Search

Many of today's construction sites rely on perimeter control practices to capture and treat sediment-laden stormwater emanating from disturbed lands. Silt fence systems are a common sediment control practice often specified by stormwater designers to be installed as perimeter control applications. Although design considerations are often given to the location and placement of these systems within the boundaries of a site, design characteristics of the silt fence itself (e.g., post size, post spacing, and fence height, among others) are rarely taken into consideration. As a result, silt fence systems often become overloaded and fail due to insufficient support or lack of effluent flow capability. Thus, this research effort sought to identify and evaluate practical methods for managing the discharge of impounded stormwater and improving the structural stability of silt fence systems. Results from full-scale testing suggest the inclusion of a plywood dewatering mechanism resulted in 96% sediment retention and effluent water quality data similar to results associated with standard silt fence installations. Silt fence dewatering time was reduced from over 24 to 4 h with minimal downstream disturbance of soil and vegetation. Finally, structural analysis data from five common silt fence support posts were used to determine post spacing based on structural load limits. Using these data and in-field observations, recommended distances for post spacing were developed for each support post type. [ABSTRACT FROM AUTHOR]

We determined 20 polycyclic aromatic hydrocarbons (PAHs) and 12 polychlorinated biphenyls (PCBs) in Oi, Oe, and Oa horizons and at 0-5 and 15-20 cm mineral soil depth of 16 Norway spruce (Picea abies) stands in north Bavaria. The sum of PAH concentrations increased along theline Oi (mean+/-SD: 841+/-330 mu g kg-1)-1) than in Oi (12.1+/-6.5) but similar in Oe and Oa (46.0+/-39.4). The sum of both PAH (0-5 cm: 666+/-707/15-20 cm: 95+/-165) and PCB concentrations (1.7+/-1.5/0.28+/-0.20) decreased sharplyin the mineral soil. The concentration ratios of an individual compound in the Oe to that in the Oi (enrichment factor, eOe/Oi) and the analogously calculated e Oa/Oe correlated significantly (p<0.001) with the octanol-water partition coefficient (Kow, r=0.94 and 0.93 for PAHs; r=0.91 and 0.83 for PCBs, respectively). The enrichment factors of PAHs were consistently higher thanthose of PCBs with comparable Kow. This may be explained by a higher volatilization rate of the PCBs or a stronger sorption ofPAHs to soil. In the mineral soil, the concentrations of most PAHs and PCBs decreased with increasing depth, except those of naphthalene and the PCBs 8, 20, 28, and 52. In the mineral soil, the enrichment factors e0-5/Oa and e15-20/0-5 of the PCBs 8, 20, 28, and 52 were, on average, 10 times higher than those of PAHs with similar Kow values indicating a more pronounced leachingof PCBs than of PAHs. The results demonstrate that the fate of PAHs in forest soils is markedly different from that of PCBs. [ABSTRACT FROM AUTHOR]

Two well-buffered mountain forest watersheds were studied with regard to streamwater chemistry and the impact of forest thinning. The areas are located in the Bavarian Alps near lake Tegernsee, 50km southwest of Munich. In order to get information about the influence of disturbances on the streamwater chemistry 40% of the trees were removed from one watershed after two years of monitoring. The trees were removed by crane to avoid soil damage and erosion. The second watershed was used as a reference. The output at the weirs is characterized, in general, by a strong export of silicate, alkali and alkaline earth cations, and bicarbonate. Acidity and nitrogen accumulate in the watersheds. Both areas are subject to a continuously increasing load of acidity. The acidity is mainly buffered by cation exchange and silicate hydrolysis. This is indicated by continuously decreasing pH values andthe dominance of Ca2+ and silicic acid in the streamwater. Strong changes in the water chemistry along the flowpath indicate that rainwater will be stored in the system for sometime, and water derived from the headwater areas influences the discharge. During precipitation events the new rainwater replaces pre-event water, stored insoils, which had a longer contact time with the biotic and abiotic soil matrix. Acute effects of the selective harvest are leveled in thestreamwater by multiple buffer reactions. The discharge of the disturbed watershed was increased by the reduction of interception and transpiration. Increased rates of mineralization and acidity loads caused an increase in ion concentration and solution load in the dischargefrom the disturbed area. NH+4 showed the strongest effects compared to the reference area and the pre-event period. The changes in the runoff returned to pre-event conditions about one year afterthe disturbance. [ABSTRACT FROM AUTHOR]

