Groundwater Level Dynamics Research Articles

Physiographic and Climatic Controls on Regional Groundwater Dynamics

AbstractThe main goal of this study is to explore whether the ideas established by surface water hydrologists in the context of predictions in ungauged basins can be useful in hydrogeology. The concrete question is whether it is possible to create predictive models for groundwater systems with no or few observations based on knowledge derived from similar groundwater systems which are well observed. To do so, this study analyzes the relationship between temporal dynamics of groundwater levels and climatic and physiographic characteristics. The analysis is based on data from 341 wells in Southern Germany with 10‐year daily groundwater hydrographs. Observation wells are used in confined and unconfined sand and gravel aquifers from narrow mountainous valleys as well as more extensive lowland alluvial aquifers. Groundwater dynamics at each location are summarized with 46 indices describing features of groundwater hydrographs. Besides borehole log‐derived geologic information, local and regional morphologic characteristics as well as topography‐derived boundary and climatic descriptors were derived for each well. Regression relationships were established by mining the data for associations between dynamics and descriptors with forward stepwise regression at a confidence level >95%. The most important predictors are geology and boundary conditions and, secondarily, climate, as well as some topographic features, such as regional convergence. The multiple regression models are in general agreement with process understanding linked to groundwater dynamics in unconfined aquifers. This systematic investigation suggests that statistical regionalization of groundwater dynamics in ungauged aquifers based on map‐derived physiographic and climatic controls may be feasible.

Impacts of long-term climate change on the groundwater flow dynamics in a regional groundwater system: Case modeling study in Alashan, China

Groundwater flow dynamics plays a crucial role in social development and ecosystem protection. This study investigated the impacts of long-term climate change on the regional groundwater flow in Alashan, China to reveal the spatial variability of groundwater flow response to climate change and the dynamic patterns of both deep and shallow groundwater flow velocity. To this end, the hydrogeologic conditions and climate evolution history were analyzed. Based on these, four future scenarios of long-term climate change were designed, including linearly varying and cyclic changes, and numerical groundwater flow modeling was then conducted to investigate the effects of long-term climate changes on groundwater flow dynamics (including groundwater level and flow velocity). It was found that groundwater level dynamics were notably influenced by climate changes; the time scale and initial change pattern of cyclic climate influenced the amplitude and mean level of groundwater level fluctuations. In addition, our results also revealed that, for a regional groundwater system, climate change impacts on groundwater level had obvious spatial variability. Groundwater level in recharge and discharge areas were sensitive to drying and wetting climates, respectively. Thus, the spatial variability of groundwater level dynamics reflected climate change information. Moreover, groundwater flow velocity dynamics were also affected by climate changes. However, linearly varying and cyclic climates had different influences. Linearly wetting climate generally increased the groundwater flow velocity in recharge and discharge areas, but decreased that in runoff area, whereas cyclic climate induced periodical fluctuation of groundwater flow velocity. The fluctuation period of shallow groundwater flow velocity matched the full climate cycle period, whereas of the deep groundwater flow velocity was only half. This unique behavior of deep groundwater flow velocity is caused by fluctuation of the vertical velocity alternating between positive (upward flow) and negative (downward flow) values. This finding of groundwater flow velocity dynamics contributes to deeper understanding of long-term climate change effects on groundwater flow dynamics.

Ecological restoration and protection of Jinci Spring in Shanxi, China

Jinci Spring is a popular karst spring in northern China and has important historical and cultural value. The spring stopped flowing since it first dried up on April 30, 1994, which has resulted in further water deficit in the area. This study aimed to further the sustainable utilization of Jinci Spring and used long-term karst groundwater monitoring data to investigate the causes of the drying up of Jinci Spring using the capture principle. The sustainable yield and the sustainability threshold of karst groundwater were quantified, and the ecological water level restrictions for early warning and water supply were determined. A simple two-dimensional (2D) numerical model of karst groundwater was used to design three restoration and protection scenarios under which the dynamics of karst groundwater level were simulated and the restoration and protection scheme was optimized. The results showed that (1) climate change and the long-term consumption of karst aquifer storage are the key factors contributing to the drying up of Jinci Spring; (2) the range of sustainable yield of karst groundwater is 0.622–2.35 m3/s; (3) the sustainability threshold of karst groundwater is (12.35 × 108 m3, 13.91 × 108 m3); (4) the ecological water level restriction for early warning and the ecological water level restriction for water supply are 803.35 meter above sea level (m asl) and 803.21 m asl, respectively; (5) Scenario 1 is the optimal restoration and protection scheme that meets the ecological criteria for Jinci Spring. The results of this study can provide an important basis for the implementation of the ecological restoration program for Jinci Spring.

