Effects Of Water Table Depth Research Articles

Effect of material hydraulic properties on temporal moisture variations and performance of unbound pavements with sprayed seals

Moisture is widely recognised as a primary factor responsible for road failures. In particular, unbound pavements with sprayed seals, a common type of flexible pavement used in Australia and New Zealand are highly susceptible to moisture-related performance losses. The wearing course of these pavements, i.e. the sprayed seals, is moderately permeable, which allows for moisture exchange between the environment and the pavement structure throughout its service life. As a result, the moisture content of pavement layers varies according to the prevailing climate, which could cause noticeable performance reductions.This study extensively investigates the moisture variations in pavement layers of unbound pavements with sprayed seals during the service life due to the variations of ambient climatic conditions. The moisture variations in 18 different typical sprayed sealed pavements were numerically simulated for 10-year climates of Melbourne and Adelaide. Both the degree of saturation (Sr) and suction (s) variations were simulated for a number of practical scenarios. The results indicated that the pavement layers reach an equilibrium condition within less than 6 months under the climates considered. A series of sensitivity analyses were performed to evaluate the effect of hydraulic properties of seal, unbound granular material (UGM), subgrade and effect of water table depth on the moisture variations of pavement layers. The parametric analysis revealed that relatively permeable seals facilitate significant wetting of the UGM layer and substantial drying due to variations in prevailing climatic conditions. Moreover, this study identified primary influencing factors that determine the equilibrium state and the temporal moisture variations of the pavement layers. The effect of water table depth is evaluated for different subgrade conditions. A pavement performance evaluation conducted following the effective stress concept, the factor Sr.s is presented in this study. Overall, the results highlight the importance of considering temporal moisture variations in the design stage to improve pavement performance.

Risk assessment and binding mechanisms of potentially toxic metals in sediments from different water levels in a coastal wetland

The excessive accumulation of potentially toxic metals (Pb and Cd) in coastal wetlands is among the main factors threatening wetland ecosystems. However, the effects of water table depth (WTD) on the risk and binding mechanisms of potentially toxic metals in sediments remain unclear. Here, sediments from different WTD obtained from a typical coastal wetland were evaluated using a newly developed strategy based on chemical extraction methods coupled with high-resolution spectroscopy. Our findings indicated that the WTD of the coastal wetland fluctuates frequently and the average enrichment factor for Pb was categorized as minor, whereas Cd enrichment was categorized as moderate. High-resolution spectroscopy techniques also demonstrated that organic functional groups and partly inorganic compounds (e.g., Fe-O/Si-O) played a vital role in the binding of Pb and Cd to surface sediments. Additionally, mineral components rather than organic groups were mainly bound to these metals in the bottom sediments. Collectively, our findings provide key insights into the potential health effects and binding characteristics of potentially toxic metals in sediments, as well as their dynamic behavior under varying sediment depths at a microscale.

Water Table Fluctuation and Methane Emission in Pineapples (Ananas comosus (L.) Merr.) Cultivated on a Tropical Peatland

Inappropriate drainage and agricultural development on tropical peatland may lead to an increase in methane (CH4) emission, thus expediting the rate of global warming and climate change. It was hypothesized that water table fluctuation affects CH4 emission in pineapple cultivation on tropical peat soils. The objectives of this study were to: (i) quantify CH4 emission from a tropical peat soil cultivated with pineapple and (ii) determine the effects of water table depth on CH4 emission from a peat soil under simulated water table fluctuation. Soil CH4 emissions from an open field pineapple cultivation system and field lysimeters were determined using the closed chamber method. High-density polyethylene field lysimeters were set up to simulate the natural condition of cultivated drained peat soils under different water table fluctuations. The soil CH4 flux was measured at five time intervals to obtain a 24 h CH4 emission in the dry and wet seasons during low- and high-water tables. Soil CH4 emissions from open field pineapple cultivation were significantly lower compared with field lysimeters under simulated water table fluctuation. Soil CH4 emissions throughout the dry and wet seasons irrespective of water table fluctuation were not affected by soil temperature but emissions were influenced by the balance between methanogenic and methanotrophic microorganisms controlling CH4 production and consumption, CH4 transportation through molecular diffusion via peat pore spaces, and non-microbial CH4 production in peat soils. Findings from the study suggest that water table fluctuation at the soil–water interface relatively controls the soil CH4 emission from lysimeters under simulated low- and high-water table fluctuation. The findings of this study provide an understanding of the effects of water table fluctuation on CH4 emission in a tropical peatland cultivated with pineapple.