The partitioning of rain water into throughfall, stemflow and interception loss when passing through plant canopies depends on propertiesof the respective plant species, such as leaf area and branch angles. In heterogeneous vegetation, such as tropical forest or polycultural systems, the presence of different plant species may consequently result in a mosaic of situations with respect to quantity and quality of water inputs into the soil. As these processes influence not only the water availability for the plants, but also water infiltration and nutrient leaching, the understanding of plant effects on the repartitioning of rain water may help in the optimization of land use systems and management practices. We measured throughfall and stemflow in a perennial polyculture (multi-strata agroforestry), monocultures of peach palm (Bactris gasipaes) for fruit and for palmito, a monoculture of cupuacu (Theobroma grandiflorum), spontaneous fallow and primaryforest during one year in central Amazonia, Brazil. The effect on rain water partitioning was measured separately for four useful tree species in the polyculture and for two tree species in the primary forest. Throughfall at two stem distances, and stemflow, differed significantly between tree species, resulting in pronounced spatial patternsof water input into the soil in the polyculture system. For two treespecies, peach palm for fruit (Bactris gasipaes) and Brazil nut trees (Bertholletia excelsa), the water input into the soil near the stemwas significantly higher than the open-area rainfall. This could lead to increased nutrient leaching when fertilizer is applied close to the stem of these trees. In the primary forest, such spatial patternscould also be detected, with significantly higher water input near apalm (Oenocarpus bacaba) than near a dicotyledonous tree species (Eschweilera sp.). Interception losses were 674% in the polyculture, 1379 and 1273% in the peach palm monocultures for fruit and for palmito,respect [ABSTRACT FROM AUTHOR]

A nutrient balance was determined for sole and alley cropped Sorghumbicolor and Acacia saligna in a runoff irrigation system in NorthernKenya. Nutrient input including precipitation and runoff, and outputthrough 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 intree biomass. A nutrient return by mulching crop residues and acacialeaves 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. [ABSTRACT FROM AUTHOR]

The input into two forested watersheds in the Bavarian Alps is characterised by 2000 mm mean annual precipitation. Evaporation from the tree crown surfaces varies between 25 and 30%. The input is influencedby multiple natural and man-made processes. In addition to the general climate, these are local weather conditions, the growing season, processes of combustion (traffic and domestic fuel), tourism, farming,and not least by processes in the canopy. The input of SO4-S is comparatively low, while high amounts of acidity and nitrogen are deposited. The input occurs mainly as dissolved salts. A considerable amount of the acidity deposited is buffered in the canopy by cation exchange and by calcareous dusts, which are blown out from the limestone and dolomite mountains nearby, and redeposited on leaf surfaces. Forest thinning (removal of 40% of the stem volume) caused markedchanges in the deposition pattern. Interception and deposition ratesof individual ions were reduced by up to 45%. The amount and chemical composition of the throughfall occupied an intermediate position between bulk precipitation and the throughfall of the control watershed. Ions which are preferentially exchanged and leached from the leaves, e.g. potassium and organic compounds, were affected the most. [ABSTRACT FROM AUTHOR]

An investigation was carried out at pilot scale to test the feasibility of using the effluent of a rotating biological contactors (RBC) unit treating wastewater generated from a university campus. The objective of the study was to cerefully monitor the impact of wastewater irrigation on the soil, percolating water, crop growth and the pathogenic condition within the immediate vicinity of wastewater application. Experimental plots with three crops: alfalfa, radish and tomato were irrigated with fresh and waste waters. The irrigation water was applied by sprinklers. Each crop was given two sub-treatments: with fertilizer and without fertilizer. The physical and chemical properties of the soil, the crop yields, and subsurface drainage were measured. In most of the cases, the yields resulted from the uses of wastewater with fertilizer were compatible with those of the uses of freshwater with fertilizer. The washings of tomato fruits grown with wastewater were analyzed for fecal coliforms. It appeared that the fruit skins were free of viable fecal coliforms 24 hours after the wastewater application. Subsurface drainage analyses did not show any alarming levels of constituents irrespective of the source of the water: wastewateror freshwater. The wastewater irrigation applied for a season had nosignificant effect on a silty loam soil. With wastewater irrigation,slight changes in the soil porosity and salinity were observed. [ABSTRACT FROM AUTHOR]

