Water Table Level Research Articles

Spatial variation of groundwater quality and assessment of water table fluctuations in Plio-Quaternary aquifer formations in Doukkala Plain, Morocco

Groundwater quality and water table fluctuation baseline study were carried out along Doukkala Plain, one of largest agricultural regions in Morocco, bringing together and comparing information from 1995s to 2016s analysis. The depths of wells, the pH, electrical conductivity, and temperature of groundwater were measured in situ for 160 groundwater samples in May 2016. The study of water table fluctuation between 1995 and 2016 showed a continuous rise of the piezometric level from 0.7 to 0.8 m/year in large irrigation schemes. While in the rainfed agriculture area the piezometric level was decreased from 5 to 10 m. The obtained results showed that the level of water table was affected by seasonal variations in consequence to rainfall, irrigation water, and groundwater over-pumping. Groundwater chemistry was also carried out in this research using laboratory analyses of major cations Na+, K+, Ca2+, and Mg2+ and anions Cl−, HCO3−, NO3− and SO42−. Electrical conductivity, nitrate levels, and total hardness were used as indicators to determine groundwater quality and suitability for drinking purposes. The values of these indicators were ranged from 640 to 11950 μS/cm, 0–152.10 mg/L, and from 149.2 to 2081.6 mg/L, respectively. While the suitability of groundwater for agricultural use was determined using sodium adsorption ratio (SAR) and sodium percentage (Na%). SAR values ranged from 1.96 to 17.96 meq/L and sodium percentage values ranged from 22.28 to 86.09%. These results showed that the chemical composition of groundwater fell above acceptable limits recommended by WHO (2011) for drinking water suitability. In contrast, groundwater is suitable for agriculture use at most locations. The unconfined Doukkala Aquifer is under stress due to the impact of anthropogenic activities and climate change. Therefore, widely sharing these results will enable farmers, public and government departments to adopt sustainable solutions for the management of Doukkala Aquifer.

Depositional settings and palynofacies assemblages of the Upper Triassic fluvio-deltaic Mungaroo Formation, northern Carnarvon Basin, Western Australia

ABSTRACTPalynofacies analysis was carried out on 92 core samples from the fluvio-deltaic Middle to Upper Triassic Mungaroo Formation, Northern Carnarvon Basin, Western Australia. The analyses demonstrate that each depositional environment (“depofacies”) sampled has a characteristic palynofacies assemblage reflecting the varied origins, transport, sorting, and preservation histories of organic particles in sediments. The sampling covered a wide range of depofacies identified in fluvial channel, floodplain, crevasse splay, distributary channel, and tidal zone paleoenvironments and included laminated to massive mudstones and siltstones, cross-bedded sandstones, immature pedogenically altered paleosols, and coals. Although each depofacies has a characteristic palynofacies association, there is a high degree of variability within and overlap between preparations. Black-opaque particles were the dominant component in active fluvial, crevasse, and distributary channels. In contrast, palynomorphs, brown wood particles, and cuticle were more common in abandoned channels, floodplain lakes, and other lower-energy environments. The composition of palynomorphs also varies greatly between depofacies due to factors including the bioproductivity of the surrounding vegetation source area, water-table levels, preservation potential, and the fluid dynamic properties of organic particles. The depofacies were grouped into five “process regimes” (active channels, abandoned channels, lakes and periodically flooded areas, paleosols and swamps, tidal mudflats) based on their dominant depositional process. Depofacies in the same process regime tended to have similar palynofacies associations. Active channels yielded similar assemblages irrespective of whether they were fluvial, crevasse, or distributary channels because their dominant characteristic is high flow energy, which encourages the bypass of finer-grained particles, enhances the mechanical degradation of plant debris, and may inhibit local vegetation growth. Organic particles found in lower-energy environments (e.g., floodplain lakes) are on average larger, more elongate, and better preserved than particles found in high-energy environments (e.g., active channels). Although this study was restricted to samples from the upper Samaropollenites speciosus and lower Minutosaccus crenulatus biostratigraphic zones in a geographically limited area, its results are not influenced by the specific taxonomic composition of the vegetation but by the physiographic structure of surrounding plant communities; this suggests that palynofacies analysis could be used to distinguish depositional environments in deltaic settings from other stratigraphic intervals.

