Environmental specimen bank samples of Pleurozium schreberi and Hylocomium splendens as indicators of the radiation environment at the surface

Pleurozium schreberi (Brid.) Mitt. and Hylocomium splendens (Hedw.) Schimp. samples from the Finnish Environmental Specimen Bank were used to study the UV-B-absorbing compounds as potential screens of the past radiation environment. The first series from southern and central Finland consisted of samples collected from 18 P. schreberi or H. splendens dominated sites in 1985 and 1995. The second series from four H. splendens dominated sites (two in southern and two in northern Finland) and two P. schreberi dominated sites (one southern and one northern) were from the years 1985, 1990, 1995 and 2000. In the first series, the moss surface area of the analyzed specimens (5 +/- 0.2 mg DW) was smaller in 1995 (40% of both species collected in June) than in 1985 (40% of P. schreberi and 55% of H. splendens collected in September). The methanol-extractable UV-B-absorbing compounds of P. schreberi in 1985 and 1995 measured as absorbance at 10 nm intervals at 280-360 nm per mg DW revealed a negative correlation with reconstructed UV-radiation data. In the second series, the UV-B-absorbing compounds per specific surface area (surface area mm2 per DW) showed significant differences between the years. The highest values in both species were obtained in 1990. In H. splendens, a difference between the southern and northern samples was observed. The preliminary study encouraged the use of environmental specimen bank samples to indicate changes in surface radiation conditions.     

Dry deposition of nitrogen and sulfur to Ponderosa and Jeffrey pine in the San Bernardino national forest in Southern California

Little is known about the concentrations, deposition rates, and effects of nitrogenous and sulfurous compounds in photochemical smog in the San Bernardino National Forest (SBNF) in southern California. Dry deposition of NO(3)(-) and NH(4)(+) to foliage of ponderosa pine (Pinus ponderosa Laws.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.) was correlated (R = 0.83-0.88) with historical average hourly O(3) concentations at 10 sites across an O(3) gradient in the SBNF. Mean deposition fluxes of NO(3)(-) to ponderosa and Jeffrey pine branches were 0.82 nmol M(-2)s(-1) at Camp Paivika (CP), a high-pollution site, and 0.19 nmol m(-2) s(-1) at Camp Osceola (CAO), a low-pollution site. Deposition fluxes of NH(4)(+) were 0.32 nmol m(-2) s(-1) at CP and 0.17 nmol m(-2) s(-1) at CAO, while mean values for SO(4)(2-) were 0.03 at CP and 0.02 nmol m(-2) s(-1) at CAO. Deposition fluxes to paper and nylon filters were higher in most cases than fluxes to pine branches at the same site. The results of this study suggest that an atmospheric concentration and deposition gradient of N and S compounds occurs along with the west-east O(3) gradient in the SBNF. Annual stand-level dry deposition rates for S and N at CP and CAO were estimated. Further studies are needed to determine if high N deposition loads in the SBNF significantly affect plant/soil nutrient relations, tree health, and the response of ponderosa pine to ozone.     

Long-term development of inorganic nutrients and chlorophyll alpha in the open northern Baltic Sea

Eutrophication is an ongoing process in most parts of the Baltic Sea. This article reports on the changes during recent decades of several eutrophication-related variables in the open sea areas surrounding Finland (wintertime nutrient concentrations, wintertime nutrient ratios, and summer time chlorophyll alpha concentrations at the surface). The sum of nitrate- and nitrite-nitrogen ([NO3+NO2]-N) was observed to increase nearly fourfold in the Northern Baltic Proper and the Gulf of Finland and almost double in the Bothnian Sea from the 1960s until the 1980s or 1990s. The increase was followed by a decrease, which was modest in the two former subregions. Phosphate-phosphorus (PO4-P) concentrations followed a similar pattern in the Northern Baltic Proper (threefold increase and subsequent slight decrease) and Bothnian Sea (30% increase and subsequent decrease), but increased throughout the study in the Gulf of Finland, with the present concentration being threefold to the measurements made in the early 1970s. The PO4-P concentration decreased throughout the study in the Bothnian Bay. Silicate-silicon (SiO4-Si) concentrations decreased 30-50% from the early 1970s to the late 1990s and increased 20-40% thereafter in the Northern Baltic Proper, the Gulf of Finland, and the Bothnian Sea. Chlorophyll alpha showed an increase of over 150% in the Northern Baltic Proper and the Gulf of Finland from the 1970s until the early 2000s. In the Bothnian Sea the chlorophyll alpha concentration increased more than 180% from the late 1970s until the late 1990s, and decreased thereafter. According to these long-term observations, the Gulf of Finland and Northern Baltic Proper show clear signs of eutrophication, which may be emphasized by hydrographical changes affecting the phytoplankton communities and thus the algal biomass.     

