Analysis of dynamics and driving forces of lakes and reservoirs in western Songnen Plain

Abstract: Lakes and reservoirs are important factors for ensuring the development of regional agricultural and animal husbandry economy and ecological security. In order to understand the changes and main driving factors of lakes and reservoirs in the western Songnen Plain from 1990 to 2013, based on the multiple-temporal images of Chinese HJ (Huanjing) and Landsat TM (thematic mapper), ETM+ (enhanced thematic mapper plus) and OLI (operational land imager) satellites, the spatial distributions of lakes and reservoirs in 1990, 2000 and 2013 were extracted using object-oriented classification method with eCognation software. Validated by a large number of field surveys, Google Earth and high-definition earth observation satellite (Gaofen-1), the accuracy of extracted results by users reached 95%, which could be applied to scientific research. Furthermore, this study investigated the area and number change of lakes and reservoirs and the driving forces of these changes from 1990 to 2013 in the western Songnen Plain. Referring to those with the area of more than 20 km2, there were a total of 20 lakes, 17 in Heilongjiang Province and 3 in Jilin Province, and a total of 9 reservoirs among which only 2 in Jilin Province. Spatially, lakes and reservoirs in study area were mainly distributed on the both sides along the Nenjiang River and Songhua River, among which the Chagan Lake and the Yueliangpao Reservoir had the largest area, respectively. Areas of lakes in 1990, 2000 and 2013 were 3633.2, 3016.3 and 2534.0 km2, and those of reservoirs were 885.9, 797.1 and 1433.2 km2, respectively. Under the combined effects of climate change and human activities, the number of lakes showed an obvious decreasing trend while that of reservoirs was opposite during the past over 20 years. From 1990 to 2013, the area of the lakes totally decreased by 1099.2 km2 and the existing area of lakes was 2534.0 km2 in 2013; the area of reservoirs decreased by 88.8 km2 at the first 10 years, and then increased to 1433.2 km2 in 2013, having a total increase of 547.3 km2. Climate factors were the important reasons for the above mentioned changes of lakes and reservoirs in the western Songnen Plain. Especially, slightly increased temperature and decreased precipitation between 1990 and 2000 and the opposite change of them from 2000 to 2013 were completely consistent with the variation of reservoirs. While for the changes of lakes, agricultural activities may be more influential than temperature and precipitation, which could be proved by obviously increased farmland and canal, and control expansion measures to avoid flood during the past over 20 years although several new reservoirs were built as well. It meant that more water had to be used for irrigation. In conclusion, climate factors, agricultural activities, and related water conservancy projects and control measures are the main and important influencing factors for the change of lakes and reservoirs in the western Songnen Plain, China. The observed results with a long time sequence in monitoring the lakes and reservoirs in study area can provide data support for ecological protection and restoration and scientific basis for regional sustainable development.