Identifying changes in the hydrological connectivity and their drivers in the Liaohe Delta wetland

Hydrological connectivity is of great significance to the formation and development of wetlands. Identifying the causes of reduced hydrological connectivity is also critical for restoring wetland systems. Despite its importance, research to identify connectivity or blockage and quantify the impact of different drivers on wetland hydrological connectivity remains a challenge due to the lack of appropriate data at large scales. This paper quantitatively analyzed the hydrological connectivity in the Liaohe Delta wetland using multispectral Landsat series datasets from 1986 to 2020 in the Google Earth Engine (GEE) by combining water area, connectivity function value (CFV), average monthly inundation frequency. The paper also defined identification criteria for connectivity or blockage and quantified the drivers of changes in hydrological connectivity by combining the identified results with wetland classification data. The results showed that (1) over the past 35 years, water area has slightly decreased and has shown a seasonal difference, with summer, autumn, and spring in decreasing order. The spatial distribution of water has expanded from land to sea. (2) CFV decreased and connectivity blockage occurred. The maximum hydrological connectivity distance has undergone fluctuations, exhibiting a decrease in its threshold value from 62.37 km between 1986 and 2011, to 55.2 km between 2011 and 2013. Subsequently, the threshold increased back to 62.37 km between 2013 and 2014, before declining to 55.17 km between 2014 and 2020. Heavy inundation and total inundation were mainly concentrated in nascent estuary areas and shallow sea areas. (3) Connectivity blockage has been a major trend in connectivity change over the past 35 years, with the most severe blockage occurring from 2006 to 2015. The factors influencing connectivity blockage were more natural than human factors before 2006, after which human factors gradually became the dominant driving factor. Over the past 35 years, hydrological connectivity has decreased and connectivity has been blocked. Human activities have become the main factor in the blockage of connectivity in the Liaohe Delta wetland since 2006. This study provides valuable insights for the conservation and restoration of hydrological connectivity in the Liaohe Delta wetland.

Automated summary

This study quantitatively analyzed the hydrological connectivity in the Liaohe Delta wetland using multispectral Landsat series datasets, and defined identification criteria for connectivity or blockage. The results showed that water area has slightly decreased over the past 35 years, and connectivity blockage has occurred. Human activities have become the main factor in the blockage of connectivity in the Liaohe Delta wetland since 2006. This study provides valuable insights for the conservation and restoration of hydrological connectivity in the Liaohe Delta wetland.