西太湖河网区恢复与退化河岸带湿地生态及水环境功能比较

The comparison of ecological and environmental functions of restored and degraded riparian wetlands in the retiform fluvial region of West Taihu Lake

对西太湖平原河网区严重退化的河岸带湿地进行恢复的基础上,开展了恢复后湿地和退化湿地内植物群落物种多样性,生物量,植物干物质体内氮、磷含量,湿地水体中悬浮物含量、氮、磷营养物质浓度以及恢复后湿地内反硝化作用等湿地生态和水环境功能方面的比较研究。结果表明:(1)已恢复湿地群落结构趋于完整,物种多样性指数值较高,一般在1.7～3之间,均匀度在0.5～0.9之间波动。退化湿地物种丰富度低,多样性指数值较低,分别在0.3～1.5(H′),0.15～0.65(J)之间波动。在水花生(Alternanthera philoxeroides)入侵的群落内,种类稀少,且分布极不均匀,仅在0.3～1(H′)和0.1～0.3(J)之间波动,群落结构严重退化。(2)在植物生长旺盛期,1m2湿地内的芦苇(Phragmites communis)、香蒲(Typha orientalis)及茭草(Zizania latifolia)分别为42,18株和17株。其在湿地内的生物量分别为:4692,5142kg和2182kg;(3)上述物种单位干物质中的氮、磷平均含量分别达到2.88mg/g和2.09mg/g;沉水植物作为滨岸带湿地群落结构的重要组成部分,不仅具有高的生物量,而且吸收氮磷能力强,单位干物质氮、磷含量分别达到7.27mg/g和4.14mg/g;(4)植物对水体及沉积物中可溶性氮、磷的有效吸收以及颗粒态磷的自然沉降作用,使得上游来水中的总氮浓度流经湿地时,降至0.15～0.89mg/L之间,平均下降了85%;总磷浓度则由进水时的0.248～0.598mg/L,降至出水时的0.002～0.083mg/L;(5)滨岸带湿地对河水中悬浮物的有效拦截、滞留和吸附作用,使得入湖河水中的悬浮物含量降低了90%以上;(6)在高温缺氧的环境中,滨岸带湿地表现出较强的反硝化作用,且由河心向河岸逐渐增强的趋势。近河心处测定的N2O通量为0.034～0.068之间,到河岸处升至0.046～0.089。反硝化作用是削减水体中氮负荷的有效途径。

The research region is located in the retiform fluvial region of west Taihu lake. With the pressure of increasing population and fast economical development, riparian buffer zones were gradually reclaimed to farmlands. In this study, the ecological and environmental functions between restored and degraded riparian wetlands were compared. The survey results show that the ecological indices of restored wetlands are higher than those of degraded ones, including species biodiversity, biomass of plants, the content of nitrogen and phosphorus nutrients in plants, the concentrations of nitrogen and phosphorusnutrients in water and the denitrification effects. The species and plant numbers in restored area were high, the biodiversity and even indices reached to 1.7 -3 and 0. 5 -0.9, respectively, indicating the relative good integrity of community structure, on the contrary, numbers of species and plants in the degraded wetland were low, the biodiversity and even indices varied between 0.3 - 1.5 and 0.15 - 0. 65, respectively. In the community invaded by alternanthera philoxeroides, the value of biodiversity and even indices were only 0.3 - 1.0 and 0.1 - 0.3, respectively, indicating serious occurred degradation of the community structure. During the growing season, the individuals per square meter of Phragmites communis, Typha orientalis and Zizania latifolia in wetland area were 42, 18 and 17, respectively. The biomasses of these three species in restored wetlands were 4692, 5142 kg and 2182 kg, respectively. The average nitrogen and phosphorus contents per unit dry biomass of these three species contained 2.88 mg/g and 2.09 mg/g, respectively. In addition, the submerged macrophytes, which were the necessary components of wetland community, inherited strong absorbency capacities and high biomass. The average nitrogen and phosphorus contents of five dominant submerged macrophytes were 7.27 mg/g and 4.14 mg/g, respectively. The concentrations of dissolved inorganic nitrogen of the outlet water of restored wetland reduced to 0.15 -0.89 mg/ L, which were about 85% lower than that of the inlet water. The concentrations of TP of the inlet water were 90% higher than that of the outlet water of restored wetland, mainly due to the salimentation and sedimentation functions of the restored wetland system. The SS contents of the upriver water were 90% lower than that of the downriver, because of the obstruction and adsorption of SS by the restored wetland. In the restored wetland, the number of denitrifying bacteria in the terrestrial area and the transition area from water to terrene area were higher than that of water area. The flux of N2O from the river center to the riverside increased gradually, N2O flux of riverside was 35% higher than that of river center. This result demonstrated that denitrification play an efficient role in eliminating the nitrogen content of the upriver water.