Large tropical rivers act as important pathways of nitrogen transport from land to the sea, with the final river reaches potentially retaining nitrogen. In the present study, a mass balance approach was used to evaluate nitrogen retention over a two-year period from a 50 km reach of the Padma River in Bangladesh, approximately 150 km upstream of where the river discharges into the Bay of Bengal. The relationship between concentration and discharge was estimated from 58 nitrogen concentration and discharge measurements. Daily nitrogen flux was then calculated daily from the hydrological inflow and outflows of the reach, and total nitrogen (TN) retention was estimated based on the flux difference of TN inflows and outflows. To compare with mass balance estimates, nitrogen loss due to water retention (NLWR), sedimentation, potential denitrification (PDR), and nitrogen fixation (NFR) were estimated from the water column of the river. NLWR and sedimentation were estimated from the nitrogen concentration and discharge. PDR and NFR were measured using the acetylene inhibition method and upscaled using outflow discharge and water travel time. Up-scaled PDR and NFR were compared with hydrologic retention and sedimentation to assess the relative contributions of these processes to retention. Monthly mass-balance measurements showed a substantial seasonal variation in nitrogen retention. Estimated maximum retention values (tonnes per month) of NLWR, sedimentation, PDR, and NFR were all associated with the monsoons. However, the percentage contribution of PDR and NFR to TN retention was higher in non-monsoon months (post-monsoon, dry/winter and pre-monsoon), suggesting nitrogen retention mechanisms varied seasonally. TN retention via NLWR accounted for the largest portion of total TN retention in every season, always exceeding 50% of total TN retention. Sedimentation was second most important in monsoon and post-monsoon seasons, while PDR in submerged geomorphic units was second most important in dry/winter and pre-monsoon seasons. Net PDR in the water column contributed the least (1-6%) to total TN retention in all seasons.

Linear disturbances within boreal Canada (e.g., seismic lines) have the potential to significantly alter carbon cycling in Canada’s northern peatlands, creating the potential to switch these significant carbon stocks from long term carbon sinks to carbon sources. While efforts have been made to quantify the impacts of linear disturbance on ecosystem, vegetation, soil composition and GHG emissions, little is currently known about the specific interactions between the disturbance to peat hydrophysical structure and composition and the resulting alterations to CO 2 and CH 4 dynamics. To this end, 16 poor fen peat cores representing the top 10 cm of the peat profile were collected on and adjacent to a seismic line reflecting four degrees of disturbance complete mulch covering, partial mulch covering, mechanical roughing only, and undisturbed. In controlled laboratory conditions cores were then subjected to two subsequent static water table conditions (3 and 8 cm below core surface) for a period of ~30 days each with GHG flux measurements occurring 2-3 days. Cores were then subdivided into 5 cm segments and underwent detailed hydro physical (i.e., bulk density, porosity, water retention) and compositional (i.e., C:N, vegetational assemblage) analysis. Results show that both peat composition and hydrophysical structure were strong predictors of greenhouse gas emissions. Higher CO 2 emissions were related to both peat with high bulk density, low total and effective porosity and low C:N ratios, which occurred at depth in the undisturbed cores and at the surface where mechanical mulching and mixing occurred. Increased CH 4 emissions occurred in disturbed cores characterized by a reduction in macropores and effective porosity near the surface; these emissions were episodic in nature and occurred where trapped gas was released during pore desaturation when water tables were lowered. Additional work should therefore be conducted at field scale to further assess the interrelationships between direct changes to hydrophysical structure and these other impacts, to better determine the long-term changes to carbon cycling in systems disturbed by seismic line creation.

