Simultaneous removal of phosphate and ammonium nitrogen from agricultural runoff by amending soil in lakeside zone of Karst area, Southern China

The loss of phosphorus(P) and nitrogen from agricultural non-point source(ANPS) is one of the main causes of eutrophication in rivers, lakes and reservoirs in the Karst region, southern China. The lakeside buffer zone has proven to be effective in reducing the input of ANPS pollutants. However, the interception efficiency of natural soil for P and ammonia nitrogen is insufficient to control ANPS pollution. In this study, natural zeolite(NZ), aluminium modified clay(AMC) and lanthanum modified bentonite(LaMB) were used to amend the natural soil collected in the lakeside zone of Kelan Reservoir, Guangxi, China. An experimental study was conducted to examine the dissolved inorganic P(DIP) and ammonia nitrogen removal efficiency and fixation mechanism of three amended soils under simulation conditions. The results showed that natural soil had a high fraction of clay and silt (particle size 95 % for the DIP at the beginning of the experiment. With the intermittent input of farmland drainage, the P removal rate of natural soil from runoff decreased gradually. Compared with the control group, P removal rates of AMC- and LaMB amended soils remained at a high level within 46 days, with means of 93.6 % and 93.9 %. However, NZ amended soil has a weak interception capacity of runoff P pollutant. The chemical sequential extraction showed that AMC increased soil P capacity by forming NaOH-P and NaHCO3-P, while LaMB by forming NaOH-P, NaHCO3-P and Residual-P. In addition, LaMB amended soil can simultaneously remove ammonia from farmland runoff, with the removal rate of 89.3 %. AMC- and LaMB amended soils are proved to be potential and effective technologies for ANPS pollution control. This study provide an important basis for the treatment of ANPS pollutants and the construction of lakeside buffer zone in eutrophic watershed.