The impact of land use on the N and P status of three contrasting river catchments within the north east of Scotland was studied over time and along the length of each river. Annual mean NO<SUB>3</SUB>-N concentrations increased significantly in the Ythan, Don (P<0.001) and Dee (P<0.05), from 1958 to 1992. Concentrations in the predominantly agricultural Ythan catchment showed the largest increase from 1.9 mg l<SUP>-1</SUP> in 1958 to 7.0 mg l<SUP>-1</SUP> in 1992. A significant increase in mean NO<SUB>3</SUB>-N concentrations in the spring from 1980 to 1992 in the Ythan appeared to reflect the increased N fertiliser usage associated with a change from winter to spring cropping which was evident over this period. Annual mean NO<SUB>3</SUB>-N loads over the period 1980-1992 were 1305, 2010 and 623 t yr<SUP>-1</SUP> for the Ythan, Don and Dee, respectively. Annual PO<SUB>4</SUB>-P loads were 17.6, 40-1 and 16.8 t yr<SUP>-1</SUP> over the same time period for the Ythan, Don and Dee respectively. These loads were found to have associated errors in the range 16-24, 16-17 and 18-32% for NO<SUB>3</SUB>-N, PO<SUB>4</SUB>-P and total P respectively. Annual loss coefficients, calculated for NO<SUB>3</SUB>-N, PO<SUB>4</SUB>-P total P, Si and suspended sediment were 27.2, 0.180, 0.319, 26.1 and 73.5 kg ha<SUP>-1</SUP>, respectively. Annual losses of N and P from forestry were calculated in the Kirkhill catchment, a small subcatchment of the Don and ranged from 0.6 to 2.5 kg ha<SUP>-1</SUP> depending on flow. Annual total P losses were also related to flow and ranged from 0.029 to 0.06 kg ha<SUP>-1</SUP>. A nutrient budget calculated for the Kirkhill catchment found the annual loss of N from the catchment accounted for 44.5% of N inputs, in contrast, only 2.7% of P input to the catchment was detected in the output.

A multi-element soil extraction procedure (P, K, Mg, and Ca) using a mixed cation/anion exchange resin has been developed and its performance evaluated. Ion uptake to and recovery from the resin were highly reproducible over the concentration ranges typically experienced in soil. The effects on the overall reproducibility of changing various experimental parameters such as soil:water:resin ratios were quantified. Plant nutrient uptake and yield parameters obtained from either field (coconut) or pot (rye-grass) experiments using tropical or temperate soils have been used to evaluate the predictive capabilities of the proposed method. Comparisons with existing more widely acceptable soil extractants are made. The proposed method generally gave highly significant correlations with crop data which were independent of soil type. The possibility of including a simultaneous multi-element analytical step, which greatly increases the overall advantages of the resin procedure, has also been assessed.

No description available.

The availability and retention of zinc by soils and minerals of relevance to the crop, especially rice, growing areas of Bangladesh was investigated. The 32 days of continuous soil submergence caused a significant decrease in available zinc, sulphate and copper. Available iron increased significantly while manganese showed a sharp increase followed by a rapid decrease. As pH increased, adsorption and/or precipitation and co-precipitation of zinc with aged or fresh iron and aluminium hydrated oxides was partially responsible for the frequently reported fixation and unavailability of zinc added to the soil. The particle size of the products increased with increasing pH and initial concentration of the relevant elements. For synthetic oxides, the adsorption capacity of manganese appeared to be higher than that of iron or aluminium varieties. The amount of zinc adsorbed by fresh or aged iron or aluminium oxides was similar, but was much different between the fresh and aged forms. The presence of nitrate and sulphate anions made no difference to the shape of the isotherm for zinc adsorption on soil. Variations in adsorption between soils were attributed to the content and nature of the clay fraction and magnitude of CEC. Soils with the highest percentages of clay and, especially, smectites had the highest adsorptive capacities for zinc. Zinc adsorption by soils, clays and synthetic hydrous oxide minerals conformed to the Langmuir isotherm model within certain limits. It was concluded that a higher content of iron, aluminium and manganese oxide hydroxides, a higher CEC and a higher proportion of smectites in the clay fraction were the principal reasons for increased retention by soils and resultant decreased availability of zinc to plants, particularly at higher pH.

