Water Table Level Research Articles

Inhibition or Facilitation? Contrasted Inter-Specific Interactions in Sphagnum under Laboratory and Field Conditions.

In a natural environment, plants usually interact with their neighbors predominantly through resource competition, allelopathy, and facilitation. The occurrence of the positive effect of allelopathy between peat mosses (Sphagnum L.) is rare, but it has been observed in a field experiment. It is unclear whether the stability of the water table level in peat induces positive vs. negative effects of allelopathy and how that is related to phenolic allelochemical production in Sphagnum. Based on field experiment data, we established a laboratory experiment with three neighborhood treatments to measure inter-specific interactions between Sphagnum angustifolium (Russ.) C. Jens and Sphagnum magellanicum Brid. We found that the two species were strongly suppressed by the allelopathic effects of each other. S. magellanicum allelopathically facilitated S. angustifolium in the field but inhibited it in the laboratory, and relative allelopathy intensity appeared to be positively related to the content of released phenolics. We conclude that the interaction type and intensity between plants are dependent on environmental conditions. The concentration of phenolics alone may not explain the type and relative intensity of allelopathy. Carefully designed combined field and laboratory experiments are necessary to reveal the mechanism of species interactions in natural communities.

Distribution, sources, and decomposition of soil organic matter along a salinity gradient in estuarine wetlands characterized by C:N ratio, δ13 C-δ15 N, and lignin biomarker.

Despite increasing recognition of the critical role of coastal wetlands in mitigating climate change, sea-level rise, and salinity increase, soil organic carbon (SOC) sequestration mechanisms in estuarine wetlands remain poorly understood. Here, we present new results on the source, decomposition, and storage of SOC in estuarine wetlands with four vegetation types, including single Phragmites australis (P, habitat I), a mixture of P. australis and Suaeda salsa (P+S, habitat II), single S. salsa (S, habitat III), and tidal flat (TF, habitat IV) across a salinity gradient. Values of δ13 C increased with depth in aerobic soil layers (0-40cm) but slightly decreased in anaerobic soil layers (40-100cm). The δ15 N was significantly enriched in soil organic matter at all depths than in the living plant tissues, indicating a preferential decomposition of 14 N-enriched organic components. Thus, the kinetic isotope fractionation during microbial degradation and the preferential substrate utilization are the dominant mechanisms in regulating isotopic compositions in aerobic and anaerobic conditions, respectively. Stable isotopic (δ13 C and δ15 N), elemental (C and N), and lignin composition (inherited (Ad/Al)s and C/V) were not completely consistent in reflecting the differences in SOC decomposition or accumulation among four vegetation types, possibly due to differences in litter inputs, root distributions, substrate quality, water-table level, salinity, and microbial community composition/activity. Organic C contents and storage decreased from upstream to downstream, likely due to primarily changes in autochthonous sources (e.g., decreased onsite plant biomass input) and allochthonous materials (e.g., decreased fluvially transported upland river inputs, and increased tidally induced marine algae and phytoplankton). Our results revealed that multiple indicators are essential to unravel the degree of SOC decomposition and accumulation, and a combination of C:N ratios, δ13 C, δ15 N, and lignin biomarker provides a robust approach to decipher the decomposition and source of sedimentary organic matter along the river-estuary-ocean continuum.

Groundwater recharge and water table levels modelling using remotely sensed data and cloud-computing

