A new approach to Assess Atmospheric Nitrogen Deposition by Way of Standardized Exposition of mosses

A standardized method of moss exposition for assessing variations in nitrogen deposition was tested in the western part of Germany. Six pleurocarpous moss species were transplanted to two sites differing in their deposition rates but being comparable as to their climatic conditions. The mosses were exposed in standardized containers over a period of 12 months; the focus of interest was the effect of N deposition on nitrogen content and on ¹⁵N natural abundance (δ¹⁵N-values). Within the first nine months only trends could be observed. However, after one year all species tested showed significantly higher N concentrations at the highly polluted site. Besides, more negative δ¹⁵N-values possibly reflecting the higher ammonium input were detected at this site. Surprisingly, most of the plants though being kept in plastic containers without a favourable substratum did not show any conspicuous deficiency symptoms. The potential advantages of a standardized moss exposition for N monitoring purposes are discussed. It is concluded that the method presented here can yield significant results in particular if the number of testing sites is increased.     

Differences in the growth response of three bryophyte species to nitrogen

The effect of nitrogen on biomass production, shoot elongation and relative density of the mosses Pleurozium schreberi, Hylocomium splendens and Dicranum polysetum was studied in a chamber experiment. Monocultures were exposed to 10 N levels ranging from 0.02 to 7.35 g N m⁻² during a 90-day period. All the growth responses were unimodal, but the species showed differences in the shape parameters of the curves. Hylocomium and Pleurozium achieved optimum biomass production at a lower N level than Dicranum. Pleurozium had the highest biomass production per tissue N concentration. Tolerance to N was the widest in Dicranum, whereas Hylocomium had the narrowest tolerance. Dicranum retained N less efficiently from precipitation than the other two species, which explained its deviating response. All species translocated some N from parent to new shoots. The results emphasize that the individual responses of bryophytes to N should be known when species are used as bioindicators.     

Long term changes in atmospheric N and S throughfall deposition and effects on soil solution chemistry in a Scots pine forest in the Netherlands

In a Scots pine forest the throughfall deposition and the chemical composition of the soil solution was monitored since 1984. (Inter)national legislation measures led to a reduction of the deposition of nitrogen and sulphur. The deposition of sulphur has decreased by approximately 65%. The total mineral-nitrogen deposition has decreased by ca. 25%, which is mainly due to a reduction in ammonium-N deposition (−40%), since nitrate-N deposition has increased (+50%). The nitrogen concentration in the upper mineral soil solution at 10 cm depth has decreased, leading to an improved nutritional balance, which may result in improved tree vitality. In the drainage water at 90 cm depth the fluxes of NO₃⁻ and SO₄²⁻ have decreased, resulting in a reduced leeching of accompanying base cations, thus preserving nutrients in the ecosystem. It may take still several years, however, before this will meet the prerequisite of a sustainable ecosystem.     

Acid Deposition in the Tuscan Appennines During the Dry Period 1988-89

The typical parameters of acid precipitation are evaluated in the forest of Vallombrosa (Tuscan Appennines) during the dry period 1988-89. Individual rain events (dry and wet deposition) were sampled in a clearing of the forest and below the canopy of an evergreen tree as well as a deciduous broadleaf tree.

In atmospheric precipitation the pH values usually vary around 4.4, with neutralization in the hot season due to calcareous material from distant sources. Relatively large concentrations of Pb and Cd are found in rain, but only in a small amount in canopy leachate. Aluminium, manganese and iron are more significantly washed off than Pb and Cd.     

大气沉降向华中丘陵区稻田输入硫通量的观测

选取我国华中丘陵区的湖南省长沙县一个典型水稻种植区,对2015与2016年2年雨水样中的SO₄²-S和大气SO₂的沉降量进行监测,分析雨水中SO₄^2-、NO₃^-的关系,解析大气硫沉降的主要来源.结果表明,研究区大气中SO₂-S和雨水中SO₄^2--S的年均浓度分别为8.5 μg/m³和1.1mg/L,大气硫沉降年均总量为26.8kgS/（hm²·a）,其中年均降雨混合沉降量18.2kgS/（hm²·a）,年均干沉降量为8.6kgS/（hm²·a）.研究区域硫素干、混合沉降量存在明显的季节差异,硫素混合沉降春季高于夏、秋、冬季,而硫素干沉降冬季高于春、夏、秋季.雨水中NO₃^-/SO₄^2-的质量比大多小于1,表明研究区大气硫素主要来自固定污染源（燃煤）.华中丘陵区稻田具有较高的硫沉降,但硫沉降量已较21世纪初出现了较大幅度下降,农业生产中需要根据农田硫素收支状况酌情补充硫肥来保证作物高产稳产.     

