Characteristics Of Water Level, Water Environment And Effects On Fish Communication And Migration In The Hukou Area Of Poyang Lake

Water level fluctuations in lakes are dominant forces controlling the functioning of lacustrine ecosystems.The ecological effects of water level fluctuations in lakes are an urgent issue.Poyang Lake is a naturally fluctuating lake.However,this lack of knowledge concerning the effects of water level fluctuations is most remarkable. Thus,there is an urgent need for data on the relationships between water levels changes and ecosystem responses in the Poyang Lake.As one of the two large lakes maintaining a connection with the mainstream of Yangtze River,Poyang Lake could be an invaluable feeding ground of juvenile black carp,grass carp,silver carp and bighead carp.So far the larval migration of black carp,grass carp,silver carp and bighead carp from Yangtze River to Poyang Lake has been scanty.In order to study the ecological effects of water level fluctuations in Poyang Lake,this paper could be distinguished two parts.(1) This paper analyzed the variation characteristics of water level and main water environmental factors in Hukou area of Poyang Lake.The relationships among water environmental factors and their responses to water level fluctuations were interpreted.(2) The effects of water level and water environmental factors on the fish community in Hukou area of Poyang Lake were illustrated simultaneously.Meanwhile,the effects of water level and water temperature on the larval migration of black carp,grass carp,silver carp and bighead carp from Yangtze River to Poyang Lake were illustrated.And the effects of the Poyang Lake Hydro-junction Project on the larval migration of the four major Chinese carps from Yangtze River to Poyang Lake were analyzed.The main conclusions have been summarized as follows:1.The water level annual fluctuation in the Hukou area of Poyang Lake was normal distribution.The relationship between water level of Poyang Lake(Hukou Station) and that of Yangtze River(Jiujiang Station) was positive and linear. Comparing with water level in the Hukou area from 1950 to 2001,the monthly average of water level in the Hukou area from 2007 to 2008 declined.Moreover,the increase speed of water level in the Hukou area slowed and the speed droop accelerated.2.The water in the Hukou area of Poyang Lake was weak alkalinity.The temporal and spatial differences of pH were not significant.But the temporal differences of other water environmental factors,such as water temperature(WT), transparency(SD),suspended matter(SS),dissolved oxygen(DO),permanganate index(COD_Mn),nitride(TN,NH₄⁺-N,NO₃^--N and NO₂^--N) and phosphide(TP, PO₄^3--P),were obvious.The water temperature and transparency in high water season were higher than that in dry season.But the concentrations of suspended matter, dissolved oxygen,permanganate index,nitride and phosphide in dry season were higher than that in high water season.The concentrations of suspended matter, permanganate index,total phosphorus,total nitrogen and dissolved inorganic nitrogen in different water layers were arranged in the following order:bottom water＞intermediate water＞surface water.And the arranging order of dissolved oxygen in different water layers was intermediate water＞surface water＞bottom water.In addition,the correlations among water environmental factors in the Hukou area of Poyang Lake were studied.There were positive correlations between suspended matter and permanganate index,nitride and phosphide.But negative correlations between dissolved oxygen and temperature,permanganate index and dissolved oxygen,transparency and suspended matter were noted.3.The effects of water level fluctuations on water environmental factors in the Hukou area of Poyang Lake were analyzed.With increases of water level,the transparency increased accordingly.The correlation model between water level and transparency was SD=0.017e^0.199(Z).But with increases of water level,the permanganate index and the concentrations of suspended matter,dissolved oxygen, nitride and phosphide declined accordingly.The correlation models between them were SS=3.479(Z)²-1246.62(Z)+1147.3,DO=-0.479(Z)+13.918,COD_Mn= -0.009(Z)²+0.091(Z)+3.345,TN=-0.006(Z)²+0.024(Z)+2.135,NH₄⁺-N = 1.645e^-0.138(Z),NO₃^--N=0.957-0.043(Z),NO₂^--N=0.062-0.003(Z),TP= -0.001(Z)²+0.005(Z)+0.152 and PO₄^3--P=0.016(Z)^-0.308.4.The chlorophyll a concentration in the Hukou area of Poyang Lake was estimated to be in the range of 2.12～6.89μg/L in 2007 and 2.02～7.72μg/L in 2008. The season variation of chlorophyll a concentration in the Hukou area of Poyang Lake was significant.The lower chlorophyll a concentration occurred in winter,and higher chlorophyll a concentration occurred in late spring to early autumn.In addition, the relationships between chlorophyll a and water level,water temperature, transparency and TN/TP were positive.But the correlations between chlorophyll a and suspended matter,dissolved oxygen,permanganate index,nitride and phosphide were negative.The correlation model between chlorophyll a concentration and water level was Chl-a=-6.696+4.627 Ln(Z).And the stepwise regressive equation between chlorophyll a concentration and water level,water environmental factors was Chl-a=-1.703-9.251(NH₄⁺-N)+0.984(pH)+0.077(TN/TP)+44.204(NO₂^--N).5.A total of 50 fish species belonging to 6 orders 12 families 43 genus were found in the Hukou area of Poyang Lake.There were 30 cyprinid fishes,accounting for 60.00%of the total fish species.In the composition of catches,the dominant fishes were Coilia brachygnathus,Pseudobrama simony,Xenocypris argentea, Saurogobio dabryi,Pelteobagrus nitidus,Pseudolaubuca sinensis and Hemiculter sp. In addition,the correlations between fish community(individual number,fish catch, fish species,species richness and community diversity) and environmental factors (water level,water temperature,transparency and chlorophyll a) were positive.6.The proportion of four major Chinese carps fry in Yangtze River ranged from 10.03%to 15.76%in 1991～2008,and with a trend of decrease first and then increase.In the composition of four major Chinese carps fry,there was a downward trend in each proportion of black carp,grass carp and bighead carp,but the proportion of silver carp showed an increasing trend.Their respective temporal variation models were y=-1.140t+29.355,y=-0.448t+51.086,y=33.288e^-0.111t and y=4.586e^0.115t.7.The dominant larvae of four major Chinese carps migrating from Yangtze River to Poyang Lake were silver carp in 2007～2008.And the larvae of bighead carp were litter.Their migrating peak ranged from July to August.The peak period of black carp,grass carp and silver carp ranged from middle of July to late August,and the peak of bighead carp appeared in July.The migratory individuals of black carp and bighead carp ranging from 5.00 to 9.00 cm in standard length were numerically dominant,and the larvae of grass carp and silver carp ranging from 5.00 to 14.99 cm were dominant.The relationships between water level of Poyang Lake(Hukou Station) and their respective daily number migrating from Yangtze River to Poyang Lake were significant positive.Moreover,the F test of correlation models between water level and respective daily immigration numbers were significant level(P＜0.05).This showed that the effects of water level fluctuations on the larval migration of four major Chinese carps from Yangtze River to Poyang Lake were significant.8.According to the data from 2007 to 2008 and the dispatching mode,the main effects of Poyang Lake Hydro-junction Project on the larval migration of four major Chinese carps from Yangtze River to Poyang Lake as follows:(1) Some larvaes of four major Chinese carps would be detained in the channel.The resources of four major Chinese carps in the Poyang Lake would be declined.(2) The migrating numbers of four major Chinese carps from Yangtze River to Poyang Lake would be shortened.