Multiscale Interdisciplinary Integration of Soil-Hydrology-Plant Interactions III: Posters
Presiding: P Wang, University of Maryland Center for Environmental Science; H Lin, Pennsylvania State University
H43B-01 1330h
Modeling the Effect of Compaction on the Soil Hydraulic Properties
Compaction affects the soil hydraulic properties, and consequently, has an important impact on rainfall-infiltration-runoff relationships. In this study, models are suggested that could quantify and predict the effect of compaction on the soil water retention curve (WRC) and the soil hydraulic conductivity function (HCF). Two expressions for the WRC are considered, and the relationships between their parameters and the bulk density of the compacted soil are determined. Two expressions were developed that predict the saturated hydraulic conductivity of compacted soils; the first is a general expression based on the Kozeny equation that requires information only on the bulk density; the second one exploits information contained in the WRC. One expression was suggested to predict the unsaturated HCF of compacted soils. The models were calibrated and validated against experimental data of soils at various levels of compaction. The relationships between the various parameters and the soil bulk density enable a relatively good prediction of the effect of compaction on the soil hydraulic properties. The relationship between the pore-size distribution index, and the coefficient of variation of the WRC, of the compacted soils was found to be similar to that previously found for a wide range of soil types. It is shown that the relationship between the power parameter in the expression for the HCF and, previously found to represent a large variety of soil types, remains valid also for compacted soils.
H43B-02 1330h
Nutrient Cycling in Riparian Soils and Sediments Bordering Cold Desert Streams and Lakes
Riparian zone processes are critical to whole watershed biogeochemistry, because hydrology links the material and energy budgets of aquatic and terrestrial ecosystems. In temperate watersheds, these riparian zones have been identified as biogeochemical "hot-spots" because of the increased microbial activity and biogeochemical exchanges between terrestrial and aquatic ecosystems. In the Antarctic Dry Valleys, riparian zones are crucial landscape features because of the scarcity of liquid water in this polar desert. Dry valley hydrological margins may therefore provide a model system for understanding physical and hydrological influences on microbial ecology and biogeochemistry. We report on our first season of field work investigating aquatic-terrestrial transition zones on the margins of 11 stream and lake systems in the dry valleys. Wetted zones extended 2-10 m from the edges of lotic and lentic systems. While capillary demand and surface evaporation drive a one-way flux of water through these zones, the scale of these transition zones is determined by the topography and physical characteristics of the surrounding soils. Nutrient concentrations and fluxes are influenced by both the hydrology and microbially mediated biogeochemical processes (e.g. denitrification). For example, nutrient concentrations are enriched near the distal boundary of the wetted fronts due to evapo-concentration of pore water in lake margin soils. Stream margin soils, in contrast, have low nutrient concentrations and appear to be flushed more regularly because of dynamic hydrologic boundary conditions. These trends in nutrient availability across aquatic-terrestrial transition zones structure distinct environments for microbial communities. Continuing work is addressing the functioning of the microbial communities and their role in controlling transformation and mobility of nitrogen in these wetted zones.
H43B-03 1330h
Scales and Uncertainties in Estimating Soil Carbon with STATSGO Database for Louisiana
The State Soil Geographic (STATSGO) database has been used in estimating soil carbon storage at regional and national scales. However, due to its coarse resolution (1:250,000), uncertainty is a problem that has been addressed by researchers when the database is applied at a finer scale. The Soil Survey Geographic (SSURGO) database at a scale of 1:24,000 apparently provides a better alternative, but the spatial data is unavailable for many areas across the nation. The primary goal of this study is to develop pedotransfer functions for Louisiana's carbon assessment using these two databases. The specific objectives of the study are to (1) compare soil carbon estimates between STATSGO and SSURGO spatially and statistically; (2) assess the uncertainty in carbon estimates by STATSGO particularly on hydric soils; and (3) identify attributes that are important for model prediction. The assessment on soil carbon at the depths from 0 to 25 and to 100 cm was conducted for Lincoln and West Baton Rouge Parishes. The compared soil attributes included a series of physical, chemical, and hydraulic properties. The results showed that not only did the two databases produce different soil carbon estimates based on their data attributes, but also the difference in estimates varied spatially across the landscape. The study demonstrated that GIS applications can be critical for improving accuracy of terrestrial carbon assessment.