Response of a Coastal Groundwater System to Natural and Anthropogenic Factors: Case Study on East Coast of Laizhou Bay, China.

With a shifting climate pattern and enhancement of human activities, coastal areas are exposed to threats of groundwater environmental issues. This work takes the eastern coast of Laizhou Bay as a research area to study the response of a coastal groundwater system to natural and human impacts with a combination of statistical, hydrogeochemical, and fuzzy classification methods. First, the groundwater level dynamics from 1980 to 2017 were analyzed. The average annual groundwater level dropped 13.16 m with a descent rate of 0.379 m/a. The main external environmental factors that affected the groundwater level were extracted, including natural factors (rainfall and temperature), as well as human activities (irrigated area, water-saving irrigated area, sown area of high-water-consumption crops, etc.). Back-propagation artificial neural network was used to model the response of groundwater level to the above driving factors, and sensitivity analysis was conducted to measure the extent of impact of these factors on groundwater level. The results verified that human factors including irrigated area and water-saving irrigated area were the most important influencing factors on groundwater level dynamics, followed by annual precipitation. Further, groundwater samples were collected over the study area to analyze the groundwater hydrogeochemical signatures. With the hydrochemical diagrams and ion ratios, the formation of groundwater, the sources of groundwater components, and the main hydrogeochemical processes controlling the groundwater evolution were discussed to understand the natural background of groundwater environment. The fuzzy C-means clustering method was adopted to classify the groundwater samples into four clusters based on their hydrochemical characteristics to reveal the spatial variation of groundwater quality in the research area. Each cluster was spatially continuous, and there were great differences in groundwater hydrochemical and pollution characteristics between different clusters. The natural and human factors resulted in this difference were discussed based on the natural background of the groundwater environment, and the types and intensity of human activity.

Comparative hydrogeology – reference analysis of groundwater dynamics from neighbouring observation wells

ABSTRACT Groundwater level fluctuations are caused by spatial and temporal superposition of processes within and outside the aquifer system. Most of the subsurface processes are usually observed on a small scale. Upscaling to the regional scale, as required for future climate change scenarios, is difficult due to data scarcity and increasing complexity. In contrast to the limited availability of system characteristics, high-resolution data records of groundwater hydrographs are more generally available. Exploiting the information contained in these records should thus be a priority for analysis of the chronical lack of data describing groundwater system characteristics. This study analyses the applicability of 63 indices derived from daily hydrographs to quantify different dynamics of groundwater levels in unconfined gravel aquifers from three groundwater regions (Bavaria, Germany). Based on the results of two different skill tests, the study aids index selection for different dynamic components of groundwater hydrographs.

Ecosystem processes in the area of the Tomsk water intake

The influence of the Tomsk water intake on the ecosystems of the Ob-Tomsk interfluve is studied. It is revealed that the exploitation of the underground water field for almost 50 years has led to the transformation of the natural environment as a result of changes in the hydrological regime in the aeration zone. The most significant changes were observed in hydromorphic ecosystems located in the area of the first stage of water intake, which is associated with both the longest exposure and the feature of the lithological structure. Here and conducted another series of studies, ongoing since 2000, the estimation of the ecosystem assessment and moisture ecotopia phytoindication method. To reconstruct phytocenoses that existed before drying (before 2000), a Botanical analysis of the upper layers of peat was performed. The dependence of changes in the hydrological regime of ecotopes on the dynamics of groundwater levels associated with the operation of the Tomsk water intake against the background of cyclical climate variability is noted. The main changes in the water regime on the territory of the Ob-Tomsky interfluve occurred at the first stages of the water intake operation and the formation of a depression funnel in the area of the first stage, before the beginning of our research in 2000. Currently, the transformation processes have slowed down and there is a stable functioning of ecosystems in the new conditions of humidification, established at a more or less constant level, in accordance with the reduced volumes of water intake. Hydroclimatic calculations for the river basin. Poros have shown that the volume of groundwater renewal in the Ob-Tomsky interfluve exceeds the current volume of water abstraction, which excludes or significantly slows down the further transformation of ecosystems.

