlation between the two parameters returned a r2=0,67. A significant r-square value (0,57) was also found between turbidity and TP and PP in the same soil. Nevertheless soils with similar condition in clay content did not show the same correlation and behaviors suggesting that parameters and properties such as pH, organic matter content and internal soil structure strongly influence characteristics of leachate water. Furthermore, results from the comparison of scales shown that larger dataset on longer term would improve the quality of the study. Turbidity and total/particulate P did not seem to show a correlation at different P levels according with soil test P (phosphorus content in ammonium lactate extract [P-AL]), therefore water transport mechanisms and subsoil properties seem to influence the P leaching more than soil test P value in the topsoil.The result of this study suggest that turbidity might be used as a surrogate method to investigate P losses associated with SS at specific intervals, but relying on turbidity measurements without a detailed knowledge of topsoil and subsoil properties is nevertheless not possible.