Groundwater Outflow Research Articles

Evaluating the Applicability of Thermal Infrared Remote Sensing in Estimating Water Potential of the Karst Aquifer: A Case Study in North Adriatic, Croatia

One of the most prominent tourist destinations in the Adriatic coast, the city of Opatija, is facing a problem concerning seasonal drinking water shortages. The existing water resources are no longer sufficient, and attention is being given to alternative resources such as the underlying karstic aquifer and several coastal springs in the city itself. However, the water potential of the area still cannot be estimated due to the insufficient hydrological data. The goal of this research was to evaluate the use of thermal infrared (TIR) remote sensing as the source of valuable information that will improve our understanding of the groundwater discharge dynamics. Ten Landsat ETM+ (enhanced thematic mapper plus) and two Landsat TM (thematic mapper) images of the north Adriatic, recorded during 1999–2004 at the same time as the field discharge measurements, were used to derive sea surface temperature (SST) and to analyze freshwater outflows seen as the thermal anomaly in the TIR images. The approach is based on finding the functional relationship between the size of the freshwater thermal signatures and the measured discharge data, and to estimate the water potential of the underlying aquifer. It also involved analyzing the possible connection between the adjusted size of the spring’s thermal signatures and groundwater level fluctuations in the deeper karst hinterland. The proposed methodology resulted in realistic discharge estimates, as well as a good fit between thermal anomalies with measured discharges and the groundwater level. It should be emphasized that the results are site specific and based on a limited data set. However, they confirm that the proposed method can provide additional information on groundwater outflow dynamics and coastal springs’ freshwater quantification.

Quantifying groundwater recharge and discharge for the middle reach of Heihe River of China using isotope mass balance method

Quantifying the inflow and outflow of groundwater is essential to understand the interaction between surface water and groundwater. It is difficult to determine these elements in relation to groundwater recharge and discharge to the river, because they cannot be directly measured through site specific study. The methods of isotope mass balance combining with water budget were used to quantify the groundwater recharge from and discharge to the Heihe River, northwest China. The mean isotope ratios of monthly monitoring data for one hydrological year were selected to be the isotope rations of end members in isotope mass balance. The results from the isotope mass balance analysis, incorporating with the 35-year hydrological data, suggest that about 0.464×109 m3/a of runoff flowing out Qilian Mountains is contributed to groundwater recharge (about 28% inflow of the Heihe River), while about 1.163×109 m3/a of runoff is discharged from groundwater in the middle reach of the river, which accounts for about 46% of river runoff in the basin. The analysis offers a unique, broad scale studies and provides valuable insight into surface water-groundwater interaction in arid area.

Physical-chemical characterization of uranium containing sediments

The presented paper is intended to study the chemical behaviour of combined geogenicanthropogenic uranium content in specific stream sediments. The sampling points have been chosen with respect to the natural conditions in the locality of groundwater outflow from a former uranium mine adit in Považský Inovec mountain range, near Kálnica village. Besides the total uranium determination and physical-chemical characterization of the relevant water- and sediment samples we carried out modified Tessier type sequential fractionation extractions of natural- and artificially contaminated sediment samples after time dependent agitation in air and in the atmosphere of argon. The obtained results have been compared with those fulfilled with montmorillonite K-10. The total uranium concentrations of the relevant groundwater samples as well as of stream sediments have been determined by ICP-MS using HP 4500. The determinations of uranium in extracts have been accomplished according STN757614, utilizing arsenazo III as a selective complex forming reagent for spectrophotometric determination of uranyl-ions at 650 nm. The total uranium concentration of the groundwater outflow and in the sediment taken in its immediate vicinity has been 31.75±0.35 μg dm-3 and 38.0±2.7 μg g-1 respectively. Unlike montmorillonit K-10, in which the carbonate-bound fraction of uranium after 1 week aeration and agitation in argon atmosphere represents 22.8% and 18.6% respectively, uranium in investigated sediments has been present predominantly in carbonate-bound fraction-reaching under similar conditions 38.6% and 26.6%, respectively.

