Bernd Huwe

Water flow modeling in the unsaturated zone with imprecise parameters using a fuzzy approach

Abstract An alternative approach, based on fuzzy set theory, is presented to express imprecision of parameters in a non-probabilistic sense. Imprecision may originate from indirect measurements, estimation routines, subjective interpretation and expert judgement of available information. One dimensional, steady state water flow in the unsaturated zone of homogeneous soils, which is described by the Darcy-Buckingham equation, was chosen to evaluate and to incorporate fuzzy soil hydraulic properties and boundary conditions in the modeling procedure. It is here used to describe soil water pressures with depth, as well as to calculate maximum evapotranspiration rates under steady state conditions. Solving the fuzzy equation for steady state water flow results in minimizing/maximizing procedures, from where resulting membership functions of the dependent variable are calculated. A comparison to a more classical stochastic approach points out the main differences between fuzzy and stochastic concepts to account for uncertainties. Finally, a sensitivity analysis shows the strong impact of different shapes of membership functions of the input parameters on the resulting membership functions of maximum evapotranspiration rates and soil water pressures.

Parameter uncertainty in chemical equilibrium calculations using fuzzy set theory

A method based on fuzzy set theory is presented to incorporate imprecise thermodynamic parameters into chemical equilibrium calculations of aqueous systems. Imprecision may arise from uncertainties in experimental parameter determination as well as from inconsistency of available data in the literature. Fuzzy numbers with different shapes of membership functions are used to express imprecision in a non-probabilistic sense. A solution algorithm for a system of nonlinear algebraic equations calculating the chemical equilibrium composition is combined with level set operations to solve the fuzzy chemical equlibrium problem. The method results in multiple minimizing/maximizing procedures from which the membership functions of equilibrium species concentrations are determined. An application of the proposed method to an aqueous cadmium-sulfide system illustrates the acquisition of membership functions for the thermodynamic constants out of given information. Stochastic information on measurement data are appropriately transformed into fuzzy numbers to allow for the combined calculation of different kinds of uncertainty. The results of four calculation scenarios show their strong impact on the resulting membership functions of chemical equilibrium composition and are discussed in the context of data evaluation and decision making in geochemistry.

Deterministic and stochastic modelling of water, heat and nitrogen dynamics on different scales with WHNSIM

With respect to groundwater quality objectives, it is difficult to understand the nitrogen balance and nitrogen dynamics of agricultural ecosystems without the support of deterministic and stochastic simulation tools. This paper focuses on the deterministic and stochastic modelling of water, heat and nitrogen dynamics in the soil compartments of agricultural ecosystems. The deterministic nitrogen simulation model for agricultural soils presented in this paper, WHNSIM, was originally designed for site conditions typical of southern Germany but can easily be applied to other regions due to its physically based design. Model results are compared with data originating from different experimental sites in Germany. Special consideration is given to the effects of spatial variability. Two different techniques of Monte Carlo simulation are used to study the impact of parameter variability on target variables of nitrogen dynamics on the field scale. Moreover, a procedure is presented that allows modelling nitrogen dynamics on the scale of small catchment areas, combining the geographical information system Arc Info with agricultural management data and model calculations.

Simulation of Runoff Patterns and Soil Erosion on Mountainous Farmland with and without Plastic-Covered Ridge-Furrow Cultivation in South Korea

Abstract. Plastic-covered ridge-furrow cultivation (plastic mulch) can substantially influence runoff and soil erosion on agricultural land. However, the impact of this management practice in combination with complex farmland topography has not been thoroughly investigated. The goal of this study was to identify how topography influences runoff patterns and erosion rates of plastic mulch cultivation. We measured runoff and sediment transport on two mountainous fields in South Korea, one with a concave topography and one with a convex topography, during monsoonal rain events. We used the EROSION 3D model to compare flow and sediment transport between plastic mulch, uncovered ridges, and a smooth soil surface. We found the highest runoff and erosion rates from both of the fields with plastic mulch due to the impermeable surface. For the uncovered ridges, we identified 140% higher erosion compared to the smooth surface on the concave field, but 20% lower erosion on the convex field. The simulated sediment transport patterns showed that the ridge-furrow system concentrated overland flow on the concave field, resulting in high erosion rates. On the convex field, the ridge-furrow system prevented flow accumulation and erosion. Our results demonstrate that the effect of ridge-furrow systems on erosion is controlled primarily by the topography. These results have practical consequences for watershed conservation planning and the application of large-scale erosion models. Nevertheless, further research is needed to fully understand the impact of this management system on runoff and erosion on mountainous farmland.