Hydrological modeling is still a challenge for better management of water resources since most of the established models are based on point data. The advent, improvement and popularization of remote sensing has brought new perspectives to modelers, allowing access to reliable and representative data over vast areas. However, several tools are still under-explored and actually used in the water resources planning and decision-making process, especially groundwater, which is a hidden resource. The objective of this work was to contribute to groundwater dynamics comprehension assessing the suitability of using remote sensing data in the water-budget equation for estimating groundwater recharge (GWR) and its impact at water table depths (WTD) in a representative Guarani Aquifer System (GAS) outcrop area. The GAS is the largest transboundary groundwater reservoir in South America, yet recharge in the GAS outcrop zones is one of the least known hydrological variables. The remotely sensed WTD model was adapted from the Water Table Fluctuation (WTF) method. We used Google Earth Engine to extract time series of precipitation, evapotranspiration, and surface runoff from the Famine Early Warning Systems Network Land Data Assimilation System (FLDAS) dataset for the Angatuba Ecological Station (EEcA), Sao Paulo State, Brazil, over 2014–2017 period. GWR and WTD were modeled in eight groundwater monitoring wells. Bias analysis of precipitation data from FLDAS were perfomed using rain gauge data (2000–2018). Two GWR scenarios (S1 and S2) were assessed as well as the impact of the specific yield values ( $${S}_{\mathrm{y}}$$ ) in the model outputs. In C1 GWR ranged from 10.8% to 19.69% of rain gauge, although in C2 GWR ranged from 0.9 to 13%. The WTD model showed RMSE values ranging from 0.36 to 1.12 m, showing better results in the shallow wells than the deeper ones. These results are useful for future studies on assessing groundwater recharge in the GAS outcrop zones. This remotely sensed approach can be reproduced in regions where data are scarce or nonexistent.

Disproportionate Changes in the CH4 Emissions of Six Water Table Levels in an Alpine Peatland

The Zoige alpine peatlands are one of the highest and largest alpine peatlands in the world and play an important role in the global carbon cycle. Drainage is the main disturbance at Zoige, and the drawdown of the water table level changes CH4 emissions. There is still much uncertainty relating to how CH4 emissions respond to multiple water table levels. Here, we simulated six gradients (−30 cm, −20 cm, −10 cm, 0 cm, 10 cm, and 20 cm) of the water table level through a mesocosm manipulation experiment in the Zoige peatlands. The water table level had a significant effect on CH4 emissions. CH4 emissions did not change with water table levels from −30 cm to −10 cm, but significantly increased as the water table level increased above −10 cm. A significant log-linear relationship (R2 = 0.44, p < 0.001) was found between CH4 emissions and a water table level range from −10 to 20 cm. This study characterized the responses of CH4 emissions to multiple water table levels and provide additional data for accurately evaluating CH4 emissions. The results of this study also have several conservation implications for alpine peatlands.

Leafing intensity decreases with increasing water table depth and plant height in Populus euphratica, a desert riparian species

Leafing intensity, which refers to the number of leaves per unit shoot size, is a key architectural trait that is closely linked to plant hydraulics. However, it remains unclear how leafing intensity is regulated by deeper water tables and greater plant heights (i.e., with both necessitating longer hydraulic paths to foliage). As there are diminishing photosynthetic returns from incrementally increased hydraulic support costs with longer hydraulic paths, we predict that leafing intensity would decrease accordingly. To test the prediction, we examined the hydraulic constraints on leafing intensity in a desert riparian species, Populus euphratica. We sampled 1863 shoots from 96 trees with varying heights at contrasting water table depths along the Tarim River corridor in Northwest China. Results showed that midday shoot water potentials decreased with water table depth and plant height. P. euphratica trees had fewer leaves for a given shoot length with deeper water tables, while the increase in leaf number per unit increment of shoot length was constant across water table levels. Although the increase in leaf number per unit increment of shoot length was slightly higher in tall P. euphratica trees, they had fewer leaves at the onset of shoot elongation, and at the grand mean of shoot length across height classes. Overall, the lower leafing intensity with increasing water table depth and plant height highlights the role of hydraulic path length in regulating leaf-shoot allometry. These results also suggest the functional significance of leafing intensity in equilibrating photosynthetic gains with water supplies under varying hydraulic constraints, especially for plants inhabiting drylands.

Soil and water nutrients in stem‐only and whole‐tree harvest treatments in restored boreal peatlands

In boreal peatlands felling and tree harvest are commonly carried out as part of peatland restoration. Stem‐only harvest is the principal harvest method and it leaves the live crown material (felling residue) containing most tree nutrients at the site. Whole‐tree harvest, where felling residue is removed, is not favored due to higher transport costs, although it might better promote the recovery of nutrient‐poor peatlands towards pristine conditions. We investigated whether initial differences in N mineralization and decomposition rates observed between tree harvest methods continued out to 6 years after restoration and whether the spatial variation in water table (WT) level and water nutrient concentrations parallels with the observed pattern in mineralization and decomposition rates. The study was done at 15 peatland sites in Natura 2000 protection areas in Finland during 2007–2013. Concentration of ammonium in soil water was higher in the stem‐only harvest treatment compared to that of the whole‐tree harvest treatment, whereas the previously observed differences in net N mineralization and decomposition rates had leveled out by the sixth year after restoration. The spatial variation created by the ditch network still affected the hydrology and peatland functions so that the nutrient concentrations were higher near ditches than in other locations, implying potential risk for nutrient leaching. Based on this study, there is no reason to prefer either harvest method over the other in nutrient‐poor drained peatlands with low tree volumes, which constitute the majority of available peatland restoration area in Finland.

