Ground freeze-thaw processes have significant impacts on infiltration, runoff and evapotranspiration. However, there are still critical knowledge gaps in understanding of hydrological processes in permafrost regions, especially of the interactions among permafrost, ecology, and hydrology. In this study, an alpine permafrost basin on the northeastern Qinghai-Tibet Plateau was selected to conduct hydrological and meteorological observations. We analyzed the annual variations in runoff, precipitation, evapotranspiration, and changes in water storage, as well as the mechanisms for runoff generation in the basin from May 2014 to December 2015. The annual flow curve in the basin exhibited peaks both in spring and autumn floods. The high ratio of evapotranspiration to annual precipitation (>1.0) in the investigated wetland is mainly due to the considerably underestimated 'observed' precipitation caused by the wind-induced instrumental error and the neglect of snow sublimation. The stream flow from early May to late October probably came from the lateral discharge of subsurface flow in alpine wetlands. This study can provide data support and validation for hydrological model simulation and prediction, as well as water resource assessment, in the upper Yellow River Basin, especially for the headwater area. The results also provide case support for permafrost hydrology modeling in ungauged or poorly gauged watersheds in the High Mountain Asia.

Increased soil nutrient availability, and associated increases in vegetation productivity, could create a negative feedback between Arctic ecosystems and the climate system, thereby reducing the contribution of Arctic ecosystems to future climate change. To predict whether this feedback will develop, it is important to understand the environmental controls over nutrient cycling in High Arctic ecosystems and their impact on carbon cycling processes. Here, we examined the environmental controls over soil nitrogen availability in a High Arctic wet sedge meadow and how abiotic factors and soil nitrogen influenced carbon dioxide exchange processes. The importance of environmental variables was consistent over the 3 years, but the magnitudes of their effect varied depending on climate conditions. Ammonium availability was higher in warmer years and wetter conditions, while drier areas within the wetland had higher nitrate availability. Carbon uptake was driven by soil moisture, active layer depth, and variability between sampling sites and years (R2 = 0.753), while ecosystem respiration was influenced by nitrogen availability, soil temperature, active layer depth, and sampling year (R2 = 0.848). Considered together, the future carbon dioxide source or sink potential of high latitude wetlands will largely depend on climate-induced changes in moisture and subsequent impacts on nutrient availability. wetland, climate change

Under the background of climate change, freeze-thaw patterns tend to be turbulent: ecosystem function processes and their mutual feedback mechanisms with microorganisms in sensitive areas around the world are currently a hot topic of research. We studied changes of soil properties in alpine wetlands located in arid areas of Central Asia during the seasonal freeze-thaw period (which included an initial freezing period, a deep freezing period, and a thawing period), and analyzed changes in soil bacterial community diversity, structure, network in different stages with the help of high-throughput sequencing technology. The results showed that the alpha diversity of the soil bacterial community showed a continuous decreasing trend during the seasonal freeze-thaw period. The relative abundance of dominant bacterial groups (Proteobacteria (39.04%-41.28%) and Bacteroidota (14.61%-20.12%)) did not change significantly during the freeze-thaw period. At the genus level, different genera belonging to the same phylum dominated in different stages, or there were clusters of genera belonging to different phylum. For example, g_Ellin6067, g_unclassified_f_Geobacteraceae, g_unclassified_f_Gemmatimonadaceae coexisted in the same cluster, belonging to Proteobacteria, Desulfobacterota and Gemmatimonadota respectively, and their abundance increased significantly during the freezing period. This adaptive freeze-thaw phylogenetic model suggests a heterogeneous stress resistance of bacteria during the freeze-thaw period. In addition, network analysis showed that, although the bacterial network was affected to some extent by environmental changes during the initial freezing period and its recovery in the thawing period lagged behind, the network complexity and stability did not change much as a whole. Our results prove that soil bacterial communities in alpine wetlands are highly resistant and adaptive to seasonal freeze-thaw conditions. As far as we know, compared with short-term freeze-thaw cycles research, this is the first study examining the influence of seasonal freeze-thaw on soil bacterial communities in alpine wetlands. Overall, our findings provide a solid base for further investigations of biogeochemical cycle processes under future climate change.

