ABSTRACT The mixed‐conifer forests of Sierra Nevada create a complex system of water, energy and nutrient cycling. Thus, this study aims to understand the spatial and temporal variability of soil moisture and stand‐scale transpiration across three central Sierra headwater catchments and their controlling factors. The mean daily average sap flow of Abies concolor varies from 0.69 ± 0.48 to 1.27 ± 0.72 L/h. Higher spatial variability in soil moisture and stand‐scale transpiration was found in the snowmelt period, followed by the soil moisture recession period when vegetation growth is not water limited. The daily average sap flow was higher on south aspect than on north aspect, but this pattern was not consistent across all seasons. The diel pattern of the sap flow revealed a larger contribution of nocturnal sap flow during the dry period (22.3%–37.8%) and a smaller contribution during the recession period (16.3%–23.9%) across all catchments. Multiple linear regression analysis suggests that sap flow during summer (recession period) was governed by the ecosystem's energy, indicated in part by vapour pressure deficit and temperature. Soil moisture regulated the subsequent dry‐period transpiration. The energy‐limited condition in winter restricted the transpiration even when sufficient soil moisture was available. Topography, explained by topographic positioning index ( tpi ), played a major role in explaining stand‐scale transpiration, especially during higher atmospheric demand periods, whereas tree size (i.e., DBH) explained more than 10% sap flow variance in all seasons. The findings of this study will provide the basis for a better understanding of the eco‐hydrological processes of the Sierra Nevada under natural and anthropogenic‐induced changes.
ABSTRACT Temperature is a fundamental control on many ecological processes, and factors that alter thermal regimes can shift species interactions and ecosystem function. Across eight streams, we assessed five aspects of summer temperature (daily mean, daily maximum, daily minimum, daily range and coefficient of variation) in relation to riparian vegetation status, geomorphology, hydrology and elevation. Using these metrics, we compared thermal regimes of streams in Yellowstone National Park with contrasting degrees of ungulate herbivory. Sites with primarily herbaceous vegetation experience heavy riparian browse by bison ( Bison bison ), which are less vulnerable to predation than other native ungulates. In contrast, sites dominated by woody vegetation, especially willows ( Salix spp.), are associated with lower ungulate browse, attributed in part to restoration of large carnivore populations. Mean daily temperatures varied during summer and were not consistently correlated with riparian vegetation state. However, streams with herbaceous vegetation had higher summer maximum temperatures than streams dominated by woody vegetation, with greater differences in later summer. Throughout summer, daily stream temperature ranges and coefficients of variation were up to five times greater in herbaceous sites. We conclude that terrestrial factors, including trophic cascades, can contribute to heterogeneous riparian vegetation states and alter stream temperature regimes. Furthermore, the link between these terrestrial dynamics and stream temperature was strongest in the late summer, when stream temperatures often exceed thermal thresholds for cold‐water biota. As this region's hydrology shifts from snowmelt to rain‐dominated, exacerbating late‐summer temperature spikes, this link between terrestrial wildlife dynamics and stream temperature may increasingly influence aquatic ecosystem processes and food webs.
ABSTRACT Understanding differences between ecological communities is key to understanding community assembly. Analysing these dissimilarities, including using various indices, helps assess community uniqueness, understand the effects of disturbances and guide conservation efforts. This approach is particularly relevant for vulnerable freshwater fish communities in regions like the Eastern Himalayas, where factors like isolation and connectivity have shaped high diversity and endemism. This study focuses on the Teesta–Jaldhaka, Manas, Kameng and Subansiri River basins of the Eastern Himalayas. We aimed to test consistency among the fish community dissimilarity and uniqueness across the freshwater basins of the Eastern Himalayas. We also aimed to identify the key ecological and biotic drivers across the river basins. We employed two approaches: a dissimilarity‐based (Jaccard index) and a uniqueness‐based (local contribution to beta diversity) approach, using variation partitioning and regression‐based models. Presence–absence data were procured from in‐field surveys and peer‐reviewed literature, along with bioclimatic, topographic and human‐induced variables. Community dissimilarity and uniqueness are driven primarily by the presence of dams, precipitation of the wettest month and slope, contributing significantly to total variation. Mid‐elevation zones in the Teesta–Jaldhaka, Subansiri and Manas basins have the highest local contributions to beta diversity, indicating greater uniqueness, particularly in the Subansiri basin. The high level of unexplained variation in community dissimilarity and uniqueness underscores the complexity of the ecological system under study. Furthermore, variation in ecological patterns has largely been attributed to anthropogenic, climatic and landscape factors. Nevertheless, the predominant focus on local environmental variables must be balanced against the broader influences of existing dams, planned hydropower development and ongoing climate change.
