Current status and 30-year changes in aquatic macrophytes in Lake Dianshan, Shanghai

Abstract

于2009年8月至2010年5月调查淀山湖水生高等植物现状,并结合历史资料分析其近30年变化,探讨水生植被的发展趋势及退化原因.淀山湖现有水生高等植物29种,隶属18科,25属,栽培种、外来种比例较过去升高.30年来水生植被(尤其是沉水植被)面积严重萎缩,主要植被类型从沉水植物占优势转变为漂浮植物占优势,沉水植被主要优势种由苦草转为竹叶眼子菜.水体营养盐升高、透明度下降以及藻类大量繁殖导致植被衰退和沉水植物优势种演替,而城市发展和渔业开发等一系列人类活动则加速了植被衰退,并影响着演替的方向和多样性格局.目前淀山湖水体营养水平高、透明度低、人为干扰强度大,水生植被难以自然恢复.;The current status of aquatic macrophytes in Lake Dianshan was surveyed from August 2009 to May 2010. The succession tendency of aquatic vegetation and reasons for the diversity loss were discussed. The results showed that the aquatic flora in the Lake Dianshan included 29 species which belong to 25 genera, 18 families, now the proportion of cultivated or exotic species was higher than that in the past. The aquatic vegetation, especially submerged vegetation, was shrinking dramatically during the past 30 years. Main vegetation type now has switched from submerged to free-floating, meanwhile Potamogeton malaianus has replaced Vallisneria naians to be the dominant species of submerged vegetation. In addition, increased nutrient concentration and decreased water transparency, combined with enhanced growth of planktonic and epiphytic algae, accounted for substantial portions of both the decline of aquatic vegetation and succession of submerged dominant species. Furthermore, a range of human activities along with urban and fisheries development have accelerated the aquatic vegetation decline as well as influenced the direction of succession and diversity patterns. The high nutrient level, low water transparency and intensive human distuitance in Lake Dianshan would make recovery of aquatic vegetation difficult.