Freezing and thawing profoundly affect soil carbon cycling. Under the influence of climate change, rising temperatures and glacier shrinkage in arid regions have increased the spring river supply to lakes. However, intense evaporation in summer and seasonal fluctuations in lake water levels alter the magnitude and direction of carbon emissions. Yet, the mechanisms of temperature and groundwater level factors on arid zone lake wetlands remain unclear. This study, through field monitoring, found that during soil freezing periods, Phragmites reduced emissions by 95.21% and increased emissions by 3.91% during thawing periods. Tamarix Chinensis and bare land exhibited a decrease in carbon uptake of 42.77% and 85.25% during soil freezing periods, and a decrease in carbon uptake of 41.98% and 2.17% during thawing periods. By constructing a freeze-thaw simulation device, we simulated CO2 emissions characteristics under different water level conditions during freeze-thaw processes, including water injection at 10 cm, 20 cm, 30 cm, 40 cm (corresponding to water levels 40 cm, 30 cm, 20 cm, 10 cm below the soil surface), as well as scenarios of anhydrous and flooding periods. The results showed that under freeze-thaw conditions, Phragmites exhibited the strongest carbon uptake when water was injected at 20 cm, transitioning from emissions during the anhydrous period to carbon uptake. Tamarix Chinensis exhibited the strongest carbon uptake during freeze-thaw cycles when water was injected at 10 cm, showing a 93.69% increase compared to the anhydrous period. Meanwhile, the bare land exhibited the strongest carbon uptake during freeze-thaw cycles in the no water period. Lower temperatures and higher water levels favor increased carbon uptake in lake wetlands. This study identifies optimal water levels for carbon uptake in lake wetlands during freeze-thaw, and the important role of water level and temperature conditions on carbon emissions, providing valuable insights for assessing the carbon feedback mechanisms in lake wetlands under future climate change.

Tropical high-Andean wetlands, locally known as 'bofedales', are key ecosystems sustaining biodiversity, carbon sequestration, water provision and livestock farming. Bofedales' contribution to dry season baseflows and sustaining water quality is crucial for downstream water security. The sensitivity of bofedales to climatic and anthropogenic disturbances is therefore of growing concern for watershed management. This study aims to understand seasonal water storage and release characteristics of bofedales by combining remote sensing analysis and ground-based monitoring for the wet and dry seasons of late 2019 to early 2021, using the glacierised Vilcanota-Urubamba basin (Southern Peru) as a case study. A network of five ultrasound loggers was installed to obtain discharge and water table data from bofedal sites across two headwater catchments. The seasonal extent of bofedales was mapped by applying a supervised machine learning model using Random Forest on imagery from Sentinel-2 and NASADEM. We identified high seasonal variability in bofedal area with a total of 3.5% and 10.6% of each catchment area, respectively, at the end of the dry season (2020), which increased to 15.1% and 16.9%, respectively, at the end of the following wet season (2021). The hydrological observations and bofedal maps were combined into a hydrological conceptual model to estimate the storage and release characteristics of the bofedales, and their contribution to runoff at the catchment scale. Estimated lag times between 1 and 32 days indicate a prolonged bofedal flow contribution throughout the dry season (about 74% of total flow). Thus, our results suggest that bofedales provide substantial contribution to dry season baseflow, water flow regulation and storage. These findings highlight the importance of including bofedales in local water management strategies and adaptation interventions including nature-based solutions that seek to support long-term water security in seasonally dry and rapidly changing Andean catchments.

Permafrost degradation by global warming is expected to alter the hydrological processes, which results in changes in vegetation species composition and gives rise to community succession. Ecotones are sensitive transition areas between ecosystem boundaries, attract particular interest due to their ecological importance and prompt responses to the environmental variables. However, the characteristics of soil microbial communities and extracellular enzymes along the forest-wetland ecotone in high-latitude permafrost region remain poorly understood. In this study, we evaluated the variations of soil bacterial and fungal community structures and soil extracellular enzymatic activities of 0-10 cm and 10-20 cm soil layers in five different wetland types along environmental gradients, including Larix gmelinii swamp (LY), Betula platyphylla swamp (BH), Alnus sibirica var. hirsute swamp (MCY), thicket swamp (GC), and tussock swamp (CC). The relative abundances of some dominant bacterial (Actinobacteria and Verrucomicrobia) and fungal (Ascomycota and Basidiomycota) phyla differed significantly among different wetlands, while bacterial and fungal alpha diversity was not strongly affected by soil depth. PCoA results showed that vegetation type, rather than soil depth explained more variation of soil microbial community structure. beta-glucosidase and beta-N-acetylglucosaminidase activities were significantly lower in GC and CC than in LY, BH, and MCY, while acid phosphatase activity was significantly higher in BH and GC than LY and CC. Altogether, the data suggest that soil moisture content (SMC) was the most important environmental factor contributing to the bacterial and fungal communities, while extracellular enzymatic activities were closely related to soil total organic carbon (TOC), nitrate nitrogen (NO3--N) and total phosphorus (TP).