Water balance model aided in estimating net groundwater inflow at Lake Maninjau, West Sumatra - Indonesia

Sustained lake functioning requires proper catchment land and water management. To address this, quantitative information and comprehensive understanding of the spatiotemporal dynamics and hydrological budget of the lake ecosystem are required. However, measuring hydrologic components such as groundwater discharge into a freshwater body is difficult, since its direct measurements are costly, time-consuming, and hardly implemented. Therefore, this study was intended to quantify groundwater inflow to the lake through an effective approach using the water balance modeling technique. Herein, groundwater discharge and contribution were calculated as the water balance residual in terms of net groundwater inflow. It can be considered a minimum estimate of groundwater inflow, as there the groundwater outflow maybe exists but not quantifiable. The approach has been applied for Lake Maninjau which is categorized as a deep, regulated, and tecto-volcanic lake located in West Sumatra Province, Indonesia. The result indicates that the groundwater inflow slightly moderately influences the fluxes of new water volume (the region between observed lowest and highest lake water level) at the upper layer of Lake Maninjau. Its contribution was equivalent to at least 20-28% according to the assessment for the years of 2013 and 2014. Annually, the new water volume recharged from the groundwater inflow corresponded to at least 182-281 million m3. Moreover, these findings enhance a previous study stated that the terrain system of Lake Maninjau is dominated by a rare groundwater aquifer.

Improved estimate of groundwater recharge in the central part of Valle Argentino, province of La Pampa, Argentina

The processes that control the recharge have difficulties for their quantification due to hydroclimatic variability and different particularities of the aquifer system. Sometimes, the different methods for recharge assessment provide results with a high degree of uncertainty. The purpose of this paper is to estimate groundwater recharge in the central part of Valle Argentino, whose hydrogeological potential comes from a sand dune system that plays an important role as recharge area. It was considered interesting to update the previous estimates with new data from the General Acha and Padre Buodo sites. The recharge was obtained from a daily water balance (Visual Balan code) and the water-table fluctuation (WTF) method. The mean yearly values of recharge obtained range from 35 to 53 mm, with maximums between 76 and 112 mm and minimums between 0 and 21 mm. The greater values caused water table rises from 0.60 to just over 1 m, while a low or null recharge is linked to a drop in water levels of between 0.4 and 0.8 m, caused by the predominance of the groundwater outflow. This fluctuation of water table has a severe impact in the water storage in the aquifer, which represents the main source of groundwater for human and livestock consumption in this area. The integration of results in a conceptual model that explain the hydrodynamic behaviour of the system constitutes a relevant contribution to groundwater resource management.

Hydrograph recession extraction algorithm (HYDRA): Minimizing influence of stage uncertainty in identification of recession events

Fine temporal resolution streamflow records offer valuable information to further our understanding of watershed function. Among the many tools to decipher watershed processes, recession analysis can be used to gain insight into storage-discharge properties and watershed storage by analyzing portions of stream hydrographs whose behavior is attributed to the relationship between aquifer structure and groundwater outflow to the steam channel. Although numerous methods have been employed to advance recession analysis methodology, no comprehensive approach to identify the cessation or continuation of recession events from fine temporal resolution data has been established. A new extraction algorithm, the HYDrograph Recession extraction Algorithm (HYDRA), is proposed to improve identification of recession events from fine temporal resolution hydrographs. HYDRA exploits site-specific stage-discharge relations to qualify the beginning or end of a hydrograph recession by accounting for stage measurement error which translates to uncertainty in the stream hydrograph. Experiments compared HYDRA to previous published methods, revealing that HYDRA led to significant improvements in identifying the continuation of recession events, resulting in superior estimation of theoretical recession parameter values. Additional case studies assert that HYDRA robustly identifies recession events across a spectrum of temporal resolution discharge records, affirming that the extraction algorithm provides a functional tool to identify recession events for further recession-based theoretical analysis.

