Hydrological Changes Research Articles

Late and Final Neolithic Land Use Reconstructions Based on Floodplain Deposits from the ‘Nachtweide’ Site in Hesse, Central Germany – a Challenge for Palynology

ABSTRACTThis study reconstructs land use history with a focus on the Late and Final Neolithic using palynological data from floodplain deposits in the state of Hesse, central Germany. Our results demonstrate that humans were using the surrounding landscape continuously from the onset of the Michelsberg culture to the transition to the Bronze Age. However, a noticeable decline in human impact was shown during the transitional stage between the Michelsberg and Wartberg cultures. During this time, changes in the floodplain environment were noted that correlate with other floodplain pollen records from the region and supra-regional climate signals, thus providing other possible drivers for this socio-cultural change in addition to the factors coming from the archaeological side. Due to its location in the peripheral uplands of the Wetterau, the economy at the ‘Nachtweide’ site was based primarily on forest pasturing. However, cereal cultivation was also important. In contrast, no evidence was found for the use of open land for grazing during the Late Neolithic and only sporadic evidence for such use during the Final Neolithic. Our study also shows that, changes in land use were accompanied by hydrological changes within the floodplain and/or changes in the river dynamics.

Core microbiota play important roles in maintaining soil multi‐nutrient cycling in lakeshore wetland of plateau lake Caohai

AbstractMicroorganisms play important roles in soil biogeochemical processes, but the relative contributions of different microbial members in soil nutrient cycling and community maintenance are unclear especially in wetland soils with water‐level fluctuation. Here, soil samples, collected from severe inundation zone (SIZ), wet–dry cycling zone (WIZ), and arid zone (NIZ) of the lakeshore wetland of plateau lake Caohai, were used to investigate the relative contributions of core and rare taxa in maintaining nutrient cycling and their associations with microbial network. Results showed that WIZ exhibited higher extracellular enzyme activities including β‐1,4‐N‐acetylglucosaminidase, L‐leucine aminopeptidase, and acid phosphatase, the level of multi‐nutrient cycling and core microbial diversity compared with the NIZ and SIZ. The values of topological features (i.e., links, average degree, clustering coefficient, and graph density) were also higher in the WIZ compared with the NIZ and SIZ. Moreover, the core taxa, specifically their community structures, were the most important driver for multi‐nutrient cycles of wetland soil. Among these taxa, Sphingomonas, Bradyrhizobium, Mortierella, and Fusarium as the most abundant taxa in lakeshore wetlands were significantly positively correlated with most extracellular enzymes. By contrast, rare taxa showed higher degree and its subnetwork complexity than those of core taxa, which potentially serve as the species pool of core taxa to maintaining the microbial community stability. In conclusion, our study suggested that core taxa play dominant roles in soil nutrient cycles, while rare microbiota could greatly influence microbial interaction under hydrological changes.

Intra-annual stable isotopes in the tree rings of Hymenaea courbaril as a proxy for hydroclimate variations in southern Amazonia

The hydrology of Amazonia is changing due to climate and land-use changes, especially in the southern region, which has warmed and dried faster than other tropical regions. Yet there are no long-term hydrological records to put these changes in a historical perspective. Here we investigate the use of tree-ring carbon (δ13C) and oxygen isotopes (δ18O) to assess the seasonal variation in climate for the southern Amazonia basin. We analysed the intra-annual variation of δ13C and δ18O in 10 segments of each tree ring from 2013 to 2017 from individuals of Hymenaea courbaril, a long-lived and widespread neotropical tree species. We find strong seasonal patterns of tree-ring δ13C supporting previous observations of annual growth rhythms for this species. The intra-annual variation in δ18O shows that the lowest values generally occur just after the middle point of ring formation, corresponding to the peak rainy season. We find strong correlations between the δ18O in the middle of the growth ring and vapour pressure deficit (r = 0.92, P = 0.02) and precipitation (r = −0.93, P = 0.02). We further find associations between the oxygen isotopic series and the discharge of the Araguaia basin’s main rivers during the rainy period. Our results show that these δ18O records are sensitive to fluctuations in rainfall and humidity, and thus to river discharge in the region. Longer reconstructions of based on tree-ring δ18O of Hymenaea courbaril could provide a novel proxy to assess past hydrological changes.

