Variations In Water Table Depth Research Articles

Evaluating the contribution of geophysics to the assessment of natural hazards

This paper discussed the role of geophysics in the evaluation of natural hazards with the view to enhancing familiarity with earth shakes, ground characteristics, landslide likelihood, and volcanic deliveries. Semantic and geophysical data were collected from seismic surveys, measurement of groundwater, electrical resistivity of the subsoil and gas emission. Seismic data analysis revealed diverse activity across sites, with magnitudes ranging from 3.234 to 6.456 Mw, emphasizing the importance of geophysical monitoring in identifying high-risk areas. Groundwater measurements indicated spatial variations in water table depth from 1.234 to 6.789 m, essential for effective resource management. Soil resistivity values ranged from 75.123 to 145.901 Ohm-m, providing insights into soil properties relevant for geotechnical and environmental studies. Landslide susceptibility assessment used the factor of slope angle, vegetation cover, and rainfall intensity; these were 10. 901° to 28. 345°, 55. 234% to 88. 456%, and 6. 789 to 20. 901 mm/hr respectively. The gas emission of SO2 ranged between 0. 123–0. 901 kg/s, that of CO2, 0. 456–1. 234 kg/s, while H2S ranged between 0. 789–1. 567 kg/s based on the emission of the several sites suitable for eruption prediction models. A statistical approach was used in which Histogram, scatter plot and radar chart were used to explain the data collected. The study conclude that the application of various geophysical methods is strikingly useful in natural hazard and risk assessment and planning and therefore beneficial in reducing disaster risks. These results provide compelling evidence about the importance of geophysics in propagating awareness in the Earth processes and improvement of hazards.

Fine-grained water availability drives divergent trait selection in Amazonian trees

Water availability is an important driver of plant functional biogeography. Most studies focus on the effects of precipitation, and neglect the contribution of groundwater as a source when the water table depth (WTD) is accessible to roots. Previous studies suggested that shallow water tables select for acquisitive traits. These studies have mostly contrasted shallow vs. deep water tables, without considering a more fine-grained perspective within shallow water tables or the temporal WTD behavior. Here we tested whether the degree of variation in WTD translates into divergent modes of trait selection. We expect constantly shallow WTD leading to the selection of acquisitive traits, whilst high fluctuation of WTD would lead to tree communities with more conservative traits. We used community and trait data (wood density and leaf traits) from 25 1-ha forest monitoring plots spread over 600 km in central Amazonia, covering a gradient of shallow to intermediate (0–8 m deep) WTD along the Purus-Madeira interfluve. Wood density was measured directly in trunk cores (498 trees) and leaf traits (Specific Leaf Area, Leaf Dry Mass Content, Leaf Thickness) of >6,000 individuals were estimated with FT-NIR (Fourier-Transformed Near-Infrared Spectroscopy) spectral models calibrated with cross-Amazonian data. We observed a turnover of families, genera, and species along the gradient of temporal WTD fluctuation range. This taxonomic turnover was accompanied by a change in wood traits, with higher wood density associated to higher WTD fluctuation and higher climatic water deficit. Leaf traits, however, varied in the opposite direction than initially hypothesized, i.e., trees had more acquisitive traits toward intermediate WTD with higher fluctuation. Based on those results, we propose that the effect of WTD selection should be conceptualized in a quadratic form, going from water excess in very shallow WTD (<2 m, limiting condition due to anoxia, selecting conservative traits), to moist in intermediate WTD (between 2 and 5 m deep, favorable condition with constant water supply, selecting acquisitive traits), to water deficit in deep WTD (>5 m, limiting condition, with conservative traits again).

Impoundment increases methane emissions in Phragmites-invaded coastal wetlands.

