Persistence of fertilization effects on soil organic carbon in degraded alpine wetlands in the Yellow River source region

In the restoration of degraded wetlands,fertilization can improve the vegetation-soil-microorganisms complex,thereby affecting the organic carbon content.However,it is currently unclear whether these effects are sustainable.This study employed Biolog-Eco surveys to investigate the changes in vegetation characteristics,soil physicochemical properties,and soil microbial functional diversity in degraded alpine wetlands of the source region of the Yellow River at 3 and 15 months after the application of nitrogen,phosphorus,and organic mixed fertilizer.The following results were obtained:The addition of nitrogen fertilizer and organic compost significantly affects the soil organic carbon content in degraded wetlands.Three months after fertilization,nitrogen addition increases soil organic carbon in both lightly and severely degraded wetlands,whereas after 15 months,organic compost enhanced the soil organic carbon level in severely degraded wetlands.Structural equation modeling indicates that fertilization decreases the soil pH and directly or indirectly influences the soil organic carbon levels through variations in the soil water content and the aboveground biomass of vegetation.Three months after fertilization,nitrogen fertilizer showed a direct positive effect on soil organic carbon.However,organic mixed fertilizer indirectly reduced soil organic carbon by increasing biomass and decreasing soil moisture.After 15 months,none of the fertilizers significantly affected the soil organic carbon level.In summary,it can be inferred that the addition of nitrogen fertilizer lacks sustainability in positively influencing the organic carbon content.

Isotopic evidence for soil water sources and reciprocal movement in a semi-arid degraded wetland:Implications for wetland restoration

Understanding water dynamics is a prerequisite for the restoration of degraded ecosystems in arid and semiarid regions.In this study,we carried out δD and δ^(18)O analyses of precipitation,unsaturated soil water,overland flow,surface runoff,and groundwater samples from a seasonally flooded wetland in the Momoge National Nature Reserve of the Songnen Plain,Northeast China,to identify the water sources and understand the mechanisms of unsaturated soil water movement.Unsaturated soil water content(W/W%)at every 20 cm along with a soil profile(0–100 cm)was collected during the growing season,and the HYDRUS-1D model was used to simulate temporal-spatial variations.The results showed that the local meteoric water line(δD=5.90δ18O-7.34,R2=0.95)had a smaller slope and intercept than the global meteoric water line because of strong evaporation at our study site under semi-arid climate.The groundwater was partly recharged by local precipitation via overland flow and unsaturated soil water infiltration.Unsaturated soil water was sourced from both precipitation and groundwater with variations at different depths.The upper soil layer at 0–15 cm was mainly sourced from limited precipitation,while the groundwater could move up to a 25 cm layer during the dry period.The unsaturated soil water content increased with soil depth in the top 40 cm,decreased at depths of 40 to 80 cm,and increased again at depths of 80 to 100 cm.The HYDRUS-1D model could simulate the unsaturated soil water dynamics well in the upper(0–40 cm)and lower(80–100 cm)sections,but poorly for depths of 40–80 cm due to the upward and downward flow.The bidirectional unsaturated soil water movement highlights the importance of capillary groundwater for wetland plants with similar climatic or hydrogeological conditions.

Mapping and understanding degradation of alpine wetlands in the northern Maloti-Drakensberg, southern Africa

The alpine terrestrials of the Maloti-Drakensberg in southern Africa play crucial roles in ecosystem functions and livelihoods,yet they face escalating degradation from various factors including overgrazing and climate change.This study employs advanced Digital Soil Mapping(DSM)techniques coupled with remote sensing to map and assess wetland coverage and degradation in the northern Maloti-Drakensberg.The model achieved high accuracies of 96%and 92%for training and validation data,respectively,with Kappa statistics of 0.91 and 0.83,marking a pioneering automated attempt at wetland mapping in this region.Terrain attributes such as terrain wetness index(TWI)and valley depth(VD)exhibit significant positive correlations with wetland coverage and erosion gully density,Channel Network Depth and slope were negative correlated.Gully density analysis revealed terrain attributes as dominant factors driving degradation,highlighting the need to consider catchment-specific susceptibility to erosion.This challenge traditional assumptions which mainly attribute wetland degradation to external forces such as livestock overgrazing,ice rate activity and climate change.The sensitivity map produced could serve as a basis for Integrated Catchment Management(ICM)projects,facilitating tailored conservation strategies.Future research should expand on this work to include other highland areas,explore additional covariates,and categorize wetlands based on hydroperiod and sensitivity to degradation.This comprehensive study underscores the potential of DSM and remote sensing in accurately assessing and managing wetland ecosystems,crucial for sustainable resource management in alpine regions.