Phytoplankton primary production in Chascomus pond (Provincia de Buenos Aires, Argentina)

In situ phytoplankton primary production in Chascomús pond (eutrophic Pampasic “laguna”) was studied by the oxygen method (light and dark bottle) between.January 1984-January 1985. Valúes obtained ranged from37,9 to 981,6 mg C • m-1 • d-1. Factors influencing it, as suspended particulate matter and hydrological changes, are discussed. Parallel determinations of the artificial light photosynthesis response proved to be useful,almostqualitatively under the experimental conditions applied, to follow the behaviour obtained by incubations in natural environment.

The importance of explicitly representing the streambed in watershed models

AbstractThe streambed is the critical interface between the aquatic and terrestrial systems and hosts important biogeochemical hot spots within river corridors. Although the streambed characteristics are significantly different from those of its surrounding soil, the streambed itself has not been explicitly represented in watershed models. Here, we explicitly incorporated a streambed layer into an integrated hydrologic model through model parameterization and discretization. We examined the hydrological effects of streambed characteristics, including hydraulic conductivity (K), layer thickness, and resolution, on the exchange fluxes across the streambed as well as the streamflow at the watershed outlet. The numerical experiments were performed in the American River Watershed, a headwater, mountainous watershed within the Yakima River Basin in central Washington. Despite having a negligible effect on the watershed streamflow, an explicit representation of the streambed with distinctive properties dramatically changed the magnitude and variability of the exchange flux. In general, a larger streambed K along with a thicker streambed layer induced larger exchange fluxes. The exchange flux was most sensitive to the streambed resolution. A finer streambed resolution increased exchange fluxes per unit area while reducing the overall exchange volumes across the entire streambed. The amount of baseflow decreased by 6% as the streambed resolution increased from 250 to 50 m. This finding is important because these hydrological changes may, in turn, affect the exchange of nutrients and contaminants between surface water and groundwater and the associated biogeochemical processes. Our work demonstrated the importance of representing streambeds in fully distributed, process‐based watershed models to better capture the exchange flow dynamics in river corridors.

An improved methodology for quantifying the impact of human activities on hydrological drought change

Study regionUpper Shiyang River in the eastern Qilian Mountains, China. Study focusQuantifying the impacts of anthropogenic and climate change on wet and dry hydrological variability was done by improving the Slope Change Ratio of Cumulative Quantities (ISCRCQ) method. New hydrological insights for the regionThe scientific method is critical to quantify the driving factors of dry-wet hydrological changes. In this study, the slope change ratio of cumulative quantity (SCRCQ) method was improved to quantify the impacts of human activities and climate change on dry-wet hydrological changes. The results show a hydrological aridification trend at an annual scale from 1961 to 2016 in the upper reaches of the Shiyang River. However, the dry-wet hydrological change trends of the six tributaries differed: the hydrological humidification of the four western tributaries was apparent, while the remaining tributaries showed hydrological aridification. The influences of human activities and climate change on dry-wet hydrological changes were also evidently distinct in the different tributaries. Changing in climate is a vital factor triggering the dry-wet hydrological changes in the western tributaries, while human activities have completely changed the direction of the dry-wet hydrological changes and intensified the hydrological aridification in the eastern tributaries. Human activities have resulted in an increase both in the frequency of droughts and in the risk of socio-economic droughts. Thus, human activities in the region of eastern tributaries should be controlled within reasonable limits.

Temporal and Spatial Pattern Change in Evapotranspiration Over the High Plains: The Impact of and Guide on Extensive Groundwater‐Fed Irrigation

AbstractAquifer depletion due to extensive and intensive irrigation in the High Plains has threatened the environmental sustainability of the region. The change of crop evapotranspiration (ET), the major form of agriculture water consumption, presents a critical signature of hydrologic cycle change. This study evaluates the relative contributions of climate and groundwater‐fed irrigation to ET temporal and spatial pattern change over the High Plains Aquifer, one of the most severely depleted aquifers in the US. We developed a framework to extend the Budyko hypothesis to assess the impact of catchment storage change on long‐term ET. It is found that irrigation from groundwater pumping contributes more than half of the increase in ET (74.1 mm) from the period of 1940–1975 to 1976–2010, despite an increase of precipitation (35.0 mm) in the region. ET seasonal variance is decreased by the decline in precipitation variability (at −20.7 mm) and increase in irrigation (at +14.2 mm). As expected, irrigation decreases ET coefficient of variability (i.e., the ratio of standard deviation to mean). Spatially, we find that the human‐induced ET heterogeneity post‐1975 superimposes over the natural east‐to‐west gradient (in precipitation and ET) of this region. A correlation between the statistics (mean vs. coefficient of variation) on ET and crop yield provides promising signatures for understanding the coupled natural and human system of High Plains agriculture. Guides are discussed regarding how to handle the tradeoffs between agricultural development and natural resource sustainability under climate variability in the High Plains and other regions with similar conditions.