In many rural areas of arid and semi-arid regions, balancing agricultural and environmental water needs is a key challenge facing resource managers. This is complicated by the tendency for the water needs of cultivated crops to be better understood than those of aquatic ecosystems. In particular, the timing and magnitude of flow needed to sustain key ecological functions remain poorly quantified in many regions. This work aims to quantify hydrologic conditions that support persistence of key ecosystem species using a functional flows framework. We use the coho ( Oncorhynchus kisutch) and Chinook ( Oncorhynchus tshawytscha) salmon run in Scott Valley, a 2,109 km 2 undammed rural watershed in northern California, USA, as a case study. Taking advantage of a nearly two-decade ecological monitoring dataset and long-term stream gauge measurements, we used lasso regression to build predictive models of coho and Chinook salmon reproductive success based on hydrologic metrics. To control for cohort effects, we chose normalized ecological response metrics for coho and Chinook (number of outmigrating smolt per spawning adult or spawning adult female). For both species, we calculated optimal prediction models using a cross-validation bootstrapping approach to resample and test on unsampled observations. Lambda values, a key fitting parameter in the lasso models, were selected based on an average relative test error threshold of 1.0. Selected lambda values were used to calculate a final predictive model, or Hydrologic Benefit function, using the full dataset for each species. Hydrology could explain a greater degree of variance in relative coho reproduction than in Chinook. The hydrologic metrics that explain the greatest variance in coho reproduction values occur during the window of their parents’ spawning and, to a lesser extent, in the spring and fall of their year of rearing in freshwater. This supports an interpretation that spawning conditions may exert a significant influence on the mortality rates of the hatching juveniles. Robustness of the results indicate that this method for empirically deriving hydrologic metrics with the highest ecological benefit for a threatened species may be useful in other watersheds, where sufficient ecological data records are available, to evaluate trade-offs and support water management decisions in human-altered novel ecosystems.

Ecohydrology engineering provides a valuable framework for addressing emerging environmental challenges by integrating ecological and environmental engineering principles. In this study, we discuss the potential of parsimonious, physically-based ecohydrological models through the lens of three case studies: sustainable irrigation, urban heat island mitigation via green roofs, and mangrove restoration for climate change mitigation. First, we investigate sustainable irrigation strategies, illustrating the trade-offs between water conservation and soil salinization. This highlights the delicate balance required to optimize crop yield while mitigating soil degradation. Second, we explore the role of green roofs in urban heat island mitigation, showing how vegetation and water dynamics on rooftops can enhance latent heat flux, thereby potentially reducing urban temperatures and improving building energy efficiency. Lastly, we assess the climate mitigation potential of mangrove restoration, accounting for the impacts of salinization and sea-level rise. We demonstrate that carbon sequestration in mangrove ecosystems may be strongly limited by productivity reduction due to salinity and reduced area availability under sea-level rise. These examples highlight the value of simple ecohydrological models in providing critical insights into sustainable environmental management. Ecohydrological engineering, therefore, offers promising avenues for developing innovative solutions that leverage the intricate connections between water and biota to address emerging challenges.

Extracting water from discrete xylem and soil samples and continuous (long-term) monitoring of water vapor across the soil-plant-atmosphere continuum remains challenging and under a large debate. Here, we present a detailed one-year study in the Fort Worth Botanic Garden (north-central Texas) to evaluate the analytical robustness of the centrifugation extraction method and understand water sourcing from three common urban tree species (Elderberry, Sambucus canadensis; Cherry Laurel, Prunus caroliniana; and Boxelder Maple, Acer negundo). Xylem (N=110) isotope ratios (δ 18O and δ 2H) are compared to local precipitation (N=498), throughfall (N=33), and soil water (N=105) at different depths (0-38 cm). Complementary soil water samples were obtained from cup suction lysimeters (N=42) (0-38 cm). Soil and xylem water extraction volumes ranged from 100 µL to 7.5 mL in plant samples and from 100 µL to 10.5 mL in soil samples. Extraction success rates were 68.8% and 75.2% for xylem and soil samples, respectively. The minimum sample total water content for effective extractions was determined as 10.6% (soil) and 17.8% (xylem). Xylem mean narrowband and broadband (proxy for organic contamination) were 0.23±0.40 (-) and 1.00±0.01 (-), respectively. These values agree with mean narrowband and broadband metrics from throughfall and soils, which highlight the non-invasive nature of centrifugated extractions. Annual mean soil δ 18O compositions (-3.6±1.7‰) corresponded with the throughfall input (-3.6±2.4‰). Xylem δ 18O compositions exhibited a strong temporal enrichment trend at the end of the winter, summer, and fall seasons. Mean spring xylem δ 18O (-2.85‰) was less variable and close to soil mean compositions (-2.82‰). For this season, Bayesian mixing analysis showed source water contributions from distinct soil depths: 0 cm to 12.7 cm for Boxelder Maple, 12.7 cm to 25.4 cm for Cherry Laurel, and 12.7 cm to 38.1 cm for Elderberry. Our results offer a standardized and effective protocol for centrifugation extractions and reveal plant water uptake preferences in a highly altered urban green space during an unprecedented warm year.

