The Dynamics of Hongjian Nur, the Largest Desert Freshwater Lake in China, during 1990–2017

China’s largest desert freshwater lake, Hongjian Nur (HN), which is the largest habitat of relict gull (Larus relictus), has rapidly changed in recent years. However, it is difficult to quantitatively monitor the dynamics of the lake and determine the causes of its changes due to the lack of in situ observation. In this study, a remote sensing-based approach was utilized to overcome these limitations. The monthly water areas during 1990–2017 were first extracted from Landsat multispectral images via an improved method based on the floating algae index (FAI). Then, lake surface elevations measured by real-time kinematics (RTK) were used to calculate the variations in the water storage of HN. Finally, the driving factors of the rapidly changed HN in different periods were investigated by correlation analysis. The result indicated that the drivers affecting the water storage of HN in different periods were not the same. Climate change was the main driving factor of lake level fluctuation during the HN relatively stable stage (1990–1998). Drought and the intensification of human activities were the main factors for the rapid shrinkage of the HN during 1999–2010. Human activities, especially coal-related industries and reservoir impoundment, likely was the primary factors driving the decrease in the water storage of HN from 2010 to 2015. After 2015, the policies that decreased the water consumed by human activities formulated by the government and humid climate were the main factor for the expansion of HN.

Spatial and Temporal Dynamics of Water Hyacinth and Its Linkage with Lake-Level Fluctuation: Lake Tana, a Sub-Humid Region of the Ethiopian Highlands

Water hyacinth originated from the Amazon Basin and has expanded to other parts of the world since the 1800s. In Ethiopia, the weed is affecting the socio-economic activities of the people whose livelihood is directly or indirectly dependent on Lake Tana. Still, the area covered by water hyacinth and the impact of water level fluctuation on the expansion of water hyacinth has not been known clearly. Therefore, the main objective of this study was to determine the spatiotemporal distribution of water hyacinth and relation with lake-level fluctuation. The area covered by water hyacinth was determined using monthly Sentinel-2 images, which were collected from November 2015 to December 2019. The impact of water level fluctuation on the expansion of water hyacinth was evaluated using hourly water level data converted to a monthly average to correlate with the area covered by the water hyacinth. In addition, MOD13Q1.006 data was used to evaluate the trend of the Normalized Difference Vegetation Index (NDVI) and its linkage with the weed. The maximum areas covered by water hyacinth were 278.3, 613.6, 1108.7, 2036.5, and 2504.5 ha in Feb 2015, October 2016, September 2017, December 2018, and in December 2019, respectively. Its areal coverage was declining from the northern corridors and increasing in eastern shores of the lake. The lake-level fluctuation was observed in the range of 1.5 to 3.98 m in this study. The annual mean maximum spatial values of the NDVI were in the range of 0.27 and 0.47. The area covered by water hyacinth was increasing significantly (P < 0.05) and positively correlated with the seasonal lake-level fluctuation. High water level enabled the expansion of the weed by extending its suitable habitat of shallow water to the flood plain. Based on the results of this study, lake-level fluctuations can have an adverse impact on the expansion of the weed.

Water-level regulation for freshwater management of Bosten Lake in Xinjiang, China

The Bosten Lake is the largest inland freshwater lake of China, in which water level and salinity fluctuate due to the imbalance between inflows and outflows under climate change and anthropogenic activities. This paper employed system dynamics as an effective methodology to grasp the regulation rules for sustainable freshwater management of the Bosten Lake. Results show the following. (1) Changing of lake water salinity is not only affected by the salinity of water entering and leaving, but is mostly a result of water exchange rate (WER) and the lake level fluctuation. (2) According to the estimated regime of lake level regulations, it is attested that surface water inflow must be larger than outflow about 10.6 × 108 m3 every year. Thus, the Bosten Lake can keep its normal water level. (3) A nonlinear equation was fitted between WER and average salinity of the Bosten Lake. This equation quantifies that when WER equals, or is larger than, 7, the Bosten Lake can be kept as a freshwater lake at all times.

Hydrological regime of Adygine lake, Tien Shan, Kyrgyzstan

This article provides a detailed analysis of the hydrological regime of the Adygine glacial lake in Tien Shan, Kyrgyzstan, and of the specific factors which affect it. Glaciers of central Tien Shan are considered to be very sensitive indicators of climate change. The studied lake belongs to a system of relatively recently formed lakes situated near the front of the retreating glacier and is numbered amongst the potentially dangerous. The lake’s water level and its dependence on the development of climatic conditions in the area were monitored in detail in 2007–2012. A substantial part of this paper is the evaluation of the inflow and outflow balance of the lake’s basin. The results confirmed that the hydrological regime is glacial and exhibits its typical characteristics, such as a seasonal evolution of runoff delay or significant diurnal fluctuation of the lake’s water level. During the monitored period, no major changes in annual lake level fluctuation were recorded.