Active Layer Groundwater Flow: The Interrelated Effects of Stratigraphy, Thaw, and Topography

AbstractThe external drivers and internal controls of groundwater flow in the thawed “active layer” above permafrost are poorly constrained because they are dynamic and spatially variable. Understanding these controls is critical because groundwater can supply solutes such as dissolved organic matter to surface water bodies. We calculated steady‐state three‐dimensional suprapermafrost groundwater flow through the active layer using measurements of aquifer geometry, saturated thickness, and hydraulic properties collected from two major landscape types over time within a first‐order Arctic watershed. The depth position and thickness of the saturated zone is the dominant control of groundwater flow variability between sites and during different times of year. The effect of water table depth on groundwater flow dwarfs the effect of thaw depth. In landscapes with low land‐surface slopes (2–4%), a combination of higher water tables and thicker, permeable peat deposits cause relatively constant groundwater flows between the early and late thawed seasons. Landscapes with larger land‐surface slopes (4–10%) have both deeper water tables and thinner peat deposits; here the commonly observed permeability decrease with depth is more pronounced than in flatter areas, and groundwater flows decrease significantly between early and late summer as the water table drops. Groundwater flows are also affected by microtopographic features that retain groundwater that could otherwise be released as the active layer deepens. The dominant sources of groundwater, and thus dissolved organic matter, are likely wet, flatter regions with thick organic layers. This finding informs fluid flow and solute transport dynamics for the present and future Arctic.

Effect of Water Table Depth on Soybean Water Use, Growth, and Yield Parameters

Water table contribution to plant water use is a significant element in improving water use efficiency (WUE) for agricultural water management. In this study, lysimeter experiments were conducted in a controlled greenhouse environment to investigate the response of soybean water uptake and growth parameters under four different water table depths (WTD) (30, 50, 70, and 90 cm). Soybean crop water use, WUE, and root distribution under the different WTD were examined. For 30, 50, 70, and 90 cm of WTD treatments, the average water table contributions were 89, 83, 79, and 72%; the grain yields were 15.1, 10.5, 14.1, and 17.2 g/lys.; and the WUEs were 0.22, 0.18, 0.25, and 0.31 g/lys./cm, respectively. Further analysis of the root mass and proportional distribution among the different soil layers illustrated that the lysimeters with 70 and 90 cm WTD had greater root mass with higher root distribution at 40–75 cm of the soil layer. The results indicated that 70 and 90 cm of constant WTD can yield higher grain yield and biomasses with greater WUE and better root distribution than the irrigated or shallow WTD treatments.

Effect of Water Table Depth on Nutrient Concentrations Below the Water Table in a Spodosol

Water table depth manipulations as implemented in sugarcane fields of Southwestern Florida, USA, were hypothesized to influence the nutrient concentrations below the water table. Concentrations of phosphorus (P), potassium (K), nitrogen (N), and bromide (Br−) were monitored above and below the water table using a column leaching experiment. Three columns were packed with Immokalee soil (A, E, and Bh horizons) classified as a spodosol and fertilizers (NPK) were applied on the soil surface as solids using rates of 11 kg P ha−1, 166 kg K ha−1, and 200 kg N ha−1. A fourth column where fertilizer mixture and bromide were not added acted as a blank. Potassium was also applied as KBr with bromide used as tracer for water movement. Water table was maintained at 30 cm for 6 weeks and lowered to 50 cm deep for another 6 weeks. Samplers were placed in A, E, and Bh horizons and outlets were placed at 30 and 50 cm deep to obtain solutions for monitoring nutrients and tracer. Solution samplers placed in E and Bh horizons were located below the water table. Slightly elevated P, N, and K concentrations in E horizon for a 50-cm water table depth treatment were observed. For both water table treatments, minimal loss of applied N, P, and K below the water table was observed. The results of the study have shown that movement of nutrients below the water table is slow, and depends on the type of nutrients applied and the water table depth.

