Regional Nitrogen Deposition Research Articles

Long-term trends of acid anion in the rain water in Lake Taihu watershed and the lake water, and its environmental implications

为揭示太湖流域降雨和湖水酸根阴离子长期变化特征及环境意义，通过历史数据收集和采样分析，对太湖流域降雨和湖水中的SO₄^2-、NO₃^-变化特征和来源进行了研究.结果表明：自1990s以来太湖流域降雨中SO₄^2-呈显著下降趋势，年平均下降率为0.28 mg/（L·a）；NO₃^-浓度却呈显著上升趋势，年平均增长率为0.05 mg/（L·a），降雨中氮污染呈现加重的趋势.与之相反，湖水中SO₄^2-呈显著上升趋势，年平均增长率为1.24 mg/（L·a）；NO₃^-浓度却呈显著下降趋势，年平均下降率为0.02 mg/（L·a）.30年以来，太湖水体SO₄^2-/NO₃^-比值不断升高，远高于降水SO₄^2-/NO₃^-比值.研究认为：流域SO₂排放引起的酸沉降是湖水SO₄^2-浓度增长的最重要原因，但氮氧化物排放并未引起湖水NO₃^-浓度升高，说明太湖流域对大气沉降的氮氧化物有滞留作用，而太湖水体是流域大气沉降硫酸盐的重要汇.综合治理太湖流域酸性物质排放对防止太湖水体酸化和治理富营养化都具有重要意义.;To explore long-term trends of acid anions in the rain water in Lake Taihu watershed, the lake water and their environmental implications, the variation characteristics, sources and the relationships of SO₄^2-, NO₃^- in the rain water and the lake water were studied via historical data collection and sampling analysis. The results indicated that SO₄^2- in the rainwater showed a significant decreasing trend since 1990s with an annual average decrease rate of 0.28 mg/(L·a), and the NO₃^- showed a significant increasing trend with an annual average increase rate of 0.05 mg/(L·a), which suggests an aggravating trend of nitrogen pollution in the rain water. In contrast, SO₄^2- in the lake water showed a significant increasing trend with an annual average increase rate of 1.24 mg/(L·a), and the NO₃^- showed a significant decreasing trend with an annual average decrease rate of 0.02 mg/(L·a). During the past 30 years, the ratio of SO₄^2-/NO₃^- in Lake Taihu water continuously increased, much higher than that of the rain water. The research indicated that the acid deposition caused by SO₂ emissions in the watershed was mainly responsible for the increased concentration of SO₄^2- in the lake water. However, the nitrogen oxides emissions did not cause an increase concentration of NO₃^- in the lake water, indicating that Lake Taihu watershed plays a significant role in the retention of nitrogen deposition, while the lake water is an important sink for sulfate deposition. The regional nitrogen deposition has an important impact on Lake Taihu water eutrophication. It is of great significance to prevent the acidification and eutrophication in Lake Taihu via comprehensive management of acid emissions in Lake Taihu watershed.

Litter quality, land-use history, and nitrogen deposition effects on topsoil conditions across European temperate deciduous forests

Topsoil conditions in temperate forests are influenced by several soil-forming factors, such as canopy composition (e.g. through litter quality), land-use history, atmospheric deposition, and the parent material. Many studies have evaluated the effects of single factors on physicochemical topsoil conditions, but few have assessed the simultaneous effects of multiple drivers. Here, we evaluate the combined effects of litter quality, land-use history (past land cover as well as past forest management), and atmospheric deposition on several physicochemical topsoil conditions of European temperate deciduous forest soils: bulk density, proportion of exchangeable base cations, carbon/nitrogen-ratio (C/N), litter mass, bio-available and total phosphorus, pHKCl and soil organic matter. We collected mineral soil and litter layer samples, and measured site characteristics for 190 20 × 20 m European mixed forest plots across gradients of litter quality (derived from the canopy species composition) and atmospheric deposition, and for different categories of past land cover and past forest management. We accounted for the effects of parent material on topsoil conditions by clustering our plots into three soil type groups based on texture and carbonate concentration. We found that litter quality was a stronger driver of topsoil conditions compared to land-use history or atmospheric deposition, while the soil type also affected several topsoil conditions here. Plots with higher litter quality had soils with a higher proportion of exchangeable base cations, and total phosphorus, and lower C/N-ratios and litter mass. Furthermore, the observed litter quality effects on the topsoil were independent from the regional nitrogen deposition or the soil type, although the soil type likely (co)-determined canopy composition and thus litter quality to some extent in the investigated plots. Litter quality effects on topsoil phosphorus concentrations did interact with past land cover, highlighting the need to consider land-use history when evaluating canopy effects on soil conditions. We conclude that forest managers can use the canopy composition as an important tool for influencing topsoil conditions, although soil type remains an important factor to consider.

