Groundwater Level Fluctuations Research Articles

Evaluating tidal impact on ground source heat exchanger performance under fluctuating groundwater levels

Coastal regions undergo dynamic changes due to tidal forces, posing distinct challenges for groundwater management and utilization of ground source heat pump (GSHP) systems. This study examines the impact of tidal fluctuations on groundwater levels and the performance of ground heat exchangers (GHEs), specifically focusing on the suitability of horizontal directional drilling (HDD) technology in high-tidal zones. Itoman City in Okinawa Prefecture, Southern Japan, serves as an ideal location for this study due to its complex coastal hydrogeological conditions and increasing interest in renewable energy solutions. Employing a comprehensive approach involving field experiments, FEFLOW software simulations, and model validation, we aim to elucidate the intricate relationship between tidal dynamics, groundwater behavior, and GHE performance. Furthermore, our investigation assesses the effectiveness of HDD-GHEs installed in highly tidal-affected zones to determine the optimal installation depth for this type of GHE in coastal regions. According to our research, the layer at a depth of 30 m is most affected by tidal influence and fluctuations in groundwater levels in coastal regions. This layer is the most suitable for installing horizontal HDD-GHEs, with an average heat exchange rate of about 89 W/m. This rate is approximately four and two times higher than the depths above and below this layer, respectively, due to groundwater saturation and flow in the formation. Furthermore, we noticed that the heat exchange rate increases from the top to the bottom of this layer, but the extent of this increase diminishes as the depth increases. This is because deeper depths are less affected by tidal fluctuations in groundwater levels.

Impacts of High-Concentration Turbid Water on the Groundwater Environment of the Tedori River Alluvial Fan in Japan

The occurrence of high-concentration turbid water due to a large landslide in the upper reaches of the Tedori River Basin in Japan in May 2015 led to a rapid decline in the groundwater levels within the alluvial fan. However, factors other than turbid water, such as changes in precipitation patterns, can have a significant impact on groundwater levels but have not been thoroughly investigated. By analyzing the relationship between river water and groundwater levels, we found that by 2018, conditions had returned to those observed prior to the turbidity events. Regarding seepage, we found that approximately 24% of the Tedori River’s discharge contributed to seepage before the turbidity event. In contrast, during the post-turbidity years, seepage decreased between 2015 and 2017 and returned to the pre-turbidity levels by 2018. Furthermore, by constructing a hydrological model and examining the contributions of turbidity and precipitation, we found that in 2015, turbidity contributed to 76% of the groundwater level changes, whereas precipitation accounted for 24%. In contrast, in 2016, turbidity contributed to 67%, while precipitation contributed to 33%. In essence, the first year was characterized by a significant contribution from turbidity, while precipitation also played a significant role in groundwater level fluctuations in the second year.

Groundwater Recharge Assessment in Central Benin: The Case of the Collines Region (West Africa)

The objective of this study was to assess groundwater recharge in the hard-rock central region of Benin so as to compare it with the water needs of the local population. To reach this objective, we applied the Water Table Fluctuation (WTF) method, which requires long-term monitoring of groundwater level fluctuations. Groundwater level time series were used in combination with other data (including time series of surface water discharge and rainfall) to estimate groundwater recharge but also to shed further light on the relationship between surface water and groundwater. The results demonstrated that the minimum inter-annual groundwater recharge amount is about 1.09 × 109 m3, which is enough to cover the basic water needs of the local population. It should be highlighted that in sub-regions where the density of the population is high, water shortage can still occur with the above estimated groundwater recharge amount. This study has also illustrated that when applying the WTF method, sites with a highly uncertain specific yield can be detected.

A system dynamics approach for sustainable groundwater management considering climate change, inter-organizational relationships, and domestic water saving

