Spatial And Temporal Distribution Characteristics Of Water Quality And Phytoplankton Functional Groups In A Temperate Seasonally Stratified Reservoir In North China

The aim of this study was to explore the seasonal variations of water quality and phytoplankton community structure in a temperate seasonally stratified reservoir in North China. 37 samplings were carried out from different depths of Zhoucun Reservoir, Zaozhuang City. The physical, chemical and phytoplankton indexes were continuously monitored in situ from July 2014 to June 2015. Study of the response characteristics of water quality to the seasonal thermal stratification in Zhoucun Reservoir, and reveals the mechanism of water circulating transformation of nitrogen, phosphorus and other elements. Analysis of the spatial and temporal distribution characteristics of phytoplankton functional groups, and their key environmental affecting factors. Analysis of the causes for water quality deterioration and eutrophication, and it necessary to using water-lifting aerator to inhibition of endogenous contamination and eutrophication prevention in reservoir. The main conclusions are as following:(1) The Zhoucun Reservoir had a long thermal stratified period lasting from April to November and a short mixing period in winter(from December to March),which showed a single-cycle mixed pattern. The temperature was the main factor that influenced the thermal stratification structure, instability and reconstruction. The upper layer water temperature was affected by the temperature significantly, and the temperature has little effect on the bottom water temperature.(2) The thermal stratification played an important role in water environment. The hypoxia in the bottom water caused by thermal stratification leaded to the nutrients and reductants release from sediment. During the stratification, the maximum concentration of total nitrogen, ammonia nitrogen, total phosphorus, manganese and sulfide were 1.64, 1.11, 0.14, 0.93 and 1.29 mg/L,respectively. During the stratification weaken period in autumn, high nutrient and reductants concentration were exchanged to the surface water body due to the vertical convection.The reducing pollutants migrated upward, leading to water quality deterioration, odor and appearance problem and fish death.(3) The phytoplankton community was divided into functional groups following the method proposed by Reynolds and Padisák. Hydrological and water quality factors were considered to reveal the driving forces for the selection of phytoplankton functional groups. The results suggested that a total of 112 species of phytoplankton, belonging to eight families and 63 genera, were detected and could be sorted into nineteen functional groups. Phytoplankton dynamics in Zhoucun reservoir exhibited remarkable seasonal variations: The S1 functional group(Lyngbya sp. and Spirulina sp.) was dominant during thermal stratification in summer and autumn; while C + D functional groups(Cyclotella meneghiniana and Synedra sp.) were dominant during the mixing period(winter) with the condition of low temperature and light level.The distribution of phytoplankton functional groups were homogeneous in vertical. Redundancy analysis(RDA) suggested that thermal stratification, precipitation, and water temperature had a major influence on phytoplankton succession in Zhoucun Reservoir.(4) The comprehensive nutrition state index(TSI) and Q index were used to evaluate the eutrophication status of Zhoucun Reservoir. TSI evaluation showed Zhoucun Reservoir were from medium eutrophication to severe eutrophication, while Q index showed results for middle level. Q index in the evaluation of the results below TSI, which may is higher in water turbidity due to the wet season, the lower water transparency and higher CODMn leading to TSI value of overall high.(5)Water quality monitoring of 3 main inflow rivers in Zhoucun Reservoir were lasted from October 2014 to August 2015. The results showed that Xu Wahe pollution was more serious, the total nitrogen and total phosphorus concentration reached 19.97 mg / L and 6.05 mg / L,respectively. The component of total nitrogen was different among the 3 main inflow rivers, the total nitrogen in Xuwa River was mainly composed of ammonia nitrogen, while the Xiashi River and Xijia River were mainly composed of nitrate nitrogen. Analysis from seasonal variations, the dry season water was relatively clean, the nitrogen and phosphorus concentration in wet season were significantly higher than dry season.