COMPUTING THE RISKS ASSOCIATED WITH WASTELOAD) ALLOCATION MODELING1

ABSTRACT: The risks associated with a traditional wasteload allocation (WLA) analysis were quantified with data from a recent study of the Upper Trinity River (Texas). Risk is define here as the probability of failing to meet an established in-stream water quality standard. The QUAL-TX dissolved oxygen (DO) water quality model was modified to a Monte Carlo framework. Flow augmentation coding was also modified to allow an exact match to be computed between the predicted and an established DO concentration standard, thereby providing an avenue for linking input parameter uncertainty to the assignment of a wasteload permit (allowable mass loading rate). Monte Carlo simulation techniques were employed to propagate input parameter uncertainties, typically encountered during WLA analysis, to the computed effluent five-day carbonaceous biochemical oxygen demand requirements for a single major wastewater treatment plant (WWTP). The risk of failing to meet an established in-stream DO criterion may be as high as 96 percent. The uncertainty associated with estimation of the future total Kjeldahl nitrogen concentration for a single tributary was found to have the greatest impact on the determination of allowable WWTP loadings.     

Sampling and analyses of colloids at the Drigg low level radioactive waste disposal site

Water samples have been extracted from inside (from standpipes) and from outside (from boreholes) of the trenches at the low level radioactive waste disposal site at Drigg in Cumbria, UK. The samples were taken anaerobically from between 8.5 and 10.0 m below the surface using a submersible pump at low flow rates to ensure that the waters in the standpipes and boreholes were maintained at constant levels. To ensure representative samples, the Eh, pH. conductivity, temperature, iron and dissolved oxygen concentrations of the waters were taken during initial purging and during sampling. The gross tritium, gross non-tritium beta, gross alpha and gamma activities of each sample were determined using suitable sample preparation and counting techniques. Samples were then anaerobically, sequentially filtered through 12 microm, 1 microm, 30 kDa and 500 Da filter membranes. The filtrates were analysed for gross alpha, gross non-tritium beta and gamma activities. SEM and STEM analyses were used to determine the colloid population. An energy dispersive analyser on the SEM was used to determine the major elements present in the colloids. UV-visible spectrophotometry, fluorescence spectrophotometry and high performance size exclusion liquid chromatography were used to analyse the waters before and after treatment with ion exchange materials to determine whether natural organic matter was present in the waters. Results showed that two major types of colloids (iron containing colloids and silicon containing colloids) were present in the waters. There were also a small number of other colloids that contain, as major elements, aluminium, calcium and chromium. Organic colloids were also present. The majority of the radioactivity in the waters was due to tritium. Waters taken from outside the trenches contained low levels of non-tritium beta activities and alpha activities which were lower than the minimum detectable amount. Waters taken from the trenches contained non-tritium beta activities and low levels of alpha emitters. Filtration of the trench waters showed that some of the alpha activity was retained by the 30 kDa and 500 Da membranes suggesting that this activity was associated with small colloids. Radioactivity was not found to be associated with colloids present in the waters taken from outside the trenches. Possible reasons for this observation could be that radionuclide bearing colloids have not yet reached the far-field or that the radionuclide concentration is diluted to below the minimum detectable amount. After concentrating two of the samples by factors of x20 and x 16 respectively, 2.4+/-0.1 and 0.6+/-0.1 Bq dm(-3) of 137Cs were measured.     

MODELING THE IMPACT OF SUBSURFACE NUTRIENT FLUX ON WATER QUALITY IN THE LOWER TRUCKEE RWER,NEVADA1

ABSTRACT: The impacts of regional groundwater quality and local agricultural activities on in-stream water quality in the Lower Truckee River, Nevada, were assessed through a detailed program of monitoring and computer simulation. An agricultural diversion and return-flow were monitored in great detail to determine mass loading rates of nutrients from agriculture in the area. Once characterized, the cumulative impacts of agricultural diversions and return-flows were evaluated using the Water Quality Assessment Program (WASP) to model nitrogen, phosphorus, periphyton, and dissolved oxygen. Monitoring showed that a significant proportion of the water diverted for agricultural purposes returned to the river as surface point return-flow (estimated at 13.9 percent $ 0.1 percent), and as groundwater diffuse return-flow (estimated at 27 percent $ 6 percent). Modeling efforts demonstrated the significant effect of assumed regional groundwater quality (nitrate) upon predicted periphyton growth and associated diel fluctuations of dissolved oxygen.     