Diagnosing Mechanisms of Hydrologic Change under Global Warming in the CESM1 Large Ensemble

Abstract Global warming is expected to cause significant changes in the pattern of precipitation minus evaporation (P − E), which represents the net flux of water from the atmosphere to the surface or, equivalently, the convergence of moisture transport within the atmosphere. In most global climate model simulations, the pattern of P − E change resembles an amplification of the historical pattern—a tendency known as “wet gets wetter, dry gets drier.” However, models also predict significant departures from this approximation that are not well understood. Here, we introduce a new method of decomposing the pattern of P − E change into contributions from various dynamic and thermodynamic mechanisms and use it to investigate the response of P − E to global warming within the CESM1 Large Ensemble. In contrast to previous decompositions of P − E change, ours incorporates changes not only in the monthly means of atmospheric winds and moisture, but also in their temporal variability, allowing us to isolate the hydrologic impacts of changes in the mean circulation, transient eddies, relative humidity, and the spatial and temporal distributions of temperature. In general, we find that changes in the mean circulation primarily control the P − E response in the tropics, while temperature changes dominate at higher latitudes. Although the relative importance of specific mechanisms varies by region, at the global scale departures from the wet-gets-wetter approximation over land are primarily due to changes in the temperature lapse rate, while changes in the mean circulation, relative humidity, and horizontal temperature gradients play a secondary role.

Body condition as a descriptor of American alligator (Alligator mississippiensis) health status in the Greater Everglades, Florida, United States.

Body condition is used as an indicator of the degree of body fat in an animal but evidence of its actual relationship with health diagnostics (e.g., blood parameters) is usually lacking across species. In American alligators (Alligator mississippiensis), body condition has been used as a performance metric within the Greater Everglades ecosystem to provide insight on hydrological and landscape changes on alligator populations. However, there is no clear evidence that spatial body condition changes relate to different health conditions (low food intake vs sickness) and whether this link can be made when relating body condition values with blood parameters. We assessed the relationship between alligator body condition and 36 hematological and biochemistry (blood) parameters in four areas across two physiographic regions (Everglades and Big Cypress) of the Greater Everglades (sample size = 120). We found very strong to weak evidence of linearity between 7 (Big Cypress) and 19 (Everglades) blood parameters and relative condition factor index, from which cholesterol (38%) and uric acid (41%) for the former and phosphorus (up to 52%) and cholesterol (up to 45%) for the latter (mean absolute error MAE = 0.18 each) were the predictors that individually explain most of the body condition variation. The best combination of blood parameters for the Everglades were cholesterol, phosphorus, osmolality, total protein, albumin, alpha 2, beta, and gamma globulins, and corticosterone accounting for 40% (37 ± 21%, MAE = 0.16) of the variation found in alligator body condition for this region. We found better predictability power in models when analyzed at smaller rather than larger scales showing a potential habitat effect on the body condition-blood parameters relationship. Overall, Everglades alligators in poorer condition are likely dehydrated or have an inadequate diet and the spatial differences found between physiographic regions suggest that these areas differ in prey availability/quality.

