Zhenshan Xue

Ecological stoichiometry of carbon, nitrogen, and phosphorus in estuarine wetland soils: influences of vegetation coverage, plant communities, geomorphology, and seawalls

PurposeLittle is known about carbon, nitrogen, and phosphorus stoichiometrical characteristics and influencing factors in estuary wetland soils. The purpose of this work is to study ecological stoichiometric characteristics of carbon, nitrogen, and phosphorus (RCN, RCP, and RNP) in estuarine wetland soils of Shuangtaizi, northeast China and the potential affecting factors like vegetation coverage, plant communities, geomorphology, and seawall.Materials and methodsDuring 2008–2010, soil samples in estuarine wetland were collected for soil organic carbon, total nitrogen and phosphorus, and other elements determination. Mole ratios of RCN, RCP, and RNP were calculated.Results and discussionAs a whole, RCN was in the range of 8.26∼52.97 (mean, 16.15), RCP was in the range of 23.21∼862.53 (mean, 90.66), and RNP was in the 0.93∼29.52 (mean, 5.07). RCN, RCP, and RNP distribution were all with high spatial heterogeneities and significantly affected by vegetation coverage, plant communities, geomorphology, and seawalls. During the typical plant succession sequence of the halophytes–the mesophyte–the hydrophyte in estuarine wetland, P might be the primary limiting elements for nutrients stoichiometrical characteristics. RCN, RCP, and RNP in soils of low-lying areas were all higher than that in highlands. Plant coverage and communities formation would help to reduce restriction from nitrogen, but to increase restrictions from phosphorus meanwhile.ConclusionsC, N, and P ecological stoichiometry had high complexities. RCN in estuarine wetland soils were generally high, whereas RCP and RNP were comparatively low, indicating that ecosystems in the estuary were limited by nutrients such as N and P, with the latter being the primary factor. Vegetation covers, plant communities, geomorphology, and seawall all affected nutrient stoichiometry in soils.

Soil C, N and P stoichiometry of Deyeuxia angustifolia and Carex lasiocarpa wetlands in Sanjiang Plain, Northeast China

PurposeThe theory of ecological stoichiometry has improved understanding of nutrient circulation processes in ecosystems. The purpose of this work was to study ecological stoichiometric characteristics of carbon, nitrogen and phosphorus in wetland soils of Sanjiang Plain, northeast China.Materials and methodsA Deyeuxia angustifolia wetland (swamp meadow) and a Carex lasiocarpa wetland (marsh) were chosen for collection of soil cores (0–30xa0cm depth). Soil organic carbon, total nitrogen and phosphorus were analyzed to study patterns of C/N (RCN), C/P (RCP), N/P (RNP), and C/N/P (RCNP) in wetland soils.Results and discussionSoil carbon, nitrogen and phosphorus stoichiometry differed between the two wetlands. Soil RCN (0–30xa0cm depth) in the D. angustifolia wetland was close to that in C. lasiocarpa wetland (12.97 and 12.80, respectively), but RCP and RNP in C. lasiocarpa soils were significantly higher than those in D. angustifolia soils. RCN changed little within soil profile, without obvious trends in both wetlands. Both RCP and RNP decreased with depth from the surface, and both RCP and RNP were higher at every depth interval in C. lasiocarpa soils compared to D. angustifolia soils. RCN in surface soil (0–10xa0cm, organic-rich “Lo” layer) was not significantly different from RCN in the entire profile (0–30xa0cm, “La layer”) of D. angustifolia wetland, while RCP and RNP were both significantly different between the Lo and La layers. In Carex lasiocarpa wetland, RCN, RCP and RNP in Lo layer were significant higher than those in La layer. RCNP in La layer of D. angustifolia and C. lasiocarpa wetlands were 65:5:1 and 163:13:1, respectively.ConclusionsSoil RCN was relatively consistent, while RCP and RNP reflected P limitation in wetlands of Sanjiang Plain. Further research is needed to determine whether these ratios hold among other wetland ecosystems.

Impacts of Agricultural and Reclamation Practices on Wetlands in the Amur River Basin, Northeastern China

Large-scale land reclamation, agricultural activities, and unsustainable practices in agricultural production have caused a lot of damage to natural wetlands in the Amur River Basin since the foundation of the People’s Republic of China. We studied several factors to address the conflicts between agricultural development and natural wetland conservation. We also investigated the effects of canalization, crop planting area, agricultural machinery and pesticides’ usage on the wetland environment. In 2010, the total area of natural wetlands was approximately 7.10u2009×u2009104xa0km2; this value was less than half the total area of natural wetlands in 1970. Canalization accompanied by land reclamation was identified as the main cause of the loss of natural wetlands. Binary regression analyses indicated that when the increments of ditches used by the state farms on the Sanjiang Plain increased by 1xa0km, or when the increment of cultivated land increased by 1xa0km2, the amount of natural wetland area lost was 0.227 and 0.557xa0km2, respectively. The influences of agricultural activities on wetlands were determined by assessing the main conflicts and providing suggestions to establish a new type of wetland-friendly green agriculture with a view to reduce negative impacts of agriculture on wetlands in the Amur River Basin.