ABSTRACT Water is the main factor limiting vegetation persistence in drylands. Despite the dry landscape, inselbergs are generally surrounded by dense vegetation cover. The hydrological mechanisms by which inselbergs mitigate the water scarcity are still poorly understood. This study assessed how surface runoff dynamics on granite inselbergs sustain the formation of microrefugia in the semiarid Caatinga, integrating geomorphological, pedological, hydrological and floristic analyses. In three inselbergs, soil and colluvial sediment profiles were opened, described and sampled along a fragmented catena. Mean annual precipitation (2017–2023) was 270 mm, concentrated between February and July (82.8% of events), peaking at 460 mm in 2020. Observed textures ranged from sandy loam to clay, and surface horizons reached 18.96% organic carbon. It was observed that convex surfaces (summit and shoulder), due to diverging surface runoff, have shallower soils with predominantly sandy sediments. In contrast, concave areas (backslope and footslope) function as deposition areas due to the convergence of surface runoff, hosting more clayey soils with higher organic carbon content, greater water retention capacity and greater depth. In these soil pockets, the network of fractures in the granitic bedrock favours localized infiltration and groundwater recharge pulses, even under torrential rains. These areas are home to denser, more diverse vegetation composed of species typical of humid phytogeographic domains, functioning as ecological refuges amid the xeric matrix of the Caatinga. In general, the volumes of water captured by the rocky slopes of inselbergs during precipitation events, followed by downstream runoff that allows for accumulation, are fundamental to the formation of microrefugia. This demonstrates that inselbergs act as “islands of moisture” essential to the conservation and resilience of the ecosystem in the face of seasonal rainfall and climate change projections.
ABSTRACT The ecological responses of urban groundwater ecosystems to anthropogenic pressures are poorly understood. Historic hand pumps offer a simple and promising access point to this hidden habitat and may facilitate the detection of groundwater fauna. This study provides a first overview of the stygofauna of Leipzig, Germany, and associated anthropogenic influences, based on investigations of historic hand pumps and groundwater monitoring wells. Statistical comparisons between sampling methods were conducted to assess potential selective effects. Leipzig's groundwater is characterized by distinct physicochemical conditions, notably elevated temperatures and reducing environments, indicating disturbed yet characteristic features of an urban aquifer in Central Europe. A total of 4500 stygofaunal individuals representing eight taxonomic groups were recorded, displaying pronounced spatial heterogeneity. Although three chemical parameters showed minor associations with faunal occurrence, these relationships should be interpreted with caution. Overall, the urban stygofauna reflects a complex interplay of natural and anthropogenic drivers. Significant differences in both physicochemical properties and faunal assemblages were observed between sampling methods. These differences likely arise from spatial factors and methodological constraints. Monitoring wells appear to alter in situ habitat conditions, limiting the representativeness of sampled fauna, while hand pumps exhibit taxon‐specific selectivity, resulting in biased community composition. Consequently, direct comparability between these sampling approaches appears to be limited.
