Pattern Of Distribution And Change Of Aquatic Plant In Taihu Lake

With the rapid development of economy,a severe eutrophication pollution and a serious outbreak of cyanobacteria bloom had been found in Taihu Lake,the third biggest fresh lake in China,from the beginning of the last century in 90s,which take a huge negative impact on water supply,aquaculture,tourism,causing serious crisis on drinking water,even harm the regional economy and human health.Aquatic plant,which plays a key role in the maintenance of healthy lake ecosystem,have an important positive role on maintain the structure and function of the ecosystem.As a typical eutrophic lake,Taihu Lake is facing the dual challenges of aquatic vegetation disappear and waterweeds overgrowth.Up to now,a large number of scientific workers have conducted a lot of research on mechanism,treatment and ecological remediation of eutrophication pollution in Taihu Lake.Those work,which confirmed the disappear of aquatic plant caused by eutrophication,could not reasonably explain the expansion of the distribution area of aquatic vegetation in the eastern part of Taihu Lake.Meanwhile,relationship between aquatic vegetation and environmental factors had been researched from various angles,but the key factor was still unknown.What's more,prior research indicated better water quality in aquatic plant distribution area,but whether the aquatic plant should be responsible for the better water quality was still unknown.In order to reveal the distribution status,seasonal changes,interannual fluctuations,and changes of aquatic vegetation,a total of 6 times of the aquatic vegetation investigation,which navigation distance was near 1000 km,were conducted with the ship loading and quadrat method in Taihu Lake in two consecutive years.Meanwhile,observed value of 153 samples with 12 environmental factors were analyzed with plant community composition,to discuss the main factors which influencing the distribution of aquatic vegetation.What's more,in order to discuss the relationships between aquatic plant and water aquality in Taihu Lake,measuring result of water nutrient content with 491 samples from four survey,which haddifferent vegetation distribution conditions,was analyzed combine with aquatic vegetation distribution conditions.The current research indicated:1)A downward trend of species number of aquatic plants was found in Taihu Lake.A total of 48 aquatic plants was found in 2014,with 18 emergent plants,9 floating-leaved plants,7 floating plants,and 14 submerged plants.There were 23 aquatic plants disappeared from 1960s,half of which disappeared from 1997.2)Generally,aquatic vegetation in Taihu Lake maintain the distribution pattern of vigorous growth in the eastern part of the lake,and almost disappeared in the western of the lake.Almost 1/3 of the water can be distributed by aquatic plants which biomass could reached 29.09 × 104 tons.Floating-leaved plant and submerged plant distributed in the open water,emergent plant only distributed along the lake coast.Under the condition of more than twenty years of continuous eutrophication pollution,aquatic vegetation had disappeared totally in northern and western of Taihu Lake,while,area and biomass of floating-leaved plant and submerged plant,especially the former,kept rising in the east and north-east.Total biomass of aquatic plant had risen from 10 ×104 tons in 1960 to 29.09× 104 tons in 2014.From the point view of ecological form,emergent plant rose first and then decline,while total biomass of submerged and floating-leaved plant had risen from 2 × 104 tons in 1960 to 26.18 x 104 tons in 2014.3)The seasonal change and annual variance of aquatic vegetation was obvious.The dominant species was potamogeton malaianus and Nymphoides peltatum in summer,which changed to Myriophyllum spicatum and P.maackianus in autumn.Community of P.crispus distributed largely in lentic habitat in winter,and become an absolute dominant species in spring,which combined with the quick recovery of p.malaianus community and Nymphoides peltatum community.Severe degradation was observed in 2015 compared with 2014,which might be due to the continuous high water level and high intensity of artificial grass harvest.The proportion of distribution area of aquatic vegetation in 2015 to 2014 was 20.14%in summer,and 8.94 in winter.4)The key factors which affected distribution of aquatic plant in Taihu Lake should be contained water depth,transparency,and sediment thickness,with the explained value of 45.4%to biomass changes.Further analysis indicated that P.maackianus adapted to hard substrate and high transparency much better,while P.crispus adapted to water with high TP concentrations,which might be explained the explore of P.crispus in eutrophic water.5)Xuhu and East Taihu,which distributed aquatic vegetation,kept the lowest nutrient level in Taihu Lake,even aquatic vegetation degenerate in these region.Distribution region of the highest nutrient level alternated among river mouths of Taihu Lake,which indicated exogenous nutrient input should be the main reason of water pollution.Aquatic plant had significant but limited affection on water nutrient level,which indicated the process of eutrophication of Taihu Lake should be very complicated.The current research systematically expounded the distribution pattern,changes,and influence factors of aquatic plant in Taihu Lake,analyzed the relationship between aquatic plant and water nutrient level,which might have significant reference value on management of vegetation and eutrophication.