Search Results (37)

This study, based on hydrological station data and wavelet analysis, explores the periodic variation characteristics and trends of the two main tributaries (Buha River and Shaliu River) in the Qinghai Lake Basin from 1960 to 2016. Wavelet transform is used to analyze the runoff data, revealing long-term periodic fluctuations and their correlation with precipitation changes. The study finds that, from 2003 to 2016, the daily peak flow and daily minimum flow of the two rivers increase compared to the period from 1960 to 2003, though the magnitude and trends of the increase differ. At the monthly scale, runoff patterns show that June to October is the main period for concentrated runoff in the basin, with July and August being the peak months. Additionally, interannual runoff changes for both rivers show a gradually increasing trend amid fluctuations, with varying fluctuation intensities observed in different years. Wavelet analysis results indicate that the main periodicity of runoff is 23 years, closely linked to changes in precipitation. This study reveals the periodic variation patterns of runoff in the Qinghai Lake Basin, providing valuable insights for watershed water resource management and hydrometeorological forecasting. Full article

Canopy hydrology and forest water inputs are directly linked to the physical properties of tree crowns (e.g., foliar and woody surfaces), which determine a tree’s capacity to intercept and retain incident rainfall. The changing forest structure, notably the decline of oak’s (Quercus) dominance and encroachment of non-oak species in much of the upland hardwood forests of the eastern United States, challenges our understanding of how species-level traits scale up to control the forest hydrologic budget. The objective of this study was to determine how the leaf water storage capacity varies across species and canopy layers, and how these relationships change throughout the growing season. We measured the leaf water storage capacity of overstory and midstory trees of native deciduous oaks (Q. alba, Q. falcata, Q. stellata) and non-oak species (Carya tomentosa, Acer rubrum, Ulmus alata, Liquidambar styraciflua, Nyssa sylvatica) using two methods (water displacement and rainfall simulation). Overstory Q. alba leaves retained 0.5 times less water per unit leaf area than other overstory species (p < 0.001) in the early growing season, while in the late growing season, C. tomentosa leaves had the lowest storage capacity (p = 0.024). Quercus falcata leaves displayed a minimal change in storage between seasons, while Q. alba and Q. stellata leaves had higher water storage in the late growing season. Midstory U. alata leaves had 3.5 times higher water storage capacity in the early growing season compared to all the other species (p < 0.001), but this difference diminished in the late growing season. Furthermore, the water storage capacities from the simulated rainfall experiments were up to two times higher than those in the water displacement experiments, particularly during the early growing season. These results underscore the complexity of leaf water storage dynamics, the methodology, and the implications for forest hydrology and species interactions. Broader efforts to understand species-level controls on canopy water portioning through leaf and other crown characteristics are necessary. Full article

Global climate change projections highlight the Mediterranean Basin as one of the most susceptible areas to the effects of intense and prolonged droughts, as well as increasing air temperatures. Accordingly, the productivity and survival of forests in this area will depend on their ability to resist and adapt to increasingly drier conditions. Different climatic conditions across the Mediterranean Basin could drive differences in forest functioning, requiring trees to acclimate to them. Sea breeze dynamics along orographic valleys can also influence climatic conditions, accentuating differences between inland and coastal forests. However, there is limited information on whether the climatic factors regulating tree transpiration in Aleppo pine forest in orographic valleys vary according to climate. This study aims to identify and compare the climatic factors that regulate tree transpiration along a gradient and determine the thresholds at which these factors affect transpiration rates. This study was carried out by means of sap flow gauges, since this technique is a key feature for quantifying and understanding tree transpiration. It was conducted in two Aleppo pine dry sub-humid forests (inland and coastal, 750 and 675 trees ha⁻¹, respectively) and in two pine semi-arid forests (inland and coastal, 600 and 400 trees ha⁻¹, respectively) in the western Mediterranean basin during January–November of 2021. No significant rainfall events or droughts were recorded during the period of study, indicating a standard climatic condition in these areas. The main findings demonstrated that the variability in sap flow could be attributed to the interaction between soil water content and vapour pressure deficit in all the forests studied. However, the highest threshold values of these climatic factors in relation to the increase or decrease in maximum sap flow (i.e., less sensitivity) were exhibited in semi-arid forests, highlighting the adaptability of Aleppo pine to more limiting climatic conditions. These findings are relevant for the consequences of the predicted increase in harsh climatic conditions and the balance among vapour pressure deficit, temperature and soil water availability. Future research will be essential to confirm forest acclimatisation in the transitional dry to semi-arid forest ecosystems predicted by global climate change projections, given their potential to strongly alter ecosystem function and water cycles. Full article

