Water Table Elevation Research Articles

Assessing the impact of surface water and groundwater interactions for regional-scale simulations of water table elevation

Groundwater flow models are increasingly considered for the regional scale simulation of hydraulic heads and water table elevation. In the most complete configuration, models explicitly simulate two-way interactions between surface water (SW) and groundwater (GW) to reproduce and forecast both SW and GW water levels. In most regional scale groundwater models, however, SW-GW interactions are represented by simplified boundary conditions that only allow one-way interaction from SW to GW, neglecting most of the dynamic exchange fluxes between SW and GW. To evaluate the potential consequences of such simplifications on the simulation of regional GW levels, we compare two models on a 36,900 km2 regional aquifer system in Southern Quebec. One model explicitly simulates both SW and GW flow with two-way SW-GW feedback and the other model only simulates GW flow with a surface boundary flux to represent a one-way interaction with the land surface. Both models are developed with the same numerical code to ensure that the only differences are the representation of SW water flow and SW-GW feedback. The one-way model simulates overall deeper water tables because it removes all exfiltrated groundwater from the system once it exits the subsurface, therefore not allowing exfiltrating groundwater to re-infiltrate. This effect is most pronounced in areas where the water table is close to the surface and for low-flow periods. The inclusion of two-way feedback also reduces the sensitivity of simulated GW levels to the magnitude of the hydraulic conductivity. This result highlights the need for additional data on other system states to improve the calibration of regional scale models that explicitly simulate two-way SW-GW interactions.

Unified 200 kyr paleohydrologic history of the Southern Great Basin: Death Valley, Searles Valley, Owens Valley and the Devils Hole cave

We present a hydroclimate synthesis of the southern Great Basin over the last two glacial-interglacial cycles focused on paleolakes in Death Valley (core DV93-1), Searles Valley (core SLAPP-SRLS17), Owens Valley (core OL92), and the Devils Hole cave. There is close agreement between the occurrence of lakes in Death Valley and the height of the water table in the Devils Hole (50 km east of Death Valley) during the last 200 kyr. Death Valley and Devils Hole have adjacent, partly overlapping, drainage areas and most likely did over the last 200 kyr. When the water table in the Devils Hole was above the threshold level of ∼5 m higher than the modern, permanent lakes existed in Death Valley. At water table elevations less than 5 m above the modern, ephemeral lakes, saline pans, and mudflats occurred in Death Valley. The close temporal agreement between inferred paleoenvironments from the sediments in the Death Valley core and the paleowater table elevation in Devils Hole suggests a common forcing and provides insight into climate variability in the southwestern United States over the last 200 kyr. Owens Valley and Searles Valley, which derived inflow waters from the Sierra Nevada via the Owens River, contain paleohydrologic records which match those from Death Valley and the Devils Hole in terms of timing and direction of water availability over the last 200 kyr, indicating a similar paleohydrologic history for the entire southern Great Basin region. Near the end of Marine Oxygen Isotope Stage 6 (MIS 6), 140 ka - 130 ka, Lake Manly in Death Valley became shallow and hypersaline, and ultimately dried up at 127.1 ka ±4.3 ka. The transition from glacial to interglacial vegetation, which involved the loss of Juniperus pollen and an increase in Quercus (oak) pollen, occurred in Death Valley core DV93-1 at 131.3 ka ±4.0 ka. Following the glacial to interglacial pollen shift, a large alkaline lake formed in Death Valley. Similar conditions (freshwater, high productivity, and a mixed, deeply oxygenated water column indicated by biomarkers) existed in Searles Lake between 135.3 +2.7/-2.9 ka and 130.1+2.7/-2.6 ka, also following the juniper-oak pollen transition. Sr isotopes in calcite and sulfate minerals (gypsum, glauberite, thenardite), and the rare occurrence of the sodium carbonate mineral northupite with a low 87Sr/86Sr ratio in core DV93-1, together with organic geochemical proxies from Searles core SLAPP-SRLS17, all suggest that at this time, late MIS 6 Lake Manly in Death Valley received alkaline water via spillover from Searles Valley into Death Valley through Panamint Valley. The hydrologic connection between Searles Valley, Panamint Valley, and Death Valley at Termination II (130 ka) is documented here for this system of pluvial lakes for the first time. The Devils Hole water table decreased to +6.5 m at 140.8 ka ±3.2 ka, rose briefly to +8 m at 137.6 ka ±0.5 ka, and then dropped 8 m by 120.36 ka ±0.45 ka, when it reached an elevation similar to the modern. The pluvial lakes in Death Valley and Searles Valley may have coincided with the rise of the Devils Hole water table at ∼137.6 ka ±0.5 ka years ago, although the age models for core DV93-1 and core SLAPP-SLRS17 during the end of MIS 6 carry large uncertainties.

