Phosphorus removal of rural wastewater by the paddy-rice-wetland system in Tai Lake Basin

Spatial and temporal changes of P and Ca distribution and fractionation in soil and sediment in a karst farmland-wetland system

Phosphorus (P) is a critical element affecting eutrophication in aquatic ecosystems. Its availability is closely related to calcium (Ca) in calcareous soils and sediments, but their relations are unclear. In this study, the spatial and temporal changes in P and Ca fractionation and distribution in a karst farmland-wetland ecosystem were investigated. The results showed that total P concentrations were 1.25-3.19 g kg^-1, with higher concentrations in paddy soil than in sediment. Total Ca concentrations were 3.93-10.2 g kg^-1, with higher Ca being accumulated in sediments than in soils. The P fractionations varied seasonally, with Ca-bound P being dominant. The moderately-stable Fe/Al-bound P showed temporal variation, while Ca was dominant in acid-soluble fraction, both probably playing an important role in controlling P availability. Correlation analysis showed seasonal relation between Ca and P distribution in soil/sediment. This study suggests that P migration from farmland to wetland may be a major source for P accumulation in sediments in a karst farmland-wetland system.

Fertilization increases paddy soil organic carbon density

Field experiments provide an opportunity to study the effects of fertilization on soil organic carbon (SOC) sequestration. We sampled soils from a long-term (25 years) paddy experiment in subtropical China. The experiment included eight treatments: (1) check, (2) PK, (3) NP, (4) NK, (5) NPK, (6) 7F:3M (N, P, K inorganic fertilizers+30% organic N), (7) 5F:5M (N, P, K inorganic fertilizers+50% organic N), (8) 3F:7M (N, P, K inorganic fertilizers+70% organic N). Fertilization increased SOC content in the plow layers compared to the non-fertilized check treatment. The SOC density in the top 100 cm of soil ranged from 73.12 to 91.36 Mg/ha. The SOC densities of all fertilizer treatments were greater than that of the check. Those treatments that combined inorganic fertilizers and organic amendments had greater SOC densities than those receiving only inorganic fertilizers. The SOC density was closely correlated to the sum of the soil carbon converted from organic amendments and rice residues. Carbon sequestration in paddy soils could be achieved by balanced and combined fertilization. Fertilization combining both inorganic fertilizers and organic amendments is an effective sustainable practice to sequestrate SOC.

Application of constructed wetland for urban lake water purification: trial of Xing-qing Lake in Xi'an city, China

A comprehensive review of the current water pollution status in China has indicated that the urban lakes in Chinese cities have suffered from serious pollution and are in high risk of eutrophication, although the pollution sources have been largely controlled. The objective of this study lies in exploring a long term restoration of the aquatic ecosystem in Chinese city lakes using treatment wetland, an environmentally friendly and cost-effective technology. Trials from a subsurface horizontal flow constructed wetland (CW) have demonstrated that the treatment wetland can be used for a purpose such as lake water quality control. Average removal of 84.2% for COD, 53.8% for NH(3)-N, 47.9% for TN, 73.3% for TP and 86.6% for SS can be achieved. Relatively, low removal of nitrogen lies in the lack of nitrification and denitrification process. Accordingly, improved configuration of the treatment wetland system has been proposed and discussed. Finally, the importance of the integrated constructed wetland especially for the application of urban lake water treatment is highlighted.