This article uses system dynamic modeling to examine the relationship between water allocation from the Ilam dam and groundwater fluctuation, as well as the effects of climate change, changes in inter-organizational relationships, and water demand management on water allocation and groundwater level fluctuations. The results showed that agricultural water allocation has a direct effect on groundwater level fluctuations. In the first scenario, which examined the effects of climate change, the comparison of three climate change scenarios (SSP126, SSP245, and SSP585) was carried out. The results illustrated that with temperature increasing and precipitation decreasing occurred in SSP585, the groundwater drawdown increases about 0.8 m more than SSP126. The second scenario examined the effects of changes in inter-organizational relationships. Based on the results of centrality measures in the social network analysis method, it was found that the organizational power of the stakeholder organization in the agriculture sector is greater than the ones in the environment sector. This causes the allocation to the agriculture sector to be prioritized over the environment. This scenario was analyzed by assuming a change in organizational power and giving priority to the water allocation of the environmental sector. The results showed that environmental needs (maximum 0.3 MCM) were almost entirely met in the second scenario, compared to the basic scenario. Also, the decrease in agricultural water allocation has led to an increase in groundwater usage by farmers, resulting in a 20 cm drop in groundwater levels. Therefore, regarding the sustainable management of water resources, directing attention towards alternative livelihoods for farmers can contribute to environmental water rights and the remediation of aquifers. The third scenario examined the effects of water demand management. The results showed that saving 20–25% of water in the domestic sector can reduce 40–50 cm maximum groundwater drawdown which align with sustainable groundwater management.

Groundwater Level Forecasting Using Machine Learning: A Case Study of the Baekje Weir in Four Major Rivers Project, South Korea

AbstractUnderstanding the impact of human‐made structures on groundwater levels is essential, with structures like dams or weirs presenting unique challenges and opportunities for study. The Baekje weir in South Korea presents an interesting case as the weir has undergone full gate opening, which is generally not the case for weirs and reservoirs, providing valuable opportunity for simulating weir removal conditions. The main objectives are investigation of groundwater level fluctuations under various weir operations, distances from the weir, and seasonal variations. The study utilizes observed data that simulates conditions with and without the weir, including scenarios of full gate opening. Multiple machine learning algorithms—Random Forest (RF), Artificial Neural Network, Support Vector Regression (SVR), Gradient Boosting, and Extreme Gradient Boosting (XGBoost)—are used to develop accurate groundwater level prediction models. The models' performance is assessed using coefficient of determination, Root mean square error (RMSE), Mean Absolute Error (MAE) indices, and visualized through Taylor diagrams. Results indicate that XGBoost outperforms other models in all three groups during both training and testing phases. Specifically, XGBoost surpasses RF by 2.09% (R2), 5.66% (RMSE), and 10.1% (MAE) in training, and outperforms SVR by 11.2% (R2), 42.0% (RMSE), and 129.2% (MAE) in testing. Additionally, the study generates groundwater level maps, providing a practical tool for managing groundwater systems and informing decision‐making in weir operations. This study not only sheds light on the dynamic relationship between weir operations and groundwater levels but also provides actionable insights for effective water management in similar hydrological settings.

Impacts of vegetation and tidal conditions on porewater and salt transport in coastal wetlands: Numerical simulations and field evidence

Coastal wetlands are crucial ecosystems with high fragility to environmental alterations. Despite early efforts, interactions of water and salt with vegetation in coastal wetlands have rarely been investigated especially with increasing anthropogenic disturbances. Here, field data and numerical simulations were utilized to understand the influences of vegetation, evapotranspiration (ETa), tide, and inundation events on porewater and salt transport in highly regulated tidal riparian wetlands. At the site, the presence of Phragmites australis significantly enhanced soil hydraulic conductivity (KS) and facilitated hydraulic connections between groundwater and surface soil, resulting in the rapid response of soil salinity to groundwater level fluctuations. Simulation results further demonstrated the combined effects of tides and ETa on the salinity distributions, revealing the formation of a high salinity zone in the middle region due to the inflow of water from the tides and ETa-driven upward movements of water and salt; however, as salinity levels increased within the high salinity zone, the growth of Phragmites australis was constrained, leading to reduced transpiration (Ta). Tidal parameters such as amplitudes and mean water levels could affect salt accumulation processes in soils and further the high-salinity zone. Finally, inundation events from extreme upstream discharge had a flushing and diluting effect on accumulated salts, alleviating salinity stress and promoting vegetation Ta and growth; however, further increases in ETa led to salt re-accumulation, potentially reinstating the salinity distribution pattern after inundation. These findings enhance our understanding of ecohydrological processes in coastal wetlands and have important implications for wetland management and restoration.

