Individual and combined impacts of carbon dioxide enrichment, heatwaves, flow velocity variability, and fine sediment deposition on stream invertebrate communities.

Climate change and land-use change are widely altering freshwater ecosystem functioning and there is an urgent need to understand how these broad stressor categories may interact in future. While much research has focused on mean temperature increases, climate change also involves increasing variability of both water temperature and flow regimes and increasing concentrations of atmospheric CO2, all with potential to alter stream invertebrate communities. Deposited fine sediment is a pervasive land-use stressor with widespread impacts on stream invertebrates. Sedimentation may be managed at the catchment scale; thus, uncovering interactions with these three key climate stressors may assist mitigation of future threats. This is the first experiment to investigate the individual and combined effects of enriched CO2, heatwaves, flow velocity variability, and fine sediment on realistic stream invertebrate communities. Using 128 mesocosms simulating small stony-bottomed streams in a 7-week experiment, we manipulated dissolved CO2 (ambient; enriched), fine sediment (no sediment; 300 g dry sediment), temperature (ambient; two 7-day heatwaves), and flow velocity (constant; variable). All treatments changed community composition. CO2 enrichment reduced abundances of Orthocladiinae and Chironominae and increased Copepoda abundance. Variable flow velocity had only positive effects on invertebrate abundances (7 of 13 common taxa and total abundance), in contrast to previous experiments showing negative impacts of reduced velocity. CO2 was implicated in most stressor interactions found, with CO2 × sediment interactions being most common. Communities forming under enriched CO2 conditions in sediment-impacted mesocosms had ~20% fewer total invertebrates than those with either treatment alone. Copepoda abundances doubled in CO2-enriched mesocosms without sediment, whereas no CO2 effect occurred in mesocosms with sediment. Our findings provide new insights into potential future impacts of climate change and land use in running freshwaters, in particular highlighting the potential for elevated CO2 to interact with fine sediment deposition in unpredictable ways.

Prioritizing the multifaceted community and species uniqueness for the conservation of lacustrine fishes in the largest subtropical floodplain, China.

Hydrological variations affect habitat characteristics and fish distribution in floodplain lakes. Assessing the contributions of the local community (i.e., LCBD, community uniqueness) and species to overall ß diversity (i.e., SCBD, species uniqueness) of fish assemblages is valuable for habitat and species conservation planning, particularly from functional and phylogenetic perspectives. We examined the changes in multifaceted LCBD and SCBD of fish across different hydrological periods in the Poyang Lake, China, and analyzed their responsive mechanisms using regression models, based on which the conservation priorities of habitats and species were evaluated. The findings revealed that taxonomic, functional, and phylogenetic LCBD and SCBD were lowest during the wet season compared to the normal and dry seasons, emphasizing the regulatory effects of hydrological regimes on fish assemblages. Taxonomic and functional LCBD were significantly impacted by the mean abundance of migratory fish, highlighting the importance of specific species combinations on community uniqueness. Taxonomic and functional SCBD exhibited positive correlations primarily with mean abundance, suggesting the potential uniqueness of certain common species. Additionally, we identified the river-lake junction (Hukou station) and natural reserve (Xingzi and Nanjishan stations) with high overall community uniqueness as critical habitats. We also emphasized the necessity for increased conservation efforts for species having high overall species uniqueness during different hydrological periods, including Coilia brachygnathus, Ctenopharyngodon idella, Coilia nasus, Saurogobio dabryi, Hypophthalmichthys molitrix, Megalobrama amblycephala, and Parabramis pekinensis. This research underscores the significance of integrating multiple ecological perspectives to manage biodiversity changes and maintain ecological conservation values effectively.

Spatial and seasonal distribution of fish eggs and larvae in one free-flowing river in the Neotropical savanna.

