Water Table Level Research Articles

Impact of subsurface drainage system on waterlogged and saline soils in a Saharan palm grove

Salinity and waterlogging associated with saline and shallow groundwater are major problems for the sustainability of irrigated agriculture in many Saharan oases located in southern Tunisia. The aim of this paper is to assess the performance of a subsurface drainage system installed in the modern Sagdoud oasis to control the perched water table depth and reclaim the saline waterlogged soils. Water and salt balances at the oasis scale and daily basis were evaluated during the hydrologic year 1995. Moreover, the water table depth, the mineralisation in the perched groundwater and the bare soil salinity were measured at 40 parcels of farmland in November 1993, October 1998 and June 2021. The results showed that the total depth of irrigation water was three times the potential evapotranspiration depth in 1995. Evaporation process and subsurface drainage system allowed the discharge of 81% and 42%, respectively, of the total volume of irrigation water. From a salt input of 4,865 tons/year by irrigation, 4,566 tons/year (94%) were exported by subsurface drainage system and about 300 tons/year were estimated to have been stored in the soil and perched groundwater. The spatial distributions of the perched groundwater depth and mineralisation, and bare soil salinity were influenced mainly by the topography. The mean water table depth increased by 87%, while the mean salinity of perched groundwater increased by 19% during November 1993-October 1998. The mean bare soil salinity in the 20–40, 40–60 and 80–100 cm depths decreased by 75%, 50% and 42%, respectively, during October 1998-June 2021. Overall, the study revealed that the subsurface drainage system allowed the control of the water and salt balances at the oasis scale, the decrease in the perched water table levels and the reclamation of saline soils. However, the provision of this system does not permit the control of the groundwater mineralisation.

Evaluating the different methods for estimating groundwater evapotranspiration using diurnal water table fluctuations

Riparian ecosystems fundamentally depend on groundwater, and thus accurate estimates of daily groundwater evapotranspiration rate (ETg) is curial for understanding the interactions between groundwater and vegetation. Up to now, various methods (i.e., White, 1932; Hays, 2003; Soylu et al., 2012) have been proposed to estimate daily ETg using the water table fluctuations. The objective of this paper was to evaluate and compare their performances under various water table conditions in field environments. For this purpose, we employed a variety of measurements (i.e., water table levels, latent heat flux and soil water contents) at a riparian forest (T. ramosissima) in Northwest China in 2017. Our results showed that the White method is suitable for use during the water table declining periods. Also, the selected time intervals could have impacts on the estimations of ETg. The Soylu method and the Hays method performed well under various water table conditions. Thus, it seems that the Hays and Soylu methods are more suitable for long-term ETg estimates in field environments. In addition, the percentage of plant transpired water from groundwater varied during the growing seasons. The riparian plants mainly use soil water during the early growing stages, and it tended to use groundwater during the late growing stages. In the future, more isotope-based studies were needed to verify the seasonal patterns of water uptake of the riparian forest.

The other side of tropical forest drought: do shallow water table regions of Amazonia act as large-scale hydrological refugia from drought?

Tropical forest function is of global significance to climate change responses, and critically determined by water availability patterns. Groundwater is tightly related to soil water through the water table depth (WT), but historically neglected in ecological studies. Shallow WT forests (WT < 5 m) are underrepresented in forest research networks and absent in eddy flux measurements, although they represent c. 50% of the Amazon and are expected to respond differently to global-change-related droughts. We review WT patterns and consequences for plants, emerging results, and advance a conceptual model integrating environment and trait distributions to predict climate change effects. Shallow WT forests have a distinct species composition, with more resource-acquisitive and hydrologically vulnerable trees, shorter canopies and lower biomass than deep WT forests. During 'normal' climatic years, shallow WT forests have higher mortality and lower productivity than deep WT forests, but during moderate droughts mortality is buffered and productivity increases. However, during severe drought, shallow WT forests may be more sensitive due to shallow roots and drought-intolerant traits. Our evidence supports the hypothesis of neglected shallow WT forests being resilient to moderate drought, challenging the prevailing view of widespread negative effects of climate change on Amazonian forests that ignores WT gradients, but predicts they could collapse under very strong droughts.

