| The lake is not only the connection point of the earth surface system at all levels and the interaction of various spheres, but also an important part of the hydrosphere indispensably. The lake has the function of regulating regional climate, record the regional environmental change, maintaining regional ecological balance system and reproduction of biodiversity. In the late stage of development of lakes are saline lake which makes up about half of the earth’s total number of lakes, especially in arid and semi-arid area, a large number of saline lake has a decisive role in maintaining regional ecological system structure and productivity. Ordos is one of the two distribution area of saline lake groups in China. The region is a sensitive, special and relative independent ecological transition zone in arid and semi-arid area of China. This paper selected the saline lake groups of Ordos region as the research object to study the dynamic and its driving factors, the structure and function of saline lake. The application of entropy theory was used to analyze the vulnerability of saline lake ecosystem. Firstly, remote sensing data (RS) combined with geographic information system (GIS) were used to analyze the lakes dynamic change of Ordos. Secondly, the effects of climate change and human activities on the lake dynamic change were studied in the specific guidance of ecology, landscape ecology, climatology, biology statistics and other disciplinary theories. Third, the species composition, density and community structure of phytoplankton were analyzed in the typical lake water in Ordos region, and in-depth analysis was made on the correlation of phytoplankton functional groups and environmental factors. Fourth, entropy theory was used to analyze and assess the vulnerability of saline lake ecosystem. Main conclusions are as follows:1. The dynamic characteristics of the salt lake groups in Ordos:the total trend of Lake area and the number was reduced.In the range of study time series, from 1980 to 2012, the lakes has disappeared or dried up a total of 26, loss rate of 31.33%. The water area has lost loss 100.52Km2, loss rate of 30%. From 1980 to 1995, the number of lakes increased from 83 in 1980 to93 in 1995, added a number of lakes for 10, and the increasing rate was 12%. Lake’s area increased from 334.52 km2 in 1980 to 372.13 km2 in 1995, and increased area value was 37.61 km2. From 1995 to 2012, the number of lakes decreased from 93 in 1995 to 57 in 2012, and decreasing rates was 38.7%. Lake’s area decreased from 372.13 Km2 in 1995 to 234 Km2 in 2012, decreased area value was 38.13 Km2. The dynamic characteristics of the salt lake groups in Ordos were changed greatly under the combined action of climate change and human activities.2.In order to in-depth analysy the climatic driving factor of the salt lake groups dynamic, so choose the climate data in Ordos area for statistical analysis from 1960 to 2012, the conclusion showed that the general trend was warming in Ordos regional climate tendency, study area temperature increase range of the change amplitude was from 0.45℃/10a to 0.6℃/10a, higher than the national average annual average increase temperature value(0.208℃/10a). The overall trend of precipitation was decreasing trend. In the 1960s precipitation fluctuations larger, in the time series from 1968 to 2012, the linear fitting decline rate value of the trend of precipitation was 4.16mm/10a. By Gray Correlation Analysis, temperature and precipitation with the lake area, had a high correlation value.3. Human disturbance is one of the major driving factor of dynamic change of lake, land is the basic resource of the survival of mankind, so the land use dynamic can reveal the human disturbance intensity. Through the study of Ordos area land use dynamic, draw the conclusion:in 1980 to 2012, Ordos area increase of land cover types was mainly grassland, forest land, construction land, the increase value respectively:1367.03 km2,424.96 km2, 204.46 km2, reduce soil cover types for the unused land and the cultivated land, reduce the number of were 1991.57 km2 and 156.291 km2; significant changes in the area of land cover types were grassland and the unused land, in the 32 years of time series, the grassland area increased 1367.03 km2 and the unused land decreased the 1991.57Km2. The lake area was decreased trend through analysed land dynamic degree in different time sequences, dynamic change of Lake in 1995-2012 time series, the dynamic degree was 3.3%.4. Landscape pattern analysis could reveal the dynamic characteristics of the salt lake of Ordos in the regional scale. Through the analysis of landscape pattern:the main landscape type in Ordos region were grassland and desert landscape pattern, alternating with cultivated land and forest land. The proportion of other landscape types were very small, consisting of a patch or band spread on the Ordos area. The landscape structure was mainly grassland, sandy land, cultivated land and saline alkali soil in plain area, which was the basis of landscape functions, the proportion of lake landscape value was very small, were 0.0044 (1980),0.005 (1995),0.0041 (2012), three phases of the Ordos Area lake landscape broken degree minimum was 1.1 (1995), average patch area and the maximum value