Reproduction is one of the most important biological aspects for the maintenance of viable populations, and understanding the spatial and seasonal patterns in the reproduction of Neotropical fish is a point that still needs considerable investigation. In this study, the main aim was to reduce knowledge gaps concerning fish eggs and larvae distribution patterns. Therefore, the River Araguaia basin, one of the main hydrographic basins of the Neotropical savanna, was used as the focal point of study. Samplings of fish eggs and larvae were carried across the hydrological regime during flooding and drought events between December 2018 and July 2020 at 15 sites distributed along a 350 km stretch of the River Araguaia basin. Fish eggs and larvae were found in all sampling sites, with the highest number of catches in the flood season. The fish larvae were represented by 5 orders, 22 families and 22 at the genus or species level. Both environments, tributary and main channel of the River Araguaia, are important for fish reproduction, and no difference was found in the use between the main channel and the tributaries. The results showed that spatial factors are important to explain the change in larval composition, which may have a wide or restricted distribution related to specific habitats. The main factors related to the reproductive activity of fish in this region are the physical and chemical changes in the water that occur in the flood season. These results indicate that the River Araguaia basin has environmental integrity and provides favourable conditions for the reproductive activity of fish, including long-distance migratory species. Considering this, mitigate measures that guarantee the preservation of the natural flow are crucial for the maintenance of fish biodiversity.

Emission dynamics of greenhouse gases regulated by fluctuation of water level in river-connected wetland.

The application of reservoirs in the upper reaches of rivers will change the hydrological rhythm of river-connected wetlands in the lower reaches, causing changes in the distribution of wetland vegetation. The differences of carbon and nitrogen sequestration and emission potential in different vegetations may lead to the dynamics of greenhouse gas emissions from wetlands during hydrological periods. For a wetland connected to the Yangzi River, China, the dynamic changes of vegetation and water areas were identified by remote sensing, and the water level, the emission fluxes of greenhouse gases and the functional bacteria of carbon and nitrogen in soil were measured in-situ. Compared with drought period, the area of phragmites zone in flooding period increased by 28.2%, while the areas of carex and phalaris zones decreased by 42.9%. The carbon and nitrogen accumulation in the soil of phragmites zone is the highest, while the cumulative amount of phalaris is the lowest. The emission fluxes of CH4 and N2O in mud/water and various vegetations were positively correlated with water level and reached the maximum during flooding period. Although the global warming potential of mud/water was highest than that of vegetations, carex zone had the highest warming potential among vegetation zones. CH4 contributes 8-37 times as much as N2O to global warming potential in the wetland. The increase of flooding time promoted the emissions of CH4 and N2O in the wetland. The anaerobic condition caused by flooding stimulated the activities of denitrifying and methanogenic bacteria, thus increasing the emission of greenhouse gases. The sequestrations and emissions of carbon and nitrogen regulated by a reservoir in the upstream suggest that the operation of water conservancies should be considered to alleviate the greenhouse gas emission from river-connected wetland.

Driving forces and recovery potential of the macrophyte decline in East Taihu Lake.

Macrophytes are of key importance to the structure and ecological services of shallow lakes and are sensitive to anthropogenic and natural perturbations. Ongoing eutrophication and hydrological regime change affect macrophytes through changes in water transparency and water level, which lead to a dramatic decrease in bottom light availability. Here an integrated dataset (2005-2021) of multiple environmental factors is used to demonstrate the driving forces and recovery potential of the macrophyte decline in East Taihu Lake by using a critical indicator, which is the ratio of the Secchi disk depth to the water depth (SD/WD). The macrophyte distribution area showed a remarkable decrease from 136.1 ± 9.7 km2 (2005-2014) to 66.1 ± 6.5 km2 (2015-2021). The macrophyte coverage in the lake and in the buffer zone decreased by 51.4% and 82.8%, respectively. The structural equation model and correlation analysis showed that the distribution and coverage of macrophytes decreased with the decrease in the SD/WD over time. Moreover, an extensive hydrological regime change, which caused a sharp decrease in SD and an increase in the water level, is likely to be the driving force that brought about the decline of macrophytes in this lake. The proposed recovery potential model shows that the SD/WD has been low in recent years (2015-2021), and that this SD/WD cannot ensure the growth of submerged macrophytes and is unlikely to ensure the growth of floating-leaved macrophytes, especially in the buffer zone. The approach developed in the present study provides a basis for the assessment of macrophyte recovery potential and the management of ecosystems in shallow lakes that suffer from macrophyte loss.