ABSTRACT Three lakes in the Menderes Basin of western Türkiye carry sharply different water regimes: brackish, lagoonal Bafa, hypertrophic in phosphorus but not in algal biomass; turbid, alkaline, endorheic Yayla; and spring‐fed karstic Işıklı, close to reference condition. No basin‐wide assessment of their phytoplankton and water chemistry has been published. We assessed 16 station‐seasons with a three‐layer fuzzy inference system aligned to the Water Framework Directive. It scores the biological and the physicochemical component separately, then combines them by the Directive's one‐out‐all‐out rule, which keeps the limiting element visible. Ordination of 97 taxa separated the three lakes along a gradient set by conductivity, temperature, phosphorus, suspended solids and transparency, the constrained axes carrying 59.4% of species inertia. With only three lakes, that separation is descriptive and cannot be tested. The phytoplankton index MPTI tracked every major stressor (phosphorus ρ = 0.976, suspended solids ρ = 0.859), whereas the alternative Phyto‐Tr index responded to phosphorus alone. Cross‐validated agreement with the MPTI‐derived reference classification was 81.2% (13/16; Cohen's κ = 0.751). That reference is itself derived from MPTI, so the figure is an internal consistency check, not external validation. The independent anchor is MPTI's agreement with Carlson's Trophic State Index (ρ = 0.879). Membership functions anchored to regional Directive thresholds matched, and did not exceed, four data‐driven recalibration schemes (13/16 against 14/16). We keep them because they express status against a fixed reference, not rank within the sample. A limiting element is attributed only where the two components lie further apart than the system can resolve, which holds at 10 of the 16 stations. The six that do not resolve are at near‐reference Işıklı and at the dry‐season Yayla stations, where both components agree. The attribution is co‐monotone with the trophic gradient and reads as transparent bookkeeping, not an emergent signature. Within‐lake clustering is strong, so the 16 observations amount to roughly three to six independent lake‐level units, and the framework is offered as a proof of concept for a single basin.
ABSTRACT Inspired by nature‐based solutions, constructed wetlands are increasingly acknowledged as effective wastewater treatment tools, with diverse structural designs suited to various contexts. In the present work, two typologies of these systems, a full‐scale farm wetland and three pilot scale systems, were tested in terms of nitrogen and phosphorus removal from agricultural runoff, as well as their potential to maintain treatment performance under intensified conditions and reduced space requirements. The farm wetland, a full‐scale surface flow wetland operating for more than 20 years on an agricultural farm in Italy, was monitored for different years. It showed high water retention rates (> 60% in most monitored years and up to 100% in some years) and high nutrient retention efficiencies, with TN retention generally exceeding 65% and TP retention exceeding 46%. However, the size of this system might be an obstacle to its wider application. With that goal, three pilot systems were tested, namely surface flow (SFCW) and horizontal sub‐surface flow (HFCW) constructed wetlands. The HFCWs were incorporated with two distinct compositions: one packed with gravel (HFCW‐G) and another containing 10% v/v biochar in addition to gravel (HFCW‐B). All CWs were monitored for 1 year, during which applied flow and nutrients concentration were studied as variables influencing their performance. The results showed that, overall, the SFCW performed the best, granting average TN reduction up to 78%, significantly higher in comparison to HFCW‐B and HFCW‐G (33% and 34%, respectively). In terms of TP removal, on average, the HFCW systems presented similarly high performances (43%) compared to SFCW system (33%). Seasonal fluctuations in nitrogen removal reflected a temperature and seasonal influence on the performance of the systems, particularly in the system containing biochar (HFCW‐B). This study therefore confirms that comparable or higher areal nutrient removal rates can be achieved under intensified operating conditions (e.g., increased hydraulic and nutrient loading rates), suggesting that farm wetland design might consider reduced footprint while maintaining treatment efficiency.
ABSTRACT Root water uptake (RWU) is a critical process regulating the hydrological cycle and sustaining ecosystems, particularly in arid and semiarid regions. However, the spatiotemporal dynamics of RWU and the external factors controlling it have not been fully characterised. In this study, a combination of in situ experiments and a deep neural network model was adopted to characterise the RWU dynamics of Salix psammophila over a complete growing season in the Mu Us Sandy Land. Furthermore, SHapley Additive exPlanations (SHAP) was applied to identify its influencing factors. The results show that the proposed Res‐CNN‐LSTM model effectively integrates the vertical profile feature extraction capability of CNN and the time series modelling capability of LSTM, while incorporating a residual structure that enhances the network's stability and interpretability in RWU simulation. The model demonstrates superior performance in modelling the nonlinear spatiotemporal dynamics of vegetation RWU, achieving R 2 values no less than 0.93. Unlike traditional numerical simulations that rely on complex physical parameters, it enables end‐to‐end prediction based on easily accessible meteorological, soil water and groundwater data. SHAP‐based interpretation further reveals that groundwater, potential evapotranspiration, precipitation and soil water collectively account for 81.23% of the total contribution to water stress, with groundwater identified as the most influential factor, contributing 30.61%. Leveraging deep learning to identify key drivers of RWU establishes a new pathway for ecohydrological research. The findings offer valuable guidance for supporting ecological restoration efforts in water‐limited ecosystems.