A Nonlinear Autoregressive Modeling Approach for Forecasting Groundwater Level Fluctuation in Urban Aquifers

The application of a nonlinear autoregressive modeling approach with exogenous input (NARX) neural networks for modeling groundwater level fluctuation has been examined by several researchers. However, the suitability of NARX in modeling groundwater level dynamics in urbanized and arid aquifer systems has not been comprehensively investigated. In this study, a NARX-based modeling approach is presented to establish a robust water management tool to aid urban water managers in controlling the development of shallow water tables induced by artificial recharge activity. Temperature data series are used as exogenous inputs for the NARX network, as they better reflect the intensity of artificial recharge activities, such as excessive lawns irrigation. Input delays and feedback delays for the NARX networks are determined based on the autocorrelation and cross-correlation analyses of detrended groundwater levels and monthly temperature averages. The validation of the proposed approach is assessed through a rolling validation procedure. Four observation wells in Kuwait City are selected to test the applicability of the proposed approach. The results showed the superiority of the NARX-based approach in modeling groundwater levels in such an urbanized and arid aquifer system, with coefficient of determination (R2) values ranging between 0.762 and 0.994 in the validation period. Comparison with other statistical models applied to the same study area shows that NARX models presented here reduced the mean absolute error (MAE) of groundwater levels forecasts by 50%. The findings of this paper are promising and provide a valuable tool for the urban city planner to assist in controlling the problem of shallow water tables for similar climatic and aquifer systems.

Suitability of a Coupled Hydrologic and Hydraulic Model to Simulate Surface Water and Groundwater Hydrology in a Typical North-Eastern Germany Lowland Catchment

Lowland river basins are characterised by complex hydrologic and hydraulic interactions between the different subsystems (aerated zone, groundwater, surface water), which may require physically-based dynamically-coupled surface water and groundwater hydrological models to reliably describe these processes. Exemplarily, for a typical north-eastern Germany lowland catchment (Tollense river with about 400 km²), an integrated hydrological model, MIKE SHE, coupled with a hydrodynamic model, MIKE 11, was developed and assessed. Hydrological and hydraulic processes were simulated from 2010 to 2018, covering strongly varying meteorological conditions. To achieve a highly reliable model, the calibration was performed in parallel for groundwater levels and river flows at the available monitoring sites in the defined catchment. Based on sensitivity analysis, saturated hydraulic conductivity, leakage coefficients, Manning’s roughness, and boundary conditions (BCs) were used as main calibration parameters. Despite the extreme soil heterogeneity of the glacial terrain, the model performance was quite reasonable in the different sub-catchments with an error of less than 2% for water balance estimation. The resulted water balance showed a strong dependency on land use intensity and meteorological conditions. During relatively dry hydrological years, actual evapotranspiration (ETa) becomes the main water loss component, with an average of 60%–65% of total precipitation and decreases to 55%–60% during comparatively wet hydrological years during the simulation period. Base flow via subsurface and drainage flow accounts for an approximate average of 30%–35% during wet years and rises up to 35%–45% of the total water budget during the dry hydrological years. This means, groundwater is in lowland river systems the decisive compensator of varying meteorological conditions. The coupled hydrologic and hydraulic model is valuable for detailed water balance estimation and seasonal dynamics of groundwater levels and surface water discharges, and, due to its physical foundation, can be extrapolated to analyse meteorological and land use scenarios. Future work will focus on coupling with nutrient transport and river water quality models.

Efficient screening of groundwater head monitoring data for anthropogenic effects and measurement errors