Evaluating the impacts of small cascade hydropower from a perspective of stream health that integrates eco-environmental and hydrological values.

With small cascade hydropower projects (SCHPs) increasingly employed in small and medium rivers, methods to assess changes in health status within the stream system have become essential to river ecological environment management. In this study, we used a cloud based fuzzy evaluation method to synthetically diagnose the health status of a stream, both as a whole and its parts (hydrological regime, riparian landscape, aquatic community, water quality, and social demand), under the impacts of SCHPs. The results indicated that: (1) average maximum and minimum flows decreased by 20% and 10% respectively, since SCHPs were implemented. Furthermore, the 38% increase in low flow frequency indicated that SCHPs might amplify droughts, the opposite of large hydropower projects which have been shown to alleviate drought; (2) implementation of SCHPs enhanced heterogeneity and fragmentation in riparian landscapes and decreased diversity of riparian vegetation, and dominant species were more likely to emerge on the upstream side of dam; (3) diversity of phytoplankton, zooplankton, and benthic animals decreased by 14%, 4%, and 16%, respectively, during high-impact period (HIP); and fish species decreased by 26% with a shift from rapid flow adapted to lentic and slow flow adapted species; and (4) the stream still exhibited a healthy state during HIP, but the degree of certainty belonging to "healthy" decreased from 0.279 to 0.192, indicating that the stream health was nearing a deteriorated state. This evaluation model clarified imperceptible and fuzzy changes in stream health which will be helpful in follow-up management decisions.

Spaceborne Satellite for Snow Cover and Hydrological Characteristic of the Gilgit River Basin, Hindukush⁻Karakoram Mountains, Pakistan.

The Indus River, which flows through China, India, and Pakistan, is mainly fed by melting snow and glaciers that are spread across the Hindukush⁻Karakoram⁻Himalaya Mountains. The downstream population of the Indus Plain heavily relies on this water resource for drinking, irrigation, and hydropower generation. Therefore, its river runoff variability must be properly monitored. Gilgit Basin, the northwestern part of the Upper Indus Basin, is selected for studying cryosphere dynamics and its implications on river runoff. In this study, 8-day snow products (MOD10A2) of moderate resolution imaging spectroradiometer, from 2001 to 2015 are selected to access the snow-covered area (SCA) in the catchment. A non-parametric Mann⁻Kendall test and Sen's slope are calculated to assess whether a significant trend exists in the SCA time series data. Then, data from ground observatories for 1995⁻2013 are analyzed to demonstrate annual and seasonal signals in air temperature and precipitation. Results indicate that the annual and seasonal mean of SCA show a non-significant decreasing trend, but the autumn season shows a statistically significant decreasing SCA with a slope of -198.36 km²/year. The annual mean temperature and precipitation show an increasing trend with highest values of slope 0.05 °C/year and 14.98 mm/year, respectively. Furthermore, Pearson correlation coefficients are calculated for the hydro-meteorological data to demonstrate any possible relationship. The SCA is affirmed to have a highly negative correlation with mean temperature and runoff. Meanwhile, SCA has a very weak relation with precipitation data. The Pearson correlation coefficient between SCA and runoff is -0.82, which confirms that the Gilgit River runoff largely depends on the melting of snow cover rather than direct precipitation. The study indicates that the SCA slightly decreased for the study period, which depicts a possible impact of global warming on this mountainous region.

Predicting hydrological impacts of the Yangtze-to-Huaihe Water Diversion Project on habitat availability for wintering waterbirds at Caizi Lake.