Missing water from the Qiangtang Basin on the Tibetan Plateau

The Qiangtang Basin is a large endorheic basin in the inner part of the Tibetan Plateau, and has been thought to be a dry region in contrast with the surrounding wet outer region that feeds all the major Asian rivers. Combining surface hydrological data with modeling and satellite data from 2002 to 2016 CE, our study reveals that an enormous amount of water, ~54 ± 4 km3, is unaccounted for annually in the Qiangtang Basin. The amount of missing water is comparable to the total annual discharge of the Yellow River. Data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission show little increase of local terrestrial water storage. Thus, the missing water must have flowed out of the basin through underground passages. Interpreting this result in the context of recent seismic and geological studies of Tibet, we suggest that a significant amount of meteoric water in the Qiangtang Basin leaks out by way of groundwater flow through deep normal faults and tensional fractures along the nearly north-south rift valleys that are oriented subnormal to and cross the surficial hydrological divide on the southern margin of the basin. Cross-basin groundwater outflow of such a magnitude defies the traditional view of a basin-scale water cycle and leads to a very different picture from the previous hydrological view of the Qiangtang Basin. This finding calls for major rethinking of the regional water balance.

Laboratory Tests of New Groundwater Table Level Regulators in Subsurface Drainage Systems

The changes in hydrological conditions observed nowadays require economical use of water. This applies to water management both on a national scale and river basins and catchments, as well as on the scale of drainage systems and individual drainage networks. Outflow regulation is carried out by extending the outflow time of surface water collected during rainfall in various forms of retention in the catchment area. One of the devices for regulating the outflow of groundwater is a drainage network, traditionally used as a drainage system. The water level regulators presented in this article enable the damming of water in the drainage network, in pipelines and in the adjacent ground. The conducted tests were aimed at determining the hydraulic characteristics and operating conditions of two innovative solutions of water level regulators in drainage systems. These regulators are characterised by the possibility of smooth regulation by the use of rotary or propeller systems for smoothly setting the damming level. Both tested regulators are characterised by the presence of an effective flow, the value of which was set at the level of Qe = 0.17 l·s−1 to Qe = 0.25 l·s−1 for the funnel regulator and Qe = 0.009 l·s−1 to Qe = 0.015 l·s−1 for a hole regulator. Laboratory tests of the prototypes showed that the funnel regulator allows one to maintain the damming level in a flow rate range of up to 5.5 l·s−1, with possible damming up to 3 cm, regardless of the height of the shaft. The hole regulator is characterised by a flow control range of up to Q = 0.65 l·s−1, greater variability of the damming levels and the need to change the position of the working openings, depending on the flow rate.

The longevity of pockmarks – A case study from a shallow water body in northern Denmark

Pockmarks or crater-like depressions formed due to fluid venting, is a well-known geological phenomenon. On a global scale, pockmarks expel a significant amount of fluids and greenhouse gasses to the marine environment and the atmosphere. Despite pockmarks being well-studied, the longevity and history of activity are rarely addressed. In this study, we analyse more than twenty nearshore seafloor depressions of varying morphology and size in the shallow waters of the western Limfjord in northern Denmark. By using high-resolution seismo-acoustic and sediment core data, we characterize the morphology and sediments of the pockmarks. We further use 14C-dating and pore water analyses to address the timing and activity of the depressions. Our results show that the depressions coincide with submarine groundwater discharge areas and hence represent freshwater pockmarks. The pockmarks most likely formed initially due to two eruptive events of thermogenic light oil/gas ca. 2000 and 900 yrs. BP, both triggered by relative sea-level fall. Freshwater seepage continues to sustain and develop the pockmark morphology and we show that pockmarks grow by collapse of pockmark walls and amalgamation of discrete erosive seepage sites at the bottom. The episodic expulsions of thermogenic fluids and the continuous seepage of freshwater probably prolonged the longevity of the studied pockmarks and further demonstrates the complex nature of pockmark formation and activity. While thermogenic and biogenic gas escape to the surface, on the global scale, is relevant for the greenhouse gas budget, the outflow of groundwater which may or may not be polluted is relevant with respect to the geochemistry, biota and productivity of the receiving marine environment especially in shallow water settings.