Growth and Wood Trait Relationships of Alnus glutinosa in Peatland Forest Stands With Contrasting Water Regimes.

Human-driven peatland drainage has occurred in Europe for centuries, causing habitat degradation and leading to the emission of greenhouse gases. As such, in the last decades, there has been an increase in policies aiming at restoring these habitats through rewetting. Alder (Alnus glutinosa L.) is a widespread species in temperate forest peatlands with a seemingly high waterlogging tolerance. Yet, little is known about its specific response in growth and wood traits relevant for tree functioning when dealing with changing water table levels. In this study, we investigated the effects of rewetting and extreme flooding on alder growth and wood traits in a peatland forest in northern Germany. We took increment cores from several trees at a drained and a rewetted stand and analyzed changes in ring width, wood density, and xylem anatomical traits related to the hydraulic functioning, growth, and mechanical support for the period 1994–2018. This period included both the rewetting action and an extreme flooding event. We additionally used climate-growth and climate-density correlations to identify the stand-specific responses to climatic conditions. Our results showed that alder growth declined after an extreme flooding in the rewetted stand, whereas the opposite occurred in the drained stand. These changes were accompanied by changes in wood traits related to growth (i.e., number of vessels), but not in wood density and hydraulic-related traits. We found poor climate-growth and climate-density correlations, indicating that water table fluctuations have a stronger effect than climate on alder growth. Our results show detrimental effects on the growth of sudden water table changes leading to permanent waterlogging, but little implications for its wood density and hydraulic architecture. Rewetting actions should thus account for the loss of carbon allocation into wood and ensure suitable conditions for alder growth in temperate peatland forests.

From the micromorphology of paleoweathering fronts to paleoenvironmental analysis: A case study of the Cretaceous dune fields of Sanfranciscana Basin, Brazil

The work investigated the paleoenvironmental significance of kaolinite-rich weathering fronts developed during the Cretaceous in stabilized dune fields of Sanfranciscana Basin in Brazil. To this, was conducted a multi-scale analysis from the outcrops of paleosols to mineral grains and soil pores. The macro and micromorphology of paleoweathering fronts allow recognizing weathering features and estimating the porosity and hydraulic parameters (permeability, capillary pressure, and saturated hydraulic conductivity). Scanning electron microscope analyses were conducted to investigate surface microtextures of quartz grains for weathering process characterization based on dissolution microfeatures. Energy-dispersive X-ray spectrometry was utilized to identify chemical elements of clay minerals. The major and trace elements were analyzed using a Philips X-ray fluorescence (XRF) spectrometer (PW 2440). Our results showed that weathering fronts expand through preferential water paths (pipe and finger flow) in bedding planes in response to textural and porosity contrasts related to the bimodality (i.e., the difference of grain size distribution between overlapped sedimentary structures) of aeolian deposits. The dissolution features present in quartz grains, such as etching, pitting, total dissolution of grains, iron coatings, and booklets of well-developed kaolinite, reveal an increase in humidity and the pedogenetic kaolinization process typical of a humid tropical environment. These weathering patterns coincide with cooling events between the Albian and the Cenomanian report in the literature. Our study indicates that during the Cretaceous, the Sanfransicana Basin underwent climatic amelioration and a rise in water table level, which likely enhanced dune stabilization and the formation of an extensive geomorphic surface.

