Isotopic ratios of lead in contemporary environmental material from Scotland

Lead emitted into the environment, primarily from the combustion of leaded petrol and industrial activities, retains the isotopic signature of the ore(s) from which it is derived. Leaded petrol, atmospheric particulates and street dust sampled in central Edinburgh between February 1989 and December 1991 had mean²⁰⁶Pb/²⁰⁷Pb ratios of 1.082 ± 0.024, 1.092 ± 0.011 and 1.109 ± 0.016 respectively. These isotope ratios were found to be depleted in²⁰⁶Pb compared with a mean of 1.160 ± 0.012 for tap water in contact with lead pipes and %typical ratios of 1.17–1.19 for British lead ore deposits and coal. Paint, with an observed wide range of 20 Pb²⁰⁷ Pb ratios (1.083–1.183), appears to have significantly influenced house dust and some street dust²⁰⁶Pb²⁰⁷ values. Such overlaps and influences may hinder the quantitative apportionment, via isotope data, of source and route in general population surveys of human exposure to lead.     

Dynamic reserve design with the union-find algorithm

When reserve networks are established over time, there is a risk that sites will be developed in areas planned for future reservation, reducing the effectiveness of reserves. We developed a dynamic reserve design model that maximizes the expected number of species conserved, taking account of the risk of future habitat loss and fragmentation. The model makes use of the union-find algorithm, which is an efficient method for maintaining a list of connected regions in a graph as nodes and edges are inserted. A simple extension of the algorithm allows us to efficiently determine, for each species, when a sequence of site selections results in a reserve in which the species can persist. The extension also allows us to determine when a sequence of deforestation events results in the species becoming non-viable. The dynamic reserve design model is much more effective than commonly used heuristics, particularly when multiple connected sites are required for species persistence. The model also is able to solve much larger problems with greater effectiveness than the only previous dynamic reserve design model that considered site connectivity relationships. The union-find algorithm has much scope for addressing ecological management problems in which dynamic connectivity needs to be considered.     

Geochemical Associations of Sellafield-Derived Radionuclides in Saltmarsh Deposits of the Solway Firth

This paper describes a study of the geochemical associations of Sellafield waste radionuclides in saltmarsh sediments from south-west s]Scotland. The contaminant radionuclides are transported to this environment in association with particulate material and ¹³⁷Cs was found to be predominantly (80-98%) non-extractable. In the case of ^239+240Pu there was a redistribution from the oxalate extractable oxide fraction to the pyrophosphate extractable organic fraction as a consequence of on-shore transfer of contaminated sediment. The relatively aggressive nature of the chemical extractants required to remove the radionuclides from the sediments suggests that they were in a form which was unlikely to result in their being released into the aquatic environment or taken up by plants. Plutonium had a greater potential mobility or bioavailability than Cs. Values of K^D for the desorption of ¹³⁷Cs from the sediment by freshwater, groundwater and seawater were all approximately 10⁵ L kg^-1, confirming its immobility in this environment. The desorption K_D values for stable ¹³³Cs were all approximately 10⁶ L kg^-1, so the stable Cs did not have a significant influence on the radiocaesium in this sediment.     

Effects of mussel aquaculture on the nitrogen cycle and benthic communities in Kenepuru Sound,Marlborough Sounds,New Zealand

