Changes in bacterial communities during rice cultivation remove phenolic constraints on peatland carbon preservation.

Northern peatlands contain ~30% of terrestrial carbon (C) stores, but in recent decades, 14% to 20% of the stored C has been lost because of conversion of the peatland to cropland. Microorganisms are widely acknowledged as primary decomposers, but the keystone taxa within the bacterial community regulating C loss from cultivated peatlands remain largely unknown. In this study, we investigated the bacterial taxa driving peat C mineralization during rice cultivation. Cultivation significantly decreased concentrations of soil organic C, dissolved organic C (DOC), carbohydrates, and phenolics but increased C mineralization rate (CMR). Consistent with the classic theory that phenolic inhibition creates a "latch" that reduces peat C decomposition, phenolics were highly negatively correlated with CMR in cultivated peatlands, indicating that elimination of inhibitory phenolics can accelerate soil C mineralization. Bacterial communities were significantly different following peatland cultivation, and co-occurrence diagnosis analysis revealed substantial changes in network clusters of closely connected nodes (modules) and bacterial keystone taxa. Specifically, in cultivated peatlands, bacterial modules were significantly negatively correlated with phenolics, carbohydrates, and DOC. While keystone taxa Xanthomonadales, Arthrobacter, and Bacteroidetes_vadinHA17 can regulate bacterial modules and promote carbon mineralization. Those observations indicated that changes in bacterial modules can promote phenolic decomposition and eliminate phenolic inhibition of labile C decomposition, thus accelerating soil organic C loss during rice cultivation. Overall, the study provides deeper insights into microbe-driven peat C loss during rice cultivation and highlights the crucial role of keystone bacterial taxa in the removal of phenolic constraints on peat C preservation.

Biological interactions control bacterial but not fungal ß diversity during vegetation degradation in saline-alkaline soil.

The patterns and mechanisms by which soil bacterial and fungal community ß-diversity respond to vegetation degradation in saline-alkaline soils are currently not clear, and in particular, the role of biotic interactions is relatively unknown. To investigate the assembly of bacterial and fungal communities in topsoil (0-10 cm) in saline-alkaline soils at different stages of vegetation degradation, the ß-Mean Nearest Classification Unit Distance, the ß-Nearest Taxon Index, and the Raup-Crick index were calculated. The relative importance of biotic and environmental factors in controlling ß diversity under deterministic processes was also quantified by using relative importance analyses. The ß diversity of soil bacterial and fungal communities responded differently in different stages of vegetation degradation in saline-alkaline soils, with bacterial ß diversity increasing with increasing vegetation degradation but fungal ß diversity showing few differences. Deterministic processes regulated soil bacterial community assembly, and biotic factors were important in driving changes in ß diversity, whereas both deterministic and stochastic processes were essential in soil fungal community assembly, and environmental factors were important in affecting fungal ß diversity. Furthermore, fungal ß diversity is far more affected by interactions between fungus and bacteria than bacteria. Our study demonstrates the different effects of vegetation degradation on bacterial and fungal communities in saline soils to provide the overall implications for saline soils microorganisms in deteriorating ecosystems.

Lignite-steel slag constructed wetland with multi-functionality and effluent reuse.

Constructed wetlands (CWs) are widely used to treat wastewater, while innovative studies are needed to support resource conservation, enhance multi-functionality, and improve the effectiveness of effluent usage. This study assessed the potential of CW's multiple functions by combining low-rank coal (lignite) and industrial waste (steel slag) in different configurations as CW substrates. The results of scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and metagenomic sequencing showed that the experimental treatment with lignite and steel slag mixtures had the highest multi-functionality, including efficient nutrient removal and carbon sequestration, as well as hydroponic crop production. Lignite and steel slag were mixed to form lignite-steel slag particle clusters, where Ca2+ dissolved on the surface of steel slag was combined with PO43- in wastewater to form Ca3(PO4)2 precipitation for phosphorus removal. A biofilm grew on the surface of lignite in this cluster, and OH- released from steel slag promoted lignite to release fulvic acid, which provided a carbon source for heterotrophic microorganisms and promoted denitrification. Moreover, fulvic acid enhanced carbon sequestration in CWs by increasing the biomass of Phragmites australis. The effluent from lignite-steel slag CW increased cherry tomato yield and quality while saving N and P applications. These results provide new ideas for the "green" and economic development of CW technology.

