Climate change in terms of regional warming and modifications in precipitation regimes has large impacts on streamflow in regions where both rainfall and snowmelt are important runoff generating processes like in Norway. Hydrological impacts of recent changes in climate are usually investigated by trend analyses applied on annual, seasonal, or monthly time series. However, neither of them can detect sub-seasonal changes and their underlying causes. Based on high-resolution trend analyses (i.e., applying the Mann-Kendall test on 10-day-moving-averaged daily time series), this study investigated sub-seasonal changes in daily streamflow, rainfall, and snowmelt in 61 and 51 catchments in Western vs. Eastern Norway (Vestlandet vs. Østlandet), respectively, over the period 1983-2012. The relative contribution of rainfall vs. snowmelt to daily streamflow and the changes therein have also been estimated to identify the changing relevance of these driving processes over the same period. Detected changes in daily streamflow were finally attributed to changes in the most important hydro-meteorological drivers using multiple-regression models with increasing complexity. Results reveal a coherent picture of earlier spring flow timing in both regions due to earlier snowmelt. Other streamflow trend patterns differ between both regions: Østlandet shows increased summer streamflow in catchments up to ~1100 m a.s.l. and slightly increased winter streamflow in about 50 % of the catchments, while trend patterns in Vestlandet are less coherent. The importance of rainfall for streamflow contribution has increased in both regions, and the trend attribution reveals that changes in rainfall and snowmelt can explain streamflow changes to some degree in periods and regions where they are dominant (snowmelt: spring and Østlandet; rainfall: autumn and Vestlandet). However, detected streamflow changes can be best explained by adding temperature as an additional predictor which indicates the relevance of additional driving processes for streamflow changes like increased glacier melt and evapotranspiration.

Aquatic vegetation, hydraulics and sediment transport have complex interactions that are not yet well understood. These interactions are important for sediment conveyance, sediment sequestration, phasing of sediment delivery from runoff events, and management of ecosystem health in lowland streams. To address this knowledge gap detailed field measurements of sediment transport through natural flexible aquatic vegetation are required to supplement and validate laboratory results. This paper contributes a field study of suspended sediment transport through aquatic vegetation and includes mechanical removal of aquatic vegetation with a weed cutting boat. It also provides methods to quantify vegetation cover through remote sensing with Unmanned Aerial Vehicles (UAVs) and estimate biomass from ground truth sampling. Suspended sediment concentrations were highly dependent on aquatic vegetation abundance, and the distance upstream that had been cleared of aquatic vegetation. When the study reach was fully vegetated (i.e. cover >80%), the maximum recorded SSC was 14.6 g/m3 (during a fresh with discharge of 2.47 m3/s), during weed cutting operations SSC was 76.8 g/m3 at 0.84 m3/s (weedcutting boat 0.5-1 km upstream from study reach), however following weed cutting operations (4.6 km cleared upstream), SSC was 139.0 g/m3 at a discharge of 1.52 m3/s. The data indicates that fine sediment was being sequestered by aquatic vegetation and likely remobilised after vegetation removal. Investigation of suspended sediment spatial dynamics illustrated changes in particle size distribution due to preferential settling of coarse particles within aquatic vegetation. Hydraulic resistance in the study reach (parameterized by Manning’s n) dropped by over 70% following vegetation cutting. Prior to cutting hydraulic resistance was discharge dependent, while post cutting hydraulic resistance was approximately invariant of discharge. Aerial surveying captured interesting changes in aquatic vegetation cover, where some very dense regions of aquatic vegetation were naturally removed leaving behind unvegetated riverbed and fine sediment.