Abstract. Groundwater levels are monitored by environmental agencies to support the sustainable use of groundwater resources. For this purpose continuous and spatially comprehensive monitoring in high spatial and temporal resolution is desired. This leads to large datasets that have to be checked for quality and analysed to distinguish local anthropogenic influences from natural variability of the groundwater level dynamics at each well. Both technical problems with the measurements as well as local anthropogenic influences can lead to local anomalies in the hydrographs. We suggest a fast and efficient screening method for the identification of well-specific peculiarities in hydrographs of groundwater head monitoring networks. The only information required is a set of time series of groundwater heads all measured at the same instants of time. For each well of the monitoring network a reference hydrograph is calculated, describing expected “normal” behaviour at the respective well as is typical for the monitored region. The reference hydrograph is calculated by multiple linear regression of the observed hydrograph with the “stable” principal components (PCs) of a principal component analysis of all groundwater head series of the network as predictor variables. The stable PCs are those PCs which were found in a random subsampling procedure to be rather insensitive to the specific selection of the analysed observation wells, i.e. complete series, and to the specific selection of measurement dates. Hence they can be considered to be representative for the monitored region in the respective period. The residuals of the reference hydrograph describe local deviations from the normal behaviour. Peculiarities in the residuals allow the data to be checked for measurement errors and the wells with a possible anthropogenic influence to be identified. The approach was tested with 141 groundwater head time series from the state authority groundwater monitoring network in northeastern Germany covering the period from 1993 to 2013 at an approximately weekly frequency of measurement.

Relationship between Time Lapse Microgravity Anomaly with Na and Cl Content for prediction of Sea Water Intrusion in Tourism Area Kota Lama Semarang Indonesia

This research is motivated by changes in infrastructure that occur in the old city, the changes in question are the frequent occurrence of flooding in this region. The flooding that occurred was estimated to be caused by subsidence. In addition, subsidence that has other effects, for example seawater intrusion in the Old City, which is located close to the north coast of Java, is also relatively close to about 3 km. The purpose of this study was to find a relationship between seawater intrusion and micro-gravity anomalies between times. The methods carried out are as follows: (1) choose Gravimeter with micro precision. For this study using the Autograv CG5 type, (2) determining the location of the measurement point, which is not expected to experience physical damage due to natural or human behavior for a certain interval, (3) measuring gravity for two different periods in September 2017 and March 2018 at the same point, (4) processing data with initial corrections, namely tidal correction to reduce tidal effects, float correction, and correction of the dynamics of groundwater levels associated with rainfall, and (5) conduct chemical tests of water samples taken from residents’ wells at the Research site. The results showed that the negative time-weight gravity anomaly correlated with an average groundwater level decrease of 15,468 cm. This is in accordance with the fact that during this range rainfall trends tend to decline from September 2017 to March 2018. This decrease in ground water causes maximum subsidence and occurs in the south-southwest 2.3 cm. This zone experiences sea water intrusion which is characterized by the content of Na (60-100%) and Cl (100-160%).

The Effect of Prolonged Irrigation on Soil-amelioration State of the Aley River Steppe in Altai Krai

On the basis of many years of research conducted at the Aley River irrigation system and generalization of literary materials, the impact of irrigation on soil fertility, composition and properties of chernozemic, meadow chernozemic and chernozemic meadow soils, their water and salt regime, and crop productivity has been established. A comprehensive assessment of the long-term impact of irrigation on the change in the hydrophysical and chemical properties of soils and the ecological and reclamation state of the irrigated area is given. The influence of long-term irrigation on the nature and direction of the dynamics of groundwater and salt levels in soils is revealed. The water and salt balance of soils has been compiled, depending on the characteristics and duration of irrigation. It is proved that in conditions of insufficient drainage of the territory, non-compliance with scientifically grounded irrigation regimes, rational irrigation techniques, violation of agricultural technology and crop rotation during long-term irrigation leads to the deterioration of some properties of soils, their salinization and alkalination. Regularities and changes in soil-amelioration conditions during prolonged irrigation of land have been established.

Projecting impacts of climate change on metal mobilization at contaminated sites: Controls by the groundwater level

Heavy metal and metalloid contamination of topsoils from atmospheric deposition and release from landfills, agriculture, and industries is a widespread problem that is estimated to affect >50% of the EU's land surface. Influx of contaminants from soil to groundwater and their further downstream spread and impact on drinking water quality constitute a main exposure risk to humans. There is increasing concern that the present contaminant loading of groundwater and surface water systems may be altered, and potentially aggravated, by ongoing climate change, through large-scale impacts on recharge and groundwater levels. We investigated this issue by performing hydrogeological-geochemical model projections of changes in metal(loid) (As and Pb) mobilization in response to possible (climate-driven) future shifts in groundwater level and fluctuation amplitudes. We used observed initial conditions and boundary conditions for contaminated soils in the temperate climate zone. The results showed that relatively modest increases (0.2 m) in average levels of shallow groundwater systems, which may occur in Northern Europe within the coming two decades, can increase mass flows of metals through groundwater by a factor of 2–10. There is a similar risk of increased metal mobilization in regions subject to increased (seasonal or event-scale) amplitude of groundwater levels fluctuations. Neglecting groundwater level dynamics in predictive models can thus lead to considerable and systematic underestimation of metal mobilization and future changes. More generally, our results suggest that the key to quantifying impacts of climate change on metal mobilization is to understand how the contact between groundwater and the highly water-conducting and geochemically heterogeneous topsoil layers will change in the future.

