Impacts of land use conversion on bankfull discharge and mass wasting

Mass wasting and channel incision are widespread in the Nemadji River watershed of eastern Minnesota and northwestern Wisconsin. While much of this is a natural response to glacial rebound, sediment coring and tree ring data suggest that land use has also influenced these erosional processes. We characterized land use, inventoried mass wasting, surveyed stream channels and collected discharge data along segments of five streams in the Nemadji River watershed. Due to natural relief in this region, wetlands and agricultural lands are concentrated in the flatter terrain of the uplands of the Nemadji watershed, while forestland (coniferous or deciduous) is concentrated in the deeply incised (50-200% slope) stream valleys. Bankfull discharge was higher where forests had been converted from coniferous to deciduous forests and where there were fewer wetlands. Mass wasting increased exponentially with bankfull flows. While mass wasting was not correlated with forest type conversion and agricultural land use, it was negatively dependent upon wetland extent in headwater areas. Interactions between the spatial distribution of land use and terrain obfuscate any clear cause-and-effect relationships between land use, hydrology and fluvial processes.     

絮凝沉淀-SBR组合工艺处理屠宰加工废水工程应用

介绍了絮凝沉淀—SBR组合工艺在屠宰加工废水处理工程中的应用实例.经过3 个月的工程调试和2 年多的实际运行效果表明,当进水COD在1300~1800mg/L之间时,经该工艺处理,出水COO可达到GB8978-1996《污水综合排放标准》一级排放标准,总去除率在90%以上.实践证明,该工艺具有较好的经济效益和环境效益.     

Using remote sensing technique to study soil sedimentation flow

Soils will behave differently when used for agriculture, forestry, and other purposes and must be managed differently. The difference is most evident in the Inverbrackie Creek catchment area in South Australia where the study reported in this article was conducted and where the soils are used extensively for grazing and dairy farming. This catchment covers an area of 8.38 km², comprising an undulating upland plain with irregularly high hills and broad interfluves. Previous information-gathering methods used to model the catchment's hydrologic activity have been derived from the downstream pluviographic point-source technique. The model input samples obtained by this technique are not truly representative of the catchment. The potential for using remote sensing color infrared imagery to delineate the areas contributing to soil sediment flow is demonstrated as a better alternative to obtaining representative samples to model this activity. This article reports on part of the work supported by the University Research Grant, University of Adelaide.     

Nutrient fluxes in a eutrophic coastal Louisiana freshwater lake

Nitrogen and phosphorus cycling in a eutrophic Louisiana freshwater lake system (Lac des Allemands) was studied. Nutrients from runoff entering the lake, as well as sediment-interstitial and lake water nitrogen and phosphorus fractions, were measured seasonally. Sedimentation rates in the lake were determined using¹³⁷Cs dating.Phosphorus levels in the lake were found to be largely dependent on concentrations in the incoming bayou water from upland drainage. Lake water concentrations appear to respond to fluctuations in incoming waters. Laboratory equilibrium studies showed bottom sediments in the lake are a major sink for the incoming dissolved orthophosphate phosphorus. Total nitrogen concentrations in the lake water generally exceeded incoming runoff concentrations, suggesting fixation by the large blue-green algae population in the lake as being the major source of nitrogen to the system.Sedimentation ranged from 0.44 cm/year to 0.81 cm/year, depending on the proximity to the inlet bayous. Even though the lake is eutrophic the sediment served as a buffer by removing large amounts of carbon, nitrogen, and phosphorus through sedimentation processes. Carbon, nitrogen, and phosphorus were accumulating in the sediment at rates of 60, 7.1, and 1.1 g/m²/year, respectively.The water quality of the lake is likely to continue to decline unless measures are taken to reduce municipal, industrial, and agricultural inputs of phosphorus into the lake.     

Pre-oxidation enhanced cyanobacteria removal in drinking water treatment: A review

Cyanobacterial bloom has many adverse effects on source water quality and drinking water production. The traditional water treatment process can hardly achieve satisfactory removal of algae cells. This review examines the impact of pre-oxidation on the removal of cyanobacteria by solid-liquid separation processes. It was reported that the introduction of chemical oxidants such as chlorine, potassium permanganate, and ozone in algae-laden water pretreatment could improve algae removal by the subsequent solid-liquid separation processes. However, over dosed oxidants can result in more serious water quality risks due to significant algae cell lysis and undesirable intracellular organic matter release. It was suggested that moderate pre-oxidation may enhance the removal of cyanobacteria without damaging algae cells. In this article, effects of moderate pretreatment on the solid-liquid separation processes (sedimentation, dissolved air flotation, and membrane filtration) are reviewed.     

Photocatalytic degradation of phenol by visible light-responsive iron-doped TiO2 and spontaneous sedimentation of the TiO2 particles

Fe-doped TiO₂ was prepared by the calcination of Fe_xTiS₂ (x = 0, 0.002, 0.005, 0.008, 0.01) and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–visible diffuse reflectance spectra. All the Fe-doped TiO₂ were composed of an anatase crystal form and showed red shifts to a longer wavelength. The activity of the Fe-doped TiO₂ for the degradation of phenol was investigated by varying the iron content during UV (365 nm) and visible light (405 nm and 436 nm) irradiation. The degradation rate depended on the Fe content and the Fe-doped TiO₂ was responsive to the visible light as well as the elevated activity toward UV light. The molar ratio of 0.005 was the optimum for both the UV and visible light irradiations. The result was discussed on the basis of the balance of the excited electron–hole trap by the doped Fe³⁺ and their charge recombination on the doped Fe³⁺ level. The Fe-doped TiO₂ (x = 0.005) was more active than P25 TiO₂ under solar light irradiation. The suspended Fe-doped TiO₂ spontaneously precipitated once the stirring of the reaction mixture was terminated.     

