Loch fleet: liming to restore a brown trout fishery

This project has been successful in meeting its objectives in terms of demonstrating that catchment liming techniques can restore acidified waters to conditions suitable for fish populations for relatively long periods. This improvement in conditions has extended to the inlet stream, which provides vital fish spawning and nursery areas, which are difficult to treat effectively be other means in remote locations. The project has also provided an assessment of the effectiveness of differing rates and modes of lime application, which suggest that only quite restricted parts of a catchment require treatment. This not only maximizes the cost-effectiveness of the treatments, but also helps to minimize any side-effects on, for example, moorland vegetation. The biological monitoring programme at Loch Fleet has also provided an assessment of the overall ecological consequences of adding limestone to naturally acidic and calcium-deficient ecosystems.     

Measurement of dry deposition of ammonia on a forest

Ammonia concentration gradients above a Douglas fir canopy were measured from 16 August to 31 December 1989 by two automated high-precision thermodenuders at the location Speulderbos in The Netherlands. Concentration gradients were used to calculate the dry deposition flux of ammonia via flux-gradient theory. Meteorological data were obtained from a nearby tower. Ammonia concentrations were highly variable with highest values during the night. Concentration gradients were very small during daytime and quite large at night. Median values of the calculated deposition flux and deposition velocity were 0.1 microg m(-2) s(-1) and 3.2 cm s(-1) respectively (N=1624).     

Ozone in the urban southeastern United States

Ozone measurements (daily maximum values) from the Aerometric Information Retrieval System database are analyzed for selected sites, during 1980 to 1988, in southeastern USA. Frequency distributions, for most sites during most years, show a typical bell-shaped curve with the higher frequency around the yearly daily maximum ozone mean of about 100 to about 110 microg m(-3) (50-55 ppbv). Abnormal years in ozone concentration may skew the distribution as the mean shifts. A correlation of daily maximum ozone concentrations above 140 microg m(-3) (70 ppbv) between sites shows a division between the sites in the northern protion of the region and those in the southern portion of the region. Variations in ozone levels are well correlated over distances of several hundred kilometers, suggesting that high values are associated with synoptic scale episodes. An ozone exposure analysis also shows higher ozone exposures (250-300 ppm days) in the northerly sites as compared to the southerly sites (150-170 ppm days).     

Modelling episodic acidification of surface waters: the state of science

Field studies of chemical changes in surface waters associated with rainfall and snowmelt events have provided evidence of episodic acidification of lakes and streams in Europe and North America. Modelling these chemical changes is particularly challenging because of the variability associated with hydrological transport and chemical transformation processes in catchments. This paper provides a review of mathematical models that have been applied to the problem of episodic acidification. Several empirical approaches, including regression models, mixing models and time series models, support a strong hydrological interpretation of episodic acidification. Regional application of several models has suggested that acidic episodes (in which the acid neutralizing capacity becomes negative) are relatively common in surface waters in several regions of the US that receive acid deposition. Results from physically based models have suggested a lack of understanding of hydrological flowpaths, hydraulic residence times and biogeochemical reactions, particularly those involving aluminum. The ability to better predict episodic chemical responses of surface waters is thus dependent upon elucidation of these and other physical and chemical processes.     

Towards an assessment of the influence of climate on wet acidic deposition in Europe

The EMEP precipitation composition network is used to examine relationships between non-marine SO4(2-), NO3-, NH4+, H+ concentrations and precipitation amount and a local zonal pressure index (an index of the atmospheric circulation). The pattern of the relationships changes across Europe with the zonal pressure gradient explaining more of the variance in ion concentrations in the west, and precipitation amount explaining relatively more of the variance in the east. There is some predictive capability for precipitation composition in the zonal pressure gradient for restricted regions in Europe; R2 values are up to 40% on a daily basis but in some seasons/months attain >60%. The zonal pressure gradient is an index which appears to include pertinent information on transport and wet removal. Preliminary analysis indicates that this approach can be useful in assessing the contributions of changing atmospheric circulation to time-trends of wet acidic deposition in an area stretching from the UK over the North Sea to Denmark. The zonal pressure gradient is known to have varied on time-scales of decades, and the simple index may be one appropriate approach to assessing future deposition patterns from future climate projections.     