With the increasing demand for water resources, the utilization of marginal water resources of poor-quality has become a focus of attention. The brackish water developed in the Loess Plateau is not only salty but also famous for its “bitterness”. In the present work, multi-isotope analysis (Sr, B) was combined with geochemical analysis to gain insight into the hydrogeochemical evolution and formation mechanisms of brackish water. These results demonstrate that groundwater in the headwater is influenced by carbonate weathering. After the confluence of several tributaries in the headwater, the total dissolved solids (TDS) of water is significantly increased. The dissolution of evaporates is shown to be the main source of salinity in brackish water, which also greatly affects the Sr isotopic composition of water. This includes the dissolution of Mg-rich minerals, which is the main cause of the bitterness. Furthermore, the release of calcium from the dissolution of gypsum may induce calcite precipitation and incongruent dissolution of dolomite, which also contributes to the enrichment of magnesium. The highly fractionated boron isotopic values observed in the upstream groundwater were explained by boron interacting with clays, illustrating the important role played by the cationic exchange reaction. The inflow of brackish groundwater is the source of the observed quality of the river water. River water with relatively enriched 11B contents reflects the occurrence of evaporation along the flow path of the river. This process further aggravates the salinization of river water, with water quality evolving to saline conditions in the lower reach. When the river reaches the valley plain, the 87Sr/86Sr ratios decreases significantly, which is primarily related to erosion of the riverbanks during runoff. These results indicate that water resource sustainability could be enhanced by directing focus to mitigating salinization in the source area of the catchment.

Many large rivers worldwide are enriched with high levels of suspended solids (SS), which are known to be hotspots of many nitrogen (N) transformation processes (e.g., denitrification, nitrification). However, the influence of SS on microbial ammonium (NH4+) recycling remains unclear. Water column NH4+ regeneration rates (REGs) and potential uptake rates (Upots) as well as community biological NH4+ demand (CBAD) was measured in the river-estuary continuum of the third longest river in the world—Yangtze River, where shows dramatic SS gradients. We found that, REGs, Upots, and CBAD all showed increasing trends along the river flow, with higher REGs, Upots, and CBAD in the estuary than in the river sections. The regeneration and uptake of NH4+ were nearly balanced in the river sections, while the positive CBAD in the estuary indicated obvious NH4+ demand of microbes. Concentrations of SS, which also controls the content of chemical oxygen demand and particulate N, were the main factor influencing NH4+ recycling rates and CBAD. SS induced regenerated NH4+ in the river-estuary continuum of Yangtze River was estimated to be 21.81 × 108 kg N yr−1 and accounted for about 25% of total N inputs, suggesting that regenerated NH4+ is an important N source for microbes and may influence nutrient dynamics in lower coasts. To our knowledge, this is the first to report NH4+ recycling in Yangtze River with an emphasis on its influencing factors and contribution to N budgets.

Local community and research interest to better understand regional climate change impacts has led to the establishment of a long-term soil moisture and weather observation network in the Roaring Fork catchment of the Colorado River Headwaters. This catchment-wide suite of 10 stations collects frequent and continuous data on soil moisture, soil temperature, rain, air temperature, relative humidity, and (at some stations) snow across an elevational gradient from 1,800m to 3,680m in elevation. We demonstrate how this effort can support research on mountain hydrology with applications for resource management and climate change adaptation decision making. We also share perspectives on the value and opportunities a community science approach can bring to catchment studies moving forward. All data from this project are publicly available.

Clay aquitards are semipermeable membranes that allow groundwater flow while retarding solute migration have been researched extensively but also subjected to much debate. In this study, we collected clay samples from drilling cores (30–90m) in the Hengshui area located in the Hebei Plain, then extracted pore water using a high-pressure squeezing device. Vertical hydrochemical and isotopic profile variation trends for the pore water were revealed using hydrochemical (Cl－, Na+, Ca2+, K+, Mg2+, and SO42-) and stable isotopic measurements of H, O, and Cl. The results showed that the hydrochemical clay interlayer pore water of the saline aquifer is Cl•SO4-Na•Mg type and the average total dissolved solids（TDS）is 10.17g/L. The hydrochemical clay aquitard pore water is of the Cl•SO4-Na•Ca type with an average TDS of 1.9g/L. The hydrochemical clay interlayer pore water of aquifer II is of Cl-Na•Ca type with an average TDS of 1.1g/L. Our results showed that the water quality of the aquifer II is not affected by the upper part of saline aquifer, thus the clay aquitard acts as a significant barrier to salt movement. A polarization layer concentrated in ions was formed between the upper part of saline aquifer and the clay aquitard. The concentration polarization layer increases the salt-inhibition effect. Isotpic H, O, and Cl results showed significant fractionation. The pore water of aquifer II lacked heavy isotopes(D、18O、37Cl), but had significant heavy isotope enrichment in the concentrated polarized layer (the δD value was -76‰, the δ18O value was -8.4‰, and the δ37Cl value was 1.59‰). Hyperfiltration thus played a significant role in isotope fractionation.