Al equilibria with soil organic matter (SOM) was studied in terms of two basic reactions involving exchangeable Al and chemically bound (complexed) Al. Ca ↔ Al exchange on eight soils of variable SOM content resulted in cation exchange capacities (CEC) which varied with the degree of Al saturation. This effect was attributed to the release of organically bound Ca by 1M KC1 as shown by the relative homogeneity of Al adsorption strength and heterogeneity of Ca adsorption revealed by Langmuir analysis. Acetylacetone extraction gave virtually no 'non-exchangeable' Ca but the exchangeable Ca following Ca saturation, was invariably greater than the corresponding Al fraction even on a wholly organic soil. A persistant pH drop, despite repeated equilibration was definitely attributed to continuing Al adsorption. The weak acid nature of the SOM polycarboxylates was analysed by slow auto-titration. Analysis of the apparent acidity constant variation with polymeric charge showed trends consistent with 'electrostatic principles' where weakening of carboxyl-acid strength, occurs as a result of polymeric charge build-up. The extent of this depended on the COOH content/density. A high COOH content also resulted in a low 'intrinsic' pKa (at zero charge) and this was assumed to be a product of chemical dipole effects. However, when the SOM fractions were compared with poly-maleic acid fractions of various molecular weights, low m.w. pure polycarboxylates and pure dicarboxylic acids some other influence on pKa values was in evidence. The exceptionally low intrinsic pKa values for fulvic acids and low m.w. water soluble soil acids were considered to be due not only to COOH clustering but also to carbonyl or hydroxyl substitution around COOH groups. A semi-empirical study of pH buffer capacity and coagulation of soluble SOM by Al was conducted on peat, and the relative complexing and coagulating powers of six metals were assessed. Complexing power depended on the individual metal, whereas coagulation was largely a function of the metal ion valence. This meant that for any degree of complex formation, the solubility of different metal complexes was variable. Transition metals apparently produced the most soluble complex species. An attempt was made to assess 'differential scanning calorimetry' as an analytical tool with respect to metal-SOM complexes. The degree of metal saturation of a SOM fraction gave regular changes in the main DeltaT peaks and different metals produced different patterns. However, it was clear from the study that the major influence on the temperatures of thermal decomposition was of a physical rather than a chemical nature. Accordingly, it is possible that the micro-configuration of coagulated SOM-metal species dictate the DSC pattern rather than the strength of metal-SOM bond as suggested by other workers. The reproducibility of the technique as well as its qualitative interpretation limit its use. In order to test the electrostatic treatment of SOM with respect to Al bonding, Cu chelation was studied so that free ionic Cu could be determined by the use of an ion selective electrode (I.S.E.) and so provide a check on the more theoretical 'pH method' with respect to species prediction. The method used required computer analysis using successive approximations to resolve a 'proton competition' constant which proved to be approximately constant over a wide range of metal:SOM ratios. Furthermore, the true co-ordination number was virtually invarient at &ap;2, indicating only a single bidentate chelate with respect to Cu bonding. The pH and ISE derived stability constants showed good agreement. From the stability constants for Cu-SOM chelation, a model of the soil solution was constructed where the proportion of Cu present as organically complexed metal was expressed exactly as a function of mg SOM l-1 and p(L-) and approximately as a function of mg SOM l-1 and pH. The techniques used to study Cu-polycarboxylate equilibria were applied to Al-SOM and complex formation with low m.w. aromatic and aliphatic carboxylic acids was studied also. The bidentate chelation constant of Al-SOM at a polymer charge of zero closely resembled Al-succinic/glutaric/adipic acid equilibria and a 1:2 Al-acetate complex. As the polycarboxylate charge increased, the Al bond strength increased. The lower m.w. soil acids bonded with Al more weakly because of the same inductive effects controlling proton association. A model of the soil solution with respect of Al chelation was constructed including allowance for hydrolysis species. The relevance of the model with respect to solubility of Al-SOM and soluble SOM in soil solution was confirmed by a coagulation study and by measuring soluble SOM concentration in agricultural topsoil solutions covering a pH range of 4.5--7.5.

