The aim of this study was to evaluate the suitability of the (Ca + Mg + K)/Al and the Ca/Al ratios in soil solution as chemical criteria for forest condition in critical load calculations for forest ecosystems. The tree species Norway spruce, Sitka spruce and beech were studied in an area with high deposition of sea salt and nitrogen in the south-western part of Jutland, Denmark. Throughfall and soil water were collected monthly and analysed for pH, NO₃-N, NH₄-N, K, Ca, Mg, DOC and Altot. Organic Al was estimated using DOC concentrations. Increment and defoliation were determined annually, and foliar element concentrations were determined every other year. The throughfall deposition was highest in the Sitka spruce stand (maximum of 40 kg N ha-¹yr-¹) and lowest in the beech stand (maximum of 11 kg N ha-¹yr-¹). The Sitka spruce stand leached on average 12 kg N ha-¹yr-¹ during the period 1988-1997 and leaching increased throughout the period. Only small amounts of N were leached from the Norway spruce stand whereas almost no N was leached from the beech stand. For all tree species, both (Ca + Mg + K)/Al and Ca/Al ratios decreased in soil solution at 90 cm depth between 1989 and 1999, which was mainly caused by a decrease in concentrations of base cations. The toxic inorganic Al species were by far the most abundant Al species at 90 cm depth. At the end of the measurement period, the (Ca + Mg + K)/Al ratio was approximately 1 for all species while the Ca/Al ratio was approximately 0.2. The lack of a trend in the increment rates, a decrease in defoliation as well as sufficient levels of Mg and Ca in foliage suggested an unchanged or even slightly improved health condition, despite the decreasing and very low (Ca + Mg + K)/Al and Ca/Al ratios. The suitability of these soil solution element ratios is questioned as the chemical criteria for soil acidification under field conditions in areas with elevated deposition rates of sea salts, in particular Mg.

Model aquatic ecosystems have been used to study the natural mechanisms involved in the distribution and transformation of inorganic mercury (IHg) in the different compartments and its interactions with the biota. Laboratory incubations in indoor freshwater microcosms, presenting a simple biological organization, were carried out at various spiked concentrations (3, 25 and 257 nmol l-¹ of IHg, as mercuric chloride) and from a single initial contamination of the water column. The different compartments of the model ecosystems (water, sediment, macrophytes Elodea canadensis and snails Lymnaea stagnalis) were investigated for mercury distribution and speciation during a 2-month experimental period. The principal results obtained have evidenced different Hg biogeochemical pathways including biotic IHg methylation and reduction and transfer to the biota. A fast transfer of IHg from the water to the aquatic organisms and to the sediment was first observed with IHg half-lives of 24 h and 8 days, respectively. IHg methylation, clearly related to biogenic processes, was also demonstrated in all contaminated microcosms after 1 week of exposure. Finally, gaseous mercury species were determined in the different microcosms and significant biological induced production of elemental Hg (Hg°) and dimethyl Hg (DMHg) was observed. This overall investigation, based on the time courses evolution of IHg and in situ produced monomethylmercury (MMHg) concentrations allows to determine uptake and elimination rate constants for IHg as well as the bioaccumulation kinetics of MMHg in macrophytes and snails. The applicability of these aquatic model ecosystems to provide real insights for pollution impact and ecotoxicological risk assessments has been demonstrated.

Agricultural soils high in both fluoride (F) and phosphate (P) are common due to long-term accumulation of F from multi-sources and extensive application of phosphate fertilizers. Iron (Fe) and aluminum (Al) (hydro)oxides in acidic soils serve as main geochemical sinks of both P and F, influencing their transport and bioavailability. Though sorption of P and F in their single-ion system has been extensively investigated, studies on co-sorption of F and P on soils are very limited. In this study, the batch technique was used to investigate mutual effects of F and P on their co-sorption/desorption in an acidic red soil with high contents of Fe and Al (hydro)oxides. Results indicate that, in F-P coexisting system, a decrease in pH enhances the sorption of both F and P. An increase in F concentration suppresses P sorption due to competitive effect. However, F sorption can be improved in the presence of P due to surface precipitation of (Al,Fe)-F-P. Sorption of F and P follows both the Langmuir and Freundlich isotherms. Different orders of F and P addition into the soil have no appreciable effect on P sorption, but exert significant impact on F sorption. The presence of F has no measurable effect on P desorption, while the stability of F in the presence of P can be significantly diminished in comparison with that in the absence of P, which would lead to an improvement of F mobility.

Automated synoptic weather typing and robust orthogonal stepwise regression analysis (via principal components analysis) were applied together to develop within-weather-type air pollution prediction models for a variety of pollutants (specifically, carbon monoxide – CO, nitrogen dioxide – NO₂, ozone – O₃, sulphur dioxide – SO₂, and suspended particles – SP) for the period 1974–2000 in south-central Canada. The SAS robust regression procedure was used to limit the influence of outliers on air pollution prediction algorithms. Six-hourly Environment Canada surface observed meteorological data and 6-hourly US National Centers for Environmental Prediction (NCEP) reanalysis data of various weather elements were used in the analysis. The models were developed using two-thirds of the total years for meteorological and air pollution data; the remaining one-third (randomly selected) was used for model validation. Robust stepwise regression analysis was performed to analytically determine the meteorological variables that might be used to predict air pollution concentrations. There was a significant correlation between observed daily mean air pollution concentrations and model predictions. About 20, 50, and 80% of the 80 prediction models across the study area possessed R ² values ≥ 0.7, 0.6, and 0.5, respectively. The results of model validation were similar to those of model development, with slightly smaller model R ² values.