Spatiotemporal Change of Vegetation Coverage and its Relationship with Climate Change in Freshwater Marshes of Northeast China

Based on the normalized difference vegetation index and climate data, this study investigated the spatiotemporal change of fractional vegetation cover (FVC) and its relationship with climate change in freshwater marshes of Northeast China from 2000 to 2016. Although freshwater marshes in Northeast China have undergone loss during the past nearly 20xa0years, the FVC of unchanged marshes has increased by 0.34% per year over the study area, with the largest increases in Songnen Plain. Correlation analysis results showed that warm growing season temperatures could enhance the FVC of marshes in the Greater and Lesser Khingan Mountains, but reduce the FVC in arid and semi-arid grassland regions of Songnen Plain and Eastern Inner Mongolia. By contrast, the increased growing season precipitation could significantly enhance the FVC of marshes in semi-arid grassland regions of Northeast China, but reduce the FVC of marshes in the Lesser Khingan Mountains and Sanjiang Plain. Under the background of future climate change, we can predict lower FVC of marshes in Songnen Plain and Eastern Inner Mongolia, but higher FVC of marshes in the Changbai Mountains in the future. This research is expected to provide valuable implications for the protection and restoration of wetland vegetation in Northeast China.

Niche modelling of marsh plants based on occurrence and abundance data

The information of species response (optimum or critical limits along environmental gradients) is a key to understanding ecological questions and to design management plans. A large number of plots (762) from 70 transects of 13 wetland sites in Northeast China were sampled along flooding gradient from marsh to wet meadow. Species response (abundance and occurrence) to flooding were modelled with Generalized Additive Models for 21 dominant plant species. We found that 20 of 21 species showed a significant response to flooding for the occurrence and abundance models, and four types of response were found: monotonically increasing, monotonically decreasing, skewed unimodal and symmetric unimodal. The species with monotonically increasing response have the deepest flooding optimum and widest niche width, followed by those with unimodal curve, and the monotonically decreasing ones have the smallest values. The optima and niche width (whether based on occurrence or abundance models) both significantly correlated with the frequency, but not with mean abundance. Abundance models outperformed occurrence models based on goodness of fit. The abundance models predicted a rather sharp shift from dominance of helophytes (Carex pseudo-curaica and C. lasiocarpa) to wet meadow species (Calamagrostis angustifolia and Carex appendiculata) if water levels drop from about 10cm above soil surface to below the surface. The defined optima and niche width based on the abundance models can be applied to better instruct restoration management. Given the time required to collect abundance data, an efficient strategy could be to monitor occurrence in many plots and abundance in a subset of these.

Distribution characteristics of iron, carbon, nitrogen and phosphorus in the surface soils of different land use types near Xingkai Lake

PurposeThe purpose of this study was to research the differences in iron, phosphorus, nitrogen and organic matter contents at two soil depths in areas with different land use types in the Xingkai Lake National Nature Reserve and to determine the causes of those differences. Additionally, this study sought to analyse the correlations between the contents of different nutrients and to determine the reasons for those correlations.Materials and methodsFive typical land use types, namely, lakeshore sandy land, grassland, forestland, dryland and wetland, were selected in the Xingkai Lake National Nature Reserve. The contents of amorphous iron (Feo), complexed iron (Fep), dithionite-extractable iron (Fed), total iron (TFe), total phosphorus (TP), total nitrogen (TN) and organic matter (OM) were measured in these soils at two depths: 0–5xa0cm (soil depth 1) and 5–10xa0cm (soil depth 2).Results and discussionFor soil depth 1 and soil depth 2, the land use type had no significant effect on the element contents. For the entire soil depth range (0–10xa0cm), the land use type had the most significant impact on the TP content (pu2009<u20090.01). Furthermore, soil depth had a significant effect on the contents of Feo (pu2009<u20090.01), TP (pu2009<u20090.01) and OM (pu2009<u20090.05). Overall, the element content at soil depth 2 was higher than that at soil depth 1. The interaction between land use type and soil depth significantly influenced the contents of TN and OM (pu2009<u20090.05). The contents of TN and OM in the lakeshore sandy land and dryland were high, and the contents of TN and OM were highly positively correlated (ru2009=u20090.90652, pu2009<u20090.01).ConclusionsDifferent land use types caused different degrees of disturbance in the soil, resulting in differences in the element contents in the soils. The differences in the distribution of soil element contents in the topsoil were the result of important natural and human factors.