Road crossings change functional diversity and trait composition of stream-dwelling macroinvertebrate assemblages

Functional diversity is regarded as a key concept in understanding the link between ecosystem function and biodiversity, and is therefore widely investigated in relation to human-induced impacts. However, information on how the intersection of roads and streams (hereafter road crossings, representing a widespread habitat transformation in relation to human development), influences the functional diversity of stream-dwelling macroinvertebrates is still missing. The general aim of our study was to provide a comprehensible picture on the impacts of road crossing structures on multiple facets of the functional diversity of stream-dwelling macroinvertebrates. In addition, we also investigated changes in trait structure. Our research showed that road crossing structures had negative impacts on functional richness and dispersion; i.e., functional diversification. However, we found no significant impact on functional divergence and evenness components. We found a decrease in functional redundancy at road crossing structures. This indicates a reduced ability of the community to recover from disturbances. Finally, we found that road crossings drive stream habitat and hydrological changes in parallel with modification of the trait composition of stream-dwelling macroinvertebrate assemblages. All these results suggest that road crossings cause notable changes in the functional diversity of stream-dwelling macroinvertebrate assemblages.

Development of multivariate standardized drought index for large lake basins based on the copula function: A case study of Hongze Lake Basin, China

Study regionThe Hongze Lake Basin, China. Study focusA drought index is an essential tool for monitoring and prediction, and the construction of a comprehensive drought index is at the cutting edge of current drought research. Considering the regulation effect of lakes, a new drought index aimed at large lake catchment areas, namely the Multivariate Standardized Drought Index for Lakes Basin (MSDILB), can comprehensively characterise meteorological and hydrological drought. Here, the Standardised Precipitation Evapotranspiration Index (SPEI), Standardised Runoff Index (SRI), and MSDILB drought indices were used to evaluate the evolution of drought in the study area. Moreover, the response and conversion relationships between the basin’s hydro-meteorological elements and the regulation of the lake were explored. New hydrological insights for the RegionThe results indicate that: 1) in a dry year, the spatial-temporal heterogeneous runoff in the basin is redistributed by the storage and regulation of large lakes, thereby reducing the frequency of drought events; 2) the MSDILB drought index merges the characteristics of hydrological drought and meteorological drought indices and can monitor the evolution of drought events in lake basins; 3) the MSDILB drought index can sensitively capture the effects of lake hydrological regime change on drought events in the basin. Thus, it has the advantage of comprehensively characterising the drought conditions in large lake basins.

Spatio-temporal variability of streamflow in major and medium rivers of Nepal

Study regionWe selected six (three on each) major and medium river basins of Nepal as a study domain for the analysis. The study areas were so selected that they represent the river basins across the country from East (Kankai basin) to West (Karnali basin). Study focusThis study focuses on the long-term hydrologic alteration in the river flow of Nepal's medium and major rivers of different river basins. The overarching objective of the study is to evaluate the spatio-temporal change in flow magnitude, duration, frequency, timing, and rate of change in the major and medium rivers in Nepal. With continuity in the development activities, it is imperative to analyze the potential impact of human activities in the hydrologic regimes. For this, we used a set of 33 indicators from the indicator of hydrologic alteration (IHA) developed by The Nature Conservancy for the pre and post-impact period. The pre and post-impact period is defined here as the time before and after which the substantial alteration occurred, possibly due to multiple reasons. The pre and post impact periods were determined using the Pettitt statistical test carried out at the most downstream of the hydrological gauge station of each river basin. Further, the trends in the annual flow were estimated using the Mann-Kendall test, and the slope of the trend was estimated using Sen’s slope. New hydrological insights for the regionThe results showed that in the post-impact period, the mean annual discharge in major and medium rivers of Nepal was found to decrease by 5.86% and 7.94%, respectively. Except for the West Rapti River (−14.3%), the hydrologic change of 1-day maximum flow is observed to have increased in the medium rivers and decreased in the major rivers. Moreover, except for the Kankai River (+14.29%), the hydrologic change of 1-day minimum flow is observed to be reduced in both the major and medium rivers. In major rivers, the overall degree of alteration ranges from 28.7% to 38.0%, which resembles the low to mid variability range. Similarly, the result of the hydrologic alteration showed that for the medium rivers, the overall degree of alteration varied from 35.8% to 46.7%, representing the medium range of variability. This suggests that the river systems undergoing moderate hydrologic alteration have experienced moderate alteration. These rivers might be capable of sustaining a healthy ecosystem, however, could be more susceptible to other stressors like drought.