Ecological Restoration of Degraded Wetlands in China

Natural wetland is one of the most important ecosystems on the earth. However, the natural wetlands in China suffered great loss and degradation due to the rapid growth of human population and economy, together with the long-term over-exploitation. Therefore, improving and restoring wetlands＇ various functions, such as slowing the runoff, flood control and drought prevention, water purification and restoring and rebuilding wetlands in the appropriate geographical places are the pressing issues human face today. Based on the fundamental concepts of the wetland restoration, this article expounded its principles and guidelines, illustrated three basic modes, and summarized the main goal and basic strategy in China. Finally the assessment and future trends of the wetland restoration were discussed.

Restoration and Rational Use of Degraded Saline Reed Wetlands:A Case Study in Western Songnen Plain, China

The protection, restoration and sustainable use are key issues of all the wetlands worldwide. Ecological, agronomic, and engineering techniques have been integrated in the development of a structurally sound, ecologically beneficial engineering restoration method for restoring and utilizing a degraded saline wetland in the western Songnen Plain of China. Hydrological restoration was performed by developing a system of biannual irrigation and drainage using civil engineering measures to bring wetlands into contact with river water and improve the irrigation and drainage system in the wetlands. Agronomic measures such as plowing the reed fields, reed rhizome transplantation, and fertilization were used to restore the reed vegetation. Biological measures, including the release of crab and fish fry and natural proliferation, were used to restore the aquatic communities. The results of the restoration were clear and positive. By the year 2009, the reed yield had increased by 20.9 times. Remarkable ecological benefits occurred simultaneously. Vegetation primary-production capacity increased, local climate regulation and water purification enhanced, and biodiversity increased. This demonstration of engineering techniques illustrates the basic route for the restoration of degraded wetlands, that the biodiversity should be reconstructed by the comprehensive application of engineering, biological, and agronomic measures based on habitat restoration under the guidance of process-oriented strategies. The complex ecological system including reeds, fish and crabs is based on the biological principles of coexistence and material recycling and provides a reasonable ecological engineering model suitable for the sustainable utilization of degraded saline reed wetlands.

Growth and Physiological Response of Organs of Phragmites australis to Different Water Compensation in Degraded Wetlands

To study the effect of different water compensation on growth and physiology of reed in degraded wetlands,three water treatments in the field were conducted to test the height and photosynthesis of reed,the ions and soluble sugar contents of different organs.In the controls(without extra water compensation for 10 years),the height of reed was only 50 cm,the net photosynthetic rate,stomatal conductance,the intercellular CO2 concentration and transpiration rate were very low.The contents of Na + and Clin rhizome were higher than those in other organs.Discontinuous water compensation(continuous for 8 years,then stopped for 2 years)increased the height(2.1-fold),the net photosynthetic rate(41.8%),stomatal conductance(1.8-fold),transpiration rate(1.3-fold)of reed(Phragmites australis),and decreased the content of Na + (62.3%)and Cl- (71.1%)of rhizome significantly.Continuous water compensation(continuous for 10 years)increased the height(3.2-fold),the net photosynthetic rate(104%),stomatal conductance(2.4-fold),transpiration rate(1.5-fold)of reed,and decreased Na + (82.5%)and Cl - (64.7%)contents in rhizome, then accumulated the K+ ,H2PO4-,SO42- and soluble sugar contents significantly in rhizome.Interrupting water compensation led to the decrease of height(25.3%),the net photosynthetic rate(30.7%),stomatal conductance(17.3%) and increase of Na + (1.16-fold)in rhizome when comparing to the continuous water compensation.These results showed that recovering the degraded reed wetlands needed continuous water compensation yearly to promote reed growth.The organs of reed had corresponding physiological response characteristic to the different water compensation condition.Under long-time dry and waterlogging condition,the rhizomes both helped reed to adapt located environment,by enriching the ions such as Na+ ,Cl- ,and K+ ,H2PO4-,SO42- ,respectively.