Drivers of barrier island water-table fluctuations and groundwater salinization

Barrier islands are threatened by climate change as sea-level rise and higher frequency storm surge lead to more flooding and saltwater intrusion. Vegetation plays a vital role in preventing erosion of barrier islands due to aeolian and hydrological forces. However, vegetation on barrier islands is threatened by rising water tables causing hypoxic conditions and storm-surge overwash introducing saline water to the root zone. To better protect barrier island ecosystems, it is critical to identify the relative influence of different hydrological drivers on water table elevation and salinity, and understand how this influence varies spatially and temporally. In this study, three barrier island sites were instrumented with groundwater wells monitoring water level and specific conductance. Using these data, a set of transfer function noise models were calibrated and used to determine the relative influence of hydrologic drivers including precipitation, evapotranspiration, bay and ocean water levels, and wave height on groundwater levels and specific conductance. We found that drivers of water-level change and specific conductance vary strongly among sites, depending primarily on the surface water connectivity and the geology of the island. Sites with close connection to inlets showed more salinization and responded to a larger number of drivers, while sites that were poorly connected to the ocean responded to fewer drivers.

Tolerance to waterlogging determines the effectiveness of biodrainage in mitigating runoff in hillslope-scale simulations

Reversal of land degradation in agricultural systems through a wide range of natural resources management tailored to the specific climate, soil, and topography is crucial. This is especially critical for subsistence farming systems such as the Ethiopian Highlands, subject to some of the highest soil erosion rates in the world. Although biodrainage is widely and successfully used for waterlogging and erosion control in arid regions, it is not widely applied in sub-humid places like the Ethiopian Highlands. Beginning with field observations of the complex vertical soil profiles and variations in lithology and soil hydraulic properties along a hillslope ridge-channel transect in the Debre Mawi watershed of the Abay (Upper Blue Nile) Basin in the Ethiopian Highlands, we construct a synthetic model hillslope in HYRDUS-2D. For the growing season coinciding with the rainy season, known as Kiremt, we calibrated the hillslope water storage using observations of water table elevation. The synthetic hillslope is then used to test the feasibility of biodrainage to mitigate saturation, a major driver of gullying and soil loss in the area, and to identify plant traits to which such mitigation is sensitive. The simulation results using bare soil, eucalyptus and maize land covers revealed that in spite of low potential evapotranspiration during the Kiremt season, biodrainage with Eucalyptus can reduce the occurrence and duration of saturation of the top 0.6 m surface soil profile of the hillslope. Of the different plant traits explored, the maximum soil water potential at which the crop can transpire at potential rates, and the LAI, which controls potential evaporation rates via the crop coefficient, provide the most important controls on the effectiveness of biodrainage in desaturating the hillslope. We conclude that biodrainage strategies to mitigate soil erosion in sub humid locales merits further investigation through empirical trials. However, implementation of biodrainage strategies should be subject to thoughtful consideration of the implications for socio-economic outcomes and the local environment.

