bluuebunny/crossref_metadata_2025 huggingface dataset:
Quasi-M-matrix Anisotropic Darcy-Flux Finite-volume Approximation for General Grids and MPFA Decoupling Analysis
Authors: Edwards Michael G. , Zheng Hongwen
Published: February 2011

This paper focuses on flux-continuous general tensor pressure equation approximation for strongly anisotropic media. Earlier methods have focused on single-parameter pointwise schemes which are effective for smaller anisotropy ratios. However they have conditional M-matrices depending on the strength of the tensor cross-terms. For strongly anisotropic full tensor cases, the methods can yield pressure solutions with severe spurious oscillations. The spurious oscillations are shown to be caused by decoupling on both structured and unstructured grids. Flow results and convergence tests confirm the decoupling theory.

Anisotropic flux-continuous full pressure continuity formulations are presented. The formulations lead to improved discretization schemes for the complete range of elliptic tensors. The new schemes are shown to be positive definite, have quasi-positive M-matrices for full-tensor fields with large anisotropy ratios, and compute well resolved solutions that are essentially free of spurious oscillations.

Anisotropic Darcy-flux schemes are presented on structured, unstructured and anisotropy favoring grids. The methods are applied to a range of geological test cases and grid-types including arbitrarily high anisotropy ratio in two and three dimensions.
Mobilization of Trace Metals and Inorganic Compounds during Resuspension of Anoxic Sediments from Trepangier Bayou, Louisiana
Authors: Shipley Heather J. , Gao Yan , Kan Amy T. , Tomson Mason B.
Published: February 2011

The release of trace metals (Mn, Ni, Co, Cu, Zn, Pb, and Cd) and inorganic compounds (As) from initially anoxic Trepangier Bayou sediments, Louisiana and the sources of the released metals were investigated. After 1 to 2 d aeration, significant amounts of trace metals (Mn, Zn, Cd, Ni, and Co) were released to the aqueous phase with increased acidity, primarily due to the oxidation of acid‐volatile sulfide and ferrous iron and iron sulfide minerals. The addition of a bacterial inhibitor, NaN3, to the Trepangier sediment during resuspension inhibited metal release, suggesting that microbial catalysis can regulate metal mobilization during sediment resuspension. In a well buffered system, oxidation of iron sulfides alone did not appear to induce trace metal release. Moreover, when Trepangier sediment was resuspended in anoxic conditions at neutral pH, <1% of the trace metal content was released, whereas a significant release of metal was observed under acidic anoxic conditions. Although oxidation of iron sulfide minerals is an essential prerequisite for the release of Zn, Co, Cd, and Ni, carbonates and oxides also play a role. The trace metals and inorganic compounds investigated could be classified into three groups according to their release characteristics: (i) Mn, Zn, Cd, Ni, and Co; (ii) Fe, Pb, and As; and (iii) Cu. The groupings appeared to depend on the sources of compounds and their relative affinity, after oxidation, to iron oxyhydroxides or organic matter.
Nitrogen Fertilizer Replacement Value of Cattle Slurry in Grassland as Affected by Method and Timing of Application
Authors: Lalor S. T. J. , Schröder J. J. , Lantinga E. A. , Oenema O. , Kirwan L. , Schulte R. P. O.
Published: February 2011

Slurry application with methods such as trailing shoe (TS) results in reduced emissions of ammonia (NH3) compared with broadcast application using splashplate (SP). Timing the application during cool and wet weather conditions also contributes to low NH3 emissions. From this perspective, we investigated whether reduced NH3 emissions due to improved slurry application method and timing results in an increase in the nitrogen (N) fertilizer replacement value (NFRV). The effects of application timing (June vs. April) and application method (TS vs. SP) on the apparent N recovery (ANR) and NFRV from cattle slurry applied to grassland were examined on three sites over 3 yr in randomized block experiments. The NFRV was calculated using two methods: (i) NFRVN based on the ANR of slurry N relative to mineral N fertilizer; and (ii) NFRVDM based on DM yield. The TS method increased the ANR, NFRVN, and NFRVDM compared with SP in the 40‐ to 50‐d period following slurry application by 0.09, 0.10, and 0.10 kg kg−1, respectively. These values were reduced to 0.07, 0.06, and 0.05 kg kg−1, respectively, when residual harvests during the rest of the year were included. The highest NFRVDM for the first harvest period was with application in April using TS (0.30 kg kg−1), while application in June with SP had the lowest (0.12 kg kg−1). The highest NFRVDM for the cumulative harvest period was with application in April using TS (0.38 kg kg−1), while application in June with SP had the lowest (0.17 kg kg−1). Improved management of application method, by using TS instead of SP, and timing, by applying slurry in April rather than June, offer potential to increase the NFRVDM of cattle slurry applied to grassland.
Modeling Liquid Distribution in Soil after Pocket Injection
Authors: Wu Binxin , Chen Ying
Published: February 2011

