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1.
Safety assessments for radioactive waste disposal require estimations of the migration of radionuclides in soils. The influence
of humic acid (HA) on the sorption of uranium in its +4 oxidation state to kaolin has been examined from pH 4 to 8, with HA
concentrations of 15–200 ppm. In the absence of HA, 20–40% of the U(IV) was in solution, with more sorption occurring at higher
pH. The presence of HA solubilised up to 90% of the uranium with higher solubilities at higher HA concentrations and higher
pH values. Uranium sorption was mapped against HA sorption, and it was found that there was a lower level of U(IV) sorption
than can be accounted for by just measuring HA sorption. However, this effect got less marked as the pH rose. Sensitivity
analysis indicated that the fraction of surface-bound HA is the controlling parameter for modelling in these systems. 相似文献
2.
Dougherty WJ Nicholls PJ Milham PJ Havilah EJ Lawrie RA 《Journal of environmental quality》2008,37(2):417-428
Fertilizer phosphorus (P) and grazing-related factors can influence runoff P concentrations from grazed pastures. To investigate these effects, we monitored the concentrations of P in surface runoff from grazed dairy pasture plots (50 x 25 m) treated with four fertilizer P rates (0, 20, 40, and 80 kg ha(-1) yr(-1)) for 3.5 yr at Camden, New South Wales. Total P concentrations in runoff were high (0.86-11.13 mg L(-1)) even from the control plot (average 1.94 mg L(-1)). Phosphorus fertilizer significantly (P < 0.001) increased runoff P concentrations (average runoff P concentrations from the P(20), P(40), and P(80) treatments were 2.78, 3.32, and 5.57 mg L(-1), respectively). However, the magnitude of the effect of P fertilizer varied between runoff events (P < 0.01). Further analysis revealed the combined effects on runoff P concentration of P rate, P rate x number of applications (P < 0.001), P rate x time since fertilizer (P < 0.001), dung P (P < 0.001), time since grazing (P < 0.05), and pasture biomass (P < 0.001). A conceptual model of the sources of P in runoff comprising three components is proposed to explain the mobilization of P in runoff and to identify strategies to reduce runoff P concentrations. Our data suggest that the principal strategy for minimizing runoff P concentrations from grazed dairy pastures should be the maintenance of soil P at or near the agronomic optimum by the use of appropriate rates of P fertilizer. 相似文献
3.
John J. Warwick Willard A. Murray 《Journal of the American Water Resources Association》1988,24(5):1041-1047
ABSTRACT: A one-dimensional, gradually varying, non-uniform, flow equation is developed to describe the movement of a variable density gravity current through a reservoir. A linearly decreasing underflow density function is used to investigate the effect of in-reservoir density reduction on typical gravity current flow profiles. Only two types of flow profiles are found to exist for varying density underflows: Type I profiles where the underflow asymptotically approaches a horizontal surface, and Type III profiles where the underflow vertically approaches critical depth. Type I profiles pass through a transitional depth as the underflow density approaches that of the upper layer. Results indicate that a reservoir can be segmented into four distinct spatial regions with well defined flow profile characteristics. The location of these regions allows the sketching of interfacial flow profiles along with identifying the location of transitional depth conditions. Transitional depth conditions are utilized as the logical starting point for Type I flow profile numerical computation. (KEY WORDS: density; fluid flow; reservoirs; hydraulics.) 相似文献
4.
Phosphorus transfer in surface runoff from intensive pasture systems at various scales: a review 总被引:2,自引:0,他引:2
Dougherty WJ Fleming NK Cox JW Chittleborough DJ 《Journal of environmental quality》2004,33(6):1973-1988
Phosphorus transfer in runoff from intensive pasture systems has been extensively researched at a range of scales. However, integration of data from the range of scales has been limited. This paper presents a conceptual model of P transfer that incorporates landscape effects and reviews the research relating to P transfer at a range of scales in light of this model. The contribution of inorganic P sources to P transfer is relatively well understood, but the contribution of organic P to P transfer is still relatively poorly defined. Phosphorus transfer has been studied at laboratory, profile, plot, field, and watershed scales. The majority of research investigating the processes of P transfer (as distinct from merely quantifying P transfer) has been undertaken at the plot scale. However, there is a growing need to integrate data gathered at a range of scales so that more effective strategies to reduce P transfer can be identified. This has been hindered by the lack of a clear conceptual framework to describe differences in the processes of P transfer at the various scales. The interaction of hydrological (transport) factors with P source factors, and their relationship to scale, require further examination. Runoff-generating areas are highly variable, both temporally and spatially. Improvement in the understanding and identification of these areas will contribute to increased effectiveness of strategies aimed at reducing P transfers in runoff. A thorough consideration of scale effects using the conceptual model of P transfer outlined in this paper will facilitate the development of improved strategies for reducing P losses in runoff. 相似文献
5.