Groundwater management under heterogeneous land tenure arrangements

We develop a groundwater extraction model that considers the Marshallian inefficiency associated with sharecropping and use data from Pakistan to simulate the impact of an open access regime and of optimal management on groundwater extractions, the state of the aquifer, and annual net benefits through time. We also evaluate a price instrument as a mechanism of inducing optimal extractions. Under both open access and optimal management, we observe notable differences in groundwater extractions and the water table level between the tenure model (which considers the behavior of both owner cultivators and sharecroppers) and the baseline model (which includes the behavior of only owner cultivators). We also find a modest difference in the aggregate net benefits generated by the two models. The results offer new insights—vis-à-vis land tenure heterogeneity—into the evaluation of more effective policies for groundwater management and aquifer sustainability.

A combined geostatistical approach of data fusion and stochastic simulation for probabilistic assessment of shallow water table depth risk

In general, water table depth risks are estimated from monitoring networks that mostly provide scarce and irregular data. When jointly analysed, environmental, agricultural and geotechnical variables, treated as stochastic spatial variables, can better describe and interpret the states of a certain system subject to estimation uncertainty. Risk assessment consists essentially in calculating the frequency (probability) with which specified criteria are exceeded or fail to be met by creating multiple stochastic realizations. The aim of this paper is to propose a novel geostatistical methodology, based on the integration into one approach of multi-source data fusion and stochastic simulation, to estimate the risk of extreme (shallow) water table depth, and illustrate a demonstrative example of application of the approach to a case study in a Cerrado conservation area in Brazil. The risk of shallow water table depth was determined by using critical thresholds for water table level and a binary transformation into an indicator variable depending on whether the conditions expressed by the threshold values are met or not. Firstly, auxiliary variables were jointly, analysed to provide a delineation of the study area into homogeneous zones. Secondly, sequential indicator simulation provided a-posteriori probabilities taking into account spatial proximity. The final maps show the most probable risk category for the whole area and spatial entropy as a measure of local uncertainty. Areas nearby watershed divisors and in the north part of the region have a high risk of shallow groundwater. Informed decision-making supported by probabilistic maps and uncertainty evaluation is essential for the success of the projects of Cerrado restoration.

Selection Cuttings as a Tool to Control Water Table Level in Boreal Drained Peatland Forests

Continuous cover management on peatland forests has gained interest in recent years, in part because the tree biomass with significant evapotranspiration capacity retained in selection cuttings could be used as a tool to optimize the site water table level (WTL) from both tree growth and environmental perspectives. This study reports WTL responses from six field trials established on fertile Norway-spruce-dominated drained peatland forests across Finland. At each site, replicates of different intensity selection cuttings (removing 17–74% of stand basal area) or clear-cut in parallel with intact control stands were established and monitored for WTL for 2–5 post-harvest years. Observed WTL rose after selection cuttings and the response increased with harvest intensity and depended on the reference WTL, i.e. larger responses were found during dry summers or in more southern location. Selection cuttings removing about 50% of stand basal area raised WTL typically by 15–40%. Using a process-based ecohydrological model, tested against data from the field trials, we show that the role of tree stand in controlling WTL clearly decreases along the latitudinal climate gradient in Finland. This suggests that the potential of controlling WTL using selection cuttings is more prominent in southern compared to northern Finland. Predictions with future climate (2070–2099) further indicated a general decrease of WTL and that the importance of the tree stand in controlling WTL will increase especially in northern Finland. The results overall thus suggest that selection cuttings can be used as a tool to control WTL in boreal drained peatland forests, and the potential is likely to increase in future climate.

Spatial and temporal variability of soil N2 O and CH4 fluxes along a degradation gradient in a palm swamp peat forest in the Peruvian Amazon.

