Spatial Characteristics Of The Shark Mosquito Subfossils In Dongping Lake And Their Relationship With Water Environment

Lake Dongping is a typical warm temperate lake located in the lower reaches of the Yellow River. As storage lake of the South-to-North Water Diversion Project of China, its water quality and trophic status are crucial for this successful operation of this project.According to the characteristic of Chironomidae being very sensitive to the changes in aquatic environment, here we study the composition and spatial distribution of chironomids and its relationship witn the water environment. The paper thoroughly analyzed assemblage of Chironomidae, and evaluated the sediment environment and the water quality and trophic status of Lake Dongping. Our results can not only provide fundamental data for restorating the water environment of Lake Dongping, but also provide scientific reference for securing the water quality of the South-to-North Water Diversion Project. The main conclusions were listed as follows:1. Our results show that 41 subfossil chironomids taxa are present in Lake Dongping.The dominant taxa consist of the eutrophic taxa of Stempellinella-Zavrelia, Propsilocerus akamusi-type and nutrient-tolerant taxa of Paratanytarsus, Cricotopus sylvestris-type.Special assemblage of chironomids can be divided into three groups. The first group was located in the northeast of lake, consisting of samplings by 1, 2, 3, 4, 5, and 6. In this group,Stempellinella-Zavrelia and Propsilocerus akamusi-type are the absolute advantageous taxa. Compared with other groups, the number of taxa is higher but the diversity is lower.Sites of 29 and 30 are the third group. The dominant taxa are mainly Hydrobaenus conformis-type, Polypedilum nubifer-type and some species closely related to plants. They are Cricotopus sylvestris-type, Endochironomus tendens-type and Dicrotendipes nervosus-type. The rest of the sampling sites belong to the second group. The major taxa are Stempellinella-Zavrelia, Propsilocerus akamusi-type, Cricotopus sylvestris-type and Chironomus plumosus-type.2. The water environment of Lake Dongping exists obvious special heterogeneity.Through the analysis of modified index of Neimiluo, water quality is obviously varied by season. Quality is well than other seasons in spring, reached the level of III. The spacedistribution indicates that the quality of north is poor than south in general. The state of water quality in Lake Dongping is greatly influenced by human activities; Comprehensive nutrition state index shows that nutrition status of spring is lower than other seasons, which is in a level of mesotrophication. All the year round, Lake Dongping is in a state of mesotrophication to eutrophication. In region of sampling points 2 and 3, they have a high nutritional status, reached mid-eutrophication level; while, other areas are at light eutrophicion state. Overall, the space distribution displays that nutritional status of north is higher than south and east higher than west.3. The sediment of Lake Dongping have abvious special characteristics. The content of sediment TOC varies from 0.74% to 2.83%, which shows a spatial distribution pattern of reducing from southeast to northwest, overally. The grain size is dominated by silt, and then followed by clay and sand. Spatial changes of silt is not obvious, only showed a lower distribution characteristics in Laohu Wharf and the estuary of Liuchang River. In general,clay is declined from northwest to southeast, while, sand increased from southeast to northwest; Average cancentration of TP in the sediment is 552.17 mg/kg, and the content of IP is higher than OP. Correlation analysis found that there is significant positive correlation(P<0.01) among TP, IP and HCl-P, indicating that the content and distribution of TP is mainly affected by HCl-P; The sediment pollution of heavy metal is mainly Cu,Pb, Zn and Ni pollution and its pollution level, potential ecological harm present a reduce trend from southeast to northwest gradually, which is greatly influenced by the pollution of Dawen River.4. Redundancy analysis and partial redundancy analysis reveal that SO42-(F=2.731,P=0.006), TP(F=2.158, P=0.038), V(F=2.100, P=0.02) and silt(F=2.522, P=0.008) are the dominant factors controlling the assemblage and spatial distribution of subfossil chironomids, explaining 29% of the cumulative variances and each of them explain 12.1%,8.3%, 7.8 and 7.7% of the variance, respectively. The interpretability of water quality factor is greater than the sedimental factor.5. Comparative analysis of chironomids and diatoms in sediment of Lake Dongping,the indicating significance of water environment on the assemblage of chironomids anddiatoms are consistent. They are both dominant by species of eutrophic taxa and tolerate-nutrition taxa; However, there exist a certain differences between chironomids and diatoms, when we study from the aspects of spatial distribution and significant environmental factor. It is not only have different on the significant impact factors, but also the indicating meaning of them varies in some rigions.