Phillip C. Arena Clifford Warwick Catrina Steedman 《Journal of Agricultural and Environmental Ethics》2014,27(2):309-330
Various captivity-related health problems have been described as arising in the farming of sea turtles at the Cayman Turtle Farm (CTF). Our study included a desktop review of turtle farming, direct onsite inspection at the CTF, assessment of visual materials and reports provided by investigators from the World Society for the Protection of Animals (WSPA), and a limited analysis of water quality for potential pathogens. In particular, we assessed physical and behavioural condition of animals for signs of stress, injury and disease. During the onsite inspection we identified three distinct signs of physical injury and disease, six distinct signs of abnormal and problematic arousal- and discomfort-related behaviour; and three distinct signs of normal quiescence- and comfort-related behaviour. On evaluation of evidence provided by the WSPA we identified ten distinct signs of physical injury and disease, and management- or genetic-related conditions; six distinct signs of abnormal and problematic arousal- and discomfort-related behaviour; and three distinct signs of normal quiescence- and comfort-related behaviour. We conclude that sea turtles at the CTF manifested important physical and behavioural signs that are indicative of problematic management and captivity-related stress, and the limitations of sea turtle adaptive plasticity in captivity. The problematic physical and behavioural signs, in our view, related to the inherent nature of intensive turtle propagation which in particular involves overt- and crypto-overcrowding and understimulating environments, and an associated failure to meet all the physical, biological and innate behavioural needs of sea turtles. 相似文献
6.
Humic and fulvic acids are present in nearly all natural waters. These acids are known to affect the transport of environmental contaminants such as metals and hydrophobic organics through the terrestrial environment. an understanding of their role in the transport of contaminants is therefore essential and is facilitated if the acid is labelled with a suitable radioactive label. This paper reports the use of 14C-methylamine and 125I to label humic acid with either 14C or 125I and investigates factors which affect the yield of these reactions. the stability and mobility of the labelled humic material through sand is also reported. 相似文献
7.
A 17-year monitoring programme of reef flats at Ko Phuket, Thailand afforded an opportunity to evaluate both univariate and multivariate measures of environmental stress in an assessment of change on coral reef ecosystems. The sites at Ko Phuket suffered the effects of dredging in 1986-1987 and then anomalously low sea levels in 1997-1998 as a result of climate-related events in the Indian Ocean. Univariate measures of species diversity and taxonomic distinctness ((*) increased across the reef flat, reflecting the greater effects of physical stresses on the inner reef flats (compared with outer reef flats) at all sites, with more congeneric species present on the inner reef and more confamilial species on the outer reef. Multivariate measures showed a clear breakdown in seriation patterns at all sites during the dredging in 1987 and in 1998, as a result of earlier negative sea-level anomalies. Recovery from environmental disturbances was obvious within 12 months in each case. The domination of the reefs by massive coral species, which are physiologically adapted to intertidal living and which display partial rather than total colony mortality, may be a factor contributing to the apparent resilience of the reef flats together with continued recruitment and survival of juvenile corals during adverse environmental conditions. Elevated sea temperatures and extensive bleaching of corals in 1991, 1995, and 1998 had no effect upon coral community measures, with many corals recovering their zooxanthellae numbers within 3-5 months of the bleaching events. 相似文献
8.
Climate change is likely to act as a multiple stressor, leading to cumulative and/or synergistic impacts on aquatic systems. Projected increases in temperature and corresponding alterations in precipitation regimes will enhance contaminant influxes to aquatic systems, and independently increase the susceptibility of aquatic organisms to contaminant exposure and effects. The consequences for the biota will in most cases be additive (cumulative) and multiplicative (synergistic). The overall result will be higher contaminant loads and biomagnification in aquatic ecosystems. Changes in stratospheric ozone and corresponding ultraviolet radiation regimes are also expected to produce cumulative and/or synergistic effects on aquatic ecosystem structure and function. Reduced ice cover is likely to have a much greater effect on underwater UV radiation exposure than the projected levels of stratospheric ozone depletion. A major increase in UV radiation levels will cause enhanced damage to organisms (biomolecular, cellular, and physiological damage, and alterations in species composition). Allocations of energy and resources by aquatic biota to UV radiation protection will increase, probably decreasing trophic-level productivity. Elemental fluxes will increase via photochemical pathways. 相似文献
9.
Macrobenthic sampling of a transect of six stations on the North coast of Central Java in October 1985 revealed three distinct communities which can be regarded as paraliels of those from north temperate waters: (i) An Amphioplus (Lymanella) laevis/Lovenia sp. community parallel with the Amphiura chiajei/Brissopsis lyrifera community. (ii) A Tellinides timorensis community parallel with Tellina spp. communities. (iii) A Laciolina philippinarum community parallel with Macoma spp. communities. A strict comparison of the structure of the first two of these communities with their counterparts in England shows that within-habitat diversity is similar in both regions. Diversity at two shallower subtidal stations is higher than at two deeper stations: this is attributed to the effects of natural, low-level, physical disturbance which maintains the communities in a sub-climax stage. Total abundance and biomass of the macrobenthic fauna was lower at the Javanese stations than in their temperate counterparts. 相似文献
10.
Detection of pollution effects on marine macrobenthos: further evaluation of the species abundance/biomass method 总被引:20,自引:0,他引:20
Further empirical data are presented to evaluate the method of detecting pollution-induced disturbance in marine benthic communities by a comparison of the distribution of numbers of individuals among species with the distribution of biomass among species. A suggested abbreviated name for the technique is the ABC method (abundance biomass comparison). Application of the technique to new data shows that it is a sensitive indicator of natural physical and biological disturbance as well as pollution-induced disturbance over both spatial and temporal scales. Changes in the configuration of ABC plots during ecological succession are the reverse of those resulting from increased pollution levels. The technique should also be applicable to intertidal sediments, where physical disturbance of the sediment by waves does not appear to preclude its utility. 相似文献