Land and water interface zones

This paper reports analyses of C pools and fluxes in land-water interface zones completed at the International Workshop: Terrestrial Biospheric Carbon Fluxes; Quantification of Sinks and Sources of CO₂ (Bad Harzburg, Germany, March 1–5, 1993). The objective was to determine the role of these zones as global sinks of atmospheric CO₂ as part of a larger effort to quantify global C sinks and sources in the past (ca. 1850), the present, and the foreseeable future (ca. 2050). Assuming the world population doubles by the year 2050, storage of atmospheric C in reservoirs will also double, as will river loads of atmospheric C and nutrients. It is estimated that C sinks in temperate and boreal wetlands have decreased by about 50%, from 0.2 to 0.1 Gt C yr^?1 since 1850. The total decrease for wetlands may be considerably larger when tropical wetlands are taken into account, however, the area and C density of tropical wetlands are not well known at this time. Changes in cultivation practices and improved sampling of methaneogenesis have caused estimates of CH₄ emissions from ricelands to drop substantially from 150 to 60 Tg yr^?1. Even with doubled N and P loads, rivers are unlikely to fertilize more than about 20% of the new primary production in the coastal ocean. The source of C for this new production may not be the atmosphere, however, because the coastal ocean exchanges large quantities of DIC with the open ocean. Until the C fluxes from air-sea exchange of CO₂ and DIC are better quantified, the C-sink potential of the coastal ocean will remain a major uncertainty in the global C cycle. Analysis of model simulations of oceanic C uptake reconfirmed that the open ocean appears to take up about 2.0 Gt C yr^?1 from the atmosphere and that model estimates are in better accord now, ±0.5 Gt C yr^?1, than ever before. Land use management must consider the unique C sinks in coastal and alluvial wetlands in order to minimize the future negative impacts of agriculture and urban development. Long-term monitoring will be essential to prove the success, or failure, of management practices to sustain wetlands in the future. Relative to the other systems examined at the workshop, the C-sink capacity of the ocean (excluding estuaries) is not likely to be measurably affected in the foreseeable future by the management scenarios considered at the workshop.     

Natural sinks of CO2: Technical synthesis from the palmas Del Mar Workshop

Natural CO₂ sinks in terrestrial and marine environments are important components of the global carbon cycle, yet the sign and magnitudes of key fluxes among them are unknown. The results of the Palmas Del Mar Workshop — Natural Sinks of CO₂ presented in this special issue and its companion hardbound volume of Water, Air, & Soil Pollution, provide a synthesis of current research on the carbon cycle, CO₂ sinks and associated processes and fluxes, and critical research needs to assess the potential role of forest and land-use management in carbon sequestration. The papers in this volume present data, observations, and model simulations that demonstrate: 1) the existence of natural CO₂ sinks that could mitigate a significant amount of CO₂ emissions from fossilfuel combustion; 2) probable, human-caused imbalances in C exchanges among vegetation, soils, and the atmosphere; 3) enhanced C storage in vegetation in response to excess atmospheric CO₂; 4) strong interactions among carbon, nutrient and hydrological cycles; and 5) an excess of carbon production over consumption in several, large managed forests. Although it appears unlikely that the search for the “missing” C sink required to balance the C budget will end in the open ocean, new estimates of C storage in mangrove wood and peat, suggest that coastal ecosystems have the capacity to store significant amounts of carbon in vegetation and sediments. Convincing analyses are also presented indicating the technical and economical feasibility of managing existing lands to sequester additional carbon. Long-term field studies of CO₂ fertilization effects and carbon cycling by plants and soils in geographically important systems, native forests, and coastal ecosystems will go a long way toward meeting the research needs identified at the workshop.     

Tropical forests: Their past,present, and potential future role in the terrestrial carbon budget

In this paper we review results of research to summarize the state-of-knowledge of the past, present, and potential future roles of tropical forests in the global C cycle. In the pre-industrial period (ca. 1850), the flux from changes in tropical land use amounted to a small C source of about 0.06 Pg yr^?1. By 1990, the C source had increased to 1.7 ± 0.5 Pg yr^?1. The C pools in forest vegetation and soils in 1990 was estimated to be 159 Pg and 216 Pg, respectively. No concrete evidence is available for predicting how tropical forest ecosystems are likely to respond to CO₂ enrichment and/or climate change. However, C sources from continuing deforestation are likely to overwhelm any change in C fluxes unless land management efforts become more aggressive. Future changes in land use under a “business as usual” scenario could release 41–77 Pg C over the next 60 yr. Carbon fluxes from losses in tropical forests may be lessened by aggressively pursued agricultural and forestry measures. These measures could reduce the magnitude of the tropical C source by 50 Pg by the year 2050. Policies to mitigate C losses must be multiple and concurrent, including reform of forestry, land tenure, and agricultural policies, forest protection, promotion of on-farm forestry, and establishment of plantations on non-forested lands. Policies should support improved agricultural productivity, especially replacing non-traditional slash-and-burn agriculture with more sustainable and appropriate approaches.     