Groundwater level response of the primary forest, ex-peatland fire, and community mix plantation in the Kampar peninsula, Indonesia

Indonesia has voluntarily committed to mitigating climate change by reducing its greenhouse gas emissions by 26 percent by 2020 and 41 percent by 2050. More than half of this reduction was originated from the forestry/peatlands sector. Avoiding peat fires is therefore crucial for Indonesia to meet its targets. However, the efforts have been hampered by the fact that a large area of peatland has been burnt. The estimated extent of peatland and mangrove burnt was 2,124,000 Ha during the forest fire in Indonesia in 1997/1998. In 1997-1998, high carbon emissions made Indonesia as one of the largest global polluters. The peat fire occurrence in Indonesia has caused severe problems from environmental, economic, health also mortality. Indonesia has the largest peatland area in the region, which is 20.6 million ha or 10.8% of the land area. These lands are spread across various islands, 7.2 million ha (35%) in the Sumatera island, 6.6 million ha (32%) in Kalimantan island, 0.6 million ha (3%) in Sulawesi island and around 6.2 million ha (30%) in Papua island. Peatland in the Sumatera island has suffered severe damage due to land clearing and burning. The objective of this research is to determine the characteristics of peatland in various land conditions, namely primary forest, ex-peatland fire, and community mix plantation as well as to learn the dynamics of peat groundwater level in each study location. Rainfall and groundwater level sensors installed in the primary forest, ex-peatland fire, and community mix plantation. Rainfall-groundwater level analysis conducted to understand the hydrological response in various peatland characteristics. The results showed that in the ex-peatland fire and mix plantation have changed the peat soil characteristics with an increase of soil bulk density. This indicates decreasing the infiltration capacity, soil porosity and increase the surface water in the peatland area. Increasing the groundwater level response to rainfall is stable in the natural peatland forest. This indicates the function of forest cover as rainfall interception and reduces the volume and lag time of rainwater before reaching the forest floor. Community plantation with low canopy diversity has lower forest cover function than in the natural peatland forest. This will increase the volume of rainwater in the peat soil and increase the rainfall-groundwater level response much higher than in the natural forest. Maintain the diversity of canopy cover and reduce the open peatland by fire will control the hydrological response in groundwater level dynamics.

Exploring temporal dynamics of spatially-distributed groundwater levels by integrating time series modeling with geographic information system

This study developed a novel framework for integrating time series modeling with geographic information system (GIS). For the first time, procedures of four statistical tests, i.e., t-test of stationarity, cumulative deviation test of homogeneity, autocorrelation technique of persistence, and variance-corrected Mann–Kendall test of trend, are implemented in GIS platform to enable use of raster dataset. Application of developed framework is demonstrated by exploring time series characteristics of pre- and post-monsoon groundwater levels in an Indian arid region. Raster dataset of 22-year (1996–2017) groundwater levels are generated using four best-fit geostatistical models, according to mean absolute error, root mean square error, correlation coefficient and modified index of agreement. Increasing groundwater level trends in central and southern parts are attributed to abrupt change-points in annual rainfall that enhanced groundwater recharge. The developed framework can be adopted in other parts of the world to explore groundwater-level dynamics in spatially-distributed manner.

Revealing the background of groundwater level dynamics: Contributing factors, complex modeling and engineering applications

Abstract Authors provide extensive analysis of groundwater level dynamics, in order to classify the observed data, to determine the role of contributing factors and to derive specific estimation models, based on the recordings made at four piezometric stations in Serbia: Leskovac, Krusevac, Negotin and Bogatic. Results obtained indicate the predominant impact of noise confirmed by surrogate data testing, determinism test and Box–Jenkins approach. It is shown that surface water level has a strong impact on the observed dynamics, while the effect of rainfall is almost statistically insignificant. Authors also propose different estimation models: as a combination of deterministic and stochastic components, as a nonlinear function of contributing factors and in a form of system of stochastic differential equations. At the end, authors illustrate simple application of some of derived models in engineering practice for slope stability analyzes.

