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A two-year field study was carried out in eastern Ontario to investigate the effects of water table management (WTM) on water quality and crop yields. Corn (Zea mays L.) and soybean (Glycine max Merr.) were planted in alternate strips across the three treatments of 50 cm controlled water table (CWT), 75 cm CWT and free drainage (FD). Drainflow volume and nitrate-N concentration of the drainage water were measured. Soil samples were collected and analysed for total N, P, K, available N, soil moisture and organic matter levels. Chlorophyll-meter readings and plant harvest parameters were also measured. Rainfall, soil and air temperatures were recorded throughout the growing seasons. / The obtained data show that in 1995, the CWT plots significantly increased total drainflow, as compared to FD. In 1996, overall drainflow and nitrate concentrations were significantly reduced. Both the corn and soybean yields were higher with WTM than with FD for both years. (Abstract shortened by UMI.)

The use of agricultural chemicals, such as nitrogen fertilizers in corn production, often results in water pollution. This research, comprising three parts, was designed to investigate the effects of nitrogen fertilizer application rates, water table management, and corn cropping systems on drainage water quality. The first part was a field study, to investigate the impact of two cropping systems and water table management on nitrate loss through tile drainage. The considered water table treatments were free drainage, and subirrigation with target water table depths at 0.5 m or 0.75 M below the soil surface. Corn (Zea mays L.) monoculture and corn intercropped with annual ryegrass (Lolium multiflorum Lam.) were investigated. The highest annual tile drainage losses of 21.9 kg N/ha were measured in monocropped, freely draining plots. Subirrigation with a water table depth of 0.5 m reduced tile drainage loss of N by over 70%, and intercropping corn with ryegrass under free drainage reduced leaching losses by 50%. / The second part of the research was a simulation study with the water quality model, DRAINMOD-N. The water quality impact of fertilizer application rate under free drainage, subirrigation and controlled drainage was evaluated. Leaching losses, denitrification and N accumulation in the soil profile were investigated. Using data obtained from the field experiment, the performance of DRAINMOD-N was evaluated. DRAINMOD-N assumes that denitrification follows first order kinetics, contrary to field measurements which showed little correlation between denitrification rate and NO$ sb3 sp-$-N concentration. Therefore, DRAINMOD-N was modified by replacing the original denitrification function with the Michaelis-Menten relationship. In so doing, denitrification is expressed as a first order process when NO$ sb3 sp-$-N concentration limits denitrification, and as a zero order process for non-limiting NO$ sb3 sp-$-N concentration. / For denitrification to be a decision making criterion of water table management, inexpensive but reliable measurement techniques are required. Thus, the purpose of the final part of this research was to formulate a technique for measuring real-time denitrification rate. Denitrification rate could be expressed as a function of soil redox potential (Eh) and temperature. Laboratory and field studies showed that factors such as soil nitrate and organic carbon had negligible effect on denitrification rate. Therefore, it can be concluded that for most agricultural soil, Eh and soil temperature will satisfactorily describe denitrification variation.