ABSTRACT Terracing is widely applied for soil and water conservation in semi‐arid regions; however, its influence on forest ecohydrological processes remains insufficiently quantified, as previous studies have largely emphasized erosion control rather than plant–soil–atmosphere interactions. This study evaluated how terracing regulates these interactions in Pinus tabuliformis plantations on the Loess Plateau, China. Field measurements during the 2023–2024 growing seasons quantified soil water content (SWC), canopy conductance (Gc), and stand transpiration (T_stand) under terraced and unterraced conditions. Terraced plots maintained higher SWC (0.11 vs. 0.09 m 3 m −3 ; +17%–23%) and greater T_stand (0.39–0.52 vs. 0.20–0.29 mm d −1 ), with peak differences of 80%. Terracing delayed diurnal transpiration peaks and enhanced midday fluxes, indicating differences in vegetation water‐use dynamics under improved soil water availability. T_stand correlated strongly with SWC ( R 2 = 0.362, p < 0.001), whereas transpiration stability improved by 38%. These findings demonstrate that terracing increases soil water availability, regulates soil–plant–atmosphere interactions and supports more stable vegetation water use under water‐limited conditions in semi‐arid forests.
ABSTRACT Tourism is one of the main anthropogenic stressors affecting tropical freshwater ecosystems, frequently causing deterioration in water quality and ecological integrity. The SARS‐CoV‐2 pandemic and the lockdown measures implemented in 2020 created a unique opportunity to evaluate ecosystem responses to reduced human activity. This study assessed changes in the ecological quality of the Gaira River, located in the Sierra Nevada de Santa Marta, before (2019), during (2020) and after (2021) the COVID‐19 Lockdown period using the phytoplankton‐based Ecological Quality Index (EQI RG‐PHY ). Eleven monitoring campaigns were conducted across four sampling stations. During Lockdown, dissolved oxygen increased from 5.4 ± 0.6 mg L −1 to 7.1 ± 1.6 mg L −1 , whereas conductivity and nutrient concentrations decreased. EQI RG‐PHY values improved from critical conditions in the Pre‐lockdown period (4.54–5.16) to moderate–good ecological quality during lockdown (5.76–6.05), followed by a decline back to critical conditions in the Post‐lockdown period (4.50–4.62). Highly significant differences among periods were observed (ANOVA), using the four sampling stations as replicates for each period. Phytoplankton diversity showed greater stability during lockdown and slight reductions afterward, particularly in dominant taxa. Results demonstrate that tourism‐related pressures strongly influence the ecological quality of tropical rivers and that short‐term reductions in anthropogenic activity can promote rapid ecosystem recovery. The study also highlights the remarkable resilience of aquatic ecosystems and emphasizes the urgent need to strengthen environmental awareness, sustainable tourism practices and conservation strategies to reduce long‐term human impacts on freshwater ecosystems.
Ecosystem functions are profoundly influenced by changes in moisture and heat conditions. Previous research predominantly focused on water-energy limitations on the Tibetan Plateau (TP) using moisture indicators, which often ignored the critical role of energy factors, and study examining water or energy limitation regimes from an ecosystem perspective remains scarce. In this study, we employed the ecosystem limitation index (ELI), which comprehensively assesses how ecosystem functional processes respond to both water and energy constraints from multiple source data, to evaluate the spatiotemporal variations of ecosystem water limitation across the TP from 1986 to 2018, and the dominant drivers behind the changes were also investigated. A widespread decrease in ecosystem water limitation across the TP was found during 1986-2018, whereas decreased ELI was observed in 54.1% of the total area, and regions with water-limited regimes exhibited a downward trend. Three dominant ecosystems, including alpine grasslands, alpine meadows and alpine deserts, showed decreases in ELI, whereas other ecosystems exhibited upward trends. At the grid scale, ELI variation in 28.4% of the total area was primarily driven by rising temperatures, followed by changes in precipitation in 23.6% of the total area. At the ecosystem scale, water and vegetation growth collectively explained over 50% of the ELI variation across all ecosystems. These findings provide insights into the ecosystem water-energy shift regime on the TP, thus improving our understanding of the carbon cycle change on the TP.