Investigating Atrazine Concentrations in the Zwischenscholle Aquifer Using MODFLOW with the HYDRUS-1D Package and MT3DMS

Simulation models that describe the flow and transport processes of pesticides in soil and groundwater are important tools to analyze how surface pesticide applications influence groundwater quality. The aim of this study is to investigate whether the slow decline and the stable spatial pattern of atrazine concentrations after its ban, which were observed in a long-term monitoring study of pesticide concentrations in the Zwischenscholle aquifer (Germany), could be explained by such model simulations. Model simulations were carried out using MODFLOW model coupled with the HYDRUS-1D package and MT3DMS. The results indicate that the spatial variability in the atrazine application rate and the volume of water entering and leaving the aquifer through lateral boundaries produced variations in the spatial distribution of atrazine in the aquifer. The simulated and observed water table levels and the average annual atrazine concentrations were found to be comparable. The long-term analysis of the simulated impact of atrazine applications in the study area shows that atrazine persisted in groundwater even 20 years after its ban at an average atrazine concentration of 0.035 µg/L. These results corroborate the findings of the previous monitoring studies.

Bacterial Diversity in Peat Soils of Forest Ecosystems and Oil Palm Plantation

Bacteria play a crucial role in regulating biogeochemical cycles in peatlands. Most of the studies on soil bacteria focus mainly on the peat surface and bacteria that exist in the deeper peat layers are still poorly known in tropical areas. This study was conducted to examine bacterial abundances along the peat depths in peat forest ecosystems (peat swamp forest (PSF) and logged-over secondary forest (LOF)) and an oil palm plantation (7.5 years after planting (7.5 YAP OPP)) at intervals of 0–30 cm, 30–40 cm, 40–50 cm, and 50–60 cm. Isolation of bacteria from peat samples was carried out on several selective and non-selective media. Bacteria identification was conducted by amplifying the 16S rRNA gene. The result showed that the same dominant bacterial taxa were found with different abundances in all study sites which were Proteobacteria, Firmicutes, and Actinobacteria. Vertical stratification of Proteobacteria and Firmicutes was observed along the depths, might due to the fluctuations of water table in the peatland mainly in 7.5 YAP OPP. Richness was highest at 0–30 cm in LOF and 7.5 YAP OPP, while PSF at 30–40 cm. This study suggests that deeper peat depth supports the bacterial growth and environmental conditions related to water table level influenced the bacterial abundances.

Method to Assess Climate Change Impacts on Hydrologic Boundaries of Individual Wetlands

Potential impacts of climate change on the position of the wetland-hydrology boundary were estimated for four sites in the Eastern U.S. Precipitation and temperature predictions were obtained from the Hadley general circulation model (UKMO-HadCM3) because it most closely approximated observed precipitation for the period 1950–2000. The DRAINMOD hydrologic model was used to compute daily water table levels over two time periods: 1983–2012 (current conditions) and 2041–2070 (future conditions). For each site and time period, the model simulated water table depths for a soil pedon (Typic Paleaquult) that previous work demonstrated was on the wetland-hydrology boundary. Results for the Pitt County site in NC showed that by 2070 the wetland-hydrology boundary would have moved “downhill” to a point that was approximately 17 cm lower in elevation than where the boundary was in 2012 due to a 20% increase in evapotranspiration. Similar analyses were done for hypothetical wetland soils in Miami FL, Easton MD, and Portland ME where the wetland hydrology boundaries were estimated to drop in elevation by 5, 10 and 25 cm, respectively. Our results demonstrated that climate change may have significant impact on wetland boundaries.