Towards the regeneration of brown mosses for fen restoration

A low rate of establishment in brown mosses is generally observed following large-scale restoration of fens. As brown mosses are important components in peat accumulation in fens, their low recovery rate has been a concern in the past decade. It was suggested that the restoration method used for bogs, the Moss Layer Transfer Technique (MLTT) should be adapted for fen restoration by identifying factors limiting the establishment and recovery of brown mosses. In this study, we evaluated the regeneration potential of four common brown mosses, Aulacomnium palustre, Campylium stellatum, Scorpidium cossonii and Tomentypnum nitens, according to three factors that can have an impact during restoration: 1) distance of the fragment below the moss apex, 2) mechanical fragmentation of mosses, and 3) enhanced nutrient availability, and this, in growth chambers (within Petri dishes) and field experiments. Under controlled conditions, similar results were obtained for all four brown mosses studied: the severe fragmentation of mosses most drastically improved their regeneration potential. Phosphate fertilization, even at the lowest dose, increased moss regeneration, and brown mosses showed higher recovery in the first 3 cm below the apex. Liming only improved the regeneration of C. stellatum. However, unclear, and even contradicting results were obtained when treatments were applied in the field, where an overall very low establishment of brown mosses was observed in response to the rather prevailing adverse environmental conditions (e.g., erosion, frost heaving, low water table level). The direct application of some of our results into an adapted version of MLTT might be challenging, as it may require a certain level of meticulosity that large-scale mechanical fen restoration cannot provide.

Hydrological behaviour of an ice‐layered snowpack in a non‐mountainous environment

AbstractThe increased frequency of mild rain‐on‐snow (R.O.S.) events in cold regions associated with climate change is projected to affect snowpack structure and hydrological behaviour. The ice layers that form in a cold snowpack when R.O.S. events occur have been shown to influence flowthrough processes and liquid water retention, with consequences for winter floods, groundwater recharge, and water resources management. This study explores interconnections between meteorological conditions, ice layer formation, and lateral flows during R.O.S. events throughout the 2018–2019 winter in meridional Quebec, Canada. Automated hydro‐meteorological measurements, such as water availability for runoff, snow water equivalent, and snowpit observations, are used to compute water and energy balances, making it possible to characterize a snowpack's internal conditions and flowthrough regimes. For compatibility assessment, water and energy balances‐based flowthrough scenarios are then compared to different hydro‐meteorological variables', such as water table or streamlet water levels. The results show an association between highly variable meteorological conditions, frequent R.O.S. events, and ice layer formation. Lateral flows were mainly observed during the early stage of the ablation period. The hydrologically significant lateral flows observed in the study are associated with winter conditions that are predicted to become more frequent in a changing climate, stressing the need for further evaluation of their potential impact at the watershed scale.

Origin of the Coloured Karst Fills in the Neogene Extensional System of NE Iberia (Spain)

Karst fills from the onshore Penedès Basin and offshore València Trough display red, pink, orange and ochre colours. Their Mössbauer spectra indicate that Fe3+ contained in goethite is the dominant species in reddish-pink fills, whereas Fe2+ contained in dolomite and clays is more dominant in the orange and ochre ones. The lower δ13C values and higher 87Sr/86Sr ratios of the karst fills with respect to their host carbonates can reflect the input of soil-derived CO2 and an external radiogenic source into the karst system. This geochemical composition, together with the non-carbonate fraction of the fills, consists of authigenic and transported illite, illite-smectite interlayers, as well as kaolinite, chlorite, pyrite, quartz, ilmenite, magnetite, apatite and feldspar, account for a mixed residual-detrital origin of fills. This polygenic origin agrees with that of the terra rossa sediments described worldwide. The different colours of karst fills are attributed to fluctuations in the water table, which control the Eh/pH conditions in the karst system. Thus, reddish colours reflect low water table levels and oxidising episodes, and orange and ochre ones reflect high water table levels and more reducing episodes. The greenish colours of fills could be related to fluctuations in the Fe3+/Fe2+ ratio.

Diurnal and seasonal dynamics of the electrical conductivity of water of the northeastern part of the Great Vasyugan Mire (Western Siberia)

In this study, we determined the diurnal and seasonal dynamics of the electrical conductivity of waters of the northeastern part of the Great Vasyugan Mire in Western Siberia. Our studies showed that the electrical conductivity of the waters for the period of April to September 2016 was characterised by a value of 35 μS/cm, and the seasonal amplitude was 25 μS/cm. In seasonal dynamics, there are three maximums of electrical conductivity in waters. The first maximum was formed in April (48 μS/cm) and is associated with snowmelt water supply. The second one was observed in May after the complete thawing of the peat deposit (39 μS/cm), and the third was observed at the end of July as a result of biochemical processes in the peat deposit (43 μS/cm). Our studies have shown the electrical conductivity hysteresis during time intervals from 3–5 to 6–10 days electrical conductivity remains constant despite the change in hydrometeorological conditions (water table level, temperature).