ABSTRACT In arid inland basins, groundwater serves as a critical buffer sustaining vegetation productivity, yet lagged and non‐linear vegetation responses to groundwater dynamics remain insufficiently quantified. Here, an integrated lag‐aware and threshold‐based framework is developed to quantify delayed and non‐linear NDVI responses to groundwater depth (GWD) and to distinguish climatic from human‐regulated pathways. Results indicate that GWD with a 2‐month lag explains approximately 35% of NDVI variability ( R 2 ≈ 0.35, p < 0.01). This lag represents an integrated ecohydrological response time rather than a direct transmission time from groundwater to the canopy. An apparent GWD threshold emerges at approximately 1.39 m, equivalent to 1390 mm. NDVI increases rapidly when the water table is shallower than this threshold (≈+0.006 NDVI m −1 , p < 0.01), whereas sensitivity weakens at greater depths. This threshold likely reflects a transition in groundwater accessibility and root‐zone water buffering, rather than a universal physiological limit. Additional response inflection points occur around CWSI ≈ 0.69 and AI ≈ 0.37 (AI = P/PET), marking a transition from climate‐dominated groundwater depletion to regimes increasingly influenced by anthropogenic recharge. PLS‐SEM analysis shows that runoff (β = −7.5), water‐use efficiency (β = +5.0) and aridity (β = +3.4) significantly regulate GWD, whereas the groundwater → NDVI pathway exerts the strongest positive effect on vegetation greenness (β ≈ +10.9, p < 0.01). The integrated model explains 37% of groundwater variance and 65% of NDVI variance. These findings provide quantitative, lag‐aware threshold references to support adaptive groundwater management under intensifying drought stress.
The Yangtze River waterway regulation plays a vital role in supporting China's water transport system. Traditionally, waterway regulation has mainly relied on engineering measures to ensure navigability and stability. However, conventional methods, although effective in many respects, may cause environmental disruptions, such as habitat degradation and water quality issues. In response, eco‐friendly green technologies have been increasingly highlighted. This review introduces typical examples of green technologies that have been implemented in the Yangtze River waterway regulations and compares their subsequent performances across different waterways, from which the significant role of spatial monitoring is highlighted. Typical examples include water‐permeable ecological riverbed protection structures and implantable ecological bank stabilisation. Comparisons indicate the following. First, by integrating green technologies with spatial monitoring that tracks ecological conditions such as hydrology and biodiversity, a balance can be obtained between waterway functionality and ecological preservation. Second, effective and lasting ecological outcomes of the green technologies require ongoing monitoring, which should be fed back into the green technologies.
Groundwater-dependent ecosystems (GDEs) are essential to ecological stability in semi-arid regions, yet their identification and mechanistic interpretation remain constrained by limited long-term observations and insufficient model interpretability. Using the West Liao River Plain as a case study, we developed a machine learning framework for dynamic GDE mapping based on groundwater depth, vegetation maps, land use/land cover, multisource remote sensing and environmental variables. XGBoost, instead of random forest, was selected to reconstruct GDE distributions in 2004 and from 2009 to 2022. The spatiotemporal evolution and driving mechanisms of GDEs were analysed by integrating groundwater-depth validation, SHAP interpretation, DBSCAN clustering, GDE dynamic type classification and logistic deviance partitioning. XGBoost showed good classification performance, supported by temporal generalisation tests and threshold sensitivity analysis. From 2009 to 2022, the GDE area showed an overall fluctuating decline followed by later recovery and was significantly negatively correlated with mean groundwater depth. SHAP identified 1 m soil moisture (SM), NDPI coefficient of variation (GS) and EVI coefficient of variation (GS) as the dominant predictors, with NDPI showing stronger discrimination under low vegetation cover. The modal groundwater depth was 3.87 m for GDEs and 3.94 m for non-GDEs, suggesting that many GDE pixels may be in a mixed water-use state transitioning from groundwater dependence to precipitation dependence. Deviance partitioning analysis showed that climate change dominated GDE degradation and recovery from 2009 to 2015, whereas from 2016 to 2022, degradation remained climate dominated but recovery showed a stronger signature of human activity control.