Soil remediation of degraded coastal saline wetlands by irrigation with paper mill effluent and plowing

Combined with anti-waterlogging ditches, irrigation with treated paper mill effluent （TPME） and plowing were applied in this study to investigate the effects of remediation of degraded coastal sa- line-alkaline wetlands. Three treatments were employed, viz., control （CK）, irrigated with 10 cm depth of TPME （I）, and plowing to 20 cm deep before irrigating 10 cm depth ofTPME （IP）. Results show that both I-treatment and IP-treatment could improve soil structure by decreasing bulk density by 5% and 8%. Irrigation with TPME containing low salinity stimulated salts leaching instead of accumulating. With anti-waterlogging ditches, salts were drained out of soil. Irrigation with 10 cm depth of TPME lowered total soluble salts in soil and sodium adsorption ration by 33% and 8%, respective!y, but there was no significant difference compared with CK, indicating that this irrigation rate was not heavy enough to remarkably reduce so!l salinity and sodicity, Thus, in-i： gation rate should be enhanced in order to reach better effects of desalinization and desodication. Irrigation with TPME significantly increased soil organic matter, alkali-hydrolyzable nitrogen and available phosphorus due to the abundant organic matter in TPME. Plowing increased soil air circulation, so as to enhance mineralization of organic matter and lead to the loss of organic matter; however, plowing significantly improvedsoil alkali-hydrolyzable nitrogen and available phosphorus. Improvements of physicochemical properties in I-treatment and IP-treatment both boosted soil microbial population and activity. Microbial biomass carbon increased significantly by 327% （I-treatment） and 451% （IP-treatment）, while soil respiration increased significantly by 316% （I-treatment） and 386% （IP-treatment）. Urease and dehydrogenase activities in both I-treatment and IP-treatment were significantly higher than that in CK. Phosphatase in IP-treatment was significantly higher than that in CK. Compared to I-treatment, IP-treatment improved all of the soil properties except for soil organic matter. The key to remediation of degraded sa- line-alkaline wetlands is to decrease soil salinity and sodicity; thus, irri- gation plus plowing could be an ideal method of soil remediation.

Degradation of Wetlands on the Qinghai-Tibet Plateau:A Comparison of the Effectiveness of Three Indicators

The Qinghai-Tibet Plateau encompasses a large quantity of wetlands, some of which have been degraded to varying severity levels. In the literature, a number of degradation indicators have been proposed to evaluate ecological health of wetlands, but their effectiveness in the plateau environment remains unknown. In this study, we assessed the effectiveness of three degradation indicators, soil moisture content at lo em deep, vegetative cover, and density of pika burrows. The degradation severity of wetlands in Maduo County on the Qinghai-Tibet Plateau is enumerated at four levels, intact, slight, moderate and severe. Analysis of xo6 samples collected in the field demonstrates that the density of pika burrows is the least reliable indicator. By comparison, vegetative cover and underlying soil moisture content are more reliable, even though neither is a perfect indicator as the difference among adjacent levels of severity as revealed by t-test is not always statistically significant. The imperfection of vegetative cover as an indicator is due to its variation among different types of wetlands. The limitation of moisture content is attributed to its non-linear relationship with wetland degradation. Above the threshold of about 50% in moisture content wetlands are unlikely to be degraded. It is recommended that moisture be measured at the point near the surface and vegetative cover be further differentiated by species in order to improve their effectiveness.