Organic soil greenhouse gas flux rates in hemiboreal old-growth Scots pine forests at different groundwater levels

AbstractTree biomass and soils (especially organic soils) are significant carbon pools in forest ecosystems, therefore forest management practices, in order to ensure carbon storage in these pools and to mitigate climate change, are essential in reaching climate neutrality goals set by the European Union. Overall studies have focused on diverse aspects of forest carbon storage and greenhouse gas (GHG) fluxes from mineral soils, and recently also from organic soils. However, the information about old-growth forests and the long-term effects of drainage on GHG fluxes of organic soils is missing. Additionally, a large proportion of Scots pine (Pinus sylvestris L.) forests on organic soils in the hemiboreal region are drained to regulate groundwater level and to improve above-ground carbon storage. The study aims to assess the intra-annual dynamics of soil carbon dioxide (CO2) and methane (CH4) fluxes in hemiboreal old-growth Scots pine stands on organic soils with diverse groundwater levels. Six old-growth stands (130–180 years old) were evaluated. In old-growth forests, the main source of soil CO2 emissions is ground vegetation and tree roots (autotrophic respiration), while heterotrophic respiration contributes to almost half (41%) of the total forest floor ecosystem (soil) respiration. The total forest floor respiration and soil heterotrophic respiration are mainly affected by soil temperature, with minor but statistically significant contribution of groundwater level (model R2 = 0.78 and R2 = 0.56, respectively). The CO2 fluxes have a significant, yet weak positive relationship with groundwater level (RtCO2 R2 = 0.06 RhCO2 R2 = 0.08). In contrast, total soil CH4 uptake or release depends primarily on groundwater level fluctuations, with a minor but significant contribution of soil temperature (model R2 = 0.67). CH4 flux has high variability between stands.

Hydrological and biogeochemical processes controlling riparian groundwater quantity and quality during riverbank filtration

Groundwater exploitation in a riparian zone causes water infiltration from the river into the aquifer. Owing to adsorption and redox reactions along the flow path, the quality of water flowing from the river to groundwater wells is variably altered. The riverbed composition often involves spatiotemporal differences due to frequent changes in hydrological conditions. These changes create uncertainties in the transport and removal of solutes in the river water. In this study, the hydrodynamic field associated with riparian groundwater, changes in the structure of riverbed sediments caused by erosion and deposition, fluctuations in surface water and groundwater levels, and the removal efficiency of pollutants from groundwater through pumping were investigated. This involved in situ monitoring and sample testing of the composition of the river water, riverbed sediments, riverbed pore water, and groundwater during dry and wet seasons. Implementation of field in situ column experiments and molecular biology evidences were conducive to identifying the main biogeochemical processes occurring in the riverbed. The findings indicated that riparian groundwater exploitation alters the natural groundwater flow field, while fine sand deposition and microbial adsorption can reduce river recharge to aquifers by diminishing riverbed hydraulic conductivity. Shallow sediments within 1 m depth mainly involve NO3− reduction and E. coli adsorption. Reductive dissolution of Mn dominates in the deeper sediments. Additionally, reductive dissolution of Fe and dissimilatory nitrate reduction to ammonium (DNRA) drive high Fe2+ and NH4+ concentrations in groundwater. The findings can improve the management of riparian groundwater and aid in the optimization of a plan for its exploitation.

Viscoelastic–plastic rheological model and its application to tunnels

Tunnels exhibit obvious continuous deformation during excavation and operation. This behavior is closely associated with the time-dependent behavior of rocks, which is induced by groundwater level fluctuation and prolonged periodic rainfall infiltration. This paper proposes a rheological model consisting of a Hooke elastomer, Kelvin body, and novel plastic element in series (called the HKP model) to describe the creep response of rocks considering the characteristics of dry–wet cycles. First, dry–wet cycle creep tests were carried out to investigate the time-dependent behavior, that is, the creep behavior of sandstone. Then, the creep equation of the viscoelastic–plastic model was derived, and the damage coefficients under the effect of dry–wet cycles and time were obtained. Finally, the HKP model was established to investigate the continuous deformation during tunnel excavation. The results reveal that dry–wet cycles have obvious effects on the physical properties and creep behavior of sandstone. The creep behavior of sandstone undergoes three stages, namely, the decaying, steady, and accelerated stages, which can be reasonably described by the proposed HKP model. The proposed model can accurately predict the creep behavior of tunnel due to excavation in practice, for this particular project. Thus, the HKP model can help in establishing tunnel maintenance strategies to ensure long–term safety.

