Hydrological Dynamics Research Articles

Soil warming effects on the transpiration of trees and shrubs in a subtropical secondary forest: A manipulative experiment

The climate warming can increase the productivity of some species while decrease that of others, therefore, knowledge of species-specific responses to warming is helpful to understand the possible trajectory of forest ecosystems. Despite the importance of the subtropical secondary broadleaf forests developed from afforestation in South China, our understanding of how the transpiration of trees and shrubs co-growing in these forests responds to soil warming is limited. To explore the effects of soil warming on transpiration and associated ecophysiological traits of trees and shrubs in wet and dry seasons, as well as to clarify respective contributions of trees and shrubs transpiration to the stand total, we conducted a manipulative experiment of soil warming (+2 ℃, WA) and control (CK) in a subtropical secondary broadleaf forest in South China, and continuously monitored the transpiration (based on sap flow) of trees, Schima superba and Acacia auriculiformis, and that (derived from leaf temperature and microclimate) of shrubs, Psychotria asiatica and Castanopsis chinensis, from 2021 to 2022. We also measured leaf water potentials, leaf nutrient status, and δ13C-derived intrinsic water use efficiency (WUEi). Soil warming did not significantly alter the transpiration of trees, with the exception of A. auriculiformis in 2022, whereas it notably increased transpiration of both shrubs. We attributed the stimulation of shrubs’ transpiration mainly to the more favorable leaf water potentials under warming condition. Due to the increased transpiration, the contribution of shrubs to stand transpiration was consequently increased, highlighting the potential role of shrubs in the hydrological dynamics of forest ecosystems. Additionally, the WUEi, soil main macro-nutrients, and leaf nutritional status of all species were not significantly affected by soil warming. These findings indicated that the carbon-water exchange and nutrient status of the studied plants can be maintained even when exposed to moderate increases in soil temperature and relatively drier condition, reflecting the resilience of the subtropical secondary broadleaf forest to possible climate warming. Further research on the interaction and competition of co-existing trees and shrubs under soil warming will improve the prediction of forest dynamics under future climate change, which benefits the efforts to conserve such forests in order to address the environmental pressure in the region.

Near-natural streams: Spatial factors are key in shaping multiple facets of zooplankton α and β diversity

In near-natural basins, zooplankton are key hubs for maintaining aquatic food webs and organic matter cycles. However, the spatial patterns and drivers of zooplankton in streams are poorly understood. This study registered 165 species of zooplankton from 147 sampling sites (Protozoa, Rotifers, Cladocera and Copepods), integrating multiple dimensions (i.e., taxonomic, functional, and phylogenetic) and components (i.e., total, turnover, and nestedness) of α and β diversity. This study aims to reveal spatial patterns, mechanisms, correlations, and relative contribution of abiotic factors (i.e., local environment, geo-climatic, land use, and spatial factors) through spatial interpolation (ordinary kriging), mantel test, and variance partitioning analysis (VPA). The study found that α diversity is concentrated in the north, while β diversity is more in the west, which may be affected by typical habitat, hydrological dynamics and underlying mechanisms. Taxonomic and phylogenetic β diversity is dominated by turnover, and metacommunity heterogeneity is the result of substitution of species and phylogeny along environmental spatial gradients. Taxonomic and phylogenetic β diversity were strongly correlated (r from 0.91 to 0.95), mainly explained by historical/spatial isolation processes, community composition, generation time, and reproductive characteristics, and this correlation provides surrogate information for freshwater conservation priorities. In addition, spatial factors affect functional and phylogenetic α diversity (26%, 28%), and environmental filtering and spatial processes combine to drive taxonomic α diversity (10%) and phylogenetic β diversity (11%). Studies suggest that spatial factors are key to controlling the community structure of zooplankton assemblages in near-natural streams, and that the relative role of local environments may depend on the dispersal capacity of species. In terms of diversity conservation, sites with high variation in uniqueness should be protected (i) with a focus on the western part of the thousand islands lake catchment and (ii) increasing effective dispersal between communities to facilitate genetic and food chain transmission.