Managing soils for negative feedback to climate change and positive impact on food and nutritional security

ABSTRACT

The increase in atmospheric concentration of carbon dioxide from 278 ppm in the pre-industrial era to 405 ppm in 2018, along with the enrichment of other greenhouse gases, has already caused a global mean temperature increase of 1°C. Among anthropogenic sources, historic land use and conversion of natural to agricultural eco-systems has and continues to be an importance source. Global depletion of soil organic carbon stock by historic land use and soil degradation is estimated at 133 Pg C. Estimated to 2-m depth, C stock is 2047 Pg for soil organic carbon and 1558 Pg for soil inorganic carbon, with a total of 3605 Pg. Thus, even a small change in soil organic carbon stock can have a strong impact on atmospheric CO₂ concentration. Soil C sink capacity, between 2020 and 2100, with the global adoption of best management practice which creates a positive soil/ecosystem C budget, is estimated at 178 Pg C for soil, 155 Pg C for biomass, and 333 Pg C for the terrestrial biosphere with a total CO₂ drawdown potential of 157 ppm. Important among techniques of soil organic C sequestration are adoption of a system-based conservation agriculture, agroforestry, biochar, and integration of crops with trees and livestock. There is growing interest among policymakers and the private sector regarding the importance of soil C sequestration for adaptation and mitigation of climate change, harnessing of numerous co-benefits, and strengthening of ecosystem services.     

Environmental biogeochemistry of mercury in Antarctic ecosystems

Polar regions are recognized as important sinks for long-range transport and deposition of Hg derived from natural and anthropogenic sources at lower latitudes. In previous studies we found enhanced Hg accumulation in soils, mosses and lichens from ice-free areas of Victoria Land facing the Terra Nova Bay coastal polynya. This study extends research to the distribution of organic C, total N, S, Hg, Al and Fe in surface soils, cyanobacterial mats and short sediment cores from four lacustrine ecosystems, each with different environmental characteristics and varying distances from the polynya. Results show that planktonic and benthic mats from lakes, along with mosses in the watershed, are the main sinks for Hg in summer meltwater. The C-normalized Hg concentrations in short sediment cores were higher in samples from lakes more exposed to marine aerosols from the coastal polynya. Reactive halogens in the aerosol promote the oxidation and deposition of atmospheric Hg in coastal ecosystems. The analysis of sediment cores did not reveal increasing Hg concentrations in recent sediments, except in the Lake 14 at Edmonson Point. The latter ice-free area is unaffected by the polynya and the increase in Hg concentrations in surface sediments could be due to local changes in lake water level and S biogeochemistry. Although change in sea ice coverage may enhance the role of Antarctic coastal ecosystems as sink in the global Hg cycle, our results seem to exclude possible risks for Antarctic terrestrial and freshwater organisms.     

Boreal forests and tundra

The circumpolar boreal biomes coverca. 2 10⁹ ha of the northern hemisphere and containca. 800 Pg C in biomass, detritus, soil, and peat C pools. Current estimates indicate that the biomes are presently a net C sink of 0.54 Pg C yr^?1. Biomass, detritus and soil of forest ecosystems (includingca. 419 Pg peat) containca. 709 Pg C and sequester an estimated 0.7 Pg C yr^?1. Tundra and polar regions store 60–100 Pg C and may recently have become a net source of 0.17 Pg C yr^?1. Forest product C pools, including landfill C derived from forest biomass, store less than 3 Pg C but increase by 0.06 Pg C yr^?1. The mechanisms responsible for the present boreal forest net sink are believed to be continuing responses to past changes in the environment, notably recovery from the little ice-age, changes in forest disturbance regimes, and in some regions, nutrient inputs from air pollution. Even in the absence of climate change, the C sink strength will likely be reduced and the biome could switch to a C source. The transient response of terrestrial C storage to climate change over the next century will likely be accompanied by large C exchanges with the atmosphere, although the long-term (equilibrium) changes in terrestrial C storage in future vegetation complexes remains uncertain. This transient response results from the interaction of many (often non-linear) processes whose impacts on future C cycles remain poorly quantified. Only a small part of the boreal biome is directly affected by forest management and options for mitigating climate change impacts on C storage are therefore limited but the potential for accelerating the atmospheric C release are high.     