Agricultural land use regulates the fate of soil phosphorus fractions following the reclamation of wetlands.

Over half of the Earth's wetlands have been reclaimed for agriculture, leading to significant soil P destabilization and leaching risks. To evaluate the effects of agricultural land use on soil P stability, we used sequential P extraction to investigate the long-term effects of wetland cultivation for rice and soybean on soil P fractions, including labile and moderately labile inorganic/organic P (LPi, LPo, MPi, and MPo), and stable P in Northeast China. The results showed that soybean cultivation decreased the total P by 35.9 %, whereas rice cultivation did not influence the total P content (p < 0.05). Both the soybean and rice cultivations significantly increased LPi (p < 0.05). Soybean cultivation significantly decreased the LPo and MPo compared to rice cultivation, and the latter increased MPi by 309.28 % compared with the reference wetlands (p < 0.05). Redundancy analysis indicated that pH, poorly crystalline Fe (Feca), crystalline Fe (Fec), and total organic carbon (TOC) explained similar variations in P fractions during soybean and rice cultivation (54.9 % and 49.7 %, respectively). Similarly, during soybean or rice cultivation, pH negatively influenced LPo and MPo, while Feca positively influenced MPi and LPi. Furthermore, TOC showed a positive role in LPo, and MPo, but a negative effect on LPi and MPi during rice cultivation. Hence, we concluded that the cultivation of soybean or rice create contrasting modifications to wetland soil P fractionation by altering TOC, Feca, Fec, and pH. Our study indicates that agricultural land use can regulate the fate of wetland soil P fractionation, with potential benefits to both i) P risk management in cultivated wetlands and ii) potential approaches for future wetland restoration.

Wetland soil organic carbon balance is reversed by old carbon and iron oxide additions.

Iron (Fe) oxides can stabilize organic carbon (OC) through adsorption and co-precipitation, while microbial Fe reduction can disrupt Fe-bound OC (Fe-OC) and further increase OC mineralization. The net effects of OC preservation and mineralization mediated by Fe oxides are still unclear, especially for old carbon (formed from plant litters over millions of years) and crystalline Fe oxides. Accelerating the recovery of wetland carbon sinks is critical for mitigating climate change and achieving carbon neutrality. Quantifying the net effect of Fe-mediated OC mineralization and preservation is vital for understanding the role of crystalline Fe oxides in carbon cycling and promoting the recovery of soil carbon sinks. Here, we explored the OC balances mediated by hematite (Hem) and lignite addition (Lig) to freshwater wetland (FW, rich in C and Fe) and saline-alkaline wetland (SW, poor in C and Fe) soil slurries, incubated under anaerobic conditions. Results showed that Lig caused net OC accumulation (FW: 5.9 ± 3.6 mg g-1; SW: 8.3 ± 3.2 mg g-1), while Hem caused dramatic OC loss, particularly in the FW soils. Hem inhibited microbial Fe(III) reduction by decreasing the relative abundance of Fe respiration reducers, while substantially enhancing OC mineralization through the shift in the microbial community structure of FW soils. Lig resulted in carbon emission, but its contribution to preservation by the formation of Fe-OC was far higher than that which caused OC loss. We concluded that crystalline Fe oxide addition solely favored the increase of OC mineralization by adjusting the microbial community structure, while old carbon enriched with an aromatic and alkyl promoted Fe-OC formation and further increased OC persistence. Our findings could be employed for wetland restoration, particularly for the recovery of soil carbon sinks.

A healthier water use strategy in primitive forests contributes to stronger water conservation capabilities compared with secondary forests.