Investigating the geographies of water use and water cover in the rural areas of Nagaon District, Assam (India): Unraveling the micro-ecological implications

The use and management of water resources are fundamental for sustainable human societies, economic development, and ecological conservation. Therefore, conducting a thorough investigation to comprehend water use (WU) patterns and assess the extent of water-covered areas (WCA) in a region is indispensable for fostering sustainable ecological and economic conditions, and for implementing effective water management practices. However, the rapid growth of human populations, particularly in developing countries, and the concomitant developmental activities have significantly influenced the WCA, leading to their degradation and loss. In this context, the present research focuses on investigating and understanding the variations in WU and WCA, with an emphasis on unraveling the ecological implications of these hydrological dynamics in the rural areas of Nagaon-a floodplain district of the middle Brahmaputra valley in Assam, India. The study also seeks to investigate the intricate and dynamic human-water relationship and their impact on the waterscapes and the associated hydroecological characteristics. The methodology employed in this study involved analyzing spatial data and conducting field surveys to procure some other relevant primary data and information to assess the current state of WU and WCA in the district. The results reveal substantial shifts in water usage patterns, with a growing reliance on groundwater and reduced dependence on surface water bodies. Notably, all wetlands, except the artificial ponds (pukhuris), have experienced significant declines in both quantity and size, resulting in a reduction of WCA and the associated aquatic vegetation cover. This reduction in WCA has consequently led to a substantial decline in wetland habitats and disruptions to their ecological conditions, posing serious threats to the floral and faunal species dependent on these aquatic ecosystems. The findings of this research will definitely help the concerned policymakers, environmental organizations, and local communities by providing a foundation for informed decision-making towards formulating effective conservation strategies to safeguard not only the WCA of the district but also to maintain the region's ecological health, proper water use, and the sustainable socio-economic development.

Spatiotemporal Variations in Snow Cover on the Tibetan Plateau from 2003 to 2020

The variations in snow cover on the Tibetan Plateau play a pivotal role in comprehending climate change patterns and governing hydrological processes within the region. This study leverages daily snow cover data and the NASA Digital Elevation Model (DEM) from 2003 to 2020 to analyze spatiotemporal snow cover days and assess their responsiveness to climatic shifts by integrating meteorological data. The results reveal significant spatial heterogeneity in snow cover across the Plateau, with a slight decreasing trend in annual average snow cover duration. Snow cover is predominantly observed during the spring and winter seasons, constituting approximately 32% of the total snow cover days annually. The onset and cessation of snow cover occur within a range of 120–220 days. Additionally, an increasing trend in snow cover duration below 5000 m altitude was observed, in addition to a decreasing trend above 5000 m altitude. Sub-basin analysis delineates the Tarim River Basin as exhibiting the lengthiest average annual snow cover duration of 83 days, while the Yellow River Basin records the shortest duration of 31 days. The decreasing trend in snow cover duration closely aligns with climate warming trends, characterized by a warming rate of 0.17 ± 0.54 °C per decade, coupled with a concurrent increase in precipitation at a rate of 3.09 ± 3.81 mm per year. Temperature exerts a more pronounced influence on annual snow cover duration variation compared to precipitation, as evidenced by a strong negative correlation (CC = −0.67). This study significantly augments the comprehension of hydrological cycle dynamics on the Tibetan Plateau, furnishing essential insights for informed decision-making in water resource management and ecological conservation efforts.

What is happening with frequency and occurrence of the maximum river discharges in Bosnia and Herzegovina?

In this study, we explored the frequency and occurrence rate of maximum river discharges in the Una and Sana rivers, to understand hydrological variations amidst climate change. We categorized maximum discharges into severe (Una River M1 > 98.2 m3/s; Sana River M1 > 118.2 m3/s) and extreme (Una River, M2, > 123.4 m3/s; Sana River M2 > 246.4 m3/s) events, and identified trends in these events, crucial for assessing environmental impacts. Our findings reveal a nuanced pattern: both rivers experience an increase in severe events from 58 to 55 and 56 to 54 days return period respectively, indicating complex hydrological dynamics. The trends underscore the significant shifts in annual event occurrences, the evolving nature of river systems and underscore the necessity for adaptive management strategies.