In boreal regions, wildfires have a major impact on vegetation and permafrost. The ecosystem-protected Xing'an permafrost is sensitive to warming climate and wildfires, particularly on the southern margin of boreal coniferous forest and patchy permafrost zone. However, it remains unclear how fire disturbances are linked with changes in ecosystem composition and soil nutrients in the permafrost zones of Northeast China. Here, 13 years after the fire in the Yile'huli mountain knots, we investigated the parameters like vegetation cover, ground temperatures, active layer thickness, and soil carbon and nitrogen storage at burned and unburned sites of shrub wetlands. The fire resulted in ground warming of 0.1-5.0 degrees C at depths of 1.0-20.0 m and active layer deepening of 0.5 m, and gravimetric soil moisture content increasing of 26%-266%. Fire also increased the number of herbs and tall shrubs. After the fire, graminoids and tall shrubs increased significantly, and the species of herbs increased by five species. However, dwarf shrubs like Ledum palustre and Vaccinium uliginosum were missing from the burned site. A massive loss of total organic carbon (TOC) (248.40 t C/hm2) and nitrogen (TN) (11.87 t N/ hm2) was observed by comparing their storage at burned and unburned sites. These results highlighted that the post-fire responses of vegetation cover and TOC and TN storage were dependent on the thermal regimes of nearsurface permafrost and active layer, recovery of vegetation and organic layer, and soil moisture content. This study can provide an important reference for carbon storage and emission in boreal shrub wetlands under a warming climate and increasing fire disturbances.

Transpiration is a globally important component of evapotranspiration. Careful upscaling of transpiration from point measurements is thus crucial for quantifying water and energy fluxes. In spatially heterogeneous landscapes common across the boreal biome, upscaled transpiration estimates are difficult to determine due to variation in local environmental conditions (e.g., basal area, soil moisture, permafrost). Here, we sought to determine stand-level attributes that influence transpiration scalars for a forested boreal peatland complex consisting of sparsely treed wetlands and densely treed permafrost plateaus as land cover types. The objectives were to quantify spatial and temporal variability in stand-level transpiration, and to identify sources of uncertainty when scaling point measurements to the stand-level. Using heat ratio method sap flow sensors, we determined sap velocity for black spruce and tamarack for 2-week periods during peak growing season in 2013, 2017 and 2018. We found greater basal area, drier soils, and the presence of permafrost increased daily sap velocity in individual trees, suggesting that local environmental conditions are important in dictating sap velocity. When sap velocity was scaled to stand-level transpiration using gridded 20 x 20 m resolution data across the similar to 10 ha Scotty Creek ForestGEO plot, we observed significant differences in daily plot transpiration among years (0.17-0.30 mm), and across land cover types. Daily transpiration was lowest in grid-cells with sparsely treed wetlands compared to grid-cells with well-drained and densely treed permafrost plateaus, where daily transpiration reached 0.80 mm, or 30% of the daily evapotranspiration. When transpiration scalars (i.e., sap velocity) were not specific to the different land cover types (i.e., permafrost plateaus and wetlands), scaled stand-level transpiration was overestimated by 42%. To quantify the relative contribution of tree transpiration to ecosystem evapotranspiration, we recommend that sampling designs stratify across local environmental conditions to accurately represent variation associated with land cover types, especially with different hydrological functioning as encountered in rapidly thawing boreal peatland complexes.