Saline tidal wetlands are important sites of carbon sequestration and produce negligible methane (CH4 ) emissions due to regular inundation with sulfate-rich seawater. Yet, widespread management of coastal hydrology has restricted tidal exchange in vast areas of coastal wetlands. These ecosystems often undergo impoundment and freshening, which in turn cause vegetation shifts like invasion by Phragmites, that affect ecosystem carbon balance. Understanding controls and scaling of carbon exchange in these understudied ecosystems is critical for informing climate consequences of blue carbon restoration and/or management interventions. Here, we (1) examine how carbon fluxes vary across a salinity gradient (4-25 psu) in impounded and natural, tidally unrestricted Phragmites wetlands using static chambers and (2) probe drivers of carbon fluxes within an impounded coastal wetland using eddy covariance at the Herring River in Wellfleet, MA, United States. Freshening across the salinity gradient led to a 50-fold increase in CH4 emissions, but effects on carbon dioxide (CO2 ) were less pronounced with uptake generally enhanced in the fresher, impounded sites. The impounded wetland experienced little variation in water-table depth or salinity during the growing season and was a strong CO2 sink of -352 g CO2 -C m-2 year-1 offset by CH4 emission of 11.4g CH4 -C m-2 year-1 . Growing season CH4 flux was driven primarily by temperature. Methane flux exhibited a diurnal cycle with a night-time minimum that was not reflected in opaque chamber measurements. Therefore, we suggest accounting for the diurnal cycle of CH4 in Phragmites, for example by applying a scaling factor developed here of ~0.6 to mid-day chamber measurements. Taken together, these results suggest that although freshened, impounded wetlands can be strong carbon sinks, enhanced CH4 emission with freshening reduces net radiative balance. Restoration of tidal flow to impounded ecosystems could limit CH4 production and enhance their climate regulating benefits.

VARIATION IN BEARING CAPACITY OF SOIL DUE TO CHANGES IN WATER TABLE DEPTH IN DHAKA, BANGLADESH

The bearing capacity of the soil is a significant topic in geotechnical engineering, especially in foundation engineering, as the stability of any foundation depends on it. A structure with a very sound design may collapse standing on poor soil with low bearing capacity. As the depth of the water table increases, the ultimate bearing capacity of soil increases. The effect of an increase in depth on safe bearing capacity is predominant due to an increase in surcharge weight. The higher the water table, the lesser is as far as possible and strength of the soil. In this research, soil test reports of different locations of Dhaka city were collected, and the bearing capacity of the soil was calculated by Terzaghi's method based on a fixed foundation depth with a variation of water table depth. Bearing capacity was compared with the depth of the water table in graphical format and it was seen that bearing capacity of soil increases with the increase of water table depth.

Identifying dominant environmental predictors of freshwater wetland methane fluxes across diurnal to seasonal time scales.

While wetlands are the largest natural source of methane (CH4 ) to the atmosphere, they represent a large source of uncertainty in the global CH4 budget due to the complex biogeochemical controls on CH4 dynamics. Here we present, to our knowledge, the first multi-site synthesis of how predictors of CH4 fluxes (FCH4) in freshwater wetlands vary across wetland types at diel, multiday (synoptic), and seasonal time scales. We used several statistical approaches (correlation analysis, generalized additive modeling, mutual information, and random forests) in a wavelet-based multi-resolution framework to assess the importance of environmental predictors, nonlinearities and lags on FCH4 across 23 eddy covariance sites. Seasonally, soil and air temperature were dominant predictors of FCH4 at sites with smaller seasonal variation in water table depth (WTD). In contrast, WTD was the dominant predictor for wetlands with smaller variations in temperature (e.g., seasonal tropical/subtropical wetlands). Changes in seasonal FCH4 lagged fluctuations in WTD by ~17±11days, and lagged air and soil temperature by median values of 8±16 and 5±15days, respectively. Temperature and WTD were also dominant predictors at the multiday scale. Atmospheric pressure (PA) was another important multiday scale predictor for peat-dominated sites, with drops in PA coinciding with synchronous releases of CH4 . At the diel scale, synchronous relationships with latent heat flux and vapor pressure deficit suggest that physical processes controlling evaporation and boundary layer mixing exert similar controls on CH4 volatilization, and suggest the influence of pressurized ventilation in aerenchymatous vegetation. In addition, 1- to 4-h lagged relationships with ecosystem photosynthesis indicate recent carbon substrates, such as root exudates, may also control FCH4. By addressing issues of scale, asynchrony, and nonlinearity, this work improves understanding of the predictors and timing of wetland FCH4 that can inform future studies and models, and help constrain wetland CH4 emissions.