Taxonomic and functional traits responses of Sphagnum peatland testate amoebae to experimentally manipulated water table

Biomonitoring tools are useful to assess the impact of environmental changes on the functioning of ecosystems. Existing tools mostly require species identification, thus allowing to estimating changes in biodiversity, and possibly inferring ecosystem functioning, using functional diversity and traits based approaches.Testate amoebae are good indicators of surface moisture conditions in Sphagnum peatlands and are routinely used in palaeoecology. Their shells (tests), on which identification is based, can also be used to define functional traits and thus to infer changes in ecosystem functioning.We investigated the response of testate amoeba communities to manipulated water table depth (wet: −4cm, intermediate: −15cm, and dry: −25cm) over time (seven time points, 19 months) using mesocosms by comparing two approaches: community structure and functional traits responses, using a combination of morphological (biovolume, length, aperture size and position) and physiological (mixotrophy/heterotrophy, shell material) traits.This is the first study investigating the effect of water table depth on testate amoeba assemblages over time using a mesocosm approach. Taxonomical and functional approaches showed similar response patterns, confirming that water level acted as a strong environmental filter. After one year Hyalosphenia papilio decreased in the dry treatment, and the community structure shifted towards a dominance of dry indicators (Nebela tincta complex, Corythion dubium, Euglypha compressa) and the selected functional traits (smaller, heterotrophic, compressed species, with a ventral aperture) corresponded to drought adaptations.In line with recent observational and transfer function studies exploring the use of testate amoebae functional traits, our experimental results illustrate how well-selected traits could be used to monitor the impact of present and past climatic changes on Sphagnum peatlands.

Evaluating the influence of water table depth on transpiration of two vegetation communities in a lake floodplain wetland

Groundwater plays an important role in supplying water to vegetation in floodplain wetlands. Exploring the effect of water table depth (WTD) on vegetation transpiration is essential to increasing understanding of interactions among vegetation, soil water, and groundwater. In this study, a HYDRUS-1D model was used to simulate the water uptake of two typical vegetation communities, Artemisia capillaris and Phragmites australis, in a floodplain wetland (Poyang Lake wetland, China). Vegetation transpiration was compared for two distinct hydrological conditions: high water table (2012) and low water table (2013). Results showed that vegetation transpiration in the main growth stage (July–October) was significantly influenced by WTD. Under high water table conditions, transpiration of A. capillaris and P. australis communities in the main growth stage totaled 334 and 735 mm, respectively, accounting for over 90% of the potential transpiration. Under low water table conditions, they decreased to 203 and 510 mm, respectively, due to water stress, accounting for merely 55% of the potential transpiration. Scenario simulations found different linear relationships between WTD and the ratio of groundwater contribution to vegetation transpiration. An increase of 1 m in WTD in the main growth stage may reduce the ratio by approximately 25%.

Contrasting ecosystem CO2 fluxes of inland and coastal wetlands: a meta-analysis of eddy covariance data.