Information on liquid distribution after injection of liquid manure is important to the evaluation of injection methods and the design of injection tools. A two‐dimensional numerical model was developed to predict liquid distribution in the soil around a soil pocket. Model outputs are the lateral spread (L), vertical thickness (T), and cross‐sectional area (A) of the liquid infiltration zone. Values of L do not vary with injection depth, whereas T and A increase with the injection depth. These model outputs are sensitive to effective saturated soil content (the difference between saturated and initial water contents). At greater effective saturated water content, values of L, T, and A are lower. Values of L vary from 0.13 to 0.23 m, values of T vary from 0.09 to 0.19 m for injection depths from 0.05 to 0.15 m, and values of A vary from 0.009 to 0.030 m2 The model results were compared with field measurements taken from six forage fields with sandy loam and clay soils. The model better predicts L than T and A. The relative average error between the predictions and field measurements vary from 10.3 to 101.9%.
Environmental and Economic Comparisons of Manure Application Methods in Farming Systems
Authors: Rotz C. A. , Kleinman P. J. A. , Dell C. J. , Veith T. L. , Beegle D. B.
Published: February 2011

Alternative methods for applying livestock manure to no‐till soils involve environmental and economic trade‐offs. A process‐level farm simulation model (Integrated Farm System Model) was used to evaluate methods for applying liquid dairy (Bos taurus L.) and swine (Sus scrofa L.) manure, including no application, broadcast spreading with and without incorporation by tillage, band application with soil aeration, and shallow disk injection. The model predicted ammonia emissions, nitrate leaching, and phosphorus (P) runoff losses similar to those measured over 4 yr of field trials. Each application method was simulated over 25 yr of weather on three Pennsylvania farms. On a swine and cow‐calf beef operation under grass production, shallow disk injection increased profit by $340 yr−1 while reducing ammonia nitrogen and soluble P losses by 48 and 70%, respectively. On a corn (Zea mays L.)‐and‐grass‐based grazing dairy farm, shallow disk injection reduced ammonia loss by 21% and soluble P loss by 76% with little impact on farm profit. Incorporation by tillage and band application with aeration provided less environmental benefit with a net decrease in farm profit. On a large corn‐and‐alfalfa (Medicago sativa L.)‐based dairy farm where manure nutrients were available in excess of crop needs, incorporation methods were not economically beneficial, but they provided environmental benefits with relatively low annual net costs ($13 to $18 cow−1). In all farming systems, shallow disk injection provided the greatest environmental benefit at the least cost or greatest profit for the producer. With these results, producers are better informed when selecting manure application equipment.
Effects of Watershed Configuration and Composition on Downstream Lake Water Quality
Authors: Gémesi Zsolt , Downing John A. , Cruse Richard M. , Anderson Paul F.
Published: February 2011

We evaluated the relationships between landscape characteristics and lake water quality in receiving waters by regressing four water quality responses on landscape variables that were measured for whole watersheds and three different buffer distances (30, 60, and 120 m). Classical percolation theory was used to conceptualize nutrient pathways and to explain nonlinear responses. The response variables were total nitrogen (TN), total phosphorus (TP), chlorophyll‐a (Chl‐a), and Secchi transparency (SD). Landscape data were obtained from satellite image‐derived maps of 130 watersheds in Iowa using geographic information systems software. We developed regression models with a stepwise protocol selecting the optimal number of significant explanatory variables. Configuration variables such as contagion, the cohesion of cropland and urban land, and the aggregation index of forest were very important and more important than variables assessing landscape composition (e.g., percentage farmland). Whole watershed models predicted between 15 and 67% of the variability in TN, TP, Chl‐a, and SD. Proximity‐explicit data offered only slightly improved statistical power over land cover data derived from the entire watershed for variables TN, Chl‐a, and SD, but not for TP.
Chemical Residence Time and Hydrological Conditions Influence Treatment of Fipronil in Vegetated Aquatic Mesocosms
Authors: Kröger Robert , Moore Matthew T.
Published: February 2011

Fipronil, a phenyl‐pyrazole insecticide, is often used in rice (Oryza sativa L.) production agriculture, with elevated runoff concentrations and loads having potential toxicological effects on downstream aquatic environments. This study evaluated two species of aquatic plants—broadleaf cattail (Typha latifolia L.) and powdery alligator‐flag (Thalia dealbata Fraser ex Roscoe)—placed in series against a nonvegetated mesocosm in reducing concentrations and loads of fipronil, and associated metabolites. Vegetation type and hydrological condition (inundated vs. dry) were treatment effects used for comparison. The vegetated mesocosms significantly reduced higher loads and concentrations of fipronil, fipronil sulfone, and sulfide in both inundated and dry hydrological conditions over nonvegetated mesocosms. Under inundation conditions, vegetated mesocosms reduced >50% of influent fipronil concentrations and between 60 and 70% of fipronil loads, which was significantly higher than the dry conditions (10–32% concentration and load). These results show that agricultural management strategies using ephemeral aquatic zones, such as drainage ditches, can be optimized to couple chemical applications with vegetation presence and hydrology to facilitate the reduction in chemical waste loads entering downstream aquatic ecosystems. Such reduction is critical for use with fipronil, where negative impacts have been demonstrated with several nontarget species.
Effect of Surface Incorporation of Broiler Litter Applied to No‐Till Cotton on Runoff Quality
Authors: Adeli A. , Shankle M.W. , Tewolde H. , Brooks J.P. , Sistani K.R. , McLaughlin M.R. , Rowe D.E.
Published: February 2011