A Novel Low-Cost, High-Resolution Camera System for Measuring Peat Subsidence and Water Table Dynamics

Peatlands are highly dynamic systems, able to accumulate carbon over millennia under natural conditions, but susceptible to rapid subsidence and carbon loss when drained. Short-term, seasonal and long-term peat surface elevation changes are closely linked to key peatland attributes such as water table depth (WTD) and carbon balance, and may be measured remotely using satellite radar and LiDAR methods. However, field measurements of peat elevation change are spatially and temporally sparse, reliant on low-resolution manual subsidence pole measurements, or expensive sensor systems. Here we describe a novel, simple and low-cost image-based method for measuring peat surface motion and WTD using commercially available time-lapse cameras and image processing methods. Based on almost two years’ deployment of peat cameras across contrasting forested, burned, agricultural and oil palm plantation sites in Central Kalimantan, Indonesia, we show that the method can capture extremely high resolution (sub-mm) and high-frequency (sub-daily) changes in peat surface elevation over extended periods and under challenging environmental conditions. WTD measurements were of similar quality to commercially available pressure transducers. Results reveal dynamic peat elevation response to individual rain events, consistent with variations in WTD. Over the course of the relatively severe 2019 dry season, cameras in deep-drained peatlands recorded maximum peat shrinkage of over 8 cm, followed by partial rebound, leading to net annual subsidence of up to 5 cm. Sites with higher water tables, and where borehole irrigation was used to maintain soil moisture, had lower subsidence, suggesting potential to reduce subsidence through altered land-management. Given the established link between subsidence and CO2 emissions, these results have direct implications for the management of peatlands to reduce high current greenhouse gas (GHG) emissions. Camera-based sensors provide a simple, low-cost alternative to commercial elevation, WTD and GHG flux monitoring systems, suitable for deployment at scale, and in areas where existing approaches are impractical or unaffordable. If ground-based observations of peat motion can be linked to measured GHG fluxes and with satellite-based monitoring tools, this approach offers the potential for a large-scale peatland monitoring tool, suitable for identifying areas of active carbon loss, targeting climate change mitigation interventions, and evaluating intervention outcomes.

Partial Harvest in Paludified Black Spruce Stand: Short-Term Effects on Water Table and Variation in Stem Diameter

The boreal forest is considered to be a low productivity forest due to its cold climate and poorly drained soils promoting paludification. These factors create conditions favouring accumulation of undecomposed organic matter, which causes declining growth rates of forest stands, ultimately converting mature stands into peatlands. Under these conditions, careful logging is conducted during winter, which minimizes soil disturbance in northwestern Quebec boreal forest. This results in water table rise, increased light availability and paludification. Our main objective was to evaluate the short-term effect of partial harvesting as an alternative method to careful logging in winter to mitigate water table rise on black spruce (Picea mariana [Mill.] B.S.P.) stands. We quantified tree stem diameter variation and daily variation in water table depth in mature spruce stands before and after partial harvest (basal area reduction of 40%) and girdling (same basal area reduction with delayed mortality) during 2016 and 2017 growing seasons. Water table variation prior to and following silvicultural treatments did not differ one year after treatment. Daily stem diameter variation in black spruce did not differ between treatments and control. Furthermore, temperature exerted a positive effect on variation in water table and on stem diameter. These results suggest that partial harvest could be more effective than clearcutting to mitigate negative effects of a high water table while limiting paludification.

A Comparison of Three Trapezoid Models Using Optical and Thermal Satellite Imagery for Water Table Depth Monitoring in Estonian Bogs