Quantifying the relationship between hydrological regime and habitat availability is the first step to predict potential impacts of water engineering projects on waterbirds, particularly in periodically flooded wetlands. The proposed Yangtze-to-Huaihe Water Diversion Project (YHWD) cuts through Caizi Lake, which is of international importance for wintering waterbirds. In order to explore the potential impacts of the project on habitat availability for the wintering waterbirds, we first built linear models to fit relationships between land cover patterns and water level dynamics in the lake, and then used generalized linear mixed models to test effects of habitat variables (water area, grassland area and mudflat area) on bird abundances of different functional groups. The avian habitat use differed among guilds, and was correlated with the land cover pattern, which was strongly dependent on seasonal water level fluctuations. Following water recession in autumn, the exposure of riparian habitats was more prominent in the eastern part of the lake, where the channel of the proposed YHWD project is located. This part of the lake is also where we located most of the important bird areas. Compared to the current situation, 54.3% of the grassland and 60.5% of the mudflats are predicted to be lost during winter due to the projected water level rise, resulting in reduced habitat availability for grass foragers, invertebrate eaters and tuber feeders. In order to mitigate potential impacts of the YHWD project, we suggest habitat compensations by construction of artificial habitats, and maintenance of water level regime at the whole lake by restoring similarity in water level fluctuations between Xizi Lake and Caizi Lake.

Fluvial network organization imprints on microbial co-occurrence networks.

Recent studies highlight linkages among the architecture of ecological networks, their persistence facing environmental disturbance, and the related patterns of biodiversity. A hitherto unresolved question is whether the structure of the landscape inhabited by organisms leaves an imprint on their ecological networks. We analyzed, based on pyrosequencing profiling of the biofilm communities in 114 streams, how features inherent to fluvial networks affect the co-occurrence networks that the microorganisms form in these biofilms. Our findings suggest that hydrology and metacommunity dynamics, both changing predictably across fluvial networks, affect the fragmentation of the microbial co-occurrence networks throughout the fluvial network. The loss of taxa from co-occurrence networks demonstrates that the removal of gatekeepers disproportionately contributed to network fragmentation, which has potential implications for the functions biofilms fulfill in stream ecosystems. Our findings are critical because of increased anthropogenic pressures deteriorating stream ecosystem integrity and biodiversity.

Influence of the Amazon Hydrological Regime on Eutrophication Indicators of a Hydroelectric Power Plant Reservoir.

Dam constructions in the Amazon have increased exponentially in the last decades, causing several environmental impacts and serious anthropogenic impacts in certain hydroelectric power plant reservoirs in the region have been identified. The assessment of the trophic status of these reservoirs is of interest to indicate man-made changes in the environment, but must take into account the hydrological cycle of the area. This can be relevant for environmental management actions, aiding in the identification of the ecological status of water bodies. In this context, physico-chemical parameters and eutrophication indicators were determined in a hydroelectric power plant reservoir in the Brazilian Amazon to assess trophic variations during the regional hydrological regime phases on the reservoir, namely dry, filling, full and emptying stages. The local hydrological regimes were shown to significantly influence TSS and turbidity, as well as NH4, NO3, PO4, with higher values consistently observed during the filling stage of the reservoir. In addition, differences among the sampling stations regarding land use, population and anthropogenic activities were reflected in the PO43- values during the different hydrological phases.

Hydrological regimes and water quality variations in the Yangtze River basin from 1998 to 2018.