Surface application of broiler litter to no‐till cotton could lead to degradation of water quality. Incorporation of broiler litter into the top surface soil (0.05 m) could alleviate this risk. A 2‐yr field study was conducted on a silt loam upland soil to determine the effect of incorporation of broiler litter into the soil surface on nutrient and bacterial transport in runoff. The experimental design was a randomized complete block with four treatments and three replications. Treatments were (i) unfertilized control; (ii) surface‐applied broiler litter at 7.8 Mg ha−1 without incorporation; (iii) surface‐applied broiler litter at 7.8 Mg ha−1 with immediate incorporation; and (iv) inorganic fertilizer N (urea ammonium nitrate, 32% N) and inorganic fertilizer P (triple superphosphate) at the recommended rate. Phosphorus was surface applied at 25 kg ha−1 and N was injected at 101 kg ha−1 into the soil using a commercial liquid fertilizer applicator. Runoff was collected from small runoff plots (2.4 m by 1.6 m) established at the bottom side of main plots (13.7 m by 6.0 m). Incorporation of broiler litter reduced total N (TN), NO3–N, water soluble P (WSP), and total P (TP) concentrations in runoff by 35, 25, 61, and 64%, respectively, and litter‐associated bacteria by two to three orders of magnitude compared with unincorporated treatment. No significant difference in total suspended solids (TSS) in runoff was obtained between incorporated and unincorporated treatments. Incorporation of broiler litter into the surface soil in the no‐till system immediately after application minimized the potential risk for surface nutrient losses and bacteria transport in runoff.
Removing Solids Improves Response of Grass to Surface‐Banded Dairy Manure Slurry: A Multiyear Study
Authors: Bittman S. , Hunt D.E. , Kowalenko C.G. , Chantigny M. , Buckley K. , Bounaix F.
Published: February 2011

Removing solids from slurry manure helps balance nutrients to plant needs and may increase soil infiltration rate to reduce loss of ammonia. The long‐term effects of applying the separated liquid fraction (SLF) of dairy slurry with surface banding applicators are not well known. This 6‐yr study compared the yield, N recovery, and stand persistence of tall fescue (Festuca arundinacea Schreb.) receiving SLF at 300 (SLF300) and 400 (SLF400) kg ha−1 yr−1 of total ammoniacal N (TAN); whole dairy slurry (WS) at 200 (WS200), 300 (WS300), and 400 (WS400) kg TAN ha−1 yr−1; and mineral fertilizer at 300 kg N ha−1 yr−1 The slurries were applied four times per year by surface banding, a technique that reduces ammonia emission and canopy contamination. Grass yield and N uptake were significantly higher for SLF300 than WS300 at equivalent rates of TAN. At similar total N, yield and N uptake were much greater for SLF than WS (2 Mg DM ha−1 and 75 kg N ha−1, respectively). Apparent total N recovery was 63% greater for SLF300 than WS300 due to less ammonia loss and less immobile N. The apparent recovery of total N was 31% higher for Fert300 than for SLF300. Yield and N uptake for SLF300 and WS300 were similar in Harvests 1 and 4, but SLF had higher values under hot and dry conditions in Harvests 2 and 3. Using SLF rather than WS will increase crop yield and allow higher application volumes near barns, which will reduce hauling costs.
Swine Manure Injection with Low‐Disturbance Applicator and Cover Crops Reduce Phosphorus Losses
Authors: Kovar J.L. , Moorman T.B. , Singer J.W. , Cambardella C.A. , Tomer M.D.
Published: February 2011

Injection of liquid swine manure disturbs surface soil so that runoff from treated lands can transport sediment and nutrients to surface waters. We determined the effect of two manure application methods on P fate in a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] production system, with and without a winter rye (Secale cereale L.)–oat (Avena sativa L.) cover crop. Treatments included: i) no manure; ii) knife injection; and iii) low‐disturbance injection, each with and without the cover crop. Simulated rainfall runoff was analyzed for dissolved reactive P (DRP) and total P (TP). Rainfall was applied 8 d after manure application (early November) and again in May after emergence of the corn crop. Manure application increased soil bioavailable P in the 20‐ to 30‐cm layer following knife injection and in the 5‐ to 20‐cm layer following low‐disturbance injection. The low‐disturbance system caused less damage to the cover crop, so that P uptake was more than threefold greater. Losses of DRP were greater in both fall and spring following low‐disturbance injection; however, application method had no effect on TP loads in runoff in either season. The cover crop reduced fall TP losses from plots with manure applied by either method. In spring, DRP losses were significantly higher from plots with the recently killed cover crop, but TP losses were not affected. Low‐disturbance injection of swine manure into a standing cover crop can minimize plant damage and P losses in surface runoff while providing optimum P availability to a subsequent agronomic crop.
Solubilization of Mixed Polycyclic Aromatic Hydrocarbons through a Rhamnolipid Biosurfactant
Authors: Yu Hui , Huang Guohe , Wei Jia , An Chunjiang
Published: February 2011