Investigating the Effects of Agricultural Water Management in a Mediterranean Coastal Aquifer under Current and Projected Climate Conditions

Coastal delta plains are areas with high agricultural potential for the Mediterranean region because of their high soil fertility, but they also constitute fragile systems in terms of water resources management because of the interaction of underlying aquifers with the sea. Such a case is the Pinios River delta plain located in central Greece, which also constitutes a significant ecosystem. Soil and Water Assessment Tool (SWAT) and SEAWAT models were combined in order to simulate the impact of current water resources management practices in main groundwater budget components and groundwater salinization of the shallow aquifer developed in the area. Moreover, potential climate change impact was investigated using climate data from Regional Climate Model for two projected periods (2021–2050 and 2071–2100) and two sea level rise scenarios (increase by 0.5 and 1 m). Modeling results are providing significant insight: although the contribution of the river to groundwater inflows is significant, direct groundwater recharge from precipitation was found to be higher, while capillary rise constitutes a major part of groundwater outflows from the aquifer. Moreover, during the simulation period, groundwater flow from the aquifer to the sea were found to be higher than the inflows of seawater to the aquifer. Regarding climate change impact assessment, the results indicate that the variability in groundwater recharge posed by the high variability of precipitation during the projected periods is increasing the aquifer’s deterioration potential of both its quantity and quality status, the latter expressed by the increased groundwater Cl− concentration. This evidence becomes more significant because of the limited groundwater storage capacity of the aquifer. Concerning sea level rise, it was found to be less significant in terms of groundwater salinization impact compared to the decrease in groundwater recharge and increase in crop water needs.

Assessments of land subsidence along the Rizhao–Lankao high-speed railway at Heze, China, between 2015 and 2019 with Sentinel-1 data

Abstract. The Heze section of Rizhao–Lankao high-speed railway (RLHR-HZ) has been under construction since 2018 and will be in operation by the end of 2021. However, there is a concern that land subsidence in the Heze region may affect the regular operation of RLHR-HZ. In this study, we investigate the contemporary ground deformation in the region between 2015 and 2019 by using more than 350 C-band interferograms constructed from two tracks of Sentinel-1 data over the region. The small baseline subset (SBAS) technique is adopted to compile the time-series displacement. We find that the RLHR-HZ runs through two main subsidence areas: one is located east of the Heze region with rates ranging from −4 to −1 cm yr−1, and another one is located in the coalfield with rates ranging from −8 to −2 cm yr−1. A total length of 35 km of RLHR-HZ is affected by the two subsidence basins. Considering the previous investigation and the monthly precipitation, we infer that the subsidence bowl east of the Heze region is due to massive extraction of deep groundwater. Close inspections of the relative locations between the second subsidence area and the underground mining reveals that the subsidence there is probably caused by the groundwater outflow and fault instability due to mining, rather than being directly caused by mining. The InSAR-derived ground subsidence implies that it is necessary to continue monitoring the ground deformation along RLHR-HZ.

Base flow in the Yarlungzangbo River, Tibet, maintained by the isotopically-depleted precipitation and groundwater discharge

The extension-induced rift systems on the Tibetan Plateau (TP) may convey large amount of groundwater to rivers, but sources and flow paths of such groundwater are unknown. The Yarlungzangbo River (YR) is the only large river that traverses the southern Tibetan plateau from west to east, following one major suture zone that is cut by extensional normal faults. The faults could influence the flow paths of groundwater discharging to the river. In this study, O and H isotopes, major ions and 222Rn concentrations are analyzed along the YR, and interpreted in relation to structural geology and tectonics. The YR exhibits an abrupt change of isotopic and chemical compositions along with a large increase in flow where the middle reach intersects NE-SW-trending rifts. Low values of δD and δ18O and high concentrations of major ions and 222Rn in the middle reach show that waters are modified isotopically and chemically by a variety of possible water origins, such as recharge of high-altitude glacier melt and discharge from groundwater. Groundwater contributes 27 to 40% of the river flow in the middle reach. Isotopically-light meltwater from high-altitude glacier melt cannot account for the isotope composition of the present outflow of groundwater. The O and H isotope data in the YR and discharging groundwater can be well explained by the groundwater originated as paleo-precipitation during a cooler time, such as the late Pleistocene to early Holocene. The paleo-groundwater discharge can account for about 36 × 108 m3 water budget unbalance in the middle reach. The study provides the first clear isotope evidence for the source of groundwater discharge into a large river through favorable conduits in large-scale active tensile fault zones and confirms the regional scale of groundwater flow on the Tibetan Plateau. Understanding the characteristics and changes of streamflow and surface-groundwater circulation on the Tibetan Plateau will help to manage water resources under a changing environment.