An automated Gas Phase Molecular Absorption Spectrometry (GPMAS) method for the determination of sulphide in solution has been developed. Sulphide ions react with 3M hydrochloric acid and the released hydrogen sulphide is swept into a gas-liquid separator by an air-stream. The absorbance was measured at 200 nm using a deuterium hollow cathode lamp. The method is relatively free from interference with a detection limit of 0.06 ug ml-1 of sulphide and relative standard deviations of 1.4-3.3% for repeated analyses. The calibration graph is linear up to 100 g ml-1 of sulphide and twenty samples can be analysed in one hour. The method has been applied to the determination of sulphate sulphur in plants. An automated procedure for determination of sulphite in aqueous solution by GPMAS was also developed. Using the optimised conditions obtained in this investigation, the method has a detection limit of 0.20 g ml-1 and relative standard deviations of 2.3% and 1.8% for 20 g ml-1 and 10 g ml-1 of sulphite respectively. The calibration graph is linear up to 120 g ml-1 and samples can be analysed at the rate of 20 per hour. The method has been applied to the determination of sulphur dioxide in synthetic samples and in white wines. The gas phase sampling introduction technique was also utilized in emission spectrometry. A sensitive and selective cool flame emission spectrometric method for the determination of sulphide in environmental solution samples was developed. The technique is based on passing the hydrogen sulphide liberated on acidification of samples with 3M hydrochloric acid into a cool, nitrogen-hydrogen diffusion flame and the resulting S2 molecular emission is measured at 384 nm. The method, which is automated, has a detection limit of 0.026 ng ml-1 for sulphide and relative standard deviations of 0.8- 2.5% for repeated analyses. Under the optimised conditions, the proposed method is applicable over the concentration range 0.1 - 8.0 g ml-1 of sulphide. Twenty samples can be analysed in 1 hour and the method has been applied to the determination of sulphide in waste water samples. The conversion of sulphite and sulphur dioxide [fixed as disulphitomercurate (II)] to hydrogen sulphide by reduction with sodium tetrahydroborate (III) has been used to provide a much improved sensitive, cool flame emission spectrometric method for the determination of sulphur dioxide and sulphite. The sample is mixed with NaBH4, acidified with 6M hydrochloric acid, and carried by a continuous-flow stream into a gas-liquid separator where the evolved hydrogen sulphide is swept by nitrogen into a cool, hydrogen- nitrogen-entrained air flame. The intensity of the blue S2 emission generated is measured at 384 nm. The proposed method has a detection limit for sulphite of 0.029 g ml-1 and relative standard deviations of 1.2 and 1.5% for 1 and 5 g ml-1 respectively. The calibration graph is linear up to 24 g m-l of sulphite and samples can be analysed at a rate of about 40 per hour. The method has been applied to the determination of sulphur dioxide in air and sulphite in wines. The proposed method, which is more sensitive than many earlier methods, is simple, versatile and capable of good precision. It is also rapid and convenient. Interferences are known but their effects may be minimized. The method is relatively free from nitrogen dioxide interference. Forty samples can be analysed in 1 hour and the results obtained by the proposed method correlate well with those obtained using an official method. The contribution of dissolved sulphate to total dissolved sulphur in a range of environmental samples was also studied. The results confirmed the importance of non-sulphate sulphur in a range of environmental samples. The importance of sample preparation in soil analysis was also demonstrated because of the effect of drying on sulphur constituents of soils.