The solubilization of phenanthrene (PHE) and pyrene (PYR) by rhamnolipid biosurfactant was systematically investigated. The solubilities of both polycyclic aromatic hydrocarbons (PAHs) were increased linearly with the biosurfactant concentration at above critical micelle concentration. A competitive effect was observed between PHE and PYR. The solubility of PHE in a mixed system was lower than that in a single PAH system, whereas the solubility of PYR in a mixed system was enhanced. This is because the hydrophobicity of PYR is higher than that of PHE, so PYR is favored in the competitive solubilization. The combined effect of biosurfactant and dissolved organic matter (DOM) on PAH solubilization was also examined. Two kinds of DOM (derived from soil and from compost) were used. There was an obvious enhancement of solubility for PHE and PYR in systems with concurrence of DOM and biosurfactant compared with systems with only DOM or biosurfactant; however, the enhancement in the mixed system was less than their additive. This could be explained as the formation of a DOM–biosurfactant complex. In addition, the solubility enhancement of PAHs in a compost–DOM system was higher than that in a soil–DOM system. This could be explained as functional group differences of two DOM types.
Quantifying Phosphorus Retention and Release in Rivers and Watersheds Using Extended End‐Member Mixing Analysis (E‐EMMA)
Authors: Jarvie Helen P. , Neal Colin , Withers Paul J.A. , Baker David B. , Richards R. Peter , Sharpley Andrew N.
Published: February 2011

Extended end‐member mixing analysis (E‐EMMA) is presented as a novel empirical method for exploring phosphorus (P) retention and release in rivers and watersheds, as an aid to water‐quality management. E‐EMMA offers a simple and versatile tool that relies solely on routinely measured P concentration and flow data. E‐EMMA was applied to two river systems: the Thames (U.K.) and Sandusky River (U.S.), which drain similar watershed areas but have contrasting dominant P sources and hydrology. For both the Thames and Sandusky, P fluxes at the watershed outlets were strongly influenced by processes that retain and cycle P. However, patterns of P retention were markedly different for the two rivers, linked to differences in P sources and speciation, hydrology and land use. On an annual timescale, up to 48% of the P flux was retained for the Sandusky and up to 14% for the Thames. Under ecologically critical low‐flow periods, up to 93% of the P flux was retained for the Sandusky and up to 42% for the Thames. In the main River Thames and the Sandusky River, in‐stream processes under low flows were capable of regulating the delivery of P and modifying the timing of delivery in a way that may help to reduce ecological impacts to downstream river reaches, by reducing ambient P concentrations at times of greatest river eutrophication risk. The results also suggest that by moving toward cleaner rivers and improved ecosystem health, the efficiency of P retention may actually increase.
Interactions between Soil Texture and Placement of Dairy Slurry Application: I. Flow Characteristics and Leaching of Nonreactive Components
Authors: Glæsner Nadia , Kjaergaard Charlotte , Rubæk Gitte H. , Magid Jakob
Published: February 2011

Land application of manure can exacerbate nutrient and contaminant transfers to the aquatic environment. This study examined the effect of injecting a dairy cattle (Bos taurus L.) manure slurry on mobilization and leaching of dissolved, nonreactive slurry components across a range of agricultural soils. We compared leaching of slurry‐applied bromide through intact soil columns (20 cm diam., 20 cm high) of differing textures following surface application or injection of slurry. The volumetric fraction of soil pores >30 μm ranged from 43% in a loamy sand to 28% in a sandy loam and 15% in a loam‐textured soil. Smaller active flow volumes and higher proportions of preferential flow were observed with increasing soil clay content. Injection of slurry in the loam soil significantly enhanced diffusion of applied bromide into the large fraction of small pores compared with surface application. The resulting physical protection against leaching of bromide was reflected by 60.2% of the bromide tracer was recovered in the effluent after injection, compared with 80.6% recovery after surface application. No effect of slurry injection was observed in the loamy sand and sandy loam soils. Our findings point to soil texture as an important factor influencing leaching of dissolved, nonreactive slurry components in soils amended with manure slurry.
Physical, Chemical, and Mineralogical Characteristics of a Reservoir Sediment Delta (Lake Powell, USA) and Implications for Water Quality during Low Water Level
Authors: Wildman Richard A. , Pratson Lincoln F. , DeLeon Michael , Hering Janet G.
Published: February 2011

Lake Powell is a large reservoir in Utah and Arizona that has experienced large changes in water level during a recent drought. As a first step in assessing the connection between hydrologic and chemical changes at Lake Powell, we characterized the particle size and solid‐phase bulk concentrations for 31 elements and 25 minerals in sediment from the inflow region and some shoreline locations by using laser diffractometry, X‐ray fluorescence, elemental analysis, and X‐ray diffraction. Our results are consistent with previous results that show a negative correlation between particle size and concentrations of most elements and most minerals other than quartz and some feldspars. In our samples, however, solid‐phase iron, rather than particle size or organic carbon, is the best predictor variable for the solid‐phase concentrations of elements and minerals. Sediment characteristics vary on a scale of tens of kilometers, with fine sediment that is enriched in trace elements nearer to the dam. These trends allow formulation of an algorithm for determining a water‐level threshold below which sediment resuspension may alter water chemistry in a generic reservoir with a long and narrow sediment delta.
Ambient Endotoxin Concentrations and Assessment of Offsite Transport at Open‐Lot and Open‐Freestall Dairies
Authors: Dungan Robert S. , Leytem April B.
Published: February 2011