11institutetext: Knowledge-based Systems and Document Processing Research Group Faculty of Computer Science Otto-von-Guericke-University Magdeburg 11email: [email protected] Chemical changes of base cations in bulk precipitation ( BP) induced by canopy alteration significantly influence the buffer action against soil acidification and the consequent biogeochemical processes in forest ecosystems. However, the underlying mechanisms that influence the varying magnitudes and directions of acid neutralizing capacities (ANC) in BP during canopy passage remain less understood. Here, we investigated the chemical compositions of base cations (potassium (K +), calcium (Ca 2+), magnesium (Mg 2+) and sodium (Na +)), the capacity of individual alkaline ions to neutralize acidity, in addition to their spatio-temporal variabilities outside and beneath the canopies of Chinese pine plantation ( Pinus tabuliformis Carr.) throughout 2019 growing season with a large proportion of annual rainfall. Results showed that volume-weighted mean concentrations of base cations in throughfall ( TF) were significantly increased with the highest enrichment ratio by K +, followed by Mg 2+, Ca 2+ and Na +. Canopy leaching mainly occurred for K + (59.06%) and Mg 2+ (54.20%) whereas dry deposition of Ca 2+ (57.27%) were the dominant net throughfall flux component. TF ANC was significantly higher than BP, indicating that rainwater beneath the pine canopy became less acidic. Ca 2+ was the predominant acid neutralizing component, followed by K + and Mg 2+ in both BP and TF. However, the capacity of Ca 2+ for neutralizing acidity was weakened whereas K + and Mg 2+ were enhanced in TF compared to BP. Additionally, the concentrations of TF base cations were significantly negatively or positively correlated to canopy cover and TF amount, with exception of TF K +. Antecedent dry period and rainfall intensity were the most influential meteorological parameters affecting the intra-event variation trend and magnitude of TF base cations. Our findings contribute to understanding the controlling processes and underlying mechanisms that drive the complex interactions between base cations nutrients and forest ecosystem.

Water potential is a crucial parameter for assessing tree water status and hydraulic strategies. However, methods for measuring water potential, such as the Scholander pressure chamber, are destructive and discontinuous, and difficult to perform in tall forests. Consequently, important dynamics in water potentials, particularly during short-term drought, are difficult to capture. Recent advancements have introduced low-maintenance sensors capable of measuring continuous, high-resolution stem water potentials. If applicable to forest trees, such sensors hold the potential to significantly enhance our understanding of tree water relations. We evaluated these sensors in a temperate, diffuse-porous tree species ( Carpinus betulus) over a growing season marked by dry-down periods and heat. Concurrent measurements of branch water potential, sap flow, and environmental factors (air temperature, vapor pressure deficit, and soil water content) were conducted. Midday stem water potentials of C. betulus reached minimum values of -3.39 ± 0.10 MPa and exhibited pronounced seasonal fluctuations, mirroring changes in environmental conditions and sap flow. Comparison of stem water potentials with Scholander-type measurements revealed a very good correlation with predawn (R 2 = 0.98) and a general agreement with midday measurements (R 2 = 0.71). Diurnal variations in stem water potentials and sap flow exhibited a hysteresis, consistent with other plant parameters. In this first assessment, the agreement with Scholander-type measurements, sap flow, and environmental parameters suggests the tested water potential sensors yield reliable data. If applicable to other tree species, including conifers, these sensors could significantly advance our understanding of tree water relations and their role in forest drought responses.

