Ditch Wetlands Research Articles

Polychlorinated biphenyls (PCBs) in sediments/soils of different wetlands along 100-year coastal reclamation chronosequence in the Pearl River Estuary, China

PCBs (polychlorinated biphenyls) were determined in sediment/soil profiles to a depth of 30 cm from three different wetlands (i.e., ditch wetlands, riparian wetlands and reclaimed wetlands) of the Pearl River Estuary to elucidate their levels, distribution and toxic risks along a 100-year chronosequence of reclamation. All detected PCB congeners and the total 15 PCBs (∑15 PCBs) decreased with depth along sediment/soil profiles in these three wetlands. The ∑15 PCBs concentrations ranged from 17.68 to 169.26 ng/g in surface sediments/soils. Generally, old wetlands tended to have higher PCB concentrations than younger ones. The dominant PCB congeners at all sampling sites were light PCB homologues (i.e., tetra-CBs and tri-CBs). According to the sediment quality guideline, the average PCB concentrations exceeded the threshold effects level (TEL, 21.6 ng/g) at most of the sampling sites, exhibiting possible adverse biological effects, which were dominantly caused by light PCB congeners. The total toxic equivalent (TEQ) concentrations of 10 dioxin-like PCBs (DL-PCBs) detected at all sampling sites ranged from 0.04 to 852.7 (10−3 ng/g), mainly affected by PCB126. Only DL-PCB concentrations in ditch and riparian wetland sediments with 40-year reclamation histories (i.e., D40 and Ri40) exhibited moderate adverse biological effects according to SQGQ values. Principal component analysis indicated that PCBs in three wetland sediments/soils mainly originated from Aroclor 1016, 1242, and 1248. Correlation analysis showed that sediment/soil organic carbon content had a significant correlation with the concentrations of several PCB congeners (P < 0.05), whereas no significant correlations were observed between any PCBs congeners and grain size or aggregate content (P > 0.05).

Organochlorine pesticides (OCPs) in wetland soils under different land uses along a 100-year chronosequence of reclamation in a Chinese estuary.

Soil profiles were collected at a depth of 30 cm in ditch wetlands (DWs), riverine wetlands (RiWs) and reclaimed wetlands (ReWs) along a 100-year chronosequence of reclamation in the Pearl River Delta. In total, 16 OCPs were measured to investigate the effects of wetland reclamation and reclamation history on OCP levels. Our results showed that average ∑DDTs, HCB, MXC, and ∑OCPs were higher in surface soils of DWs compared to RiWs and ReWs. Both D30 and D20 soils contained the highest ∑OCP levels, followed by D40 and D100 soils; lower ∑OCP levels occurred in D10 soils. Higher ∑OCP levels were observed in the younger RiWs than in the older ones, and surface soils exhibited higher ∑OCP concentrations in the older ReWs compared with younger ReWs. The predominant percentages of γ-HCH in ∑HCHs (>42%) and aldrin in ∑DRINs (>46%) in most samples reflected the recent use of lindane and aldrin. The presence of dominant DDT isomers (p,p’-DDE and p,p’-DDD) indicated the historical input of DDT and significant aerobic degradation of the compound. Generally, DW soils had a higher ecotoxicological risk of OCPs than RiW and ReW soils, and the top 30 cm soils had higher ecotoxicological risks of HCHs than of DDTs.

Fractionation, transfer, and ecological risks of heavy metals in riparian and ditch wetlands across a 100-year chronosequence of reclamation in an estuary of China

The effect of reclamation on heavy metal concentrations and the ecological risks in ditch wetlands (DWs) and riparian wetlands (RWs) across a 100-year chronosequence in the Pearl River Estuary of China was investigated. Concentrations of 4 heavy metals (Cd, Cu, Pb, and Zn) in soil and plant samples, and sequential extracts of soil samples were determined, using inductively coupled plasma atomic absorption spectrometry. Results showed that heavy metal concentrations were higher in older DW soils than in the younger ones, and that the younger RW soils contained higher heavy metal concentrations compared to the older ones. Although the increasing tendency of heavy metal concentrations in soil was obvious after wetland reclamation, the metals Cu, Pb, and Zn exhibited low or no risks to the environment based on the risk assessment code (RAC). Cd, on the other hand, posed a medium or high risk. Cd, Pb, and Zn were mainly bound to Fe–Mn oxide, whereas most of Cu remained in the residual phase in both ditch and riparian wetland soils, and the residual proportions generally increased with depth. Bioconcentration and translocation factors for most of these four heavy metals significantly decreased in the DWs with older age (p<0.05), whereas they increased in the RWs with younger age (p<0.05). The DW soils contained higher concentrations of heavy metals in the organic fractions, whereas there were more carbonate and residual fractions in the RW soils. The non-bioavailable fractions of Cu and Zn, and the organic-bound Cd and Pb significantly inhibited plant growth.

