Removal Ability On The Nutrients And Organic Pollutants Of Reed Wetlands At Liao River Estuary

Wetland is one of the important ecosystems universally. Wetlands are rich in natural resources, and have a great role for the production and living of human. However, with the economic development, most of wetlands were exploited. So how to protect and use existing wetland resources has become an important direction of current researches. The plant of nature wetlands at Liao River Estuary was dominated by reed. And the wetlands has a strong purification ability for nitrogen and phosphorus. According to the research for the temporal and spatial variations of nutrients and organic matter in the reed wetlands at Liao River Estuary from October in 2008 to September in 2009, the article elaborates on the behavioral characteristics of nutrients and organic pollutants in the wetland, and evaluates the removal ability of wetlands for pollutant. The research can provide the data support for rational management and utilization of wetlands. The research is of great significance for the protection of wetland resources.Nutrients and organic pollutants in the water of reed fields in the growth period of reeds ware monitored. Results show that, the composition of nitrogen in the water kept on changing during the whole growth period of reed. The nitrogen content gradually decreased with the growth of reeds, and was maintained at a low level finally. The organic nitrogen was always the main component of nitrogen, and the content of the organic nitrogen was about 1.64~90.74 times as many as that of the inorganic nitrogen. In the primary growth of reed, the nitrate nitrogen was the main component of inorganic nitrogen (they accounted for 80.22%), then the ammonium nitrogen was the main component (They accounted for 76.46~85.95%). The purification of inorganic nitrogen was faster than that of organic nitrogen. The variation of phosphorus was different from that of nitrogen. Organic phosphorus and inorganic phosphorus were degraded faster, and their contents changed alternately. Organic phosphorus was comparable with inorganic phosphorus in May (54.3%), dominated in July (87.1%), while was minor in other period (<30%). The oil content in the water gradually decreased with the growth of reeds. From May to June, the oil content decreased faster (75.26%), and then did not change significantly. After August oil content remained at a low level (0.168 mg/L). The variation of COD content was more complex. COD content first increased and then decreased. Before July COD content is higher affected by twice water inflow, and then decreased a few. From August to Septemper, COD content decreased by 55.87%. The composition and variation of pollutants in the water of reed fields were influenced by water inflow in a short time. From May to September, the amount removed of nitrogen, phosphorus, COD and oil by reed wetlands at Liao River Estuary were 2365 mg/m~2, 126.4 mg/m~2, 21390 mg/m~2 and 550.5 mg/m~2 respectively, and the purifying effects were 97.4%, 84.3%, 72.6%å'Œ94.0% respectively. The wetland can purify pollutants well.The distribution characteristics of nitrogen, phosphorus, organic carbon and oil in the soil of reed wetlands at Liao River Estuary were analyzed. Research results indicated that the nitrogen, phosphorus and organic carbon contents were gradually descending from top to bottom in the soil. And their contents of the surface soil (TN were 0.67%, TP were 0.088%, TOC were 6.5%) were all significantly higher than those of the underlying soil (TN were 0.045 %~0.26 %,TP were 0.034%~0.06%, TOC were 0.33%~2.4%). The total nitrogen had a good correlation with the organic carbon (correlation coefficient was 0.9980). The oil contents in the soil were 2.39~747 mg/kg and had not significant variation in the vertical distribution. Higher oil contents occurred in the bottom of the soil, and the oil may be moved in the soil. The horizontal and vertical variabilities of total nitrogen and total phosphorus in the soil of Liaohe river mouth reed wetlands all were medium variability or strong variability. Overall, the total phosphorus in the soil was relatively uniform in horizontal and vertical distributions. The organic carbon in the soil was relatively uniform in the horizontal distribution, while the uniformity in the vertical distribution of the organic carbon was inferior.The uniformity in the horizontal and vertical distributions of oil were both inferior.Nitrogen and phosphorus contents in different organs of the reed were analyzed in differet growth periods. Results show that the variations of nitrogen and phosphorus contents in different organs were different. The nitogen content was higher than the phosphorus. Compared with phosphorus, nitrogen can be absorbed more by reeds. The variation of nitrogen and phosphorus contents in different organs of reeds are closely related with the growth characteristics of reeds. The quantity of nitrogen and phosphorus removed by reed harvesting in October were 2.14 mg/m~2 and 0.11 mg/m~2 respectively, and accounted for 90.6% and 84.7% of the removal abilities of the wetland for total nitrogen and total phosphorus respectively. The reed absorption was the main way of purify nitrogen and phosphorus in the wetland system.