Understanding the long-term variations in basins that undergo large-scale hydroelectric projects is crucial for effective dam operation and watershed management. In this study, comprehensive analyses were conducted on a dataset spanning over 20 years (1998-2018) of hydrological regime and physicochemical parameters from the Yangtze River basin to evaluate the potential impacts of the Three Gorges Dam. Water level significantly increased from 128.75±58.18 m in 2002 to 136.78±55.05 m in 2005, and the mean flow velocity significantly decreased from 2004 to 2010. However, no significant change in the flow was observed in the basin. Meanwhile, remarkable fluctuations in physicochemical parameters, including dissolved oxygen, chemical oxygen demand, conductivity, hardness, and alkalinity, were mainly observed during impoundment (2003-2009). After that, the above parameters tended to stabilize, and some even returned to their original levels. The dam's retention effect significantly reduced the suspended solids (SS) in both up- and downstream, to only one-third of the pre-operation level. And total phosphorus and chemical oxygen demand also significantly decreased with the decline of SS. Particularly, ammonium also showed a significant downward trend, with the up- and downstream of the dam falling by 36.8 % and 26.1 %, respectively. However, the increasing total nitrogen (7.5 % and 20.0 % up- and downstream of the dam, respectively) still threatened the water quality of the basin, especially in the estuaries. Additionally, the significant decline in dissolved oxygen downstream (from 8.53±1.08 mg/L to 8.11±1.36 mg/L) also exacerbated the hypoxia in the Yangtze River estuary. The results demonstrated the long-term impact of the construction of the Three Gorges Dam on the environmental elements of the Yangtze River basin, which provides reference data and guidance for the construction of big dams in major rivers in the future.

Temporal and spatial biosonar activity of the recently established uppermost Yangtze finless porpoise population downstream of the Gezhouba Dam: Correlation with hydropower cascade development, shipping, hydrological regime, and light intensity.

Numerous dams disrupt freshwater animals. The uppermost population of the critically endangered Yangtze finless porpoise has been newly formed below the Gezhouba Dam, however, information regarding the local porpoise is scarce. Passive acoustic monitoring was used to detect the behaviors of porpoises below the Gezhouba Dam. The influence of shipping, pandemic lockdown, hydrological regime, and light intensity on the biosonar activity of dolphins was also examined using Generalized linear models. Over the course of 4 years (2019-2022), approximately 848, 596, and 676 effective monitoring days were investigated at the three sites, from upstream to downstream. Observations revealed significant spatio-temporal biosonar activity. Proportion of days that are porpoise positive were 73%, 54%, and 61%, while porpoise buzz signals accounted for 78.49%, 62.35%, and 81.30% of all porpoise biosonar at the three stations. The biosonar activity of porpoises was much higher at the confluence area, particularly at the MZ site, during the absence of boat traffic, and during the Pandemic shutdown. Temporal trends of monthly, seasonal, and yearly variation were also visible, with the highest number of porpoises biosonar detected in the summer season and in 2020. Significant correlations also exist between the hydrological regime and light intensity and porpoise activity, with much higher detections during nighttime and full moon periods. Hydropower cascade development, establishment of a natural reserve, fish release initiatives, and implementation of fishing restrictions may facilitate the proliferation of the porpoise population downstream of the Gezhouba Dam within the Yichang section of the Yangtze River. Prioritizing restoration designs that match natural flow regimes, optimize boat traffic, and reduce noise pollution is crucial for promoting the conservation of the local porpoises.

Increased Yangtze finless porpoise presence in urban Wuhan waters of the Yangtze River during fishing closures.

Wuhan, a highly urbanized and rapidly growing region within China's Yangtze Economic Zone, has historically been identified as a gap area for the critically endangered Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) based on daytime visual surveys. However, there has been a noticeable increase in porpoise sightings since 2020. This study employed passive acoustic monitoring to investigate porpoise distribution in Wuhan between 2020 and 2022. Generalized linear models were used to explore the relationship between shipping, hydrological patterns, light intensity, and porpoise biosonar activity. Over 603 days of effective monitoring, the daily positive rate for porpoise biosonar detection reached 43%, with feeding-related buzz signals accounting for 55% of all porpoise biosonar signals. However, the proportion of minutes during which porpoise presence was detected was 0.18%, suggesting that while porpoises may frequent the area, their visits were brief and mainly focused on feeding. A significant temporal trend emerged, showing higher porpoise biosonar detection during winter (especially in February) and 2022. Additionally, periods without boat traffic correlated with increased porpoise activity. Hydrological conditions and light levels exhibited significant negative correlations with porpoise activity. Specifically, porpoise sonar detections were notably higher during the night, twilight, and new moon phases. It is highly conceivable that both fishing bans and COVID-19 pandemic-related lockdowns contributed to the heightened presence of porpoises in Wuhan. The rapid development of municipal transportation and shipping in Wuhan and resulting underwater noise pollution have emerged as a significant threat to the local porpoise population. Accordingly, it is imperative for regulatory bodies to effectively address this environmental stressor and formulate targeted protection measures to ensure the conservation of the finless porpoise.