Soil carbon stocks and their primary origin at mature mangrove ecosystems in the estuary of Fukido River,Ishigaki Island,southwestern Japan

ABSTRACT

Mangrove ecosystems play an important role in carbon (C) accumulation in tropical and subtropical regions. Below-ground deep anoxic soil is especially important for C accumulation. However, quantitative data on below-ground soil C stocks in mangrove ecosystems are lacking compared with data on above-ground biomass. In addition, soil C accumulation processes in mangrove ecosystems have not been sufficiently clarified. In this study, we quantified soil C stocks and focused on the mass of fallen litter and below-ground roots, which are produced by tree and that may directly influence soil C stocks in a mature subtropical mangrove in the estuary of Fukido River, Ishigaki Island, southwestern Japan. The principal species in this study site were Bruguiera gymnorhiza and Rhizophora stylosa, and total above-ground biomass at the site was 80.7 ± 1.3 (mean ± SD) Mg C ha^?1 over the period from 2014 to 2016. Litter was collected in six litter traps from May 2013 to November 2016, it ranged from 7.8 to 11.5 Mg C ha^?1, with the major proportion of litter being from foliage (leaves and stipules). The root C density at 90-cm depth was 27.1 ± 11.3 Mg C ha^?1. The soil C stock in the mangrove forest at a depth of 90 cm at the study site was 251.0 ± 34.8 Mg C ha^?1, and it seems to be lower value in the tropical region but it to be higher in subtropical East Asian mangrove sites. Dead roots, especially dead fine roots, but not fallen litter, were significantly positively correlated with soil C stocks. The δ¹³C values obtained from soils ranged from ?29.3‰ to ?27.0‰; these values are consistent with those for below-ground fine roots. These results strongly suggest that dead fine roots could be a main factor controlling soil C stocks at this study site.     

Simulating the carbon flux between the terrestrial environment and the atmosphere

A Terrestrial C Cycle model that is incorporated in the Integrated Model to Assess the Greenhouse Effect (IMAGE 2.0) is described. The model is a geographically explicit implementation of a model that simulates the major C fluxes in different compartments of the terrestrial biosphere and between the biosphere and the atmosphere. Climatic parameters, land cover and atmospheric C concentrations determine the result of the dynamic C simulations. The impact of changing land cover patterns, caused by anthropogenic activities (shifting agriculture, de- and afforestation) and climatic change are modeled implicitly. Feedback processes such as CO₂ fertilization and temperature effects on photosynthesis, respiration and decomposition are modeled explicitly. The major innovation of this approach is that the consequences of climate change are taken into account instantly and that their results can be quantified on a global medium-resolution grid. The objectives of this paper are to describe the C cycle model in detail, present the linkages with other parts of the IMAGE 2.0 framework, and give an array of different simulations to validate and test the robustness of this modeling approach. The computed global net primary production (NPP) for the terrestrial biosphere in 1990 was 60.6 Gt C a^?1, with a global net ecosystem production (NEP) of 2.4 Gt C a^?1. The simulated C flux as result from land cover changes was 1.1 Gt C a^?1, so that the terrestrial biosphere in 1990 acted as a C sink of 1.3 Gt C a^?1. Global phytomass amounted 567.5 Gt C and the dead biomass pool was 1517.7 Gt C. IMAGE 2.0 simulated for the period 1970–2050 a global average temperature increase of 1.6 °C and a global average precipitation increase of 0.1 mm/day. The CO₂ concentration in 2050 was 522.2 ppm. The computed NPP for the year 2050 is 82.5 Gt C a^?1, with a NEP of 8.1 Gt C a^?1. Projected land cover changes result in a C flux of 0.9 Gt C a^?1, so that the terrestrial biosphere will be a strong sink of 7.2 Gt C a^?1. The amount of phytomass hardly changed (600.7 Gt C) but the distribution over the different regions had. Dead biomass increased significantly to 1667.2 Gt C.     

Removal of Zinc from Tidal Water by Sediments of a Mangrove Ecosystem: A Radiotracer Study

The removal of ⁶⁵Zn from tidal water by underlaying sediment cores collected in a mangrove forest and a tidal creek that drains this forest in Sepetiba Bay (SE Brazil) was investigated. After 30-h experiments in laboratory microcosms, the ⁶⁵Zn half-removal times from tidal creek and mangrove forest sediments were 8.7?±?1.8 and 9.2?±?0.9 h respectively. Depth penetration of ⁶⁵Zn was mainly restricted to the upper 3 cm in mangrove forest cores, while detectable ⁶⁵Zn activities were found in all layers (0–7 cm depth) of tidal creek cores. An unexpected ⁶⁵Zn release back to the overlaying water was observed for one of the tidal creek experiments in the 12–18 h interval (corresponding to a return of 17% of the initial ⁶⁵Zn activity in overlaying water), suggesting a reversibility of the ⁶⁵Zn removal process (e.g., by adsorption) in tidal creek sediments. The results indicate that mangrove-vegetated sediments allowed a lower vertical mobility of Zn than observed in creek sediments and mangrove sediments appear to be less susceptible to a reversion in the process of zinc removal from overlaying water, suggesting a greater capacity to retain this metal near the water–sediment interface. This first radiotracer approach on the mangrove sediments removal of Zn from tidal waters supports earlier experimental studies employing stable Zn, contributing for a better understanding of the metal uptake kinetics by such sediments and suggesting that these sediments act as active sinks for trace metals.     