Estimating water balance in a Brazilian semiarid watershed using different spatial data

This study advances water balance (WB) estimation in the Paraguaçu River watershed, Brazil, by leveraging spatial data to mitigate the challenges of sparse monitoring, particularly in the semiarid region. By combining precipitation (PPT) and actual evapotranspiration (ETR) data from diverse methodologies, including IMERG, TMPA, TerraClimate (TC), and IDW interpolation, alongside ETR sources like MOD16, GLEAM, and TerraClimate, we aim to capture the watershed's physical and climatic nuances. The analysis reveals that TerraClimate data (PPTTC and ETRTC) most accurately reflect spatial variations, effectively capturing orographic effects and the semiarid climate, thus emerging as the optimal combination for depicting WB (WBTC_TC). Key findings highlight the variable precision of PPT and ETR data sources in characterizing spatial distribution and magnitude across the watershed, with TerraClimate data showing superior sensitivity to regional disparities. This sensitivity is crucial for accurately modeling the hydrological dynamics in regions with contrasting climatic conditions, from humid orographic areas to the semiarid zones. Moreover, the study underscores the importance of data validation and careful integration of spatial data, particularly in under-monitored or climatically extreme regions, to enhance the reliability of hydrological analyses. The successful integration of spatial data underscores its value in remote or data-scarce regions, reinforcing the necessity for rigorous spatial and temporal validation. This approach not only improves water management strategies but also enriches the integration with climatic and hydrological models, offering a comprehensive toolkit for addressing the complexities of watershed management in the face of climate variability.

Socio-hydrological modelling using participatory System Dynamics modelling for enhancing urban flood resilience through Blue-Green Infrastructure

Cities are complex systems characterised by interdependencies among infrastructural, economic, social, ecological, and human elements. Urban surface water flooding poses a significant challenge due to climate change, population growth, and ageing infrastructure, often resulting in substantial economic losses and social disruption. Traditional hydrological modelling approaches for flood risk management, while providing invaluable support in the analysis of hydrological dynamics of floods, lack an understanding of the complex interplay between hydrological and non-hydrological (i.e., social, environmental, economic) aspects in an urban system, hindering effective flood risk management strategies. In this context, socio-hydrological modelling methods offer a complementary perspective to traditional hydrological models by integrating hydrological and social processes, thereby enhancing the understanding of the complex interactions driving flood resilience.The present work proposes a participatory socio-hydrological modelling approach based on System Dynamics (SD) to quantitatively analyse the interactions and feedback between flood risk and different aspects of the urban system. By combining scientific expertise with stakeholder knowledge, the modelling approach aims to provide decision-makers with a comprehensive understanding of flood dynamics and the effectiveness of resilience-building measures. Furthermore, the role of Blue-Green Infrastructure (BGI) in enhancing urban flood resilience, considering its interplay with grey infrastructure and interactions with various sub-systems, is explored.The results reveal i) the contribution of SD quantitative modelling in supporting the analysis of interactions between flood risk reduction measures and different sub-systems thus offering decision-makers actionable insights into the multifaceted nature of flood risk and resilience; ii) the added value provided by the combination of scientific and stakeholder knowledge in tailoring the model to the case study, quantifying socio-hydrological modelling dynamics limitedly explored in the scientific literature and supporting the selection of measures for increasing flood resilience; iii) the ability of BGI to provide not only hydrological benefits (mainly about the reduction of surface runoff) but also multiple social and environmental benefits (i.e., the co-benefits), especially when coupled with well-functioning grey infrastructure. Reference is made to one of the case studies of the CUSSH and CAMELLIA projects, namely Thamesmead (London, United Kingdom), a formerly inhospitable marshland currently undergoing a process of urban regeneration, with an increasing vulnerability to flooding.