Endotoxins are derived from gram‐negative bacteria and are a potent inducer of inflammatory reactions in the respiratory tract when inhaled. To assess daily fluctuations of airborne endotoxin and their potential for transport from dairies, endotoxin concentrations were monitored over an 8‐h period at upwind (background) and downwind (5 m from edge of dairy) locations on three separate days at two dairies. The dairies consisted of an open‐lot or an open‐freestall production system, both of which were stocked with 10,000 milking cows. Upwind concentrations were stable throughout the sampling period, averaging between 1.2 and 36.8 endotoxin units (EU) m−3, whereas downwind concentration averages ranged from 179 to 989 EU−3 Downwind endotoxin concentrations increased with wind speed, animal activity, and lot management practices, resulting in concentrations up to 136‐fold higher than upwind concentrations. An area‐source model was used to predict downwind ground‐level endotoxin concentrations at distances up to 2000 m from the production facilities. Predicted concentrations decreased with distance and reached background levels within 500 to 2000 m, depending on the source emission rate and meteorological conditions.
Biochar Incorporation into Pasture Soil Suppresses in situ Nitrous Oxide Emissions from Ruminant Urine Patches
Authors: Taghizadeh‐Toosi Arezoo , Clough Tim J. , Condron Leo M. , Sherlock Robert R. , Anderson Craig R. , Craigie Robin A.
Published: February 2011

Nitrous oxide (N2O) emissions from grazing animal excreta are estimated to be responsible for 1.5 Tg of the total 6.7 Tg of anthropogenic N2O emissions. This study was conducted to determine the in situ effect of incorporating biochar, into soil, on N2O emissions from bovine urine patches and associated pasture uptake of N. The effects of biochar rate (0–30 t ha−1), following soil incorporation, were investigated on ruminant urine‐derived N2O fluxes, N uptake by pasture, and pasture yield. During an 86‐d spring‐summer period, where irrigation and rainfall occurred, the N2O fluxes from 15N labeled ruminant urine patches were reduced by >50%, after incorporating 30 t ha−1 of biochar. Taking into account the N2O emissions from the control plots, 30 t ha−1 of biochar reduced the N2O emission factor from urine by 70%. The atom% 15N enrichment of the N2O emitted was lower in the 30 t ha−1 biochar treatment, indicating less urine‐N contributed to the N2O flux. Soil NO3−‐N concentrations were lower with increasing biochar rate during the first 30 d following urine deposition. No differences occurred, due to biochar addition, with respect to dry matter yields, herbage N content, or recovery of 15N applied in herbage. Incorporating biochar into the soil can significantly diminish ruminant urine‐derived N2O emissions. Further work is required to determine the persistence of the observed effect and to fully understand the mechanism(s) of the observed reduction in N2O fluxes.
Errors in Modeling Carbon Turnover Induced by Temporal Temperature Aggregation
Authors: Weihermüller L. , Huisman J.A. , Graf A. , Herbst M. , Vereecken H.
Published: February 2011

Modeling of C turnover is a common tool for the prediction of C stocks and CO2 efflux. It is well recognized that the choice of the input data (e.g., C pool sizes, hydraulic parameters, atmospheric boundary conditions) determines the outcome of these prediction. Temperature is known to be one of the most important driving factors and it varies in a range of temporal scales. Typically, the time discretization of most models is flexible and can range from minutes to months. However, the implications of variable time discretization for predicted soil C turnover are seldom discussed. In this study, we demonstrated that averaging of input temperature data will lead to changes in predicted C turnover in terms of daily amplitude and the impact of extreme temperatures. The results indicate that averaging from hourly to daily or monthly temperatures will lead to relative errors >4% yr−1 for cumulative CO2 efflux. Instantaneous CO2 fluxes are even more affected, where daily and monthly averaging will lead to estimation errors exceeding 20%. We also show that a constant or daily variable temperature amplitude for rescaling daily average temperature did not decrease the error when using daily or monthly mean temperature instead of hourly data. Therefore, instantaneous fluxes are only accurately predicted when hourly temperature input is used. For long‐term modeling (e.g., years to centuries), the relative error in cumulative efflux, and therefore in C stocks loss, is reasonably low (∼4–5% annual error) but will accumulate with time again.
Energy Fluxes above Three Disparate Surfaces in a Temperate Mesoscale Coastal Catchment
Authors: Ringgaard Rasmus , Herbst Mathias , Friborg Thomas , Schelde Kirsten , Thomsen Anton G. , Soegaard Henrik
Published: February 2011

