Nutrient Enrichment Bioassays In The Subsided Lakes Around The Huainan And Huaibei Coal Mine Areas

Landscapes of many subsided lakes have formamed due to the coal mining activities around the Huiannan and Huaibei coal mine areas. Research on the structes and functions of such freshwater ecosystem is meaningful to the reconstruction and recovery for regional ecosystem, water resources utilization and management. One of important research issues is the eutrophciation and nutrient balance in the water column of such subsided lakes.Four research waters of different trophic states in the Huaibei and Huainan Coal Mine Subsidence Areas, including PXPJ site, PXGQ site, PXXQ site and HBNH site, were chosen to performed nutrient enrichment bioassays in four seasons from2012to2013. The main research results showed as follows:1) Address their nutrient content, ratio of nitrogen to phosphorus (N:P), and nutrient limitation. Averaged annual concentrations of total phosphorus (TP) in the four sites are0.100mg/L,0.044mg/L,0.053mg/L and0.040mg/L, while the total nitrogen (TN) concentrations are2.27mg/L,1.89mg/L,0.80mg/L and0.77mg/L, respectively. The four studied waters present two trophic levels of "light to meso-eutrophciation" at PXPJ site and "meso-trophic to light eutrophication" at PXGQ site, PXXQ site and HBNH site.2) Four seasons’treatments were cultured with appropriate concentrations under nutrient content of the research sites. PXPJ showed features of P and N mutual limitation in autumn, P limitation in the other three seasons, PXGQ showed P and N mutual limitation in spring, P limitation in winter and N limitation in summer and autumn, HBNH and PXXQ presented P limitation in the every season. The results of this research give implication of the importance of P control to these subsidence waters in the Huainan and Huaibei Coal Mine Areas.3) The four seasons’phytoplankton were identified, Chlorophyta is the largest number of all of the phytoplankton. PXPJ identified6phylum,39species of phytoplankton. The dominated species were Cyclotella catenata of Bacillariophyta, Palmella and Chlorella vulgaris of Chlorophyta, Limnothrix and Merismopedia minima of Cyanophyta. PXXQ identified5phylum,34species of phytoplankton. The dominated species were Pseudanabaena, Raphidiopsis curvata, Arthrospira platensis, Aphanizomenon flos-aquae, Synedra acus and Synedra ulna. PXGQ identified6phylum,39species of phytoplankton. The dominated species were Pseudanabaena, Arthrospira platensis, Aphanizomenon flos-aquae, Cyclotella catenata,Melosira granulate Synedra acus and Actinastrum fluviatile. HBNH identified5phylum,34species of phytoplankton. The dominated species were belong to Bacillariophyta and Chlorophyta.4)The effects of nitrogen and phosphorus on the growth of phytoplankton were investigated by using the Monod equation. The maximum growth rate and semisaturation constants of phytoplankton to P in PXPJ, PXXQ and HBNH were0.48d-1,0.015mg/L,0.57d-1,0.073mg/L,0.71d-1,0.018mg/L, respectively. The semisaturation constants of PXPJ and HBNH were smaller, that phytoplankton on P affinity is strong. The phytoplankton absorbed P more easily when the phosphorus concentration is low. Although very low phosphate concentrations, the three sites still have rather high primary production. The maximum growth rate and semisaturation constants of phytoplankton to N in PXGQ were0.78d-1,0.336mg/L.