Comparing GHG Emissions from Drained Oil Palm and Recovering Tropical Peatland Forests in Malaysia

For agricultural purposes, the drainage and deforestation of Southeast Asian peatland resulted in high greenhouse gases’ (GHGs, e.g., CO2, N2O and CH4) emission. A peatland regenerating initiative, by rewetting and vegetation restoration, reflects evidence of subsequent forest recovery. In this study, we compared GHG emissions from three Malaysian tropical peatland systems under the following different land-use conditions: (i) drained oil palm plantation (OP), (ii) rewetting-restored forest (RF) and (iii) undrained natural forest (NF). Biweekly temporal measurements of CO2, CH4 and N2O fluxes were conducted using a closed-chamber method from July 2017 to December 2018, along with the continuous measurement of environmental variables and a one-time measurement of the soil physicochemical properties. The biweekly emission data were integrated to provide cumulative fluxes using the trapezoidal rule. Our results indicated that the changes in environmental conditions resulting from draining (OP) or rewetting historically drained peatland (RF) affected CH4 and N2O emissions more than CO2 emissions. The cumulative CH4 emission was significantly higher in the forested sites (RF and NF), which was linked to their significantly higher water table (WT) level (p &lt; 0.05). Similarly, the high cumulative CO2 emission trends at the RF and OP sites indicated that the RF rewetting-restored peatland system continued to have high decomposition rates despite having a significantly higher WT than the OP (p &lt; 0.05). The highest cumulative N2O emission at the drained-fertilized OP and rewetting-restored RF sites was linked to the available substrates for high decomposition (low C/N ratio) together with soil organic matter mineralization that provided inorganic nitrogen (N), enabling ideal conditions for microbial mediated N2O emissions. Overall, the measured peat properties did not vary significantly among the different land uses. However, the lower C/N ratio at the OP and the RF sites indicated higher decomposition rates in the drained and historically drained peat than the undrained natural peat (NF), which was associated with high cumulative CO2 and N2O emissions in our study.

Soil genesis on the soft slopes of ancient coastal plains, southeastern Brazil

Coastal plains are characterized by low-elevation and small altitude variation and occupy an area of 57 million km2 worldwide. Ancient coastal plains that occur in the State of Rio de Janeiro (RJ), Brazil, have their pedological diversity neglected due to the generalization of some soil classes, underestimating the diversity of soils in these regions, hence limiting the evaluation for use and management. The aim of this study was to characterize the diversity of soils in a toposequence along an ancient coastal plain and to understand the pedogenetic processes involved. For this, soil pits were opened in the lower third (P1), middle third (P2), upper third (P3) and at the top (P4) of a toposequence. Soil profiles were characterized for morphological, physical, chemical, mineralogical and micromorphological properties. Profile P1 was classified as Planosol, being formed from colluvial sediments. In this profile, a lithological discontinuity was identified based on the irregularity of the values of silt/clay and coarse sand/fine sand ratios in subsurface. In this profile, limited drainage conditions were also observed. The main formation processes identified were ferrolysis and clay eluviation/illuviation, which promoted the increase of the textural gradient and thickening of the E horizon. Profiles P2 and P3 were classified as Ferralsols, were kaolinitic, with no redox conditions, and with predominance of eluviation/illuviation processes associated with pedoturbation, with a small increment of clay in the subsurface in both profiles. In profile P2, more so than in P3, there was still a strong influence of colluvial sediments, identified by the presence of a lithological discontinuity. For profile P4, a Plinthosol, located at the top of the toposequence, its formation was related to the action of weathering on the underlying acidic granite-gneiss rock. Despite the presence of plinthite, which denoted the occurrence of plinthization, the micromorphological description made it possible to state that it was a relictual condition whose formation occurred under past climatic conditions with higher water table level and which is currently being destroyed.