An initial assessment of mobile dam efficiency in raising low-flow water levels in the Vietnamese Mekong Delta

In recent years, the Tien and Hau rivers have experienced a downtrend in water levels during the low flow season. This decrease has led to detrimental effects on agricultural production and ecological health in the VMD’s upper regions, such as the Long Xuyen Quadrangle (LXQ) and the Plain of Reeds (PoR). This research employs a numerical hydraulic model for a preliminary assessment of the potential effectiveness of mobile dams in increasing water levels in the VMD’s upper part. A calibrated 1D hydraulic model was utilized to evaluate the performance of the proposed mobile dams: one situated near the My Thuan bridge on the Tien river, and the other near the Can Tho bridge on the Hau river. Initial results indicate that setting the crest of mobile dams at -1.0 m could raise minimum and maximum water levels in the Tien river near Tan Chau by 1.0 m and 0.15 m, respectively, and in the Hau river near Chau Doc by 1.1 m and 0.07 m, respectively. Furthermore, these mobile dams could significantly enhance the minimum and maximum water levels in An Binh channel within the PoR and Ba The channel in the LXQ, by up to 0.55 m and 0.26 m, and 0.42 m and 0.29 m, respectively. These findings provide an essential foundation for initially understanding how mobile dams can improve water resource management in the VMD. However, additional investigation is required to assess the effects of mobile dams on salinity intrusion, ecological balance, hydrological dynamics, sediment deposition, and erosion.

Intertidal spring dynamics and coastal nutrient loading revealed through geophysics, drone surveys, and in‐situ monitoring

AbstractCoastal eutrophication poses an increasing risk to ecosystem health due to enhanced nutrient loading to the global coastline. Submarine groundwater discharge (SGD) represents a significant pathway for nitrate‐nitrogen (NO3‐N) transport to the coast, but diffusive SGD transport is difficult to monitor directly, given the low flux rates and expansive discharge areas. In contrast, focused SGD from intertidal springs can potentially be sampled and directly gauged, providing unique insight into SGD and associated contaminant transport. Basin Head is a coastal lagoon in Prince Edward Island, Canada that is a federally protected ecosystem. Nitrate‐nitrogen is conveyed from agricultural fields in the contributing watershed to the eutrophic lagoon via intertidal groundwater springs and groundwater‐dominated tributaries. We used several field methods to characterize groundwater discharge, nutrient loading, and in‐channel mixing associated with intertidal springs. The tributaries and intertidal springs were gauged and sampled to estimate a representative summer nitrate load to the lagoon. Our analysis revealed that NO3‐N export to the lagoon through tributaries and springs throughout summer 2023 was on average 401 kg N/month, with the combined spring loading comparable in magnitude to the combined tributary loading. We collected thermal infrared and visual imagery using drone surveys and found spatial overlap between cold‐water plumes from the spring discharge and macroalgae blooms, indicating the local thermal and ecosystem impacts of the focused SGD. We also mapped the electrical resistivity (salinity) distribution in the water column around one large spring with electromagnetic geophysics at different tidal stages to reveal the three‐dimensional spring plume dynamics. Results showed that the fresher spring water floated above the saline lagoon water with the brackish plume oriented in the direction of the tidal current. Collectively, our multi‐pronged field investigations help elucidate the hydrologic, thermal, and nutrient dynamics of intertidal springs and the cascading ecosystem impacts.

Peatland carbon chemistry, amino acids and protein preservation in biogeochemically distinct ecohydrologic layers

AbstractPeatlands play a significant role in global carbon and nitrogen cycles due to their carbon storage capabilities. However, there are key knowledge gaps in our understanding of how peatland hydrology influences the biogeochemical properties that drive peatland functioning and health. This study examines peatland hydrology and biogeochemical dynamics by exploring the variations in carbon chemistry, total amino acid (‘protein’) content and amino acid composition in the ecohydrologic layers: acrotelm, mesotelm and catotelm. The dynamic movement of the water table recorded half‐hourly over 4 years was used to assist in identifying the boundaries between these layers. Peat amino acids were measured using liquid chromatography‐tandem mass spectrometry (LC‐MS/MS). Carbon chemistry was analysed by solid state Cross Polarization Magic Angle Spinning (CPMAS) 13C Nuclear Magnetic Resonance (NMR) spectroscopy, with the alkyl:O‐alkyl ratio used to quantify the extent of decomposition. Our result revealed a strong positive correlation between the extent of decomposition and total protein content, indicating selective preservation of proteinaceous materials during peat decomposition. Each ecohydrologic layer displayed a distinct amino acid composition and carbon functional group composition. The acrotelm was relatively enriched in seven amino acids and two carbon functional groups. The mesotelm was relatively enriched in four amino acids, while the catotelm was relatively enriched in three amino acids and four carbon functional groups. The variations in amino acid composition reflect differences in microbial function and efficiency, while variations in carbon functional groups provide insights into long‐term carbon sequestration in peatland. Collectively, these results provide more insights into nutrient cycling and changes in organic matter composition during peat decomposition. These findings demonstrate that peatland biogeochemistry is closely linked to ecohydrology and suggest that changes to water table dynamics could affect the ability of peatlands to sequester and store carbon in the future.