Marsh surface sediment deposition and the role of tidal creeks: Implications for created and managed coastal marshes

The need to understand the processes contributing to marsh sedimentation has become more urgent with the recent recognition of the role of tidal marshes as sea defences, as well as the many restoration efforts currently under way. This study was designed to build upon previous sedimentation work at Scolt Head Island by Combining techniques for measuring short-term sedimentation, with detailed assessment of hydroperiod, previously used only in comparison with longer-term accretion measurements or in micro-tidal systems. Measurements of water level, sediment deposition (at various distances from the creek margin) and suspended sediment concentration (SSC) (creek margin and an interior site) were made at Hut Marsh over three sequential over-marsh tides during May 1994. Sediment trap data show a significant trend of declining sediment deposition away from the creek when data from all three tides are combined. All tides show higher SSC on the flood tide than on the ebb tide at the creek margin location. There is little difference in flood and ebb SSCs at the interior site. An order of magnitude decrease in sediment deposition within 20 m on the creek shows the rapidity with which sediment is deposited on these marshes. Higher tides influence both the magnitude and pattern of marsh surface sediment deposition. Increased creek velocities on higher tides provide more potential for resuspension within the creek and increase the supply of sediment to the marsh surface. This study suggests that the design of tidal creeks may be essential for the development of sustainable coastal marshes in restoration projects.     

Plutonium as a chronomarker in Australian and New Zealand sediments: a comparison with Cs

The construction of high resolution chronologies of sediment profiles corresponding to the last 50-100 years usually entails the measurement of fallout radionuclides ²¹⁰Pb and ¹³⁷Cs. The anthropogenic radionuclide, ¹³⁷Cs, originating from atmospheric nuclear weapons testing can provide an important “first appearance” horizon of known age (1954-1955), providing much-needed validation for the sometimes uncertain interpretations associated with ²¹⁰Pb geochronology. However, while ¹³⁷Cs usually provides a strong signal in sediment in the northern hemisphere, total fallout of ¹³⁷Cs in the southern hemisphere was only 25% that of the north and the low activities of ¹³⁷Cs seen in Australian and New Zealand sediments can make its horizon of first appearance somewhat arguable. Low ¹³⁷Cs fallout also limited the size of the 1963-1964 fallout peak, a peak that is usually seen in northern hemisphere sediment profiles but is often difficult to discern south of the equator.This paper shows examples of the use of nuclear weapons fallout Pu as a chronomarker in sediment cores from Australia (3 sites) and New Zealand (1 site). The Pu profiles of five cores are examined and compared with the corresponding ¹³⁷Cs profiles and ²¹⁰Pb geochronologies. We find that Pu has significant advantages over ¹³⁷Cs, including greater measurement sensitivity using alpha spectrometry and mass spectrometric techniques compared to ¹³⁷Cs measurements by gamma spectrometry. Moreover, Pu provides additional chronomarkers associated with changes in the Pu isotopic composition of fallout during the 1950s and 1960s. In particular, the ²³⁸Pu/^239+240Pu activity ratio shows distinct shifts in the early 1950s and the mid to late 1960s, providing important known-age horizons in southern hemisphere sediments. For estuarine and near-shore sediments Pu sometimes has another significant advantage over ¹³⁷Cs due to its enrichment in bottom sediment relative to ¹³⁷Cs resulting from the more efficient scavenging of dissolved Pu in seawater by sediment particles.     

Importance of natural sedimentation in the fate of microcystins

Sedimentation processes of microcystins (MCs), cyanobacterial toxins, were studied in three reservoirs located in Central Spain in which the cyanobacterial community was dominated by the genus Microcystis. MCs were detected in the sediment traps deployed in all reservoirs. In Santillana reservoir, MCs were identified in sediment traps even though they could not be found in the pelagial samples. In the other reservoirs studied, sedimentation rates for MC-containing particles during the bloom period ranged from 0.43 to 2.53 mg m⁻² d⁻¹. Interestingly, this very high sedimentation of toxic biomass is not exclusively related to decaying blooms or autumnal sedimentation due to a drop in water temperature. Instead, it seems that MC-containing colonies may be settling constantly during the bloom period and we were able to estimate that during such a Microcystis dominated bloom, around 4.5% of pelagial MCs may be involved in sedimentation. Further, these settling colonies seem to maintain good cell integrity and MCs seem not to be excreted massively. A certain loss of toxin content along the vertical settling may be attributed to minor losses due to cell lysis or to variations in MC cell quota explained by reduced production or internal consumption. Our results for the first time establish specific settling rates for MC-containing particles in freshwaters and definitely identify sedimentation as a major destination for these toxins. These data may contribute to improve managing strategies concerning risks associated with MCs.     

改良沉淀集卵法检测固体中蛔虫卵方法研究

采用改良后的沉淀集卵法对低(10个/100 g)、中(20个/100 g)、高(40个/100 g)3种不同浓度的加标样品进行蛔虫卵检测,比较其回收率。结果表明:不同浓度加标样品的回收率为高浓度中浓度低浓度。与相关文献实验结果比较表明,该方法不仅回收率较高、稳定性较好,且在检测低浓度样品时较漂浮集卵法具有一定优势。