Pinus brutia (pine) and Cupressus sempervirens (cypress) are two important forestry species in the Mediterranean region, with different strategies to cope with water stress. The overall goal of this study is to investigate ecohydrological processes of these two species. Specific objectives are: (i) to quantify their transpiration; (ii) to analyze relations between meteorological variables, soil moisture, sap flow, leaf conductance and twig water potential; and (iii) to assess differences in soil water balances and dynamics between three canopy cover conditions (under canopy, edge of canopy, open area). The study site is a plantation forest in Athalassa Forest Park, in Cyprus with a long-term average annual rainfall of 315 mm. The site was converted from rainfed agriculture in 2011. Observations of sap flow (12 trees for 20 months, 4 trees for 24 months) and soil moisture (66 sensors, 24 months) were made hourly. Soil moisture sensors were installed under the tree canopy, at the edge of the canopy and in the open area at 10-, 30- and 50-cm soil depths. Mid-day twig water potential ( Ψ) and leaf conductance ( gs) were measured monthly. The sap flow of cypress trees was double that of pine. Pine seems to regulate its stomata and shows less response to rainfall compared to cypress. Soil water balance computations showed that evapotranspiration from the 60-cm soil depth of the areas without tree canopy cover was higher than that of areas with canopy cover, likely due to preferential flows caused by the tree canopy and roots.

Snowmelt is a critical water resource in the Sierra Nevada impacting populations in California and Nevada. In this region, forest managers use treatments like selective thinning to encourage resilient ecosystems but rarely prioritize snowpack retention due to a lack of simple recommendations and the importance of other management objectives like wildfire mitigation and wildlife habitat. We use light detection and ranging (lidar) data collected over multiple snow accumulation seasons in the Sagehen Creek Basin, central Sierra Nevada in California, USA, to investigate how snowpack accumulation and ablation are affected by forest structure metrics at coarse, stand-scales (e.g., fraction of vegetation, or fVEG) and fine, tree-scales (e.g., a modified leaf area index, and the ratio of gap-width to average tree height). Using a newly developed lidar point cloud filtering method and an “open-area reference” approach, we show that for each 10% decrease in fVEG there is a ~30% increase in snow accumulation and a ~15% decrease in ablation rate at the Sagehen field site. To understand variability around these relationships, we use a random forest analysis to demonstrate that areas with fVEG greater than ~30% have the greatest potential increased accumulation response after forest removal. This spatial information allows us to assess the utility of completed and planned forest restoration strategies in targeting areas with the highest potential snowpack response. Our new lidar processing methods and reference-based approach are easily transferrable to other areas where they could improve decision support and increase water availability from landscape-scale forest restoration projects.

Coastal dunes are the highest natural features on the beach. They protect the beach communities and low-energy environments from storms by virtue of their elevation. Their formation is a result of delicate coupling between accretional and erosional processes. Here we study the influence of vegetation on dune growth and recovery under water-driven erosion utilizing a process-based coastal model under a stochastic framework. An equivalence of this model is first established with a recently developed stochastic model of dune evolution under water-erosional stress. From the model vegetation parameters: the vegetation growth time and colonization time are quantified and their relation with characteristic dune growth times is established. Vegetation causes an initial lag in dune formation due to the colonization time. Also, the dune growth under the influence of vegetation is found to be divided into two regimes, stable and mobile. Within the stable regime, the influence of vegetation on dune recovery is quantified by the colonization time, and its competition with water-driven erosion is analyzed. This leads to the development of a phase space relating to flooding frequency, intensity, dune growth, and dune establishment times. The dune state transitions from high to barren based on the competing dune recovery time controlled by vegetation and the flooding frequency. Finally, a vulnerability indicator is obtained from the transition threshold as a minimum base elevation after an overwash required by the beach for vegetation to recover and establish dunes that overcome frequent flooding.