Soil Cellulase Activity and Fungal Community Responses to Wetland Degradation in the Zoige Plateau, China

Four soil types(peat, marsh, meadow, and sandy) in the Zoige Plateau of China are associated with the severity of wetland degradation. The effects of wetland degradation on the structure and abundance of fungal communities and cellulase activity were assessed in these 4 soil types at 3 depths using DGGE(Denatured Gradient Gel Electrophoresis), q PCR(Quantitative Real-time PCR),and 3,5-dinitrosalicylic acid assays. Cellulase activity and abundance of the fungal community declined in parallel to the level of wetland degradation(from least to most disturbed). DGGE analysis indicated a major shift in composition of fungal communities among the4 soil types consistent with the level of degradation.Water content(WC), organic carbon(OC), total nitrogen(TN), total phosphorus(TP), available nitrogen(AN), and available phosphorus(AP) were strongly correlated with cellulase activity and the structure and abundance of the fungal community.The results indicate that soil physicochemical properties(WC, OC, TN, TP, AN, and AP), cellulase activity, and diversity and abundance of fungal communities are sensitive indicators of the relative level of wetland degradation. WC was the major factorinvolved in Zoige wetland degradation and lower WC levels contributed to declines in the abundance and diversity of the fungal community and reduction in cellulase activity.

Soil Carbon, Nitrogen and Phosphorus Concentrations and Stoichiometries Across a Chronosequence of Restored Inland Soda Saline-Alkali Wetlands, Western Songnen Plain, Northeast China

Soil carbon(C), nitrogen(N) and phosphorus(P) concentrations and stoichiometries can be used to evaluate the success indicators to the effects of wetland restoration and reflect ecosystem function. Restoration of inland soda saline-alkali wetlands is widespread, however, the soil nutrition changes that follow restoration are unclear. We quantified the recovery trajectories of soil physicochemical properties, including soil organic carbon(SOC), total nitrogen(TN), and total phosphorus(TP) pools, for a chronosequence of three restored wetlands(7 yr, 12 yr and 21 yr) and compared these properties to those of degraded and natural wetlands in the western Songnen Plain, Northeast China. Wetland degradation lead to the loss of soil nutrients. Relative to natural wetlands, the mean reductions of in SOC, TN, and TP concentrations were 89.6%, 65.5% and 52.5%, respectively. Nutrients recovered as years passed after restoration. The SOC, TN, and TP concentrations increased by 2.36 times, 1.15 times, and 0.83 times, respectively in degraded wetlands that had been restored for 21 yr, but remained 29.2%, 17.3%, and 12.8% lower, respectively, than those in natural wetlands. The soil C∶N(RC N), C∶P(R CP), and N∶P(R NP) ratios increased from 5.92 to 8.81, 45.36 to 79.19, and 7.67 to 8.71, respectively in the wetland that had been restored for 12 yr. These results were similar to those from the natural wetland and the wetland that had been restored for 21 yr(P > 0.05). Soil nutrients changes occurred mainly in the upper layers(≤ 30 cm), and no significant differences were found in deeper soils(> 30 cm). Based on this, we inferred that it would take at least 34 yr for SOC, TN, and TP concentrations and 12 yr for RC N, R CP, and RN P in the top soils of degraded wetlands to recover to levels of natural wetlands. Soil salinity negatively influenced SOC(r =-0.704, P < 0.01), TN(r =-0.722, P < 0.01), and TP(r =-0.882, P < 0.01) concentrations during wetland restoration, which indicates that reducing salinity is beneficial to SOC, TN, and TP recovery. Moreover, plants were an important source of soil nutrients and vegetation restoration was conducive to soil nutrient accumulation. In brief, wetland restoration increased the accumulation of soil biogenic elements, which indicated that positive ecosystem functions changes had occurred.