Fine root turnover (<2 mm) was determined from repeated measurementsof root distribution up to 120 cm soil depth by core sampling in four month intervals. Sole cropped Sorghum bicolor and Acacia saligna were compared with the agroforestry combination in an alley cropping system in semiarid Northern Kenya. Three methods for the calculation ofroot production were used: the max-min, balancing-transfer and compartment-flow method. The highest root biomass was found in the topsoilfor all cropping systems, though trees had a deeper root system. Trees and crops had a similar amount of below-ground biomass during the vegetation period (0.3 and 0.4 Mg DM ha-1 120 cm-1), but in the agroforestry combination root biomass was more than the sum of the sole cropped systems (1.1 Mg DM ha-1 120 cm-1). The tree system showed a very static root developmentwith little fluctuation between seasons, whereas root biomasses werevery dynamic in the crop and tree + crop systems. Root production was highest in the tree + crop combination with 2.1 Mg DM ha-1 a-1, with about 50% less in sole cropped trees and crops. Root N input to soil decreased in the order tree + crop>tree>crop system with 13.5, 11.0 and 3.2 kg N ha- 1 a-1, and cannot be estimated from total below-ground biomass or carbon turnover, as N is accumulated in senescing roots. Such low N input to soil stresses the need for investigating other processes of nutrient input from roots to soil. Areas of highest N input were identified in the topsoil under the tree row in the tree system. Resource utilisation and C and N input to soil were highest with a combination of annualand perennial crops. [ABSTRACT FROM AUTHOR]

The northwestern province of Costa Rica is a marginal coffee growingarea. At the onset of the rainy season low redox potentials probablyinduce the mobilization of soil Mn resulting in enhanced plant uptake of Mn. To test this hypothesis we monitored from April to the end of June 1995 the mobile Mn in the soil and nutrient and Mn concentrations in leaves and xylem sap of coffee plants. Every 2 weeks we took aggregate and bulk soil samples. The aggregates were mechanically separated into interior and exterior, air-dried and all soil samples wereextracted with 1 M NH4NO3. We also extracted the field moist soil with distilled water. In addition, the 3rd and the youngest pair of coffee leaves and xylem sap were sampled and analyzed. According to the results of leaf analyses the nutrient supply ofthe coffee plants in general seemed to be balanced. However, Mn concentrations of 223 mg kg-1 in the 3rd leaf pair at 18 Aprilwere above the optimum and the youngest leaves indicated Fe deficiency, but senescent leaves accumulated Fe and overcame the deficiency. Manganese concentrations in the xylem sap showed a pronounced maximum2 weeks prior to a similar maximum of mobile Mn in the aggregate exterior. But in general the temporal variation of nutrient concentrations (especially Ca and Mg) in the plants are well correlated with the easily extractable nutrient concentrations in bulk soil. Probably dueto its specific absorption and high rates of redistribution within the plant, K in the soil extracts did not correlate with plant concentrations. Element concentrations of youngest leaves could not be correlated with soil concentrations and are not considered to be an adequate tool for monitoring current nutrient uptake. Since plant element concentrations did not correlate with the aggregate interior, plants probably cannot use that nutrient source efficiently. [ABSTRACT FROM AUTHOR]

The effects of green manures, sorghum residues and farmyard manure on N dynamics and crop yields were studied during three dry and wet seasons on a Typic Sombriudox in South Rwanda. In addition, a resin core study was conducted within a 4-year green manure field experiment to follow the seasonal pattern of N mineralization and leaching after application of residues from Tephrosia vogelii, Sorghum bicolor, a mixture of both materials, and farmyard manure.During the dry season, topsoil (0-20 cm) mineral N remained constant. At the beginning of thewet season, the rainfall pattern determined N availability. With lowrainfall intensities a mineralization flush occurred, doubling topsoil mineral N concentrations within 5 days after wetting. In contrast,under heavy rains at the onset of the rainy season, topsoil mineral N decreased by 50-70% within the first two weeks.The application of organic fertilizers has a strong influence on N availability, but the effects can be negated by heavy rainfall. Incorporation of leaves from Tephrosia vogelii (2.7 t dm ha-1) and farmyard manure (7t dm ha-1) doubled the mineralization flush after the first rains. During the rest of the wet season, N release by the green manure was small, whereas the farmyard manure was found to mobilize N after a period of N immobilization. Incorporation of sorghum residueshad only a small effect, while mixing the straw with green and farmyard manure immobilized N temporarily.Nitrogen leaching, measured by exchange resins at a depth of 20 cm, was increased up to 50% by the incorporation of green and farmyard manure. This points to rapid N translocation of easily mineralizable N. The additional incorporation of sorghum residues reduced N leaching of both materials significantly. Since rainfall is often unpredictable, the synchronization of N released from crop residues with crop N demand may require additional management practices. [ABSTRACT FROM AUTHOR]