ABSTRACT Grassland response to changes in water availability is closely tied to the traits of the plant community. Plants can adopt either moderate and efficient (conservative) or rapid and demanding (acquisitive) resource use strategies. These strategies combined with the plant interactions with microbes, such as arbuscular mycorrhiza fungi (AMF), determine the grassland productivity and efficiency. This study compares the drought response of two hay‐meadow seed mixtures commonly used in agricultural grassland that differ in their resource use strategies, representing conservative and acquisitive strategies. The mixtures were tested in 12 small‐scale lysimeters in an experimental garden under two irrigation levels (drought and wet). We measured water fluxes, aboveground and belowground phytomass and AMF spore productivity throughout a drought of 62 days. Despite differing resource use strategies, both mixtures exhibited similar reductions in actual evapotranspiration and aboveground phytomass under drought. However, the conservative mixture showed higher water use efficiency (WUE) when accounting only for aboveground phytomass and a less pronounced compositional shift. In the acquisitive mixture, the root:shoot ratio of grasses and the AMF spore abundance in the soil were reduced compared with the conservative mixture. We also identified legume productivity, roots and AMF spores' community composition as key factors influencing WUE. In a changing climate with greater frequency and severity of droughts in the European Alps, opting for grassland mixtures with more conservative characteristics should be considered, as they (i) reach the productivity of acquisitive grassland even under wetter conditions and (ii) show higher efficiency and delayed senescence under drought conditions.
ABSTRACT Floodplain lakes are biodiversity hotspots whose ecological functioning is strongly controlled by hydrological connectivity and flow variability. This study investigates the relationships between hydraulic conditions and benthic macroinvertebrate habitat suitability in Jama Roma, a representative floodplain lake of the near‐natural Bug River system in eastern Poland. The lake is characterised by a contrafluent–confluent exchange regime, in which the direction and magnitude of river–lake connectivity vary dynamically with flood stage. A two‐dimensional ecohydraulic model (Iber v3.3.1) was used to simulate spatial and temporal patterns of water depth and flow velocity during a real flood event. Habitat suitability was assessed using field‐derived habitat preference curves based on macroinvertebrate sampling data, supported by biodiversity metrics and statistical analyses of relationships between hydraulic variables and macroinvertebrate occurrence. The results demonstrated that the highest habitat suitability and macroinvertebrate abundance occurred under moderate hydraulic conditions, particularly at depths of 0.5–1.0 m and velocities below 0.15 m/s. Spatial and temporal changes in hydrological connectivity strongly influenced the distribution and persistence of suitable habitats, with low‐velocity littoral and central lake zones functioning as key ecological refugia during floodplain inundation. The study advances ecohydrological assessment of floodplain lakes by integrating dynamic hydrodynamic modelling with field‐based biological preferences in a spatially explicit framework. Beyond site‐specific findings, the results provide environmentally relevant reference conditions for near‐natural floodplain systems and demonstrate a transferable approach for evaluating flow–habitat interactions in river–floodplain landscapes under changing hydrological regimes.
ABSTRACT The increase in wildland fires in recent decades due to long‐term fire suppression policies and increasingly favourable climate factors has also increased the elevation range of wildland fires. In the mountainous western United States, this has led to an increasing influence of fire on landscape‐level vegetation patterns in snow‐dominated ecosystems. The resulting hydrological implications of these fire‐driven changes in vegetation patterns are being studied. In forests, fires consume surface fuels and understory vegetation, reduce tree canopy cover, darken tree boles and deposit black carbon. Together, these impacts alter snow accumulation and persistence in burned areas compared to pre‐fire conditions. In this study, we use field measurements and remote sensing of snow and fire conditions within the footprint of the Caldor Fire, a large wildland fire in the central Sierra Nevada, California, that burned in 2021. In this work, we explain the variability in snow accumulation and persistence and compare these findings to measurements at snow pillow and course stations within and near the Caldor Fire boundary. We show that north‐facing slopes at mid‐ to high‐elevation see snowpack accumulation benefit from fire, especially in areas burned at low and moderate severity. Other elevations, aspects and fire severity classes experienced decreases in snowpack. Compared to established snow measurement sites, this response to fire led to deviations in the behaviour of snowpack within the burned area. This work shows how the locations of established monitoring sites differ from the surrounding basin in their response to a major disturbance and can inform the interpretation of snow measurements in post‐fire landscapes.