Water conservation is an important ecological function of forest ecosystems, plant water use strategy is a key factor in regulating forest ecosystem water balance. However, there are still insufficient studies on the water conservation capacity and water use strategies of different forest types, especially in climate-sensitive areas. In this study, we determined the stable isotope values (δD, δ18O and d-excess) of plant water, soil water and precipitation from two typical stand types (primary forest and secondary forest) on Changbai Mountain to reveal plant water use and evaluated the water conservation capacity. The results indicated that rainwater infiltrated into the soil combined with piston flow and preferential flow in the primary forest, and preferential flow was the only form of flow in the secondary forest. The main tree species in the primary forest formed a relatively stable water use niche. Among them, the water use pattern of Quercus mongolica Fisch. ex Ledeb (Qm.) was transformed between shallow and deep soil layers with strong ecological plasticity. The dominant species in secondary forest derived water from similar soil layers with intense interspecific competition. By comparing the water use patterns, the secondary forest conformed to the hypothesis of "two water worlds", while the primary forest conformed to the hypothesis of one reservoir. The primary forest ecosystem had stronger water conservation capacity than secondary forest ecosystem due to the regulable water use strategies of plants and the stable water conservation capacity of the soil. These results will provide theoretical support and a reference for plan future forest management strategies in the climate-sensitive areas.

Combined effects of multi-land use decisions and climate change on water-related ecosystem services in Northeast China.

Land use intensification and climate change have resulted in substantial changes in the provision of ecosystem services, particularly in China that experienced sharp increases in population growth and demands for goods and energy. To protect the environment and restore the degraded ecosystems, the Chinese government has implemented multiple national ecological restoration projects. Yet, the combined effects of climate change and land use and land cover change (LULCC) over large spatial scales that brace multiple land use decisions and great environmental heterogeneity remain unclear. We assessed the combined effects of LULCC and climate change on water-related ecosystem services (water provision and soil conservation services) from 1990s to 2020s in Northeast China using the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model. We found that water yield decreased by 9.78% and soil retention increased by 30.51% over the past 30 years. LULCC and climate change exerted negative effects on water yield whereas they both enhanced soil retention; LULCC interacted with climate change to have relatively small inhibitory effects on water yield and large facilitation effects on soil retention. Changes in water yield were mainly attributed to climate change, while soil retention was largely influenced by LULCC and its interaction with climate change. Our research highlights the importance of land use decisions and its interactive effects with climate change on ecosystem services in a heavily disturbed temperate region, and provides important information to inform future land management and policy making for sustaining diverse ecosystem services and ensuring human wellbeing.

Geographical Distribution of Iron Redox Cycling Bacterial Community in Peatlands: Distinct Assemble Mechanism Across Environmental Gradient.

Microbial-mediated iron (Fe) oxidation and reduction greatly contribute to the biogeochemistry and mineralogy of ecosystems. However, knowledge regarding the composition and distribution patterns of iron redox cycling bacteria in peatlands remains limited. Here, using high-throughput sequencing, we compared biogeographic patterns and assemblies of the iron redox cycling bacterial community between soil and water samples obtained from different types of peatland across four regions in Northeast China. A total of 48 phylotypes were identified as potential iron redox bacteria, which had greater than 97% similarity with Fe(II)-oxidizing bacteria (FeOB) and Fe(III)-reducing bacteria (FeRB). Among them, Rhodoferax, Clostridium, Geothrix, Sideroxydans, Geobacter, Desulfovibrio, and Leptothrix could be used as bioindicators in peatlands for characterizing different hydrological conditions and nutrient demands. Across all samples, bacterial communities associated with iron redox cycling were mainly affected by pH, dissolved organic carbon (DOC), and Fe2+. Distance-decay relationship (DDR) analysis indicated that iron redox cycling bacterial communities in soil, but not in water, were highly correlated with geographic distance. Additionally, null model analysis revealed that stochastic processes substituted deterministic processes from minerotrophic fens to ombrotrophic bogs in soils, whereas deterministic processes were dominant in water. Overall, these observations suggest that bacteria involved in iron redox cycling are widespread in diverse habitats and exhibit distinct patterns of distribution and community assembly mechanisms between soil and water in peatlands.

