No abstract

Agricultural activities, especially reclamation, are considered major threats to the wetland ecosystems in Sanjiang Plain, the largest concentrated area of the freshwater wetlands in China. In the past decades, the area of the cultivated land and its grain production have been increased at the cost of wetlands shrinkage. The large-scale land reclamation severely affected the ecosystems in this region. However, such effects at the regional scale are seldom evaluated quantitatively. We used three datasets of LANDSAT MSS and/or TM imagery to estimate the area changes and the transition of land use types from 1980 to 2000. We also valued changes in ecosystem services delivered by each land category using value coefficients published by Costanza et al. Sensitivity analysis suggested that these estimates were relatively robust. Finally, the contribution of various ecosystem functions was ranked to the overall value of the ecosystem services in this study. According to our estimates, the total annual ecosystem service values in Sanjiang Plain have declined by about 40% between 1980 and 2000 (156284-182572.18 million US dollars in total over 20 years). This substantial decline is largely attributed to the 53.4% loss of wetlands. For individual ecosystem functions, waste treatment, water supply and disturbance regulation account for more than 60% to the total ecological values. During those two decades, the contribution of disturbance regulation, cultural and recreation decreased, while the contribution of water regulation, nutrient cycling, food production, raw materials and climate regulation increased during the same period. We also put forward a few proposals concerning the future land use policy formulation and sustainable ecosystems. They are adjusting the 'food first' agricultural policy, establishing more nature reserves for wetlands, creating systems for the rational use of water, harnessing the degraded cultivated land and encouraging eco-tourism.

Humans benefit from multiple ecosystem services of wetlands, but massive wetland loss has occurred worldwide due to rapid urbanization. To assess the problem, it is necessary to quantify the spatial extent of urbanization‐induced wetland loss. Here, we investigated the amount and pattern of wetland loss in China due to urbanization from 1990 to 2010, based on the China National Land Cover Database (ChinaCover). Our results show that, during these 20 years, China lost 2,883 km2 of wetlands to urban expansion, of which about 2,394 km2 took place in the eastern regions (Northeast China, North China, Southeast China, and South China). The rate of urbanization‐induced wetland loss was 2.8 times higher between 2000 and 2010 (213 km2 year−1) than between 1990 and 2000 (75 km2 yr−1). Of all wetland categories, reservoirs/ponds and marshes suffered the most severe losses. Most of the wetland loss was due to the expansion of urban built‐up areas rather than industrial or transportation lands. Four hotspots of urbanization‐induced wetland loss in China were identified: the Beijing–Tianjin metropolitan region, the Yangtze River Delta, the Jianghan Plain, and the Pearl River Delta. Urbanization and industrialization continue to unfold in China for the next few decades, and the rapid expansion of small‐ and middle‐sized cities and urban traffic networks is expected to encroach on more wetlands. Although great efforts have been made towards wetland conservation in recent years, China must prevent more wetlands from being wiped out by urbanization if the country is to ahieve its sustainable development goals.