Water quality dynamics depend strongly on hydrologic flow paths and transit time within catchments. In this paper we use a travel time tracking method to simulate stream salinity (as measured by electrical conductivity) in the Duck River catchment, NW Tasmania, Australia. The approach couples the StorAge transit time modelling approach with two different approaches to model electrical conductivity. The first assumes the catchment has a cyclic salt balance (rainfall source, stream flow sink) that is in dynamic equilibrium and evapoconcentration of salt is the only process changing concentration. The second assumes that the salinity of water in catchment storages is a function of water age in those stores, without explicitly simulating salt mass balance processes. The paper compares these alternate approaches in terms of salinity simulation, simulated stream water age distributions, and simulated storage age distributions. Both salinity simulation approaches reproduce stream salinity with high fidelity under calibration and perform well under validation. The simulations using the age-related solute concentration approach produce less biased results and thus high model efficiencies for validation periods. This approach also produces more consistent model parameter estimates between periods. There are systematic differences in the resultant age distributions between models, particularly for the solute balance based simulations where parameters (catchment storage size) changed more between calibration periods. The effect of time varying versus static storage selection functions are compared, with clear evidence that time varying storage selection functions with parameters linked to catchment conditions (flow) are essential for adequate simulation of event concentration dynamics.

Jarvis-type model with a flexible parameterization of stress functions can improve the descriptions of physiological behaviour for specific vegetation species. However, it is criticized for the empirically formulated multiplicative equation that can deviate from the mutual impact of intercorrelated stress factors, e.g., vapor pressure deficit (VPD) and air temperature ( Ta). This study proposed a modified Jarvis model by adding reduction factors in the stress functions of VPD and Ta to provide a better description of stomatal conductance. The sap flow data of transpiration rate in a beech forest in the mid-latitude of Centre Europe was used to inversely estimate the stomatal conductance, which facilitated the formulation of stress functions. Taking two recommended parameterization strategies for general deciduous broadleaf forest (DBF) led to severe overestimation of transpiration rate with a maximum value of ~2 mm/day in rainless days, which suggested that the beech forest had rather different stomatal response. With the parameterization using boundary analysis, the unmodified and modified Jarvis model provided the better simulation of transpiration with NSE values of 0.75 and 0.77. The results suggested that modelling transpiration can be improved through a more specific parameterization of stomatal conductance, especially for a vegetation species featuring its own stomatal behaviour that differed from its belonged general vegetation type. Particularly, the modified Jarvis model can further improve the description of stomatal conductance and modelling of transpiration in vegetated areas, especially under dry environment conditions with relatively high VPD.

The weakened connectivity of wetland systems is the key factor leading to the destruction, degradation, and disappearance of wetlands. The study of the change of wetland system connectivity enables understanding the hydrological process in wetland system and providing significant support for the study of ecological water demand. However, research on the connectivity of wetland systems has primarily focused on the intuitive connectivity in terms of hydrology and geomorphology in recent years, while the impact of wetland systems on habitat has been ignored. In this study, an innovative method was applied to evaluate and regulate the stereoscopic spatial connectivity (SSC) of the wetland system in the Heilongjiang River Basin in China (HRBC). In this method, the water requirements of typical organisms in the region were considered, and the hydrological trend in the wetland system as well as the health conditions of the SSC were analyzed using remote sensing image. A regulation mode for improving the stereoscopic spatial connectivity index (SSCI) was proposed. The results revealed that over the past 35 years, the wetland system in the study area shrank significantly, with the SSCI decreasing from 41.30% in 1980 to 35.08% in 2015. By comparing the correlation among temperature, precipitation, agricultural land, construction land, and the wetland system during the same period, it was proven that human activity is the major driving force behind the observed wetland system shrinkage. Subsequently, the key protected areas required to maintain the SSC of the wetland system were clarified, and the key recovery areas were determined according to the three scenarios of ‘high–medium–low’ feasibility, which greatly improved the SSCI and generalization route (GR) after regulation. In general, the proposed SSC evaluation methods can fully reflect the ecohydrological process of wetland systems. The methods also scientifically quantify the significant effects of the regulation mode, which has certain relevance for the evaluation and regulation of wetland systems in other regions.

