Phosphorus Release from the Sediments in Rongcheng Swan Lake under Different pH Conditions

Abstract

Rongcheng Swan Lake is a coastal lagoon in eastern Shandong Peninsula, China, whose water quality and ecological environment has deteriorated in recent years. The effect of pH on phosphorus (P) release from the sediments and the contribution of P fractions to release in Swan Lake were investigated. The results showed that the sediments released significant amount of P under the strong acidic (pH 3) and alkaline conditions (pH 9), especially at pH 3; whereas under the strong alkaline (pH 10) and neutral conditions, a low quantity of P was released in this lagoon. The sediments in northwestern lake (site 1) showed significantly higher P release than that in the west (site 2). Under the strong acidic condition, the maximum release rates at sites 1 and 2 were 204.49 and 159.12 μg/m2/day, respectively; while at pH 9, the maximum were 190.52 and 10.12 μg/m2/day, respectively. P fractions in the sediments indicated that P release was mainly from BD-P, HCl-P and NaOH-P fractions in Swan Lake. Under the strong acidic condition, the contribution of HCl-P to release was high; whereas under alkaline condition the release of NaOH-P was great. Due to the high proportions of mobile P (NaOH-P+BD-P) to total P in surface sediments, P release potential in northwestern sediments is large under the slightly alkaline environment of Swan Lake.