Use of multi-objective dredging for remediation of contaminated sediments: a case study of a typical heavily polluted confluence area in China

Abstract

Sediments in confluence areas are typically contaminated by various pollutants that have been transported there by inflowing rivers. In this study, we evaluated the pollution status of a confluence area in Lake Chaohu (China). Both the nutrients and hazardous pollutants were analysed. Most sediment cores showed large variations in nutrient concentrations at depths of 10 to 18 cm. Positive release rates of NH4(+)-N and PO4(3-)-P were detected in sediment cores. Hg and Cd were the most typical problematic metal contaminants encountered, and their contamination levels extended to depths of 20 and 25 cm, respectively. Polycyclic aromatic hydrocarbons (mostly acenaphthene and fluorine) were the primary persistent organic pollutants (POPs) present in sediments, and contamination levels frequently could be detected up to a depth of 16 cm. Simulated dredging operations were implemented in the laboratory, with a dredging depth of 15 cm found to be suitable for nutrient suppression. With the goal of suppressing nutrients release and removing high-risk metals and POPs, a multi-objective dredging plan was developed. This plan subdivides the confluence area into five parts that were treated with different dredging depths. A demonstration area was dredged in the most heavily polluted part, and the observed dredging effects were consistent with those expected on the basis of the plan. Such an approach to dredging might also be useful in other areas in the future.

Application of plow-tillage as an innovative technique for eliminating overwintering cyanobacteria in eutrophic lake sediments

“…6. Both the release rates of NH 4 þ eN (2.04e4.94 mg m À2 d À1 ) and SRP (1.14e4.11 mg m À2 d À1 ) for the Blank treatment remained at low levels during the experiment, similar to a previous study in this area during winter (Liu et al, 2015a). The release rates of CK were low at the beginning of the experiment but increased quickly after the deposition of the cyanobacteria.…”

“…The frequent strong spring winds in this area lead to the resuspension of overwintering cyanobacteria and polluted sediment, along with the release of N and P into the overlying water. Serious releases of NH 4 þ -N and SRP from the sediment in the study area have occurred in the spring (Liu et al, 2015a). The resuspended cyanobacteria, accompanied by the polluted sediment, released nutrients, illumination, and warm temperatures, can recover quickly in spring (Deng et al, 2014;Duan et al, 2014).…”

“…The release of NH 4 þ -N and SRP (soluble reactive phosphorus) from the sediment was measured using the homothermal incubation method according to Liu et al (2015a). The concentrations of NH 4 þ eN and PO 4 3À eP in the water were estimated using Nessler's reagent (Chinese EPA, 2002) and molybdenum blue (Murphy and Riley, 1962) spectrophotometry methods, respectively.…”

“…The concentrations in the plowed treatments decreased with increasing PT depth. This may be due to lower rates of cyanobacterial degradation (Zhu et al, 2013) and lower amounts of mobile nutrients (Liu et al, 2015a;Zhong et al, 2008) in the surface sediment after PT. Therefore, deeper PT favored decreasing nutrient concentrations in the overlying water.…”

Nitrogen and Phosphorus Exchanges Across the Sediment–Water Interface in a Bay of Lake Chaohu

“…High internal N and P loadings have been proven to boost the growth of algae and aggravate the eutrophic status in many lakes (N¨urnberg et al, 2013;Orihel et al, 2013). Most of the eutrophic lakes around the world have high internal N and P loadings, such as Lake Taihu (Wang et al, 2017) and Lake Chaohu (Liu et al, 2015) in China, Lake Kinneret in Israel (Orihel et al, 2013), Lake Simcoe in Canada (N¨urnberg et al, 2013), and others. The sediment-water interface (SWI) is the major place for the exchange of N and P between the sediment and the overlying water.…”