This study is part of the long‐term catchment‐scale hydrological observatory, HOBE, situated in the Skjern River catchment covering 2500 km2 on the western coast of Denmark. To gain a more detailed knowledge of how evapotranspiration is controlled by the local surface and atmospheric processes, eddy‐covariance systems have been installed over an agricultural field, over a spruce [Picea abies (L.) H. Karst.] plantation, and on wet grassland. Measurements started in fall 2008, and the first annual series showed large differences in evaporative response among the surfaces. The annual sum was about 500 mm for the wet grassland and spruce plantation, while it was about 300 mm for the irrigated agricultural site. In winter, the actual evapotranspiration rate of the grassland and the forest were much larger than the available energy evaluated from the radiation balance, while at the same time large‐scale sensible heat flux directed toward the ground was measured. At the agricultural site, the evapotranspiration rate was controlled by crop development with a leaf area index ≥3 being the threshold where actual evapotranspiration reached the potential rate. At the forest site, transpiration rates were severely limited due to stomatal control, which could be related to soil moisture and vapor pressure deficits. The interception evaporation was very important for total evapotranspiration. At the meadow, summer low flow in the river coincided with drying out of the meadows, which limited evapotranspiration. In late summer, evapotranspiration rates at the meadow and forest sites again increased significantly compared with radiative available energy, and again sensible heat flux directed toward the ground was observed.
Modeling Nitrous Oxide Emissions from Potato‐Cropped Soil
Authors: Klier C. , Gayler S. , Haberbosch C. , Ruser R. , Stenger R. , Flessa H. , Priesack E.
Published: February 2011

Intensive agricultural land use is considered to be the major source of the anthropogenic contribution to the increase in atmospheric N2O concentration during the last decades. A reduction of anthropogenic N2O emissions therefore requires a change in agricultural management practices. Mathematical models help to understand interacting processes in the N cycle and state variables affecting N2O emissions. The aim of this study was to test two modeling approaches for their ability to describe and quantify the seasonal variations of N2O fluxes in a potato (Solanum tuberosum L.)‐cropped soil. Model 1 assumes a fixed N2O/N2 ratio for N2O production and neglects the transport of N2O in the soil profile; Model 2 explicitly considers N2O transport and assumes a dynamic reduction of N2O to N2 Data for model evaluation came from an experiment where N2O fluxes were monitored during the vegetation period using a closed chamber technique. Generally, both modeling approaches were able to describe the observed seasonal dynamics of N2O emissions and events of high N2O emissions due to increased denitrification activity after heavy precipitation. The inclusion of a gas transport module in the modeling approach resulted in simulated N2O emission dynamics showing a smoother transient behavior. Extremely high emission rates from the interrow soil of the potato field were underestimated by both models. The lower N2O release from the ridge soil was mainly due to better aeration because of a lower soil bulk density and lower water contents caused by lateral runoff and root water uptake.
Effects of Different Rock Fragment Contents and Sizes on Solute Transport in Soil Columns
Authors: Zhou B. B. , Shao M. A. , Wang Q. J. , Yang T.
Published: February 2011

The presence of rock fragments in soil can have a great impact on solute transport processes, as well as on soil bulk density, soil structure, and water storage properties. In the laboratory, we studied the effects of different gravimetric rock fragment contents (Rc) and different rock fragment sizes (Rs) on the solute transport processes in soil columns. Using CaCl2 as a tracer, the solute transport processes were accurately described by both the convection–dispersion equation (CDE) and a two‐region model, although the latter model fitted the experimental data slightly better than the CDE. Smooth breakthrough curves were obtained, even for a large Rs or Rc, although the presence of rock fragments impeded solute transport to different degrees depending on the content and size of fragments in the columns. The two models produced the same trends in dispersivity, but the values determined by the two‐region model were smaller than those from the CDE. The Rc and Rs values had a significant effect on the mobile–immobile partition coefficient and the mass transfer coefficient.
Evaluation of Climate Input Biases and Water Balance Issues Using a Coupled Surface–Subsurface Model
Authors: Stisen Simon , Sonnenborg Torben O. , Højberg Anker L. , Troldborg Lars , Refsgaard Jens Christian
Published: February 2011

A physically based, coupled and distributed hydrologic model has been set up for the Ringkøbing Fjord catchment, Denmark. This transient model, built with the MIKE SHE/MIKE 11 code, comprises all major components of the terrestrial water cycle, including a three‐dimensional finite‐difference groundwater model. The dynamic coupling of the hydrologic processes secures physically sound feedback and makes the model an ideal tool for evaluating the overall water balance and quantifying potential water balance issues. Historically, failure to obtain water balance closure has been a persistent and much debated problem in Denmark, presumably arising mainly from uncertainties in precipitation, actual evapotranspiration, and groundwater flow to the sea. In this study, the water balance issues were addressed within the modeling framework through analysis of different rain gauge catch corrections and potential evapotranspiration input. The analysis focused on the effect of different rain gauge catch corrections on the model performance, the optimized parameter sets, and state variables not included in the model calibration. The results suggest that water balance problems can be reduced by using a dynamic rain gauge catch correction based on daily wind speed and temperature fields. The model optimization and performance evaluation revealed, however, that several parameter sets gave similar performance compared with the observed groundwater head and river discharge data but still resulted in significant differences with respect to internal water fluxes such as evapotranspiration, groundwater recharge, and stream flow components. New observational data are needed to constrain the model further and thus reduce the water balance uncertainties convincingly.
A Hybrid Finite‐Element Finite‐Volume Method with Embedded Discontinuities for Solute Transport in Heterogeneous Media
Authors: Nick H.M. , Matthäi S.K.
Published: February 2011