This study explored the potential of optical and thermal satellite imagery to monitor temporal and spatial changes in the position of the water table depth (WTD) in the peat layer of northern bogs. We evaluated three different trapezoid models that are proposed in the literature for soil moisture monitoring in regions with mineral soils. Due to the tight capillary connection between water table and surface soil moisture, we hypothesized that the soil moisture indices retrieved from these models would be correlated with WTD measured in situ. Two trapezoid models were based on optical and thermal imagery, also known as Thermal-Optical TRApezoid Models (TOTRAM), and one was based on optical imagery alone, also known as the OPtical TRApezoid Model (OPTRAM). The models were applied to Landsat imagery from 2008 to 2019 and the derived soil moisture indices were compared with in-situ WTD from eight locations in two Estonian bogs. Our results show that only the OPTRAM index was significantly (p-value < 0.05) correlated in time with WTD (average Pearson correlation coefficient of 0.41 and 0.37, for original and anomaly time series, respectively), while the two tested TOTRAM indices were not. The highest temporal correlation coefficients (up to 0.8) were observed for OPTRAM over treeless parts of the bogs. An assessment of the spatial correlation between soil moisture indices and WTD indicated that all three models did not capture the spatial variation in water table depth. Instead, the spatial patterns of the indices were primarily attributable to vegetation patterns.

A numerical examination of the effect of sulfide dissolution on silicate weathering

Silicate weathering regulates climate on geological time scales as a net, climate-sensitive sink of atmospheric CO2. On the other hand, sulfuric acid produced through sulfide dissolution affects silicate weathering, diminishing its effectiveness as a climate regulator based on evidence from river chemistry. This study takes a theoretical approach to quantitatively examine the effect of sulfide dissolution, coupling a one-dimensional model of pyrite weathering to that of albite transformation to kaolinite. The coupled model reveals that when the reaction front of sulfide is deeper than that of silicates reacting with CO2, the silicate-weathering feedback on climate is not directly affected by sulfide dissolution, but only indirectly through oceanic processes such as reverse weathering and carbonate deposition. In turn, when sulfide dissolution occurs within zones of CO2-silicate reactions close to the surface, the feedback between climate and silicate weathering can be significantly weakened because sulfuric acid competes effectively with carbonic acid in mineral dissolution. As the depth of the sulfide reaction front can be changed by variations in water table depth, the latter feedback weakening could have occurred in concert with climate-change-driven water table fluctuations, amplifying atmospheric CO2 variations during the Phanerozoic.

Estimation of water table depth using DUALEM-2 system

Most of the agricultural fields are generally irrigated or drained uniformly without considering the spatial and temporal variation in water table depth (WTD). Investigating WTD is important for scheduling irrigation, drainage system designs and water balance models. The objective of this study was to develop a software interface to estimate the variations in WTD via electromagnetic induction (EMI) methods using frequencies of a DUALEM-2 system. Two fields (Field 1: 45.38°N, 63.23°W and Field 2: 45.37°N, 63.25°W) were selected and thirty perforated observation wells were installed to calibrate the DUALEM-2 for predicting WTD. Boundaries of the selected sites and location of the wells were marked using a real time kinematics global positioning system (RTK-GPS). The user interface program was developed in Delphi 5.0 software and imported in a laptop computer to retrieve data from the DUALEM-2 system. The horizontal co-planar (HCP) geometry, perpendicular co-planar (PRP) geometry and WTD were recorded simultaneously from each well before and after every significant rainfall for three consecutive days. Comprehensive surveys were conducted to measure apparent ground conductivity (ECa) with DUALEM-2 and corresponding locations of the sampling points using Trimble Ag GPS 332. The regression model showed significant correlation between the HCP and WTD with co-efficient of determination (R2 = 0.71) for field 1 and (R2 = 0.53) for field 2. Maps were generated in ArcGIS 10 software to examine the accuracy of predicted WTD in comparison with actual values. Results indicated that the DUALEM-2 system was efficient in mapping variation rapidly and reliably in WTD in a non-destructive fashion rather than following conventional way of repeated well drilling for WTD determination. This information could be used for measuring the depletion of WTD during dry periods (droughts), site-specific irrigation and drainage design with the aided advantage of labor and time savings in case of observing precision water management practices at large fields.