Insights to the water balance of a Boreal watershed using a SWAT model

The hydrological characteristics of a watershed play a crucial role in shaping ecosystems within the Boreal zone and have a significant impact on regional environments. Knowing these characteristics, such as the distinctive topography, vegetation, soil composition, and climatic conditions in the Canadian Boreal ecozone, is essential for implementing sustainable water management. This study focuses on assessing the hydrological dynamics of the Upper Humber River Watershed (UHRW) in western Newfoundland, Canada, using the Soil and Water Assessment Tool (SWAT) model. The UHRW includes sub-basins and hydrological response units (HRUs), with diverse land uses, soil types, and slope characteristics. Key parameters influencing streamflow simulation were identified through sensitivity analysis, including the runoff curve number, the effective hydraulic conductivity, the temperature lapse rate, the soil evaporation compensation factor, and the available water capacity of the soil layer. The SWAT model, using data from the Reidville hydrometric station, shows favorable performance metrics, with R2 values of 0.79 and 0.83 during the calibration and evaluation periods, respectively. The model effectively captures seasonal and monthly flow patterns, displaying right-skewed distributions and seasonal variations. The analyzed hydrological parameters, such as precipitation, evaporation, transpiration, surface runoff, and groundwater flow, reveal their significant contributions to the water balance. The flow duration curve analysis indicates the model’s capability to estimate peak and low flows, with slight under-prediction during the recession phase. Seasonal analysis further supports the model’s performance, with positive Nash-Sutcliffe Efficiency (NSE) values ranging from 0.65 to 0.91. The study concludes that the SWAT model is suitable for simulating the hydrological processes in the studied watershed providing valuable insights for sustainable water resource management and decision-making in the UHRW. The results can be useful for other Boreal ecozone watersheds.

Porewater microbiomes in buried wetland soils: Synergic effects of water chemistry and redox gradients associated with hydrological processes

Abstract Interstitial water or pore water occupies the space between soil particles and provides “hotspots” and “fluvial networks” for microbial activities in floodplain soil. However, to date, we know very little about the microorganisms living in pore water and how they respond to environmental changes. This study aimed to understand microbial distribution and assemblage in riparian pore waters, and how they respond to water chemistry and redox gradients associated with hydrological processes. We analysed the annual changes of porewater microbial communities from the east and west banks of the White Clay Creek, a site at the Christina River Basin – Critical Zone Observatory, Pennsylvania, USA. Microbial abundances were quantified by epifluorescence microscopy and detailed community structures were characterised by high‐throughput sequencing. Water chemistry and redox gradients were also monitored and recorded, and their interactions with porewater microbiomes were analysed using correlations and multivariate analyses. Abundance of microbial cells increased during summer and late autumn. Wetland porewater microbiomes mainly contained Acidobacteria, Bacteroidetes, Nitrospirae and Proteobacteria, and microbiome structures were easily distinguishable from those in the underlying hyporheic gravel layer. Seasonal dynamics of bacterial community structure in the east and west wetlands were distinct, responding to floodplain topography and associated hydrological/geochemical processes. Iron (Fe)‐cycling bacteria (mainly Gallionellaceae and Rhodoferax spp.) dominated the porewater microbiome, and their relative abundance was significantly higher in the east than the west wetland. Furthermore, Fe‐oxidising bacteria (Gallionellaceae) were negatively correlated with Fe‐reducing bacteria (Rhodoferax spp.) at the east wetland. Microbial abundances (cell density) in pore waters showed similar seasonal patterns across stream banks, but microbial community structure did not. Microbiome assembly in pore water is correlated with water chemistry and redox gradients primarily associated with local hydrological processes. As a consequence of their significance for carbon (C) mineralisation and Fe reduction at terrestrial–aquatic interfaces, microbiomes in riparian pore waters and associated microbial activity play an essential role in C and mineral dynamics. These findings will inform future studies of the response of freshwater ecosystems to hydrological dynamics influenced by global climate change.