Suspended sediment (SS) has a wide range of negative effects such as increased water turbidity, altered habitat structures, sedimentation, and effects on hydraulic systems and environmental engineering projects. Nevertheless, the methods for accurately determining SS sources on a basin-scale are poorly understood. Herein, we used a simplified neural network analysis (NNA) model to identify the sources of SS in Japan’s Oromushi River Catchment Basin. Fine soil samples were collected from different locations of the catchment basin, processed, and separately analysed using X-ray fluorescence (XRF) and X-ray diffraction (XRD). The sampling stations were grouped according to the type of soil cover, vegetation type and land-use pattern. The geochemical components of each group were fed into the same neural network layer, and a series of equations were applied to estimate the sediment contribution from each group to the downstream side of the river. Samples from the same sampling locations were also analysed by XRD, and the obtained peak intensity values were used as the input in the NNA model. SS mainly originated from agricultural fields, with regions where the ground is covered with volcanic ash identified as the key sources through XRF and XRD analysis, respectively. Therefore, based on the nature of the surface soil cover and the land use pattern in the catchment basin, NNA was found to be a reliable data analytical technique. Moreover, XRD analysis does not incorporate carbon, and also provides detailed information on crystalline phases. The results obtained in this study, therefore, do not depend on seasonal uncertainty due to organic matter. Full article

The effectiveness of using enhanced evapotranspiration rates of willow plantation is a modern environmentally friendly practice for advanced treatment of effluent WWTP flow. The key idea is that through advanced willow evapotranspiration rates, a significant proportion of the effluent flow can be transferred into the atmosphere through the physical process of evapotranspiration. This study further discusses the concept in a real-world problem using a wide dataset consisting of a recent PET monthly remote dataset namely RASPOTION, monthly recorded rainfall gauge, and experimental willow evapotranspiration surveys across Ireland, to identify the monthly cropping pattern. A Monte Carlo water balance model has been developed for the period 2003–2016. The model was applied in an existing willow plantation at Donard WWTP co. Wicklow, Ireland to identify the exceedance probability of willow plantation runoff against estimated low flows (i.e., Q₉₅, Q₉₉) at the adjacent small tributary. In this case study, any failure which can lead to river quality deterioration was not assessed. The overall framework aims to provide new insights considering the multiple sources of uncertainty (i.e., monthly willow cropping pattern and WWTP effluent flow) in associated environmental engineering problems. Full article

Urban trees play a pivotal role in mediating the hydrological and nutrient cycles within urban ecosystems, yet the mechanisms by which bark characteristics influence these processes remain underexplored. This study aimed to investigate the impact of the bark morphology—specifically texture, depth, and number of furrows—on the water absorption capacity and to determine the relationship between this capacity and ion concentration in stemflow across various urban tree species. Our findings reveal significant variations in water absorption and ion concentration related to the morphological traits of bark among tree species, highlighting the intricate relationship between bark physical and chemical characteristics and stemflow nutrient composition. Notably, species with furrowed textures, greater depth, and a higher number of furrows demonstrated pronounced differences in ion enrichment in their stemflow. However, a canonical redundancy analysis suggested a low association between bark absorption capacity and ion concentration, indicating the influence of other, possibly external, environmental factors on ion leaching. The results underscore the complexity of nutrient transport mechanisms in urban trees and show a new understanding of tree bark’s ecohydrological roles. This study contributes valuable insights into ecohydrology science and emphasizes the need for further research to unravel the multifaceted influences on nutrient dynamics in urban landscapes. Full article