Diatom evidence for mid-Holocene peatland water-table variations and their possible link to solar forcing

Peatlands located at the northern edge of the East Asian monsoon (EAM) are well placed to provide a terrestrial record of past climate and hydrological changes for this globally sensitive region. Here we present a middle to late Holocene, diatom-derived water-table records from a peatland in the Greater Hinggan Mountains, northeastern China. An age-depth model was achieved through AMS14C dating and Bayesian piece-wise linear accumulation modelling. The diatom-based water-table reconstructions show that the peatland water-table rose from 5100 to 3500 cal. yr BP, but fell approximately 3500 cal. yr BP. From about 2800 to 1500 cal. yr BP, the peatland water-table stabilized. After about 1500 cal. yr BP, several rapid hydrological shifts, which correspond with global climate anomalies such as ice-rafted debris (IRD) events, were registered in the reconstructed water-tables. Compared with other paleoclimate records in East Asia, the general trend of peatland water-table fluctuations follows the variations in the East Asian summer monsoon (EASM) intensity. Spectrum analysis of the water-table profile yielded a statistically significant periodicity of 470-year that may be related to the “~500-year” inherent solar irradiation cycles. In addition, positive correlation between the peatland water-table levels and cosmic-isotope-reconstructed sunspot numbers underscores the role of the sun in regulating hydrological processes in the EASM margin area. The data suggest that the regional climate and hydrological variations at the EASM margin were first triggered by changes in solar output, but may have been amplified by interactions with oceanic and atmospheric circulations.

Laboratory study of low-sulfide tailings covers with elevated water table to prevent acid mine drainage

The use of monolayer covers combined with an elevated water table (EWT) is a promising reclamation method that relies on the low gas-diffusivity of water to limit oxygen ingress into potentially acid-generating tailings. A monolayer cover is installed over the sulfidic material and the water table level is controlled to maintain the tailings close to saturation. A protocol including laboratory columns was conducted to evaluate the sensitivity of the technique to parameters including cover thickness, water table level, and the presence of an anti-evaporation layer. Two types of desulfurized tailings were evaluated: silty tailings from Westwood mine and sandy tailings from Goldex mine. Data used to evaluate the covers performances included volumetric water content, suction, oxygen concentrations, and oxygen consumption. Results showed that both cover materials could be used to maintain the reactive tailings at a degree of saturation ≥90% when the EWT level was maintained at a maximum distance of 1 m below the tailings surface. The finer Westwood material showed a better capacity for limiting oxygen migration through the cover, with a maximum flux of 5.7 mol·m−2·year−1 measured near the cover base.

Hydrogeology of the western Po plain (Piedmont, NW Italy)

ABSTRACT This paper describes the hydrogeological map of the western Po Plain, located in Piedmont (north-western Italy). Po plain represents a hydrogeological system of European relevance, and the Piedmont Plain is the most important groundwater reservoir of the Region. The 1:300,000 scale map was realised using previous and new data to update the knowledge of this area. The map provides information about the hydrogeological complexes and their type and degree of permeability, water table levels and depth, piezometric level fluctuation, lithostratigraphic cross-sections, thickness, and percentage of the permeable deposits between 0 and 50 m from the ground surface. All this information is essential to public administrations, stakeholders, researchers, and professionals for defining possible tools for groundwater protection and management and for planning new groundwater exploitation (i.e. municipal drinking water supplies).

EVASOR, an Integrated Model to Manage Complex Irrigation Systems Energized by Photovoltaic Generators

The carbon footprint and energy cost of irrigation are increasing due to the modernization of irrigation systems, which also necessitates highly efficient use of water resources. Alternatives to conventional energy sources to power irrigation systems are renewable sources, primarily photovoltaic energy. Photovoltaic energy has the main disadvantage of producing a highly variable amount of energy, which affects the irrigation uniformity. Modeling irrigation systems in an integrated manner generates useful information about system performance for technicians that helps in the decision-making process. The EVASOR (EVAluation of SOlar iRrigation systems) model integrates different modules to simulate the whole solar irrigation system using a holistic approach: (1) I-Solar, which simulates the instantaneous power generated by the photovoltaic system, (2) AS-Solar, which simulates the variable speed pumping system, (3) Solar-Net, which simulates the hydraulic performance of the water distribution network, and (4) PRESUD-Irregular, which determines the discharge and pressure of all the emitters of the subunits together with irrigation quality parameters (coefficient of uniformity (CU), emission uniformity (EU), and coefficient of variation of the emitter discharge in the subunit (CVq) for any pressure at the subunit inlet. The integrated model EVASOR determines the irrigation quality parameters of complex irrigation systems with information on irradiance, air temperature, wind speed, and water table level for any combination of open subunits. To validate the model, results are presented regarding a case study located in southeast Spain.