Biomonitoring is an approach that uses indicators or sentinel species to assess the health or pollution of an environment, combining diversity based on specific taxonomic groups with the taxa’s indicator of pollution into a single index or score. Benthic macroinvertebrates are among the most preferred and valuable indicators of the biotic index. Our study aims to evaluate water quality and ecological status using biotic and diversity indices based on benthic macroinvertebrates. The macroinvertebrate samples used in this study were collected seasonally from 16 stations determined in Karasu Stream. These samples consist of 14747 specimens belonging to 9 orders and 40 families of Insecta, Malacostraca, Hirudinea and Oligochaeta. In addition, some physicochemical parameters were measured at the stations. The data obtained were analyzed using the Turkey-Biological Monitoring Working Group (TR-BMWP), Average Score per Taxon (ASPT), Family Biotic Index (FBI), Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxon richness index, and Shannon-Wiener (SWDI), Simpson (SDI) and Hill’s diversity indices. Our results showed that the last six stations of Karasu Stream were under pressure due to various anthropogenic effects. According to biotic indexes, the ecological quality status of the water in the stations was determined to be High or Good in the first ten stations and Average, Poor, or Bad in the last six stations. The results of our study showed that TR-BMWP, FBI, and EPT indices are more reliable in determining water quality than the ASPT index and reflect the environmental situation better. Since the TR-BMWP index is adapted to macroinvertebrate taxa distributed in Türkiye, it can be used as a suitable tool for evaluating other rivers’ water quality in Türkiye.

Reservoir is a vital tool for human utilization of water resources, and the deterioration of its water quality can seriously threaten the water cycle and sustainable urban development. However, there are relatively few studies in academia that analyze and evaluate the water quality of multiple reservoirs at the same time. To address this knowledge deficit, we collected 108 water samples from three different reservoirs in Chuzhou City for 36 months (from 2019 to 2021), explored the drivers of changes in water quality parameters over time and the extent of eutrophication. Our results indicated that the water quality of the reservoirs was deteriorating during the study period, among which Huanglishu Reservoir and Shahe Reservoir reached mild eutrophic status, and both had higher eutrophication levels than Chengxi Reservoir. Secchi Depth (SD), Total Nitrogen (TN), and Total Phosphorus (TP) were the principal factors inducing eutrophication. The biased utilization of reservoir functions was the major contributor to the discrepancy in the degree of eutrophication. Furthermore, Pearson Correlation Analysis revealed that there are significant correlations between many water quality parameters. Cluster Analysis (CA) grouped the 12 months of each year into three clusters (stable water level period, rainy season high flow period, and winter low flow period). Based on this, Analysis of Variance (ANOVA) showed that most water quality parameters varied considerably between the clusters. Collectively, this study identified the actual water quality conditions of three reservoirs in Chuzhou City and provided guidance for local water quality management and environmental protection.

Southern African savanna rangelands are facing a widespread degradation pattern called bush encroachment. This is associated with implications for various aspects of the water cycle and in particular canopy transpiration. At the individual-tree scale, it is estimated by scaling sap-flux density by sapwood area. However, the direct measurement of sapwood area is impracticable at landscape scale and general allometric equations of the West-Brown-Enquist (WBE) model relating sapwood area to primary size measures seem to fail for some species and climates. Therefore, we conducted intensive field measurements to establish species-specific allometric relationships between sapwood area and sizes (stem diameter, crown area) in six dominant shrub species involved in bush encroachment in Namibia ( Colophospermum mopane, Senegalia mellifera, Vachellia reficiens, Dichrostachys cinerea, Vachellia nebrownii, Catophractes alexandri). We found strong allometric relationships between sapwood area and stem diameter as well as between sapwood area and crown area for all six species. These relations are largely in line with the WBE theory but still provide estimates that are more accurate. Only in D. cinerea, the sapwood area was significantly smaller than predicted by the WBE theory, which might be caused by a larger need for stabilizing heartwood. Our results are useful to estimate water loss via transpiration at a large scale using remote sensing techniques and can promote our understanding of the ecohydrological conditions that drive species specific bush encroachment in savannas. This is particularly important in the light of climate change, which is considered to have major implications on ecohydrological processes in savannas.