H43B-04 1330h
Novel Soil Amendment Technology for Minimising Nutrient Losses From Pastures for the Protection of Water Bodies
The inevitable loss of P and DOC in runoff from pastures into water courses and water bodies poses a major environmental problem for industries such as dairy. We report a study of a novel approach to amending soils in dairy pastures. It is a test of the applicability to the field of the results of laboratory work that had shown that addition to soils of a water soluble polymer (Poly-DADMAC) - widely used as a coagulant in drinking water treatment - considerably enhanced the uptake by soils of anions, including phosphate. Its successful application in the field promises to provide a safe, easily-applied and relatively low-cost chemical as an soil amendment to restrain P and DOC in the soil against their loss downslope in runoff. Using a rainfall simulator to generate runoff, we show that most (on average >70%) of both the P and DOC that is lost from untreated pastures can be retained in the soil. It is only necessary to treat a buffer strip comprising 10% of the whole area in order to retain most of the P and DOC at a cost for polymer for one treatment of between $200 and $400/hectare of pasture. Whereas the effectiveness of the polymer treatment diminishes with time and was minimal after 85 days of treatment, the seasonality of rainfall in Southern Australia, where the research was conducted, means that most of the total year's losses of P and DOC can be restrained by one well-timed application in a normal year. Further application may be necessary in a wet year, but this aspect requires further research. When rainfall was exceptionally heavy, losses of P could not be contained by the treatment, although it remained effective in restraining DOC. The treatment did not enhance erosion and erosion losses could be decreased relative to untreated controls with low additions of polymer.
H43B-05 1330h
Role of Soils in Landscape Hydrology of a Forested Catchment
The value of detailed soil mapping includes an understanding of water flow paths and soil depth variation over the landscape. Mapping the fabric of soils over a catchment and characterizing soil layering helps the interpretations of the spatio-temporal organization of soil moisture, landscape-scale preferential flow pathways, and their relationships with catchment hydrology. We used this hydropedological approach to investigate soil moisture patterns at multiple depths in a 7.9-ha forested catchment in central Pennsylvania. A total of 73 sites were monitored from July to December 2004 using Time Domain Reflectometries, tensiometers, pizometers, thermocouples, observation wells, rain gauges, and a stream gauge. Soil distribution and topographic metrics were correlated with the observed soil moisture patterns to reveal the relationships with soil type, depth to bedrock, topographic wetness index, slope, precipitation, and stream discharge. Four main flow pathways downslope were identified in this V-shaped forested catchment, i.e., subsurface macropore flow, subsurface lateral flow at A-B horizon interface, return flow at footslope and toeslope, and flow at the soil-bedrock interface. There were complex interplays between soils and topography in this steep terrain. Time series data showed quick stream flow responses to precipitation forcing in the catchment, indicating the rapid movement of water within the catchment into the stream channel. We developed a conceptual model of the hillslope hydrology that elaborated the patterns of soil moisture distribution along the hillslope and within different soil profiles in the catchment. This conceptualization enhances the understanding and modeling of preferential flow dynamics at the catchment scale, particularly with regard to the role of detailed soil mapping and lateral flow in hillslope hydrology.