Spatial modeling of the water table and its historical variations in Northeastern Italy via a geostatistical approach

Groundwater resources are the most important freshwater source for any human use and its preservation in the context of climatic variability is of crucial importance. So far, no systematic spatial estimation of the water table in Northeastern Italy has ever been made available, whereas the Veneto Region (North-Eastern Italy) provides a free database with recorded water table measurements between 1999 and 2022. These starting data have been cleaned, leading to a final database of 53 yearly water table data. The lack of knowledge about the spatial estimation of the water table within the historical period is overcome through the well-known geostatistical technique of cokriging. The latter is the most suitable approach for reproducing water table elevations upon local terrain elevation as an auxiliary variable. Results underline modest decrements between 1999 and 2022, which are more pronounced in the Prealps area and in general in sedimentary soils, and less in the Fontanili belt, a crucial freshwater source area. Moreover, the estimated water table change is highly non-linear in time from year to year and highly varying in space. The results seem particularly interesting in the plain areas and within the Fontanili belt, where the management of groundwater resources is becoming crucial. However, the spatial estimation in the Prealps area needs to be improved for a better assessment and future reliable predictions.

Land drainage functioning and hydrological impacts in rural catchments: model development and field experiments

The development of an integrated theory of subsurface drainage based on hydrology and hydrogeology concepts is presented. The historical context, the main hypothesis derived from the Boussinesq equation and the validation of the model predictions are discussed. Theoretical developments of this equation demonstrate that a single parameter (σ)—a combination of soil and drainage system properties—is sufficient for predicting the dynamics of subsurface drain flow rates. We also demonstrate that these drain flow rates are a function of the level of water replenishment in the system (classically the water table elevation), of the recharge intensity of the aquifer and of a buffer function related to the swelling or deflation of the water table shape during recharge events. For values of σ>1, the buffer role of the water table is negligible. In that case approx. 13% of the water table recharge contributes to the flow rate, which is shown to explain the observed disconnection between water table elevations and peak flow rates at the outlet of classic agricultural drainage systems and to predict these peak flow rates accurately. A modelling approach based on this theory and validated experimentally (SIDRA model) allowed us to test the quality of the peak flow prediction. The SIDRA model also includes a surface runoff module and has been coupled to different modelling tools and used to analyse the impacts of subsurface drainage on water quality. The approach contributed towards the development of tools that helped to connect better the drainage systems to the hydrological functioning of watersheds.

Effect of Flooding on Water-Table Elevation and Salinity in an Abandoned Coastal Agricultural Field

Effect of Flooding on Water-Table Elevation and Salinity in an Abandoned Coastal Agricultural Field

Groundwater Flooding on Atolls Caused by Storm Surges: Effects of the Dual‐Aquifer Configuration

AbstractStorm surges associated with tropical cyclones endanger atolls through groundwater flooding, where groundwater is discharged from the land surface as the sea level rises. Atolls are characterized by a “dual‐aquifer” configuration, where recent Holocene sediments unconformably overlie highly permeable Pleistocene limestone, creating an interface called a “Thurber discontinuity.” This study aimed to quantitatively analyze how the dual‐aquifer configuration of atolls controls the temporal dynamics of groundwater flooding caused by storm surge. To this end, we ran surface‐subsurface coupled synthetic numerical simulations using HydroGeoSphere and compared 12 scenarios with different Thurber discontinuity elevations and hydraulic conductivities of the Pleistocene aquifer (KP). The results showed that the shallower the Thurber discontinuity and the higher the KP value, the higher the maximum water depth in the freshwater swamp on the atoll during the storm surge and the longer the flooding duration. Despite the effects of the different dual‐aquifer configurations, the initial water table elevation and salinity distribution were almost identical in all the simulation cases. These findings suggest that accurate information on the dual‐aquifer configuration is necessary to evaluate the potential risk of groundwater flooding on atolls accompanying storm surges. Furthermore, the results indicate that groundwater flooding caused by storm surges substantially contributes to cyclone‐driven flooding on atolls, and hence, it should not be neglected in flood predictions to avoid underestimation.

