Seasonal changes of phosphorus concentrations in lime filter drainage water

Abstract

The drainage outflow may be identified as the leading source of water quality in agricultural regions. Phosphorus concentrations above background levels increase the risk of eutrophication in water bodies. Various technologies are currently being developed to reduce non-point source pollution. Chemical amendments to the soil are one of the means to reduce movement of phosphorus via subsurface tile drainage systems. The field studies were performed to determine if the chemical treatment with lime could increase P retention in drainage backfill and reduce P transport to receiving waters. The site was located in the South-West Lithuania. Composite subsurface drainage systems with drain spacing of 16 and 24 m were installed in heavy-textured clay loam soils, drainage trenches were backfilled with soil mixed with 0.6% CaO. This paper reports the results of eleven-year studies (1999 – 2009). Water samples were analysed for total phosphorus (TP) and phosphate phosphorus (PO4–P). Concentrations were determined by the spectrometric method, according to the water quality investigation standards (LAND 58:2003). The reliability of the results was determined by processing them with the help of mathematical-statistical methods and using MS Excel 2000 Data Analysis Tool Pack. The significant differences between phosphorus concentrations in control drainage water and in the treatments with lime added into the trench backfill were estimated within winter-spring period (November – May). During the summer–autumn months (June – October) the mean concentrations differed insignificantly. Phosphorus concentrations in control drainage water exceeded the concentrations determined in stream water during the entire year. The highest amounts of phosphorus from drainage systems are transported in winter and spring.