Spatial heterogeneity of long-term environmental changes in a large agricultural wetland in North China: Implications for wetland restoration

Abstract

Understanding long-term environmental changes and man-land interactions within wetlands is important for their ecological maintenance and restoration. However, there has been little focus on the spatial heterogeneity of environmental variations of wetlands, especially large agricultural wetlands, which hinders the development of targeted management programs for specific areas. We conducted a multi-proxy study of the sediments of a typical agricultural wetland, Lake Baiyangdian in North China, to assess the spatial heterogeneity of environmental changes over the past 70 years. The results reveal that the environmental changes in Lake Baiyangdian were spatially heterogeneous, mainly reflected by the response to hydrological variations before the 1970 s, and by changes in trophic level and land cover transitions since the 1990 s, which are strongly linked to changes in agricultural land use. Pollen and grain-size analyses revealed the large-scale spatial heterogeneity of changes in the sedimentary environment. Areas with greater openness, shallower water depths, and proximity to inflowing rivers were generally more sensitive to hydrological processes and provided regional records of environmental change. In contrast, populated areas far from inflows tended to capture more local changes related to anthropogenic impacts. Intensive agricultural activity has led to a continuous increase in nutrient enrichment and significant land cover transitions in Lake Baiyangdian, mainly the loss of natural wetland. Variations in Humulus pollen were a key indicator of these anthropogenic impacts. Hydrological processes and land use changes were together responsible for the spatial heterogeneity of the environmental variations in Lake Baiyangdian over the last 70 years, indicating the dominant role of human impacts on the spatio-temporal pattern of the evolution of this wetland ecosystem, and the complexity of its environmental management.