Are N and S deposition altering the mineral composition of Norway spruce and Scots pine needles in Finland?

Data from a large-scale foliar survey were used to calculate the extent to which N and S deposition determined the mineral composition of Scots pine and Norway spruce needles in Finland. Foliar data were available from 367 needle samples collected on 36 plots sampled almost annually between 1987 and 2000. A literature study of controlled experiments revealed that acidifying deposition mediates increasing N and S concentrations, and decreasing Mg:N and Ca:Al ratios in the needles. When this fingerprint for N and S elevated deposition on tree foliage was observed simultaneously with increased N and S inputs, it was considered sufficient evidence for assuming that acidifying deposition had altered the mineral composition of tree needles on that plot in the given year. Evidence for deposition-induced changes in the mineral composition of tree foliage was calculated on the basis of a simple frequency model. In the late eighties the evidence was found on 43% of the Norway spruce and 27% of Scots pine plots. The proportion of changed needle mineral composition decreased to below 8% for both species in the late nineties.     

Simulating the long-term chemistry of an upland UK catchment: major solutes and acidification

CHUM-AM was used to investigate changes in soil and water chemical variables in four moorland sub-catchments in Cumbria UK, to which non-marine S deposition has declined by 65% since the 1970s. The principal processes represented in the model comprise N and S uptake and release, water movements, the binding of cations by soil organic matter, chemical interactions in solution, and chemical weathering. CHUM-AM reproduced reasonably well the current soil pH and pools of N and S, and changes in streamwater chemistry over the period 1970-2000, notably decreases in the concentrations of alkaline earth cations and sulphate, and increases in pH. The model also predicts streamwater pH-Al relationships in agreement with observations. Predictive calculations suggest that constant atmospheric deposition of N at present rates will lead to N saturation and re-acidification, whereas a 50% reduction in N would stabilise soil and streamwater pH at about the present levels.     

Climate change impact on atmospheric nitrogen deposition in northwestern Europe: a model study

A high-resolution chemical transport model, driven by meteorology representing current and future climate, was used to investigate the effects of possible future changes in climate on nitrogen deposition in northwestern Europe. The model system was able to resolve the climatology of precipitation and chemical properties observed in northern Europe during the 1980s, albeit with some underestimation of the temporal and spatial variability of meteorological parameters and chemical components. The results point toward a substantial increase (30% or more) in nitrogen deposition over western Norway as a consequence of increasing precipitation but more moderate changes for other areas. Deposition of oxidized nitrogen will increase more than the deposition of reduced nitrogen. Over Sweden, oxidized nitrogen will increase only marginally and reduced nitrogen will decrease, although annual precipitation is expected to increase here as well. This is probably because more reduced nitrogen will be removed further west in Scandinavia because of the strong increase in precipitation along the Norwegian coast. The total deposition of oxidized nitrogen over Norway is expected to increase from 96 Gg N y(-1) during the current climate to 107 Gg N y(-1) by 2100 due only to changes in climate. The corresponding values for Sweden are more modest, from 137 Gg N y(-1) to 139 Gg N y(-1).     

Contemporary (1979-1988) and inferred historical status of headwater lakes in North Central Ontario, Canada

Fifty-six headwater Canadian Shield lakes were repetitively sampled from 1979 to 88 to determine their response to changes in acidic deposition of the period. Annual wet sulphate loadings varied between 38 and 83 meq m(-2), with highest deposition in the late 1970s followed by somewhat lower but variable deposition in the 1980s. Median pH of the lakes increased 0.42 pH units from 1979 to 1985 and decreased by 0.15 units between 1985 and 1988. Short water renewal times (x=1.1 y) promoted rapid equilibration. Since lake were so responsive to changes in SO4(2-) inputs, they were at or near steady state at all times. Comparison of predicted original pH and ANC with 1979 data indicate a median decline of 0.45 pH units and a loss of 34 microeq litre(-1). ANC. Four of 9 lakes were found to be historically fishless, based on the continued presence of Chaoborus americanus in sediment cores. The remaining five lakes historically had fish populations, but fish were not collected in 1979 when pH ranged betwen 4.6 and 5.3. By 1987, fish species were found in five of these lakes where pH had increased on average by 0.9 pH units. Our data indicate that water quality improvements could allow for the reinvasion or resumption of recruitment for a significant number of Ontario lakes.     