Mauritia flexuosa palm swamp, the prevailing Peruvian Amazon peatland ecosystem, is extensively threatened by degradation. The unsustainable practice of cutting whole palms for fruit extraction modifies forest's structure and composition and eventually alters peat‐derived greenhouse gas (GHG) emissions. We evaluated the spatiotemporal variability of soil N2O and CH4 fluxes and environmental controls along a palm swamp degradation gradient formed by one undegraded site (Intact), one moderately degraded site (mDeg) and one heavily degraded site (hDeg). Microscale variability differentiated hummocks supporting live or cut palms from surrounding hollows. Macroscale analysis considered structural changes in vegetation and soil microtopography as impacted by degradation. Variables were monitored monthly over 3 years to evaluate intra‐ and inter‐annual variability. Degradation induced microscale changes in N2O and CH4 emission trends and controls. Site‐scale average annual CH4 emissions were similar along the degradation gradient (225.6 ± 50.7, 160.5 ± 65.9 and 169.4 ± 20.7 kg C ha−1 year−1 at the Intact, mDeg and hDeg sites, respectively). Site‐scale average annual N2O emissions (kg N ha−1 year−1) were lower at the mDeg site (0.5 ± 0.1) than at the Intact (1.3 ± 0.6) and hDeg sites (1.1 ± 0.4), but the difference seemed linked to heterogeneous fluctuations in soil water‐filled pore space (WFPS) along the forest complex rather than to degradation. Monthly and annual emissions were mainly controlled by variations in WFPS, water table level (WT) and net nitrification for N2O; WT, air temperature and net nitrification for CH4. Site‐scale N2O emissions remained steady over years, whereas CH4 emissions rose exponentially with increased precipitation. While the minor impact of degradation on palm swamp peatland N2O and CH4 fluxes should be tested elsewhere, the evidenced large and variable CH4 emissions and significant N2O emissions call for improved modeling of GHG dynamics in tropical peatlands to test their response to climate changes.

Decision Support System Based on Genetic Algorithms to Optimize the Daily Management of Water Abstraction from Multiple Groundwater Supply Sources

The use of irrigation water extracted from aquifers with submerged pumps is essential to ensure agricultural production mainly in water-scarce regions.. However, the use of the water source requires of a considerable energy consumption by water user associations (WUAs) being key factor to consider due to their high share of total management, operation, and maintenance costs. In this work, a new tool (MOPWE, model to optimize water extraction) to optimize the water and energy use of wells in WUAs was developed. MOPWE was applied to a real WUA located in Castilla-La Mancha region (southeast of Spain). This WUA utilizes groundwater as water source that is extracted from several different wells of different characteristics (discharges, water table levels, efficiency, variable speed drives…).. Therefore, these kind of WUAs must decide not only which well to activate at a certain time but also at what frequency the variable-speed drive should run the pump. With the aim of aiding decision-making in groundwater abstraction, a new management model (MOPWE), which is based on multi-objective genetic algorithms and is implemented in MATLAB®. This model helps determine the optimal daily management of a WUA with multiple underground supply sources and focuses on the management of wells while considering the water reservoir level. After 18,000 generations of the genetic algorithm, the pareto front was obtained with the best WUA managements achieving a water and energy savings of 25% and 54%, respectively. At the end of the irrigation season, the optimal total energy consumption per unit of water applied was 38% lower than that achieved by the current management. Results showed that a more realistic approach can be implemented when several water supplies operate jointly under a collaborative principle.

Probability Assessment of Rainfall-Induced Landslides Based on Safety Factors Using Soil Moisture Estimation From SAR Images