PAH mobility in contaminated industrial soils: a Markov chain approach to the spatial variability of soil properties and PAH levels

The consideration of spatially variable contaminant sources and sinks is crucial for the quantification of contaminant transport in industrial soils. To assess the seepage of polycyclic aromatic hydrocarbons (PAH) at a former manufactured gas plant, a combined approach was used comprised of a field survey, stochastic representation of site heterogeneity and numerical simulation of contaminant mobility. Based on field and laboratory data, the vertical transition probabilities of soil materials and PAH-contamination classes were derived and a non-stationary Markov chain model of site heterogeneity was developed. The model was used to generate representative soil profiles by stochastic simulation. Eighty profiles covered 61% of the spatial variability of the site in terms of soil forming materials and PAH levels. Positions and thickness of horizons agreed with the field survey. The seepage of different PAH (fluoranthene, pyrene, benzo(b)fluoranthene, phenathrene, and benzo(a)pyrene) was calculated by numerical simulation using experimentally derived isotherm data. The cumulative output for the individual PAH covered a range of three orders of magnitude, demonstrating the effect of site heterogeneity on contaminant transport. While calculated local maximum concentrations exceeded the critical values for potable water, the weighted average of PAH concentration in seepage water was low. Stochastic generation of soil profiles based on Markov chain theory provides a powerful tool for the consideration of soil variability at contaminated industrial sites. Total profile probability relates to the area fractions represented by each profile. Therefore, contaminant seepage may be estimated without a costly three-dimensional deterministic representation of the field site.

GIS-based regionalization of soil profiles with Classification and Regression Trees (CART)

A map of soil texture profiles was derived from readily available spatial data in combination with information from soil profiles using CART (classification and regression trees). The primary purpose was to provide a regionalized predictor for the vertical hydraulic conductivity profiles to be used as an input variable to an evapo-transpiration model. In contrast to former studies, the texture of 110 soil profiles taken in the 10 km2 area was not averaged vertically but the profiles were grouped according to their hydraulic properties. Therefore, it was possible to include site specific profiles, e.g. with histic or argillic horizons. Despite of small sampling quantities (110 soil profiles grouped into 8 classes) a prediction probability of 60 to 70 % was achieved in most classes. The resulting map provides valuable information for the granulometric and hydrologic characterization of the study area. GIS-gestutzte Regionalisierung von Bodenprofilen mit Classification and Regression Trees (CART) Auf der Grundlage weniger Profilaufnahmen sowie flachenhaft vorhandener Gelandedaten wurde eine Bodenartenkarte erstellt. Motivation fur dieses Regionalisierungsverfahren war die flachenhafte Abschatzung der Bodenwasserleitfahigkeit zur weiteren Verwendung in einem Verdunstungs-Modell. Im Gegensatz zu vorangegangenen Studien wurde die Textur der 110 Bodenprofile nicht vertikal gemittelt, sondern die Bodenprofile uber ihren vertikalen Aufbau hinsichtlich hydraulischer Eigenschaften in acht Gruppen zusammengefasst. Dadurch wurde die Regionalisierung gebietstypischer Sonderformen, wie stark wechselgelagerte Profile mit teilweise anmoorigen oder tonigen Horizonten, moglich. Trotz des verhaltnismasig geringen Stichprobenumfangs von 110 Datensatzen, gruppiert in 8 Profilgruppen, konnten Prognosewahrscheinlichkeiten von 60 bis 70 % fur die meisten Profilgruppen erreicht werden. Fur die Charakterisierung der Bodenartenverhaltnisse im Untersuchungsgebiet liefert die abgeleitete Karte somit ausreichende Informationen.