Comparison of episodic acidification in Canada, Europe and the United States

Episodic acidification is practically a ubiquitous process in streams and drainage lakes in Canada, Europe and the United States. Depressions of pH are often smaller in systems with low pre-episode pH levels. Studies on European surface waters have reported episodes most frequently with minimum pH levels below 4.5. In Canada and the United States, studies have also reported a number of systems that have had minimum pH levels below 4.5. In all areas, change in water flowpath during hydrological events is a major determinant of episode characteristics. Episodic acidification is also controlled by a combination of other natural and anthropogenic factors. Base cation decreases are an important contributor to episodes in circumneutral streams and lakes. Sulphate pulses are generally important contributors to episodic acidification in Europe and Canada. Nitrate pulses are generally more important to episodic acidification in the Northeast United States. Increases in organic acids contribute to episodes in some streams in all areas. The sea-salt effect is important in near-coastal streams and lakes. In Canada, Europe and the United States, acidic deposition has increased the severity (minimum pH reached) of episodes in some streams and lakes.     

Observations of H2O2 and PAN in a rural atmosphere

Measurements of gaseous H2O2 and peroxyacetyl nitrate (PAN) concentrations in air are given for a site in rural southern England over an approximately 4-year period. In both cases the data show both diurnal and seasonal patterns. Temperature and wind direction had clear influences on the recorded concentrations of both species. There was an indication of increasing H2O2 concentrations with time. The use of a two-dimensional global model confirmed that this would be expected to occur alongside growth in ozone formation. It is suggested that, during photochemical episodes, the sequential build-up of ozone, PAN and H2O2 could be important in influencing the ability of vegetation to resist the effects of aggressive pollutants.     

Cadmium availability to the cyanobacterium Synechocystis aquatilis in solutions containing chloride

Availability of cadmium to Synechocystis aquatilis (estimated by 109Cd sorption and cadmium toxicity-14C method) in solutions containing cadmium and complexing (KCl) or non-complexing (KNO3) salts, in the range of 0-0.5 m was investigated. Both cadmium surface adsorption and transport into the cells were lower in solutions containing cadmium chloride complexes (CdCl+, CdCl2, CdCl3-) than in those containing cadmium in the form of Cd2+. Also, cadmium toxicity in solutions of higher KCl concentrations, in which CdCl+ and CdCl2 forms predominated, was significantly limited.     

The effect of temperature and salinity on copper body-burden and copper toxicity to Hediste (Nereis) diversicolor

Temperature from 12 to 22°C and salinity from 30.5 to 7.6 increased accumulation of copper in Hediste diversicolor. Copper accumulated ranged from 85.83 to 217.14 g g^-1. Sediments reduced accumulation of copper under temperature-salinity combinations. Accumulated copper ranged from 90.19 to 153.26 g g^-1.However, mortality of the worms was not solely dependent upon copper body-burden. It ranged from 34 to 45% and from 38 to 80% in the presence of sediment. A combination of osmoregulatory and thermal stresses increased the toxic effect of copper to the worms.     

The effects of salinity,temperature and sediment on the toxicity of copper to juvenile Hediste (Nereis) diversicolor (O. F. Muller)

Without sediment, increasing salinity (7.3 to 29.2) and increasing temperature (12 to 22 °C) reduced the toxicity of copper to juvenile Hediste diversicolor. The LC₅₀ values ranged from 357 gL^-1 in 7.3 to 513 g L^-1 in 29.2 at 12°C and from 247 to 500 g L^-1 at 22°C. In deionized water all the juvenile were dead in all solutions to which copper was added (100 to 600 g L^-1). Dead worms were swollen and everted their pharynxs. In higher doses of copper (500 to 600 g L^-1) the worms were abnormal in behaviour in all salinities (0 to 29.2). The ability to swim or crawl was disturbed.With sediments increasing temperature and increasing salinity increased the toxicity of copper to the worms. The LC₅₀ values ranged from 3200 to 4100 g L^-1 at 22°C. The response of the juvenile to copper was antagonistic to increasing temperature and salinity and synergistic to increasing salinity and increasing temperature without and with the sediment respectively.