Nitrogen pools and transformations and benthic communities at a Perna canaliculus farm and a nearby reference site without direct influence of marine farming in Kenepuru Sound, New Zealand, were compared on four dates between September 1982 and May 1983. The organic nitrogen pool in the top 12 cm sediment was 7.4 to 10.8 mol m^-2 at the mussel farm and 6.1 to 8.9 mol m^-2 at the reference site. The nitrate and nitrite pools were similar in both sediments, but the ammonium pool in the mussel farm sediment was about twice as high as in the reference sediment. In January, the sediment ammonium concentrations ranged from 418 nmol cm^-3 (surface) to 149 nmol cm^-3 (12 cm depth) at the mussel farm and from 86 to 112 nmol cm^-3 at the reference site. The molar C:N ratio of the sediment organic matter was 6.2 to 7.2 at the mussel farm and 7.9 to 10.0 at the reference site. The molar N:P ratio of the sediment organic matter was 4.3 to 7.2 and 3.3 to 6.1 at mussel farm and reference site, respectively. The total nitrogen mineralisation rate in the top 12 cm sediment ranged from 21.7 to 37.1 mmol m^-2 d^-1 at the mussel farm and from 8.5 to 25.0 mmol m^-2 d^-1 at the reference site. Ammonium excretion by mussels was about 4.7% (January) and 7.4% (May) of the combined nitrogen mineralisation by mussels and sediment. The sediment-denitrification rate was 0.7 to 6.1 mmol m^-2 d^-1 at the mussel farm and 0.1 to 0.9 mmol m^-2 d^-1 at the reference site. In January, 76 and 93% of the nitrate reduced in the sediments were denitrified at the mussel farm and reference site, respectively. The denitrification rate on the mussel lines (determined on detritus-covered mussels) was twice the mussel farm sediment-denitrification rate and 10 times the reference sediment-denitrification rate. Total denitrification at the mussel farm was 21% higher than at the reference site. The loss of nitrogen through mussel harvest and denitrification was 68% higher at the mussel farm. The surface layers of both sediments contained about 75 mg m^-2 chlorophyll a. Sediment phaeophytin levels were 52 mg m^-2 at the reference site and 137 mg m^-2 at the mussel farm. While the benthic infauna of the mussel-farm sediment consisted only of polychaete worms, the reference sediment contained also bivalve molluscs, brittle stars and crustaceans.     

Lake sediments record sensitivity of two hydrologically closed upland lakes in Mexico to human impact

We provide evidence of rapid, recent environmental change in two lakes in the highlands of central Mexico. Multiple sediment cores were obtained from Lago de Zirahuén (Michoacán) and Laguna de Juanacatlán (Jalisco). Analysis of diatom assemblages, magnetic susceptibility, and metal concentrations was carried out, with the chronology provided by 210Pb dating, 14C dating, and tephrochronology. There is evidence of catchment disturbance during the colonial period in both basins, but the most striking feature at both sites is the rapid change in diatom assemblages during the last 20 y, indicating the onset of eutrophication. Limnological data from Lago de Zirahuén support this interpretation, although none are available from Laguna de Juanacatlán. Paleolimnology is a powerful tool in tracking recent change, particularly in the absence of regular limnological monitoring programs. These lakes appear to be highly sensitive to changes in catchment exploitation, which must be considered in future drainage basin management.     

Environmental leadership plus total quality management equals continuous improvement

Xerox was one of the first U.S. companies to discover that environmentally sound practices not only result in good community relations, but also often more than pay for themselves. This case study describes the application of the quality process to environmental management at Xerox and shows how a focus on prevention, employee involvement, teamwork, and the use of quality principles and tools can improve profitability for any company.     

Development of solid phase adsorption toxin tracking (SPATT) for monitoring anatoxin-a and homoanatoxin-a in river water

Sampling and monitoring for cyanotoxins can be problematic as concentrations change with environmental and hydrological conditions. Current sampling practices (e.g. grab samples) provide data on cyanotoxins present only at one point in time and may miss areas or times of highest risk. Recent research has identified the widespread distribution of anatoxin-producing benthic cyanobacteria in rivers highlighting the need for development of effective sampling techniques. In this study we evaluated the potential of an in situ method known as solid phase adsorption toxin tracking (SPATT) for collecting and concentrating anatoxin-a (ATX) and homoanatoxin-a (HTX) in river water. Fifteen different adsorption substrates were screened for efficiency of ATX uptake, nine of which retained high proportions (>70%) of ATX. Four substrates were then selected for a 24-h trial in a SPATT bag format in the laboratory. The greatest decrease in ATX in the water was observed with powdered activated carbon (PAC) and Strata-X (a polymeric resin) SPATT bags. A 3-d field study in a river containing toxic benthic cyanobacterial mats was undertaken using PAC and Strata-X SPATT bags. ATX and HTX were detected in all SPATT bags. Surface grab samples were taken throughout the field study and ATX and HTX were only detected in one of the water samples, highlighting the limitations of this currently used method. Both Strata-X and PAC were found to be effective absorbent substrates. PAC has the advantage that it is cheap and readily available and appears to continue to sorb toxins over longer periods than Strata-X. SPATT has the potential to be integrated into current cyanobacterial monitoring programmes and would be a very useful and economical tool for early warning of ATX and HTX contamination in water.