Increasing anthropogenic activities are threatening freshwater ecosystems worldwide. Sand mining in Poyang Lake has significantly impacted the wetland ecosystem over the past 20 years, yet a quantitative analysis of these impacts remains insufficient. Here, we used 63 Landsat images taken from 2000 to 2020 along with the support vector machine (SVM) method and a retrieval model of suspended sediment concentration (SSC) to identify sand mining vessels and areas affected by sand mining. Then, we analyzed the changes in landscape patterns in the areas affected by sand mining. The potential impact of underwater noise generated by sand mining vessels on Yangtze finless porpoises was analyzed by a sound propagation model. The number of sand mining vessels in Poyang Lake during the flood, normal, and dry seasons increased from 2000 to 2016 but rapidly decreased from 2017 to 2020. Sand mining vessels were mainly distributed in the northern channel from 2000 to 2006, moved toward the center of the lake from 2007 to 2010, then moved northward in 2017. Within the areas affected by sand mining, water and mudflats declined, grassland and sandbars increased, and the landscape discontinuity increased. The habitat of the Yangtze finless porpoise affected by underwater noise from sand mining vessels in all seasons has significantly increased overtime. The mean area of the affected habitats was 70.65% (dry), 64.48% (normal), and 63.30% (flood) of the total habitat areas. The porpoise habitats in the northern channel and the west branch of the Ganjiang River are more seriously affected by the underwater noise of sand mining vessels than the southern lake. The impact of sand mining activities on wetland landscape and aquatic species demands systematic investigation in the future.

Background: Oncomelania hupensis is the only intermediate host of Schistosoma japonicum and plays a decisive role in its transmission. The variation of water level greatly affects the reproduction and growth of snails. Therefore, in this paper, we analyze the variations of water level in the Poyang Lake region from 1993 to 2016 combined with satellite imagery to elucidate the evolution of the snail breeding environment. Methods: By employing remote sensing data from 1993 to 2016 (April–June and September–November), the vegetation area of Poyang Lake and the vegetation area at different elevations were extracted and calculated. Moreover, the average daily water level data from the four hydrological stations (Hukou station, Xingzi station, Tangyin station and Kangshan station) which represent the typical state of Poyang Lake were collected from 1993 to 2016. The variance of the monthly mean water level, inundation time and the average area were analyzed by variance to find a significance level of α = 0.05. Results: According to hydrological data before and after 2003, the average water level after 2003 is significantly lower than that before 2003 in Poyang Lake. After 2003, the time of inundateing the snail breeding period was later in April to June than that before 2003, while the time of wate-falling stage in September to November moved forward after 2003 than before 2003. Of them, the lowest water level affecting the breeding and growing period of O. hupensis in the northern part of Poyang Lake decreased from 11 m to 9 m. After 2003, the expansion of meadow area in the north part of Poyang Lake was mainly concentrated in the elevation of 9–11 m, and the newly increased infested-meadow in the lake area was mainly concentrated in the north part of Poyang Lake. Conclusions: By comparing the change of water level characteristics in different parts of the Poyang Lake area as well as changes in meadow area before and after 2003, it is found that the water level changes mainly affect the snail breeding area in the northern part of Poyang Lake. The results are helpful for improving scientific measures for snail control in Jiangxi Province. This approach could also be applicible to Dongting Lake area and other lake areas affected by water level changes and can bring significant guidance for snail control in lake areas.

Freshwater cetaceans that inhabit river basins with seasonally changing hydrological regimes have a higher risk of stranding, leading to increased mortality and population decline. In Poyang Lake, the stranding risk of the critically endangered Yangtze finless porpoise are high, due to the significant differences in hydrological and landscape conditions between the flood and dry seasons. However, this stranding information is not well recorded, resulting in poorly guided investigation and rescue efforts. We here employ remote sensing and hydrodynamic modeling to obtain four evaluation indicators in dry, normal, and flood scenarios in Poyang Lake. Results show that nearly 50% of the largest habitat range of the porpoises in the flood season will be land areas during the dry season, and that landscape fragmentation between land and water has increased over the past three decades. In all scenarios, the mean water depth of the habitat varied from 1.77 to 4.89 m from September–February. In the dry scenario, about 59% of the habitat experiences a water depth of 251.04 km² in the normal scenario, and >90.12 km² in the flood scenario. High-stranding risk areas are located within city boundaries, where porpoise stranding cases have been recorded, especially in Duchang, which has the most high-risk areas in all scenarios. In all scenarios, the high stranding risk area has an average bathymetry of 7.81 m and an average water depth between 1.75 and 5.54 m. Our results can guide future investigations to establish sound stranding networks, and the methods proposed here are also applicable to studies of other freshwater cetaceans facing severe stranding risk.