Investigation On Diversity And Biomass Of Aquatic Organisms In Hongjiannao Lake

Hongjian-Nur lake locates in the Ordos Plateau and the Mu Us Sandland interchanges,across Shenmu County and Ejin Horo Banner, Inner Mongolia (39°03’42.17"-39°08’01.53" N,109°56’02.41"-109°49’28.26"E)(from Google Earth).The perimeter is32.78km (from Google Earth), and the area is32.88km2(Shaanxi Agricultural Remote Sensing information Center).Hongjian-Nur lake is China’s largest desert freshwater lake, known as the "Pearl of the Frontier". The lake has played an extremely important role in the maintenance of ecological safety of Maowusu sandy area, water regulation, climate stabilization and protection of rare wild animals and so on. In recent years, due to various reasons, Hongjiann lake continues to shrink, declining water quality, environmental deterioration trend, and aquatic biodiversity is under serious threat.The earliest investigation of species diversity of aquatic organisms in Hongjian-Nur lake, according to published historical data, dates back to2002(Xie Zuohun and Zhou Yibing,2002). Xie Zuohun and Zhou Yibing reported the benthos collected from April in1981to January in1982in Hongjian-Nur, of which the total number of species is26species and the density324.5/m2, biomass3970.0mg/m2. Liu Wenying et al (2008) reported that14kinds of phytoplankton, eight kinds of zooplankton and nine kinds of benthic animals were collected in Hongjian-Nur in2006. The rotifer has the maximum density in8kinds of zooplankton.The biomass of rotifers and cladocerans accounted for an absolute advantage.The nine kinds of benthic animals were all aquatic insect larvae. Liu Wenying et al (2009) reported that15species and18species of phytoplankton collected in2006and2007in Hongjian-nur separately.The algae collected most were those species that can adapt to salinity in freshwater or salt lake. Lan Jiece, etc.(2010) reported that the dominant species of plant is Potamogeton pectinatus collected in three bays of Hongjian-nur lake in2008. Benthic animals that Culicoides (Culicoides sp.), Chironomids (Chaoborus sp.), and considerable chironomids (Tanypus sp.) are the dominant species. The experiment was implented in May, July, September three months, the survey studied phytoplankton, zooplankton, benthic species diversity and biomass of animals of Hongjian-Nur lake following conclusions:1. The phytoplankton has a total of3phylum,3classes,10orders,13families and19genera which belong to Cyanophyta, Chlorophyta, Bacillariophyta. Cyanophyta were the dominant species in three months, and Chlorella and Stigeoclonium of Chlorophyta in July summer was the dominant species. There were a total of eight kinds of zooplankton, of which one kind of protozoa, two kinds of rotifers of linear phylum, five kinds of cladocerans copepods. Moina mongolica and rectispinosus were the dominant species in three months. Benthos included two kinds of Annelida, two kinds of Mollusca, one kind of Ostracoda in Arthropoda and9genera10species of Insecta in Arthropoda. Chironomids and Culicoides were the dominant species in3months.2.There was no significant difference among different sampling points quantified by Biomass, Margalef richness index, shannon biological diversity index, evenness (J), and diversity threshold; Among different months, each index was significantly different. These indicate that seasonal factor impacts Hongjian-Nur aquatic biodiversity, without considering the human factor into account.3. Based on Margalef richness index, the values of Hongjian-Nur plankton and benthic animals were less than1, indicating serious water pollution. Based on Shannon diversity index,the value of phytoplankton was greater than1and less than2, indicating moderately polluted water of Hongjian-Nur, high species richness and more uniform distribution of the individuals.The value of benthos was greater than0and less than1, indicating Hongjian-Nur had heavy water pollution, low species richness and the uneven distribution of the individual. Based on diversity threshold, except that the calculated value of zooplankton among the different sampling points was less than0.6, indicating poor diversity, other taxa values were between0.6and1.5, indicating that the diversity was in general. Taking these few parameters into consideration, Hongjian-Nur had moderate or severe water pollution and the biodiversity was general or lower.4. Compared with Hongjian-Nur lake historical research data (1981-1982,1993-1994,2008,2011), we can get the conclusions that the chloride, total hardness (Ca2+, Mg2+), show an increasing trend in salinity,the PH value was gradually increased and there was a significant increase of COD. All these phenomenon show that a gradual salinization of water quality and there were a lot of organic pollutants in lakes. Organic pollution sources may be chemical waste, pesticides and organic fertilizers.The reduced number of species and a change dominant species indicated that Hongjia-Nur lake has a reduced biodiversity and the structure of the population evolved into a few dominant populations.5.Compared with the salty lakes in Inner Mongolia, which includes Xinjiang and Tibet lagoon, we can conclude that the most saline lakes of the entire Mongolian Plateau and Tibetan plateau were characterized by low biological diversity, the small number of species, and the uneven distribution of species. The density and biomass of the dominant species were large. Some areas had local endemic aquatic plants such as Potamogeton Malaianus in Kanas Lake. Some species were owned by most of the lake surveyed, such as Limnodrilus hoffineisteri and Chironomidae were the dominant species in the salty lakes in Inner Mongolia and Xinjiang.