Responses of soil inhabiting nitrogen-cycling microbial communities to wetland degradation on the Zoige Plateau,China

The wetlands on the Zoige Plateau have experienced serious degradation,with most of the original marsh being converted to marsh meadow or meadow.Based on the 3 wetland degradation stages,we determined the effects of wetland degradation on the structure and relative abundance of nitrogencycling(nitrogen-fixing,ammonia-oxidizing,and denitrifying) microbial communities in 3 soil types(intact wetland:marsh soil;early degrading wetland:marsh meadow soil;and degraded wetland:meadow soil) using 454-pyrosequencing.The structure and relative abundance of nitrogen-cycling microbial communities differed in the 3 soil types.Proteobacteria was the predominant phylum in most soil samples but the most abundant soil nitrogenfixing and denitrifying microbial bacteria differed at the class,order,family,and genus levels among the 3soil types.At the genus level,the majority of nitrogenfixing bacterium sequences related to Bradyrhizobium were from marsh and marsh meadow soils;whereas those related to Geobacter originated from meadow soil.The majority of ammonia-oxidizing bacterium sequences related to Nitrosospira were from marsh(except for the 40-60 cm layer),marsh meadow and meadow soils;whereas those related to Candidatus Solibacter originated from 40-60 cm layer of marsh soil.The majority of denitrifying bacterium sequences related to Candidatus Solibacter and Anaeromyxobacter were from marsh and meadow soils;whereas those related to Herbaspirillum originated from meadow soil.The distribution of operational taxonomic units(OTUs)and species were correlated with soil type based upon Venn and Principal Coordinates Analysis(PCoA).Changes in soil type,caused by different water regimes were the most important factors influencing compositional changes in the nitrogen-fixing,ammonia-oxidizing,and denitrifying microbial communities.

Effects of diet shift on the gut microbiota of the critically endangered Siberian Crane

Wetlands worldwide have suffered from serious degradation and transformation,leading to waterbirds increasingly dependent on agricultural fields for feeding.Although gut microbiota is an essential component of host health,the impacts of agricultural feeding on gut microbial community and pathogen transmission remain poorly understood.To fill this knowledge gap,we used 16S rRNA sequencing to characterize the fecal bacterial community of the Siberian Crane(Grus leucogeranus),a Critically Endangered species,that recently has shifted its foraging from largely Vallisneria tubers in Poyang Lake natural wetlands to crops(i.e.,rice seeds and lotus rhizomes) in agricultural fields.We compared the bacterial communities between tuber foraging cranes and crop foraging cranes.Our results indicate that diet shift greatly modified the gut microbiota diversity,composition and function.Crop foraging cranes had higher microbiota diversity than tuber foraging cranes.The alteration in microbiota composition and function were correlated with change in food nutrition.Tuber(i.e.,high in fiber)foraging cranes were enriched in Clostridiaceae with fiber digestion ability,and crop(i.e.,high in carbohydrate)foraging cranes were enriched in bacterial taxa and functions related to carbohydrate metabolism.The flexibility of gut microbiota might enhance Siberian Cranes’ ability to adapt to novel diet and environment.However,many enriched families in crop foraging cranes were pathogenic bacteria,which might increase the susceptibility of cranes to pathogenic infection.Special caution should be taken to agricultural feeding waterbirds in Asia,where the widespread poultry-keeping in over-harvested rice fields might increase the transmission probability of pathogenetic bacteria among wild birds,domestic poultry and humans.

Quantifying land degradation in the Zoige Basin,NE Tibetan Plateau using satellite remote sensing data