Seasonal variation of hydrochemical characteristics of open-pit groundwater near a closed metalliferous mine in O’Kiep, Namaqualand Region, South Africa

In this study, the hydrochemical characteristic changes of open-pit groundwater (OPGW) near a closed metalliferous mine proposed for drinking and irrigation usage were investigated. Water samples from an OPGW in O’Kiep were collected in April (dry season) and August (wet season), 2017. Data analysis methods, such as the coefficient of variation, correlation coefficient, piper trilinear plot analysis and sodium adsorption ratio (SAR) among others were used to assess of the seasonal variation in the OPGW quality. The hydrochemical characteristics of the OPGW were also compared with drinking water guidelines. Based on the results, it was evident that the OPGW quality varied seasonally. The most abundant cation and anions were Ca2+ and SO42−, with recorded concentrations of 631 and 6020 mg/L, (dry season); 541 and 4450 mg/L (wet season), respectively. The OPGW was relatively rich in SO42− > Cl− > Mg2+ > Ca2+ > Na+ > K+ during the dry season; however, these cations and anions were reduced during the wet season with Cl− and Na+ subsequently increasing. PHREEQC indicated that cation exchanges played a significant role in the OPGW chemistry with Sb and Ca appearing to be the minerals with the highest precipitation potential followed by Cu7S4 and Blaubleil, respectively. Covellite, CdSe2 and NiSe were likely to be in equilibrium while Ca3Sb2 will remain in a dissolution state. Furthermore, the seasonal fluctuation in the OPGW quality characteristics was attributed to the water table level fluctuations and the water quality did not satisfy the guidelines stipulated by the South African National Standard, SANS241-1 (2015) and World Health Organisation, WHO (2011). The trilinear piper plot classified the OPGW into three types: Ca2+–Mg2+–Cl−–SO42; Ca2+–Mg2+–F−; and Ca2+–Mg2+–SO42−. Overall, the SAR values were within the permissible levels for irrigation purposes; however, long-term use of the OPGW might be detrimental for plant growth.

Rozšírenie, ekológia a ochrana kotúľky štíhlej (Anisus vorticulus) na Slovensku [Distribution, ecology and conservation of the Little whirlpool ramshorn snail (Anisus vorticulus) in Slovakia

The main aim of this article is to summarise data on the biology and conservation of the Western Palaearctic planorbid gastropod Anisus vorticulus (Troschel, 1834). This aquatic gastropod is a threatened species at European level and endangered species in Slovakia according to IUCN red list classification. This paper also deals with comprehensive data on the species distribution in Slovakia between 1953 and 2019. According to the Habitat Directive, Slovakia realised regular monitoring of the species at 10 permanent monitoring plots and established 11 sites of community interest (SCI) within the NATURA 2000 network exclusively for its protection. In results, there are monitoring assessments available as well as the overall assessment of the species conservation status. In the last twenty years, Anisus vorticulus has been confirmed in Slovakia at 23 sites. The most recent research shows that the species prefers small and old drainage ditches (36% out of all its sites) and plesiopotamal channels, flooded by surface water only at a high water table levels (25% of sites). To a lesser extent, the species also inhabits stagnant water bodies which are not in contact with surface floods (i.e. paleopotamal; 16% of sites).

Upper bound seismic limit analysis of geosynthetic-reinforced unsaturated soil walls

The assessment of the internal stability of geosynthetic-reinforced earth retaining walls has historically been investigated in previous studies assuming dry backfills. However, the majority of the failures of these structures are caused by the water presence. The studies including the water presence in the backfill are scarce and often consider saturated backfills. In reality, most soils are unsaturated in nature and the matric suction plays an important role in the wall's stability. This paper investigates the internal seismic stability of geosynthetic-reinforced unsaturated earth retaining walls. The groundwater level can be located at any reinforced backfill depth. Several nonlinear equations relating the unsaturated soil shear strength to the matric suction and different backfill type of soils are considered in this study. The log-spiral failure mechanism generated by the point-to-point method is considered. The upper-bound theorem of the limit analysis is used to evaluate the strength required to maintain the reinforced soil walls stability and the seismic loading are represented by the pseudo-dynamic approach. A parametric study showed that the required reinforcement strength is influenced by several parameters such as the soil friction angle, the horizontal seismic coefficient, the water table level, the matric suction distribution as well as the soil types and the unsaturated soils shear strength.