Artificial subsurface (tile) drainage is used to increase trafficability and crop yield in much of the Midwest due to soils with naturally poor drainage. Tile drainage has been researched extensively at the field scale, but knowledge gaps remain on how tile drainage influences the streamflow response at the watershed scale. The purpose of this study is to analyze the effect of tile drainage on the streamflow response for 59 Ohio watersheds with varying percentages of tile drainage and explore patterns between the Western Lake Erie Bloom Severity Index to streamflow response in heavily tile-drained watersheds. Daily streamflow was downloaded from 2010-2019 and used to calculated mean annual peak daily runoff, mean annual runoff ratio, the percent of observations in which daily runoff exceeded mean annual runoff (TQmean), baseflow versus stormflow percentages, and the streamflow recession constant. Heavily-drained watersheds (> 40 % of watershed area) consistently reported flashier streamflow behavior compared to watersheds with low percentages of tile drainage (< 15% of watershed area) as indicated by significantly lower baseflow percentages, TQmean, and streamflow recession constants. The mean baseflow percent for watersheds with high percentages of tile drainage was 20.9 % compared to 40.3 % for watersheds with low percentages of tile drainage. These results are in contrast to similar research regionally indicating greater baseflow proportions and less flashy hydrographs (higher TQmean) for heavily-drained watersheds. Stormflow runoff metrics in heavily-drained watersheds were significantly positively correlated to western Lake Erie algal bloom severity. Given the recent trend in more frequent large rain events and warmer temperatures in the Midwest, increased harmful algal bloom severity will continue to be an ecological and economic problem for the region if management efforts are not addressed at the source. Management practices that reduce the streamflow response time to storm events, such as buffer strips, wetland restoration, or drainage water management, are likely to improve the aquatic health conditions of downstream communities by limiting the transport of nutrients following storm events.

Forested watersheds provide many ecosystem services that have become increasingly threatened by wildfire. Stream nitrate (NO 3 -) concentrations often increase following wildfire and can remain elevated for decades. We investigated the drivers of persistent elevated stream NO 3 - in nine watersheds that were burned to varying degrees 16 years prior by the Hayman fire, Colorado, USA. We evaluated the ability of multiple linear regression and spatial stream network modeling approaches to predict observed concentrations of the biologically active solute NO 3 - and the conservative solute sodium (Na +). Specifically, we quantified the degree to which landscape and stream network characteristics predict stream solute concentrations. No landscape variables were strong predictors of stream Na +. Rather, stream Na + variability was largely attributed to flow-connected spatial autocorrelation, indicating that downstream hydrologic transport was the primary driver of spatially distributed Na + concentrations. In contrast, vegetation cover, measured as mean normalized differenced moisture index (NDMI), was the strongest predictor of spatially distributed stream NO 3 - concentrations. Furthermore, stream NO 3 - concentrations had weak flow-connected spatial autocorrelation and high spatial variability. This pattern is likely the result of spatially heterogeneous wildfire behavior that leaves intact forest patches interspersed with high burn severity patches that are dominated by shrubs and grasses. Post-fire vegetation also interacts with watershed structure to influence stream NO 3 - patterns. For example, severely burned convergent hillslopes in headwaters positions were associated with the highest stream NO 3 ‑ concentrations due to the high proportional influence of hillslope water in these locations. Our findings suggest that reforestation is critical for the recovery of stream NO 3 - concentrations to pre-fire levels and targeted planting in severely burned convergent hillslopes in headwater positions will likely have a large impact on stream NO 3 - concentrations.