Anthropogenic disturbances caused declines in the wetland area and carbon pool in China during the last four decades.

Wetlands are among the natural ecosystems with the highest soil carbon stocks on Earth. However, how anthropogenic disturbances have impacted the quantity and distribution of wetland carbon pool in China is not well understood. Here we used a comprehensive countrywide wetland inventory and Landsat 8 data to document the spatial patterns in China's wetland areas and carbon pools and to understand the underlying causes of their changes from the 1980s to 2010s. We found that the wetland area and carbon pool have decreased from 4.11 × 105  km2 and 15.2 Pg C in the 1980s to 2.14 × 105  km2 and 7.6 Pg C in the 2010s, respectively. Using the human influence index (HII) as a quantitative measure of anthropogenic disturbance intensity, we found a positive relationship between the HII values and wetland decreases in many regions and across China as a whole-which have increased 17% during the time period-indicating that anthropogenic disturbances have been a major factor causing wetland destruction in recent decades. This study provides new evidence for recent changes in China's wetland carbon pool and emphasizes the importance of mitigating anthropogenic disturbances for wetland conservation.

Wetland plant litter decomposition occurring during the freeze season under disparate flooded conditions.

To investigate the heterogeneity of plant litter decomposition in the freeze and freeze-free seasons and the responses to disparate flooded conditions in seasonally frozen wetlands, in situ simulation experiments of litter decomposition were performed in the Sanjiang Plain, Northeast China. The experiments were conducted using the litter bag method for representative plants, Carex lasiocarpa and Calamagrostis angustifolia, in both non-flooded and flooded areas between November 2011 and November 2013. Heterogeneous effects of the freeze season and its interaction with hydrological regimes on the decomposition of the litter of various species and organs were observed. The litter decomposition occurred during the freeze season and made a significant contribution to the loss throughout the year. The two-year mass-loss of C. lasiocarpa and C. angustifolia and their organs were ordered differently between the freeze season and the freeze-free season. The proportion of litter mass-loss during the freeze season accounting for the whole year in the flooded area were greater than that in the non-flooded area, except for the C. angustifolia root litter. The litter mass-losses of entire C. lasiocarpa and C. angustifolia during the freeze season were greater than those during the freeze-free season in the flooded area, while the pattern was opposite in the non-flooded area. The effect of environmental factors on litter decomposition might override the effects of litter substrate quality. The total N and P of the litter of the entire C. lasiocarpa and entire C. angustifolia increased significantly relative to the initial values after two years and tended to enrich more in the litter under flooded conditions than under non-flooded conditions. The results highlighted the heterogeneous effects of the freeze season and its interaction with hydrological regimes on various species and organs, which would provide management and restoration options for degraded wetlands caused by climate change.

Ecological aesthetic assessment of a rebuilt wetland restored from farmland and management implications for National Wetland Parks.

While wetlands are usually used as a natural approach to remove biodegradable pollutants in surface water, their purification efficiencies coupled with their aesthetic features are of less concern. The water quality, plant landscape, acoustic environment and odour indicators were investigated in the surface water inlet and outlet of the Fujin National Wetland Park (FNWP), restored from farmlands in Northeast China. Major concentrations of pollutants in the inlet and the outlet subjected to surface flow wetland treatment were monitored, and the removal efficiencies were calculated based on 54 water samples (6 sites×3 seasons×3 replicates). The results showed that the total nitrogen (TN) and organic carbon in surface water decreased significantly after the wetland treatment, while the total phosphorus (TP) did not decrease significantly. The removal efficiencies for TN and BOD5 changed seasonally and reached 69.08% and 60.44%, respectively. An ecological aesthetic index (EAI) was developed based on the trophic state index coupled with plant landscape, acoustic and odour indicators, and the calculated EAI showed that the outlet delivered a more aesthetically harmonious appearance than the inlet in spring and autumn, but not in summer. Based on the current aquatic macrophyte species and documented purification efficiencies in FNWP, we recommend an improved ecological aesthetic management approach that utilizes and arranges diverse native plants from the surrounding wetlands (e.g. Scirpus validus) in addition to local Nelumbo nucifera, Nymphaea tetragona and Myriophyllum spicatum, and conserves the indicative and endangered species (Aldrovanda vesiculosa), from the visual appeal of the waterscape.