H43B-06 1330h
Measuring and Modeling Solute Transport in the Rootzone: Protecting the Receiving Water Environments of the Coral Atolls of Tonga
Intensification of agriculture on the raised coral atolls of the Tongan archipelago, notably through squash-pumpkin production, has lead to increased use of agrichemicals. Agrichemicals, both fertilisers and pesticides, pose a risk to these fragile environments. Sustainable land-management practices are needed for small-island developing states. On Tongatapu, solutes leaving the rootzone of the squash can rapidly find their way to the underlying freshwater lenses. These lenses are hydraulically linked to the internal lagoon, and the fringing reefs. We have used buried, non-suction fluxmeters to monitor both the quantity and quality of drainage leaving the rootzone of squash. Fertiliser is traditionally applied at planting. During establishment of the squash in 2003, some 350 mm of rain fell, with 70 % of this leaving the rootzone of this permeable soil as drainage. The concentration of nitrate-N in the drainage water was measured at around 50 mg-N/L. All of the initial fertiliser dressing had been lost, along with N mineralised from the plowed-in grass. Pesticides are needed in humid tropical environments to control weeds, pests and diseases. These chemicals can leach though the rootzone to contaminate receiving waters. We modeled the transport and fate of the presticides used in squash production, and we developed a Decision Support Tool (DST). Our DST can be used to select the best pesticides for local conditions, to tailor practices for minimising leaching losses below the rootzone, and to avoid the build-up of residues in the soil. This project, funded by the European Union and NZAID, took a multi-disciplinary approach through measurement and modeling protocols. Our DST enabled us to engage the wider community and stakeholders. There has been increased awareness of the impacts and risks associated with productive land management in the fragile hydrological environments of this small-island developing state.
http://www.croppro.alterra.nl
H43B-07 1330h
Heavy Metal Displacement in Chelate-Assisted Phytoremediation of Biosolids Soil
Heavy metals in biosolids (sewage sludge) applied to land contaminate the soil. Phytoremediation, the use of plants to clean up toxic heavy metals, might remove them. Chelating agents are added to soil to solubilize the metals for enhanced phytoextraction. Yet no studies follow the displacement and leaching of heavy metals in soil with biosolids following solubilization with chelates. The objective of this work was to determine the mobility of heavy metals, as affected by a chelate, in soil (Haynie very fine sandy loam) from a 25-year old sludge farm. Soil columns (105 cm long; 39 cm in diameter) either had a plant (hybrid poplar; Populus deltoides Marsh. x P. nigra L.) or no plant. When the poplars were 144 days old, the tetrasodium salt of the chelating agent EDTA (ethylenediamine-tetraacetic acid) was irrigated onto the soil at a rate of 1 g per kg of soil. Drainage water, soil, and plants were analyzed for three toxic heavy metals (Cd, Ni, Pb) and four essential heavy metals (Cu, Fe, Mn, Zn). Without EDTA, concentrations of the seven heavy metals in the leachate from columns with or without plants were low or below detection limits. With or without plants, the EDTA mobilized all heavy metals and increased their concentration in drainage water. Without plants, the concentrations of Cd, Cu, Fe, Pb, and Zn in the leachate from columns with EDTA were above drinking-water standards. (There is no drinking-water standard for Ni.) The presence of poplar plants in the soil reduced the concentrations of Cu, Fe, and Zn in the leachate so it fell within drinking-water standards. Concentrations of Cd and Pb in the leachate remained above drinking-water standards with or without plants. At harvest (124 days after the EDTA application), total concentration of each heavy metal in the soil at different depths in the columns with EDTA was similar to that in the columns without EDTA. The chelate did not affect the concentration of heavy metals in the roots, stems, or leaves. However, the wood, which contains the xylem, from plants grown with EDTA had a higher concentration of Ni and Pb than did wood from plants grown with no EDTA. The results showed that heavy metals in soil with sludge treated with EDTA could contaminate ground water, even in the presence of plant roots. (This research is part of the dissertation of M.S. Liphadzi, who was supported by a Fulbright Fellowship.)