Wetlands play an important role in regulating the atmospheric carbon dioxide (CO2 ) concentrations and thus affecting the climate. However, there is still lack of quantitative evaluation of such a role across different wetland types, especially at the global scale. Here, we conducted a meta-analysis to compare ecosystem CO2 fluxes among various types of wetlands using a global database compiled from the literature. This database consists of 143 site-years of eddy covariance data from 22 inland wetland and 21 coastal wetland sites across the globe. Coastal wetlands had higher annual gross primary productivity (GPP), ecosystem respiration (Re ), and net ecosystem productivity (NEP) than inland wetlands. On a per unit area basis, coastal wetlands provided large CO2 sinks, while inland wetlands provided small CO2 sinks or were nearly CO2 neutral. The annual CO2 sink strength was 93.15 and 208.37gCm-2 for inland and coastal wetlands, respectively. Annual CO2 fluxes were mainly regulated by mean annual temperature (MAT) and mean annual precipitation (MAP). For coastal and inland wetlands combined, MAT and MAP explained 71%, 54%, and 57% of the variations in GPP, Re , and NEP, respectively. The CO2 fluxes of wetlands were also related to leaf area index (LAI). The CO2 fluxes also varied with water table depth (WTD), although the effects of WTD were not statistically significant. NEP was jointly determined by GPP and Re for both inland and coastal wetlands. However, the NEP/Re and NEP/GPP ratios exhibited little variability for inland wetlands and decreased for coastal wetlands with increasing latitude. The contrasting of CO2 fluxes between inland and coastal wetlands globally can improve our understanding of the roles of wetlands in the global C cycle. Our results also have implications for informing wetland management and climate change policymaking, for example, the efforts being made by international organizations and enterprises to restore coastal wetlands for enhancing blue carbon sinks.

Effect of watertable depth and salinity on growth dynamics of Rhodes grass (Chloris gayana)

Depending on their depth, watertables can have a positive effect on plants by supplying water, a negative effect by creating waterlogged and/or saline conditions or a neutral effect. Rhodes grass (Chloris gayana), a tropical perennial forage adapted to saline soils, floods and droughts, is a viable choice for the lowlands in the Pampas region of Argentina. The effects of the depth and salt concentration of the watertable on the growth dynamics and biomass accumulation of Rhodes grass were quantified in a greenhouse experiment. The experiment consisted of 10 treatments, resulting from the factorial combination of five watertable depths (25, 75, 125, 175 and 225 cm) and two salt treatments (EC 1.4 and 20.5 dS m–1). The presence of non-saline watertable at a depth of 25 cm produced a 5-fold greater biomass and showed an increase in water consumption of equal magnitude compared with deeper watertables. The increase in shoot biomass was explained primarily by higher tiller and stolon density, which increased 3.3- and 7.7-fold respectively, at watertables that were 25 cm deep compared with deeper treatments. Furthermore, groundwater use efficiency was 30% higher in non-saline watertables at 25 cm depth. Similarly, at this depth, the leaf blades were 50% longer compared with the deepest watertables evaluated. In contrast, the presence of saline watertables at 25 cm depth had a detrimental effect on the production of biomass and its components, whereas the effect at 125 cm and greater depths was neutral. Therefore, Rhodes grass is a species that can take advantage of the widespread shallow watertable environments of the Pampas region as long as the salinity levels are low.

Effects of water-table depth and soil moisture on plant biomass, diversity, and distribution at a seasonally flooded wetland of Poyang Lake, China