Hubungan Evapotranspirasi, Hujan dan Elevasi Muka Air Tanah pada Lahan Gambut Tropis Sebagai Awal Penentuan Kondisi Lahan Basah

The relationship between parameters in wetlands, especially peatlands, as a part of the analysis is interesting to study. The analysis is expected to show the condition of the peatland or the state of the wetlands in general. The water table elevation (WTE) is measured daily, so to compare it with evapotranspiration and rain, daily values for these two parameters are also required. The study was conducted between June-July and August 2022 on shallow peatlands in Gambut District, Banjar Regency, South Kalimantan Province. Evapotranspiration in this study was calculated using the Hargreaves and Modified Hargreaves method which presents a daily evapotranspiration calculation. The methods only depend on the maximum and minimum temperature, the number of outer space radiation whose magnitude depends on its location on the earth's surface, and the time when the research is conducted. The results showed that the highest daily evapotranspiration value generally occurred in August, which was in accordance with previous studies, but the magnitudes were different. The daily evapotranspiration value in this study ranged from 0.5 mm to 1.8 mm, while previously, the values were greater. WTE values show a strong relationship with rainfall, where rainfall increases the WTE value, and conversely, the absence causes the WTEs to decrease gradually. In general, the condition of the peatlands in the study area based on the groundwater elevation conditions still looks quite good with a fast response to rain. The relationship of evapotranspiration with rain and water table elevation cannot be clearly seen in this study because alterations in rainfall and WTE do not directly indicate changes in evapotranspiration values, so a more extended study covering other months and more in-depth covering parameters and other methods is needed to draw valid conclusions more accurate.

Scaling of groundwater flow subject to managed aquifer recharge using injection boreholes: Physical experiments and upscaled numerical models

Managed aquifer recharge (MAR) holds great promise for solving the issue of groundwater resource depletion and quality deterioration in urban areas, but the scaling of groundwater flow patterns under MAR influence from controlled laboratory experiments to complex field scale conditions has not been fully resolved. This study applied physical and numerical groundwater flow experiments at the laboratory scale (100 m) along with ten numerical models at increasing spatial scales (100–103 m) for porous media representative of unconsolidated sand aquifers. We considered several spatial and temporal features that characterize groundwater flow patterns, such as the water table elevation, the thickness of the capillary fringe, the MAR lens geometry (defined as formed by the plume of artificially recharged water), the locations of stagnation points (defined as the points of convergence between ambient groundwater flow and injected water flow), and the groundwater travel times, which were examined at relative scales for comparison. The analysis showed that small-scale sandbox experiments overall underestimate the magnitude of the effects of MAR on groundwater flow pathways. The trends with increasing scales for these parameters were non-linear and could be fitted to power law relationships. These trends were more prominent at scales <20 times the size of the laboratory sand tank. Importantly, the heterogeneity of the sand material, as reflected by non-uniform spatial distributions of hydraulic conductivities (K) also had a major effect on the scaling of groundwater flow patterns, even for the relatively low degree of heterogeneity considered. Specifically, an increase in the average K and its standard deviation further exacerbates the scale dependency. This study provides insights into the appropriate scaling techniques to be used when applying small scale experimental results (e.g., from laboratory) to predict MAR-induced groundwater flow dynamics at larger field scales in moderately heterogeneous, unconsolidated sands.

Experimental and numerical studies of dynamic variation of liquid water and water vapor flow in the vadose zone

In arid and semi-arid regions, the depth of water table has a significant effect on evaporation. The soil in these regions is unsaturated, and the transport of liquid water and water vapor is accompanied by variation of the water table depth. In this study, we designed a laboratory experimental apparatus to conduct evaporation experiments of soil under shallow and deep water table conditions through continuous monitoring of water content and temperature variation in the vadose zone. A numerical model was used to simulate the coupled transport of liquid water, water vapor and heat in the vadose zone under two different water table elevations. The experimental and numerical results were in good agreement. Liquid water and water vapor fluxes driven by pressure head and temperature gradient were calculated and analyzed to illustrate the distribution of the water content. Both isothermal liquid flux and thermal vapor flux dominates the variation of water content. By determining the location of the evaporation front and analyzing its dynamic variation, we found that the evaporation front ranged from the surface to a depth of 2.5 cm under a shallow water table. For a deep water table, the evaporation front was nearly at a constant depth of 15 cm.

