Assessment of soil erosion in the Dongting Lake Basin, China: Patterns, drivers, and implications

Soil loss caused by erosion is a global problem. Therefore, the assessment of soil erosion and the its driving mechanism are of great significance to soil conservation. However, soil erosion is affected by both climate change and human activities, which have not been quantified, and few researchers studied the differences in the driving mechanisms of soil erosion depending on the land use type. Therefore, the spatiotemporal characteristics and changing trends of soil erosion in the Dongting Lake Basin were analyzed in this study. Geographic detectors were used to identify the dominant factors affecting soil erosion in different land use types. In this study, a sensitivity experiment was conducted to clarify the relative contributions of climate change and human activities to soil erosion changes. In addition, we studied the effects of different land use types and vegetation cover restoration on soil erosion. The results show that soil erosion in the Dongting Lake Basin decreased from 2000 to 2018. Human activities represented by land use types and vegetation coverage significantly contributed to the alleviation of soil erosion in the Dongting Lake Basin, whereas climate change represented by rainfall slightly aggravated soil erosion in the study area. The restoration of grassland vegetation and transfer of cultivated land to woodlands in the study area improved the soil erosion. The slope steepness is the key factor affecting the intensity of soil erosion in dry land, paddy fields, and unused land, whereas the vegetation coverage is the key factor affecting the intensity of soil erosion in woodland, garden land, and grassland. Detailed spatiotemporally mapping of soil erosion was used to determine the connections between soil erosion and potential drivers, which have important implications for vegetation restoration and the optimization of land use planning.

Dynamics Variation of Soil Labile Organic Carbon Fractions in Different Wetland Types of Dongting Lake under Seasonal Water Level Fluctuation

Soil labile organic carbon (LOC) fractions are very sensitive to environmental change and closely related to soil quality. They play an important role in the study of terrestrial carbon cycles. This study aimed to explore the sensitivity of soil LOC fractions to environmental changes and analyze their main influencing factors during three seasonal water level periods for scientific management of Dongting Lake wetlands. Soil under three typical wetland types (Carextristachya wetland (CTW), Phragmites australis wetland (PAW) and Salix babylonica (SBW)) in East Dongting Lake in China were collected during the normal season (May), rainy season (August) and dry season (December). Seasonal dynamics of soil LOC fractions (i.e., dissolved organic carbon (DOC), microbial biomass carbon (MBC) and easily oxidized carbon (EOC)) within these wetlands and their relationship to soil nutrients and carbon-cycle enzyme activity were analyzed. The results showed that the soil DOC contents of the three wetlands first increased and then decreased, with the exception of CTW from the normal season to the dry season, while the seasonal changes of soil MBC and EOC for all wetlands followed an opposite pattern. CTW had the largest DOC concentration (228.29 mg·kg−1) during dry season, while the highest contents of soil DOC, MBC and EOC were found in PAW during the three observed seasons, which ranged from 82.05 to 203.60 mg·kg−1, 262.54 to 325.74 mg·kg−1 and 3.30 to 4.61 g·kg−1, respectively. However, the contents of soil DOC and their proportions to soil organic carbon (SOC) of all wetlands during the normal season were 56.58~82.05 mg·kg−1 and 0.41~0.47%, respectively, which were the lowest among the three seasons. Nevertheless, the contents of both MBC and EOC as well as their ratios to SOC in these wetlands showed similar seasonal dynamics, with the lowest values recorded in the rainy season. From the normal season to the dry season, invertase activity in all wetlands increased, while cellulase activity decreased by 12.5–31.3%. The seasonal variation of catalase activity for all wetlands was less distinctive, and the highest enzyme activity was during the rainy season. Correlation analysis revealed that soil LOC fractions for all wetlands were closely related to SOC, TN, TP and invertase for the three seasons, especially during the rainy season, but were negatively correlated with TK, cellulase and catalase activity. Generally, soil LOC fractions of the three wetlands were affected by the seasonal fluctuations of water levels and presented different distribution characteristics.

Dyke demolition led to a sharp decline in waterbird diversity due to reduction in habitat quality: A case study of Dongting Lake, China

Waterbird responses to habitat changes are of great concern in ecology. Dongting Lake is the second-largest freshwater lake in China, and its vast wetland area provides an important wintering habitat for migratory waterbirds of the East Asian–Australasian Flyway. However, lake reclamation and illegal human-made dykes have degraded the Dongting Lake wetland area at different degrees in the recent decades, seriously threatening the ecology of this area. In 2017, to restore the natural properties of Dongting Lake, the Chinese government completely demolished 459 dykes and preserved 14 dykes for various purposes (biodiversity conservation and flood control). However, the direct impact of dyke demolition on wintering waterbirds has not been comprehensively assessed. In this study, based on annual (2013/14–2020/21) waterbird census data, we compared the differences in species composition of waterbirds in the dyke-demolished and dyke-preserved areas. The results indicated that waterbird diversity, in terms of species number, abundance, the proportion of abundance, number of rare waterbirds species, and exclusive species, was higher in the dyke preserved areas than in the previously demolished areas. Species turnover and reordering further identified dynamic differences in the spatial and temporal distributions of waterbirds. Therefore, we used long-term habitat data to explore whether habitat changes were responsible for the changes in waterbirds; the results showed significantly decreased water and mudflat areas, but a significantly increased vegetation area in the dyke-demolished areas. The water area was significantly positively correlated with waterbirds in this habitat. Compared to the dyke-demolished areas, the stable and suitable habitat area in the dyke-preserved areas might be closely related to the higher waterbird diversity. Our study revealed habitat changes in the context of large-scale dyke demolition in Dongting Lake and demonstrated the dynamic response of waterbirds to habitat changes.