Temporal trends in spheroidal carbonaceous particle deposition derived from annual sediment traps and lake sediment cores and their relationship with non-marine sulphate

Spheroidal carbonaceous particles (SCPs) provide an unambiguous indication of atmospherically deposited contamination from industrial sources. SCP data from a 12 year annual sediment trapping and coring programme at 14 lakes based on the UK Acid Waters Monitoring Network, were used to consider temporal trends in deposition and to compare these with measured non-marine sulphate fluxes. Results show good temporal coherence across a broad area of northern UK and that SCP deposition levels and are now at their lowest since the 1940s, in agreement with modelled sulphate data. SCP fluxes show reasonable linearity with measured non-marine sulphate depositional fluxes from the nearest UK Acid Deposition Monitoring Network sites, especially over the post-flue-gas desulphurisation period, but comparisons prior to 1972 are not possible due to lack of data. We speculate on whether palaeolimnological SCP data might be used to reconstruct the history of non-marine sulphate fluxes from industrial sources.     

Recovery from acidification in Swedish forest streams

Sulphur deposition in Sweden has decreased to less than half of the levels recorded in 1970 and now signs of recovery from acidification of surface waters are beginning to appear. We investigated time trends of water chemistry between 1985 and 1998 in 13 streams draining small forested catchments with generally shallow acid sensitive soils. At nine of the catchments, bulk deposition was monitored as well. Sulphate concentrations decreased in both stream water and deposition, although with somewhat smaller trends in stream water compared with deposition. The magnitude of the trends in sulphate increased from north to south, following a gradient of increasing industrial influence. Five sites in the southern half of the country showed weak signs of recovery from acidification in terms of increasing concentrations of acid neutralising capacity and decreasing concentrations of hydrogen ions, corresponding to annual increases of 0.01 pH units. Changes in stream discharge and concentrations of marine salts and organic acids could not explain the observed decrease in acidity and the results were interpreted as recovery from anthropogenic acidification. For the northern half of Sweden, any changes in water chemistry could be attributed to natural variation in climate and marine influence, and the effect of anthropogenic acidification was negligible.     

Atmospheric deposition inputs and effects on lichen chemistry and indicator species in the Columbia River Gorge, USA

Topographic and meteorological conditions make the Columbia River Gorge (CRG) an 'exhaust pipe' for air pollutants generated by the Portland-Vancouver metropolis and Columbia Basin. We sampled fog, bulk precipitation, throughfall, airborne particulates, lichen thalli, and nitrophytic lichen distribution. Throughfall N and S deposition were high, 11.5-25.4 and 3.4-6.7 kg ha(-1) over 4.5 months at all 9 and 4/9 sites, respectively. Deposition and lichen thallus N were highest at eastern- and western-most sites, implicating both agricultural and urban sources. Fog and precipitation pH were frequently as low as 3.7-5.0. Peak NO(x), NH(3), and SO(2) concentrations in the eastern CRG were low, suggesting enhanced N and S inputs were largely from particulate deposition. Lichens indicating nitrogen-enriched environments were abundant and lichen N and S concentrations were 2x higher in the CRG than surrounding national forests. The atmospheric deposition levels detected likely threaten Gorge ecosystems and cultural resources.     

Changes in the density, population structure, growth and reproduction of perch, Perca fluviatilis L. in two acidic forest lakes in southern Finland

The density of the perch populations decreased rapidly during the 1980s in two acidified lakes in southern Finland. In an acid-humic lake the density of the perch population decreased from 240 to 60 ha(-1) and in an acid clearwater lake from 150 to 20 ha(-1). In both lakes the rapid decrease was mainly due to failures in reproduction, although post-spawning mortality of adult fish was also recorded. The perch spawned annually in both lakes but according to the field exposures of egg strands, most of the eggs died before hatching. Nevertheless, some new recruits appeared in both lakes. These perch, born in 1983-1986, grew faster than those of the more abundant year-classes of the late 1970s, indicating a clear density-dependent growth response. According to the mortality estimate and the age distribution of perch, the latest year-classes that produced more than 100 adult perch ha(-1) were born in 1978 or 1979 in both lakes. It was calculated that the density of both populations was >500 ha(-1) in the early 1980s.     