Slope stability models developed based on the physical mechanism of landslides show the effectiveness in landslide probability assessment, while they have rarely been applied in the field of radar remote sensing. Inspired by the related work, this article proposes a new quantitative method for rainfall-induced landslide probability assessment based on safety factors (SFs) using soil moisture estimation from synthetic aperture radar (SAR) images. In order to combine slope stability models with SAR measurement, first, soil moisture that plays a vital role in slope stability models is estimated by SAR techniques from vegetated slope terrain. In this article, we propose a new SAR data processing model for potential landslide areas and a modified physical-based scattering model for short vegetation. The estimated results are qualitatively verified by the tropical rainfall measuring mission (TRMM) instrument and are quantitatively verified by the field investigation. Second, we study the water table level that plays another vital role in slope stability models and cannot be retrieved from SAR data. The analysis indicates that it can be treated as a constant in the case of unsaturated soil moisture. Combining with other geotechnical parameters that do not change with external circumstances, we simplify the slope stability model, of which effectiveness is tested by the visual interpretation. Finally, the SF maps are obtained by the simplified slope stability model using soil moisture estimated from the corresponding SAR images. The field investigation shows that all the observed landslides are located in the unstable areas, indirectly verifying the proposed method.

Modeling of Evaporation-Driven Multiple Salt Precipitation in Porous Media with a Real Field Application

Soil and groundwater salinization are very important environmental issues of global concern. They threaten mainly the arid and semiarid regions characterized by dry climate conditions and an increase of irrigation practices. Among these regions, the south of Tunisia is considered, on the one hand, to be a salt-affected zone facing a twofold problem: The scarcity of water resources and the degradation of their quality due to the overexploitation of the aquifers for irrigation needs. On the other hand, this Tunisian landform is the only adequate area for planting date palm trees which provide the country with the first and most important exportation product. In order to maintain the existence of these oases and develop the date production, a good understanding of the salinization problem threatening this region, and the ability to predict its distribution and evolution, should not be underestimated. The work presented in this paper deals with the Oasis of Segdoud in southern Tunisia, with the objective of modeling the evaporation-driven salt precipitation processes at the soil profile scale and under real climatic conditions. The model used is based on the one developed and presented in a previous work. In order to fulfil the real field conditions, a further extension of the geochemical system of the existing model was required. The precipitated salts considered in this work were halite (NaCl), gypsum (CaSO4) and thenardite (Na2SO4). The extended model reproduces very well the same tendencies of the physico-chemical processes of the natural system in terms of the spatio-temporal distribution and evolution of the evaporation and multiple-salt precipitation. It sheds new lights on the simulation of sequences of salt precipitation in arid regions. The simulation results provide an analysis of the influence of salt precipitation on hydrodynamic properties of the porous medium (porosity and permeability). Moreover, the sensitivity analysis done here reveals the influence of the water table level on the evaporation rate.

Plant functional type indirectly affects peatland carbon fluxes and their sensitivity to environmental change

AbstractThe sensitivity of peatland carbon (C) fluxes to changes in climate and hydrology are uncertain due to the complex interactions between plants and peat properties. In this study we examine how peat cores taken from under three plant functional types (PFT) (bryophyte, graminoid and ericoid) differ in their biotic and abiotic properties and how this indirectly modulates the response of C fluxes to environmental change. Peat cores taken from under three PFTs had their aboveground vegetation removed to exclude direct plant‐mediated effects, and were incubated in a temperature × water table factorial experiment at 12, 14 and 16°C (air temperature) with the water table level −25, −15 or −5 cm below the peat surface. Carbon dioxide (CO2) and methane (CH4) fluxes were measured over 11 months. Emissions of CO2 and CH4 increased with temperature, with strong positive (CH4) and negative (CO2) interactions with increasing water table level. There were significant effects of removed PFT on the environmental sensitivity of CH4, but not CO2 fluxes. CH4 emissions were greatest in peat with graminoid PFT removed at the warmest temperature but these indirect effects were not explained by peat abiotic or biotic properties, which did not differ between PFTs. These results show that climate change‐induced expansion of graminoids in northern peatlands will have direct and indirect effects on C fluxes and the stability of peatland C stores. These responses will be determined by the interactive effects of vegetation composition, hydrology and warming on methane‐cycling microbial communities.Highlights Peatland carbon flux strength under a changing climate is influenced by PFT. Peat from under graminoid PFT emits more methane than peat from under bryophyte or ericoid PFT. Prior PFT cover influenced methane emissions, but did not affect peat abiotic or biotic properties. Increases in graminoid cover with climate change could indirectly increase peatland methane fluxes.