Investigating hydrological dynamics and mean residence times of springs in the Tawi catchment, India: Insights into recharge mechanisms and water source variability

This study investigates the hydrological dynamics and Mean Residence Times (MRTs) of springs in the Tawi catchment, India, aiming to elucidate recharge mechanisms and water source variability. The catchment's characteristics, including altitude, geology, and land use, are examined in relation to isotopic composition and residence times of springs at six distinct locations. The study examines seasonal variations in isotopic signatures of precipitation, revealing distinct patterns during Western Disturbances (WDs) and Indian Summer Monsoon (ISM). In addition, a composite δ18O – δ2H regression line (LMWL) is developed, that suggests significant secondary evaporation from falling raindrops as a major process shaping precipitation isotopes in the catchment. The isotopic data from six stations within the catchment demonstrate specific variations influenced by local factors. Enriched rain samples in urban areas like Udhampur and Jammu show higher secondary evaporation, while depleted samples in Chenani and Mantalai suggest a canopy cover influence. Temporal and spatial variations in spring water isotopes suggest either a consistent recharge source or isotopic damping. Mean Residence Times (MRTs) of springs indicate variations in aquifer characteristics, with longer MRTs in Chenani and Mantalai indicating deeper and more complex systems. Moderate MRTs in Pangara Jagir, and Udhampur springs, suggest a balance between storage and recharge. Hydrograph separation analysis demonstrates the dominance of WDs as the precipitation source, except for Chak Rakwal, which exhibits karstified behavior with significant contribution during the ISM. The study underscores the importance of understanding recharge elevations and delineating recharge zones for sustainable groundwater management and preservation of water quality in the Tawi catchment. By elucidating these critical aspects, the study contributes to informed decision-making and effective water resource management in complex catchment areas.

Biotic and abiotic factors driving water hyacinth, Pontederia crassipes, phenology in Nyanza Gulf, Lake Victoria, Kenya

While isolated patches of water hyacinth have persisted in most parts of Lake Victoria since the rapid decline in biomass beginning in 1999/2000, Nyanza Gulf has maintained extensive but cyclical coverage over the years. High water hyacinth productivities were found to coincide with the western region associated with upwelling and regenerated nutrients, and also with periods of complete lake turnover. River discharge sites, which are numerous in the eastern region, expressed relatively low water hyacinth productivities. High productivity meant better nutritional quality, a state preferred by the Neochetina weevils. Although the difference in productivities between the eastern and western regions were statistically insignificant, the feeding scars were notably different. This implies that any slight change in water hyacinth’s nutritional quality as a result of change in resource water quality, significantly affects the weevil’s productivities. During complete lake turnover, water hyacinth productivity is highly enhanced, likely due to upwelling of hypolimnetic nutrient enriched waters with subsequent spontaneous weevil invasion. During times of such high nutrient quality, the rates of leaf turnover outstrips the herbivory by the weevils. The nutrient dynamics from primary sources coupled with secondary regenerated loads through lake turnovers influences the water hyacinth’s varying nutritional quality and weevil population, which ultimately determines the water hyacinth phenology within the semi-enclosed Nyanza Gulf. The objectives of this study were to study the spatial influence of resource water quality to the consumer water hyacinth productivity and how temporal hydrologic dynamics drives its cyclicity.

Unveiling hydrological dynamics in data-scarce regions: experiences from the Ethiopian Rift Valley Lakes Basin