Response of the Plastic Lake catchment, Ontario, to reduced sulphur deposition

As a consequence of decreases in the emission rate of sulphur in eastern North America in the late 1970s and early 1980s, sulphate deposition in central Ontario declined by about 40%, but has remained constant for about six years. Plastic Lake, a small, dilute lake on the Precambrian shield that the authors have studied since 1979, acidified between the start of the study and about 1986, but since then has not changed. The authors also monitored the chemistry of streamwater draining the Plastic Lake catchment. Water quality of runoff from an upland site improved rapidly (pH and alkalinity increased, SO4(2-) and Al decreased), but two factors offset these improvements. A small wetland area downstream reversed most of these changes, resulting in a constant output of strong acid from the catchment. In addition, in extremely dry years (1983, 1987, 1989) there were very high concentrations of SO4(2-) in the streamwater, suggesting substantial re-oxidation of reduced S in the catchment.     

Recent changes in trophic state of the Baltic Sea along SW coast of Finland

Drawing reliable conclusions on changes in the trophic state of various subareas of the Baltic Sea is problematic, in large part because the monitoring of productivity parameters exhibiting high natural variability is based on sparse sampling. This emphasizes the importance of long-term data sets. Here we present a 30-year chlorophyll alpha data set from the western Gulf of Finland. The trophic state of the study area showed an increasing trend in the 1970s and 1980s manifested mainly as strengthened vernal blooms. This trend did not continue in the 1990s, and the seasonal phytoplankton biomass maxima since then has begun to show some bias toward the late summer. The changes in seasonal maxima of phytoplankton blooms probably reflect i) decreased availability of N suppressing the magnitude of the vernal bloom, which increases the P reserves for the summer, and ii) enhanced internal P loading, which further increases the summer P reserves.     

Heterogeneous response of central European streams to decreased acidic atmospheric deposition

We investigated the relations between mountain streamwater chemistry and atmospheric pollution in an arca of 1611 km2 of the Czech Republic by comparing concentrations of SO4. NO3, Cl, Ca and the pH at 432 localities at the time of high (1984-1986) and relatively low (1996-2000) acidic atmospheric deposition. Medians of Cl. SO4, and NO3 decreased by 17, 96 and 60 microeq l(-1), or by 23, 17 and 49%, respectively, during 12 +/- 2 years. The decreased Cl corresponds to decreased emission of industrial Cl (as HCl). The decreased stream SO4 was proportionally lower than the 71% decrease in S-emissions due to leaching of previously accumulated SO4 from soils and non-zero background concentrations. Decreases of NO3 up to 60% in streamwaters with pH < or = 6 was greater than the decrease of N emission in central Europe, about 35%. Extensive regional decrease of NO3 is surprising and is probably described for the first time. The difference in NO3 concentrations between the two periods was probably enhanced by (a) an increase of mineralisation of forest floor in the mid-1980s and (b) by higher uptake of N in the late-1990s. The median pH of the 432 streams did not change but the pH of the sub-population with pH < 6 in the mid-1980s recovered substantially. The pH of circum-neutral streams (pH > 6.5) decreased even as acidic atmospheric deposition decreased.     

Modelling the long-term soil response to atmospheric deposition at intensively monitored forest plots in Europe

The dynamic soil chemistry model SMART was applied to 121 intensive forest monitoring plots (mainly located in western and northern Europe) for which both element input (deposition) and element concentrations in the soil solution were available. After calibration of poorly known parameters, the model accurately simulated soil solution concentrations for most plots as indicated by goodness-of-fit measures, although some of the intra-annual variation especially in nitrate and aluminium concentrations could not be reproduced. Model evaluations of two emission-deposition scenarios (current legislation and maximum feasible reductions) for the period 1970-2030 show a strong reduction in sulphate concentrations between 1980 and 2000 in the soil due to the high reductions in sulphur emissions. However, current legislation hardly reduces future nitrogen concentrations, whereas maximum feasible reductions reduces them by more than half. Maximum feasible reductions are also more effective in increasing pH and reducing aluminium concentrations, mostly below ‘critical’ values.     

Assessing the Impacts of Long-Range Sulfur and Nitrogen Deposition on Arctic and Sub-Arctic Ecosystems

For more than a decade, anthropogenic sulfur (S) and nitrogen (N) deposition has been identified as a key pollutant in the Arctic. In this study new critical loads of acidity (S and N) were estimated for terrestrial ecosystems north of 60° latitude by applying the Simple Mass Balance (SMB) model using two critical chemical criteria (Al/Bc = 1 and ANC_le = 0). Critical loads were exceeded in large areas of northern Europe and the Norilsk region in western Siberia during the 1990s, with the more stringent criterion (ANC_le = 0) showing the larger area of exceedance. However, modeled deposition estimates indicate that mean concentrations of sulfur oxides and total S deposition within the Arctic almost halved between 1990 and 2000. The modeled exceeded area is much reduced when currently agreed emission reductions are applied, and almost disappears under the implementation of maximum technically feasible reductions by 2020. In northern North America there was no exceedance under any of the deposition scenarios applied. Modeled N deposition was less than 5 kg ha⁻¹ y⁻¹ almost across the entire study area for all scenarios; and therefore empirical critical loads for the eutrophying impact of nitrogen are unlikely to be exceeded. The reduction in critical load exceedances is supported by observed improvements in surface water quality, whereas the observed extensive damage of terrestrial vegetation around the mining and smelter complexes in the area is mainly caused by direct impacts of air pollution and metals.     