Sulphate-reducing bacteria (SRB) mediate the reduction of metals/metalloids directly or indirectly. Bioremediation of arsenic contaminated water could be a cost-effective process provided a cheap carbon source is used. To this end, molasses was tested as a possible source of carbon for the growth of sulphate-reducing bacteria (SRB). Its chemical composition and the tolerance of SRB toward different arsenic species [As (III) and As (V)] were also investigated. Batch culture studies were carried out to assess 1, 2.5 and 5 g l-1 molasses as suitable concentrations for SRB growth. The results indicate that molasses does support SRB growth, the level of response being dependent on the concentration; however, growth on molasses was not as good as that obtained when lactate, the usual carbon source for SRB, was used. The molasses used in this study contained several metals including Al, As, Cu, Fe, Mn and Zn in concentrations ranging from 0.54-19.7 ìg g-1, but these levels were not toxic to the SRB. Arsenic tolerance, growth response and sulphate-reducing activity of the SRB were investigated using arsenite and arsenate solutions at final concentrations of 1, 5 and 20 mg l-1 for each species. The results revealed that very little SRB growth occurred at concentrations of 20 mg l-1 As (III) or As (V). At lower concentrations, the SRB grew better in As (V) than in As (III). Batch cultures of sulphate-reducing bacteria (SRB) in flasks containing pine bark, sand and polystyrene as support matrices and Postgate medium B were used to study formation of biofilms. The effects of the support matrices on the growth of the organisms were evaluated on the basis of pH and redox potential change and the levels of sulphide production and sulphate reduction. Characterisation of the matrix surfaces was done by means of environmental scanning electron microscopy (ESEM). A consortium of SRB growing on polystyrene caused a 49% of original sulphate reduction whereas on sand a 36% reduction occurred. Polystyrene was further examined for its durability as a long-term support material for the growing of SRB in the presence of As(III) and/or As(V) at concentrations of 1, 5 and 20 mg l-1. Both sulphate reduction and sulphide production were greater in this immobilised system than in the matrix-free control cultures. With pine bark as support matrix no significant sulphate reduction was observed. The kinetics of sulphate reduction by the immobilised cells were compared with those of planktonic SRB and found to be superior. The leaching of organic compounds, particularly phenolic substances, from the pine bark had a detrimental effect on the growth of the SRB. Different proportions of pine bark extract were used to prepare media to investigate this problem. Growth of SRB was totally inhibited when 100% pine bark extract was used. Analysis of these extracts showed the concentration of phenolics increased from 0.33 mg l-1 to 7.36 mg l-1 over the extraction interval of 15 min to 5 days. Digested samples of pine bark also showed the presence of heavy metals. The effects of nitrate, iron and sulphate and combinations thereof were investigated on the growth of a mixed culture of sulphate-reducing bacteria (SRB). The addition of 30 mg l-1 nitrate does not inhibit the production of sulphide by SRB when either 50 or 150 mg l-1 sulphate was present. The redox potential was decreased from 204 to -239 mV at the end of the 14 day batch experiment in the presence of 150 mg l-1 sulphate and 30 mg l-1 nitrate. The sulphate reduction activity of the SRB in the presence of 30 mg l-1 nitrate and 100 mg l-1 iron was about 42% of original sulphate, while if no iron was added, the reduction was only 34%. In the presence of 20 mg l-1 either As(III) or As(V), but particularly the former, growth of the SRB was inhibited when the cells were cultured in modified Postgate medium in the presence of 30 mg l-1 nitrate. The bioremoval of arsenic species [As(III) or As(V)] in the presence of mixed cultures of sulphate-reducing bacteria was investigated. During growth of a mixed SRB culture adapted to 0.1 mg l-1 arsenic species through repeated sub-culturing, 1 mg l-1 of either As(III) or As(V) was reduced to 0.3 and 0.13 mg l-1, respectively. Sorption experiments on the precipitate produced by batch cultured sulphate-reducing bacteria (SRB-PP) indicated a removal of about 77% and 55% of As(V) and As(III) respectively under the following conditions: pH 6.9; biomass (2 g l-1); 24 h contact time; initial arsenic concentration,1 mg l-1 of either species. These results were compared with synthetic iron sulphide as adsorbent. The adsorption data were fitted to Langmuir and Freundlich isotherms. Energy dispersive x-ray (EDX) analysis showed the SRB-PP contained elements such as sulphur, iron, calcium and phosphorus. Biosorption studies indicated that SRB cell pellets removed about 6.6% of the As(III) and 10.5% of the As(V) from water containing an initial concentration of 1 mg l-1 of either arsenic species after 24 h contact. Arsenic species were precipitated out of synthetic arsenic-contaminated groundwater by reacting it with the gaseous biogenic hydrogen sulphide generated during the growth of SRB. The percentage removal of arsenic species was dependent on the initial arsenic concentration present. Lastly, laboratory scale bioreactors were used to investigate the treatment of arsenic species contaminated synthetic groundwater. A mixed culture of SRB with molasses as a carbon source was immobilised on a polystyrene support matrix. The synthetic groundwater contained either As(III) or As(V) at concentrations of 20, 10, 5, 1 or 0.1 mg l-1 as well as 0.1 mg l-1 of a mixture with As(III) accounting for 20, 30, 40, 60 and 80% of the total. More that 90% and 60% of the As(V) and As(III) respectively were removed by the end of the 14-day experiment. At an initial concentration of 0.1 mg l-1 total arsenic had been reduced to below the WHO acceptable level of 10 ìg l-1 when the proportion of As(III) was 20 and 30%, while at 40% As(III) this level was reached only when the treatment time was increased to 21 days. The efficiency of As(III) removal was increased by first oxidising it to As(V) using MnO2. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

The Star Fire Coal Mine is a large strip mining operation (10,000 acre permit) that produces mine spoil consisting of sandstones, shales, siltstones, and underclays of the Pennsylvanian Breathitt Formation. Chemical analysis of groundwater from the saturated mine spoil show unusually high magnesium concentrations, with magnesium constituting between 27 and 47 percent of the major cations. Excess magnesium in water is detrimental to plant metabolism, and its content in groundwater may limit its use for irrigation and other uses during a post-mining land use plan. Petrological methods (thin section point count analysis and x-ray diffraction) and geochemical methods (electron microprobe analysis and water extraction experiments) were performed to determine the source of magnesium in sandstone and shale samples of the Breathitt Formation. Based on mineral percents and concentrations of magnesium found in samples used for waterrock interaction samples, magnesium-rich siderite was found as the primary contributor of magnesium to the groundwater. / Department of Geology

A study was conducted to measure pesticide concentrations from two tile-drained potato fields in Saint-Leonard d'Aston, Quebec. Soil and water samples were analysed for the pesticides metribuzin, fenvalerate and aldicarb in 1989, and for metribuzin and phorate in 1990. / Metribuzin concentrations up to 3.47 $ mu$g/l were detected in the tile drain water. Surface runoff samples had metribuzin concentrations up to 47.086 $ mu$g/l. Aldicarb was not detected in any of the water samples. Fenvalerate was detected in surface runoff at a level of 0.05 $ mu$g/l during the 1989 growing season. Phorate was not detected in subsurface drain water in the 1990 growing season. / Pesticide levels were higher in the surface soil layer (0-5 cm), than at 25 cm depth. Fenvalerate was detected at a level of 0.013 $ mu$g/g in the surface (0-5 cm) soil samples. Phorate concentrations of up to 0.020 $ mu$g/g were detected in soil samples. Aldicarb was not detected in the soil samples. Metribuzin was found mostly in the soil surface layer with concentrations of up to 0.23 $ mu$g/g during the 1990 growing season.