Elevated arsenic concentrations in groundwater of the Upper Indus Plain of Pakistan across a range of redox conditions

Groundwater of the Ravi River floodplain is particularly elevated in arsenic (As) on both sides of the Pakistan-India border. To understand this pattern, 14 sites were drilled to 12–30 m depth across floodplains and doabs of Pakistan after testing over 20,000 wells. Drill cuttings were collected at 1.5 m intervals, 132 of which were sand overlain by 77 intervals of clay and/or silt. Radiocarbon dating of clay indicates deposition of the aquifer sands tapped by wells 20–30 kyr ago. Most (85 %) of the sand samples were gray in color, indicating partial reduction to Fe(II) oxides, whereas most (92 %) of the clay and/or silt samples were orange. Associations between groundwater electrical conductivity, dissolved Fe, sulfate, and nitrate suggest that wells can be elevated (>10 μg/L) in As in the region due to either reductive dissolution of Fe oxides, evaporative concentration, or alkali desorption. In the Ravi floodplain, 47 % of 6445 wells tested contain >10 μg/L As compared to only 9 % of 14,165 tested wells in other floodplains and doabs. The As content of aquifer sands in the Ravi floodplain of Pakistan averages 4 ± 4 mg/kg (n = 66) and is higher than the average of 2 ± 2 mg/kg (n = 51) for aquifer sands outside the Ravi. Synchrotron spectroscopy and column-based speciation indicate predominance of As(V) over As(III) in both aquifer sands and groundwater. Whereas multiple processes may be responsible for elevated levels of As in groundwater across the region, spatial heterogeneity in groundwater As concentrations in the Ravi floodplain seems linked to variations in As concentrations in aquifer sands. Regulation by the solid phase may limit variations in groundwater As over time in response to natural and human-induced changes in hydrology. This means spatial heterogeneity could be taken advantage of to lower the exposure across the region with more testing and targeted drilling.

Two-phase hydrological changes during the mid-to late Holocene transition in Southwest China

The Indian summer monsoon (ISM) rainfall feeds a vast majority of the densely populated Asian continent. A deep understanding of the ISM rainfall variations and the underlying driving mechanisms during the Holocene is essential to predict its future behaviors and formulate improved mitigating strategies under the context of global warming. It has been widely recognized that the ISM intensity declined from the early to late Holocene, with a mid-to late Holocene transition. However, the nature of hydrological changes during this critical transition still remains vague. In this study, hydrological changes in Southwest China during the mid-to late Holocene transition are reconstructed based on the molecular and compound-specific carbon and hydrogen isotopic compositions of leaf waxes (δ13C and δD of n-alkanes) from the Yanjiang peat deposit in western Yunnan. Results reveal two-phase changes of hydroclimate during the mid-to late Holocene transition in Southwest China. During the first phase (5.5–4.2 cal kyr BP), Southwest China experienced an abrupt drying as indicated by the pronounced increases in both δ13C and δD values of the C29n-alkane (δ13CC29 and δDC29) by 2.2% and 26‰, respectively. The second phase (4.2–2.6 cal kyr BP) witnessed shortening in the duration of the ISM season without further aridification, as demonstrated by an increase up to 35‰ in the δDC29 values and moderate oscillations in the δ13CC29 values. Such a two-phase hydrological transition is likely to have been triggered by the changes in the summer solar insolation and amplified by the ocean-atmosphere interactions. The first phase is primarily modulated by the positive Indian Ocean Dipole mean state, while the second phase is mainly linked with a more El Niño-like mean state over the Pacific Ocean.

Unravelling the elevation-dependent warming in the Indus Basin

The Elevation Dependent Warming (EDW) in the mountain regions have wider implications to its cryosphere, hydrological, and ecological systems. This paper explores an EDW in the Indus River Basin, considering Jhelum, Kabul, and Indus sub-basins to improve the accuracy and understanding of cryospheric and hydrological changes in the basin. We use the maximum (Tmax), minimum (Tmin), and mean (Tmean) near surface atmospheric temperature data from 21 ground stations for the 1988–2021 period and applied the Mann-Kendall (MK) trend tests for exploring the trends in the data. The results show that Tmax and Tmin has significant (p < 0.001) warming trends in the Upper Indus Basin (UIB) until 2210 mean above sea level (m asl). Tmax has increased with a rate of 0.031 °C yr−1 (p < 0.001) while Tmin increased with a rate of 0.029 °C yr−1 (p < 0.001), hence the “diurnal temperature range (DTR) also increased significantly” (0.015 °C yr−1, p < 0.001). In this study, a symmetric pattern of increasing trends has been observed in Tmax and Tmin. Moreover, Tmax has increasing trends throughout the period in the middle and high-altitude regions, except in Autumn and Monsoon seasons, respectively. While more significant and prominent increasing trend observed in Tmax during the winter season. Thus, this consistent warming trends in all seasons with more prominent trend in the winter season for Tmax can have harmful impact on the cryosphere of the region and ultimately, leading to water scarcity and extreme droughts.

