Introduction
Wetlands are important components of the natural landscape for their functions in cleaning and retaining water naturally and providing habitats and food sources for a wide variety of plant and animal species. As a result of economic development and human population growth, intensive agriculture (croplands), as well as changes in water use and availability, increasing urbanisation and infrastructure development, disease control (especially mosquitoes), aquaculture, etc., global wetlands continue to convert and degrade. Historical reports indicate a loss of 87% of the world’s natural wetland area since the start of the 18th century (Davidson. 2014). What is more, the natural Wetland Extent Trends index, excluding human-made wetlands, declined by approximately 30% between 1970 and 2008 globally (Dixon et al. 2016). Losses of natural inland wetlands have been consistently greater, and at faster rates, than of natural coastal wetlands.
The severe loss of wetlands worldwide has significantly increased the threat to wetland-dependent organisms such as waterfowl (Gregory et al. 2010). For example, China has 65940 km2 of wetlands, spanning multiple latitudes and accounting for about 10% of the world’s wetland area, with abundant habitat types, species and quantities of biological resources. Over the past decade, however, 50% of China’s bird population density has declined significantly, with inland waters and marshes experiencing the biggest declines. (Nanjing Institute of Environmental Sciences, 2018). To counter these negative trends, many wetland conservation and restoration projects worldwide aim to improve the wetland biome and increase the diversity of wetland birds (Platteeuw et al. 2010). How to increase wetland biodiversity rapidly is a hot topic in global discussions. In China, the basic state policy of ecological civilization construction (the Eighteenth National Congress of the Communist Party of China, 2012) highlights the pivotal role of wetland ecosystems and their ecological status for wetland biota. Thus, both protecting existing wetlands and creating and restoring the functions of degraded wetlands and their supporting aquatic environments are vital strategic areas for ecological civilization construction.
For wetland biological management, this importance has led to the goal of attracting diverse and abundant waterfowl communities from adjacent habitats. In addition, a variety of foraging habitats and suitable living conditions (water depth, vegetation, food) can improve the survival rate of individual birds, as well as the nesting rate and reproductive success rate of waterbirds in the area. The abundance and distribution of resources such as fish, plants and macroinvertebrates are critical to this end (Masero et al. 1999). However, for waterbirds, access to food resources such as macroinvertebrates and aquatic plants is constrained by water depth, and the required foraging depths vary widely among species (Taft et al. 2002; Wood et al. 2012). Additionally, hydrophytes, depth and substrate affect the abundance and distribution of macroinvertebrates (Al-Sayed et al. 2008; Di Giovanni et al. 1996). Consequently, manipulating the water depth and substrate in wetlands can be a valuable tool that provides habitats for multiple species.
Building artificial ecological islands (islands for short) is an important technique for improving wetland topography and providing a diversity of foraging depths for waterbirds (Burton et al. 1996; Wang et al. 2014). However, the biodiversity effects of building these islands have never been systematically assessed. Furthermore, almost 7 years after these islands were built, it is still unknown whether this technique for protecting biodiversity actually protects or promotes biodiversity growth. For comparative purposes, we therefore surveyed differences in bird and macroinvertebrate species richness and abundance between sites (Water with and without islands in the same wetlands). We hypothesized that when islands are built, there would be differences in the biodiversity components between sites. Whether biodiversity is affected by islands was assessed in Fujin National Wetland Park, and the wetland effects were quantified. From the perspective of restoration ecology, whether this wetland restoration project of building islands with human intervention represents a suitable strategy for improving waterfowl and macroinvertebrate habitats and increasing both their diversity and abundance were evaluated. This study proposes a technical example of wetland restoration via a project that provides technical support and a scientific basis for protecting wetland birds, increasing biodiversity and protecting and utilizing wetlands on the Sanjiang Plain.