Hydrological feedbacks on peatland CH4 emission under warming and elevated CO2: A modeling study

Peatland carbon cycling is critical for the land–atmosphere exchange of greenhouse gases, particularly under changing environments. Warming and elevated atmospheric carbon dioxide (eCO2) concentrations directly enhance peatland methane (CH4) emission, and indirectly affect CH4 processes by altering hydrological conditions. An ecosystem model ELM-SPRUCE, the land model of the E3SM model, was used to understand the hydrological feedback mechanisms on CH4 emission in a temperate peatland under a warming gradient and eCO2 treatments. We found that the water table level was a critical regulator of hydrological feedbacks that affect peatland CH4 dynamics; the simulated water table levels dropped as warming intensified but slightly increased under eCO2. Evaporation and vegetation transpiration determined the water table level in peatland ecosystems. Although warming significantly stimulated CH4 emission, the hydrological feedbacks leading to a reduced water table mitigated the stimulating effects of warming on CH4 emission. The hydrological feedback for eCO2 effects was weak. The comparison between modeled results with data from a field experiment and a global synthesis of observations supports the model simulation of hydrological feedbacks in projecting CH4 flux under warming and eCO2. The ELM-SPRUCE model showed relatively small parameter-induced uncertainties on hydrological variables and their impacts on CH4 fluxes. A sensitivity analysis confirmed a strong hydrological feedback in the first three years and the feedback diminished after four years of warming. Hydrology-moderated warming impacts on CH4 cycling suggest that the indirect effect of warming on hydrological feedbacks is fundamental for accurately projecting peatland CH4 flux under climate warming.

Lagged Wetland CH4 Flux Response in a Historically Wet Year

AbstractWhile a stimulating effect of plant primary productivity on soil carbon dioxide (CO2) emissions has been well documented, links between gross primary productivity (GPP) and wetland methane (CH4) emissions are less well investigated. Determination of the influence of primary productivity on wetland CH4 emissions (FCH4) is complicated by confounding influences of water table level and temperature on CH4 production, which also vary seasonally. Here, we evaluate the link between preceding GPP and subsequent FCH4 at two fens in Wisconsin using eddy covariance flux towers, Lost Creek (US‐Los) and Allequash Creek (US‐ALQ). Both wetlands are mosaics of forested and shrub wetlands, with US‐Los being larger in scale and having a more open canopy. Co‐located sites with multi‐year observations of flux, hydrology, and meteorology provide an opportunity to measure and compare lag effects on FCH4 without interference due to differing climate. Daily average FCH4 from US‐Los reached a maximum of 47.7 ηmol CH4 m−2 s−1 during the study period, while US‐ALQ was more than double at 117.9 ηmol CH4 m−2 s−1. The lagged influence of GPP on temperature‐normalized FCH4 (Tair‐FCH4) was weaker and more delayed in a year with anomalously high precipitation than a following drier year at both sites. FCH4 at US‐ALQ was lower coincident with higher stream discharge in the wet year (2019), potentially due to soil gas flushing during high precipitation events and lower water temperatures. Better understanding of the lagged influence of GPP on FCH4 due to this study has implications for climate modeling and more accurate carbon budgeting.

Assessing the Economic and Environmental Impacts of High Water Table Level on Soil Productivity in Ezbet

Assessing the Economic and Environmental Impacts of High Water Table Level on Soil Productivity in Ezbet

Nitrous oxide and nitrate as indicators of subsoil removal of N in pig slurry applied to Luvisols in Western Denmark