Comparison of Terrestrial Water Storage Changes in the Tibetan Plateau and Its Surroundings Derived from Gravity Recovery and Climate Experiment (GRACE) Solutions of Different Processing Centers

The GRACE twin satellite gravity mission from 2002 to 2017 has considerably improved investigations on global and regional hydrological changes. However, there are different GRACE solutions and products available which may yield different results for certain regions despite applying the same postprocessing and time span. This is especially the case for the Tibetan Plateau (TP) with its special hydrological conditions represented by localized but strong signals that can overlap or merge with signals inside the plateau, which can falsify the determination of terrestrial water storage (TWS) changes in the TP area. To investigate the effect of GRACE solution selection on inverted TWS changes, we analyze quantitatively the secular and monthly changes for 14 glacier areas and 10 water basins in and around the TP area that have been calculated from 16 different available GRACE solutions. Our analysis provides expectable results. While trend results from different spherical harmonic (SH) GRACE solutions match well, there are significant differences to and between mascon GRACE solutions. This is related to the different processing concepts of mascon solutions and their forced handling in our comparisons. SH solution time series match each other when mass changes are strong with a large amplitude and regular periodicity. However, for regions where small TWS changes are associated with small amplitudes, trends, and/or unstable signal periods, SH solutions can also yield different results. Such behavior is known from a time series analysis. Interestingly though, we find that the COST-G and ITSG SH GRACE solutions are closest to the average of all solutions. Therefore, these solutions appear to be preferable for TWS investigations in regions with highly variable hydrological conditions, such as in the Tibetan Plateau and its surroundings. This also indicates that combined solutions such as COST-G provide a promising pathway for an improved TWS analysis, which should be further elaborated.

Arctic-boreal lakes of interior Alaska dominated by contemporary carbon

Northern high-latitude lakes are critical sites for carbon processing and serve as potential conduits for the emission of permafrost-derived carbon and greenhouse gases. However, the fate and emission pathways of permafrost carbon in these systems remain uncertain. Here, we used the natural abundance of radiocarbon to identify and trace the predominant sources of methane, carbon dioxide, dissolved inorganic and organic carbon in nine lakes within the Yukon Flats National Wildlife Refuge in interior Alaska, a discontinuous permafrost region with high landscape heterogeneity and susceptibility to climate, permafrost, and hydrological changes. We find that although Yukon Flats lakes primarily process young carbon (modern to 1290 ± 60 years before present), permafrost-derived carbon is present in some of the sampled lakes and contributes, at most, 30 ± 10% of the dissolved carbon in lake surface waters. Apportionment of young carbon and legacy carbon (carbon with radiocarbon age ⩾5000 years before present) is decoupled among the dissolved inorganic and organic carbon species, with methane showing a stronger legacy signature. Our observations suggest that permafrost-thaw-related transport of carbon through Yukon Flats lacustrine ecosystems and into the atmosphere is small, and likely regulated by surficial sediments, permafrost distribution, wildfire occurrence, or masked by contemporary carbon processes. The heterogeneity of lakes across our study area and northern landscapes more broadly cautions against using any one region (e.g. Yedoma permafrost lakes) to upscale their contribution across the pan-Arctic.