Suspended particulate mercury associated with tidal fluxes in a lagoon environment impacted by cinnabar mining activity (northern Adriatic Sea)

The Isonzo River has been demonstrated to be a continuing point source of mercury(Hg)in the Gulf of Trieste although the Idrija mine was last active in 1996. The present study aims to investigate the role of the suspended particulate matter(SPM) associated with tidal fluxes to disperse particulate Hg(PHg) into the Grado coastal lagoon system. PHg concentrations(avg. 3.11 ± 2.62 μg/g, d.w.), notwithstanding the ebb or flood tides, were significantly higher than the local sediment background(0.13 μg/g). The relative affinity of Hg for the particulate phase in surface waters was confirmed by higher average distribution coefficient(Kd) values(5.6–6.7). PHg contents showed the highest values in ebb tide conditions, thus suggesting their origin from the erosion of tidal flats and saltmarshes of the lagoon. When compared to river discharge, high PHg surface concentrations in flood tide are related to rainfall events occurring within the river basin. Results can be used to make an indicative assessment of the amount of Hg bound to SPM which is transported in and out of the lagoon basin following the action of tidal fluxes. A simple estimation provides a negative budget for the Grado lagoon sub-basin which loses between 0.14 and 1.16 kg of PHg during a tidal semi-cycle. This conclusion is in agreement with the evidence of morphological deterioration which has emerged from recent studies on the lagoon environment, and which testifies to a current sedimentary loss from the lagoon into the northern Adriatic Sea.     

Sulphate, Nitrogen and Base Cation Budgets at 21 Forested Catchments in Canada, the United States and Europe

To assess the concern over declining base cation levels in forest soils caused by acid deposition, input-output budgets (1990s average) for sulphate (SO₄), inorganic nitrogen (NO₃-N; NH₄-N), calcium (Ca), magnesium (Mg) and potassium (K) were synthesised for 21 forested catchments from 17 regions in Canada, the United States and Europe. Trend analysis was conducted on monthly ion concentrations in deposition and runoff when more than 9 years of data were available (14 regions, 17 sites). Annual average SO₄ deposition during the 1990s ranged between 7.3 and 28.4 kg ha⁻¹ per year, and inorganic nitrogen (N) deposition was between 2.8 and 13.8 kg ha⁻¹ per year, of which 41–67% was nitrate (NO₃-N). Over the period of record, SO₄ concentration in deposition decreased in 13/14 (13 out of 14 total) regions and SO₄ in runoff decreased at 14/17 catchments. In contrast, NO₃-N concentrations in deposition decreased in only 1/14 regions, while NH₄-N concentration patterns varied; increasing at 3/14 regions and decreasing at 2/14 regions. Nitrate concentrations in runoff decreased at 4/17 catchments and increased at only 1 site, whereas runoff levels of NH₄-N increased at 5/17 catchments. Decreasing trends in deposition were also recorded for Ca, Mg, and K at many of the catchments and on an equivalent basis, accounted for up to 131% (median 22%) of the decrease in acid anion deposition. Base cation concentrations in streams generally declined over time, with significant decreases in Ca, Mg and K occurring at 8, 9 and 7 of 17 sites respectively, which accounted for up to 133% (median 48%) of the decrease in acid anion concentration. Sulphate export exceeded input at 18/21 catchments, likely due to dry deposition and/or internal sources. The majority of N in deposition (31–100%; median 94%) was retained in the catchments, although there was a tendency for greater NO₃-N leaching at sites receiving higher (<7 kg ha^-1 per year) bulk inorganic N deposition. Mass balance calculations show that export of Ca and Mg in runoff exceeds input at all 21 catchments, but K export only exceeds input at 16/21 sites. Estimates of base cation weathering were available for 18 sites. When included in the mass balance calculation, Ca, Mg and K exports exceeded inputs at 14, 10 and 2 sites respectively. Annual Ca and Mg losses represent appreciable proportions of the current exchangeable soil Ca and Mg pools, although losses at some of the sites likely occur from weathering reactions beneath the rooting zone and there is considerable uncertainty associated with mineral weathering estimates. Critical loads for sulphur (S) and N, using a critical base cation to aluminium ratio of 10 in soil solution, are currently exceeded at 7 of the 18 sites with base cation weathering estimates. Despite reductions in SO₄ and H⁺ deposition, mass balance estimates indicate that acid deposition continues to acidify soils in many regions with losses of Ca and Mg of primary concern. The U.S. Government's right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged. The Canadian Crown reserves the right to retain a non-exclusive, royalty free licence in and to any copyright.     