Holy waters in the Podlasie region, Poland, as a witness of hydrological and hydrochemical changes

In the lowlands, springs are quite rare. In the north-eastern Poland, many springs are attributed miraculous properties and water is considered sacred. Due to their cultural and spiritual importance they have survived to present times. Thus, they can be used to study the hydrological and hydrochemical changes in the aquifer. The level of hydrological and hydrochemical changes of the first aquifer in the North Podlasie Lowland has been assessed.We have studied 25 springs and wells considered holy waters, historically present in the geographical region of the North Podlasie Lowland. The main hydro- and physicio-chemical parameters were measured. Currently, majority of the springs have been transformed into shallow dug wells due to groundwater level lowering; only in few cases (6) did the springs survived as groundwater outflows. Their performance was relatively small; from 0.3 dm3ˑs−1. The remaining objects (19) are different depth wells capturing the first aquifer. The largest lowering of groundwater level, exceeding 3 m, was found in Bielska Plain.Their waters were characterized by excessive iron concentration, typical for shallow groundwater of the Quaternary aquifer, and increased concentration of biogenic elements associated with agricultural activity and natural processes contribute, therefore using it as a drinking water requires treatment. Elevated concentrations of DOC, nitrogen and phosphorus compounds could have been caused by changes in hydrological conditions in the region, transformation of the a spring niche through housing of the outflow or presence of surrounding buildings. The studied water bodies were of the bicarbonate-calcium type.

Mire Development and Disappearance due to River Capture as Hydrogeological and Geomorphological Consequences of LGM Ice-Marginal Valley Evolution at the Vistula-Neman Watershed

The advances and retreats of ice sheets during Pleistocene significantly changed high- and mid-latitude landscapes and hydrological systems, albeit differently, in North America and Europe. On the southern margin of the Last Glacial Maximum (LGM) in the Baltic Sea basin, a specific type of valley has developed between glacial margins and upland or mountain slopes. We studied new geological data (boreholes, electrical resistivity imaging (ERI) from this geomorphic setting in Northeast Poland to understand: (1) how the landscape and river network evolved to eventually produce peat mires during the Holocene, and (2) the nature of groundwater recharge to fens in the upper Biebrza Valley. We present the results on a geological cross-section with hydrogeological interpretation. We also discuss regional geomorphology. In addition, we present the LGM extent derived from a spatial distribution of Vistulian (Weichselian) terminal moraines. These end moraines are also interpreted as Saalian kames. Thus, we additionally present another method of LGM extent delineation from a physicogeographical division. We link the steep slopes of the studied valley walls (kame terrace fronts) with thermokarst erosion in the periglacial zone. We then document the hydrogeological window (DISCONTINUITY in the till layer over the confined aquifer), which enables the outflow of groundwater into the peat bog. Although minerotrophic fen mire development in the study area is likely to be sustained in the near future through sufficient groundwater supply, the projected capture of the Biebrza River by the Neman River will not allow for sustaining peatland development.

Multi‐kilometre long pathway of geofluids migration: Clues concerning an ophiolite serpentinization setting possibly responsible for the inferred abiotic provenance of methane in thermal water outflows of the South‐West Carpathians (Romania)

AbstractMethane occurrences displaying signatures of a possible abiotic origin had previously been reported in the South‐West Carpathians (Romania). Such an accumulation, at Tisoviţa, was intercepted by a well drilled in an ophiolitic rocks massif, whereas in two other localities—situated tens of kilometres faraway—the concerned methane is released via thermal groundwater outflows that are apparently not associated with any ultramafic products. By using groundwater ionic compositions, corroborated with previously published isotopic (13C‐CH4, 2H‐CH4, 3He/4He) and molecular gas analyses, we assessed in more detail the conjectured abiotic provenance of methane, and quantitatively investigated the hypothesis of a progressive mixing between two, abiotic and thermogenic, methane end‐members. The corresponding geofluids behaviour was modelled by hypothesizing a “concealed” ophiolite serpentinization setting (largely similar to that at Tisoviţa), whose abiotic methane production was “diverted” towards remote discharges at ground surface, via a ~20‐km‐long flowpath supposedly generated by recently operating extensional tectonics.

