Materials and Methods
Study Area and Artificial Ecological Islands
The
Sanjiang Plain, located in northeast China, is the largest concentrated
distribution area of freshwater marshes in China. It is not only an
important ecological resource and environmental protection barrier, but
also an important stopover site for many Palaearctic-realm migratory
waterbird species.
In
past years, the wetland resources in Sanjiang Plain have been seriously
degenerated or lost due to long-term excessive and unreasonable
utilization and development. From 2000 to 2015, the total area of
wetlands in the Sanjiang Plain decreased by 2508.56
km2, the vegetation coverage of wetlands decreased
from 91.8% to 74.0%, and the habitat area that is suitable for
waterfowl decreased by 20.33%. These results indicate that the support
capacity of waterfowl habitats in the Sanjiang Plain has decreased
significantly in the past 15 years (Liu et al. 2018; He et al. 2017).
Fujin National Wetland Park (the park for short), which covers an area
of 22 km2, is located in the hinterland of the
Sanjiang Plain, Heilongjiang Province, Northeast China (E
131°41′02.8″-131°46′09.2″, N 46°53′18.8″-46°56′18.5″). (National wetland
park refers to a specific area approved by the state forestry
administration and protected and managed in accordance with relevant
regulations for the purpose of protecting wetland ecosystem, making
rational use of wetland resources, carrying out wetland publicity,
education and scientific research) (National Forestry and Grassland
Administration. 2017).This area has a temperate continental monsoon
climate with distinct seasons. There is less rain in spring and more in
summer, and the temperature drops sharply and differs in autumn.
The
annual precipitation is approximately 608.6 mm, and the average
temperature is -20.4°C in January and 22.2°C in July.
Before 2004, the park’s cofferdams were crisscrossed and cultivated, the
wetlands were almost all reclaimed, and the wetland resources were
severely damaged. To fully protect the wetland ecosystem, the local
government decided to strengthen wetland restoration projects in 2005,
through water diversion, increasing vegetation diversity, the
establishment of artificial ecological island and other measures to
carry out ecological restoration of the wetland, which has become a
successful example of China’s conversion of farmland to forest wetland.
Due to the park’s flat terrain and the relatively uniform distribution
of various environmental factors, the vegetation is dominated by a
single community, including Phragmites australis andTypha . The plant diversity is low, and can only provide a single
resting and foraging habitat for animals; therefore, there are few
animal species and waterfowl. To create good habitats for birds and
other aquatic organisms, attract birds and increase the integrity of the
wetland ecosystem of the park, the local government hired
the
Wildfowl and Wetlands Trust (WWT, The U.K.) and domestic experts to make
a scientific plan and design for the park. The city also cooperated with
the German government for technical and financial purposes regarding
wetland biodiversity conservation and ecological environment restoration
projects.
In this project, through the construction of ecological island, the
purpose of increasing the micro-habitat types and enhancing the
heterogeneity of various abiotic environmental factors such as hydrology
and topography was achieved. These islands can provide habitats for more
species of hydrophytes and increase the diversity of plants to improve
primary production in wetlands. Wildlife diversity, such as benthic
animals and fish, depends on plant growth; plant growth attracts birds
that feed on them, and their settling achieves the purpose of having
more biological species in a relatively smaller area. The project built
6 islands in the open waters of the park in 2011 and 2013, and 12
islands were created in total. To build the islands, canals were dug in
the park; the canals were expanded, and the slope habitat was increased
to strengthen the hydraulic connection among water patches. The original
low-lying areas were dug to a depth of more than 2 metres according to
the terrain, and as a result, the water levels were distributed in
different layers and regions that were adapted to the requirements of
different overwintering wildlife. At the same time, the excavated earth
was designed according to the terrain and stacked on relatively higher
ground to form soil substrate islands (SSIs) above the water. Pebbles
were placed on some of the soil islands to form pebble substrate islands
(PSIs). As a result, the original plateau is now more prominent, and
there is always a certain area of land at the highest water level to
achieve significant topographic differences. The island shape is the
frustum of a cone, with the highest point of the island rising
approximately 1 m above the water surface on average (Figure 2). The
edge slope of each island is different, and the shallow water zone is
very limited. The total island area was approximately 0.1
km2 after it was built. Due to island collapse, the
size of each island that extends out of the water currently varies from
200 m2 to 5000 m2.
Topographic changes can affect the formation of landscape patterns in
the park in a way that the water, soil and other conditions also change;
thus the diversity and distribution range of plants and animals in the
park have been greatly enriched. Ecological islands provide a place for
birds to forage, reproduce and rest. These structures, which have a good
field of vision and are inaccessible to mammalian predators, can attract
waterbirds, increasing the birds’ nesting population and success rate.