Accurate numerical simulation of solute transport or multiphase flow through heterogeneous porous media is still a challenge. One reason is that in continuum models, sharp material interfaces are difficult to represent. The finite‐element method allows representation of such discontinuities as element‐to‐element variations of materials; however, result variables are discretized on the finite‐element nodes and when a complementary node‐centered finite‐volume mesh is used to model transport, this discretization smears out potential discontinuities in nodal concentration or saturation. To overcome this dilemma there are two options: either the nodes can be enriched at the interfaces by additional degrees of freedom or the model can be “exploded” along the interfaces. In the latter technique, interface nodes are multiplied so that they match in number the material domains that they join. We develop this latter approach, implementing a transport model that can evolve dependent variable discontinuities at material interfaces. For transport, we developed a new scheme that is higher order accurate in space, even across these discontinuities, and verify that it is consistent with the continuous method. This analysis shows that the new scheme removes a first‐order dependence on mesh refinement observed for the continuous method so that coarser meshes can be used for material interfaces.
Spatial Distribution of Seepage at a Flow‐Through Lake: Lake Hampen, Western Denmark
Authors: Kidmose Jacob , Engesgaard Peter , Nilsson Bertel , Laier Troels , Looms Majken C.
Published: February 2011

The spatial distribution of seepage at a flow‐through lake in western Denmark was investigated at multiple scales with integrated use of a seepage meter, lake–groundwater gradients, stable isotope fractionation (δ18O), chlorofluorocarbon (CFC) apparent ages, land‐based and off‐shore geophysical surveys, and lake bed coring. Results were compared with a three‐dimensional catchment‐scale groundwater flow model using the MODFLOW and LAK3 codes for simulating lake–groundwater interaction. Seepage meter and model results of discharging groundwater to the lake compared well, if direct seepage measurements from near shore were combined with measurements from deeper parts of the lake. Discharge rates up to 9.1 × 10−7 m s−1 were found. Ground‐penetrating radar used to map the lake bed sediments proved very effective in recognizing low‐ and high‐permeability areas but also in understanding the complex recharge pattern of the lake and relating these to the geologic history of the lake. Recharge of the surrounding aquifer by lake water occurs offshore in a narrow zone, as measured from lake–groundwater gradients. A 33‐m‐deep δ18O profile at the recharge side shows a lake δ18O plume at depths that corroborates the interpretation of lake water recharging offshore and moving down gradient. Inclusion of lake bed heterogeneity in the model improved the comparison of simulated and observed discharge to the lake. The apparent age of the discharging groundwater to the lake was determined by CFCs, resulting in ages between 3 and 36 yr with an average of 16 yr. The simulated average groundwater age was 13.2 yr.
Comparison of Petrophysical Relationships for Soil Moisture Estimation using GPR Ground Waves
Authors: Steelman Colby M. , Endres Anthony L.
Published: February 2011

Soil water content measurement using ground‐penetrating radar (GPR) requires an appropriate petrophysical relationship between the dielectric permittivity and volumetric water content of the soil. The suitability of different relationships for GPR soil water content estimation has not been thoroughly investigated under natural field conditions for a complete range of seasonal soil conditions. In this study, we examined the ability of various empirical relationships, volumetric mixing formulae, and effective medium approximations to predict near‐surface volumetric soil water content using high‐frequency direct ground wave (DGW) velocity measurements for three soil textures. The estimated water contents were compared with values obtained from gravimetric sampling. The accuracy of soil water content predictions obtained from the various relationships ranged considerably. The best predictions for the overall data set in terms of RMSE were obtained with a differential effective medium approximation based on a coated sphere model (RMSE = 0.045 m3 m−3); however, an empirical relationship (RMSE = 0.052 m3 m−3) and a volumetric mixing formula (RMSE = 0.048 m3 m−3) also performed well. These best‐fitting relationships do exhibit some degree of textural bias that should be considered in the choice of petrophysical relationship for a given data set. Further improvements in water content estimates were obtained using our best‐fit third‐order polynomial relationship (RMSE = 0.041 m3 m−3) and our three‐phase volumetric mixing formula with geometric parameter α = 0.36 (RMSE = 0.042 m3 m−3); these optimized relationships were developed using the DGW permittivity and soil water content data collected in this study.
Improvement of Water Movement in an Undulating Sandy Soil Prone to Water Repellency
Authors: Oostindie Klaas , Dekker Louis W. , Wesseling Jan G. , Ritsema Coen J.
Published: February 2011

The temporal dynamics of water repellency in soils strongly influence water flow. We investigated the variability of soil water content in a slight slope on a sandy fairway exhibiting water‐repellent behavior. A time domain reflectometry (TDR) array of 60 probes measured water contents at 3‐h intervals in a transect along the slope at four depths across a length of 4.5 m. A recently developed animation program was used to visualize the complex way water infiltrates into the soil. Measurements commenced 14 May 2003. Starting on 29 Mar. 2004, the same equipment was used to determine the effects of soil surfactant applications on preventing the development of water repellency and reduction of heterogeneous wetting of the soil along the slope. Additionally, soil water contents in the upper 5 cm of both the untreated and surfactant‐treated areas were measured with a hand‐held TDR device on five occasions between 10 May 2005 and 22 Mar. 2006. On the same dates, soil cores were taken to determine the presence of soil water repellency. The temporal dynamics of water repellency along the slope strongly influenced water flow and the appearance of preferential flow paths. Variability of the soil water content in the untreated slope following rain events is illustrated with two “movies” constructed using the actual measurements. Surfactant applications prevented the development of actual water repellency, which resulted in a more homogeneous wetting even during the summer period of 2005. The soil water contents in the surfactant‐treated area are shown in a third “movie.” The ability to animate the data allows better representation of the actual dynamics of water flow in the sloped test area.
Precipitation and Soil Impacts on Partitioning of Subsurface Moisture in Avena barbata
Authors: Salve Rohit , Torn Margaret
Published: February 2011