Large-scale mercury variations in Lake Vänern (Sweden) 1974-98

Lake V?nern, the largest lake in Sweden, has been seriously contaminated with mercury during the 20th century. In the 1970's and 80's the direct load, mainly from a chlor-alkali industry in the area, of mercury was drastically reduced as a response to new legislation, from three to five tons down to between five and ten kg yr(-1). Large amounts of the disposed pollutant have accumulated in the sediments. The question posed in this work is now, is the effect of the drastic load reduction after more than two decades visible in the sediments? The question is relevant as large areas still are blacklisted for fishing, but also as a follow-up of a major remedy action. The lake also serves as a freshwater reservoir for even Sweden's second largest city. This work synthesises and compares data of mercury in the sediments from three major field programs, in 1974, 1984 and 1998. The interest is focused on both spatial heterogeneity and temporal trends. In 1974, the surface concentrations are significantly higher than in subsequent surveys. Significant differences are also found between 1984 and 1998. Significant spatial differences within the lake are found for respective year. The most contaminated area is located in the north, close to the major point source (a former chlor-alkali industry). This is also the area with the largest improvement, as a direct response to the reduction in load. Further from the outlet, the recovery is more affected by burial and transport processes out into the deeper basins.     

The Monitoring and Risk Assessment of Zn Deposition Around a Metal Smelter in Latvia

Heavy metal concentrations in Hylocomium splendens collected around a metal smelter in Latvia showed very high concentrations of Zn (>200 g/g), and elevated concentrations of Pb (38.3 g/g) and Cu (18.3 g/g). In an attempt to better evaluate the potential toxicity of the high Zn concentrations, a serial elution method was used to determine the concentrations of zinc in intercellular, extracellular exchangeable cell wall, intracellular, and particle fractions. The intercellular Zn concentrations represent the water soluble component of the total concentrations, and were low with no clear trends. Zn concentrations in the extra- and intracellular and particle fractions decreased exponentially from the pollutant source. Intracellular Zn concentrations in moss close to the emission source are within the range considered to be potentially toxic, from other single element exposure studies. The proportion of Zn in the relatively insoluble particle fraction, which is least associated with environmental risk, was greater closer to the pollution source, reaching > 30% in the oldest Hylocomium splendens segments.     

A Global Overview of Atmospheric Acid Deposition Fluxes

This paper presents a summary of globalacid deposition flux data taken from a globalassessment report on acid deposition prepared forUNEP/WMO (Whelpdale and Kaiser, 1996). There is a largevariation in the spacial coverage and reliability ofmonitoring around the world. Many more stationsmeasure wet deposition than collect appropriate datafor estimating dry deposition. The widespread regionswith highest precipitation concentrations anddeposition fluxes of sulphate and nitrate coincideclosely with the regions of highest density ofSO₂ and NO_x precursor emissions occurringprimarily in the mid-latitude, northern hemispherebelt where a large fraction of the worlds fossilfuels is consumed. Organic acids in precipitation makea minor contribution to acidity (<20%) inindustrial regions, but in the rest of the world theyare of same order, or even exceed, inorganic acids.Less is known about dry deposition, but it appears topredominate near strong emission sources with wetdeposition predominating farther downwind. The molarratio of the N/S contribution to acidic deposition isclose to 1.0 over large areas of Europe and NorthAmerica, but is highly variable elsewhere, beinghighest in equatorial regions due to biomass burningand lowest near smelters and other large sources of SO₂.