Carbon-isotope, petrological and floral record in coals: Implication for Bajocian (Middle Jurassic) climate change

Much of our existing knowledge of Middle Jurassic paleoclimate is based on well-dated marine isotopic records that show fluctuations between warm (greenhouse effected) and cool climates. In contrast, much less is known from contemporaneous terrestrial deposits that are often difficult to correlate stratigraphically with marine successions, and are typically considered as showing regional rather than global signals. In this paper we show that the carbon-isotopic, petrological and floral record through 20 m thick coals in the Northern Qaidam Basin (NW, China) represents a relatively comprehensive northern hemisphere Bajocian (Middle Jurassic) record for terrestrial climatic change. δ13Ccoal values for 88 samples from the Yuqia area in Northern Qaidam Basin range from–25.3‰ to –22.5‰, indicating that C3 plants were the main coal-forming vegetation in the region during the Middle Jurassic. This isotopic variation follows fluctuations in the composition of ferns and gymnosperms, where higher ratios correspond to more negative δ13C values. The similar carbon isotope values of gymnosperms and coal from the Yuqia area indicate that the coal comprises a high proportion of organic material derived from gymnosperm taxa, which is consistent with the very high abundance of diterpenoids in coal and especially pimarane and abietane that are produced primarily by gymnosperms. Results from the coal matrix provide an opportunity to record paleoclimate changes, showing several striking and regular coal-forming cycles with distinct long- and short-term variations. Trends of δ13Ccoal values changes coupled with the evolution of coal-forming plants may record a gradual increase in paleo-CO2 (pCO2) concentration, water-table level changes and the decrease in abundance of Classopollis conifer pollen through Bajocian. This result is in accordance with the published marine carbonate records for this time, with correlation enabled through matching carbon isotope curves from the terrestrial succession at Yuqia and marine records. The similarity of the terrestrial and marine geochemical and floral record is an indication that the observed paleoclimate signal is a global phenomenon. Furthermore, the high-frequency fluctuation of δ13Ccoal values, along with the coal petrologic variations may record short-term changes of environmental factors (e.g. temperature or humidity/precipitation), especially during intervals when palaeobotanical composition has not fluctuated intensely.

Groundwater hydrodynamic behaviours based on water table levels to identify natural and anthropic controlling factors in the Piedmont Plain (Italy).

Water table level monitoring and analysis are among the tools available to identify variations in the quantitative state of groundwater. Moreover, these levels highlight the response of groundwater to climate change and other global change drivers, including land use changes. In this study, water table level (37 monitoring wells) and rainfall (30 rain gauges) data analyses were performed in an alluvial unconfined aquifer in the Piedmont Plain (NW Italy) for the 2002-2017 period. The aim of this study was to identify possible trends in the time series and classify the groundwater hydrodynamic behaviours, as well as their spatial distributions and the main drivers of change in the plain. Moreover, two different sub-periods (2002-2008 and 2009-2017), which were identified with a change point analysis, were analysed to highlight possible variations in the groundwater hydrodynamic behaviours. The results of this study highlighted the lack of a trend in the rainfall time series, while a trend was detected for the water table. To explain this inconsistency, water table behaviours were analysed during the year, highlighting different groundwater hydrodynamic behaviours. Over time, the groundwater hydrodynamic behaviour generally showed the dependence of the water table level on rainfall occurrence. This correlation was also underscored by analysing the standardised anomalies of rainfall and groundwater levels. A different behaviour was observed in the paddy field areas, where the main driver of water level modification is the agricultural technique of rice cultivation. Furthermore, a reduction in the maximum water table level period was observed in 2009-2017 in this area. More specifically, the high water table period passes from 4 to 3 months, which could be the result of changes in irrigation methods. In this study, by analysing the present resource status, a first step is made to obtain future insights into flow dynamics and trends in storage.