Comparative analyses of wetland plant biomass accumulation and litter decomposition subject to in situ warming and nitrogen addition.

The effects of climate warming on boreal wetland plant structure and carbon (C) sequestration on local scale may be overestimated. An in situ passive warming experiment manipulated by open-top chambers and artificial nitrogen (N) addition was deployed in a lacustrine wetland of Xingkai Lake for 3 consecutive years. The annual changes and allocations of the aboveground biomass of Glyceria spiculosa, and decomposition dynamics of the total litter and cotton strips as standard references were observed. Results showed that the aboveground biomass was significantly affected by warming and increased from 99.43 ±â€¯10.59 g m-2 (ambient) to 112.02 ±â€¯8.08 g m-2 (ca. +1 °C) and 117.21 ±â€¯9.92 g m-2 (ca. +2 °C). N addition had a more positive effect on the annual aboveground biomass accumulations than warming, for the relative importance weights of N addition were 2.60 and 1.49 times greater than warming in 2011 and 2013 respectively. Their main effects on the allocations had significant interannual variations, and their interaction effects were dependent on organ and year. The decomposition constant (k-value) of the litter and cotton strips were 0.747 yr-1 and 2.057 yr-1, respectively. Compared to warming and N addition, the internal quality characterized by Lignocellulose index and soil organisms reflected by litterbag size played overwhelming role in decomposition dynamics, with 2 orders greater of relative importance weights in 2011 and 2012. Our results highlight the importance of interannual variation for differentiating the contributions of external and internal factors to boreal wetland plant biomass accumulation and decomposition. Given the asymmetric responses of accumulation and decomposition, the C storage in the litter would increase in long term.

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 14.46 × 109 t in the 1980s to 4.70 × 109 t 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.

Thin ferrihydrite sediment capping sequestrates phosphorus experiencing redox conditions in a shallow temperate lacustrine wetland.

Synthesized ferrihydrite (Fh) with the dosages of 0.3, 0.6 and 0.9 cm thickness (labeled as Fh, 2Fh and 3Fh respectively, equivalent to 248-774 g/m2) were deployed to serve as the reactive capping layer covering the Ornamental Lake sediments, the Royal Botanic Garden of Melbourne. The sediments were exposed to an alternating regime of oxic/anoxic conditions using laboratory reactors for 45 days. Dynamics of dissolved oxygen (DO), pH, filterable reactive phosphorus (FRP), filterable ammonium (NH4+), nitrate and nitrite (NOx), total dissolved nitrogen (TDN) and dissolved iron (Fe) of overlying water were examined. After incubation, O2 and H2S profiles across the water-sediment interface were observed with microelectrodes. The element distributions in the upper sediments were tested as well. Results showed that DO and pH kept relatively stable during oxic period, while decreased significantly during anoxic period. Fh cappings decreased both DO and pH, and inhibited the release of FRP. No significant increments of FRP in overlying waters were observedduring anoxic period. Fh cappings prompted the releases of NH4+ and TDN, while inhibited that of NOx.NH4+increased while NOx decreased during anoxic period. Fe(II) and TFe increased only in 3Fh, especially during anoxic conditions. Fh cappings increased O2 and H2S concentrations across the water-sediment interfaces. TP and TN in the sediments decreased after capping, while TFe increased significantly. We concluded that 0.6 cm thickness of (496 g/m2) Fh capping could sequestrate P, even experiencing redox conditions.

[Effects of Canalization on the Iron Deposition in Sanjiang Plain].