Nitrogen removal from polluted river water in a novel ditch–wetland–pond system

To remove nitrogen from polluted river water in situ, a ditch–wetland–pond system (DWPS) with a length of 25m was designed and built near the Liu River, Tianjin, China. Average ammonia (NH4+-N), total nitrate (NO3−-N) and nitrogen (TN) removal efficiencies of 76.90%, 54.24% and 58.71%, respectively, were attained by the DWPS under optimum operating conditions. A DWPS application project with a length of 500m was then constructed near Qilihai Wetland, Tianjin to treat polluted river water from the Chaobaixin River, and average NH4+-N, NO3−-N and TN removal percentages of 52.04%, 33.33% and 38.66%, respectively, were observed during monitoring. Moreover, denitrification and nitrification were found to be the most important processes associated with nitrogen removal. The DWPS, which was designed to be elongated and including duplicate units, was found to be technologically feasible and applicable to treat polluted water from rivers or ditches in situ; therefore, its use will be expanded locally and to similar areas.

Research on the Influencing Factors of Hydraulic Efficiency in Ditch Wetlands

The hydraulic retention time is an important factor that affects treatment performance of constructed wetlands, and it should be taken into consideration in hydraulic optimization design. In these days, the theoretical retention time is more considered to design the constructed wetlands. But the water doesn’t flow the wetlands uniformly and stagnant water area exists in the wetlands. So the hydraulic retention time is less than or equal to the theoretical retention time and it will cause the overestimation of designation. In this article, the effective retention time and hydraulic efficiency were put forward to optimize the treatment performance and to improve hydraulic efficiency of the ditch wetlands. And the factors which influence the hydraulic efficiency (t10/T) were studied. The experiment results of ditch wetlands verified that the total ratio between the ditch length and ditch width is one of the key factors influencing the hydraulic efficiency (t10/T). The bigger the ratio is, the bigger the value of t10/T is. And the flow is more close to ideal Piston flow. The growth rate of t10/T begins to slow down along with the ratio (L/W) increasing.

Removal of Agricultural Non-Point Source Pollutants by Ditch Wetlands of the Maixi River, Guizhou Province, China

A natural ditch wetland grown with nature annual bluegrass (Poa annua L.), alligator weed (Alternanthera philoxeroides (Mart.) Griseb.), common duckweed (Lemna minor L.) and curly pondweed (Potamogeton crispus L.) etc. were selected to study the removal capacity of agricultural non-point source pollutants in the Maixi River in Guiyang City, the capital of Guizhou Province, China. The removal characteristics and seasonal variation of chemical oxygen demand (COD), total phosphorus (TP), ammonia-nitrogen (NH+4-N), and suspended solids (SS) in the ditch water was studied. The results showed that there existed a certain seasonal diversity in the removal characteristics of nitrogen, phosphorus and organic pollutants by the ditch. The removal efficiency of TP, COD and SS demonstrated an increasing tendency with their increasing concentration at the ditch inlet, whereas that of the NH4+-N displayed contrary tendency as the concentration of NH4+-N increased.

Advances on the Effects of Ditch Wetland on Hydrology and Eco-environment

Ditch system is important to reduce pollution and prevent eutrophication in rivers and lakes.Firstly,this paper gives the definition of ditch and ditch wetland;secondly,we review the research advances in the effects of ditch wetland on hydrology and eco-environment at home and abroad,and explain explicitly the mechanism that ditch wetlands intercept nutrient(nitrogen and phosphorus,etc.) and contamination(pesticide and herbicide,etc.);additionally,it introduces the advances in ditch modeling and ditch management study;finally,in order to be helpful to ditch studies,we point out the present insufficient research and put forward some suggestions that include strengthening research on field monitoring,modeling ditch and managing ditch.

Removal of agricultural non-point source pollutants by ditch wetlands: implications for lake eutrophication control

Removal of agricultural non-point source pollutants by ditch wetlands: implications for lake eutrophication control