The work presented in this thesis investigates the effects of precipitation chemistry on the chemical characteristics of upland organic soils in the UK and their associated drainage waters. It also describes effects on a number of microbially-mediated processes and concludes with a study on methods for the amelioration of peat acidification. Data presented in chapters 3, 5 and 6 have recently been published or accepted for publication (Sanger et al. 1993 a. 1993 b and 1993 c). The first chapter describes the nature of soil acidity and reviews the relevant literature on the effects of acidic deposition, with particular emphasis on upland organic soils and their drainage waters. Chapter 2 describes a field survey carried out in the UK which investigates relationships between the exchangeable and total element chemistry of peat and precipitation chemistry. The results showed that peat collected from areas receiving high concentrations of H+, NH4+, SO42- andNO3- in precipitation were characterised by high extractable NH4+ and total P. and low extractable NO3-, base saturation and exchangeable Ca2+ and Mg2+. TheNH4+ concentration in precipitation was strongly related to a number of soil chemical parameters and the results suggest that future changesin NH4+ inputsto peatscould significantlyeffect soil and drainage water chemistry. The results also show that (1) processes involved in the cycling of N and P may have been altered by precipitation chemistry (2) exchangeable Ca2+ and Mg2+ have been displaced by NH4+ and H+ in areas with high acidic deposition. Peat from areas with a high marine input in precipitation contained high concentrations of exchangeable N+ and K+. Laboratory simulation studies (chapter 3 and 4) using intact peat monoliths were carried out to complement the regional survey described in chapter 2. They were set up to examine element fluxes from peats in relation to precipitation chemistry.

No description available.

No description available.