This one-year study examined effects of autumn- vs. spring- application of pig slurry, and the effect of a nitrification inhibitor (DMPP) for autumn-applied slurry, on transport and transformations of nitrogen in the soil profile. Duplicate field plots had ceramic suction cells at 50, 100, and 150 cm depths to calculate leaching for each treatment using NO3− concentrations and percolation simulated using a water transport model. Furthermore, soil moisture, soil texture and bulk density at 50, 100 and 150 cm depth, and water table level, were recorded. During campaigns, subsurface N2O concentrations at 20, 50, 100, and 150 cm depths, and N2O fluxes to the atmosphere, were monitored for indicators of denitrification activity. Autumn-applied pig slurry showed evidence for NO3− removal between 50 and 100 cm depth, and N2O concentration profiles indicated high denitrification activity around 50 cm depth. Autumn-applied slurry showed higher N2O emissions and lower crop yields compared to spring application, indicating losses occurred during winter. DMPP did not reduce average NO3− leaching, nor affect N2O emissions, but treatment effects were confounded by heterogeneity in compaction, clay content, and water table depth at plot level. The study showed that accounting for transport and transformations of N in the subsoil can contribute to understanding the environmental controls of N leaching, as well as direct and indirect N2O emissions.

Environmental modifiers of the relationship between water table depth and Ellenberg’s indicator of soil moisture

Ellenberg indicator values for plant species are widely used metrics in ecology, providing a proxy measure of environmental conditions, without direct measurements. They integrate environmental conditions over time since species will only persist where conditions are favourable. Ellenberg moisture (F) values summarise the hydrological environment experienced by plants. However, the relationship between indicator values and hydrological metrics appears to be influenced by a range of other abiotic and biotic factors, limiting our ability to fully interpret Ellenberg F. Focussing on Ellenberg F, we evaluated how the unweighted mean plant community F value to hydrology, specifically water table depth, is influenced by other environmental factors, ground cover type and alpha diversity in UK seasonal coastal wetlands (dune slacks). As expected, water table depth had the strongest influence on unweighted mean Ellenberg F. We show that unweighted mean Ellenberg F was more sensitive to changes in water table levels for plant communities that were more nutrient limited, when the organic matter layer was thicker and there was less bare ground cover. Unweighted mean Ellenberg F was consistently lower for a given water table depth, when there was lower atmospheric nitrogen deposition, lower loss of ignition (a measure of organic matter content) and more diverse plant communities. These findings help us to better interpret what Ellenberg F indicator values tell us about hydrological conditions, by understanding the factors which alter that relationship.

Delineation of Water Logging and Salinity for Salvaging Built Environment

Millions of acres of splendidly productive land and valuable infrastructure are deteriorated continuously. The reason for such deterioration in majority of areas is mainly due to water logging and salinity. Rise of water table level and the dearth of drainage and lack of continuous monitoring and timely remedial measures, extended the circle of devastation to historical heritage and precious archeological sites as well.&#x0D; Mohenjo-Daro has been selected for this study, it has global significance but due to water logging and salinity, it is in danger of total destruction. The archeological buildings and other infrastructure and land in its environs are being gradually eroded by the capillary rise of saline ground the intensity of which constitutes a serious threat.&#x0D; For delineating and periodic monitoring of the salinity and waterlogging and to effectively implement the appropriate remedies, use of the latest technologies is essential. In this study the remote sensing technologies are used to address this issue with the help of Soil investigation parameters mainly EC and pH.&#x0D; The aftermaths of this study would provide a methodological framework along with practical application in delineation saline areas using satellite technology. The final value-added products of this research would be useful for all interested stakeholders including conservationists, environmentalists, archeologists, planners and decision-makers at various levels. The international community at large would be the beneficiary of this study since Mohenjo-Daro is the heritage of entire mankind.

Effects of waterlogging and salinity increase on CO2 efflux in soil from coastal marshes