Hydrology and meteorological data from relatively undisturbed watersheds aid in identifying effects on ecosystem services, tracking hydroclimatic trends, and reducing model uncertainties. Sustainable forest, water, and infrastructure management depends on assessing the impacts of extreme events and land use change on flooding, droughts, and biogeochemical processes. For example, global climate models predict more frequent high-intensity storms and longer dry periods for the southeastern USA. We summarized 17 years (2005–2021) of hydrometeorological data recorded in the 52 km², third-order Turkey Creek watershed at the Santee Experimental Forest (SEF), Southeastern Coastal Plain, USA. This is a non-tidal headwater system of the Charleston Harbor estuary. The study period included a wide range of weather conditions; annual precipitation (P) and potential evapotranspiration (PET) ranged from 994 mm and 1212 mm in 2007 to 2243 mm and 1063 in 2015, respectively. The annual runoff coefficient (ROC) varied from 0.09 in 2007 (with water table (WT) as deep as 2.4 m below surface) to 0.52 in 2015 (with frequently ponded WT conditions), with an average of 0.22. Although the average P (1470 mm) was 11% higher than the historic 1964–1976 average (1320 mm), no significant (α= 0.05) trend was found in the annual P (p = 0.11), ROC (p = 0.17) or runoff (p = 0.27). Runoff occurred on 76.4% of all days in the study period, exceeding 20 mm/day for 1.25% of all days, mostly due to intense storms in the summer and lower ET demand in the winter. No-flow conditions were common during most of the summer growing season. WT recharge occurred during water-surplus conditions, and storm-event base flow contributed 23–47% of the total runoff as estimated using a hydrograph separation method. Storm-event peak discharge in the Turkey Creek was dominated by shallow subsurface runoff and was correlated with 48 h precipitation totals. Estimated precipitation intensity–duration–frequency and flood frequency relationships were found to be larger than those found by NOAA for the 1893–2002 period (for durations ≥ 3 h), and by USGS regional frequencies (for ≥10-year return intervals), respectively, for the same location. We recommend an integrated analysis of these data together with available water quality data to (1) assess the impacts of rising tides on the hydroperiod and biogeochemical processes in riparian forests of the estuary headwaters, (2) validate rainfall–runoff models including watershed scale models to assess land use and climate change on hydrology and water quality, and (3) inform watershed restoration goals, strategies, and infrastructure design in coastal watersheds. Full article

Droughts impact the water cycle, ecological balance, and socio-economic development in various regions around the world. The Orinoco River Basin is a region highly susceptible to droughts. The basin supports diverse ecosystems and supplies valuable resources to local communities. We assess the spatiotemporal patterns and impacts of droughts in the basin using remote sensing data and surface observations. We use monthly precipitation (P), air temperature near the surface (T2M), enhanced vegetation index (EVI) derived from Earth observations, and average daily flow (Q) data to quantify drought characteristics and impacts. We also investigated the association between drought and global warming by correlating the drought intensity and the percentage of dry area with sea surface temperature (SST) anomalies in the Pacific (Niño 3.4 index), Atlantic (North Atlantic Index [NATL]), and South Atlantic Index [SATL]) oceans. We evaluate the modulating effect of droughts on the hydrological regime of the most relevant tributaries by calculating the trend and significance of the regional standardized precipitation index (SPI) and percentage area affected by dry conditions. El Niño events worsen the region’s drought conditions (SPI vs. Niño 3.4 index, r = −0.221), while Atlantic SST variability has less influence on the basin’s precipitation regime (SPI vs. NATL and SATL, r = 0.117 and −0.045, respectively). We also found that long-term surface warming trends aggravate drought conditions (SPI vs. T2M anomalies, r = −0.473), but vegetation greenness increases despite high surface temperatures (SPI vs. EVI anomalies, r = 0.284). We emphasize the irregular spatial-temporal patterns of droughts in the region and their profound effects on the ecological flow of rivers during prolonged hydrological droughts. This approach provides crucial insights into potential implications for water availability, agricultural productivity, and overall ecosystem health. Our study underlines the urgent need for adaptive management strategies to mitigate the adverse effects of droughts on ecosystems and human populations. The insights derived from our study have practical implications for developing strategies to address the impacts of droughts and ensure the protection of this ecologically significant region. Full article

