Spatiotemporal variation of marsh vegetation productivity and climatic effects in Inner Mongolia, China

Net primary productivity (NPP) is a vital ecological index that reflects the ecological function and carbon sequestration of marsh ecosystem. Inner Mongolia has a large area of marshes, which play a crucial role in the East Asian carbon cycle. Under the influence of climate change, the NPP of Inner Mongolian marsh has changed significantly in the past few decades, but the spatiotemporal variation in marsh vegetation NPP and how climate change affects marsh NPP remain unclear. This study explores, for the first time, the spatiotemporal variation of marsh NPP and its response to climatic change in Inner Mongolia based on the MODIS-NPP and climate datasets. We find that the long-term average annual NPP of marsh is 339.85 g⋅C/m2 and the marsh NPP shows a significantly increasing trend (4.44 g⋅C/m2/a; p < 0.01) over Inner Mongolia during 2000–2020. Spatially, the most prominent increase trend of NPP is mainly distributed in the northeast of the region (Greater Khingan Mountains). The partial correlation results show that increasing autumn and summer precipitation can increase the NPP of marsh vegetation over Inner Mongolia. Regarding the temperature effects, we observe a strong asymmetric effect of maximum (Tmax) and minimum (Tmin) temperature on annual NPP. A high spring Tmax can markedly increase marsh NPP in Inner Mongolia, whereas a high Tmin can significantly reduce it. In contrast to spring temperature effects on NPP, a high summer Tmax can decrease NPP, whereas a high Tmin can increase it. Our results suggest different effects of seasonal climate conditions on marsh vegetation productivity and highlight the influences of day-time and night-time temperatures. This should be considered in simulating and predicting marsh carbon sequestration in global arid and semi-arid regions

Riverbed sediment, riverbed hydraulic conductivity, riparian groundwater measurement, and predicted river discharge and river stage data of the Second Songhua River in China

River infiltration is an important part of groundwater recharge at riverbank filtration (RBF) sites. It is not only affected by the hydraulic gradient between the river stage and the groundwater table but also largely depends on the riverbed hydraulic conductivity (RHC). However, owing to the hydrodynamic conditions and sediment thickness during river scouring and deposition, the lithology of riverbed sediments undergoes strong spatial and temporal changes, which lead to a highly uncertain RHC. The influence of river scouring and deposition on RHC is not completely clear, resulting in calculation inaccuracies in the rate of river water infiltration to the aquifer and evaluation of the regional groundwater resource quantity. Based on the geological and hydrogeological settings at a typical RBF site in the middle reaches of the second Songhua River in China, we determined the relationship between RHC and sediment particle size using stepwise regression analysis and a genetic algorithm. We established a hydrodynamic and sediment transport model based on Delft3D to simulate the spatial distributions of sediment particle sizes. On this basis, a numerical groundwater flow model was established using Visual MODFLOW, in which the river boundary was generalized into a third type of boundary condition, and RHC zoning was performed to improve the accuracy of the simulation. We conclude that accurate prediction of RHC is essential for the assessment of groundwater resources in riparian zones. The exploitation of groundwater should fully consider the river infiltration and avoid a series of ecological and environmental problems caused by excessive groundwater exploitation. The dataset is the basic data of the above research

Optimum water supplement strategy to restore reed wetland in the Yellow River Delta

In order to supply optimum water to restore reed wetlands used for bird habitats, a field investigation and greenhouse experiment were conducted. Three water supplementation stages (early stage at 20 May, middle stage at 20 July and later stage at 20 September, respectively) and five depths (0, 10, 15, 20 and 35 cm over the surface, respectively) were established, with three replicates for each treatment combination. Reed growth characteristics (survival rate, height, density and biomass) and soil properties of field investigation and experiment were recorded to determine the impacts of water supplementation on reed wet-land restoration. The field investigation showed that reeds in natural wetlands grow better than those in degraded wetlands and soil properties in degraded wetlands were significantly different from soils in natural wetlands. With freshwater supplementation, reed growth characteristics and soil properties greatly improved. As water depth increased, reed growth decreased gradually. Reeds grew best in shallow water depth (<= 10cm) than in the greater flooding depths. Saturated soils with no standing water at the early stage of reed growth increased reed survival and water depth can be increased as the reeds grow. During the process of water supplementation, soil salinity was reduced significantly. Soil salinity was reduced dramatically at early and middle stages of reed growth, but it increased slightly at the later stage. Soil pH increased greatly during the experiment. Soil total nitrogen (TN) and total organic carbon (TOC) showed contrasting changes, with soil TN decreasing and TOC increasing. To best manage reed wetlands restoration, we suggest saturating wetland in the spring to stimulate reed germination, increasing surface water depth up to 15cm at the stage of reed rapid growth, and then reducing water depth during the later growth stage