Two experimental basins – the Cariri basins – were installed in a typically semiarid region in the State of Paraíba, Brazil, for obtaining reliable estimates of runoff and soil erosion in different scales to evaluate the influence of the human activities and other factors over the processes of runoff and erosion. In the first basin, located in the municipality of Sumé, the field studies were carried out at three different scales: four micro-basins with an area of around 0.5 ha; nine standard Wischmeier-type erosion plots of 100 m2 and seven sample plots of 1 m2. The experimental units had varied vegetal cover and management and, except the sample plots, were subjected to natural rainfall events only, and were monitored from 1982 to 1991. The total runoff and total sediment yield were determined for each of the events of precipitation. The installations of the second basin, in the near municipality of São João do Cariri, were planned for the continuation of the studies initiated at Sumé, and include erosion plots (100 m2), micro-basins, and sub-basins, which are being monitored for runoff and sediment production up to now. Among them, two nested micro-basins were monitored to detect any scale effect at the micro-basin level. Nearly 600 events of natural precipitation, that produced runoff in at least one of the experimental units, have been registered. This bulk of data was utilised to evaluate the influence of various factors, including cultivation practices. The data collected so far has been successfully used to calibrate hydrological models for plots and micro-basins. Parameters have been tested by means of cross validations among micro-basins and sub-basins. The data sets, in part, have been made available to researchers in Brazil and now the updated data files are being made available to all the researchers in hydro-sedimentology at: https://doi.org/10.5281/zenodo.4044690

Macrophyte community diversity and composition respond to ecosystem conservation and local environmental factors. In this study, we developed a multidimensional diversity framework for macrophyte communities, including the taxonomic and functional alpha and beta diversity. We used the framework to explore the relationships among water level regimes and these diversity parameters in a case study of China’s Baiyangdian Lake. Analysis of indicators of hydrologic alteration divided the water level from 1959 to 2019 into four regimes (dry, <6.42 m; low, 6.42 to 7.23 m; medium, 7.23 to 8.19 m; high, >8.19 m). Alpha and beta diversity were significantly higher in the medium regime than in the low and high regimes. Redundancy analysis indicated that the maximum water depth significantly affected taxonomic alpha diversity, and total nitrogen (TN) and chemical oxygen demand (COD) concentration significantly affected functional alpha diversity, respectively. Mantel tests showed that TN, Secchi depth, and water depth in the high water level regime significantly increased the total beta diversity and turnover components. TN was the main factor that increased total taxonomic beta diversity. Interspecific competition decreased with the decreasing range (variation) of TN values and differed opposite with the variation of COD values in response to increasing water level, and reached its maximum in the medium regime. Ecosystem stability was promoted by maintaining high species richness and evenness and high differences among communities, and by reducing competition. Based on our results, the water level should be maintained between the medium and high water level regimes to promote restoration of the macrophyte community and improve ecosystem stability.

A document by Hanshe Lim. Click on the document to view its contents.

Agricultural land use can increase runoff and erosion leading to detrimental downstream impacts. This paper examines the impact of agricultural land cover change on runoff and sediment generation at event scales using a model-based approach. SHETRAN, a physically based, spatially distributed model, was applied in two southwest England catchments to represent: (a) changes in the land cover (cropland extent and spatial arrangement), (b) changes in crop type, and (c) use of riparian buffer strips. A total of 84 simulated events within a 4-year period were used to quantify flow and sediment generation impacts. We found past changes in land cover resulted in significant differences in sediment yield (p < 0.05). Linear regression showed an increase in flow and sediment yield proportional to increases in arable crop area (p < 0.001). The spatial arrangement of cropped fields and riparian buffer strips produced no significant differences in event flow or sediment yield (p > 0.05). However, buffer strip scenarios compared with the base run showed sediment load reductions in specific events, up to 20% and 15% for woodland and grass riparian buffers, respectively. When comparing crop types with and without the use of post-harvest cover crops, we observed non-significant differences (both Qv and Sy). However, large reductions in modelled sediment yields occurred for some events (e.g., up to 60% for winter cereals, 50% for maize and 74% for spring cereals). For these scenarios, examination of rainfall event magnitude emphasized the importance of ground cover in mitigating soil erosion for maize and spring cereals, but not for winter cereals. Our findings indicate that significant changes in sediment delivery at the event scale are associated with cropland extent and crop types, depending on rainfall magnitude, but not on the spatial arrangement of cropped fields or the use of riparian buffer strips.