Hydrological regime has been widely recognized as one of the major forces determining vegetation distribution in seasonally flooded wetland. Poyang Lake, the largest freshwater lake in China, has been encountering dramatic changes in hydrological conditions in last decade, which greatly influenced the wetland vegetations. To explore the relationships between hydrology and vegetation distribution, water-table depth, soil moisture, species composition, diversity and biomass were measured at a seasonally flooded wetland section at Wucheng National Nature Reserve. Three plant communities, Artemisia capillaris, Phragmites australis and Carex cinerascens communities, were examined which are zonally distributed from upland to lakeshore with decreasing elevation. Canonical correspondence analysis (CCA), spearmen correlation and logistic regression were adopted to analyze the relationships between vegetation characteristics and hydrological variables of water-table depth and soil moisture. Results show that significant hydrological gradient exist along the wetland transect. Water-table demonstrates a seasonal variation and is consistently deepest in A. capillaris community (ranging from–0.5 m above ground to +10.3 m below ground), intermediate in P. australis community (–2.6 m to +7.8 m) and shallowest in C. cinerascens community (–4.5 m to +6.1 m). Soil moisture is lowest and most variable in A. capillaris community, highest and least variable in P. australis community, and intermediate and moderate variable in C. cinerascens community. The CCA ordination indicated that variables of water-table depth and soil moisture are strongly related to community distribution, which explained 81.7% of the vegetation variations. Species diversity indices are significantly positively correlated with soil moisture and negatively correlated with moisture variability, while above- and belowground biomass are positively correlated with moisture. Above- and belowground biomass present Gaussian models along the gradient of average water-table depth in growing season, while species diversity indices show bimodal patterns. The optimal average water-table depths for above- and belowground biomass are 0.8 m and 0.5 m, respectively, and are 2.2 m and 2.4 m for species richness and Shannon-Wiener indices, respectively. Outcomes of this work improved the understandings of the relationship between hydrology and vegetation.

Modelling effects of seasonal variation in water table depth on net ecosystem CO<sub>2</sub> exchange of a tropical peatland

Abstract. Seasonal variation in water table depth (WTD) determines the balance between aggradation and degradation of tropical peatlands. Longer dry seasons together with human interventions (e.g. drainage) can cause WTD drawdowns making tropical peatland C storage highly vulnerable. Better predictive capacity for effects of WTD on net CO2 exchange is thus essential to guide conservation of tropical peat deposits. Mathematical modelling of basic eco-hydrological processes under site-specific conditions can provide such predictive capacity. We hereby deploy a process-based mathematical model ecosys to study effects of seasonal variation in WTD on net ecosystem productivity (NEP) of a drainage affected tropical peat swamp forest at Palangkaraya, Indonesia. Simulated NEP suggested that the peatland was a C source (NEP ~ −2 g C m−2 d−1, where a negative sign represents a C source and a positive sign a C sink) during rainy seasons with shallow WTD, C neutral or a small sink (NEP ~ +1 g C m−2 d−1) during early dry seasons with intermediate WTD and a substantial C source (NEP ~ −4 g C m−2 d−1) during late dry seasons with deep WTD from 2002 to 2005. These values were corroborated by regressions (P < 0.0001) of hourly modelled vs. eddy covariance (EC) net ecosystem CO2 fluxes which yielded R2 > 0.8, intercepts approaching 0 and slopes approaching 1. We also simulated a gradual increase in annual NEP from 2002 (−609 g C m−2) to 2005 (−373 g C m−2) with decreasing WTD which was attributed to declines in duration and intensity of dry seasons following the El Niño event of 2002. This increase in modelled NEP was corroborated by EC-gap filled annual NEP estimates. Our modelling hypotheses suggested that (1) poor aeration in wet soils during shallow WTD caused slow nutrient (predominantly phosphorus) mineralization and consequent slow plant nutrient uptake that suppressed gross primary productivity (GPP) and hence NEP (2) better soil aeration during intermediate WTD enhanced nutrient mineralization and hence plant nutrient uptake, GPP and NEP and (3) deep WTD suppressed NEP through a combination of reduced GPP due to plant water stress and increased ecosystem respiration (Re) from enhanced deeper peat aeration. These WTD effects on NEP were modelled from basic eco-hydrological processes including microbial and root oxidation-reduction reactions driven by soil and root O2 transport and uptake which in turn drove soil and plant carbon, nitrogen and phosphorus transformations within a soil-plant-atmosphere water transfer scheme driven by water potential gradients. Including these processes in ecosystem models should therefore provide an improved predictive capacity for WTD management programs intended to reduce tropical peat degradation.