Effects of Land Use Changes on the Plant Community Characteristics in the Wetlands of the Semi-Arid Regions

Human disturbance is the main driving factor of wetland vegetation degradation, and plant community changes can directly characterize the process of wetland degradation. The wetlands in semi-arid region of Songnen Plain perform the important ecological functions, especially the habitat of waterbirds. Recently, the succession of wetland plant community has been accelerated by land use changes. In this study, we investigated the variations of plant community in wetlands undergoing land use changes (natural, mowing, light grazing + mowing, moderate grazing and heavy grazing wetlands) in the western Songnen Plain. The results showed that the plant communities were significantly affected by land use changes. The typical wetland plant Calamagrostis angustifolia was the dominant species in natural wetlands, and its dominance was gradually decreased in mowing or grazing wetlands in where Carex spp. or Artemisia selengensis acting as the dominant species. The height, density, and biomass in natural wetlands were significantly higher than those in other wetlands, whereas the species diversity and richness in natural wetlands were significantly lower. The similarity index of plant community in wetlands undergoing land use changes to natural wetlands ranged from 17.7–45.1%, being the highest in mowed wetlands and the lowest in heavily grazed wetlands. The linear regression further indicated that the plant diversity index was negatively correlated with the aboveground biomass of grasses and positively correlated with the aboveground biomass of forbs. Therefore, the land use changes in wetlands drove the replacement of dominant species of wetland vegetation and changed plant community characteristics and the species diversity, and the maintenance of species diversity is linked with the variability in plant functional strategies. The results of community variations and their relationships with functional changes can be used for assessing the effects of degradation and ecological function in response of land use changes in wetlands

Effects of Land Use Changes on the Plant Community Characteristics in the Wetlands of the Semi-Arid Regions

Human disturbance is the main driving factor of wetland vegetation degradation, and plant community changes can directly characterize the process of wetland degradation. The wetlands in semi-arid region of Songnen Plain perform the important ecological functions, especially the habitat of waterbirds. Recently, the succession of wetland plant community has been accelerated by land use changes. In this study, we investigated the variations of plant community in wetlands undergoing land use changes (natural, mowing, light grazing + mowing, moderate grazing and heavy grazing wetlands) in the western Songnen Plain. The results showed that the plant communities were significantly affected by land use changes. The typical wetland plant Calamagrostis angustifolia was the dominant species in natural wetlands, and its dominance was gradually decreased in mowing or grazing wetlands in where Carex spp. or Artemisia selengensis acting as the dominant species. The height, density, and biomass in natural wetlands were significantly higher than those in other wetlands, whereas the species diversity and richness in natural wetlands were significantly lower. The similarity index of plant community in wetlands undergoing land use changes to natural wetlands ranged from 17.7&ndash;45.1%, being the highest in mowed wetlands and the lowest in heavily grazed wetlands. The linear regression further indicated that the plant diversity index was negatively correlated with the aboveground biomass of grasses and positively correlated with the aboveground biomass of forbs. Therefore, the land use changes in wetlands drove the replacement of dominant species of wetland vegetation and changed plant community characteristics and the species diversity, and the maintenance of species diversity is linked with the variability in plant functional strategies. The results of community variations and their relationships with functional changes can be used for assessing the effects of degradation and ecological function in response of land use changes in wetlands

Plant growth and diversity performance after restoration in Carex schmidtii tussock wetlands, Northeast China

Plant performance, which considers plant growth, community composition, and diversity, demonstrated the wetland plants’ restoration efficiency of wetland plants following restoration. Carex tussocks are widespread in temperate freshwater wetlands and streams, well as characterizing with rich biodiversity. However, tussock wetlands sharply shrank and plant performance has changed due to the interaction of long-term drought, and human disturbance (road construction, grazing and mowing). In recent decades, ecological restoration has been widely conducted in degraded tussock wetlands in semi-arid area. A field investigation was done in a restored tussock wetland (R) after restoration for 10 years in order to evaluate efficacy of tussock restoration. Tussock wetlands were chosen as reference wetlands, both natural (N) and degraded (D). In semi-arid zones, the results showed that wetlands were affected by drought and flooding. After 10 years, wetland restoration effectively restored the growth and yield of Carex schmidtii tussocks compared to D, but did not reach to the natural state. The importance value (IV) of C. schmidtii has sharply decreased in R. Xerophyte species (Artemisia integrifolia) have occupied dominant position growth. Furthermore, the IV of other wetland species has dropped through time, and some have even disappeared as a result of drought and flooding. R and N have much lower species richness and Shannon–Wiener index than D. Flooding in August, following a drought, boosted the Simpson index and Evenness index in R and N. Obvious differences in species composi- tion and community structure were found using principal component analysis among N, R, and D. Ecological restoration substantially alleviated wetland degradation in the semi-arid zone, but subsequent hydrological management is required to further promote plant growth and diversity performance