was 0.91 Km2 (1995)5. In order to further on the regional scale of saline lakes ecological system in the Ordos area,we selected six typical lakes as ecological survey object in september 2012, through the analysis of the phytoplankton community in lake water to reveal the lake ecosystem structure and function. the study identified a total of 40 species of phytoplankton belonging to 28 genera and 5 phyla. Among these species which Cyanophyta 8 genera and 11 species, Chlorophyta 16 species of 11 genera, Bacillariophyta 7 genera and 9 species, Euglenophyta 1 genera and 3 species, Pyrrophyta 1 genus and1 specie; phytoplankton dominant species were the eurybiontic species, such as Dactylococcopsis rupestris, spirulina, Chlorella, Dunaliella, Scenedesmus quadricauda, Cyclotella meneghiniana, Navicula cicapitellata. Six Lake phytoplankton species distribution was as follows:Haotongyin Chagan Nur 5 phyla,20 genera and 25 species, Hongjiannao 5 phyla,19 genera and 24 species, Qiho Nur 4 phyla,15 genera and 16 species, Chahan Nur 3 phyla,8 genera and 10 species, Harimangren Nur 2 phyla,3 genera and 4 species, Baga Nur 2 phyla 2 genera and 3 species. pH was the main limiting factor of phytoplankton density, and the salinity was the main limiting factor of phytoplankton species diversity.6. For more in-depth study of the Saline Lakes ecosystem structure and function in Ordos area, selected Hongjian Nur lake and Haotongyin Chagan Nur as the research object, the experiment in the field of ecological survey methods, combined with the phytoplankton functional groups and canonical correspondence analysis method, the phytoplankton seasonal dynamic analysis and their relations with environmental factors.Through to the ecological investigation and laboratory analysis of the Hongjiannao and Haotongyin Chagan Nur, Hongjian Nur Lake phytoplankton were divided into 14 functional groups:X2/X1/W1/TD/C/J/M/G/Wo/MP/H1/P/S2 /Tc, and the seasonal changes in summer (J/X1/X2/W1/P/TD/C/M) and autumn (G/P/X1/W1/Wo/MP/H1/TD/S2/Tc); Haotongyin Chagan Nur Lake phytoplankton were classified into 8 functional groups:X1/F/P/D/W1/Wo/J/Tc, and the seasonal dynamics in summer (X1/Tc/J/P/W1/F/D) and autumn (X1/Tc/J/P/W1/F/D/Wo). The phytoplankton functional groups in Hongjiannao and Haotongyin Chagan Nur were mainly stressed by pH, the total ion (Tds), increased electrical conductivity (CON), which needed to supplement ecological use for water effectively. PH was the main factor affecting the structure of phytoplankton community.7. Lake ecosystem is multi factor interaction of complex systems and interaction of each component in the structure of the system is nonlinear and the dynamic is a by the information flow driven by the composition and environmental coupling in together with the self-organization process, entropy is the main theoretical tool of the analysis of complex system. In order to scientific analysis of Saline Lakes ecosystem condition, so in evaluation ecological fragility of the saline lakes ecological system in Ordos use entropy theory is scientific, through the construction of evaluation index system, using integrated information entropy model method to analyze the vulnerability of ecosystem, we can get the conclusion:the information entropy of typical lakes in Ordos were HT<BG<HJ<QH<HR=CH, namely the Ecosystem vulnerability degree of order. According to the different concerned factors, the comprehensive analysis of information entropy was made on multiple factors and different factors. Main conclusions are as follows:the entropy sequence was QH<CH<HR<HT<BG<HJ when considering the two indicators of phytoplankton and the lake area. The entropy value of HJ (Hongjiannao) was the maximum. The information entropy of land use structure in Ordos region were 2.74 in 1980,2.71 in 2012 and 2.54 in 1995. The interannual variability of entropy value was very small, which meant the land use diversity was similar in nearly 32 years. While the land-use evenness calculated by the information entropy were 0.598 in 1980,0.56 in 1995 and 0.6 in 2012. The numeric values were bigger, which indicated the greater volatility of land use types, human activities disturbance degree was strong.The saline lake dynamic change in Ordos area was mainly as a result of climate change and the disturbance of human activities, which lead to changes in the lake ecosystem structure and function, especially the disturbance of human activities increased lake ecosystem vulnerability, in the light of the lake for the ecological system of irreplaceable importance, should strengthen the restoration and protection of the ecological system of the lake. Through this study more systematically grasp the change of saline lakes in arid and inland area and driving mechanism,and made important supplement for the saline lakes ecosystem in arid and semi-arid area, strengthened the physics, biology, ecology, remote sensing, geographic information system, theory of landscape ecology and other subjects in comprehensive application in the field of ecology, and provides a new way of thinking in the study of arid and semi-arid area, In order to provide scientific data to support for the ecological civilization construction of arid and semi arid area. |
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