Water use conflict between wetland and agriculture

To analyze the water use conflict and its driving factors between wetland and agriculture at both regional and local scales, agricultural water consumption and wetland water storage changes in the Sanjiang Plain, the main grain-producing area in Heilongjiang Province of Amur River Basin, were investigated based on statistical data, field survey and GIS calculation. A specific case study in the Qixing River National Nature Reserve (QNNR) wetland-farmland system was completed using a water balance approach. Results showed that the proportion of agricultural water increased from 71.8% to 88.0% while that of ecological water only hovered around approximately 1% in Heilongjiang Province during 2004-2015. Due to wetland loss and degradation, the total surface water storage in the Sanjiang Plain wetlands decreased from 14.46u202f×u202f109u202ft in the 1980s to 4.70u202f×u202f109u202ft in 2010. Agricultural development in successive years, and the dramatic increased requirement for water in paddy fields, intensified the water use conflict between wetlands in the QNNR and surrounding farmlands. Groundwater extraction for irrigation was approximately twice as high as the total infiltration recharge from wetlands and farmlands. It is concluded that the degraded natural water resource endowments are struggle to sustainably support stable grain production as a mainstay of national food safety, which determined the competitive relationship between wetland and agriculture. To mitigate this conflict, adaptive wetland (e.g. water transfer at stagger time, precise water recharge, resourced meltwater) and agricultural techniques (e.g. water-saving irrigation and planting, soil water capacity increment, rainfed agriculture) and five key management solutions were recommended.

Development of a multi-metric index based on aquatic invertebrates to assess floodplain wetland condition

The construction of levees breaks the connection of floodplains with river channels. Few assessments have examined the impacts on aquatic ecosystems. We developed a multi-metric index (MMI) based on aquatic invertebrates to assess floodplain wetland condition in the Wusuli River, northeastern China. We sampled the aquatic invertebrate communities in 18 floodplain wetlands along the Wusuli River including wetlands from headwater, middle river, and downstream reaches. Each site included paired wetlands with a wetland connected to the river floodplain and a wetland isolated from the floodplain by levees. Metrics related to the aquatic invertebrate community were selected as candidate metrics for the MMI. Then, a range test, discrimination analysis, and correlation analytics were used to select the candidate metrics based on their ability to distinguish reference and isolated wetlands. Four core indicators were selected to build the MMI: total number of taxa, %Gastropoda, Pielou’s index, and %Collector-Gatherers. Four ordinal rating categories were defined: poor, fair, good, and excellent condition. The results showed 88.9% of the levee-isolated wetlands, which were identified as being in poor or fair condition. Levee construction has a consistent negative impact on floodplain wetland condition. Our MMI provides a biomonitoring way to determine the success of restoration strategies.

Review of Rapid Transformation of Floodplain Wetlands in Northeast China: Roles of Human Development and Global Environmental Change

Northeast China is the region with the largest area of wetlands in China. The Sanjiang Plain and the Songnen Plain are large freshwater marsh distribution regions that are affected by climate warming and by the increasing frequency and density of extreme weather and are the regions most subject to disturbances by human activities in Northeast China. The wetlands of the Sanjiang Plain and the Songnen Plain have shrunk severely in the past 60 years, and wetland functions have been reduced substantially because of climate change, unreasonable land use, fire episodes, engineering and construction works and urbanization. Large-scale agricultural development started in the 1950s has been the most important driving factor for wetland loss and degradation in the Sanjiang Plain. Water shortage has been the most important factor for degradation and fragmentation of wetlands in the Songnen Plain. To mitigate wetland degradation and better protect wetlands, special regulations, long-term mechanisms and technical support of wetland protection should be established. A wetland compensation program should be implemented, and technologies for increasing the adaptive capacity of wetlands should be developed. Moreover, it is most important to find the balanced threshold between agricultural development and wetland protection.

Warming in Spring and Summer Lessens Carbon Accumulation over the Past Century in Temperate Wetlands of Northeast China

Deciphering how climate change affects carbon accumulation rates (Carbonsq) is vital to understanding climate-carbon pool feedbacks on century scales. Carbon, nitrogen, and phosphorus accumulation rates were estimated by isotopic 210Pb dating technology from 10 temperate wetlands in Northeast China. Soil carbon, nitrogen and phosphorus accumulated at average rates of 164.75 gC m−2xa0yr.−1, 5.61gN m−2xa0yr.−1, and 1.83gP m−2xa0yr.−1 during the past 153xa0years, respectively. Climate warming tended to grow increasing along the latitude and was faster in winter than in summer. Asymmetrical warming in spring and summer would lessen Carbonsq and oppose wetland functions as carbon sinks. High positive correlation coefficients between precipitation and Carbonsq meant that increasing precipitation facilitated Carbonsq greatly. Conversely, it was shown that warming in conjunction with subsequent drought was impairing Carbonsq in wetlands. There were strong positive feedbacks between climate warming and Carbonsq that could weaken wetlands functioning as carbon sinks in Northeast China.