Estuarine wetland restoration often rests on the assumption that expanding water surface area equates to restoring ecological function. However, the trade-offs between artificial interventions and natural hydrological connectivity remain poorly quantified. Focusing on the Liaohe Estuary, a region subject to intense anthropogenic disturbance, we quantitatively disentangled the interactions between natural drivers (climate and ocean dynamics) and anthropogenic landscape modifications. Using a long-term dataset (1984-2021) from the JRC Global Surface Water Explorer, we applied Graph Theory and Partial Least Squares Structural Equation Modelling (PLS-SEM) to identify the determinants of hydrological connectivity. Results identify Hydrological Landscape Fragmentation (HLF) as the dominant negative driver of connectivity (beta = -0.443, p < 0.001), indicating that landscape spatial configuration outweighs total water surface area in importance. Crucially, we reveal a 'connectivity paradox' driven by Potential Artificial Water Surface (PAWS): whereas PAWS expands water area (beta = +0.302), it simultaneously compromises hydrological connectivity through a significant negative indirect effect (indirect effect = -0.13) by exacerbating fragmentation. Furthermore, contradicting conventional wisdom, we confirm that ocean dynamics and air temperature act as positive controls on connectivity. Our findings suggest that recent restoration projects exhibit 'fragmented recovery,' where water area expansion comes at the expense of landscape integrity. Consequently, we argue for a paradigm shift from 'water replenishment and expansion' to 'structural reintegration,' prioritizing the synergy between landscape connectivity and natural tidal forces.
Environmental DNA (eDNA) is emerging as a promising hydrological tracer, complementing its established role in ecological monitoring. Here, we develop a feasible and easily realisable method for including eDNA sampling in automated hydrological time-series sampling. The 3D printable and reusable frames, appropriate for common filter membranes, passively sample eDNA in triplicate replication. The influence of the frames on other hydrological parameters, such as the composition of ions and organic matter, was assessed, as well as the impact of standing time. No significant influence on water chemistry measurements could be detected through the presence of eDNA passive samplers. As expected, the impact of standing time could be observed for both biodegradable parameters, organic matter and eDNA. Simultaneously, an increase in total DNA content was observed over time, probably related to biofilm growth. Surprisingly, the concentration of a spike fragment stabilised after 24 h of exposure to sampling water and remained at that level even until 7 days of exposure to sampling water. Biofilm formation could play a role in this stabilisation of free eDNA over longer periods. Due to the reusability and adaptability of the 3D printable frames, there is no need for additional devices to integrate eDNA sampling. Our results show that passive eDNA sampling can be seamlessly integrated into automated hydrological time series monitoring by simultaneously sampling the composition of ions and organic matter and, under certain limitations, e.g., the use of microbial communities, even if several days of standing times are necessary. The adaptability of the frame to various membrane formats and the reusability of the model make it broadly applicable in research and applied cases.
ABSTRACT In river systems, vegetation undergoes varying degrees of a quasi‐static lodging posture under flow conditions. Under steady flow conditions, after reaching dynamic equilibrium with the ambient flow, the vegetation maintains a relatively stable quasi‐static lodging posture. This process significantly alters the flow–vegetation interaction mechanisms. To investigate the impact of submerged vegetation patch lodging morphology on the flow characteristics of engineered rivers with ecological objectives, taking the quasi‐static lodging posture as a conceptual basis, this study conducted numerical simulations of rectangular vegetation patches parameterized by rigid cylinders with four different prescribed lodging morphologies (0°, 20°, 40° and 60°) under submerged conditions based on the three‐dimensional Reynolds Stress Model (RSM). The reliability of the model was verified through flume experiments, and the effects of lodging morphology variations on velocity distribution, wake characteristics and turbulent kinetic energy were systematically analysed. The results indicate the following: (1) For upright vegetation patches, the flow velocity distribution at different submerged positions of the vegetation layer varies significantly, and the vegetation lodging effect plays an important role in effectively weakening this difference in flow velocity distribution. (2) Increasing lodging morphologies substantially reduces patch flow resistance, leading to enhanced internal velocity, weakened lateral flow divergence and shortened wake scale and velocity recovery length, thereby systematically regulating spatial heterogeneity in the local flow velocity field. (3) As the lodging morphology of vegetation increases, the turbulent kinetic energy of water flow within and behind it decreases significantly, which is not conducive to the construction of a highly heterogeneous spatial turbulence field. This study clarifies the quantitative relationship between vegetation lodging morphology and hydraulic factors and provides basic hydraulic parameters and preliminary theoretical references.