Considerable efforts have been dedicated to desertification research in the arid and semi-arid drylands of central Asia. However,there are few quantitative studies in conjunction with proper qualitative evaluation concerning land degradation and aeolian activity in the alpine realm. In this study,spectral information from two Landsat-5 TM scenes(04.08.1994 and 28.07.2009,respectively) was combined with reference information obtained in the field to run supervised classifications of eight landscape types for both time steps. Subsequently,the temporal and spatial patterns of the alpine wetlands/grasslands evolutions in the Zoige Basin were quantified and assessed based on these two classification maps. The most conspicuous change is the sharp increase of ~627 km^2 degraded meadow. Concerning other land-covers,shallow wetland increases ~107 km^2 and aeolian sediments(mobile dunes and sand sheets) have an increase of ~30 km^2. Considering the deterioration,an obvious decrease of ~440 km^2 degraded wetland can be observed. Likewise,decrease of deep wetland(~78 km^2),humid meadow(~80 km^2) and undisturbed meadow(~88 km^2) were determined. These entire evolution matrixes undoubtedly hint a deteriorating tendency of the Zoige Basin ecosystem,which is characterized by significantly declined proportion of intact wetlands,meadow,rangeland and a considerable increase ofdegraded meadow and larger areas of mobile dunes. In particular,not only temporal alteration of the landcover categories,the spatial and topographical characteristics of the land degradation also deserves more attention. In the alpine rangelands,the higher terraces of the river channels along with their slopes are more liable to the degradation and desertification. This tendency has significantly impeded the nomadic and agriculture activities. The set of anthropozoogenic factors encompassing enclosures,overgrazing and trampling,rodent damaging and exceedingly ditching in the wetlands are assumed to be the main controlling mechanisms for the landscape degradation. A suite of strict protection policies is urgent and indispensable for self-regulation and restoration of the alpine meadow ecosystem. Controlling the size of livestock,less ditching in the rangeland,and the launching of a more strict nature reserve management by adjacent Ruoergai,Maqu and Hongyuan Counties would be practical and efficacious in achieving these objectives.

Process analysis and mitigation strategies for wetland degradation caused by increasing agricultural water demand:an ecology-economy nexus perspective

Background Farmland expansion has played a major role in wetland degradation in Heilongjiang Province,China in recent decades.Farmland expansion increases the demands for water,thereby affecting wetland water cycles,and promoting the shrinkage of wetland areas and degradation of ecosystem functions.As an open system,agricultural production is limited by both ecological and socioeconomic conditions.However,our understanding of wetland degradation caused by farmland expansion from the perspective of the ecology-economy nexus is limited.Methods A correlation between farmland expansion and agricultural economic activities was established,and wetland degradation driven by agroeconomic activities was inversely derived using a multi-regional input-output(MRIO)analysis.We developed an ecology-economy nexus framework to explore the ecological process of the area and water demand tradeoffs between wetland degradation and farmland expansion,the economic process of wetland degradation driven by food consumption,and the nexus between the two processes.We finally explored strategies to mitigate wetland degradation due to increased agricultural water demand.Results Farmland expansion contributed to 93.76%of the total degraded wetland area.There was a significant negative correlation between wetland area and the water consumption for crop production,but no significant correlation between wetland area and the ecological footprint of croplands.The direct wetland degradation caused by local final demand accounted for 63.02%,while the indirect degradation caused by non-local final demand accounted for 36.98%.Hebei,Shandong,Liaoning,Inner Mongolia,and Shanghai were the top five provinces contributing to indirect wetland degradation in Heilongjiang.Our findings indicated that a mixed scenario combining water footprint reduction per unit yield with food export reduction could maximize wetland restoration while reducing local farmland-wetland competition for water.Conclusions Our research highlights the effects of economic processes in the agricultural sector on wetland degradation,and showed that the adjustment of food trade patterns can effectively promote wetland restoration.

Re-recognition of the Dajiuhu Wetland in Shennongjia Mountains,Central China

The Dajiuhu wetland,a famous sub-alpine wetland located in the the Shennongjia Mountains,north-subtropical region of Central China,has suffered from adverse impacts of unsustainable human practices over the past 60 years.The Dajiuhu wetland reflects the development process that has been accompanied by human activities.Based on field survey data,high resolution remote sensing image and historical records,the present paper provided a review on exploitation and restoration of the wetland.The results showed that the Dajiuhu wetland degraded quickly from 1950 to 2005.During that time,bog shrinkage,lake disappearance,biodiversity decline,sphagnum reduction,and vegetation succession from wetland communities to terrestrial communities in the Dajiuhu wetland,which were the main manifestations of the wetland degradation.Human activities,such as agricultural reclamation and construction of drainage works,have been the main factors resulting in ecological degradation of the wetland since 1986.Poverty and the short-term economic benefits had been the driving forces for wetland drainage and reclamation over the past years.