High-resolution temporal monitoring of rare earth elements in acidic drainages from an abandoned sulphide mine (iberian pyrite belt, Spain).

Rare earth elements (REE) are strategic elements due to their economic importance. However, the studies dedicated to the distribution and behaviour of REE in aquatic systems have been scarce until a few decades ago. This work studies the seasonal variations of REE concentrations in acid mine drainage (AMD) affected water courses and the factors controlling their mobility under different hydrological conditions. To address this issue, a high-resolution sampling was performed for two years in selected sampling sites. REE concentrations were very high (median values of 2.7-3.4 mg/L, maximum of 7.0 mg/L). These values are several orders of magnitude higher than those found in natural waters, highlighting the importance of AMD processes on the release of REE to the hydrosphere. No good correlations were found between pH and REE concentration, while REE correlated positively (r Spearman coefficient of 0.78-0.94) with EC and negatively (r -0.88 to -0.90) with discharge in AMD-affected streams. A conservative behaviour of REE was observed due to the strongly acidic conditions observed in the study area. The waters also showed an enrichment in MREEs over LREEs and HREEs (mean values of GdN/LaN>1.8 and YbN/GdN < 0.7), typical of AMD waters. An asymmetry in the content of LREE and HREE was observed in AMD samples studied, which could be explained by the preferential dissolution of LREE or HREE-enriched minerals within each waste heaps. Multivariate analysis suggests the influence of Mn-rich minerals existent in the study area as a potential source of LREE.

Anthropogenic activity, hydrological regime, and light level jointly influence temporal patterns in biosonar activity of the Yangtze finless porpoise at the junction of the Yangtze River and Poyang Lake, China.

Under increasing anthropogenic pressure, species with a previously contiguous distribution across their ranges have been reduced to small fragmented populations. The critically endangered Yangtze finless porpoise ( Neophocaena asiaeorientalis asiaeorientalis), once commonly observed in the Yangtze River-Poyang Lake junction, is now rarely seen in the river-lake corridor. In this study, static passive acoustic monitoring techniques were used to detect the biosonar activities of the Yangtze finless porpoise in this unique corridor. Generalized linear models were used to examine the correlation between these activities and anthropogenic impacts from the COVID-19 pandemic lockdown and boat navigation, as well as environmental variables, including hydrological conditions and light levels. Over approximately three consecutive years of monitoring (2020-2022), porpoise biosonar was detected during 93% of logged days, indicating the key role of the corridor for finless porpoise conservation. In addition, porpoise clicks were recorded in 3.80% of minutes, while feeding correlated buzzes were detected in 1.23% of minutes, suggesting the potential existence of localized, small-scale migration. Furthermore, both anthropogenic and environmental variables were significantly correlated with the diel, lunar, monthly, seasonal, and annual variations in porpoise biosonar activities. During the pandemic lockdown period, porpoise sonar detection showed a significant increase. Furthermore, a significant negative correlation was identified between the detection of porpoise click trains and buzzes and boat traffic intensity. In addition to water level and flux, daylight and moonlight exhibited significant correlations with porpoise biosonar activities, with markedly higher detections at night and quarter moon periods. Ensuring the spatiotemporal reduction of anthropogenic activities, implementing vessel speed restrictions (e.g., during porpoise migration and feeding), and maintaining local natural hydrological regimes are critical factors for sustaining porpoise population viability.

Microbially mediated Fe-N coupled cycling at different hydrological regimes in riparian wetland.