Canalization is the representative process and landscape of wetland reclamation. A typical ditch system of four levels near the Honghe National Nature Reserve in Sanjiang Plain was selected. Deposition plates were set on the sediments along the ditch level and the remained natural wetland nearby was quantitatively sampled for two years as the control. The deposition fluxes, total iron concentration, iron oxides and their components, as well as biogenic elements in the sediments collected by deposition plates were measured. The results showed that the litter, mud/sand and total deposition fluxes showed no significant differences between different ditch levels, with the means of (57.00 ± 16.90) g x (m2 x a)(-1), (3 997.57 ± 798.98) g x (m2 x a)(-1) and (4054.57 ± 792.91) g x (m2 x a)(-1), respectively. The litter flux decreased with the increase of ditch level, and the flux in the natural wetland [ (120.26 ± 19.42) g x (m2 x a)(-1) ] was significantly greater than that of the ditches. The mud/sand [ (35.41 ± 11.15 ) g x (m2 x a)(-1)] and total deposition fluxes [ (155.67 ± 20.75) g x ( m2 x a](-1) ] were significantly smaller than those of the ditches. There were no significant differences in the total iron between different ditches and natural wetland, while the free iron oxide content in the ditch sediments was significantly lower than that of natural wetland sediment. Except for the main ditch, the amorphous and complex iron oxides in the other ditch and natural wetland sediments showed no significant differences. The free degree of the iron oxide in ditch sediments was 60.2% of that in the natural wetland, while the differences in the complex degree and the activated degree were insignificant. The differences in the total organic carbon, total nitrogen and total phosphorus were insignificant, and all were smaller than those of the natural wetland, with the percentages of 14.6%, 31.6% and 41.0%, respectively. It could be concluded that the effects of canalization on iron and biogenic elements were significant. Consequently, rational agricultural water managements are strongly recommended to avoid the potential environmental and ecological risks caused by canalization in Sanjiang Plain.

Response of two dominant boreal freshwater wetland plants to manipulated warming and altered precipitation.

This study characterized the morphological and photosynthetic responses of two wetland plant species when they were subject to 2-6 °C fluctuations in growth temperature and ± 50% of precipitation, in order to predict the evolution of natural wetlands in Sanjiang Plain of North-eastern China. We investigated the morphological and photosynthetic responses of two dominant and competitive boreal freshwater wetland plants in Northeastern China to manipulation of warming (ambient, +2.0 °C, +4.0 °C, +6.0 °C) and altered precipitation (-50%, ambient, +50%) simultaneously by incubating the plants from seedling to senescence within climate-controlled environmental chambers. Post-harvest, secondary growth of C. angustifolia was observed to explore intergenerational effects. The results indicated that C. angustifolia demonstrated a greater acclimated capacity than G. spiculosa to respond to climate change due to higher resistance to temperature and precipitation manipulations. The accumulated effect on aboveground biomass of post-harvest secondary growth of C. angustifolia was significant. These results explain the expansion of C. angustifolia during last 40 years and indicate the further expansion in natural boreal wetlands under a warmer and wetter future. Stability of the natural surface water table is critical for the conservation and restoration of G. spiculosa populations reacting to encroachment stress from C. angustifolia expansion.

Surface sediments in the marsh-sandy land transitional area: sandification in the western Songnen Plain, China.

The development of sandification process was studied, by monitoring the changes of sediment characteristics, at marsh-sandy land intersections in China's Songnen region. A series of sediment collection plates were deployed in the region; after one year, sediments in these plates were analyzed for changes of mass and chemical characteristics. The sediment flux and the sand content of the sediments decreased with the increasing longitudinal distance between the sampling site and the centre line of a sand dune. The mean sediment flux was 29 ± 14 kg m(-2) yr(-1) and 0.6 ± 0.3 kg m(-2) yr(-1) in the sandy land and marsh, respectively. Strong, positive correlations were found between the concentrations of organic matter, total nitrogen, P, Fe, Ti, V and Zr, all of which were also negatively correlated with the sand content. The concentrations of organic matter, total nitrogen, P, Fe, Ti, V and Zr in the marsh sediment samples were all significantly greater than the corresponding concentrations of the sandy land (p<0.001). Sand content and Ti, V and Zr concentrations all proved to be valid indicators of sandification intensity, and they showed that the marsh could be divided into three distinct zones. Sand expansion extended about 88 m into the marsh. The mean sand content in the sediments of the sandy land was 91% and then 64% in the marsh, which in turn was higher than that of marshes outside the influence of sandification, suggesting that the marsh in the marsh-sandy land transitional area has already undergone extensive sandification in the past. The study results provide information on the wetland's function of indicating and buffering the sandification process.