A New Kinematical Admissible Translational–Rotational Failure Mechanism Coupling with the Complex Variable Method for Stability Analyses of Saturated Shallow Square Tunnels

Tunnels are commonly constructed in water-bearing zones, which necessitates stability analyses of saturated tunnels based on the upper bound of the plastic theory. Previous kinematical approaches have the following drawbacks: (1) using an empirical approach to estimate pore-water pressure distributions; (2) using failure mechanisms that are not rigorously kinematically admissible. To overcome these shortcomings, we proposed a rigorously kinematically admissible translational–rotational failure mechanism for an underwater shallow square tunnel where velocity discontinuity surfaces were derived. Then, the pore-water pressure field surrounding the tunnel under the boundary of constant water pressure is analytically generated based on the complex variable method and imported into the kinematically admissible velocity field. Work rates performed by external forces and the internal dissipation rate are numerically computed to formulate the power balance equation, followed by a mixed optimization algorithm to capture the critical states of the surrounding soils of tunnels. The outcomes of pore-water pressure distributions, safety factors, and failure mechanisms are in tandem with those given by the numerical simulation but show higher computational efficiency than the numerical simulation. In the end, we highlight the advantages of the proposed model over the empirical approach, where soil properties and water table elevation effects are analyzed.

A 350,000-year history of groundwater recharge in the southern Great Basin, USA

Estimating groundwater recharge under various climate conditions is important for predicting future freshwater availability. This is especially true for the water-limited region of the southern Great Basin, USA. To investigate the response of groundwater recharge to different climate states, we calculate the paleo recharge to a groundwater basin in southern Nevada over the last 350,000 years. Our approach combines a groundwater model with paleo-water-table data from Devils Hole cave. The minimum water-table during peak interglacial conditions was more than 1.6 m below modern levels, representing a recharge decline of less than 17% from present-day conditions. During peak glacial conditions, the water-table elevation was at least 9.5 m above modern levels, representing a recharge increase of more than 233–244% compared to present-day conditions. The elevation of the Devils Hole water-table is 3–4 times more sensitive to groundwater recharge during dry interglacial periods, compared to wet glacial periods. This study can serve as a benchmark for understanding long-term effects of past and future climate change on groundwater resources.

Slope geometry optimization considering groundwater drawdown scenarios at an open-pit phosphate mine, southeastern Brazil

The design of open-pit mines should balance safety and economy. However, safe geotechnical conditions generally involve redesigning the geometry of slopes and groundwater drawdown, significantly increasing the costs of mining operations. The use of numerical models to simulate groundwater drawdown and slope stability can be an alternative to assess cost–benefit trade-offs for decision-making. This study documents a mining plan using groundwater drawdown scenarios that illustrate how geotechnical, economic, and environmental indicators can be combined to obtain optimum slope geometry for open-pit mining. The optimization approach analyzed different scenarios of groundwater drawdown for the final pit of a phosphate mine to improve the pit slopes stability. The groundwater simulation scenarios included the combination of deep horizontal drains and pumping wells. Stability analyses using the limit equilibrium method were used to obtain the bench, inter-ramp, and overall factors of safety of different representative sections. The factors of safety obtained, the drawdown costs and the water table elevation of each section were selected as indicators for obtaining the optimal drawdown scenario using a multi-objective tool. The groundwater control system obtained with 11 horizontal drains and 1 pumping well was considered the most adequate from the geotechnical and economic perspectives. Slope geometry optimization obtained with this drawdown scenario led to adequate inter-ramp and overall safety factors for the final pit design, reducing the barren-to-ore ratio to 0.38, much less than the present ratio (≈ 3). The results are important for optimizing the slope geometry of open-pit mines and can be replicated in other regions.