H43B-08 1330h
Recharge-Driven Sulfur Cycling and its Role in Natural Attenuation in an Alluvial Aquifer Riparian Zone Contaminated With Landfill Leachate
In an alluvial aquifer riparian zone contaminated with leachate from an unlined municipal landfill, recharge represented a possible mechanism for natural attenuation. This study, at the USGS Toxic Substances Hydrology Program Norman Landfill research site in Oklahoma, examined whether recharge is supplying electron acceptors to stimulate microbiological activity in the transition zone between leachate and recharge water, facilitating biodegradation of organic compounds in the leachate. Water samples were collected monthly from May 1998 to May 2000 at 15-cm depth intervals in the top 2 m of the aquifer at contaminated and uncontaminated sites. At both sites, the temporal concentration-depth profiles showed a seasonal cycle of dissolved sulfate production and loss within the aquifer. The average concentration of dissolved sulfate present within the top 1 to 2 m of aquifer was 2.2 mM, with maximum concentrations of 15 mM. Sulfides were oxidized near the water table by dissolved oxygen in the recharge water, and were also oxidized at depths up to 1 meter below the water table, possibly by colloidal iron transported vertically in the recharge water. Sulfate concentrations then declined, due to root uptake by phreatophytes and microbial reduction in the mixing zone between the recharge water and the methanogenic leachate plume. Estimated net sulfate reduction rates (reduction exceeding oxidation) in the groundwater ranged from 0.007 - 0.61 mmol L-1 d-1 (bulk rates, calculated between sampling periods, over depth intervals ranging from 0.45 - 1.75 m). Higher rates of sulfate reduction followed periods of little or no recharge at both sites. Numerical modeling with VS2DTI, a variably saturated aquifer solute transport model, helped to quantify the relative importance of sulfate reduction and transpiration root uptake on sulfate concentrations in the shallow aquifer. These results suggest that sulfate reduction associated with infiltration of recharge can be a significant contribution to natural attenuation processes in similar alluvial plain riparian environments.
H43B-09 1330h
Natural Advection In Porous Media: Transfer of Soil Moisture Beneath a Tree
At a suburban site in Atlanta, Georgia, soil temperature and moisture data were acquired at different soil depths over a six-week period. These measurements were made in support of an experiment to study the periodic response of sweetgum trees to transpiration and groundwater availability. Given that the temperature and water content was known at different depths, the vertical energy and moisture balance of the soil could be observed as a function of depth. For the numerical study of natural advective heat transfer in porous media, researchers at Clark Atlanta University have developed a two-dimensional finite element numerical model for transient or steady state analysis of coupled processes of advective and conductive heat transfers in a porous continuum and advective groundwater flow in a saturated porous medium. The governing equations consist of a set of coupled, quasilinear partial differential equations that are based on the physical laws of fluid continuity and conservation of momentum and energy. The numerical simulation results are compared with experimental data in the vertical. The results show that the numerical simulation of advective heat transfer of water in porous media agrees well with the experimental data. The results of the advective groundwater simulation are used to explain the distortion of the diurnal response of sweetgum trees to evapotranspirative pumping.
H43B-10 1330h
Nitrate Mobility in Unsaturated Soil Affected by the Presence of Different Clay Mineral Types
Transient unsaturated soil column experiments were conducted to assess the magnitude of the anion adsorption/exclusion effects on nitrate mobility due to the type of clay mineral present. In all tests, a manufactured soil was employed that was comprised of 90 percent by weight medium sand and 10 percent by weight clay mineral (kaolin, illite, or montmorillonite). Prior to initiating an experiment, the soil within the column was completely dry. The Nitrate-N solution concentration injected at the soil column inlet was 200 mg/L. During testing, the moisture content at the soil column inlet was maintained at a constant value. All tests were replicated to ensure accuracy of results. For the 10 percent kaolin tests, soil solution Nitrate-N concentrations greater than 200 mg/L near the soil column inlet, and soil solution Nitrate-N concentrations less than 200 mg/L at the wetting front edge indicate that anion adsorption is an important process impacting nitrate mobility when kaolin is the dominant clay mineral type present. The 10 percent illite tests showed Nitrate-N concentrations less than 200 mg/L near the column inlet and Nitrate-N concentrations of 800 mg/L at the wetting front edge, thereby providing strong evidence that anion exclusion is an important transport process affecting nitrate mobility in soils having illite as the dominant clay mineral. The 10 percent montmorillonite test results also had Nitrate-N concentrations less than 200 mg/L near the column inlet, but with greater Nitrate-N concentrations of 1200 mg/L at the wetting front edge, thereby implying, that with montmorillonite the dominant clay mineral, there is an even stronger anion exclusion impact on nitrate mobility. Consequently, the overall test results suggest that either anion adsorption or anion exclusion can significantly impact nitrate mobility in unsaturated soil based on the clay mineralogy present. These findings may have important implications with regard to agricultural fertilizer application, particularly when initial soil conditions are relatively dry.