The contribution of ammonia emissions from agriculture to the deposition of acidifying and eutrophying compounds onto forests

In the vicinity of a large ammonia emission area, dry and wet deposition of acidifying and eutrophying compounds onto Douglas Fir forests was studied by sampling throughfall, stemflow and bulk precipitation. Deposition amounts of NH(4)(+) and SO(4)(2-) were recognised to be among the highest of Central Europe, resulting in extremely high inputs of (potential) acid to the forest soils (13.1 kEq ha(-1) year(-1)). The contribution of NH(3) emissions from agriculture to the total acid deposition to the forests was 52%. The total nitrogen deposition amounted to 115.0 kg ha(-1) year(-1), 83% originating from NH(3) emissions and 17% from NO(x) emissions. Calculated mean dry deposition velocities of NH(3) and SO(2) were much larger than reported in the literature. A synergistic effect between NH(3) and SO(2) in the process of dry deposition is suggested and evidence for this effect is discussed. When deposition models do not take this interaction into account, they will underestimate NH(3) and SO(2) deposition amounts in areas with intensive animal husbandry.     

Dry deposition of O3, SO2, and HNO3 to different vegetation in the same exposure environment

Agricultural meteorological modeling techniques are used to investigate the relative and absolute dry deposition fluxes of SO2 (as sulfur), HNO3 (as nitrogen) and O3 to large fields of maize, soybeans, and alfalfa exposed in conditions as measured in northern Illinois, central Pennsylvania, and eastern Tennessee. For HNO3, the differences in seasonal deposition rates among the three types of plant species are small. Within the same environment, the soybean canopy has the potential to receive substantially more gaseous dry deposition of SO2 and O3 than the maize and alfalfa (which are about the same), as a result of lower stomatal resistance and consequently higher deposition velocities. Deposition differences among the sites are small except for the case of SO2, for which deposition rates estimated for northern Illinois are nearly double those at the other locations. The high SO2 deposition at the northern Illinois location is a consequence of the higher air concentrations observed there.     

Nitrate reductase activity as an indicator of ponderosa pine response to atmospheric nitrogen deposition in the San Bernardino Mountains

Determinations of nitrate reductase (NR) activity in ponderosa pine (Pinus ponderosa Dougl. ex. Laws.) needles were performed during summer 1994 in two areas (consisting of six different sites) with different nitrogen (N) deposition levels in the San Bernardino Mountains, southern California. Nitrate reductase activity was used as an integrative indicator of atmospheric nitrogen deposition to pine trees (direct uptake of N species from the atmosphere and N transported from the soil). Deposition of nitrate (NO3-) to pine branches was measured in order to determine dry atmospheric inputs of the oxidized N species to tree foliage. High NR activity was detected in all of the experimental sites. Activity of the enzyme was significantly higher at the locations characterized by higher NO3- deposition to branches--slight positive correlation between branch deposited NO3- and NR activity was found. However, high variability of NR in time and between the experimental sites discredit the NR assay as a reliable indicator of N deposition for ponderosa pine in the field conditions. This could be caused by substantial interference from other abiotic and biotic factors with tropospheric ozone as probably the most important one.     

Trends in needle and soil chemistry of Norway spruce and Scots pine stands in South Sweden 1985-1994

The nutrient status of the trees and soil in 42 stands of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) in Scania, South Sweden was followed from 1985 to 1994. Samples from needles taken in winter 1985, 1987, 1990, and 1994, and soils in 1988 and 1993 were analyzed. Concentrations, as well as ratios to N, of K and Cu in needles of both species decreased by approximately 40% from 1985 to 1994. Soil analyses indicate ongoing soil acidification and leaching of mineral nutrients from the soil profile. Together with deposition data and corroboration from modeled scenarios, these data support the recent contention that one consequence of enhanced deposition of N and S will be the development of nutrient imbalances in trees growing in southern Sweden.