Abstract. The hydrological system of the Rift Valley Lakes in Ethiopia has recently experienced changes over the past 2 decades. Potential causes for these changes include anthropogenic, hydro-climatic, and geological factors. The main objective of this study was to utilize an integrated methodology to gain a comprehensive understanding of the hydrological systems and potential driving factors within a complex and data-scarce region. To this end, we integrated a hydrologic model, change point analysis, indicators of hydrological alteration (IHA), and a bathymetry survey to investigate hydrological dynamics and potential causes. A hydrologic model (the Soil and Water Assessment Tool Plus, SWAT+) was parameterized for the gauged watersheds and extended to the ungauged watersheds using multi-site regionalization techniques. The SWAT+ model performed very well to satisfactorily for daily streamflow in all watersheds with respect to the objective functions of the Kling–Gupta efficiency (KGE), the Nash–Sutcliffe efficiency (NSE), and percent bias (PBIAS). The findings reveal notable changes in lake inflows and lake levels over the past 2 decades. Lake Chamo experienced an increase in area of 30.1 km2 (9.5 %), an increase in depth of 4.4 m (30.9 %), and an increase in volume of 7.8×108 m3 (27.2 %). In contrast, Lake Abijata witnessed an extraordinary 68 % decrease in area and a depth decrease of 1.6 m (37.2 %). During the impact period, the mean annual rainfall experienced a decrease of 6.5 % and 2.7 % over Lake Abijata and Lake Chamo, respectively. Actual evapotranspiration decreased by 2.9 % in Lake Abijata but increased by up to 4.5 % in Lake Chamo. Surface inflow to Lake Abijata decreased by 12.5 %, while Lake Chamo experienced an 80.5 % increase in surface inflow. Sediment depth in Lake Chamo also increased by 0.6 m (4.2 %). The results highlight that the changing hydrological regime in Lake Chamo is driven by increased surface runoff and sediment intrusion associated with anthropogenic influences. The hydrological regime of Lake Abijata is affected by water abstraction from feeding rivers and lakes for industrial and irrigation purposes. This integrated methodology provides a holistic understanding of complex data-scarce hydrological systems and potential driving factors in the Rift Valley Lakes in Ethiopia, which could have global applicability.

MORPHOLOGY AND MORPHOMETRY CHARACTERISTIC OF RAYA WATERSHED

The study of watershed morphology and land use patterns significantly affects hydrological processes and runoff coefficients, highlighting the quantitative nature of watershed characteristics. The Raya Watershed in West Kalimantan influences local communities and aims to enhance understanding of its physical attributes and hydrological dynamics through detailed analysis of topography, soil composition, land use, and river networks. Findings inform watershed management and conservation strategies. The analysis of the Raya Watershed, spanning 29,982.96 hectares (87.34% of total area) with elevations below 100 meters, reveals flat terrain vulnerable to flooding, particularly in low-lying or sea-level regions, exacerbated by limited natural drainage. Lower elevations support crucial wetland and floodplain ecosystems. Hydrological disruptions from land use changes and climate fluctuations can harm biodiversity and water quality. Effective land use planning is vital to address flood risk and environmental concerns, mitigating impacts like property damage and population displacement. Soil-type mapping informs conservation efforts, ensuring ecosystem resilience. Sustainable land management practices, guided by watershed characteristics like drain density and stream frequency, are essential to mitigate biodiversity loss and ecological imbalances.

The Antarctic Subglacial Hydrological Environment and International Drilling Projects: A Review

Subglacial lakes and hydrological systems play crucial roles in Antarctic subglacial hydrology, water balance, subglacial geomorphology, and ice dynamics. Satellite altimetry has revealed that some recurrent water exchange occurs in subglacial lakes. They are referred to as ’active lakes’, which prominently influence a majority of subglacial hydrological processes. Our analysis indicates that active subglacial lakes are more likely to be situated in regions with higher surface ice flow velocities. Nevertheless, the origin of subglacial lakes still remains enigmatic and uncertain. They could have potential associations with geothermal heat, ice sheets melting, and ice flow dynamics. Subglacial lake drilling and water sampling have the potential to provide valuable insights into the origin of subglacial lakes and subglacial hydrological processes. Moreover, they could also offer unique opportunities for the exploration of subglacial microbiology, evolution of the Antarctic ice sheets, and various fundamental scientific inquiries. To date, successful drilling and sampling has been accomplished in Lake Vostok, Lake Mercer, and Lake Whillans. However, the use of drilling fluids caused the water sample contamination in Lake Vostok, and the drilling attempt at Lake Ellsworth failed due to technical issues. To explore more of the conditions of the Antarctic subglacial lakes, the Lake Centro de Estudios Científicos (Lake CECs) and Lake Snow Eagle (LSE) drilling projects are upcoming and in preparation. In this study, we aim to address the following: (1) introduce various aspects of Antarctic subglacial lakes, subglacial hydrological elements, subglacial hydrology, and the interactions between ice sheets and the ocean; and (2) provide an overview and outlook of subglacial lakes drilling projects.