Biomonitors of atmospheric nitrogen deposition: potential uses and limitations.

Atmospheric nitrogen deposition is the third largest cause of global biodiversity loss, with rates that have more than doubled over the past century. This is especially threatening for tropical regions where the deposition may soon exceed 25 kg of N ha-1 year-1, well above the threshold for physiological damage of 12-20 kg of N ha-1 year-1, depending on plant species and nitrogenous compound. It is thus urgent to monitor these regions where the most diverse biotas occur. However, most studies have been conducted in Europe, the USA and recently in China. This review presents the case for the potential use of biological organisms to monitor nitrogen deposition, with emphasis on tropical plants. We first present an overview of atmospheric chemistry and the nitrogen metabolism of potential biomonitors, followed by a framework for monitoring nitrogen deposition based on the simultaneous use of various functional groups. In particular, the tissue nitrogen content responds to the rate of deposition, especially for mosses, whose nitrogen content increases by 1‰ per kilogram of N ha-1 year-1. The isotopic signature, δ15N, is a useful indicator of the nitrogen source, as the slightly negative values (e.g. 5‰) of plants from natural environments can become very negative (-11.2‰) in sites with agricultural and husbandry activities, but very positive (13.3‰) in urban environments with high vehicular activity. Mosses are good biomonitors for wet deposition and atmospheric epiphytes for dry deposition. In turn, the nitrogen saturation of ecosystems can be monitored with trees whose isotopic values increase with saturation. Although given ecophysiological limitations of different organisms, particular studies should be conducted in each area of interest to determine the most suitable biomonitors. Overall, biomonitors can provide an integrative approach for characterizing nitrogen deposition in regions where the deployment of automated instruments or passive monitoring is not feasible or can be complementary.

The Influence of Marcellus Shale Extraction Emissions on Regionally Monitored Dry Reactive Nitrogen Deposition

Emissions of nitrogen oxides (NOx) in the United States (U.S.) from large stationary sources, such as electric generating units, have decreased since 1995, driving decreases in nitrogen deposition. However, increasing NOx emissions from emerging industries, such as unconventional natural gas (UNG) extraction, could offset stationary source emission reductions in shale gas producing regions of the U.S. The Marcellus Shale in the northeastern U.S. has seen dramatic increases in the number of wells and associated natural gas production during the past 10 years. In this study, we examine the potential impacts of shale gas development on regional NOx emission inventories and dry deposition fluxes to Clean Air Status and Trends (CASTNET) sites in Pennsylvania and New York. Our results demonstrate that the current distribution of CASTNET sites is ineffective for monitoring the influence of Marcellus well NOx emissions on regional nitrogen deposition. Despite the fact that existing CASTNET sites are not influenced by UNG extraction activity, NOx emissions densities from shale gas extraction are substantial and are estimated to reach up to 21 kg NOx ha-1 year-1 in some regions. If these emissions deposit locally, UNG extraction activity could contribute to critical nitrogen load exceedances in areas of high well density.

Why is the relative abundance of Asterionella formosa increasing in a Boreal Shield lake as nutrient levels decline?

