Study On The Structure Of Plankton Community And Its Environmental Indicators Of Karst Spring In Wuming Basin

As a significant water source for human life and production,karst water sources have been affected by climate change and human activities greatly in recent years.Water quality and quantity changed in varying degrees,and these changes have led to the change of aquatic community structure in the lake area formed by karst groundwater discharge,which play an important role in maintaining the health of ecosystem.Under natural conditions,karst water is poor nutrient environment with rich calcium,and alkali.Groundwater stores and migrates in the lightless,and relatively constant temperature of karst conduit or fractures,so it is vulnerable to external threats and damage.Karst groundwater ecosystem is easy to lose balance,and the damaged karst water ecosystem is difficult to recover.In view of the fact that plankton is very sensitive to change in water environment,its species and abundance changes can reflect water quality condition more accurately.In April,July and October 2016 and January 2017,four Sub-sampling surveys were carried out in five karst springs in Wuming Basin.The water-bearing medium of the five karst springs in the Wuming basin was dominated by karst fissures or small conduits.In which,the Dongfeng Spring and the Luobotan aquifer medium were large conduits,developed in the limestone strata.Nitrate nitrogen was the main nitrogen nutrient.CODMn,chlorophyll and dissolved oxygen had significant correlation among each other.The eutrophication condition evaluated by the total phosphorus and chlorophyll concentration showed Lingshui and Dongfeng Spring were the Poor-middle nutrition type,while Sandong spring and Luobotan were the poor nutrition type.Qinzhu Spring had a trend of eutrophication.A total of 5 phylum,and 53 species of phytoplankton were identified,and the species and abundance of chlorella and diatomophytes were the highest.The species and abundance of phytoplankton were affected by nitrogen nutrition.Along the direction of water flow,the species and abundance increased.In Dongfeng Spring and Luobotan Spring,the abundance of phytoplankton decreased with the increase of water depth.Through the plankton similarity analysis,the growth and water environment of submerged plants in karst spring were compared,indicated that the death of submerged plants in Lingshui could be directly related to the concentration of nitrogen in the karst spring.A total 3 phylum and 24 species of Zooplankton were identified,in which the species and abundance of rotifer was the highest.The species and abundance of zooplankton were consistent with the water flow direction and water depth changes.The community structure of Zooplankton was mainly affected by producer sources.Similarity analysis showed that the water environment and submerged plants had a great influence on the community structure of zooplankton.The results of water quality evaluation of five karst springs by using the biodiversity index of plankton showed:Sandong and Luo Bo Tan were light pollution type,Dongfeng farm and Lingshui spring were light-medium pollution type;Qinzhu spring was medium pollution type.The RDA and correlation analysis of plankton community structure and environmental factors showed that the structure of plankton community was positively correlated with nitrogen nutrition,chlorophyll,dissolved oxygen and transparency,but negatively correlated with CODMn,pH,HCO3-and Ca2+.The ecosystem of Luobotan and Sandong Spring was healthy.Qinzhu Spring was in a sub-healthy condition.Lingshui and Dongfeng Spring belonged to the unhealthy ecosystem.Therefore,a deduction was proposed that the closer the ratio to 1 of phytoplankton to zooplankton species and abundance is,the better ecosystem health they have.