Vegetation controls of water and energy balance of a drained peatland forest: Responses to alternative harvesting practices

We quantified the response of peatland water table level (WTL) and energy fluxes to harvesting of a drained peatland forest. Two alternative harvests (clear-cut and partial harvest) were carried out in a mixed-species ditch-drained peatland forest in southern Finland, where water and energy balance components were monitored for six pre-treatment and three post-treatment growing seasons. To explore the responses caused by harvestings, we applied a mechanistic multi-layer soil-plant-atmosphere transfer model. At the clear-cut site, the mean growing season WTL rose by 0.18 ± 0.02 m (error estimate based on measurement uncertainty), while net radiation, and sensible and latent heat fluxes decreased after harvest. On the contrary, we observed only minor changes in energy fluxes and mean WTL (0.05 ± 0.03 m increase) at the partial harvest site, although as much as 70% of the stand basal area was removed and leaf-area index was reduced to half. The small changes were mainly explained by increased water use of spruce undergrowth and field layer vegetation, as well as increased forest floor evaporation. The rapid establishment of field layer vegetation had a significant role in energy balance recovery at the clear-cut site. At partial harvest, chlorophyll fluorescence measurements and model-data comparison suggested the shade-adapted spruce undergrowth was suffering from light stress during the first post-harvest growing season. We conclude that in addition to stand basal area, species composition and stand structure need to be considered when controlling WTL in peatland forests with partial harvesting. Our results have important implications on the operational use of continuous cover forestry on drained peatlands. A continuously maintained tree cover with significant evapotranspiration capacity could enable optimizing WTL from both tree growth and environmental perspectives.

Intelligent approach to predict future groundwater level based on artificial neural networks (ANN)

To depict hydrogeological variables and understand the physical processes taking place in a complex hydrogeological system, artificial neural networks (ANNs) are widely used as a good alternative approach to tedious numerical models. The aim of this study was to predict the dynamic fluctuations in piezometric levels in Nebhana aquifers (NE Tunisia) using ANNs. A correlation analysis carried out between piezometry, evapotranspiration and rainfall during the period 2000 to 2018 revealed that piezometric levels were influenced by monthly rainfall, evapotranspiration and initial water table level. These informative variables were used as input variables to train the ANN to predict future monthly water table levels for four hydrogeological systems. The minimal and maximal computed relative errors were 0.01 and 19.00%, respectively; root mean square error (RMSE) varied between 0.41 and 2.06; the determination coefficient (R2) ranged between 0.93 and 0.99; and the Nash–Sutcliffe (NASH) efficiency coefficient ranged from 85.32 to 97.82%. To test the generalization capacity of the developed ANN models, we used the ANNs to predict monthly piezometric levels for the period September 2016 to August 2018. The results were satisfactory for all piezometers. Indeed, the minimal and maximal computed RE were − 12.00 and 0.03%, respectively; RMSE was between 0.44 and 1.74; R2 varied between 0.95 and 0.98; the NASH coefficient ranged from 60.00 to 98.99%. These models developed in this study can be adopted for future groundwater level prediction to accurately estimate trends in piezometric levels as well as water pumping costs.

Impact of control structures on hydrologic restoration within the Great Dismal Swamp

The Great Dismal Swamp (GDS) is a 45,000-ha state and federally protected Coastal Plain peatland located on the border of North Carolina and Virginia that contains stands of Bald cypress and the globally threatened Atlantic white cedar. Centuries of drainage and logging have substantially altered the hydrology of the GDS, negatively affecting its ecosystem structure and function. To restore a seasonally flooded, saturated hydrologic regime to portions of the swamp, adjustable water control structures (WCS) were installed at strategic locations within existing drainage ditches. The objective of this study was to determine if the installation of the WCSs significantly altered the hydropatterns of two target restoration areas, resulting in hydrologic conditions comparable to nearby reference sites with desired forest communities. The water table (WT) was monitored for three years prior to WCS installation (pre-WCS) and three years after WCS installation (post-WCS). Comparison of WT data from the pre and post-WCS periods, using jurisdictional wetland criteria and empirical cumulative distribution functions (ECDFs), indicated increased saturated conditions within the target restoration areas following installation of the WCS. Paired Before-After Control-Impact (BACIP) statistical analysis revealed the WCS installation had a significant positive impact on WT levels in the target restoration areas relative to the reference sites. Hydrologic restoration will aid the effort to restore target forest communities within the swamp, reduce fire susceptibility, prevent peat oxidation, maintain carbon storage, and reduce non-target vegetation competition.