Nitrogen (N) budget was estimated with dissolved inorganic N (DIN) and dissolved organic N (DON) in a forested mountainous watershed in Tsukui, Kanagawa Prefecture, about 50 km west of Tokyo in Central Japan. The forest vegetation in the watershed was dominant by Konara oak (Quercus serrata) and Korean hornbeam (Carpinus tschonoskii), and Japanese cedar (Cryptomeria japonica). Nitrate (NO₃ -) concentration in the watershed streamwater was averagely high (98.0 ±± 19 (±± SD, n = 36) μmol L-¹) during 2001-2003. There was no seasonal and annual changes in the stream NO- ₃ concentration even though the highest N uptake rate presumably occurred during the spring of plant growing season, a fact indicating that N availability was in excess of biotic demands. The DON deposition rates (DON input rates) in open area and forest area were estimated as one of the main N sources, accounting for about 32% of total dissolved N (TDN). It was estimated that a part of the DON input rate contributed to the excessive stream NO- ₃ output rate under the condition of the rapid mineralization and nitrification rates, which annual DON deposition rates were positively correlated with the stream NO₃ - output rates. The DON retention rate in the DON budget had a potential capacity, which contributed to the excessive stream NO- ₃ output rate without other N contributions (e.g. forest floor N or soil N).

High mortality rates due to predation from fish may reduce densities of preferred prey animals. Predation may also depress the rate of recovery from environmental stress. In an alpine ecosystem damaged by acidification, we compared three different techniques of monitoring the recovery of two large species of crustaceans, the amphipod Gammarus lacustris and the notostrachan Lepidurus arcticus. The methods used were: (1): benthic littoral kick samples, (2): artificial substrate in the form of jute bags, (3): examination of brown trout stomachs. The monitoring took place in two limed lakes at the Hardangervidda mountain plateau in Central Norway, L. Svartavatn and L. Svartavasstjørni. Brown trout, Salmo trutta, is the only fish species in the lakes. Liming as a water quality improvement measure was started in 1994. All stomach samples were negative with respect to Gammarus and Lepidurus during the period 1987-1998. In 1999, the first records of both species were done in trout stomachs collected from Lake Svartavatnet. In Lake Svartavasstjørni, Lepidurus and Gammarus reappeared in fish stomachs in 2001 and 2002, respectively. During the period of monitoring, no records of these crustaceans were done in benthic samples and on artificial substrate in any of the two lakes. In an unacidified reference site, Lake Skiftesjøen, both benthic samples and the jute bags indicated a dense population of Gammarus. Our results strongly indicate that studies of fish stomachs are the best method for monitoring low-density populations of attractive fish food animals.

Analysis of the sensitivity of soils to acidification caused by the deposition of atmospheric pollutants has been one of the major scientific issues in Europe during the past few decades. In the present study, critical loads of acid deposition were calculated using the most accurate datasets available at present for European soils, by the “Simple Mass Balance” method. The results show that the soils most sensitive to acid deposition are Histosols, Cryosols and Podzols in cold areas in northern countries, followed by Lithic and Haplic Leptosols (Dystric) developed on acid parent materials. The highest critical loads corresponded to soils developed over calcareous rocks and soils in areas subject to high precipitation, even those dominated by poorly weatherable primary mineral. In the latter case critical alkalinity leaching is the main variable that determines the value of critical loads, because of the buffering action of the dissolution of aluminium compounds. The results were compared with those obtained by the Stockholm Environmental Institute in the same area, but with a different method of analysis. It was found that the results are highly dependent on the method used to perform the analysis.

Interactions between Zn and Cd on the accumulation of these metals in coontail, Ceratophyllum demersum were studied at different metal concentrations. Plants were grown in nutrient solution containing Cd (0.05–0.25 mg l⁻¹) and Zn (0.5–5 mgl⁻¹). High concentrations of Zn caused a significant decrease in Cd accumulation. In general, adding Cd solution decreased Zn accumulation in C. demersum except at the lowest concentration of Zn in which the Zn accumulation was similar to that without Cd. C. demersum could accumulate high concentrations of both Cd and Zn. The influence of humic acid (HA) on Cd and Zn accumulation was also studied. HA had a significant effect on Zn accumulation in plants. 2 mg l⁻¹ of HA reduced Zn accumulation at 1 mg l⁻¹ level (from 2,167 to 803 mg kg⁻¹). Cd uptake by plant tissue, toxicity symptoms and accumulation at 0.25 and 0.5 mg l⁻¹, were reduced (from 515 to 154 mg kg⁻¹ and from 816 to 305 mg kg⁻¹, respectively) by addition of 2 mg l⁻¹ of HA. Cd uptake reached a maximum on day 9 of treatment, while that of Zn was observed on day 15. Long-term accumulation study revealed that HA reduced toxicity and accumulation of heavy metals.