Effects of Plow-Tillage on Preventing and Controlling the Black Water Events in Shallow Lakes

The high organic loading sediment in the areas of algal accumulation are the primary cause of frequent occurrence of black water in the western Chao Lake. Through an algal accumulation experiment, plow-tillage based on resuspension characteristics and its effect on lake sediment was assessed using a large device capable of simulating lake-winds and sediment resuspension. The dynamics of overlying water coloration, ρ(Fe2+), ρ(S2-) in the process of black water induction, the key physicochemical characteristics of newly formed water–sediment interface, and iron and sulfur variations in interstitial-water and their response to plow-tillage were examined. The results showed that plow-tillage depth significantly influenced black-water formation; a 15 cm plow-tillage depth helped in controlling black-water. When black water occurred in other plow-tillage controls, i.e., (2, 5, and 10 cm), along with blank-treatments during day 8 to 14, typical overlying water characteristics [ρ(Fe2+) and ρ(S2-)] of the plow-tillage 15 cm treatments were 68.6%, 79.5%, 48.1%, 46.7%, and 51.3%; and 75.2%, 65.7%, 57.1%, 74.5%, and 75.0%, respectively, in comparison to that of the other plow-tillage controls and blank-treatments. Further analysis of the bottom-water and bottom-sediments revealed that the 15 cm plow-tillage depth treatment significantly enhanced the tolerance of the fresh water–sediment interface to algal accumulation and anoxic environments. Through the black water induction simulation, the dissolved oxygen concentration, redox potential, and pH of the bottom-water and at the interface were observably much higher than those in the black-water groups. However, ρ(ΣH2S) was significantly lower than that of other treatments. The ρ(Fe2+) in the surface-sediment water was 0.54 mg/L, which corresponds only 25.3–33.7% that of the black-water groups. Fe2+ accounted for 25.2% of the total iron, being considerably lower than ~40.0% of the black-water groups. The concentration of acid-volatile sulfides was 0.51 µg/g, which corresponds only 14.6–17.2% that of the black-water groups. Overall, plow-tillage helped to physically improve sediment in areas of algal accumulation. Plow-tillage could help turn surface-sediment overloaded with organic pollutants to the lower-layer, blocking material migration and supply of contaminated surface-sediment, and controlling anaerobic microbial activity. It could prevent the formation of black water-generating substances in the water column where algae accumulate and die, effectively preventing the occurrence of black water.