Growth characteristics of three Sphagnum species in restored extracted peatland

Peatlands are essential ecosystems in global carbon cycle. However, they have been drained for economic benefits for centuries; large peatland areas have turned from carbon storage ecosystems to the carbon emitters. Because of the slow spontaneous revegetation of abandoned extracted peatlands, there is urgent need for their active restoration, required also for mitigation of global climate change effects. The selection of Sphagnum species suitable for restoration may also have crucial effects to reach the restoration aims. In 2012, we began a restoration experiment in abandoned extracted peatland in central Estonia. We aimed to elucidate whether Sphagnum species, specific to natural North European bogs, have different growth characteristics under altered growth conditions in restored extracted peatland. We studied growth characteristics of S. fuscum, S. medium, and S. rubellum at restoration sites with two different water table levels and in two natural bogs. We estimated total cover of Sphagnum carpet and cover of three target species and measured shoot growth characteristics at each site. Linear models with correlated errors were used for temporal trends studies. Our results showed that studied Sphagnum species have different growth characteristics in restoration sites and that the main growth promoter is the water table depth (WTD). Results showed that greater Sphagnum cover (over 70%) can be achieved in wetter conditions with WTD higher than circa 20 cm. On wetter restoration sites S. medium and S. fuscum could be recommended for restoration, whereas S. fuscum perform well also in drier sites.

Impact of water table fluctuations on the seasonal effectiveness of the pump-and-treat remediation in wet–dry tropical regions

The pump-and-treat (P&T) method is a common remediation approach that is used to mitigate occurrences of hydrocarbon contamination. In a well-studied site that had been contaminated by a large volume of jet fuel, continuous monitoring of the water table and floating phase thickness revealed the most significant process governing the effectiveness of the site’s active remediation system. The floating phase thickness recorded in the wells monitored varied greatly (> 0.50 m) and was negatively correlated with the water table level. Although the dependence of light non-aqueous phase liquid (LNAPL) thickness on water table fluctuations is widely recognized, LNAPL recovery, which is governed by alternating cycles of LNAPL release and entrapment in pore spaces, has been poorly described. Thus, we present a specific case in which LNAPL recovery is expected only episodically, when the water table falls sufficiently. In the period spanning from 2006 to 2008, LNAPL remediation recovered nearly 180 m3 of oil. In later years, the volume of recovered LNAPL declined and ceased between 2010 and 2014, when the water table rose. Importantly, our research demonstrates that the P&T remediation approach is solely effective during a period of 4 months in dry years. Thus, cleanup methods and contaminated site management strategies should be reconsidered.

Biochar impacts on nutrient dynamics in a subtropical grassland soil: 1. Nitrogen and phosphorus leaching.

Despite the numerous benefits of biosolids, concerns over nutrient losses restrict the extent to which biosolids can be beneficially reused. We evaluated the effectiveness ofbiochar in controlling the lability of nutrients in agriculturalland. This study was designed to investigate the potential impacts of co-applying biochar with biosolids or inorganic fertilizer on N and P leaching losses. A companion paper focuses on greenhouse gas responses. Nutrients were surface applied as biosolids (aerobically digested Class B) and inorganic fertilizer (ammonium nitrate and triple superphosphate) to an established perennial pasture at equivalent annual rates typical of field practices. Biochar was applied at an annual rate of 20 Mg ha-1 . Leachate N and P were monitored using passive-capillary drainage lysimeters. Results demonstrated significant temporal variability in leachate N and P, with larger pulses generally occurring during periods of high water table levels or after intensive rainfall. Inorganic fertilizer generally resulted in greater leachate N and P losses than biosolids. No differences in leachate N and P losses between biosolids and control were observed. Approximately 1% of applied N was lost via leaching from biosolids treatments vs. 16% for inorganic fertilizer. Regardless of the P source, negligible (0.1-0.2% of applied P), cumulative P leaching occurred during the 3-yr study. Biochar had no effect on P leaching but reduced N leaching from treatments receiving inorganic fertilizer by 60%. Prudent nutrient management is possible even on biosolids-amended Spodosols with high water tables.