Assessment of effects of climate change and grazing activity on grassland yield in the Three Rivers Headwaters Region of Qinghai–Tibet Plateau, China

Inter-annual dynamics of grassland yield of the Three Rivers Headwaters Region of Qinghai–Tibet Plateau of China in 1988–2005 was analyzed using the GLO-PEM model, and the herbage supply function was evaluated. The results indicate that while grassland yield in the region showed marked inter-annual fluctuation there was a trend of increased yield over the 18 years of the study. This increase was especially marked for Alpine Desert and Alpine Steppe and in the west of the region. The inter-annual coefficient of variation of productivity increased from the east to the west of the region and from Marsh, Alpine Meadow, Alpine Steppe, Temperate Steppe to Alpine Desert grasslands. Climate change, particularly increased temperatures in the region during the study period, is suggested to be the main cause of increased grassland yield. However, reduced grazing pressure and changes to the seasonal pattern of grazing could also have influenced the grassland yield trend. These findings indicate the importance of understanding the function of the grassland ecosystems in the region and the effect of climate change on them especially in regard to their use to supply forage for animal production. Reduction of grazing pressure, especially during winter, is indicated to be critical for the restoration and sustainable use of grassland ecosystems in the region.     

Pre-concentration of naturally occurring radionuclides and the determination of (212)Pb from fresh waters

A novel technique has been developed for determining the ²¹²Pb activity of fresh waters. This is of interest to environmental monitoring programmes that utilise gross α-activity methods to screen for anthropogenic radionuclides. The contribution from ²¹²Pb varies, and is difficult to experimentally measure due to its relatively short half-life (t_½ = 10.6 h) and low environmental activity (<0.1 Bq l⁻¹). The use of a three-stage technique that encompasses a unique form of pre-concentration, separation and analysis by liquid scintillation counting allows a lower detection limit of 0.006 Bq l⁻¹ with a chemical yield of 92.5 ± 5.6%. The measurement can be obtained within 7 h of sample collection, and is calculated using the radioactive decay of ²¹²Bi. Other naturally occurring radionuclides may also be extracted using the pre-concentration stage of the technique, with efficiencies above 90% at a range of pH values.     

The application of an indicator based on taxonomic distinctness for UK marine biodiversity assessments

Mankind needs to use the resources and opportunities offered by the marine environment while protecting ecological processes and systems. This is the foundation for sustainable development, which can only be achieved by adopting an appropriate management approach. Whether internationally or at a regional scale, successful management of marine ecosystems needs to be based on a scientifically robust approach to monitoring environmental change. Within such a framework, the conservation of marine biological diversity is problematic, as many conventional measures of diversity are not appropriate for measuring the types of change that require management. New indicators are required and in this paper we summarise some of the current methodology being used to derive such indices, which may be used to evaluate the effectiveness of marine stewardship initiatives. Through a series of examples we demonstrate the application of the taxonomic distinctness indicator of biodiversity to marine environmental assessment and its development towards becoming an operational tool.     