Observations of reduced ET and persistent elevated water table beneath a riparian forest gap following emerald ash borer invasion and tree mortality

AbstractEmerald ash borer (EAB) (Agrilus planipennis Fairmaire), an invasive, phloem‐feeding beetle native to Asia, has killed millions of ash (Fraxinus spp.) trees in North America since it was detected in southeast Michigan in 2002. Consistently high mortality of black ash (Fraxinus nigra) and green ash (F. pennsylvanica) which often occur in riparian forests is a concern given their role in regulating soil moisture and shallow groundwater levels. We monitored and compared hydrologic processes in a riparian forest impacted by EAB invasion and an adjacent unimpacted riparian forest site in southwest Michigan. From 2018 to 2022, we recorded soil moisture, depth to groundwater and meteorological variables at 15‐min intervals throughout the growing season in a canopy gap following EAB‐caused ash mortality and in adjacent, unaffected forest in the Augusta Creek riparian zone. Groundwater contributions to evapotranspiration (ETG) were estimated using a groundwater level fluctuation (WLF) method. Significant differences in volumetric soil moisture content (16%–26% higher in the gap than forest), average depth to water (10 cm in the gap vs. 70 cm below land surface in the forest) and mean daily ETG (0.6 in the gap vs. 3.0 mm per day in the forest) persisted across four growing seasons. Within the gap, prolonged saturation of the near surface may be contributing to a shift from a forested riparian ecosystem to herb and sedge‐dominated wetland. These differences have implications for an array of riparian zone ecosystem services, a concern given the extent of ash mortality already sustained in much of eastern North America.

Geochemical constraints on the Gano karst bauxite deposit, eastern Alborz Mountains, northern Iran: Implications for provenance, elemental mobility, and distribution of critical metals

The Gano karst bauxite deposit is located in the eastern Alborz Mountains, 90 km NE of Semnan city, northern Iran. The layers and lenticular patches of bauxite are hosted in the Triassic karstified carbonate rocks interbedded with calcareous shale of the Elika Formation, unconformably overlain by siliciclastics of the early Jurassic Shemshak Formation. The bauxite ores have a mineral assemblage dominated by diaspore and hematite, with lesser kaolinite, illite, chlorite, goethite, anatase, dolomite, and quartz. In the Gano area, intrusions range from monzonite to quartz monzonite in composition with an alkaline composition that generated in an extensional regime within a plate tectonic setting during the Devonian age. Geochemical signatures of the Gano bauxite ores suggest a derivation from the monzonite intrusions at the base of the Elika Formation, although a contribution of interbedded calcareous shale of the Elika Formation cannot be excluded. Based on the variation of Ce anomaly across the studied profile and the integration of petrographic evidence and mineralogical and geochemical data, the Gano deposit formed in an oxidized environment under warm-humid climates, significantly linked to rainfall seasonality and groundwater-level fluctuations. Gallium, Nb, and V median values of the Gano bauxite ores are a bit above the maximum value of these critical metals in the northwestern Iranian and Alborz bauxite data set, making diaspore-, anatase-, and hematite-rich layers and lenses valuable for further exploration of these critical metals.

Loading effect of phreatic level variations induced by river tide on groundwater head fluctuations in tidal river aquifer systems

The unconfined groundwater level variations caused by the river tide can impact the fluctuation of the groundwater head in the underlying confined aquifer by loading effect. In this study, we proposed a mathematical model and provided an analytical solution for a confined aquifer system considering the loading effect when the aquifer system is eroded by the tidal river to varying extents. The results demonstrated that the loading effect tends to amplify the amplitude of the tide-induced head fluctuation while reduce its phase shift in the confined aquifer. These effects are more significant with a larger tidal loading efficiency, a wider tidal river, and a smaller tidal propagation parameter of the unconfined aquifer. The analytical solution was validated by the observed groundwater level fluctuations from a groundwater level monitoring well near a tidal river in the Peral River Delta of China, and provided reliable estimations of aquifer parameters in the region.