Season-induced variation in water table depth and selected chemical parameters of groundwater in Lagos Coastal Plain Sand Aquifer, Nigeria

In-situ measurement of depth to aquifer and water table was undertaken in 45 protected dug wells over two seasons. Samples were also analyzed for pH, EC, TDS, Ca, Cl, K, HCO 3 , CO 3 , SO 4 , Mg, K, and Na using universally accepted laboratory techniques. The study was aimed at examining seasonal variations in the chemistry of groundwater in the Lagos Coastal Plain Sand aquifer and its potability using the WHO standards. The study area covered parts of the Lagos Metropolis and the entire settlements of Ikorodu, Epe, and Badagry. The sample locations were mapped with ArcMap 9.3 software while the data were analyzed using descriptive statistics, paired sample T-test, correlation and multivariate statistical techniques using SPSS software 17.0 version. The result shows that about 60% of the samples had pH below the WHO minimum standard of 6.5 in both the dry and wet seasons. Mean EC and TDS levels were excessively high at Igando in both seasons. Some major ions, calcium, magnesium, potassium and sodium, and chloride exceeded the WHO limit at Oko-Oba, Ilogbo, Shomolu and Shogunle in the dry season. They were also excessively high in the wet season at Igando, Oko-Oba, Odo-Onosa, Ilogbo, Shomolu, and Shogunle. Correlation analysis shows that a significant relationship exists between the parameters at p<0.05 with the exception of Mg 2+ and K + in both seasons. The result of the paired sample T-test also shows significant variations among pH, Ca 2+ , HCO 3 - and Mg 2+ with higher mean values in the dry than the wet season except for pH. Factor analysis identified salinity and anthropogenic activities as the two major sources of pollution. These account for about 74.48% and 84.21% of the total variances in dry and wet seasons, respectively. Consequently, protection of the recharge areas of the aquifer from environmental pollution and formulation and enforcement of appropriate policies that will stem the rate of indiscriminate groundwater exploitation and prevention of saline water intrusion in the coastal settlements are recommended. Keywords: Aquifer; Coastal Plain Sand; Groundwater; Lagos; Seasonal variations, Water quality parameters

Spatiotemporal Dynamics of Water Table Depth Associated with Changing Agricultural Land Use in an Arid Zone Oasis

Investigating spatiotemporal dynamics and varying relationships between water table depth (WTD) and land use changes is critical for efficient groundwater management and land use planning in arid zones. The primary objective of the present study is to combine satellite and field measured data to quantitatively analyze variations in WTD and its relationship with land use change in the Ogan–Kucha River Oasis in the northwest arid zones of China, and reveal the spatial heterogeneity and variations in the abovementioned relationship at spatiotemporal scales. The spatiotemporal variations in WTD and land use change at different time intervals (1997–2007, 2007–2017, and 1997–2017) were analyzed based on geostatistical analysis methods and grid cell approaches. The relationships between land use types and changes in WTD were assessed using correlation and ordinary least square analyses. The relationships between spatiotemporal variations in WTD and land use change were explored using local level geographically weighted regression. The results indicated that influences of human activity on the variation of WTD have gradually increased, and that WTD has declined rapidly in most parts of the study area. The spatial distribution of WTD exhibited significant spatiotemporal heterogeneity, and WTD was lower in the inner parts of the oasis and shallower in the oasis-desert ecotone. The WTD decline rates in the irrigation area were much higher than those in the oasis-desert ecotone. The cultivated land area has expanded markedly, whereas the shrub covered area has shrunk rapidly. Changes in WTD were positively correlated with changes in cultivated land area, and the expansion center of cultivated land has gradually moved from upstream of the alluvial fan to downstream of the alluvial fan and to the oasis-desert ecotone. The relationships between changes in cultivated land and WTD in the ecotone were more prominent than those in the inner parts of the oasis. Therefore, agricultural land expansion and planning in the study area should be integrated based on spatiotemporal changes in the groundwater depth to maintain the stability of groundwater systems and sustainable groundwater exploitation.

Application of an improved global-scale groundwater model for water table estimation across New Zealand