The freshwater diatom Asterionella formosa Hassall is a widely distributed species whose populations have been increasing in the recent sediments of numerous lakes worldwide. This taxon’s proliferation has commonly been associated with nutrient enrichment and, more recently, with twentieth century increases in atmospheric nitrogen deposition. However, a growing number of studies have reported increases in A. formosa in the absence of increased nutrients and have thus raised questions about whether alternative causative factors (such as recent climate warming) may be important. Here we assess the relative importance of nutrients and climate warming on A. formosa by comparing regional air temperature trends and 20 years of annually measured lake water nutrients (total inorganic nitrogen, total nitrogen, and total phosphorus) with past changes in relative abundance of this taxon from a sediment core obtained from a soft-water, Boreal Shield lake (George Lake, Killarney, Ontario). Measured lake water total phosphorus has always been very low and remains so to the present (<10 µg L−1). Total inorganic nitrogen (TIN) and total nitrogen (TN) concentrations, however, show distinct declining trends (p < 0.05) at George Lake since the 1990s, when substantial increases in mean annual and mean winter air temperatures (p < 0.01) were also recorded. These declines in lake water nitrogen concentrations match declines in atmospherically deposited nitrogen in this region. Since the late-1980s and early-1990s, there has been a marked increase in the relative abundance of A. formosa, which had been virtually absent from the lake’s sediment record in earlier intervals. A. formosa trends closely track increasing regional air temperatures, but also clearly coincide with declines in lake water nutrients and decreases in regional nitrogen deposition (p < 0.01). These trends have also occurred in other lakes in the region. Our results show that increases in nitrogen deposition and/or nutrient enrichment are not pre-conditions for increases in the relative abundance of A. formosa. Instead, warming-related changes including longer open water periods, changes in lake mixing regimes, and lake thermal properties might have contributed to the recent increase in the relative abundance of A. formosa in this lake and likely elsewhere.

Multi-model mean nitrogen and sulfur deposition from the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP): evaluation of historical and projected future changes

Abstract. We present multi-model global datasets of nitrogen and sulfate deposition covering time periods from 1850 to 2100, calculated within the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP). The computed deposition fluxes are compared to surface wet deposition and ice core measurements. We use a new dataset of wet deposition for 2000–2002 based on critical assessment of the quality of existing regional network data. We show that for present day (year 2000 ACCMIP time slice), the ACCMIP results perform similarly to previously published multi-model assessments. For this time slice, we find a multi-model mean deposition of approximately 50 Tg(N) yr−1 from nitrogen oxide emissions, 60 Tg(N) yr−1 from ammonia emissions, and 83 Tg(S) yr−1 from sulfur emissions. The analysis of changes between 1980 and 2000 indicates significant differences between model and measurements over the United States but less so over Europe. This difference points towards a potential misrepresentation of 1980 NH3 emissions over North America. Based on ice core records, the 1850 deposition fluxes agree well with Greenland ice cores, but the change between 1850 and 2000 seems to be overestimated in the Northern Hemisphere for both nitrogen and sulfur species. Using the Representative Concentration Pathways (RCPs) to define the projected climate and atmospheric chemistry related emissions and concentrations, we find large regional nitrogen deposition increases in 2100 in Latin America, Africa and parts of Asia under some of the scenarios considered. Increases in South Asia are especially large, and are seen in all scenarios, with 2100 values more than double their 2000 counterpart in some scenarios and reaching &gt; 1300 mg(N) m−2 yr−1 averaged over regional to continental-scale regions in RCP 2.6 and 8.5, ~ 30–50% larger than the values in any region currently (circa 2000). However, sulfur deposition rates in 2100 are in all regions lower than in 2000 in all the RCPs. The new ACCMIP multi-model deposition dataset provides state-of-the-science, consistent and evaluated time slice (spanning 1850–2100) global gridded deposition fields for use in a wide range of climate and ecological studies.

Regional nitrogen deposition model for integrated assessment of acidification and eutrophication

To complement the continent-scale integrated assessment of emission abatement strategies with regional studies, tools with high resolution are needed. For this purpose, the regional nitrogen transport and deposition model DAIQUIRI using linear transfer matrices, i.e. source-receptor relationships, was developed at the Finnish Environment Institute. The model is based on results of a regional dispersion and deposition model of the Finnish Meteorological Institute (FMI-RM). This paper describes the second phase of model development and validation. The transfer matrices constructed for years 1993 and 1995 were used for generating deposition fields, which were then compared with the results of FMI-RM and continent-scale EMEP model, and with measurements. In addition, the model performance in applications was evaluated: the impacts of regional deposition modelling on exceedances of ecosystem critical loads for acidification were calculated and compared with those using the EMEP model. Both regional models gave comparable results, although some differences existed especially for areas where other land-use types than forest dominate. Also the comparison with measurements showed that estimation of deposition for coastal and sea areas is fraught with uncertainties. For reduced nitrogen, the resolution of the models was insufficient to describe the fine-resolution deposition pattern close to emissions. The comparison with results of the EMEP model, however, showed the ability of regional models to represent the spatial deposition pattern in more detail in areas near emissions. The use of regional modelling resulted in larger estimates of areas at risk of acidification than when using only the continent-scale EMEP model.