Contemporary and pre-industrial global reactive nitrogen budgets
Increases and expansion of anthropogenic emissions of both oxidized nitrogen compounds, NOx, and a reduced nitrogen compound, NH3, have driven an increase in nitrogen deposition. We estimate global NOx and NH3 emissions and use a model of the global troposphere, MOGUNTIA, to examine the pre-industrial and contemporary quantities and spatial patterns of wet and dry NOy and NHx deposition. Pre-industrial wet plus dry NOx and NHx deposition was greatest for tropical ecosystems, related to soil emissions, biomass burning and lightning emissions. Contemporary NOy+NHx wet and dry deposition onto Northern Hemisphere (NH) temperate ecosystems averages more than four times that of pre-industrial N deposition and far exceeds contemporary tropical N deposition. All temperate and tropical biomes receive more N via deposition today than pre-industrially. Comparison of contemporary wet deposition model estimates to measurements of wet deposition reveal that modeled and measured wet deposition for both NO3– and NH4+ were quite similar over the U.S. Over Western Europe, the model tended to underestimate wet deposition of NO3– and NH4+ but bulk deposition measurements were comparable to modeled total deposition. For the U.S. and Western Europe, we also estimated N emission and deposition budgets. In the U.S., estimated emissions exceed interpolated total deposition by 3-6 Tg N, suggesting that substantial N is transported offshore and/or the remote and rural location of the sites may fail to capture the deposition of urban emissions. In Europe, by contrast, interpolated total N deposition balances estimated emissions within the uncertainty of each.
Journal Information
Biogeochemistry publishes original papers and occasional reviews dealing with biotic controls on the chemistry of the environment, or with the geochemical control of the structure and function of ecosystems. Cycles are considered, either of individual elements or of specific classes of natural or anthropogenic compounds in ecosystems. Particular emphasis is laid on the interactions of element cycles. Global aspects of biogeochemistry are covered in the form of work on the global carbon and sulfur cycles, for instance, and studies on both natural and artificial ecosystems are published when they contribute to a general understanding of biogeochemistry. Biogeochemistry is an important, international journal on a topic of acute current interest. The impact factor: 2.125 (2004) Section ‘Environmental Sciences’: Rank 17 of 134 Section ‘Geosciences’: Rank 16 of 128
Publisher Information
Springer is one of the leading international scientific publishing companies, publishing over 1,200 journals and more than 3,000 new books annually, covering a wide range of subjects including biomedicine and the life sciences, clinical medicine, physics, engineering, mathematics, computer sciences, and economics.
Bio-atmospheric coupling of the nitrogen cycle through NOx emissions and NOy deposition
The tropospheric and terrestrial nitrogen cycles are connected to one another through the emissions of NOx and NHx from soils and vegetation and the subsequent redeposition of these compounds and their products elsewhere. These connections play an important role in the Earth system influencing tropospheric concentrations of NOx, O3, and CO2. Estimates of the biogenic sources of NOx, soil emissions and biomass burning, are amongst the most variable terms in the global budget of NOx and are eclipsed only by lightning. A 3-D chemistry transport model, IMAGES, was used to examine how soil emissions and biomass burning influence tropospheric concentrations of NOx and O3 as well as NOy deposition. Soil and biomass burning emissions of NOx contributed the most to atmospheric NOx concentrations closest to the surface and south of 30 degrees N. The influence of these emissions on tropospheric O3 and NOx concentrations dissipated with height suggesting that these surface emissions are most important to surface ozone concentrations. The removal of either the soil or biomass burning source resulted in a 5-20% difference in tropospheric O3 concentrations over large regions of the atmosphere. Both sources are also important contributors to N deposition, particularly south of 30 degrees which, in turn, can generate significant carbon storage. These exercises demonstrate both the importance and complexity of the connections between atmospheric chemistry and the terrestrial biosphere.
The fate of carbon in grasslands under carbon dioxide enrichment
The concentration of carbon dioxide (CO2) in the Earth’s atmosphere is rising rapidly, with the potential to alter many ecosystem processes. Elevated CO2 often stimulates photosynthesis, creating the possibility that the terrestrial biosphere will sequester carbon in response to rising atmospheric CO2 concentration, partly offsetting emissions from fossil-fuel combustion, cement manufacture, and deforestation,. However, the responses of intact ecosystems to elevated CO2 concentration, particularly the below-ground responses, are not well understood. Here we present an annual budget focusing on below-ground carbon cycling for two grassland ecosystems exposed to elevated CO2 concentrations. Three years of experimental CO2 doubling increased ecosystem carbon uptake, but greatly increased carbon partitioning to rapidly cycling carbon pools below ground. This provides an explanation for the imbalance observed in numerous CO2 experiments, where the carbon increment from increased photosynthesis is greater than the increments in ecosystem carbon stocks. The shift in ecosystem carbon partitioning suggests that elevated CO2 concentration causes a greater increase in carbon cycling than in carbon storage in grasslands.
Stimulation of grassland nitrogen cycling by increased soil moisture under elevated CO2
Nitrogen (N) limits plant growth in many terrestrial ecosystems, potentially constraining terrestrial ecosystem response to elevated CO2. In this study, elevated CO2 stimulated gross N mineralization and plant N uptake in two annual grasslands. In contrast to other studies that have invoked increased C input to soil as the mechanism altering soil N cycling in response to elevated CO2, increased soil moisture, due to decreased plant transpiration in elevated CO2, best explains the changes we observed. This study suggests that atmospheric CO2 concentration may influence ecosystem biogeochemistry through plant control of soil moisture.
Fluxes of nitric oxide from soils following the clearing and burning of a secondary tropical rain forest
At sites in the Atlantic Lowlands of Costa Rica, clearing and burning of a secondary tropical rain forest caused a significant increase in soil nitric oxide (NO) emissions. Soil-atmosphere NO fluxes averaged 0.5 ng N cm−2 hr−1 prior to clearing and increased to 4.1 ng N cm−2 hr−1 following clearing and to greater than 12.0 ng N cm−2 hr−1 following burning. Soil NO emissions were elevated for a period of 3–4 months following clearing, and fluxes peaked for 1–3 days following burning. We conducted a series of experiments with intact soil cores to determine the probable mechanism responsible for elevated NO emissions from soils. In one set of experiments we added substrates for microbial nitrification (ammonium), denitrification (nitrate), and chemical denitrification (nitrite) to autoclaved (killed) and nonautoclaved (live) soil cores. Water-only additions were used as controls. Compared to water or nitrate additions, ammonium caused a significant increase in NO emissions from live cores. Water, ammonium, and nitrate additions had no effect on emissions from autoclaved cores. Nitrite solution additions resulted in highly significant increases in NO emissions from both autoclaved and nonautoclaved soil cores. In a second set of experiments we treated intact soil cores with acetylene (1 kPa C2H2) to selectively inhibit nitrification and oxygen to inhibit denitrification. The oxygen treatment had no effect on NO production while acetylene significantly reduced NO emissions. The results from the substrate addition and inhibition experiments demonstrate that microbial denitrification is not a major pathway for NO production in these soils. In contrast, microbial nitrification appears to be a critical process responsible for NO emissions throughout the clearing and burning period. Field experiments with acetylene as an inhibitor show that immediately following burning, chemical denitriflcation of nitrite deposited in ash supports a large peak in NO fluxes.