Abstract. Many studies underline the importance of groundwater assessment at the larger, i.e. global, scale. The groundwater models used for these assessments are dedicated to the global scale and therefore not often applied for studies in smaller areas, e.g. catchments, because of their simplifying assumptions. In New Zealand, advanced numerical groundwater flow models have been applied in several catchments. However, that application is piecemeal: only for a limited amount of aquifers and through a variety of groundwater model suites, formats, and developers. Additionally, there are large areas where groundwater models and data are sparse. Hence, an inter-catchment, inter-regional, or nationwide overview of important groundwater information, such as the water table, does not exist. The investment needed to adequately cover New Zealand with high-resolution groundwater models in a consistent approach would be significant and is therefore not considered possible at this stage. This study proposes a solution that obtains a nationwide overview of groundwater that bridges the gap between the (too-)expensive advanced local models and the (too-)simple global-scale models. We apply an existing, global-scale, groundwater flow model and improve it by feeding in national input data of New Zealand terrain, geology, and recharge, and by slight adjustment of model parametrisation and model testing. The resulting nationwide maps of hydraulic head and water table depths show that the model points out the main alluvial aquifers with fine spatial detail (200 m grid resolution). The national input data and finer spatial detail result in better and more realistic variations of water table depth than the original, global-scale, model outputs. In two regional case studies in New Zealand, the hydraulic head shows excellent correlation with the available groundwater level data. Sensitivity and other analyses of our nationwide water tables show that the model is mostly driven by recharge, model resolution, and elevation (gravity), and impeded by the geology (permeability). The use of this first dedicated New Zealand-wide model can aid in provision of water table estimates in data-sparse regions. The national model can also be used to solve inconsistency of models in areas of trans-boundary aquifers, i.e. aquifers that cover more than one region in New Zealand. Comparison of the models, i.e. the national application (National Water Table model: NWT) with the global model (Equilibrium Water Table model: EWT), shows that most improvement is achieved by feeding in better and higher-resolution input data. The NWT model still has a bias towards shallow water tables (but less than the EWT model because of the finer model resolution), which could only be solved by feeding in a very high resolution terrain model that incorporates drainage features. Although this is a model shortcoming, it can also be viewed as a valuable indicator of the pre-human water table, i.e. before 90 % of wetlands were drained for agriculture since European settlement in New Zealand. Calibration to ground-observed water level improves model results but can of course only work where there are such data available. Future research should therefore focus on both model improvements and more data-driven, improved estimation of hydraulic conductivity, recharge, and the digital elevation model. We further surmise that the findings of this study, i.e. successful application of a global-scale model at smaller scales, will lead to subsequent improvement of the global-scale model equations.

Access roads impact enzyme activities in boreal forested peatlands

We investigated the impacts of resource access roads on soil enzyme activities in contrasting forested boreal peatlands (bog and fen). In August 2016, a total of 72 peat samples were collected from twelve 20 m long transects perpendicular to access roads, with a further six samples collected from undisturbed reference areas. Sampling locations represent a range in three variables associated with roads: 1) side of the road (upstream/downstream), 2) distance to a culvert (longitudinal; <2 and >20 m), and 3) distance from the road (lateral; 2, 6, and 20 m). Phenol oxidase and hydrolase (glucosidase, sulfatase, xylosidase, glucosaminidase, and phosphatase) enzyme activities were determined for each sample, in addition to water table depth, phenolic concentration, pH, and peat temperature. The average hydrolase activities in the fen were ~four times higher than in the bog. At the bog, the water table depth, phenolic concentration, pH and the activities of phenol oxidase, sulfatase, glucosidase, xylosidase and glucosaminidase were all significantly influenced by one or more road associated factors. The highest enzyme activities in the bog occurred on the downstream side of the road at plots located far from the culvert. In contrast, the flow of water in the fen was not perpendicular to the road. Consequently, no significant variations in water table depth, phenolic concentration, pH or enzyme activity were found with respect to road associated factors. Results indicate that road crossings in boreal peatlands can indirectly alter enzyme activities, likely as part of a causal chain following changes to hydrology and redox conditions. Two of six investigated enzymes had significantly higher activities in the road disturbed areas compared to undisturbed areas, suggesting ultimately that roads may enhance organic matter decomposition rates. However, adequate hydrologic connections through culverts and road construction parallel to the water flow can minimize the road-induced impacts.