Since Ellison (1947) described the process of erosion as comprising a) the detachment of soil particles from the soil mass by raindrop impact, b) detachment by runoff, c) the transport of the detached particles by raindrop impact, and d) transport by runoff, research has been directed into the mechanics of each of these four phases and how the phases might be linked together in the form of a soil erosion model, such as the Meyer-Wischmeier (1969) model. From a literature review, it became evident that in spite of this work, gaps in knowledge still exist and that i) most studies on soil erosion tend to lump the processes together; ii) whilst a considerable amount of investigation has been carried out on splash erosion, the other processes have received very little attention; iii) there is no explicit study on the effects of factor-interactions on the processes and the role of the laboratory as a place for studying interactions by controlling factors has not attracted much attention; iv) equipment and techniques for the separate evaluation of the detachment and transport of soil particles by overland flow are not available; and v) studies on the hydraulic characteristics of overland flow in relation to the detachment and transport of soil particles in such flows are scarce. This study was therefore specifically aimed at establishing a sounder research base for modelling the subprocesses and ultimate~ for soil conservation design b,y: i) evaluating separate~ each of the above subprocesses; ii) assessing the influence of the factors affecting the processes, particular~ their interactioDS; and iii) examining the hydraulics of soil particle detachment and transport by overland flow with and without rain. As a means to achieve these objectives, a factorial experiment vas set up in the laboratory to examine both the individual effects of rainfall intensity (50, 80, 110, 140 mm h- 1 ) , soil ~ (standard sand, ISIUld, clay loam and clay) and slope steep:1.8Ss (3.5, 7.0, 10.5 and 14.0 per cent) and their interactions on each of the above subprocesses. Additionally, the effects of four rates of runoff (1.0, 1.6, 2.2 and 2.8 ~min) on the hydraulic characteristics of flow such as velocity, depth, Reyuolds number, Froude number and friction factor were examined and used in characterizing the detachment and transport of soil particles in these flows. For each subprocess, these variables were replicated four times. Splash detachment and transport were determined by simulating rainfall from a nozzle simulator over a target soil placed in a rectangular soil tray (10 x 20 x 4 cm) which being set in the centre of a catching tray (90 x 80 x 30 cm) allows for the separate determination of ups lope and downslope splash. The separate measurement of the detachment and transport of soil particles by overland flow with and without rain was carried out b,y using a specially designed rainfall simulator - bed flume facility with runoff and sediment input and measuring devices. The results were analysed by analysis of variance to show the Significance of soil type, rainfall in tensi ty, flow rate t slope steepness and their first and second order interactions in influencing the processes studied. Multiple correlation techniques were used to search for the best associations between the erosion influencing variables and soil loss. RegreSSion analySis was used for establishing predictive equations for detachment and transport rates. Detachment of the test soils by splash can be placed in rank order of standard sand, sand, clay and clay loam with increasing resistance. For splash transport the order is standard sand ) clay > sand > clay loam. For each soil type there are significant increases in splash detachment and transport with increasing rain intensity and slope steepness. The most significant interactions influencing the two splash processes are soil x intensity and slope x intensity for detachment and transport respectivel,J. Significant interactions show that the factors are not independent of each other; the simple effects of a factor differ, and the magnitude of any simple effect varies according to the level of the other factors of the interaction term. The factors influencing detachment by flow without rain rank in ~ order of importance as soil type, slope steepness and discharge. The corresponding order for flow with rain is discharge, slope steepness and soil type. The order of soil detachability for both flow with and without rain is standard sand , sand ~ clay loam> clay. There are also significant increases in detachment rate as slope steepness and flow rate increase. It is further shown that the first and second order interactions of the above factors Significantly influence detachment by flow. On a relative basis, the second order interaction is small and the importance of the first order interactions can be placed in an increasing order of slope x soil, slope x discharge t and discharge x soil for flow without rain. For flow with rain, they rank as slope x soil, discharge x soil, and slope x discharge. The slope x soil interaction showed that as slope steepens the influence of each Boil on detachment rates increases with the proportionate increase being greater for sand and standard sand than for clay and clay loam. The slope x discharge interaction revealed significant increases in detachment rate for all slopes as discharge increased. The magnitude of the response is however greater at the lower than higher slopes. As slope steepness increases, detachment rates by flow with and without rain are also enhanced. The increase was proportionately more for the 1.0 and 1.6 J/min than 2.2 and 2.8 J/min flows. The Boil x discharge interactiC?n also indicated that, for flow without rain, detachability increases more for clay and clay loam than for the sand and standal'd sand as discharge increases. In the presence of rain however, the response of the soils did not differ much. Detachment by flow without rain is predominantly by rilling. In the presence of rain, detacbment rates by flow are increased about three fold and relatively even removal of soil particles from the eroding bed is characteristic. Raindrop impact thus appears to inhibit rill formation by overland flow especially on small slope steepnesses. There is a critical slope steepness at which both raindrop impact and overland flow contribute equally to total detachment. At slopes lower than the critical value, raindrop impact is the main detaching agent whilst flow predominates the detachment process at steeper slopes. The critical slope steepness is soil specific and decreases in the order of clay ~ clay loam ) sand ~ standard sand. The transport of soil particles by combined flow and rain is significantly influenced by soil type, slope steepness, flow rate and their first and second order interactions. Transport rates decreased in the order of sand > standard sand ) clay ) clay loam. Increases in discharge and slope steepness significantly increased transport capacity. For a discharge range of 1.0 - 2.8 l/min, transport capacity increased four fold. The most significant interaction that influences transport capacity is slope x soil. Where factors interact significantly, interpretation of results based solely on the main effects of the influencing factors m&1 result in loss of vital information and lead to wrong conclusions. For example, examination of the slope x soil interaction showed that at lower slopes (3.5 and 7.0 per cent) combined flow and rain has a greater transport capacity for the larger clay and clay loam aggregates than for the fine grains of sand and standard sand. This is obscured when effects are averaged over all the slopes as is the case when only main effects are considered.