Nutrient cycling in an agroforestry system with runoff irrigation in Northern Kenya

A nutrient balance was determined for sole and alley cropped Sorghum bicolor and Acacia saligna in a runoff irrigation system in Northern Kenya. Nutrient input including precipitation and runoff, and output through harvest and leaching were measured for N, P, K, Ca and Mg using adsorption resins, tensiometry and suction cups. Various management scenarios are discussed with respect to nutrient return. Nutrient input with rainfall was generally low in comparison to nutrient uptake or leaching losses. The irrigation water, however, constituted an important nutrient input, especially for Ca and Mg. Nutrient export with the harvest was large for N and K, but can effectively be reduced by a nutrient return with mulch. Nutrient leaching losses from the topsoil (0–30 cm) were lower in the sorghum monoculture than in the tree-based systems. In the subsoil (120 cm), however, leaching was effectively reduced by the trees. In the agroforestry system, leaching losses of N under the sorghum were 53% lower than in the sorghum monoculture. This could be attributed to a higher root abundance and a higher ratio of nutrient uptake-to-leaching in the agroforestry system than in the monocultures indicating a higher nutrient efficiency. The lower leaching losses in the agroforestry system compared to the crop monoculture could not compensate for the additional nutrient export in tree biomass. A nutrient return by mulching crop residues and acacia leaves was essential for a positive nutrient balance in the agroforestry system. Combining annual and perennial crops provided a higher internal nutrient cycling than the monocultures.

FuN-Balance: a fuzzy balance approach for the calculation of nitrate leaching with incorporation of data imprecision

Abstract The nitrogen-leaching model Fuzzy Nitrogen-Balance (FuN-Balance) presented in this paper was developed for the field-specific determination of nitrate concentrations of percolating water in agricultural catchments. The use of fuzzy numbers (uncertain numbers) allows one to estimate the accuracy of the models results even when the available data are not suitable for statistical analysis. Hence, the model is especially designed for situations where expert knowledge must be included and quantitative values about the accuracy of the results are required. The calculations of nitrate concentrations in percolating water were carried out in the 31 km2 catchment “Weisenstadter See” (Fichtelgebirge, Northern Bavaria). Fertilizer rates and plant uptake were estimated by the local department of agriculture. As the available data were insufficient for a statistical analysis, minimal, maximal and typical values were used to set up fuzzy numbers, which in turn were used to estimate the accuracy of the results. Additionally, the model takes into account the interdependence between different fuzzy variables. This accounts for the fact that uncertainties concerning input parameters are not independent of one another and leads to more reliable estimates of the expected range of results. The models results were compared with Nmin data obtained at more than 50 sites in the area studied. To make FuN-Balance a convenient tool for practical use, the developed FORTRAN code was integrated in a Visual Basic 6.0 user interface.

Spatial extrapolation of agrometeorological variables

Agrometeorological variables are especially subject to variations in space ‐ a fact that makes calculations of areal mean values for e.g. evaporation extremely elusive. Wind, temperature, and humidity cannot be measured continuously in space. In this paper we present simple methods to determine values of those variables for non-ideal positions from measurements at a single ideal point and test these spatial functions by measurements at three non-ideal points in a catchment. For wind, we were able to obtain a relatively good fit by taking the sheltering effects of the catchment rims into account. Temperature was not regionalizable with simple approaches, but needs to be regionalized with spatially and temporally differentiated models. Specific humidity can be assumed to be homogeneously distributed even though there were sinks and sources for water vapor in the study area. # 1999 Elsevier Science B.V. All rights reserved.

Is Ridge Cultivation Sustainable? A Case Study from the Haean Catchment, South Korea

Non-sustainable agricultural practices can alter the quality of soil and water. A sustainable soil management requires detailed understanding of how tillage affects soil quality, erosion, and leaching processes. Agricultural soils in the Haean catchment (South Korea) are susceptible to erosion by water during the monsoon. For years, erosion-induced losses have been compensated by spreading allochthonous sandy material on the fields. These anthropogenically modified soils are used for vegetable production, and crops are cultivated in ridges using plastic mulches. To evaluate whether the current practice of ridge cultivation is sustainable with regard to soil quality and soil and water conservation, we (i) analysed soil properties of topsoils and (ii) carried out dye tracer experiments. Our results show that the sandy topsoils have a very low soil organic matter content and a poor structure and lack soil burrowers. The artificial layering induced by spreading sandy material supported lateral downhill water flow. Ridge tillage and plastic mulching strongly increased surface runoff and soil erosion. We conclude that for this region a comprehensive management plan, which aims at long-term sustainable agriculture by protecting topsoils, increasing soil organic matter, and minimizing runoff and soil erosion, is mandatory for the future.