Linking soil respiration and water table depth in tropical peatlands with remotely sensed changes in water storage from the gravity recovery and climate experiment

Carbon dioxide (CO2) emissions from Southeast Asia peatlands are contributing substantially to global anthropogenic emissions to the atmosphere. Peatland emissions associated with land-use change, and fires are closely related to changes in the water table level. Remote sensing is a powerful tool that is potentially useful for estimating peat CO2 emissions over large spatial and temporal scales. We related ground measurements of total soil respiration and water table depth collected over 19 months in an Indonesian peatland to remotely sensed gravity recovery and climate experiment (GRACE) terrestrial water storage anomoly (TWSA) data. GRACE TWSA can be used to predict changes in water storage on land. We combined ground observations from undrained forest and drained smallholder oil palm plantations on peat in Central Kalimantan to produce a representation of the peatland landscape in one 0.5° × 0.5° GRACE grid cell. In both ecosystem types, total soil respiration increased with increasing water table depth. Across the landscape grid, monthly changes in water table depth were significantly related to fluctuations in GRACE TWSA. GRACE TWSA explained 76% of variation in water table depth and 75% of variation in total soil respiration measured on the ground. By facilitating regular sampling across broad spatial scales that captures essential variation in a major driver of soil respiration and peat fires, our approach could improve information available to decision makers to monitor changes in water table depth and peat CO2 emissions. This would enable measures better targeted in space and time to more effectively mitigate CO2 emissions from tropical peat drainage and fires. Testing over larger regions is needed to operationalize this exploratory approach.

Holocene peatland development and carbon stock of Zoige peatlands, Tibetan Plateau: a modeling approach

Despite the many studies about peatland development and carbon dynamics in China, especially for Zoige peatlands on the eastern edge of the Tibetan Plateau, few apply modeling as an effective approach to study peatland development. In order to fill up the knowledge gaps of China alpine peatland development and to provide a comparison with previous research, we studied the Zoige peatlands in Holocene with a modeling approach. Simulated results were obtained by the Holocene peatland model (HPM). Driving data was reconstructed based on paleoclimate studies. Model calibration and performance index validation were done by comparing the model output with literature data about peat age depth. Based on our results, the peat cohort mass mean accumulation rate was 0.45 mm year(-1) (ranging from 0.38 to 0.50 mm year(-1)). The mean C accumulation rate was about 0.026 kg C m(-2) year(-1) (ranging from 0.023 to 0.029 kg C m(-2) year(-1)), with a peak accumulation rate around 7 ka to 6 ka BP during the Holocene. The peat depth was 5.38 m (ranging from 4.6 to 5.99 m). The total peat storage in Zoige was about 1.76 Pg (ranging from 1.58 to 2.29 pg), and the carbon stock was estimated as 0.432 pg C (ranging from 0.348 to 0.479 pg C) in Zoige peatlands during the Holocene. After model calibration and validation, simulated results indicated that peat development and carbon accumulation were controlled by variation of water table depth (WTD). Simulated results indicated that the Zoige peatlands are the most important component of peatlands in China in terms of carbon stock. Though HPM lacks in driving data of temperature and incomplete climate factors, its limitations in the parameter setting should not offset the added value of the modeling approach in improving our understanding of peatland carbon and their controlling factor dynamics at the long-term scales in the Zoige region where there are very few studies so far.

Water use efficiency and yield of cowpea and nutrient loss in lysimeter experiment under varying water table depth, irrigation schedules and irrigation method

Lysimeter experiment was conducted at Govind Ballabh Pant University of Agriculture &amp; Technology, Pantnagar during summer season 2013 to study the effect of irrigation schedules and methods on yield, nutrient uptake and water use efficiency of cowpea as well as nutrient loss from silty clay loam soil under fluctuating water table conditions. The experiment was laid out in factorial randomized block design having three irrigation schedules at IW/CPE ratio of 0.3. 0.2 and 0.15 with two irrigation methods (flood and sprinkler) and at 30±1.5, 60±1.5 and 90±1.5 cm water tables replicated thrice. Maximum root length (129.4 cm) and root length density (0.395 cm/cm3) were obtained when irrigation was scheduled at IW: CPE 0.3 associated with 30±1.5 cm water table depth using sprinkler method. Increase in water table depth and IW: CPE ratio decreased water use efficiency where IW: CPE 0.3 produced highest grain yield (1411.6 kg ha-1) with the WUE of 1.15 kg ha mm-1. Significant nutrients uptake response was observed owing to variation in water table depth, irrigation schedules and methods. Analysis of lysimeter leached water showed that with deep drainage and more IW:CPE, leaching losses of N,P and K were more however water applied through sprinkler saved 20.1, 53.7 and 24.4% N, P and K, respectively, over flooded method. Irrigation given at IW: CPE 0.3 through sprinkler form at 60±1.5 cm water table depth favours the higher grain yield and nutrient uptake by crop whereas flooded irrigation with deep water table condition accelerated nutrient leaching.SAARC J. Agri., 14(2): 46-55 (2016)