(Momose et al. 1998). Therefore, the structure and function of the
wetland ecosystem has been gradually restored, and the biodiversity of
the wetland has improved.
Methods
In order to observe birds of high abundance and variety, bird monitoring
was conducted and macroinvertebrate samples were collecting in the
summer of 2015-2017 (mid-August). In order to analyze the effect of
human disturbance on bird distribution, we asked the park management
center to provide the visitor data of the wetland park for three years
as a reference. In order to investigate the heterogeneity of vegetation
structure and composition, a field survey was conducted in July-August
2015.
Monitoring began a half hour before sunrise and sunset, lasting 3-5
hours (04:00–9:00, 15:00-18:00) for three successive days (days without
heavy wind and rains). Due to domain and time limitations, we set one
line transect (about 16.3 km)
and chose four open water areas that were at fixed locations inside the
park for bird spotting. Each site was visited at roughly the same time
of day to reduce the noise from systematic patterns (e.g., regular
diurnal bird movements) that would obscure the trends observed within
the park (Figure 1).
A
10X binocular (SWAROVSKI SLC 10x42 WB) was used to identify and count
birds. Numbers and species of all birds present within 300 m on both
sides of the transect were recorded. Birds flying forward were excluded,
and only those feeding in and flying within the sampling areas were
recorded, and the maximum observed value was used to calculate the
abundance (Taft et al. 2002; John. 2000; Chang et al. 1995; Jing et al.
2007). We use field binoculars to identify bird areas (swimming,
foraging, resting, etc.) between islands versus non-island areas.
Macroinvertebrate samples were collected in a 1 m2quadrat from 20 sites with D-frame kick nets (30 cm aperture, 500 mm
mesh) and then sieved with water. The retained macroinvertebrates were
transferred into pre-labelled polyethylene containers. The faunal
samples were fixed using buffered formalin (4%) and subsequently
preserved using 70% ethanol. The organisms were identified and counted
to the ”species” level (Al-Sayed et al. 2008).
Due to the collapse of some islands, 9 islands (Figure 1) were selected.
Survey sample points were set on those islands, and two depth gradients
were established on each island, namely, a shallow water level area
(depth <40 cm) and a deep water level area (40 cm<
depth <80 cm). Samples were randomly collected at each depth
gradient, and repeated sampling was conducted in three directions in the
shallow water habitat ”around” the islands. To prevent disturbance
caused by the migration of macroinvertebrates from the islands to the
open water, 11 samples were randomly selected from an open-water area
(50 cm < depth < 130 cm) that was far from the
islands in the park. The distance between the open-water sampling points
depends on the size of the floating raft between the sampling points,
ranging from 100 to 300 meters. In total, 20 samples were taken (Figure
1).
At each sampling site, we calculated the mean macroinvertebrate
abundance and recorded the species. For the benthic communities in each
group identified by the cluster analysis, the average density and number
of species (considering each taxon as a species) were determined. An
initial multivariate analysis was performed using the standardized
species matrix in a cluster analysis (Bray–Curtis hierarchical
clustering), and non-metric multi-dimensional scaling (MDS) was
performed using the similarity scores generated from the cluster
analysis (Clarke. 1994). These analyses were performed to find any
“natural groupings” based on the species matrix to check if the
grouping was consistent with the artificial grouping results based on
the species matrix (Butcher. et al. 2003).
We used Q-Q plots of the residuals in SPSS to compare the fit of the
common distributions (normal, Poisson, negative binomial). The procedure
indicated that the normal distribution fit the data well. We also
calculated traditional measures of biodiversity, the Shannon-Wiener
index (H’, log e) (Shannon. 1948), Margalef index (d) (Margalef. 1958)
and Pielou evenness index (J) (Pielou. 1975) (species
level).
Due to the different sensitivities of different species of
macroinvertebrates and waterfowl to environmental changes, one-way ANOVA
was carried out at the order level to compare differences in the
macroinvertebrates and waterfowl species abundance among the various
sites in 3 years. The taxa abundances were log (x + 1) transformed to
dampen the effects of the few most abundant taxa.
Analysis
of similarities (ANOSIM) was used to evaluate the community similarity.
Moreover, similarity percentage analysis (SIMPER) was used to determine
the contributions of individual taxa towards the dissimilarity between
and similarity within the groups identified by cluster analysis, both of
which were included in the PRIMER V5.2 software package (Clarke. 1994;
Clarke. 2006).
Pearson correlation test was carried out to prove the close relationship
among waterfowl, plant and macroinvertebrate, both of which were
included in the IBM SPSS Statistics 20 software package.