Abstract
Ecological water replenishment (EWR) has been increasingly applied to the restoration and maintenance of wetland hydrological conditions across China since the beginning of the 21st century. However, little is known about whether EWR projects help protect and/or restore wetland ecohydrology. As one of the earliest and longest-running EWR projects in China, water has been released from the Nenjiang River into the Zhalong wetland since 2001. It is important to examine the ecohydrological effects of this EWR project. In this study, long time series remote sensing data were used to extract the water area, inundation frequency, and normalized difference vegetation index (NDVI) to explore how eco-hydrological conditions changed during the pre- (1984–2000) and post-EWR (2001–2018) periods in the Zhalong wetland. Results show that the inundation area decreased due to the reduced surface water inflow during the pre-EWR period. Similarly, monthly vegetation NDVI in the growing season generally exhibited a decreasing and an increasing trend during the pre- and post-EWR periods, respectively. In the post-EWR period, NDVI increased by 19%, 73%, 45%, 28%, 13% for the months of May through September, respectively. Due to EWR, vegetation growth in areas with low inundation frequency was better than in areas with high inundation frequency. We found that the EWR project, runoff, and precipitation contributed 25%, 11%, and 64% to changes in the NDVI, respectively, and 46%, 37%, and 17% to changes in inundation area, respectively. These results indicate that the EWR project has improved hydrological conditions in the Zhalong wetland. For further maximum benefits of EWR in the Zhalong wetlands, we suggest that implementing similar eco-hydrological projects in the future should focus on flood pulse management to increase the inundation area, improve hydrological connectivity, and create new habitats.
Highlights
The hydrological regime is the key factor in wetland development, affecting vegetation and pedological dynamics [1,2,3,4]
Changes in hydrological conditions of a wetland ecosystem caused by climate change and human activities are likely to lead to habitat and ecosystem degradation [5]
A total of 420 scenes of global surface water (GSW) [31] from the European Commission’s Joint Research Centre (JRC) Monthly Water History v1.1 were downloaded from Google Earth Engine (GEE) for the period 1984–2018 and analyzed before V.1.2 was released
Summary
The hydrological regime is the key factor in wetland development, affecting vegetation and pedological dynamics [1,2,3,4]. EWR is an important and well-recognized way to restore hydrological regimes, solving water shortage issues, and maintaining the stability and health of wetland ecosystems. With climate change and the large-scale conversion of wetlands into agricultural cropland, the Zhalong wetland faced severe drought, water shortage and habitat loss for endangered waterbirds, including red-crowned cranes Grus japonensis [19,20]. In 2001, an EWR project was initiated to introduce water from the Nenjiang River into the Zhalong wetland with the aim being to restore the hydrological conditions in the area. A major concern of EWR projects is to examine if and to what extent they could enhance ecohydrology conditions in wetlands, such as vegetation growth, inundation regime, and hydroperiod. 2. MateriaTlhsisanstdudMy eatimhosdtos investigate the long-term effect of the implementation of an ecological water replenishment project on ecohydrological conditions for a large wetland area. By 2018, a total of 27.86 × 108 m3 of water had been replenished to Zhalong Wetland, with an annual maximum of 3.43 × 108 m3 and an annual average of 1.55 × 108 m3
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