[DNDC model, a model of biogeochemical processes: Research progress and applications].

Denitrification-decomposition (DNDC) model can estimate the emission fluxes of soil trace gases such as carbon dioxide (CO2), methane (CH4) , and nitrous oxide (N2O) via the coupling of the denitrification and decomposition processes driven by soil environmental factors. At present, DNDC model is one of the most successful models in the world in simulating the terrestrial biogeochemical cycles. This paper mainly reviewed the development process of the DNDC model, its structure, model validation, and sensitive factor analysis, and summarized the hot fields in the applications of the model.

[Effect of reclamation on the vertical distribution of SOC and retention of DOC].

Contents and density of soil organic carbon (SOC) in soil profiles and dissolved organic carbon (DOC) of soil solution in different soil depths in wetland, soybean and paddy field reclaimed from the wetland around Xingkai Lake were determined to investigate how reclamation of wetland for soybean and rice farming impacts vertical distribution of SOC and retention of DOC. SOC contents in 0-40 cm soil layers were significantly influenced. SOC contents in 0-10, 10-20, 20-30 and 30-40 cm soil layers in soybean and paddy field were 79.07% and 82.01%, 79.01% and 82.28%, 79.86% and 92.90%, 37.49% and 78.05% respectively lower than those in wetland. Before and after reclamation, SOC contents in soil layers deeper than 40 cm were not significantly different. SOC densities in soybean and paddy field were 25.50% and 47.35% respectively lower than those in wetland. However, either in wetland or farm land, most of the SOC storage in 0-100 cm soil layer was stored in 0-50 cm soil layer. The relationships between SOC content and soil depth in wetland and two farm lands all could be described by exponential functions; cultivation did not change the variation of SOC content with soil depth. The retention of DOC was more obvious for soybean farming than wetland and rice farming, and that was roughly the same for wetland as rice farming.

[Waterborne iron migration by groundwater irrigation pumping in a typical irrigation district of Sanjiang Plain].

The iron concentration in groundwater, iron's seasonal migration from groundwater to sun-basked pools, paddy fields and drainage canals, and its distribution in the sediments/soils were observed in the Jiansanjiang Branch Bureau, Heilongjiang Agricultural Cultivation Bureau. The results suggested that the total iron mass concentration of the studied area was (1.73 +/- 0.41) mg x L(-1), ranging from 0.01 to 11.4 mg x L(-1), with the variation coefficient of 1.29%. The annual iron input mass from groundwater to paddy fields and other surface water bodies was 4 976.40 t in 2010, according to the rice planting area and rating irrigation volume. Dissolved Fe2+, Fe3+ and iron, as well as the total iron (dissolved and particle) had seasonal variation, with greater values presented in June and July. These waterborne irons in paddy field waters were greater than those in sun-basked pools and drainage canals. Obvious enrichment effect was observed in sun-basked pools and paddy fields, with their total iron mass concentrations were 6.17 and 21.65 times greater than that in groundwater. Either the total iron or iron oxides in sun-baked pool sediments were greater than that in paddy field soils, field canal and main canal sediments. The differences of the total iron and iron oxides in paddy field soils, field canal and main canal sediments were not significantly different. Considerable irons were precipitated within sun-basked pools and paddy fields during the transfer from groundwater to surface water, with a part of irons exporting into canals through drainage and then precipitated there. Not only the change of total iron mass, but the transformation of iron chemical speciation was observed during the transfer, which was affected by paddy irrigation management directly. The long-term irrigation pumping could cause the substantial enrichment of iron in paddy soils and canal sediments, resulting in the increase of potential pollution risk.