Drought is a significant natural hazard with widespread socioeconomic and environmental impacts. This study investigated the long-term drought characteristics in a Mediterranean oak forest ecosystem using the Standardized Precipitation Evapotranspiration Index (SPEI) at various time scales and seasons. The analysis was based on a long-term time series dataset obtained from a meteorological station located at the University Forest of Taxiarchis in Greece. The dataset encompassed a substantial time span of 47 years of continuous monitoring, from 1974 to 2020. To accomplish the goals of the current research, the SPEI was calculated for 3, 6, 12, and 24-month periods, and drought events were identified. The Mann-Kendall (M-K) test was used to analyze the trends in drought severity and evaluate the trends significance. The results showed that shorter time scales (SPEI3 and SPEI6) were more efficient for identifying short-term droughts, while longer time scales (SPEI12 and SPEI24) were better for identifying less frequent but longer-lasting drought episodes. The analysis consistently revealed positive trends across all seasons and time scales, indicating an overall transition towards wetter conditions. Nearly all the data series for SPEI12 and SPEI24 exhibited statistically significant upward trends (wetter conditions) at a 95% confidence level. However, more intense events were detected during the recent decade using the seasonal analysis. Additionally, as the time scale expanded, the magnitude of these trends increased. The findings contributed to a better understanding of drought dynamics in Mediterranean oak forests and provided valuable information for forest management and climate change adaptation planning. Full article

Estimation of hydrological processes is critical to water resource management, water supply planning, ecological protection, and climate change impact assessment. Mountains in Central Asia are the major source of water for rivers and agricultural practices. The disturbance of mountain forests in the region has altered the hydrological processes and accelerated soil erosion, mudflow, landslides, and flooding. We used the SWAT (Soil and Water Assessment Tool) model calibrated and validated with remote sensing data to quantify the mountainous hydrological processes in the Aktash River watershed (ARW) of Uzbekistan, Central Asia. Simulations showed that the daily surface runoff and streamflow closely responded to daily precipitation. Groundwater discharge reached its maximum in winter because of snowmelt. The wet months were from July to December, and the dry months were from January to June. The magnitudes of the seasonal hydrological processes were in the following order: fall > summer > winter > spring for precipitation and surface runoff; summer > spring > fall > winter for evapotranspiration (ET); winter > spring > fall > summer for snowmelt; fall > winter > summer > spring for water yield and streamflow; and winter > fall > spring > summer for groundwater discharge. The Mann–Kendall statistical test revealed a significant increasing trend for the annual precipitation (τ = 0.45, p < 0.01) and surface runoff (τ = 0.41, p < 0.02) over the past 17 years from 2003 to 2019. Compared to rangeland, forested land decreased monthly and annual average surface runoff by 20%, and increased monthly and annual average groundwater recharge by about 5%. Agricultural land had much higher unit-area values (mm/km²/y) of ET, groundwater recharge, and water yield than those of urban, forest, and range lands. Our research findings provide useful information to farmers, foresters, and decision makers for better water resource management in the ARW, Central Asia, and other mountain watersheds with similar conditions. Full article

Soil moisture (SM) and temperature (ST) are critical factors in forest eco-hydrological research. In this study, we investigated the inter- and intra-annual changes in SM and ST profiles in a mixed Mediterranean maquis forest stand together with soil and meteorological parameters. Hourly data from three field measurements points at four depths (−5, −20, −40 and −70 cm) for 6 years were interpolated using the kriging method to produce annual SM and ST profiles. The results indicate that air temperature highly affects the upper 5 cm of the mineral soil. In general, it increases with depth in winter at an average rate of 0.036 °C/cm and decreases in summer (0.035 °C/cm), presenting higher values compared to air temperature from April to August and lower ones during the rest of the period. Precipitation is the main factor driving SM variations up to a superficial soil depth of 40 cm. The upper soil layer (0–40 cm) infiltrates water faster and presents high SM variability, especially in monthly and seasonal (year to year) time steps. The maquis forest stands are likely to be strongly affected by climate change, therefore the results of this study could be useful in hydrological and climate change studies focused on maquis vegetation water management. Full article