Simulation of groundwater level fluctuations in response to main climate parameters using a wavelet–ANN hybrid technique for the Shabestar Plain, Iran

In recent decades, increasing global water demand, coupled with the effects of climate change, has led to increased variation in groundwater level depletion. In this work, the effect of climate parameters is investigated with respect to groundwater levels in the Shabestar Plain, Iran. In the first step, the best models for the study region were selected from the general circulation models provided under the Fifth Assessment Report of the United Nations Intergovernmental Panel on Climate Change. To increase the spatial resolution of the precipitation data, downscaling of the models was performed using the Long Ashton Research Station weather generator for three representative concentration pathway (RCP) scenarios (RCP2.6, RCP4.5, RCP8.5) for the future period 2020–2049. The results of these models illustrated an increase in temperature and a decrease in precipitation for the study region. In the next step, an artificial neural network (ANN) technique for studying aquifer behavior was used. To increase the efficiency of the model, spatial and temporal preprocessing of data was performed using k-means clustering and wavelet transform de-noising, respectively. A fuzzy inference system was also used as a tool for estimating groundwater extraction and reducing uncertainty of illegal extraction. The results of ANN for five selected observation wells showed correlation coefficients of 0.92, 0.86, 0.76, 0.57 and 0.94 for the simulation. The model simulation under the three above-mentioned scenarios and the trend in groundwater decline in the Shabestar Plain for the base and future periods illustrated that the groundwater level dynamics were not related solely to climate parameters and that the impact of anthropogenic factors would be high.

Methodology for Determining the Die-Off Coefficient of Enterococci in the Conditions of Transport through the Karst Aquifer—Case Study: Bokanjac–Poličnik Catchment

This paper presents the methodology for determining the die-off coefficient of faecal indicator bacteria (enterococci) when transported in a karst environment. The main problem in exploring karst environments, which this methodology strives to cope with, is lack of field measurements, poor data on karst rock formation, fractures and channels within it, and groundwater level dynamics. The analysed karst catchment (Bokanjac–Poličnik) is situated in the hinterland of the city of Zadar (Republic of Croatia) and covers an area of 235.07 km2. In the water supply wells within the analysed catchment, a frequent occurrence of enterococci was observed. The proposed methodology consists of two basic steps. Preliminary analyses as the initial step were used in the accumulation of certain assumptions related to the detection of increased concentrations of enterococci as well as in determination of the potential source of pollution. In the second step, the analytical model was constructed with the aim of resolving processes of sorption and die-off and determining the dominant factor in the process of natural removal of enterococci when transported in karst environment. Within the model, two parts of the pollutant transport are integrated: vertical percolation and horizontal seepage flow and transport. The mean value of the total die-off coefficient by transport through the unsaturated zone in the analysed case is k t o t = 8.25. Within the saturated zone the total die-off coefficient k t o t is within the limits of 0.1 and 0.5.

Groundwater dynamics in a restored tidal marsh are limited by historical soil compaction

In places where tidal marshes were formerly embanked for agricultural land use, these marshes are nowadays increasingly restored with the aim to regain important ecosystem services. However, there is growing evidence that restored tidal marshes and their services develop slowly and differ from natural tidal marshes in many aspects. Here we focus on groundwater dynamics, because these affect several key ecosystem functions and services, such as nutrient cycling and vegetation development. We hypothesize that groundwater dynamics in restored tidal marshes are reduced as compared to natural marshes because of the difference in soil structure. In the macro-tidal Schelde estuary (Belgium), in both a natural and a restored (since 2006) freshwater tidal marsh, we measured depth profiles of soil properties (grain size distribution, LOI (loss on ignition), moisture content and bulk density) and temporal dynamics of groundwater levels along a transect with increasing distance from a tidal creek. X-ray micro CT-scanning was used to quantify soil macroporosity. The restored marsh has a two-layered soil stratigraphy with a topsoil of freshly accreted sediment (ranging in depth between 10 and 60 cm, deposited since 2006) and a subsoil of compact relict agricultural soil. We found that both the soil in the natural marsh and the topsoil of the restored marsh consist of loosely packed sediment rich in macropores and organic matter, whereas the relict agricultural soil in the restored marsh is densely packed and has few macropores. Our results show that groundwater level fluctuations in the restored marsh are restricted to the top layer of newly deposited sediment (i.e. on average 0.08 m depth). Groundwater level fluctuations in the natural marsh occur over a larger depth of the soil profile (i.e. on average 0.28 m depth). As a consequence, the reduced groundwater dynamics in restored tidal marshes are expected to alter the subsurface fluxes of water and nutrients, the source-sink function and the development of marsh vegetation.