Purpose Warming-induced permafrost degradation is anticipated to change the global carbon cycle. We attempted to determine the effect of permafrost degradation on carbon emissions and carbon sequestration of seven wetlands in three zones of Northeast China, aiming to investigate the responses of carbon sources/sinks to permafrost degradation. Methods Three zones (permafrost zone, PZ; discontinuous permafrost zone, DPZ; and permafrost degradation zone, PDZ) were selected to represent permafrost degradation stages. In each zone, we selected seven wetlands along the moisture gradient, namely, marsh (M), thicket swamp (TS), forested swamps (alder swamp, FAS; birch swamp, FBS; and larch swamp, FLS), forested fen (larch fen, FLF), and forested bog (larch bog, FLB). We determined the annual carbon emissions of soil heterotrophic respiration from seven wetlands and the annual net carbon sequestration of vegetation, evaluated the net carbon balance by calculating the difference between annual net carbon sequestration and annual carbon emissions, and then determined the magnitude and direction of carbon-climate feedback. Results and discussion With permafrost degradation, most forested wetlands (excluding FAS in PDZ) still acted as carbon sinks in DPZ (0.30 - 1.88 t ha(-1) year(-1)) and PDZ (0.31 - 1.76 t ha(-1) year(-1)) in comparison to PZ (0.46 - 2.43 t ha(-1) year(-1)). In contrast, M and TS acted as carbon sources in DPZ (-1.72 and -0.82 t ha(-1) year(-1)) and PDZ (-2.66 and -0.98 t ha(-1) year(-1)) in comparison to PZ (-0.86 and 0.03 t ha(-1) year(-1)), this result could be attributed to the increased CO2 emissions (promoted by warmer soil temperatures) and CH4 emissions (promoted by warmer soil temperatures, higher water tables and greater thaw depths), the two significantly increased the annual carbon emissions (increased by 8.8 - 14.4% in DPZ and by 35.0 - 46.0% in PDZ), and the annual carbon emissions > the annual net carbon sequestration. Furthermore, in terms of net radiative forcing, five forested wetlands still showed negative net radiative forcing in DPZ (-6.90 to -1.10 t CO2-eq ha(-1) year(-1)) in comparison to PZ (-8.91 to -1.62 t CO2-eq ha(-1) year(-1)). In contrast, in PDZ, only FLB showed negative net radiative forcing (-6.29 t CO2-eq ha(-1) year(-1)) and significantly increased by 288.3% compared to PZ (P < 0.05), indicating an ever-increasing net cooling impact, while the other four forested wetlands all turned into positive net radiative forcing (0.84 - 53.56 t CO2-eq ha(-1) year(-1)) because of higher CH4 (CO2-eq) emissions, indicating net warming impacts. Conclusions Our results indicated that permafrost degradation affected the carbon sources/sinks of seven wetlands via different mechanisms. M and TS acted as carbon sources in both DPZ and PDZ, while permafrost degradation did not change the overall direction of the net carbon balance of five forested wetlands. Most forested wetlands (excluding FAS in PDZ) still acted as carbon sinks in both DPZ and PDZ, although there were fluctuations in carbon sink values. Moreover, despite being carbon sinks, most forested wetlands (excluding FLB) in PDZ showed positive net radiative forcing compared to DPZ and PZ (negative net radiative forcing) when using the methodology of CO2 equivalent, indicating climatic warming impacts, while FLB showed negative net radiative forcing, indicating a climatic cooling impact. Therefore, FLB should be protected as a priority in the subsequent carbon sink management practices in permafrost zones.

Reactive iron (Fe) plays an important role in regulating soil organic carbon (SOC) biogeochemical cycles in different ecosystems. However, little is known about the factors which dominate the content of iron-bound organic carbon (OC-Fe) in permafrost wetland soils. In this study, we determined OC-Fe contents in permafrost wetland soils along the Yarlung Tsangbo River (YTR). The relations between the amount of OC-Fe and multiple environmental factors, including soil water content (SWC), element contents (SOC, total iron, manganese, and chromium), and pyrolysis products of SOM, were explored. The concentrations of OC-Fe ranged between 0.01 and 3.61% and it accounted for 11.3 +/- 7.7% of the SOC pool. The percentage of organic carbon attached to iron in SOC (f(OC-Fe)) in subsoils (13.16 +/- 1.01%) was significantly higher than that of the topsoils (9.41 +/- 0.77%, p < 0.01). Notably, SOC, Fe, and SWC were dominating factors affecting the content of OC-Fe, while the degree of importance of them was different in topsoils and subsoils. It suggested that the increase of SWC could enhance more SOC bounded by per unit iron in subsoils than in topsoils. The f(OC-Fe) was correlated with different factors in topsoils and subsoils. Aromatic compounds were the most important factor affecting f(OC-Fe), and aromatics could be selectively preserved by iron oxides in the soil. The results of this study demonstrate that SWC and molecular factors of SOC may have larger importance in controlling carbon stability than expected previously.