Groundwater contamination caused by agricultural fertilization is a widely recognized problem. In Hawaii, nitrogen fertilization from pineapple and sugarcane fields has posed a threat to several basal aquifers and has been implicated in coastal algae blooms. The concentration of nitrate-N in the Pearl Harbor basin on the island of Oahu was below 2.3 mg/L in the 1950’s and 1960’s, and has increased to as much as 7.6 mg/L in 1992 to 1994. The objective of this dissertation research is to develop a practical methodology for realistically estimating nitrate leaching from fertilized agricultural lands. Numerous mechanisms have impact on the distribution and migration of nitrate in the soil. Nitrogen fertilizer undergoes many N transformations and interactions with the soil and the plant after applications. In this study, an analysis of soil samples was performed to understand the leaching process of nitrate in the root zone of three different cropped fields in Hawaii. A detailed discussion is given to address various factors which control the nitrate transport process. To judge the sampling plan in relation to spatial variation, the field measurements were evaluated statistically by an uncertainty index, which is represented as the density of samples required for the estimate of sample mean of the nitrate concentration to fall within a defined limit of accuracy. In order to predict the effect of nitrogen fertilization on the groundwater contamination with very limited input data, a simple, analytical, lumped parameter model (LPM), was developed. The model can estimate the average nitrate leaching from the root zone in response to agricultural practices, N transformations and other related processes. The model was tested against the field data and two detailed numerical models, LEACHM-N and CERES-Maize. It provides an alternative way to assess nitrate leaching from the root zone with acceptable accuracy. A listing of the program is provided in Appendix 2. Owing to the complex nature of nitrogen behavior in the unsaturated zone, some degree of uncertainty is involved in the development of modeling approaches. In this study, five major sources of uncertainty were identified. These are: uncertainty due to spatial variation, uncertainty related to the accuracy of the input data, uncertainty due to simplifications in the development of the models, uncertainty due to the modeling parameters, and uncertainty due to the complexity of the unsaturated zone in Hawaii. The impact of these uncertainties on simulation results is evaluated. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1996. / Includes bibliographical references (leaves 202-215). / UHM: Has both book and microform. / Water Resources Research Center, University of Hawaii at Manoa

The ever-increasing detection of harmful organic and inorganic compounds in habitable areas throughout the world has led to mounting research into applications and techniques for the treatment of contaminated soils, surface and groundwaters, and chemical and industrial wastewaters. Chemical oxidation technologies, in particular Fenton-based remediation systems, have exhibited considerable potential for the effective treatment and remediation of such contaminated waters and soils. The use of Fenton-based oxidation systems for the treatment of contaminated waters and wastewaters warrants the development of kinetic models capable of accurately simulating system behaviour. In this thesis, the kinetics of Fenton-mediated oxidation systems and kinetic models based on its governing reaction mechanism are investigated in order to highlight those parameters and conditions that effect Fenton chemistry and oxidation performance, and to demonstrate the application of such kinetic models to design and improve treatment systems. Experimental and simulated data describing the oxidation of formic acid by Fenton's reagent at low pH (3 to 4) and under a variety of initial conditions, operating regimes, and solution environments supports a proposed reaction mechanism that nominates the hydroxyl radical (OH) as the active oxidizing intermediate in Fenton-based oxidation systems. Laboratory experiments demonstrate that formic acid oxidation is inhibited in the presence of oxygen, and model simulations of these systems reveals that such behaviour is due to the effect organic radical intermediates and/or by-products have in assisting or hindering the redox cycling of the catalytic iron species. The critical role that iron redox cycling plays in affecting oxidation performance is further highlighted by experimental and simulated studies at alternate pHs and using different target organics, including those that react directly with iron in a redox capacity. Experiments at pH 4 reveal an increase in the redox cycling of iron and improved oxidation performance compared to pH 3 as the higher pH favours the superoxide radical, a stronger reductant than the hydroperoxyl radical that predominates at pH 3. Other laboratory and modelling studies on the Fenton-mediated oxidation of certain aromatic compounds highlight the manner in which quinone and quinone-like compounds, being added directly or generated as oxidation by-products, can improve oxidation performance via redox reactions with iron. Further simulations reveal the type of practical design and operating information kinetic models can provide for treatment processes, though it is noted an appropriate understanding of the oxidation mechanism of the target species is necessary for the accurate application of the model.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

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