EVALUATION OF PULL-OUT CAPACITIES OF DIFFERENT PILE MODELS EMBEDDED IN UNSATURATED SANDY SOIL

The rises of capillary water above the water table level in soil layers and make the soil partially saturated that is considered one of the most challenging problems that a geotechnical engineer may encounter. Partially saturated soils contain large percentages of voids between the structural soil particles that are filled by water instead of air. Physical and mechanical properties of partially saturated soils are different than the other soils (i.e. dry or saturated) such as effective stress, shear strength and seepage. In present work, pile models manufactured from steel with different geometry (H-pile, hallow square pile, and closed-ended pipe pile) of the same surface area embedded in partially saturated sand soils to investigate the uplift capacity. Poorly graded fine sand obtained from Baghdad city was used throughout this research. Partially saturated soils were obtained by lowering water level below soil surface to a depth of (i.e. 150 and 450 mm). Test results showed from the suction profiles of the soil that the matric suction increases with the lowering of water table. The ultimate uplift pile capacity was different in values based on the matric suction values. A comparison was made between the behaviors of steel pipe pile with other shapes of pile models used in terms of uplift capacities. The results showed that the degree of improvement in values of uplift capacity for first lowering of water level 150mm were (2.36, and 1.11) times than that of H-pile, and square piles, respectively. While the improvement in uplift capacity for a pipe pile when the water table level was lowering to a depth of 450mm, were greater than those of H-pile, and square steel piles by (2.22, and 1.10), respectively.

Groundwater Level Fluctuations Affect the Mortality of Black Alder (Alnus glutinosa Gaertn.)

Since the 1990s, a decline of riparian black alder (Alnus glutinosa Gaertn.) has been observed over Europe. The fungus-like eukaryotic pathogen Phytophthora alni subsp. alni is thought to be a causal agent of this process; however, abiotic factors may also be involved. Previous studies suggest that climate conditions and, especially, depletion of groundwater level may be among the most important factors that trigger this phenomenon. We investigated the radial growth and wood vessel diameter of black alder trees of various vigour classes as well as their response to groundwater level changes to search for the link between soil water resources availability and mortality related to alder dieback. Samples were collected in the natural stand located near Sieraków village in the Kampinoski National Park, central Poland, in the area where alder dieback has been recently observed. Based on the crown defoliation level, three vigour classes (healthy, weakened, and dead trees) were distinguished. Cross sections were prepared with a sliding microtome, and Cell P image analysis software was used for the measurements. Tree-ring width (TRW) and vessel diameter (VD) were determined and correlated with the monthly values of precipitation and groundwater level. Alders of the analysed vigour classes exhibited similar patterns of TRW and VD changes over the analysis time. The narrowest tree rings were observed in weakened alders, while the largest vessels were noted in healthy trees. In the case of TRW and VD chronologies, the weakest, and hence insignificant, resemblance was found for healthy and dead trees. TRW and VD of the analysed alders were not correlated with the monthly sum of precipitation, but a negative influence of rainfall in April was observed. In turn, groundwater level had an impact on the radial growth and wood anatomical features of the analysed trees. A negative effect of the highest water table level was found for TRW of weakened and dead trees as well as for VD of healthy and weakened alders. The lowest groundwater level and the amplitude of the water table positively affected VD of the dead trees. Alder decline has a polyetiological nature, and groundwater level fluctuations are one of many factors contributing to disease development.

Comparative analyses of finite element and limit-equilibrium methods for heavily fractured rock slopes

Limit-equilibrium method (LEM) and finite element method (FEM) with shear strength reduction (SSR) technique are the most widely used analysis tools in slope stability assessment. Recently, researchers have reported that both factor of safety (FOS) values and failure surfaces obtained from LEM and FEM are generally in good agreement except in some particular cases. On the other hand, the consistency between two methods has not been adequately discussed for heavily fractured rock mass models by employing Generalized Hoek–Brown Criterion (GHBC). In this study, the FOS values and failure surfaces derived from LEM and FE-SSR based on GHBC were compared concerning static and pseudo-static conditions, various overall slope angles, geological strength index (GSI) values, and various water table levels. In this context, three homogeneous, highly fractured rock slope models with irregular geometry and different slope heights were generated by two-dimensional Slide and Phase2 software. Limit-equilibrium (LE) analyses were performed by Bishop, Fellenius, Morgenstern–Price, and Spencer techniques. The comparisons of global minimum FOS values for 431 cases and the effects of variables on two methods were investigated by statistical analyses. Consequently, it was determined that the difference between the FOS values are statistically significant. However, if the seismic coefficient is higher than 0.1 g, slope angle is higher than 34°, and the slope is assumed to be fully saturated, Morgenstern–Price is the most well-matched technique with FE-SSR than the others. For the same cases, the failure surfaces detected by Fellenius is more similar to the ones detected by FE-SSR.