This study provides a new perspective on understanding the intricacies of water-mediated connectivity in ecosystems, bridging landscape ecology and geomorphology through network science. We highlight dryland and river floodplain ecosystems as distinct examples of contrasting water-controlled systems. We (1) discuss central considerations in developing Structural Connectivity (SC) and Functional Connectivity (FC) networks of water-mediated connectivity; (2) quantify the emergent patterns in these networks; and (3) evaluate the capacity of network science tools for investigating connectivity characteristics. Connectivity is quantified using seven parameters at both network and node levels. We find that Link Density, Betweenness Centrality, and Page Rank Centrality are highly sensitive to directionality; Global Efficiency and Degree Centrality are particularly sensitive to weights; while Relative Node Efficiency remains unaffected by weights and directions. Our study underscores the potential to transform how we quantify and understand water-mediated connectivity, especially in consideration of the role(s) of weights and directionality. This interdisciplinary review has implications for both theoretical insights and practical applications in environmental management and conservation efforts.

A document by Fabian Bernhard. Click on the document to view its contents.

The alpine grassland shrubbization of the northern Qinghai-Tibet Plateau on the background of global change and overgrazing, is a prominent and serious problem. However, the water competition ability of shrubs and alpine grasslands is rarely reported. Here, we tracked the δ 18O and δ 2H of soil water, plant water, precipitation, and groundwater, analysed sources of water use in shrub and grassland by Mix SIAR model. Our results showed that both δ 18O and δ 2H in soil, precipitation, and plant varied significantly over time, groundwater remained relatively stable in P. fruticosa shrub and alpine grassland sites during observation. Considering groundwater, precipitation, soil water, and plant water, a progressive enrichment in δ 18O or δ 2H existed from groundwater and precipitation to soil water to plant water for each month. Alpine grassland was more susceptible to drought stress, had a stronger partitioning effect in dynamic transport than shrub. The P. fruticosa shrub displayed more flexible water utilisations, and was more competitive for water than grasslands. Furthermore, the plants in alpine shrub and grassland reached water use balance in August. Shrubs degraded from alpine grassland changed water use pattern of grassland, thereby changing soil water storage. These results contribute to in-depth understanding the alpine grassland shrubbization from water use patterns of grassland and shrub plants on the northern Qinghai-Tibet Plateau.

Little is known about the short‐term dynamics of tree water use strategies particularly for neighbouring co-occurring species. Here, we quantify the high frequency changes in water sources and sap flux patterns of two commonly co-occurring tropical rainforest tree species: Dendrocnide photinophylla (Kunth; Chew) and Argyrodendron peralatum (F.M. Bailey; Edlin ex J.H. Boas). A combination of continuous sap flux measurements and hourly sampling of xylem water stable isotope composition (δDand δ 18O) were used to observe water use strategies through a 24 h transpiration cycle. Sap flux ranged from 2.82-28.50 L d -1 and was 66.67% higher in A. peralatum compare to D. photinophylla. For both tree species, sap flux increased with tree size and diurnal sap flux increase resulted in more isotopically enriched xylem water. A Bayesian Mixing Model analysis using sampled soil water isotopic composition from five soil depths from of 0 to 1 m showed that D. photinophyllaused very shallow or surface layer (0-20 cm) water, while A. peralatum sourced its water mostly from deeper in the soil profile (>20 cm). We hypothesize that these differences in species’ water consumption patterns are reated to plant water storage capacity and, wood anatomical features. Our study shows that combning xylem isotope composition and sap flux measurements can help reveal species level water use strategies—useful for improved process understanding for ecohydrological modeling.

This article used three diversion power stations with different operating years along Dicun stream of the source of Jiulong River to study the riparian plant community and discussed the impact of power station development on riparian plants. The results showed that:(1)There were significant differences in the plant diversity of herbs, shrubs and trees among all sample plots in the study area (P < 0.05).(2) The species number of the second and third diversion power stations with longer operation time was larger than that of the fourth diversion power station with short operation time.(3) The water-borne plants were concentrated in the herb layer in the influence area of the diversion power station, and the Richness, Shannon- Wiener, Simpson and Pielou indexes of water-borne plants in the study area were significantly different (P < 0.05). (4) The appearance of diversion power station leaded to the change of environmental factors, and the river depth and flow rate had significant positive correlation with the diversity index of riparian plants and water water-borne plants (P < 0.05). In general, with the increase of the operation time of the power station, the surrounding riparian plant will form a new stable community.