Loss and Fragmentation of Marshes in the Sanjiang Plain, Northeast China, 1954–2005

Abstract

Marshes in the Sanjiang Plain of Northeast China have undergone dramatic loss and fragmentation over the past decades. This paper analyzed the loss and fragmentation of these marshes for the period 1954-2005 using historical land-cover information and remote sensing data. In 1954, marshes covered one-third of the total land area but have decreased by 77% over the 50 year period. Results showed two distinct periods of impact : 1954-1986 and 1987-2005. In the earlier period, the number of marsh patches fell from 4,799 to 1,476 (−69.2%), and total marsh area decreased from 35,270 km 2 to 13,893 km 2 (−60.6%). In the latter period, the number of marshes declined from 1,476 to 1,037 (−29.7%), and the total area decreased from 13,893 km 2 to 8,100 km 2 (−41.7%). The rapid decrease in the number and area of marshes during 1954-1986 was largely attributed to extensive agricultural reclamation under the "Food First" agricultural policy. This resulted in many negative ecological consequences. In contrast, the slower reduction of marsh areas during 1987-2005 was due to the implementation of governmental policies for protecting and restoring marshes. Increasing air temperature would otherwise have enhanced crop yields and stimulated the conversion of marsh into crops.

The Effects of Spatiotemporal Changes in Land Degradation on Ecosystem Services Values in Sanjiang Plain, China

“…Human activities play a significant role in land degradation [56][57][58], and land degradation is particularly related to increases in population and intensive agriculture [64]. Our study showed that human activities (89.67%) were the dominant factors responsible for land degradation in the study area.…”

“…Marsh mainly became croplands (22.5%) and these changes were caused by human reclamation and environmental deterioration. Grassland mostly transformed to dry farmland and forest whereas dry farmland mostly changed to paddy, and these changes were caused by reclamation, forestation and government policies "to develop paddy and to promote conversion from dry farmland to paddy" in the 1990s, respectively [57,58]. Transformations between dry farmland and paddy occurred frequently in the study area.…”

“…Paddy and settlement increased continuously from 1954 to 2013 while forest, grassland and marsh showed declining trends. Dry farmland expanded first from 1954 to 1986 and then declined from 1986 to 2013, which had a great relationship with the government policy "to develop paddy and to promote conversion from dry farmland to paddy" in northeast China in 1990s [57,58]. During the past 60 years, dry farmland had the largest increase (21.5%), followed by Comparison of our maps showing the spatial distributions of different LULCC types allowed us to identify six main LULCC types, which proceeded in four stages ( Figure 3).…”

“…As the largest freshwater marsh in China, Sanjiang Plain is vulnerable to global change and human disturbance. High-intensity human activities, especially large-scale reclamation, have led to intensive land degradation since the 1950s in this region [56][57][58][59]. Meanwhile, climate change [60], elevated atmospheric CO2 [61], and other natural factors [59] have also caused some degree of land degradation in this region.…”

“…Meanwhile, climate change [60], elevated atmospheric CO2 [61], and other natural factors [59] have also caused some degree of land degradation in this region. Many studies [56][57][58]62,63] have examined spatiotemporal changes in land degradation and its driving factors over part or all of Sanjiang Plain. However, information on the land use structure changes and quantitative analysis of human impacts are still lacking for this area.…”