Investigating climatic and human effects on the decline in the groundwater level (a case study of the Kuhdasht plain)

Abstract This study has been investigated using the new criterion measuring complexity Hilbert-Huang entropy (HHE), changes, and fluctuations in groundwater levels under the influence of climate change factors and humans. In this regard, the 120-month time series of groundwater level, precipitation, temperature, and runoff parameters (period 2009–2018) are first divided into five 24-month periods, then by applying the Hilbert-Huang transform. Eachperiod is decomposed down into smaller periods, and finally, the HHE criterion measures the complexity of the time series. The examination of changes in the HHE complexity criterion shows a decrease of 2.02, 2.93, and 29.58% in the groundwater level in the second, third, and fourth periods. Also, according to the results of changes in the complexity of precipitation and temperature time series as climate change factors, these two parameters have decreased in the third and fourth periods, with the rate of decrease for the temperature time series being 18.8 and 8.3%, respectively, and for the precipitation time series is obtained by 30.6 and 4.4%, respectively. Hence, according to the results, the discharge parameter, as a human factor in the second and fourth periods, shows a decrease of 8.6 and 39.1%, respectively.

Using stable isotopes in deciphering climate changes from travertine deposits: the case of the Lapis Tiburtinus succession (Acque Albule Basin, Tivoli, Central Italy)

Quaternary stable isotope records of marine and lacustrine carbonate deposits as well as speleothems were extensively studied to reconstruct global and regional climatic evolution. This study demonstrates how stable isotope records of travertine provide fundamental information about climate and the consequences of its evolution on groundwater level fluctuations. The deposition of the Lapis Tiburtinus travertine succession occurred during the Late Pleistocene (150–30 ka), coeval with the last activity of the Colli Albani volcanic complex. Two boreholes (Sn1 and Sn2) were drilled into the Acque Albule Basin (23 km E of Rome), crossing the entire Lapis Tiburtinus succession. The Sn1 borehole in the central part of the basin crosscuts a travertine succession of 62.1 m in thickness, while the Sn2 borehole in the southern part of the basin is characterized by a travertine succession 36.3 m in thickness. Carbon and oxygen stable isotope ratios were analysed on 118 samples (59 samples both for Sn1 and Sn2 boreholes) representative of the entire Lapis Tiburtinus travertine succession crossed by the boreholes. Values, measured and correlated in the two drilled boreholes, permitted determination of the sensitivity of the travertine depositional system to glacial and interglacial cycles, unravelling the complex oxygen and carbon cycle dynamic recorded in such sedimentary succession. Moreover, the results obtained correlated with available pollen curves of the Mediterranean area (from the Castiglione crater, 25 km E of Rome). Regional and global oxygen isotope continental and marine curves, calibrated with the stratigraphy of the Acque Albule Basin, and available U/Th dating allow the identification of at least three phases of the last interglacial (Marine Isotope Stage 5-MIS5). The carbon isotope record, compared with CO2 flux reconstructed and associated with the volcanic activity of the Colli Albani volcanic complex, instead shows an influence from groundwater level changes. In particular, positive shifts that occurred during arid phases are associated with a lower groundwater level and increased CO2 degassing, inducing a major fractionation effect on carbon isotopes. Instead, the negative shifts occurring during more humid periods indicate the inhibition of CO2 degassing and increase in pressure, attesting to a rise in groundwater level. In this view, travertine deposits, frequently studied to define the tectonic setting and activity of the area where they develop, can thus also be used as a tool to understand climate changes and groundwater variations apparent in their stable oxygen and carbon isotope signature.

Contribution of standardized indexes to understand groundwater level fluctuations in response to meteorological conditions in cold and humid climates

Understanding the fluctuations in groundwater levels in response to meteorological conditions is challenging, especially given the slow transit time associated with groundwater reservoirs and the short duration of time series for groundwater levels. Nevertheless, this knowledge is crucial for water resource management, especially given that global warming will drastically impact the hydrological dynamics in cold and humid climates. The objective of this work was to quantify how standardized indexes contribute to understanding groundwater level fluctuations in response to meteorological conditions in cold and humid climates and with short time series (10 to 23 years). The relationships between the standardized precipitation index (SPI), standardized temperature index (STI), global climate indexes, and standardized groundwater index (SGI) were analyzed. The reactivity of groundwater levels was examined between 2000 and 2022 using groundwater level measurements from 152 wells located between 46 °N and 52 °N in the province of Quebec (Canada). The results showed that the available time series were sufficient to provide new insights into the role of precipitation and temperature on groundwater fluctuations, demonstrating the usefulness of the indexes. One of the main contributions of this study was that hydrogeological systems in cold and humid climates go through an annual reset due to the prolonged freezing period. This annual reset was one of the drivers isolating year-to-year hydrogeological conditions, contributing to short-duration droughts.