The effect of water table levels and short-term ditch restoration on mountain peatland carbon cycling in the Cordillera Blanca, Peru

Many tropical mountain peatlands in the Andes are formed by cushion plants. These unique cushion plant peatlands are intensively utilized for grazing and are also influenced by climate change, both of which alter hydrologic conditions. Little is known about the natural hydroperiods and greenhouse gas fluxes of these peatlands or the consequences of hydrologic alteration for these fluxes. Therefore, our objectives were to assess how carbon dioxide (CO2) and methane (CH4) fluxes varied across a hydrological gradient caused by ditching and evaluate how short-term carbon cycling responds after rewetting from ditch blocking in a tropical mountain peatland. The study was carried out in Huascaran National Park, Peru using static chamber methods. Comparing reference to highly drained conditions, mid-day net ecosystem exchange (NEE) was higher (1.07 ± 0.06 vs. 0.76 ± 0.11 g CO2 m−2 h−1), and the light compensation point for CO2 uptake was lower. Gas fluxes were relatively stable in the rewetted and reference treatments, with small positive responses of NEE to rising water tables. CH4 emissions averaged 2.76 ± 1.06 mg CH4 m−2 day−1, with negative fluxes at water tables >10 cm below the soil surface, and positive fluxes at higher water levels. Our results indicate that undrained peatlands appear to be carbon sinks, highly drained peatlands were likely carbon sources, and rewetting of moderately drained peatlands increased NEE and the ability to store carbon to undrained reference conditions. Ditching of peatlands will likely increase their susceptibility to negative climate change impacts, and hydrologic restoration could moderate these impacts.

Iron-oxidizer hotspots formed by intermittent oxic–anoxic fluid mixing in fractured rocks

Subsurface environments host most of the fresh water on Earth as well as diverse microorganisms that may constitute a significant part of the biosphere. However, the dynamics and spatial distribution of subsurface microorganisms and their response to hydrological processes are poorly understood. Here we used chemical and metagenomic analyses of groundwater in a fractured rock aquifer in western France to determine the role of fractures in the formation of deep microbial hotspots in the subsurface. The majority of fractures, sampled in a 130-m-deep borehole, were anoxic, but a fracture carrying oxic groundwater was detected at 54-m depth, associated with a fivefold increase in the abundance of iron-oxidizing bacteria. We developed a mechanistic model of fluid flow and mixing in fractures and found that such microbial hotspots are sustained by the mixing of fluids with contrasting redox chemistries at intersections of fractures. The model predicts that metre-scale changes in near-surface water table levels cause intermittent oxygen delivery through deep fractures, which can extend the depth of the habitable zone for iron-oxidizing bacteria hundreds of metres into the subsurface. Given that fractures are ubiquitous at multiple scales in the subsurface, such deep microbial hotspots may substantially influence microbial communities and their effect on Earth’s biogeochemical cycles. Subsurface iron-oxidizing bacteria are sustained by intermittent oxygen delivery through rock fracture networks, according to biological and geochemical analyses of borehole fluids combined with a fluid mixing model.

Effect of Moisture on Full-Scale Pavement Distress

Abstract The effect of moisture is fundamental in determining pavement responses. It becomes more important in tropical regions where high precipitation rates and high variability in water table levels are present. The results indicate that when comparing the quantitative performance of pavement sections that are subjected to near saturation conditions, the bearing capacity of the pavement structure can be as low as 5 % of that associated to the same structure but with optimum water content. The damage in the saturated pavement sections is greatly accelerated because of pumping of fines from the subgrade and the subbase. All the pavement layers are affected by loading (decrease or increase in layer moduli) but to a different degree depending on the moisture conditions. Furthermore, the effect of moisture is greater in the cohesive soils and contaminated granular materials. Finally, the relatively stiffer layers (i.e., hot mix asphalt and cement-treated base layers) are the ones that are more susceptible to a higher deterioration rate, particularly under saturated or near saturated conditions.