Methane emissions from natural and drained peatlands in the Zoigê, eastern Qinghai-Tibet Plateau

Peatlands are one of the major natural sources of methane (CH4), but the level of CH4 efflux is uncertain, especially in alpine peatlands. In this study, CH4 emission fluxes from natural and drained peatlands on the Qinghai-Tibet Plateau, southwest China, were measured from June to October in 2013 using the opaque static chamber technique and the Fast Greenhouse Gas Analyzer (DLT-100, Los Gatos Research Corp.). CH4 emission fluxes ranged from 2.07 to 56.33 mg m−2 h−1 in natural peatlands and from 0.02 to 0.42 mg m−2 h−1 in drained peatlands. Mean CH4 emission flux was 19.13 mg m−2 h−1 in natural peatlands and 0.14 mg m−2 h−1 in drained peatlands. These results showed that drainage led to a significant decrease in CH4 emissions. CH4 emission fluxes for all sampling plots were significantly correlated with variation in water table depth for linear (R 2 = 0.453, P < 0.01) and exponential functions (R 2 = 0.429, P < 0.01).

An unstandardized selective variance reduction script for elevation, latitude and longitude decorrelation stretch of multi-temporal LST imagery

A selective variance reduction (SVR) script is presented that applies linear regression models to the principal components (PCs) of multi-temporal night monthly averaged land surface temperature (LST) imagery, in an attempt to spit the variance associated to elevation, latitude, longitude. The recently released version 6, MODIS LST data (MYD11C2) with spatial resolution 0.05° is used while the method is applied in SW USA. The innovation relies on the use of un-standardized PCs. Thus, the reconstructed LST should express the deviation in degrees Celsius, from the elevation, latitude, longitude predicted LST. The reconstructed data quantifies the temporal and spatial patterns of thermal anomalies. The modeling of the frequency distributions of the reconstructed LST imagery indicate that possibly snow melting and variations in water table depth are associated to the negative thermal anomaly observed during the Spring. The GNU OCTAVE 4.0 SVR software implementation is available at http://selective-variance-reduction.sourceforge.net for testing and evaluation.

How hydrology determines seasonal and interannual variations in water table depth, surface energy exchange, and water stress in a tropical peatland: Modeling versus measurements

AbstractSoil carbon stocks in tropical peatlands have declined recently from water table depth (WTD) drawdown caused by increased frequency and intensity of climate extremes like El Niño and by artificial drainage. Restoration of these carbon stocks under these climatic and anthropogenic disturbances requires improved predictive capacity for hydrological feedbacks to ecological processes. Process‐based modeling of tropical peatland ecohydrology could provide us with such capacity, but such modeling has thus far been limited. We aimed at using basic processes for water and O2 transport and their effects on ecosystem water, carbon, and nitrogen cycling to model seasonal and interannual variations of WTD and surface energy exchange. We tested these processes in a process‐based model ecosys in a drained tropical Indonesian peatland from an El Niño year 2002 to a wetter year 2005. WTD was modeled from hydraulically driven water transfers controlled vertically by precipitation versus evapotranspiration (ET) and laterally by discharge versus recharge to or from an external reference WTD. These transfers caused WTD drawdown and soil drying to be modeled during dry seasons, which reduced ET and increased Bowen ratio by lowering stomatal conductance. More pronounced dry seasons in drier years 2002–2004 versus wetter year 2005 caused deeper WTD, more intense peat drying, and greater plant water stress. These modeled trends were well corroborated by site measurements as apparent in regression statistics of modeled versus observed WTD (R2 &gt; 0.8), latent heat (R2 &gt; 0.8), and sensible heat (R2 &gt; 0.7) fluxes. Insights gained from this modeling would aid in predicting the fate of tropical peatlands under future drier climates.