Although the significance of the coupled Fe- and N- cycling processes on biogeochemical transformation in riparian wetlands is well-known, the regulation associated with the changes on the microbiotas during different hydrological regimes remains unclear. This study performed field investigations on the bacterial community compositions (BCC) and specific genera associated to Fe- and N- cycling in the rhizosphere soil and sediments in a riparian wetland in Poyang lake, China. The predominant phyla Proteobacteria, Acidobacteria, and Nitrospirae from all the samples remarkably decreased after long-term continuous flooding, while Actinobacteria, Firmicutes and Bacteroidetes were enriched. For the family level, the relative abundances of iron-oxidizing bacteria (FeOB) Gallionellaceae, and N fixing bacteria Nitrospiraceae and Bradyrhizobiaceae significantly declined upon the long-term flooding and then increased with dewatering, which were consistent with the functional genes sequencing analysis. In which, the Bradyrhizobiaceae (RA 2.0 %-34.6 %) was the dominant nirS denitrifier and potential iron-reducing bacteria (FeRB), Sideroxydans lithotrophicus was one of the dominant FeOB (RA 1.7 %-23 %), which was also identified to be the nirS dentrifier (RA 0.2 %-4.3 %). The absolute quantification of the functional genes levels including nirS, nirK, FeRB (Geobacter spp.) showed their significant increases by 3-7 times upon desiccation compared to that under post-CF. The PCA and RDA results indicated the linkage between redox changes of N and Fe during inundation mediated by FeRB, NOB, and FeOB, which were closely related to hydrochemical indices NO3-, Fe2+ and SO42-. These evidences all implied the likely occurrence of nitrate reduction coupled to Fe(II) oxidation (NRFeOx) under oligotrophic conditions, which was potentially facilitated by metabolizers consisting of highly correlated Bradyrhizobiaceae and Sideroxydans (rho = 0.86, p < 0.01). These findings provide an interpretation of the biological reactions in the microbially mediated NRFeOx processes driven by hydrological change, which could assist the mechanistic understanding of the global biogeochemical cycles of iron and nitrogen in riparian wetlands.

Changes in the flow regime of High Arctic catchments with different stages of glaciation, SW Spitsbergen.

This study investigates the response of four High Arctic catchments with differing proportions of glacierization to changing climatic conditions. The study area located in SW Spitsbergen, has experienced a warming of 4.5 °C in the last 40 years along with a large increase in autumn rainfall. The changes in flow regime were determined based on available hydro-meteorological data and simulations of a semi-distributed rainfall-runoff model, which allowed reconstruction of streamflow in the period 1979-2020 and trend analyses for each calendar day. Similar trends of change were detected in all studied catchments. These include earlier onset of snowmelt driven floods (by two weeks over the period of analysis), large increases in autumn flows, prolongation of the hydrologically active season (starts earlier and lasts longer), decrease in flows in the latter half of June and the early part of August (except for the Breelva catchment). As a result of increases in autumn precipitation, the flood regime in these catchments has changed from snowmelt-dominated to the bi-modal with peaks in both July/August and September. The results also indicate differences in the magnitude of hydrological response depending on the percentage of glacial coverage in the catchments. The larger the glacierized area is, the larger the changes in the flow regime. The hydrological regime of SW Spitsbergen catchments has undergone dramatic changes over the last four decades. Such a shift in hydro-climatic conditions is larger than that observed in lower latitudes and has significant environmental implications.

Simulating the hydrological regime of the snow fed and glaciarised Gilgit Basin in the Upper Indus using global precipitation products and a data parsimonious precipitation-runoff model.