Performance of three reanalyses in simulating the water table elevation in different shallow unconfined aquifers in Central Italy

AbstractWater table elevation is a key feature for identifying the groundwater behaviour. Accordingly, appropriate measurements—in terms of both frequency and spatial distribution—play a crucial role for capturing the aquifer response to recharge and withdrawals. However, numerical models simulating the main features of the behaviour of the water table elevation may help groundwater management, as an additional tool. In this article, soil moisture data from three well‐established global reanalyses (ERA5, CFS, and JRA‐55) are used for evaluating the flux in the vadose zone towards shallow unconfined aquifers, , in the Umbria region (central Italy). Then, according to the methodology proposed in Bongioannini Cerlini et al. (2021), where for the considered aquifers most of the recharge derives from the unsaturated zone, is used for simulating the water table evolution in time. With the aim of assessing which reanalysis is the most appropriate in simulating the evolution of groundwater levels, the properties of the correspondent land surface models (LSM) are examined, as they provide . For the considered aquifers, the analysis of the performance of the selected reanalyses confirms the validity of the proposed approach. Moreover, it points out the crucial role of the spreading of the water table elevation with respect to its mean value, as a significant parameter for selecting the most adequate reanalysis to use. In addition, the role in the LSM of the explored soil depth, hydraulic conductivity curve, and spatial resolution is highlighted. These results, in line with recent literature on the performance of the reanalyses, suggest to extend future work to other regions of the world.

Changes to Water Table Elevation Across Kansas Wells

Ground water is a valuable resource for all aspects of society whether used for agriculture, commerce, industry, and more. Monitoring the depth of the water table is crucial when determining accessibility and use of this resource, especially in agriculture-heavy regions like Kansas. By subtracting the altitude of the surface from the depth of water in a well, the depth of the local water table can be determined. Using this well data gathered from various locations in Kansas at different can be used to observe past behavior of the water table as well as help predict future behavior.

Land Cover Changes and Their Influence on Recharge in a Mediterranean Karstic Aquifer (Alicante, Spain)

Groundwater plays a key role in the subsistence of people and their activities throughout the globe, particularly in arid zones. In the highly dynamic context of the Mediterranean landscape, a deep understanding of aquifer systems is essential for their optimal management. The aim of this study was to estimate the influence of land cover on recharge in the Almudaina-Segaria aquifer, through the simulation of different land cover scenarios. The results showed a 32% decrease in the total water volume + entering the aquifer when extensive agriculture was replaced by natural forests, with a remarkable drop in the water table elevation for a large portion of the aquifer, depending on geology and topography. Considering the demographic evolution and ongoing climatic changes, it is fundamental to incorporate a management perspective where surface and underground processes are integrated as a fundamental part of a sustainable system.

Change Detection of Groundwater Level and Quality in Coastal Aquifers of Malabar Region in Kerala, India

A study was conducted to assess the changes in groundwater level and quality for the period 2005-2020 in the coastal aquifer of the Vatakara-Koyilandy stretch in the Kozhikode district of Kerala. Hydrogeochemical analysis of groundwater quality parameters, irrigation water quality analysis and preparation of spatial variability of groundwater level and salinity were used for the study. The Piper diagram was used to track the change in the hydrochemical parameters of groundwater sources in 2005 and 2020 and identify changes in the chemical facies of the groundwater. The Gibbs diagram was used to identify the source of the dissolved ions present in the groundwater in both years. The United States Salinity Laboratory diagram was used to assess the groundwater's suitability for irrigation. The spatial variation of water table elevation and salinity were compared using the ordinary kriging method of interpolation. An increase in seawater intrusion into the wells and a reduction in irrigation water quality was indicated by the change in the Hydrochemical facies, and the shifting of more groundwater samples in the evaporation dominance zone in the Gibbs plot. The spatial variability of groundwater level indicates a reduction in premonsoon in both years. On the North coast, a 4% increase in the area under groundwater level &lt; 2m. the reduction in the groundwater table on the coast increases the chance of sweater intrusion and thereby increased salinity. Even though the study area receives heavy rainfall during monsoon and recharging of the coastal aquifer, seawater intrusion progressed landward from 2005 to 2020 during the premonsoon and affected the groundwater level and quality over this period.

