Climate change due to greenhouse gas emissions is predicted to raise the mean global temperature by 1.0–3.5°C in the next 50–100 years. The direct and indirect effects of this potential increase in temperature on terrestrial ecosystems and ecosystem processes are likely to be complex and highly varied in time and space. The Global Change and Terrestrial Ecosystems core project of the International Geosphere-Biosphere Programme has recently launched a Network of Ecosystem Warming Studies, the goals of which are to integrate and foster research on ecosystem-level effects of rising temperature. In this paper, we use meta-analysis to synthesize data on the response of soil respiration, net N mineralization, and aboveground plant productivity to experimental ecosystem warming at 32 research sites representing four broadly defined biomes, including high (latitude or altitude) tundra, low tundra, grassland, and forest. Warming methods included electrical heat-resistance ground cables, greenhouses, vented and unvented field chambers, overhead infrared lamps, and passive night-time warming. Although results from individual sites showed considerable variation in response to warming, results from the meta-analysis showed that, across all sites and years, 2–9 years of experimental warming in the range 0.3–6.0°C significantly increased soil respiration rates by 20% (with a 95% confidence interval of 18–22%), net N mineralization rates by 46% (with a 95% confidence interval of 30–64%), and plant productivity by 19% (with a 95% confidence interval of 15–23%). The response of soil respiration to warming was generally larger in forested ecosystems compared to low tundra and grassland ecosystems, and the response of plant productivity was generally larger in low tundra ecosystems than in forest and grassland ecosystems. With the exception of aboveground plant productivity, which showed a greater positive response to warming in colder ecosystems, the magnitude of the response of these three processes to experimental warming was not generally significantly related to the geographic, climatic, or environmental variables evaluated in this analysis. This underscores the need to understand the relative importance of specific factors (such as temperature, moisture, site quality, vegetation type, successional status, land-use history, etc.) at different spatial and temporal scales, and suggests that we should be cautious in "scaling up" responses from the plot and site level to the landscape and biome level. Overall, ecosystem-warming experiments are shown to provide valuable insights on the response of terrestrial ecosystems to elevated temperature.

/pdf/a-meta-analysis-of-the-response-of-soil-respiration-net-4y6fejl9qw.pdf

A meta-analysis of the response of soil respiration, net nitrogen mineralization, and aboveground plant growth to experimental ecosystem warming

The world's soils contain about 1500 Gt of organic carbon to a depth of 1m and a further 900 Gt from 1-2m. A change of total soil organic carbon by just 10% would thus be equivalent to all the anthropogenic CO2 emitted over 30 years. Warming is likely to increase both the rate of decomposition and net primary production (NPP), with a fraction of NPP forming new organic carbon. Evidence from various sources can be used to assess whether NPP or the rate of decomposition has the greater temperature sensitivity, and, hence, whether warming is likely to lead to an increase or decrease in soil organic carbon. Evidence is reviewed from laboratory-based incubations, field measurements of organic carbon storage, carbon isotope ratios and soil respiration with either naturally varying tempera- tures or after experimentally increasing soil temperatures. Estimates of terrestrial carbon stored at the Last Glacial Maximum are also reviewed. The review concludes that the temper- ature dependence of organic matter decomposition can be best described as: d(T) = exp(3.36 (T 40)/(T + 31.79)) where d(T) is the normalised decomposition rate at temperature T (in C). In this equation, decomposition rate is normalised to '1' at 40 C. The review concludes by simulating the likely changes in soil organic carbon with warm- ing. In summary, it appears likely that warming will have the effect of reducing soil organic carbon by stimulating decomposition rates more than NPP. However, increasing CO2 is likely to simultaneously have the effect of increasing soil organic carbon through increases in NPP. Any changes are also likely to be very slow. The net effect of changes in soil organic carbon on atmospheric CO2 loading over the next decades to centuries is, therefore, likely to be small.

Will changes in soil organic carbon act as a positive or negative feedback on global warming