Testing the applicability of neural networks as a gap-filling method using CH<sub>4</sub> flux data from high latitude wetlands

Abstract. Since the advancement in CH4 gas analyser technology and its applicability to eddy covariance flux measurements, monitoring of CH4 emissions is becoming more widespread. In order to accurately determine the greenhouse gas balance, high quality gap-free data is required. Currently there is still no consensus on CH4 gap-filling methods, and methods applied are still study-dependent and often carried out on low resolution, daily data. In the current study, we applied artificial neural networks to six distinctively different CH4 time series from high latitudes, explain the method and test its functionality. We discuss the applicability of neural networks in CH4 flux studies, the advantages and disadvantages of this method, and what information we were able to extract from such models. Three different approaches were tested by including drivers such as air and soil temperature, barometric air pressure, solar radiation, wind direction (indicator of source location) and in addition the lagged effect of water table depth and precipitation. In keeping with the principle of parsimony, we included up to five of these variables traditionally measured at CH4 flux measurement sites. Fuzzy sets were included representing the seasonal change and time of day. High Pearson correlation coefficients (r) of up to 0.97 achieved in the final analysis are indicative for the high performance of neural networks and their applicability as a gap-filling method for CH4 flux data time series. This novel approach which we show to be appropriate for CH4 fluxes is a step towards standardising CH4 gap-filling protocols.

Effect of Water Table Depth on Growth and Yield of Soybean Yudou 16

AbstractIn 2005–2006, a multilysimeter study was conducted to determine the effect of various water table depths (WTDs) (0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 3.0, 4.0, and 5.0 m) on the growth of soybean variety Yudou 16 in the transitional zone of northern semitropical and warm temperate climatic conditions of the Huaibei Plain, Anhui Province, China. In the experiment, precipitation was accounted for and WTD was controlled. The yield of Yudou 16 soybeans was greatest with a WTD of 2 m; yield decreased when the WTD was deeper or shallower than 2 m. From 0.2 through 2.0 m soybean yield increased rapidly with increasing WTD because shallow WTDs produced an oversupply of water in the root zone. From 2 through 5 m yield decreased slowly with increasing WTD under the experimental conditions. This was apparently because deeper WTDs could not compensate (through phreatic evaporation) for rainless periods of moisture stress during the growing season. When the constant WTD changes from 0.8 to 4.0 m, the yield is equal t...

Assessing the effects of water table depth on water use, soil salinity and wheat yield: Searching for a target depth for irrigated areas in the upper Yellow River basin

The irrigation districts of the upper Yellow River basin face a progressive reduction of water allocation and the need to apply water-saving practices due to increasing water scarcity. The adoption of such practices will lead to lower water tables, hopefully in conjunction with controlled soil salinity levels and improved crop yields. However, excessive water saving associated with excessive increase of the water table depth may decrease capillary rise and affect crop production. In view of understanding the related processes in Qingtongxia Irrigation District, the physically based agro-hydrological model, SWAP, was adopted to explore the response of soil water and solute dynamics, and crop yield to water table changes. With this purpose, SWAP was modified through the inclusion of a simplified crop growth module, a method of variable active-nodes, and a nonlinear osmotic head-dependent function for a better description of the effects of salinity stress on root water uptake. The model was calibrated and validated using wheat's experimental data from 2007 and 2008. Simulations of soil water content, salinity concentration, biomass, and crop yield fitted well with field observations. The calibrated model was then used to predict changes in crop yield, soil water dynamics and soil salinity considering scenarios with different groundwater depths and irrigation strategies. The present irrigation strategy favors salt leaching even when considering the increase of water table depth that results in small crop yield reduction (<6%) due to salt stress. The 80% and 60% reduced irrigation strategies led to increased soil salinity and, eventually, crop yield reductions of 6–14% and 13–21%, respectively, when the depth of the water table increased. A target groundwater depth of 1.0–1.5m is suggested to be optimal for wheat's growth season with the aim of maintaining crop yields under the present conditions.