Abstract: Kathmandu, the capital of Nepal, faces increasing environmental problems such as heavy air pollution and lack of proper waste management. The aim of this study was to examine if the soils are also affected by pollution, with the focus on polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). The sum of 20 PAHs in surface soils ranged between 184 and 10279μgkg−1. The most abundant PAHs were perylene (14.6%), benzo(b+j+k)flouranthene (10.7%), naphthalene (10.7%) and phenanthrene (9.8%), with perylene concentrations varying strongly. The significantly more positive δ13C values of perylene in samples with elevated concentrations indicate biological production, possibly by anaerobic degradation of perylene quinones. PAH ratios also indicate the influence of petrogenic PAH sources, especially at petrol stations and some street samples. The sum of 12 PCBs ranged from 356 to 44710ngkg−1. The most abundant were congeners 52 (19.4%), 101 (14.3%), 118 (13.4%) and 138 (11.7%). The low PCB concentrations and pattern were interpreted as a diffuse background contamination being the main PCB source in the urban soils. Indications for recent contamination were found in river sediments from the inner city, as well as in industrial and street samples. Classified by land use, the samples taken from the gutter contained the highest PAH and PCB concentrations as a result of accumulation. The lowest values were found in surface soils from Swayambunath (a park) and a garden area. A gradual decrease in concentration with depth was present for both compound classes in the profiles sampled at Swayambunath. No trend was visible in the garden profiles as a result of soil disturbance of the soil by agricultural treatment. Enhanced microbial degradation and volatilization in the warm/humid monsoon climate is probably the main cause for low pollutant concentrations. Increased photodegradation and the short accumulation period might be other important factors. Concerning its state of soil pollution, Kathmandu fits rather well into a global distribution pattern of persistent organic pollutants, with high concentrations in temperate (higher latitude) regions and very low ones in the tropics (lower latitude regions) due to global distillation. [Copyright &y& Elsevier]

Abstract: Salt-affected soils differ in their chemical properties to all other soils. Sodicity and salinity may affect the soil organic matter component of these soils. In a field experiment, we investigated organic matter decomposition in nonsaline nonsodic Aquic Argiudoll, a nonsaline sodic Typic Natraquoll, nonsaline nonsodic Petrocalcic Paleudoll and a saline sodic Typic Natralboll in the Pampa Deprimida, Argentina. The objectives were to identify the degree of stabilization of organic matter by association with mineral particles in these soils and to follow in particular the fate of lignin in these soils. We measured organic carbon, total nitrogen and the extent of lignin alteration with soil depth and in various particle size fractions. The salt-affected soils contained much less organic carbon and nitrogen in their mollic epipedons than the nonsaline nonsodic soils, and bioturbation into deeper layers was restrained. In the salt-affected soils most of the organic matter was in sand-sized particles. Retarded degradation of plant residues was indicated by the pattern of lignin-derived phenols, suggesting less alteration of lignin in the salt-affected soils than in the nonsaline nonsodic soils. We suggest that this results from the effects of high pH, high sodicity, and high salinity on the microorganisms and their enzymatic activities. The high pH and high concentrations of monovalent cations decreased formation of solid organo-mineral complexes. We conclude that in the salt-affected soils oxidatively altered organic compounds are susceptible to losses in dissolved or colloidal forms, because these compounds are not stabilized against leaching and mineralization by chemical bonding to soil minerals. [Copyright &y& Elsevier]

The relationship between organic P status of 4 soils, 20 microorganisms isolated from these soils (2 bacteria and 3 fungi for each soil) and 13 dominant plant species of typical natural ecosystems of these soils was evaluated. The soils used were represented by two pairs with different ratios of monoester and diester P, and of DNA and other diester P. A Dystric Podzoluvisol and an alpine Umbric Leptosol were characterized by a relatively high proportion of diester P including much DNA P, while a Calcic Chernozem and subalpine Umbric Leptosol had lower proportion of diesters containing relatively less DNA P. The proportions of P compounds in bacteria and plants were very similar on average, based on the monoester to diester P ratio and on the proportions of different diesters in alkaline extract, whereas fungi contained considerably higher proportions of monoesters and polyphosphates, and a higher proportion of phospholipids in the diester fraction. The results showed that the Porg composition of NaOH extracts from different soils was more similar to the composition of extracts from different groups of microorganisms. There was no clear correspondence between soil and microbial diester P proportion and composition. A high proportion of polyphosphate P including pyrophosphate P in soil extracts indicates a significant contribution of fungal P compounds in the soil while the monoester to diester P ratio, and DNA to non-DNA P ratio should be used with caution to interpret the origins of soil Porg. The relative contributions of microorganisms and plants to monoester and diester P in soils is only partially understood. [Copyright &y& Elsevier]