Coastal marshes play a notable role in sequestering carbon in plants and soil; however, coastal ecosystems are vulnerable to global change in terms of sea-level rise and saltwater intrusion. The effects of independent and interactive hydrological treatments of waterlogging and elevated salinity on soil CO2 effluxes in Spartina alterniflora marshes were investigated based on a mesocosm approach. This study highlighted the importance of respective soil respirations during inundation (nondrainage, Rs.ND) and reaeration (drainage, Rs.D) in the marshes soils. We found that waterlogging treatments heavily suppressed Rs.ND but increased the Rs.D, regardless of salinity levels. Light salinity enhanced soil respiration, whereas high salinity inhibited soil CO2 efflux, regardless of the water table level. Waterlogging strengthened the negative effects of salinity on Rs.ND and offset the negative effects on Rs.D. The variations in soil respiration under the hydrological treatments can be mainly attributed to changes in root biomass; indigenous soil microbial biomass; and activities of sucrase, cellulase and dehydrogenase, as well as ionic concentrations and oxidation-reduction potential. The temperature sensitivity (Q10 value) of soil respiration (only for Rs.D) after drainage showed a notable decline under the conditions of waterlogging and high salinity. The effect degree of coupled hydrological treatments on soil respiration and Q10 values was similar to a single waterlogging factor before drainage and more strongly than a single factor after drainage. We suggest that the soil CO2 efflux under water flooding and reaeration, inundation duration, and salinity levels need to be considered to understand the impacts of future hydrological changes on coastal marshes.

Managing water table depth thresholds for potato subirrigation

Subirrigation requires precise control of the water table level to provide adequate soil water content (SWC) for promoting plant growth. Optimizing water table level management has been shown to improve soil aeration, reduce N-leaching, and reduce risk of crop losses. The objectives of this study were to: i) assess if water table level and N-fertilizer rate impact potato growth, root development, plant N uptake, or tuber yield; and ii) estimate the optimum water table level threshold that provides sufficient soil upward water flux to meet plant water requirements. The study was conducted in 2013 and 2014 in Hastings, FL, USA. Water table level was automatically controlled in three independent irrigation zones of 1.4 ha at 36, 54, and 71 cm from the top of the hilled row, termed as high (HWT), medium (MWT), and low (LWT) water table treatments, respectively, and SWC measured at 22 cm depth was used as covariate to compare treatments. A randomized complete block with three replications was used to evaluate potato cultivars ‘Atlantic’ and ‘FL1867′ under 0, 112, 224, and 336 kg ha−1 of N-fertilizer within water table treatments. Marketable yield in 2013 was lower than 2014, owing to the high precipitation (421 mm) during tuber bulking that led to high SWC and tuber decay. Total and marketable tuber yields were maximized when N fertilizer rates ranged from 243 to 336 kg ha−1. The highest yield and proportion of large tubers occurred when SWC at 22 cm ranged from 0.13 to 0.16 m3 m−3. The HWT significantly limited root length, diameter, and surface area, compared to the LWT. In 2014, variation of SWC at 22 cm depth had little effect on tuber yield. The HWT was not detrimental to tuber yield, but rather it compounded the negative effect that high precipitation rate had on fluctuating SWC in the root zone, resulting in reduced yield and tuber quality. Optimal SWC in the root zone can be achieved by adjusting the water table level and upward soil water flux throughout the season, according to the crop evapotranspiration for each crop stage, which reduces irrigation water requirements and minimizes the risks of soil water saturation and tuber yield losses.

Water table level and soil texture are important drivers of dung beetle diversity in Amazonian lowland forests

The high biodiversity of the Amazon region is related to variation in soil physical properties and water-table depths. Dung beetles are efficient bioindicators that feed and breed on the soil surface and below ground, affecting soil properties and being affected by them. Here, we investigate the influence of soil physical characteristics (proportions of sand, silt, clay) and water-table depth on dung beetle assemblages and functional groups in a forest in central Amazonia. We sampled beetles in 29 transects with different soil physical properties and water-table maximum levels, and analyzed beetle species richness, abundance and species composition for the total assemblage and for each functional group (rollers, tunnellers, dwellers). Dung beetle abundance increased with soil clay content (GLMM; p = 0.009) whereas dweller (GLMM; p = 0.017) and tunneller species richness increased with clay and silt contents (GLMM; p = 0.018). Sites with deeper water table had greater roller-beetle abundance (GLMM; p = 0.049). Dung beetle assemblage composition was strongly influenced by clay content. Our results suggest that soil texture and water-table levels determine dung beetle distributions, both for the whole assemblages and for each functional group separately. These findings highlight the role of soil structure in determining dung beetle assemblages.