Climate and groundwater effects on the establishment, growth and death of Prosopis caldenia trees in the Pampas (Argentina)

Semiarid woodlands dominated by Prosopis caldenia thrive at the dry edge of the Argentinean Pampas. Deforestation and increased precipitation have driven sustained water table level rise in the region that are likely to affect the dynamics of remnant woody vegetation patches. Here we analyze the effect of climate and groundwater level on the establishment, growth and death of P. caldenia located on lowland (current water table <0.5 m deep) and upland (current water table 8 m deep) positions within rolling sandy landscape. Standard dendrochronological techniques were applied on 98 cross sections and cores of P. caldenia trees. Results allowed us to estimated that trees in the lowland established a few years earlier than in the upland (1929 vs. 1936) and died between 1991 and 2002, while trees in higher positions are still alive. As a result of a faster growth in the lowland, maximum mean basal area increment took place earlier (1950s vs. 1990s) and achieved a higher mean value than in the upland (41.63 vs. 37.41 mm 2). While mean annual chronologies were not associated across stands, an opposite highly significant association was found for the mean growth trends suggesting long-term effects of water table depths on growth. We found a different association between mean annual growth and climate, with lowland trees showing a negative response to precipitation before and during the growing season, and upland trees displaying a positive response to summer rainfall inputs. Temperature at the end of the growing season had a positive effect in the lowland whereas temperature during the growing season had a positive effect in the upland. These results show how groundwater can induce diverging sensitivity of forest growth and survival to climate variability, enhancing growth at optimum depths (2–8 m in our study) but depressing it or even killing trees when it approaches the surface (<2 m in our study). Groundwater dynamic should be considered in forest management and conservation strategies in semiarid woodlands in Central Argentina.

Influence of water table level and soil properties on emissions of greenhouse gases from cultivated peat soil

A lysimeter method using undisturbed soil columns was used to investigate the effect of water table depth and soil properties on soil organic matter decomposition and greenhouse gas (GHG) emissions from cultivated peat soils. The study was carried out using cultivated organic soils from two locations in Sweden: Orke, a typical cultivated fen peat with low pH and high organic matter content and Majnegarden, a more uncommon fen peat type with high pH and low organic matter content. Even though carbon and nitrogen contents differ greatly between the sites, carbon and nitrogen density are quite similar. A drilling method with minimal soil disturbance was used to collect 12 undisturbed soil monoliths (50 cm high, O29.5 cm) per site. They were sown with ryegrass (Lolium perenne) after the original vegetation was removed. The lysimeter design allowed the introduction of water at depth so as to maintain a constant water table at either 40 cm or 80 cm below the soil surface. CO2, CH4 and N2O emissions from the lysimeters were measured weekly and complemented with incubation experiments with small undisturbed soil cores subjected to different tensions (5, 40, 80 and 600 cm water column). CO2 emissions were greater from the treatment with the high water table level (40 cm) compared with the low level (80 cm). N2O emissions peaked in springtime and CH4 emissions were very low or negative. Estimated GHG emissions during one year were between 2.70 and 3.55 kg CO2 equivalents m-2. The results from the incubation experiment were in agreement with emissions results from the lysimeter experiments. We attribute the observed differences in GHG emissions between the soils to the contrasting dry matter liability and soil physical properties. The properties of the different soil layers will determine the effect of water table regulation. Lowering the water table without exposing new layers with easily decomposable material would have a limited effect on emission rates.