Old-Aged groundwater contributes to mountain hillslope hydrologic dynamics

Understanding connectivity between the soil and deeper bedrock groundwater is needed to accurately predict a watershed’s response to perturbation, such as drought. Yet, the bedrock groundwater dynamics in mountainous environments are typically under-constrained and excluded from watershed hydrologic models. Here, we investigate the role of groundwater characterized with decadal and longer water ages on the hydrologic and mass-transport processes within a steep snow-dominated mountain hillslope in the Central Rocky Mountains (USA). We quantify subsurface and surface water mass-balance, groundwater flowpaths, and age distributions using the ParFlow-CLM integrated hydrologic and EcoSLIM particle tracking models, which are compared to hydrometric and environmental tracer observations. An ensemble of models with varied soil and hydrogeologic parameters reproduces observed groundwater levels and century-scale mean ages inferred from environmental tracers. The numerical models suggest soil water near the toe of the hillslope contains considerable (>60 % of the mass-flux) contributions from bedrock flowpaths characterized with water ages >10 years. Flowpath connectivity between the deeper bedrock and soil systems is present throughout the year, highlighting the potentially critical role of groundwater with old ages on processes such as evapotranspiration and streamflow generation. The coupled numerical model and groundwater age observations show the bedrock groundwater system influences the hillslope hydrodynamics and should be considered in mountain watershed conceptual and numerical models.

Unravelling a specialised diet of an Amazonian catfish in a controlled flood-pulse area by combining stomach-content and stable-isotope analyses

Context Hydrological dynamics are crucial in fish ecology. Aims To evaluate the effect of the flood pulse on the feeding ecology of Doras higuchii in the reduced-flow section of the Belo Monte dam, Xingu River, Brazil. Methods Collections were conducted between December 2020 and November 2021. The fish were measured and had their stomachs removed. Muscle tissue was also extracted for stable-isotope analysis. Stomach contents were inspected to assess diet, testing the influence of hydrological periods by using GLM. In addition, we evaluated the effect of the flood pulse on the δ13C and isotopic ratios of individuals Results In total, 362 specimens of D. higuchii were analysed, highlighting a diet mainly on the basis of sediment (74.9%) and aquatic insects (24.8%), not varying between periods characterising the species as a specialist for having detritivorous habit, as well as the extension of the trophic niche. There was variation in food intensity, with higher average food consumption in the flood period. The isotopic composition (δ13C and δ15N) also did not differ between periods. Finally, δ15N did not vary by length class. Conclusions This information helps understand the interface between environmental and biological factors in an environment affected by a hydroelectric dam. Implications Our results may help fill gaps in knowledge about the diet of doradid fishes.

Unprecedented insights into extents of biological responses to physical forcing in an Arctic sub-mesoscale filament by combining high-resolution measurement approaches.

In Fram Strait, we combined underway-sampling using the remote-controlled Automated Filtration System for Marine Microbes (AUTOFIM) with CTD-sampling for eDNA analyses, and with high-resolution optical measurements in an unprecedented approach to determine variability in plankton composition in response to physical forcing in a sub-mesoscale filament. We determined plankton composition and biomass near the surface with a horizontal resolution of ~ 2km, and addressed vertical variability at five selected sites. Inside and near the filament, plankton composition was tightly linked to the hydrological dynamics related to the presence of sea ice. The comprehensive data set indicates that sea-ice melt related stratification near the surface inside the sub-mesoscale filament resulted in increased sequence abundances of sea ice-associated diatoms and zooplankton near the surface. In analogy to the physical data set, the underway eDNA data, complemented with highly sampled phytoplankton pigment data suggest a corridor of 7km along the filament with enhanced photosynthetic biomass and sequence abundances of sea-ice associated plankton. Thus, based on our data we extrapolated an area of 350 km2 in Fram Strait with enhanced plankton abundances, possibly leading to enhanced POC export in an area that is around a magnitude larger than the visible streak of sea-ice.