The effect of pH on phosphorus sorbed from sediments in a river with a natural pH gradient

Abstract

Phosphorus (P) is an essential nutrient for algal growth and its increase in water bodies produces eutrophication. On the other hand, sediments play an essential role in the processes of transformation and accumulation of P in aquatic systems. pH became a major factor to control the availability of P bound sediment not only for algal utilization and the consequent eutrophication of lakes but also for P precipitation to sediment. Most studies focused on the effect of pH on P release from sediments were performed in laboratories where the pH gradient was simulated by adding hydrochloric acid solutions or sodium hydroxide. The aim of this paper is to evaluate the effect of pH on sediment P dynamics (release/uptake) in a river (River Agrio, Argentina) with a natural pH gradient (1.5–6.7) both in water and in sediments. The results obtained showed that: all chemical species analyzed in water decreased according to pH-gradient increase; pH affects sediment P retention capacity, demonstrating that P retention capacity is lower at high pH; P retention capacity is different dependent on the time of year: in fall, the average retention coefficient (R) was 41; in winter, the average R was 38; and in summer, the average R was 46. It was found that sediment P, in all the pH gradient, was controlled, mainly, by the oxyhydroxides of Fe and Al and, to a lesser extent, by the Organic Matter and not by Ca as would be expected in higher pH sediments.