Experimental wet heath translocation in Dorset, England

Heathland has become fragmented throughout its European range with many countries losing 60–90% of their heathland area during the 20th century. A small, isolated area of wet heathland within permitted ball clay workings in Dorset (England) was translocated in October 1993 to an engineered receptor cell fed by groundwater and direct precipitation in order to mitigate the otherwise total loss of the wet heath. The aims were to rescue the wet heathland and to re-establish a community type similar to the wet heath that originally occurred at the donor site prior to the recent development of vegetation communities and birch colonisation associated with drier conditions. Vegetation monitoring over 12 years up to 2005 indicated that the experimental translocation successfully fulfilled the aims for a period of 7 years when the hydrological regime of the receptor site was actively managed. There was development of a mosaic of wet heath and mire vegetation community types including Sphagnum lawns and open bog pools. However, when active management ceased, the receptor site became drier and species were lost. Multivariate analysis revealed a trajectory of progressive rapid chronological change during 1994 and 1995 followed by a period of relative stability between 1996 and 2000 which coincided with greater species density. Subsequently up to 2005, the plant community became less species-rich and the plant community reverted to a species structure similar to that which occurred in 1994/1995. The importance of hydrological regime for plant community structure was tested using fixed-quadrat data and the water level measurements made in the period 1995–1998. Canonical Correspondence Analysis (CCA) multivariate analysis revealed a hydrological gradient with a significant seasonal effect of water table depth in the first half of the year and close association of the least wet quadrat location and non-mire species. Overall, the results support the use of translocation as a means of rescuing wet heath habitat which would otherwise be lost due to change in land use. There is a risk of failure when translocating a complex ecosystem such as wet heath but ecological engineering provides an insight into defining the risk. Our results demonstrated that an ecologically acceptable outcome for a wet heath translocation can be achieved with careful design and implementation and sensitive management of the receptor site. However, it is essential to secure long-term hydrological and vegetation management in order to provide a sustainable outcome for long-term survival of a target wet heath community.

Change in runoff initiation probability over a severe drought in a peat soil – Implications for flowpaths

Severe drying of soils can lead to cracking and thus the generation of new hydrological pathways. In soils that show hydrophobic behaviour upon drying, it is possible that such flowpaths survive beyond the period of the drought that caused the initial cracking. Change in flowpaths in peat following severe droughts has been proposed as an explanation for long-term increases in DOC concentration leaving peat-covered catchments across the Northern Hemisphere With changes in climate making dry summers and summer drought more likely in the UK, this study aims to understand whether there have been long-term flowpath changes in a peat soil following a 1 in 33 year drought. The measure used by this study to analyse changes in the flowpaths present in peat soils is the probability of runoff initiation. The probability of runoff initiation represents a method for comparing the occurrence of runoff from the catchment in comparison to the precipitation inputs relative to the antecedent conditions of the catchment. The study examines 1674 rainfall events over a five year period before and after a severe drought and shows that the most important factor for controlling runoff initiation is the total amount of rainfall in any event and that the system is capacity rather than rate limited. The time of year is found to have a significant influence upon the probability of runoff initiation above and beyond the effect of water table depth and rainfall character. However, the study can find no persistent effect of severe drought beyond the period of drought itself, suggesting that, in terms of the factors investigated here, peat flowpaths are stable against changes in drought frequency and severity with climate change and cannot contribute to long-term changes in DOC runoff.

Sugarcane Morphological, Photosynthetic, and Growth Responses to Water-Table Depth

ABSTRACT High water tables threaten the sustainability of sugarcane (Saccharum spp.), the primary crop of Florida's Everglades Agricultural Area (EAA). The purpose of this study was to evaluate the effects of water-table depth on morphological characters, single-leaf net photosynthetic rate (Ps), and growth of sugarcane. In pot studies, single stools of sugarcane cultivar CP 80-1743 were grown at eight equally spaced water-table depths from 5 to 33 cm (2 to 13 in). Large-tiller number of CP 80-1743 increased by 0.2 for each cm (0.4 in) increase of water-table depth, and stalk diameter increased as water-table depth increased from 5 through 23 cm (2 through 9 in). In lysimeter studies, responses of two genotypes to periodic floods and several water-table depths were compared. Yields of genotype CP 95-1429 were not affected by water-table depth and CP 95-1429 had similar stalk numbers and diameters across water-depth treatments. Yields of genotype CP 95-1376 increased as water-table depth increased, and stalk numbers and diameters of CP 95-1376 also increased as water-table depth increased. Quantifying large tiller number and stalk diameter in sugarcane should facilitate identification of genotypes and agronomic practices with improved tolerance to shallow water-tables.