Response of CO2 and CH4 emissions from Arctic tundra soils to a multifactorial manipulation of water table, temperature and thaw depth

Significant uncertainties persist concerning how Arctic soil tundra carbon emission responds to environmental changes. In this study, 24 cores were sampled from drier (high centre polygons and rims) and wetter (low centre polygons and troughs) permafrost tundra ecosystems. We examined how soil CO2 and CH4 fluxes responded to laboratory-based manipulations of soil temperature (and associated thaw depth) and water table depth, representing current and projected conditions in the Arctic. Similar soil CO2 respiration rates occurred in both the drier and the wetter sites, suggesting that a significant proportion of soil CO2 emission occurs via anaerobic respiration under water-saturated conditions in these Arctic tundra ecosystems. In the absence of vegetation, soil CO2 respiration rates decreased sharply within the first 7 weeks of the experiment, while CH4 emissions remained stable for the entire 26 weeks of the experiment. These patterns suggest that soil CO2 emission is more related to plant input than CH4 production and emission. The stable and substantial CH4 emission observed over the entire course of the experiment suggests that temperature limitations, rather than labile carbon limitations, play a predominant role in CH4 production in deeper soil layers. This is likely due to the presence of a substantial source of labile carbon in these carbon-rich soils. The small soil temperature difference (a median difference of 1 °C) and a more substantial thaw depth difference (a median difference of 6 cm) between the high and low temperature treatments resulted in a non-significant difference between soil CO2 and CH4 emissions. Although hydrology continued to be the primary factor influencing CH4 emissions, these emissions remained low in the drier ecosystem, even with a water table at the surface. This result suggests the potential absence of a methanogenic microbial community in high-centre polygon and rim ecosystems. Overall, our results suggest that the temperature increases reported for these Arctic regions are not responsible for increases in carbon losses. Instead, it is the changes in hydrology that exert significant control over soil CO2 and CH4 emissions.

The hydrological regime of Taihu Lake under the influence of anthropogenic activities

Study regionThe Taihu Lake is located at the downstream of the Yangtze River, China, which serves various functions such as regional flood control, drought resistance, and drinking water for many vital cities in China such as Shanghai, Hangzhou and Suzhou. Since 1950 s, Taihu Lake has experienced three stages of anthropogenic management. Due to these managements, the natural hydrologic properties of Taihu Lake are gradually disappearing, and the Taihu Lake tends to become an artificially controlled lake. Study focusTo understand how anthropogenic activities have impacted the hydrological regime of Taihu Lake at different stages, this study has analyzed daily average water level of Taihu Lake for 70 years and daily average precipitation data of the Taihu Lake Basin for 60 years. And finally it reveals the natural and anthropogenic effects on trend, amplitude, period and extreme water level of Taihu Lake. New hydrological insights for the regionThe multi-year average water level of Taihu Lake witnesses an increment of 0.23 m, and the contribution from anthropogenic activities account for 34.78%. The maximum decrements of frequency of extreme high and low water level drops by 29.55% and 7.69% recently due to anthropogenic activities. The anthropogenic activities on the hydrological regime in Taihu Lake has become increasingly pronounced, and these hydrological changes are beneficial for basin flood control and water resources.

Impact of climate change on the hydrological projections over a western Himalayan river basin and the associated uncertainties

Melt water from snow and glaciers is a major contributor to the streamflow over the Himalayan mountainous region. However, rising temperatures and uncertain precipitation trends may change the timing of snow melt and snow accumulation, altering the hydrological cycle. This study investigated future hydrological changes and the associated uncertainties over a snow-fed catchment of the western Himalayan River, Astore. A process-based hydrological model (WRF-Hydro/Glacier) was used with meteorological forcing from global climate models (GCMs), bias correction methods (BCMs), and multiple optimized hydrological parameters (MPs). The simulated results of streamflow, the snow-covered area (SCA), and evapotranspiration (ET) were examined over three periods: baseline (BL; 2000–2019), mid-future (MF; 2040–2059), and far-future (FF; 2080–2099). With early snow melt and late accumulation of snow, the peak streamflow is projected to shift from July during the BL, to mid-June during MF, and to mid-May during FF. Moreover, a decrease in the SCA and an increase in ET was projected during both MF and FF periods, leading to reduced solid water reserves in snow and glaciers. Furthermore, by quantifying the uncertainty contribution of GCMs, BCMs, and MPs in projecting future hydrological components, it was determined that more emphasis should be placed on the selection of an appropriate GCM and MP than that of a BCM in projecting streamflow and SCA. When projecting SCA, the GCM and MP are major contributors to uncertainty in fall–winter and spring–summer, respectively. Conversely, when projecting ET, GCM and BCM have more influence than MP. Overall, this study highlights the importance of uncertainty assessments to develop robust adaptation plans in ensemble-based climate change projections over the western Himalayan region.