In many high altitude river basins, the hydro-climatic regimes and the spatial and temporal distribution of precipitation are little known, complicating efforts to quantify current and future water availability. Scarce, or non-existent, gauged observations at high altitudes coupled with complex weather systems and orographic effects further prevent a realistic and comprehensive assessment of precipitation. Quantifying the contribution from seasonal snow and glacier melt to the river runoff for a high altitude, melt dependent region is especially difficult. Global scale precipitation products, in combination with precipitation-runoff modelling may provide insights to the hydro-climatic regimes for such data scarce regions. In this study two global precipitation products; the high resolution (0.1°â€¯× 0.1°), newly developed ERA5-Land, and a coarser resolution (0.55°â€¯× 0.55°) JRA-55, are used to simulate snow/glacier melts and runoff for the Gilgit Basin, a sub-basin of the Indus. A hydrological precipitation-runoff model, the Distance Distribution Dynamics (DDD), requires minimum input data and was developed for snow dominated catchments. The mean of total annual precipitation from 1995 to 2010 data was estimated at 888 mm and 951 mm by ERA5-Land and JRA-55, respectively. The daily runoff simulation obtained a Kling Gupta efficiency (KGE) of 0.78 and 0.72 with ERA5-Land and JRA-55 based simulations, respectively. The simulated snow cover area (SCA) was validated using MODIS SCA and the results are quite promising on daily, monthly and annual scales. Our result showed an overall contribution to the river flow as about 26% from rainfall, 37-38% from snow melt, 31% from glacier melt and 5% from soil moisture. These melt simulations are in good agreement with the overall hydro-climatic regimes and seasonality of the area. The proxy energy balance approach in the DDD model, used to estimate snow melt and evapotranspiration, showed robust behaviour and potential for being employed in data poor basins.

[Response of Riverine Nitrogen Exports to Land Use Pattern and Hydrological Regime in the Jiulong River Watershed].

Watershed land use patterns combined with hydrological regimes affect riverine nitrogen (N) sources, transformation pathways, and exports, which can affect watershed health and freshwater ecosystem service supply. Understanding how land use and hydrological regimes affect riverine N exports is therefore useful for developing sustainable watershed management strategies. Based on in-situ observations during the period 2010-2017, watershed modeling, geospatial technology, and statistical analysis were coupled in this study to explore the responses of riverine nitrogen exports to watershed land use pattern and hydrological regime in a medium-sized watershed. Results showed that nitrate was the major form of dissolved inorganic N in the Jiulong River watershed; agricultural and urban watersheds had higher N exports and greater temporal variability than those in natural watershed. The seasonal fluctuation for watershed N concentrations and exports was obvious in wet years compared with dry years. Compared with the hydrological regime, the land use pattern had significant effects on N concentrations and exports. This study demonstrated that spatiotemporal variations of riverine nitrogen exports were mainly contributed by the coupled effects of watershed land use pattern and hydrological regime.

Win-win-win pathway for ecological restoration by balancing hydrological, ecological, and agricultural dimensions: Contrasting lessons from highly eroded agroforestry.

Ecological restoration projects (ERP) can effectively reverse ecosystem degradation. However, some ERPs have failed to restore ecosystems under environmental constraints, and they were unable to achieve the desired ecological and economic benefits. To achieve a win-win-win target that balances the hydrological, ecological, and agricultural dimensions, we introduced the contrasting lessons from hotspots of ecosystem restoration in the arid Loess Plateau (LP) and the humid Karst Plateau (KP) in China, and discussed a novel strategy for coordinating ecosystem restoration, water and food security, and residents' livelihoods. The biophysical models and related statistical records showed that aggressive ERPs and soil and water conservation projects (SWCPs) significantly promoted vegetation restoration and reduced soil erosion and sediment yield in both areas. However, excessive afforestation in the arid LP exhausted water resources and threatened ecosystem sustainability. The accelerated replacement of cropland since 1999 in the LP aggravated cropland shortage which led to carbon sequestration and grain productivity declines in the initial years. However, the construction of terrace and check-dam fields and improvements in the conditions of agricultural production reconciled the cropland shortage and stabilized food security. The positive involvement of stakeholders in ERPs effectively minimized land degradation through economic development and the improved livelihoods of local residents. Therefore, based on the evidence from the KP and LP, the proposed win-win-win strategy is potentially applicable in other global regions that suffer from land degradation. This strategy can achieve considerable success if the planners have a good understanding of local environmental conditions as well as the social and economic needs of residents affected by ERPs.