Thin-layer fine-sand capping of polluted sediments decreases nutrients in overlying water of Wuhan Donghu Lake in China

Abstract

Capping water body sediments with a thin layer of sand is an effective technique to decrease nutrient concentrations in the water column and accelerate ecological restoration of eutrophic water bodies. However, long-term effects of thin-layer sand capping in shallow lakes are reported less often. Using clean fine sand and geotextile mats as capping materials for sediments collected from Wuhan Donghu Lake in China, we designed a 290 d tank experiment with 3 cm of sand capping at four percentages of sediment coverage from 25-100% and a control (no capping). We monitored total nitrogen (TN), total phosphorus (TP), nitrate (NO 3 −), ammonia (NH 4 +) and soluble reactive phosphorus (SRP) in the overlying water every 7 d. Mean TN and NO 3 − concentrations were significantly the lowest (P<0.05) at 50% coverage. Further increase in coverage kept them fluctuating. NH 4 + concentration was significantly lowest (P<0.05) at 75% coverage. The relation between coverage and mean TP and SRP concentrations indicated that 75% coverage significantly decreased (P<0.05) them, and increasing coverage to 100% decreased them even more. The fluxes of TN and TP estimated between sediments and overlying water showed that the thin finesand layer significantly increased the function of sediments as a sink of TN from overlying water and the potential of a sand layer to block release of TP from sediments (P<0.05). Our results suggested that if thin-layer sand capping were applied to Wuhan Donghu Lake, more than 50% coverage is required to decrease nutrients in the lake's water.

Evaluation of the Potential Release Risk of Internal N and P from Sediments—A Preliminary Study in Two Freshwater Reservoirs in South China

“…Potential release risks of N and P from sediments were evaluated via static incubation experiments by simulating the apparent flux of N and P during a given period of static incubation [46]. Temperatures in deep water in freshwater reservoirs in these regions ranged from 15 • C in winter to 25 • C in summer [47].…”

Temporal and Spatial Variations of Chlorophyll a Concentration and Eutrophication Assessment (1987–2018) of Donghu Lake in Wuhan Using Landsat Images

“…In 1985, serious cyanobacterial blooms broke out across the whole lake. In the 1990s, Wuhan's government began to treat urban sewage by adopting various engineering measures such as external sewage interception, internal sewage removal, ecological restoration and water level regulation [30], which improved the water quality of Donghu Lake in the years that followed in spite of its instability. At the beginning of the 20th century, some sewage interception and decontamination projects were put into use, and the large sewage draining exits in Miao Hu, the southern part of Donghu Lake, and the Hongshan District were closed.…”

“…As a typical urban lake, the change of water quality in Donghu Lake was closely related to the development of Wuhan City. Given that the current research on Donghu Lake mainly focuses on TN and TP [5,[27][28][29], sediment [30], bacterioplankton [31,32], aquatic vegetation, etc., and few studies have been conducted on the prolonged changes of Chl-a concentration in medium and small urban lakes, it is difficult to accurately assess the long-term dynamic changes of urban lakes.…”

Application of calcium-rich mineral under nonwoven fabric mats and sand armor as cap layer for interrupting N and P release from river sediments

“…In situ capping is an effective method for mitigating potential water-body eutrophication by impeding the nutrient migration from polluted sediments to the water above them (Jiao et al 2020). Compared to monitored natural recovery and dredging, this treatment method is less costly, less disruptive, and less time-consuming (Ghosh et al 2011).…”