Land use changes and mounting water demands reduce freshwater inflows into estuaries, impairing estuarine ecosystems and accelerating coastal seawater intrusion. However, determining minimum river inflows for management guidelines is hampered by a lack of ecosystem-flow link data. This study describes the development of freshwater inflow guidelines for the Wami Estuary, combining scarce river flow data, hydrological modeling, inferring natural salinity regime from vegetation zonation and investigating freshwater requirements of people/wildlife. By adopting the Building Blocks Methodology, a detailed Environmental Flows Assessment was performed to know the minimum water depth/quality seasonal requirements for vegetation, terrestrial/aquatic wildlife and human communities. Water depth requirements were assessed for drought and normal rainfall years; corresponding discharges were obtained by a hydrological model (HEC-RAS) developed for the river channel upstream of estuary. Recommended flows were well within historically occurring flows. However, given the rapidly increasing water demand coupled with reduction in basin water storage due to deforestation/wetland loss, it is critical to ensure these minimum flows are present, without which essential ecosystem services (fisheries, water quality, mangrove forest resources and wildlife/tourism) will be jeopardized. The EFA process is described in painstaking detail to provide a reference for undertaking similar studies in data-poor regions worldwide. Full article

The mobility of a metal in mining-impacted sediments is determined by the environmental conditions that influence the metal’s oxidation state and bonding environment. Coeur d’Alene Lake, USA, has been impacted by legacy mining practices that allowed the hydrologic transport of mining waste to the lakebed, resulting in substantial amounts of redox-sensitive Fe and Mn along with Ag, As, Cd, Cu, Hg, Pb, Sb, and Zn. Future lake conditions may include algal blooms and additional algal detritus at the sediment–water interface, which may alter Fe and Mn forms that can influence their, and other metal(loid)s, mobility during seasonal anoxia. Cores of the lakebed sediments were exposed to anoxic and anoxic + algal detritus conditions for 8 weeks. Sediment samples were collected biweekly for analysis of Fe and Mn oxidation states and bonding environments by synchrotron-based X-ray absorption spectroscopy. Over the 8-week period and at a location 12.5 cm deep in the sediments, anoxic and anoxic + algae conditions produced limited changes in Fe and Mn oxidation states and bonding environments. At a location 2.5 cm below the sediment–water interface, the anoxic condition promoted a relatively stable environment in which Fe and Mn oxidation states and bonding environments did not vary greatly during the experiment. At the 2.5 cm depth, the anoxic + algae condition substantially altered the Mn oxidation state distribution and bonding environment, but this condition did not strongly influence the Fe oxidation state distribution or bonding environment. The anoxic + algae condition increased the presence of Mn³⁺, produced Mn⁴⁺ at select times, altered the Mn bonding environment, and temporarily increased the release of Mn into porewater. The algae influence on sediment and porewater Mn likely occurred because of the increased formation of organo-Mn complexes produced during algae-enhanced enzymatic processes. The lack of influence of algal detritus on sediment and porewater Fe and the formation of soluble organo-Mn complexes may limit the potential increase in the mobility of other metal(loid)s with future lake conditions. Full article

Over the past century, increases in indigenous woody plant species, also known as woody encroachment (WE), has occurred in grasslands and savannas across the globe. While the impact on grassland and savanna composition and productivity has been well studied, little is known of the impacts on the hydrological cycle. WE may increase evapotranspiration (ET) losses, leading to reduced infiltration and ultimately reduced freshwater availability, which is of particular concern in arid and semi-arid areas. The aim of this study was to determine the effect of Colophospermum mopane (mopane) encroachment on ET in a semi-arid savanna located in South Africa. Mopane is widely distributed across southern Africa, and is one of the main encroaching species of the region. Following an assessment of the validity of two surface renewal approaches, SR1 and SRDT, against short eddy covariance campaigns for sensible heat flux estimation, the SR1 approach was used to estimate ET at an experimental woody plant clearing trial from November 2019 to July 2022. For the two drier years of the study, the removal of mopane trees had little effect on ET. However, for the wettest year of the study, the removal of mopane trees decreased ET by 12%, supporting the hypothesis that the conversion from grass dominance to woody dominance can increase ET. Annual ET exceeded annual rainfall in all 3 years, indicating that the vegetation supplements its water use with soil water that has accumulated during previous wet seasons, or that tree roots facilitate hydraulic lift of deep soil water, or groundwater, to depths within the rooting depth of both trees and grasses. Further research is needed to confirm the exact mechanism involved, and the consequences of this for groundwater and streamflow at landscape scales. Full article