Groundwater modeling in the Mediterranean area: case of the Gareb-Bouareg coastal aquifer (Rif, Morocco)

The Gareb-Bouareg aquifer is located in northeastern Morocco. This aquifer extends continuously and expansively under the two plains of Gareb and Bouareg. The introduction of irrigated agriculture utilizing only surface water to these plains has resulted in an alarming rise in the level of the water table, leading to waterlogging and salinization, which have adversely affected crop growth and rendered large areas of the plains unproductive. Therefore, a study of the water-table fluctuations in response to the agricultural development of this area was carried out. Two potential methods of lowering the water table of the brackish alluvial aquifer—the installation of subsurface and deep drainage networks—were proposed. Due to a lack of sufficient data at the local scale (agricultural parcels), it was not possible to simulate the functioning of the agricultural drainage system, so a regional MODFLOW model based on a hydrodynamic modeling approach was used to determine the optimal method of lowering the groundwater level and preventing it from rising above safe levels, thus preserving the quality of the soil and improving growing conditions for crops. After successful calibration and validation of the model, several pump-draining scenarios were simulated to evaluate their impacts on the water table in an area of the plains that suffers from waterlogging. The results for the most realistic scenario revealed that pump draining performed via 10 wells at a rate of 30 l/s per well (i.e., 300 l/s overall) would lower the water table by a maximum of 5.42 m, which would approximate its original level before the water table began to rise due to irrigation. The zone sensitive to this abstraction process would cover an area of approximately 14 km2. This technique could be improved by reducing inflows through the use of water-saving irrigation practices and/or applying corrective measures to increase groundwater outflows, which would eventually be demineralized.

Protection of recovery projects and developed areas from flooding

The article discusses the formulation and solution of scientific, theoretical, and practical problems in the field of land reclamation of irrigated lands in general and, in particular, the protection of land reclamation facilities and the territory of cities and settlements from the effects of groundwater. In the Aral Sea basin, due to the intensive commissioning of new irrigated areas and various types of hydraulic structures (reservoir, village storage, canals, etc.), on a large scale, there is a violation of the natural laws of the regime and balance of groundwater. As a result of the hydrotechnical impact on water resources, the usual “losses” affecting the water balance and runoff, in the initial stage of their formation, cause processes such as flooding and flooding of adjacent territories, excessive wetting of non-irrigated lands and worsen the operation of reclamation projects. The open collector-drainage network existing around the land reclamation projects and cities does not provide a normal outflow of groundwater; its maintenance into a working and sanitary state requires large capital expenditures. High groundwater level with high salinity leads to the destruction of the basement of buildings and structures, the complete flooding of groundwater communications, the death of green spaces. According to some available data, losses incurred from exposure to aggressive groundwater in a number of cities in Uzbekistan range from 2.5 to 10 million dollars. The objects of reclamation control are established depending on the main factor determining the reclamation state of irrigated lands, on the degree of their natural drained. Essential criteria for determining the relationship of groundwater with soil – soils and their influence on the reclamation state of irrigated lands are the depth of groundwater table and the degree of mineralization, as well as their seasonal and long-term regime. The presented dissertation is devoted to the study of this insufficiently solved problem. Scientific and technical solutions to this problem are considered on the example of the built-up areas of irrigated areas of the Republic of Uzbekistan, where there are problems of engineering protection from the negative effects of groundwater.