Cost‐Effectiveness of Using Small Vertebrates as Indicators of Disturbance

In species‐rich tropical forests, effective biodiversity management demands measures of progress, yet budgetary limitations typically constrain capacity of decision makers to assess response of biological communities to habitat change. One approach is to identify ecological‐disturbance indicator species (EDIS) whose monitoring is also monetarily cost‐effective. These species can be identified by determining individual species’ responses to disturbance across a gradient; however, such responses may be confounded by factors other than disturbance. For example, in mountain environments the effects of anthropogenic habitat alteration are commonly confounded by elevation. EDIS have been identified with the indicator value (IndVal) metric, but there are weaknesses in the application of this approach in complex montane systems. We surveyed birds, small mammals, bats, and leaf‐litter lizards in differentially disturbed cloud forest of the Ecuadorian Andes. We then incorporated elevation in generalized linear (mixed) models (GL(M)M) to screen for EDIS in the data set. Finally, we used rarefaction of species accumulation data to compare relative monetary costs of identifying and monitoring EDIS at equal sampling effort, based on species richness. Our GL(M)M generated greater numbers of EDIS but fewer characteristic species relative to IndVal. In absolute terms birds were the most cost‐effective of the 4 taxa surveyed. We found one low‐cost bird EDIS. In terms of the number of indicators generated as a proportion of species richness, EDIS of small mammals were the most cost‐effective. Our approach has the potential to be a useful tool for facilitating more sustainable management of Andean forest systems. Rentabilidad del Uso de Pequeños Vertebrados como Indicadores de Perturbaciones     

Ecophilosophy and science

Summary This paper aims to do two main things: first, to provide an introduction to ecophilosophy by presenting a spectrum of positions that have been developed to characterise the relationship between humans and their environment; second, to examine the variety of ways in which scientific work impacts upon human thought in regard to each of these positions. The import of this discussion should be twofold: first, it should help to acquaint readers with, and hopefully, interest them in, the kinds of developments that have been occurring in the area of ecophilosophy; second, it should help to acquaint environmentally concerned people with, and, hopefully, interest them in, the relevance of science to their arguments. Although many environmentally concerned people are scientifically informed, this second aim is worth stating because a number of environmentally concerned people unfortunately remain suspicious of the role of science in general.Dr Warwick Fox is a Research Fellow at the Centre for Environmental Studies at the University of Tasmania. His first degree, in experimental psychology from the University of Western Australia, was followed by PhD in environmental philosophy. Currently his research interests are concerned with the development of a comprehensive and coherent oriented world view, from epistemology and cosmology to psychology, ethnics and politics.     

SIMULATING SEDIMENT TRANSPORT IN THE CARSON RIVER AND LAHONTAN RESERVOIR,NEVADA, USA1

ABSTRACT: The discovery of the Comstock Lode in western Nevada in 1859 initiated the use of liquid mercury (Hg) or “quicksilver” to remove gold (Au) and silver (Ag) from crushed ore. Today, Hg is present in historic mill tailings piles, in alluvial deposits adjacent to the Carson River, and in Lahontan Reservoir. Mercury concentrations in Carson River water have been reported as high as 61 μg/L by the U.S. Geological Survey. Fish from Lahontan Reservoir have methylmorcury (MeHg) concentrations as much as four times the 1.0 μg/g limit for human consumption. Since more than 95 percent of total Hg in water can be associated with particulates, the transport of sediment must be quantified to understand the fate of Hg in the system. By linking the RIVMOD hydrodynamic model with the WASP5 water quality model, and using suspended sediment rating curves along with bedload transport equations, reliable predictions of sediment transport can be made. Measured suspended sediment data from the Carson River, and an estimate of annual sediment loading to Lahontan Reservoir, were used to create a calibrated sediment transport model. Model simulations predicted the long term transport of sediment into Lahontan Reservoir, the transport of sediment into Lahontan Reservoir during a flood year (1986 water year), and concentrations of total Hg in the Carson River using an estimate of sediment Hg concentrations. This research will eventually be used with an Hg model to predict the fate of Hg in the river and reservoir system.     

The simultaneous modelling of metal ion and humic substance transport in column experiments

Pulsed column experiments using Co, fulvic acid and porous sediment packing, along with up/down-flooding experiments using Eu, humic acid and intact sandstone blocks have been performed. The elution of metal and humic and their distribution along the sandstone columns have been measured. A mixed equilibrium and kinetic coupled chemical transport model has been used to simulate the results. In both cases, one exchangeable and one non-exchangeable component have been used to simulate the interaction of metal and humic substance. For the pulsed experiments, a simple equilibrium approach was used to model humic sorption, while a two component, kinetic model was required for the sandstone columns.