. This paper presents a comprehensive assessment of historical (1990–2010) global anthropogenic particulate matter (PM) emissions including the consistent and harmonized calculation of mass-based size distribution (PM1, PM2. 5, PM10), as well as primary carbonaceous aerosols including black carbon (BC) and organic carbon (OC). The estimates were developed with the integrated assessment model GAINS, where source- and region-specific technology characteristics are explicitly included. This assessment includes a number of previously unaccounted or often misallocated emission sources, i.e. kerosene lamps, gas flaring, diesel generators, refuse burning; some of them were reported in the past for selected regions or in the context of a particular pollutant or sector but not included as part of a total estimate. Spatially, emissions were calculated for 172 source regions (as well as international shipping), presented for 25 global regions, and allocated to 0.5°  ×  0.5° longitude–latitude grids. No independent estimates of emissions from forest fires and savannah burning are provided and neither windblown dust nor unpaved roads emissions are included. We estimate that global emissions of PM have not changed significantly between 1990 and 2010, showing a strong decoupling from the global increase in energy consumption and, consequently, CO2 emissions, but there are significantly different regional trends, with a particularly strong increase in East Asia and Africa and a strong decline in Europe, North America, and the Pacific region. This in turn resulted in important changes in the spatial pattern of PM burden, e.g. European, North American, and Pacific contributions to global emissions dropped from nearly 30 % in 1990 to well below 15 % in 2010, while Asia's contribution grew from just over 50 % to nearly two-thirds of the global total in 2010. For all PM species considered, Asian sources represented over 60 % of the global anthropogenic total, and residential combustion was the most important sector, contributing about 60 % for BC and OC, 45 % for PM2. 5, and less than 40 % for PM10, where large combustion sources and industrial processes are equally important. Global anthropogenic emissions of BC were estimated at about 6.6 and 7.2 Tg in 2000 and 2010, respectively, and represent about 15 % of PM2. 5 but for some sources reach nearly 50 %, i.e. for the transport sector. Our global BC numbers are higher than previously published owing primarily to the inclusion of new sources. This PM estimate fills the gap in emission data and emission source characterization required in air quality and climate modelling studies and health impact assessments at a regional and global level, as it includes both carbonaceous and non-carbonaceous constituents of primary particulate matter emissions. The developed emission dataset has been used in several regional and global atmospheric transport and climate model simulations within the ECLIPSE (Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants) project and beyond, serves better parameterization of the global integrated assessment models with respect to representation of black carbon and organic carbon emissions, and built a basis for recently published global particulate number estimates.

/pdf/global-anthropogenic-emissions-of-particulate-matter-1vryzejd54.pdf

Global anthropogenic emissions of particulate matter including black carbon

Rising atmospheric CO2 and temperatures are probably altering ecosystem carbon cycling, causing both positive and negative feedbacks to climate. Below-ground processes play a key role in the global carbon (C) cycle because they regulate storage of large quantities of C, and are potentially very sensitive to direct and indirect effects of elevated CO2 and temperature. Soil organic matter pools, roots and associated rhizosphere organisms all have distinct responses to environmental change drivers, although availability of C substrates will regulate all the responses. Elevated CO2 increases C supply below-ground, whereas warming is likely to increase respiration and decomposition rates, leading to speculation that these effects will moderate one another. However, indirect effects on soil moisture availability and nutrient supply may alter processes in unexpected directions. Detailed, mechanistic understanding and modelling of below-ground flux components, pool sizes and turnover rates is needed to adequately predict long-term, net C storage in ecosystems. In this synthesis, we discuss the current status of below-ground responses to elevated CO2 and temperature and potential feedback effects, methodological challenges, and approaches to integrating models and measurements.

https://www.fs.fed.us/rm/pubs_other/rmrs_2004_pendall001.pdf

Below-ground process responses to elevated CO2 and temperature: a discussion of observations, measurement methods, and models

We compiled regional and continental data on inorganic nitrogen (N) in seepage and surface water from temperate forests. Currently, N concentrations in forest waters are usually well below water qu...

Leaching of nitrate from temperate forests effects of air pollution and forest management

Boreal forest ecosystems are sensitive to global warming, caused by increasing emissions of CO2 and other greenhouse gases. Assessment of the biological response to future climate change is based mainly on large-scale models. Whole-ecosystem experiments provide one of the few available tools by which ecosystem response can be measured and with which global models can be evaluated. Boreal ecosystem response to global change may be manifest by alterations in nitrogen (N) dynamics, as N is often the growth limiting nutrient. The CLIMEX (Climate Change Experiment) project entails catchment-scale manipulations of CO2 (to 560 ppmv) and temperature (by + 3 to + 5 °C) to whole forest ecosystems in southern Norway. Soil temperature is increased at 400-m2 EGIL catchment by means of electric cables placed on the soil surface. Soil warming at EGIL catchment caused an increase in nitrate and ammonium concentrations in runoff in the first year of treatment. We hypothesize that higher temperature increased N release by mineralization. Whether these responses are only transient will be shown by additional years’ treatment.