H43B-11 1330h
Impact of vegetation root distribution and soil moisture on evaporation simulations
An accurate description of root distributions and soil moisture regimes has great impacts on evapotranspiration simulations, leading to difference in surface energy partitioning. We have designed three scenarios to test the effects of different parameterization schemes of root distributions on energy flux partitioning (i.e. change in Bowen ratio) using the off-line NCAR CLM2.0 land-surface model. We use the data measured in a coniferous forest in Alaska (63° 53' N 145° 44' W) in the 2002 summer (from June 20 to August 10, 2002). Compared with the fluxes measured over the black spruce forest, the uniform root distribution in our simulations leads to ~12% less latent heat fluxes and ~15% higher sensible heat fluxes. Because the soil moisture increases with depth in our site, the uniform root distribution may cause the reduced transpiration in the root layer. Also, the transpiration rates are limited in the upper layer by the lower soil moisture even though there is an increased root density. The exponential root distribution leads to ~16% higher latent heat fluxes and ~15% lower sensible heat fluxes. The higher latent heat flux may be due to the higher soil moisture content that is set below 40 cm depth with a higher root density in this model than the real root density for the black spruce. The triangular root distribution gives a reasonable result even though the latent heat flux is 6% higher than measurements and sensible heat flux is 8% lower than measurements. The difference could be due to the other factors that control energy partitioning or due to the discrepancy between the real root distribution and the triangular root distribution. It is expected that these results have large implications on boundary layer developments. For example, the uniform root distribution could lead to a drier and higher planetary boundary layer while the exponential root distribution could cause a moister and lower planetary boundary layer relative to the real one.
H43B-12 1330h
Nitrogen Dynamics in a Northeast Forest Ecosystem - Spatial and Temporal Patterns in Stream Water and Soil Solution Chemistry.
Distinct patterns in soil solution and stream water chemistry are manifested across landscape position at the Hubbard Brook Experimental Forest (HBEF) in the White Mountains of New Hampshire. The objective of this study was to examine the spatial and temporal patterns in the concentrations and fluxes of nitrogen (N) species and dissolved organic carbon (DOC) in soil solutions and stream water along an elevational gradient (525-775m) at the HBEF. A 12 year record (1992-2003) of measurements of soil water and stream chemistry in Watershed 6 (W6), the biogeochemical reference watershed at the HBEF, were used in this analysis. Solutions were largely comprised of NO3- and DON, as NH4+ concentrations were generally low particularly in mineral soil solutions and stream water. Dissolved organic N and DOC concentrations were elevated in the high elevation spruce-fir-white birch portion of the watershed, while NO3- was the dominate N species in the lower elevation hardwood portion of the watershed. Surprisingly, seasonal patterns of NO3- in soil leachate were not as strong as one might expect given the importance and availability of NO3- as a plant and microbial nutrient. However, distinct seasonal patterns were evident for NO3- in stream water, suggesting the importance of hydrological flow paths and/or in-stream processes in regulating watershed NO3- loss. Understanding patterns of N and DOC dynamics in stream and soil solution is critical for evaluating the response of forest ecosystems to changes in the deposition of anthropogenic N and the potential for nutrient retention within terrestrial ecosystems.