Effect of urbanization on groundwater resources hydrodynamics and bearing capacity: a case study from the Bayraklı region, İzmir, Türkiye

The bearing capacity of soil is a critical factor in the design of foundations for civil engineering structures. The bearing capacity depends on soil properties, as well as the location of the water table. A rise in the groundwater level can be dramatic, especially in highly urbanized regions, and can affect the bearing capacity of foundations. In this study, groundwater-level fluctuations in a highly urbanized region in İzmir, the third largest city in Türkiye, was monitored over a 1 year period, and its effect on reducing the bearing capacity, which is not considered in foundation design and construction, was investigated. For this purpose, four observation wells equipped with groundwater data loggers were used to determine the variations in groundwater level over 1 year. Using the Terzaghi approach to calculate the bearing capacity, normalized bearing capacity plots for various foundation width/depth ( B / D f ) ratios were generated for all four observation wells. Remarkable bearing capacity changes of 10.94, 8.21, 7.62 and 9.29% were observed in four different observation wells (OW-1, OW-3, OW-6 and OW-9, respectively). The study showed that changes in groundwater level in the region caused by urbanization poses a potential risk to the sustainability of previously constructed foundations.

Regional scale evaluation of nitrate fluctuations in groundwater using cluster analysis and standardised hydrometeorological indices

Temporal fluctuations in nitrate in groundwater can result in concentrations temporarily exceeding drinking water standards. This can bring about the need for costly water treatment or blending. Despite this, the extent and potential controls on these fluctuations are poorly understood, particularly at regional to national scales. Applied to Southeast England (UK), here we develop the first application of cluster analysis and standardised hydrometeorological indices to evaluate nitrate fluctuations in groundwater at the regional scale. Hierarchical and K-means cluster analysis of 96 groundwater nitrate time series for the period 1995–2022 showed that nitrate time series can be divided into 4 clusters: (1) long term increasing trends (n = 23, mean trend = 0.26 mg NO3/l/a), (2) long term decreasing trends (n = 19, mean trend = − 0.65 mg NO3/l/a), (3) long term increasing trends with seasonal fluctuations (n = 24, mean trend = 0.29 mg NO3/l/a) and (4) long term increasing trends superimposed on near-decadal scale fluctuations (n = 30, mean trend = 0.22 mg NO3/l/a). Boreholes in cluster 1 appear to be deeper than boreholes in cluster 2. In comparison to shallower boreholes, deeper boreholes are likely to be intersecting longer groundwater flow systems where nitrate concentrations are affected by historic “legacy nitrate” leaching. There is weak spatial coherence in the clustering, with clusters 3 and 4 present in the South and North Downs respectively. Cross-correlation analysis between groundwater nitrate time series with precipitation and groundwater level indices showed that rapid seasonal fluctuations in nitrate concentrations in cluster 3 in the South Downs are associated with rapidly responding groundwater level fluctuation. This is likely due to the highly fractured and faulted nature of the Chalk aquifer in this area. This is in contrast with the slower near-decadal fluctuations in cluster 4 in the North Downs. The strongest correlations between groundwater levels and nitrate concentrations in cluster 3 occurred when cross-correlating at a lag of zero months, which would suggest that matrix diffusion is unlikely to be a significant control on nitrate seasonality. Seasonal fluctuations in nitrate concentrations are likely to be associated with a combination of piston displacement at the water table and changing groundwater flow paths to the borehole. Future climate change may change the magnitude and timing of seasonal fluctuations caused by these processes. The methodology developed here is generic and can be applied wherever there is a large body of groundwater nitrate time series data.

Two decades of dune slack restoration in North Wales: diversity, community and habitat specialists