Variation in riverine dissolved organic matter (DOM) optical quality during snowmelt- and rainfall-driven events in a forested wetland watershed

The spring snowmelt period is an important time for organic matter mobilization and export in peatland and wetland dominated systems. The hydrologic flowpaths that transport melting snow and soil water to surface waters can vary over relatively short time periods (several days to weeks) depending on the timing and rate of melt and the occurrence of freeze–thaw cycles and rain-on-snow events. Dynamic flowpaths can alter dissolved organic carbon (DOC) concentrations and dissolved organic matter (DOM) optical properties in surface waters due to differential melt and mobilization of snow, ice, and soil waters. In 2018 and 2020, we measured the DOC concentration and DOM optical properties in a woody wetland-dominated watershed in northern Minnesota during spring snowmelt (2018 & 2020) and early growing season (2018 only) events. We examined patterns in riverine DOC, DOM, and hydrochemical tracers across event hydrographs to infer changes in hydrologic connectivity across this seasonal transition. Measurements of riverine DOM optical properties, calcium concentration, and water isotopic composition indicated that DOM shifted from a primarily groundwater source and more fresh character during the dormant season to a more shallow wetland soil source and recalcitrant character during the early growing season. Seasonal variations in DOM optical properties and highly complex hysteresis patterns of DOM indices (e.g., Fluorescence Index, Humification Index, β/α, E250:E365, and the fluorescence peak ratio T:C) during individual events may reflect spatial heterogeneity in soil thawing throughout the watershed and temporal variations in water table elevation, affecting flowpath depths and connectivity to DOM pools within the soil profile. This study provides an important seasonal and event-scale baseline against which to evaluate potential changes in riverine DOM quantity and quality associated with predicted changes in climate and snow cover in organic matter-rich ecosystems.

Soil frost controls streamflow generation processes in headwater catchments

The relationship between snowmelt and spring streamflow is changing under warming temperatures and diminishing snowpack. At the same time, the hydrologic connectivity across catchment landscape elements, such as snowpack and surface wetlands, can play a critical role in controlling the routing of snowmelt to streams. The role of hydrologic connectivity is important in headwater regions of the continental northern latitudes, where catchments have low topographic relief and seasonally frozen ground. Nevertheless, the effects of soil frost on the sequence, timing, and magnitudes of hydrologic events that drive the movement of water from a snowpack to a stream are not fully understood. Therefore, we examine two questions: First, what is the flowpath that snow melt and precipitation from spring rain events takes to generate spring streamflow, and second, what hydrologic, climatic, or landscape variables exert the most control on the magnitude of streamflow? Here, we use long-term hydrological records from the two reference basins at the Marcell Experimental Forest in northern Minnesota to analyze the cascading effects across precipitation, snow, water table elevation, soil frost, and streamflow in peatland-dominated headwater catchments. We identify a sequence of fill-and-spill effects across the landscape that control the timing of spring streamflow generation. Then, we use stepwise regression to show that soil frost is a key supporting predictor for both the magnitude of streamflow in the spring as it adds significantly to the predictive power of precipitation and water table elevation. Our results highlight the importance of recognizing the role of soil frost, when present, on the partitioning of snowmelt between overland runoff and water table recharge during the critical snowmelt period, as well as the later partitioning between evapotranspiration and subsurface flows.