Experimentally increased soil temperature causes release of nitrogen at a boreal forest catchment in southern Norway

White precipitates collected from stream bottoms and well tubes in the Senne area consist of amorphous aluminium hydroxide, coprecipitated with minor amounts of sulfate, phosphate and silica. The precipitates have presumably formed by the interaction of slightly alkaline water from calcareous subsoil sediments, with acidic water draining off sandy soils affected by high inputs of acidic atmospheric deposition. From many hydrochemical studies, precipitation of aqueous aluminium is known to occur in subsurface horizons of acid soils affected by acid rain. On the basis of presumed equilibrium with soil solutions, jurbanite, AlOHSO4 · 5H2O, is often assumed to be the secondary mineral involved. However, direct evidence for jurbanite from solid phase analysis is lacking. This first analysis of such a secondary phase does not support the jurbanite hypothesis, and shows that amorphous Al hydroxide can be formed instead.

Aluminium precipitates from groundwater of an aquifer affected by acid atmospheric deposition in the Senne, Northern Germany.

The release of previously stored soil SO4
2− is tightly connected with the reversibility of soil and water acidification. Thus soil SO4
2− dynamics have to be included when predicting the reversibility of acidification. Our aim was to compare two modelling approaches: The model MAGIC (Cosby et al., 1985) describes SO4
2− dynamics with the Langmuir sorption isotherme. In the SO-MODEL (Prenzel, 1991) a precipitation/ dissolution of jurbanite is defined. Even though it was possible to calibrate both models to lysimeter data of the Solling D1 site in 1 m depth, the prognosis for SO4
2− concentrations in the soil solution differed significantly. While MAGIC predicted the observed gradual decrease of SO4
2− concentration with decreasing deposition, the SO-MODEL calculated stable concentrations up to the year 2026 followed by a sudden drop. Because the prognosis established with the SO-MODEL is incompatible with observed field data, we concluded that the predicted SO4
2− dynamic of the SO-MODEL was unrealistic.

Describing soil SO42-dynamics in the Solling roof project with two different modelling approaches

Atmospheric deposition has resulted in an accumulation of inorganic sulfur (S) in many forest soils. At Sosemulde (Harz Mountains) samples from 5–240 cm depth were analysed. Most sulfate (SO4) is accumulated at about 30–60 cm depth: 8.5–9.5 mmolc kg−1. Large amounts can also be retained in > 100 cm. To assess changes in SO4 dynamics in time,adsorption isotherms have been included in several process-oriented models, e.g., in MAGIC. The Lange Bramke (LB) Model is the first model used on the catchment scale containing solubility products for the hydroxosulfate minerals jurbanite and alunite. By reconstructing the long-term acidification history (140 years) both models were successfully calibrated to a 14-year deposition, soil and streamwater data set at Lange Bramke catchment (Harz Mountains). According to MAGIC the present accumulation of SO4 in 0 –80 cm is 8.7 mmolc kg−1, while according to the LB-Model 10.2 mmolc kg−1 are stored as jurbanite. Both models predicted 4.5 mmolc kg−1 SO4 in the subsoil layer, retained as alunite in the LB Model. These values correspond to the amounts measured in soil and subsoil samples at Sosemulde, respectively. However, for future scenarios with decreasing S inputs the models show different developments in SO4 concentrations. Changes in MAGIC are gradual whereas the LB model predicts stepwise decreasing SO4 values as soon as previously stored hydroxosulfates are fully dissolved. Such concentration “jumps” have not been observed.

Measured and modelled retention of inorganic sulfur in soils and subsoils (Harz Mountains, Germany)

Primary particulate matter is emitted directly into the atmosphere from various anthropogenic and natural sources such as power plants (combustion of fossil fuels) or forest fires. Secondary particles are formed by transformation of SO2, NOx, NH3, and VOC in the atmosphere. They both contribute to ambient particulate matter concentrations, which may have adverse effects on human health. Health hazards are caused by small particulate size, high number of especially fine (< 2.5 µm) and ultra-fine (< 0.1 µm) particles and/or their chemical composition. As part of an integrated assessment model developed at IIASA, a module on primary particulate matter (PM) emissions has been added to the existing SO2, NOx, NH3 and VOC sections. The module considers so far primary emissions of total suspended particles (TSP), PM10 and PM2.5 from aggregated stationary and mobile sources. A primary PM emission database has been established. Country specific emission factors for stationary sources have been calculated within the module using the ash content of solid fuels.

Anke Lükewille

Papers

Experimentally increased soil temperature causes release of nitrogen at a boreal forest catchment in southern Norway

Aluminium precipitates from groundwater of an aquifer affected by acid atmospheric deposition in the Senne, Northern Germany.

Describing soil SO42-dynamics in the Solling roof project with two different modelling approaches

Measured and modelled retention of inorganic sulfur in soils and subsoils (Harz Mountains, Germany)

A module to calculate primary particulate matter emissions and abatement measures in Europe