Humid dunes slacks are a highly threatened habitat, listed as vulnerable in the EU habitat red list. Accelerated successional processes in dune systems have resulted in the loss and degradation of ideal conditions for specialist dune slack species, hence the need for conservation management. We investigated the restoration of a dune slack in North Wales, UK, where vegetation and soil removal to 10 cm depth was undertaken to reinstate nutrient‐poor, open and damp conditions. We assessed the outcomes of the management for dune slack communities over the 18 years since restoration. We also assessed the differences between restored and unrestored areas of dune slacks. The dunes were restored in the winter of 2004/2005, after which we conducted vegetation surveys in fixed quadrats for most years in the restored and adjacent, un‐restored dune slacks. Species diversity and plant community composition changes over time were assessed using Shannon's index, multivariate analysis and indicator species analysis. Comparisons between the restored and unrestored areas of the dune slacks were also made. Ellenberg indicator values (EIVs) were examined to identify potential environmental drivers of post management successional changes. After 18 years the restored dune slacks developed a species‐rich and diverse community. compared to the unrestored slacks. The establishment of species occurred rapidly in the first three years, followed by continued but slower increases in species richness and diversity. This is due to the addition of new species without losses of established species. EIVs show no significant difference over time suggesting the restored areas are still at an early stage of succession. Distinct stages of community change since restoration are characterised by different indicator species. Plants are likely to be largely recruited from an existing seed bank. Restoration by turf removal may be suitable for other low nutrient, species rich habitats dependent upon fluctuating groundwater levels.

A new strategy for groundwater level prediction using a hybrid deep learning model under Ecological Water Replenishment.

Accurate prediction of the groundwater level (GWL) is crucial for sustainable groundwater resource management. Ecological water replenishment (EWR) involves artificially diverting water to replenish the ecological flow and water resources of both surface water and groundwater within the basin. However, fluctuations in GWLs during the EWR process exhibit high nonlinearity and complexity in their time series, making it challenging for single data-driven models to predict the trend of groundwater level changes under the backdrop of EWR. This study introduced a new GWL prediction strategy based on a hybrid deep learning model, STL-IWOA-GRU. It integrated the LOESS-based seasonal trend decomposition algorithm (STL), improved whale optimization algorithm (IWOA), and Gated recurrent unit (GRU). The aim was to accurately predict GWLs in the context of EWR. This study gathered GWL, precipitation, and surface runoff data from 21 monitoring wells in the Yongding River Basin (Beijing Section) over a period of 731days. The research results demonstrate that the improvement strategy implemented for the IWOA enhances the convergence speed and global search capabilities of the algorithm. In the case analysis, evaluation metrics including the root mean square error (RMSE), mean absolute error (MAE), mean absolute percentage error (MAPE), and Nash-Sutcliffe efficiency (NSE) were employed. STL-IWOA-GRU exhibited commendable performance, with MAE achieving the best result, averaging at 0.266. When compared to other models such as Variance Mode Decomposition-Gated Recurrent Unit (VMD-GRU), Ant Lion Optimizer-Support Vector Machine (ALO-SVM), STL-Particle Swarm Optimization-GRU (STL-PSO-GRU), and STL-Sine Cosine Algorithm-GRU (STL-SCA-GRU), MAE was reduced by 18%, 26%, 11%, and 29%, respectively. This indicates that the model proposed in this study exhibited high prediction accuracy and robust versatility, making it a potent strategic choice for forecasting GWL changes in the context of EWR.

Estimation of groundwater recharge from groundwater level fluctuations and baseflow rates around Mount Meru, Tanzania

Estimating groundwater recharge, direct runoff and baseflow is essential for understanding groundwater resource availability and managing groundwater systems. This study estimates groundwater recharge, direct runoff and baseflow on two slopes of Mount Meru: the northern and southern slopes using the water-table fluctuation (WTF) method and baseflow separation technique. High-frequency groundwater level measurements in five shallow wells over three hydrological years from 2018 to 2021 were analysed, while streamflow data in four gauging stations over nine hydrological years from 2010 to 2019 were used. The results of the WTF method show that the aquifer undergoes an average recharge of 544 mm/year and 90 mm/year on the south-western and north-eastern slopes, respectively. On average, this recharge is about 53% and 13% of the annual rainfall on each slope. The baseflow results show that the aquifer on the south-eastern and north-western slopes recharges an average of 88 mm/year and 54 mm/year, respectively, which is on average about 12% and 7% of annual rainfall, respectively. In general, the high recharge on the south-western slope is attributed to the high rainfall, and the high hydraulic conductivity and high hydraulic diffusivity of the pyroclastic deposits compared to the debris avalanche deposits on the north-eastern slope. In addition, debris avalanche deposits show homogeneous recharge conditions, while pyroclastic deposits show heterogeneous recharge conditions. The WTF method can be useful to identify areas of preferential recharge so that preferential groundwater flow paths can be mapped for focused recharge of surface runoff during the rainy season.