Modelling groundwater level dynamics under different cropping systems and developing groundwater neutral systems in the North China Plain

Over-exploitation of groundwater for irrigation has led to a series of ecological and environmental problems in the North China Plain (NCP). Identifying the water consumption and groundwater level dynamics under different cropping systems can help to develop groundwater neutral system in the NCP. The WHCNS (soil Water, Heat, Carbon and Nitrogen Simulator) model was applied to quantify the effects of different cropping systems (2H1Y, two harvests in one year; 3H2Y, three harvests in two years; and 1H1Y, one harvest in one year) on groundwater use and crop growth, and to explore the trade-offs of possible scenarios on the decline of groundwater level and cereal yield. Results showed that WHCNS performed well in simulating soil water content, leaf area index, dry matter and crop yield, as well as groundwater level dynamics, with the Nash and Sutcliffe Efficiency > 0.4 and index of agreement > 0.8. The simulated results indicated that the groundwater levels of 2H1Y decreased faster than those of other cropping systems, at a decline rate of 0.33 m yr−1. Irrigation of 300 mm yr−1 for the remaining high yield of winter wheat mainly resulted in the decline of groundwater level in the NCP. Scenario analyses showed that the groundwater levels would stop decreasing when the current planting area of winter wheat decreased by 76%. However, the reduction of wheat planting area (scenario 1) will also decrease the annual yield by 27% (from 13,547 to 9909 kg ha−1). Fallowing (scenario 2) may reduce annual yield by 50% (from 13,547 to 6834 kg ha−1) in order to maintain groundwater level. The SNWT (South to North Water Transfer) project (scenario 3) may have to provide 50% of irrigation water (130 mm yr−1), to prevent groundwater decline while maintaining the current yield. Scenario 3 could be better than scenario 1 only if the water price was less than 8 ￥m-3. In the future, reducing winter wheat planting area (especially for low-yield cropland) may be a good option to mitigate groundwater decline while maintaining relatively high yield and income for local farmers in the NCP.

ASSESSMENT OF DATA MONITORING OF THE GROUND WATERS REGIME ON THE ODESSA REGION TERRITORY

AbstractProblem Statement and Purpose. The problem of land flooding has become especially important in Ukraine in recent decades. The purpose of the work is to identify the features of the spatial and temporal regime of the groundwater level in natural and technogenic conditions in the territory of the Odessa region; to establish the connections between groundwater levels and climatic (atmospheric precipitation) and astronomic (axis rotational velocity of the Earth) factors.Data & Methods. The work is based on observations of the annual average levels of groundwater and atmospheric precipitation for period 1965-2014, the data of the speed of axial rotation of the Earth and climatic indices were used. 21 wells were selected for statistical processing. They cover the entire territory of the area. The processing and display of statistical information was earned out using Microsoft Excel, Statistica and Surfer programs. The methods of multivariate scaling, correlation, regression, spectral, mutual spectral analysis and mapping were used. Results. Flooding is one of the ecological problems of the Odessa region, about 40% of its territory is affected by this process. Favorable conditions for the development of the flooding process exist on the territory of the region. The precipitation field is due to the processes occurring in the North Atlantic and expressed by the climatic index NAF (North Atlantic Fluctuation). The connection of the groundwater level and atmospheric precipitation has a complex nonlinear character. The statistical series are non-stationary. Atmospheric precipitation is not the main factor that affects the dynamics of groundwater. The connection of the groundwater level with precipitation in the winter period is detected in 15% of wells. The dynamics of groundwater level is controlled by such an astronomical factor as the speed of axial rotation of the Earth.It causes a change in the hydraulic efficiency of structural and tectonic drains. The model of rotational exotectogenesis for the territory not only in Odessa (Shmuratko, 2001), but for the Odessa region is confirmed. Continued monitoring of the ground water regime will improve the quality of statistical methods for forecasting flooding process.