Impact of regional water chemistry on the phosphorus isothermal adsorption of the sediments in three subsidence waters of the Huainan Mine Areas

Abstract

Three research sites of subsidence waters, including Panji (PJ), Guqiao (GQ) and Xieqiao (XQ) located in the Huainan "Panxie" Mine Area have been selected to address their phosphorus (P) adsorption behavior in the sediments considering the site-specific regional water chemistry. The P isothermal adsorption was measured in pure water and four different types of ion solutions, prepared through additions of sodium chloride (NaCl), calcium chloride (CaCl2), sodium bicarbonate (NaHCO3), and a mixture of sodium bicarbonate and calcium chloride (NaHCO3+CaCl2). The first four settings were studied to analyze the individual impact of each solution on P adsorption while the last one was to study their combined effect. In general, Ca2+ could enhance P adsorption on sediment surfaces while weakly alkaline conditions caused by bicarbonates were unfavorable for its adsorption. As a comprehensive effect, the positive effect of the former was greater than the negative effect of the latter. The zero equilibrium phosphorus concentrations (EPC0) in the three sites were 0.059, 0.032 and 0.040 mg·L-1, respectively, showing trends of P releasing to the overlying water column. The site of PJ showed greater P releasing potential than those at the GQ and XQ sites, probably due to its higher nutrient level. Overall, P releasing risks in the researched sediments are weaker than those in eutrophic lakes, while they are very similar to lakes with lower trophic levels, because of their unique sedimentary environments from inundated agricultural soils.