We combine physics-based groundwater reactive transport modeling with machine learning techniques to quantify hydrogeologic model and solute transport predictive uncertainties. We train an artificial neural network (ANN) on a dataset of groundwater hydraulic heads and 3H concentrations generated using a high-fidelity groundwater reactive transport model. Using the trained ANN as a surrogate model to reproduce the input-output response of the high-fidelity reactive transport model, we quantify the posterior distributions of hydrogeologic parameters and hydraulic forcing conditions using Markov-chain Monte Carlo (MCMC) calibration against field observations of groundwater hydraulic heads and 3H concentrations. We demonstrate the methodology with a model application that predicts Chlorofluorocarbon-12 (CFC-12) solute transport at a contaminated site in Wyoming, USA. Our results show that including 3H observations in the calibration dataset reduced the uncertainty in the estimated permeability field and infiltration rates, compared to calibration against hydraulic heads alone. However, predictive uncertainty quantification shows that CFC-12 transport predictions conditioned to the parameter posterior distributions cannot reproduce the field measurements. We found that calibrating the model to hydraulic head and 3H observations results in groundwater mean ages that are too large to explain the observed CFC-12 concentrations. The coupling of the physics-based reactive transport model with the machine learning surrogate model allows us to efficiently quantify model parameter and predictive uncertainties, which is typically computationally intractable using reactive transport models alone.

Field measurements were conducted to study the influence of aquatic vegetation on flow structures in floodplains with the hydrodynamic conditions dominated by combined current and wind-driven wave. Wave and turbulent flow velocity components were decomposed from the time series of instantaneous velocity and analyzed separately. With the ratio of wave excursion to stem spacing less than 0.5, the interaction between wave and vegetation was weak in present study, leading to the vertical distributions of time-averaged velocity (Uhoriz) and turbulent kinetic energy (TKE) with the presence of vegetation similar with the vegetated flow structures under pure current conditions. For emergent vegetations, Uhoriz and TKE distributed uniformly through the entire water column or increased slightly from bed to water surface. Similar distributions were present in the lower part of submerged vegetations. Within the upper part of submerged vegetations, Uhoriz and TKE increased rapidly toward water surface and TKE reached its maximum near the top of vegetation. With small Ew/S the wave orbital velocity (Uw) within vegetation was not attenuated when compared with the Uw above vegetation, and Uw through the entire water column can be predicted by the linear wave theory. However, wind-driven waves made the turbulence generated near the top of canopy penetrate a deeper depth into vegetation than predictions under pure current conditions.

The Hammond Hill Research Catchment (HH) is a small (120 ha), temperate, second order tributary to Six Mile Creek, Cayuga Lake, and the Great Lakes (42.42°, -76.32°). The HH has been monitored since January 2017 for the purpose of understanding how recent infiltration mixes with antecedent soil water on hillslope forest floors and the spatial and temporal patterns of Root Water Uptake (RWU) by temperate northeastern US tree species (eastern hemlock [Tsuga canadensis], American beech [Fagus grandifolia], and sugar maple [Acer saccharum]). These data are informing us about the hydrologic consequences of anticipated tree species composition change and supporting the development of more refined ecohydrological models. The glaciated catchment is underlain by a shallow confining siltstone layer (1 – 1.5 m depth) and dense with a regrowth (approximately 60 years old) mixed species forest of hemlock, beech, and other deciduous tree species common to the northeastern US. Current datasets from the HH include fixed-internal precipitation snow water equivalent, and discharge, and associated isotopic water compositions (2H & 18O). Frequent (<1 month) measurements of shallow (top 10 cm) soil water content and bulk soil water and hemlock and beech xylem isotopic compositions are made at six locations across a topographic wetness gradient. The near-term role of the HH is to support an understanding of the environmental and ecological drivers of plant RWU competition and ecohydrologic education.