The primary objective of this study was to assess the impact of two grassland soils and precipitation regimes on soil‐moisture dynamics. We set up an experiment in a greenhouse and monitored the soil moisture dynamics in mesocosms planted with Avena barbata, an annual species found in California grasslands. By repeating the precipitation input at regular intervals, we were able to observe plant manipulation of soil moisture during well‐defined periods during the growing season. We found that the amount of water partitioned to evapotranspiration, seepage, and soil storage varied among different growth stages. Furthermore, both soil type and precipitation regime had a significant impact on redistributing soil moisture. Whereas in the low‐precipitation treatments most water was released to the atmosphere as evapotranspiration, major losses from the high‐precipitation treatment occurred as gravity drainage. Observations from this study emphasize the importance of understanding intraseasonal relationships between vegetation, soil, and water.
Catchment‐Wide Atmospheric Greenhouse Gas Exchange as Influenced by Land Use Diversity
Authors: Herbst Mathias , Friborg Thomas , Ringgaard Rasmus , Soegaard Henrik
Published: February 2011

The turbulent fluxes of carbon dioxide between the land surface and the atmosphere were measured with the eddy covariance technique above three contrasting land use types in the Skjern River catchment in western Denmark, namely an agricultural area, a forest plantation, and a wet grassland. The measurements also included the turbulent fluxes of methane above the wet grassland and of nitrous oxide above the agricultural area and ran continuously throughout the year 2009. The highest CO2 uptake rates (around 30 μmol m−2 s−1) were observed at the agricultural site; however, the site was a CO2 sink only from April to June and a CO2 source during the rest of the year. Over the whole year the forest plantation fixed about 1850 g CO2 m−2 compared to only 870 g m−2 at the agricultural site, and it remained a CO2 sink throughout all seasons. The wet grassland site was a CO2 sink from March to October, and its annual CO2 fixation was only marginally higher than that of the agricultural site. The emission of CH4 from the wet grassland showed large seasonal variations. Its annual total corresponded to 276 g CO2 equivalents m−2 (based on a 100‐yr time horizon) and reduced the greenhouse gas sink strength of the site by one‐third. At the agricultural site this sink strength was reduced by 9% through the N2O emissions. Scaled up to the catchment, the observed net uptake of CO2 by the land surface was reduced by roughly one‐tenth, in terms of CO2 equivalents, due to the emission of CH4 and N2O.
Comparing Evapotranspiration Rates Estimated from Atmospheric Flux and TDR Soil Moisture Measurements
Authors: Schelde Kirsten , Ringgaard Rasmus , Herbst Mathias , Thomsen Anton , Friborg Thomas , Søgaard Henrik
Published: February 2011

Measurements of water vapor fluxes using eddy covariance (EC) and measurements of root zone soil moisture depletion using time domain reflectometry (TDR) represent two independent approaches to estimating evapotranspiration. This study investigated the possibility of using TDR to provide a lower limit estimate (disregarding dew evaporation) of evapotranspiration on dry days. During a period of 7 wk, the two independent measuring techniques were applied in a barley (Hordeum vulgare L.) field, and six dry periods were identified. Measurements of daily root zone soil moisture depletion were compared with daily estimates of water vapor loss. During the first dry periods, agreement between the two approaches was good, with average daily deviation between estimates below 1.0 mm d−1 Toward the end of the measurement period, the estimates of the two techniques tended to deviate due to different source areas contributing to the flux estimates. With certain limitations, TDR‐based evapotranspiration estimates are a promising approach for confining EC‐based evapotranspiration.
An Episodic Transit Time Model for Quantification of Preferential Solute Transport
Authors: Larsbo Mats
Published: February 2011

Variations in the concentrations of naturally occurring isotopes in rainfall provide a “continuous” signal that has the potential to generate more information on how weather conditions control solute transport than traditional field tracer experiments. An isotopically distinct rainfall event can be rapidly transferred through the system when preferential flow occurs. The objective of this study was to develop and test an approach for analyzing how rainfall and soil moisture control preferential transport to tile drains. An episodic solute transit time distributions model that accounts for these effects was developed. The model was tested on artificial data (daily values of tile drain discharge and 18O concentrations in the drainage water) generated by the MACRO model for soils with different potentials for preferential flow. The results showed that the transit time model gave an excellent fit to the artificial data for the soil with a high potential for preferential flow. The dynamics of the preferential flow events were well captured also for the soil with medium potential for preferential flow but the magnitude was sometimes poorly simulated. Once the model parameter values have been determined, the model can be used to calculate the amount and distribution with time of preferential flow to tile drains for all daily rainfall data. Model calculations integrate the soil's potential for preferential flow and the effects of weather conditions and are, therefore, highly relevant as site‐specific indicators for the risk of preferential leaching of agrochemicals. The approach needs to be evaluated against real field data, however, before its usefulness can be established.