Connectivity of fractures and groundwater flows analyses into the Western Andean Front by means of a topological approach (Aconcagua Basin, Central Chile)

The misunderstanding of hydrogeological processes together with the oversimplification of aquifer conceptual models result in numerous inaccuracies in the management of groundwater resources. In Central Chile (32–36°S), hydrogeological studies have exclusively focused to alluvial aquifers in valleys (~15% of total area) and mountain-front zones remain considered as no-flux boundary conditions. By a topological approach and an analysis of fractures, the hydrogeological potential of the Western Andean Front along the N–S-oriented Pocuro Fault Zone (PFZ) in the Aconcagua Basin were determined. Perennial springs (23) show evidence of groundwater flows into the fractured Principal Cordillera. Topology allows for quantification of the density of connected fractures within the fault zone and its relationship with groundwater circulation. The study results highlight two areas where the density of fractures and connected nodes (Nc) is high (>2.4 km/km2, 2.5 Nc/km2). Both areas are topologically related to the main springs of the PFZ: Termas de Jahuel (discharge ~14.0 m3/h at 22 °C) and Termas El Corazon (discharge ~7.2 m3/h at 20 °C). Outcrop-scale mapping reveals that groundwater outflows from NW–SE fractures, which is consistent with the preferential orientation of the fracture network (N30–60 W) within the PFZ. The results indicate that oblique basement faults are discrete high-permeability structures conducting groundwater across the Western Andean Front from the Principal Cordillera up to adjacent alluvial aquifers (focused recharge). Therefore, the simplistic hydrogeological view of the Western Andean Front (i.e. impervious limit) is partially erroneous.

Sponge Basin Characteristics of the Original Ecosystem in Ziquejie Terraces and its Adaptive Water Supply and Demand Balance Mechanism

Based on the analysis of the observation results of rainfall and runoff and hydrogeological exploration in the Ziquejie terraces, the concept of “equal slope underground sponge reservoir” in the terraces is proposed. Compared with the ordinary linear storage and drainage process of groundwater in the basin, the “equal slope underground sponge reservoir” has a very significant characteristic of “sponge basin” which can adjust peak and relieve dry and prolong the outflow time. The calculation formula of non-linear outflow of underground water in the “sponge basin” is given. The characteristics of this “sponge basin” and its non-linear outflow principle and the coupling relationship among irrigation, water supply and drainage of ancient terraces are demonstrated. An adaptive balance model of water supply and demand in the original ecosystem of ancient terraces is established. The model is applied to simulate a long series of water supply and demand balance in the original ecosystem of the ancient terraced field, and the check results are highly consistent with the Historical Drought Resistance records of the ancient terraced field. It is proved that the principle of non-linear groundwater outflow in sponge basin and its calculation formula are correct and practical. The research results have important guiding significance for the development, utilization and protection of other ancient terraces, and also have important reference value for the development of sloping farmland.

Factors affecting the abundance and activity of the bacterioplankton in lowland forest springs in north-eastern Poland

The paper summarises the results of bacteriological and hydrochemical studies on the lowland springs in the big forest complex of the Podlasie region in NE Poland. In this area, 75 springs were investigated in the summer period of 2014 and 2015 to determine bacterial number, biomass and hydrolytic activity. All investigated objects were categorized by direct catchment land use and hydrobiological type. The number and biomass of bacteria in the water of the investigated springs is much smaller than in other types of surface water in lowland areas and ranges from 0.29 to 2.94 106 cells cm−3. The best reflection of the habitat quality within lowland groundwater outflows is their hydrobiological typology (helocrene, rheocrene and limnocrene). Despite differing development of spring niches, their hydrology, as well as the geological material and its graining cause unification of the bacterial numbers. The number of bacteria cells were correlated with the concentration of some nitrogen compounds (NH4+, NO2−), and the hydrolytic activity of bacteria with phosphorus compounds mainly dissolved phosphorus. The presence of dissolved organic carbon compounds turned out to be the most disturbing factor in the development of bacterioplankton. Concentrations of these parameters were found to be conditioned by the management of the direct outflow catchment. Furthermore in rheocrene springs, bacterial activity during hydrological stress is clearly lower, despite a large number of bacterial cells in the water (r=-0.38; p<0.005). Our results show that lowland springs are a very sensitive objects to changes in land use, which has a significant impact on water quality and thus the number and activity of bacteria.