Carbon stocks of soil and vegetation on Danubian floodplains

Riparian forests are assumed to play a crucial role in the global carbon cycle. However, little data are available on C stocks of floodplains in comparison to other terrestrial ecosystems. In this study, we quantified the C stocks of aboveground biomass and soils of riparian vegetation types at 76 sampling sites in the Donau‐Auen National Park in Austria. Based on our results and a remotely sensed vegetation map, we estimated total C stocks. Carbon stocks in soils (up to 354 t ha^–1 within 1 m below surface) were huge compared to other terrestrial ecosystems. As expected, soils of different vegetation types showed different texture with a higher percentage of sandy soils at the softwood sites, while loamy soils prevailed at hardwood sites. Total C stocks of vegetation types were significantly different, but reflect differences in woody plant biomass rather than in soil C stocks. Mature hardwood and cottonwood forests proved to have significantly higher total C stocks (474 and 403 t ha^–1, respectively) than young reforestations (217 t ha^–1) and meadows (212 t ha^–1). The C pools of softwood forests (356 t ha^–1) ranged between those of hardwood/cottonwood forests and of reforestations/meadows. Our study proves the relevance of floodplains as possible C sinks, which should be increasingly taken into account for river management. Furthermore, we conclude that plant‐species distribution does not indicate the conditions of sedimentation and soil C sequestration over the time span of interest for the development of soil C stocks.     

Mercury Accumulation in Sediments of a Mangrove Ecosystem in SE Brazil

The Hg accumulation in sedimentary environments of a mangrove ecosystem in Sepetiba Bay, SE Brazil, was investigated. These environments include sediments of a mangrove forest, the main tidal creek that drains the forest, and the bare seaward-edge mud flat adjacent to forest and tidal creek. Maximum Hg concentration peaks in sediments from the mud flat (184 ng g^-1), tidal creek (98 ng g^-1), and mangrove forest (60 ng g^-1) correspond to enrichment factors of 6.1, 3.3, and 2.0 above the estimated average background level, respectively. Average inventories of Hg excess (background-corrected) concentrations were substantiallydifferent between environments, decreasing from mud flat sediments (5.2 mg m^-2) to creek sediments (3.3 mg m^-2)to mangrove forest sediments (0.9 mg m^-2). Mercury concentration profiles indicated a consistently higher accumulation of Hg in surface layers of mud flat and tidal creeksediments, whereas mangrove forest sediments showed a higher Hgaccumulation in root-rich subsurface layers, in agreement with an enrichment of Fe and organic matter contents. While Hg distribution in mud flat and tidal creek sediments appears to belargely affected by contamination, its distribution in mangrove forest substrate appears to be greatly affected by root-sedimentinteractions. Mercury levels in the study site were comparable tothose observed in coastal sediments under moderate Hg contamination at local and regional scales. Results indicate thatsedimentary environments surrounding the mangrove forest retain most of the anthropogenic Hg reaching the ecosystem. Since tidal waters have been previously demonstrated as the main source of metals to the site, it is suggested that the Hg retention in mudflat sediments precede and may avoid a higher Hg accumulation inlandward environments.     

The interaction of climate and land use in future terrestrial carbon storage and release

The processes controlling total carbon (C) storage and release from the terrestrial biosphere are still poorly quantified. We conclude from analysis of paleodata and climate biome model output that terrestrial C exchanges since the last glacial maximum (LGM) were dominated by slow processes of C sequestration in soils, possibly modified by C starvation and reduced water use efficiency of trees during the LGM. Human intrusion into the C cycle was immeasurably small. These processes produced an averaged C sink in the terrestrial biosphere on the order of 0.05 Pg yr^?1 during the past 10,000 years. In contrast, future C cycling will be dominated by human activities, not only from increasing C release with burning of fossil fuels, and but also from indirect effects which increase C storage in the terrestrial biosphere (CO₂ fertilization; management of C by technology and afforestation; synchronous early forest succession from widespread cropland abandonment) and decrease C storage in the biosphere (synchronous forest dieback from climatic stress; warming-induced oxidation of soil C; slowed forest succession; unfinished tree life cycles; delayed immigration of trees; increasing agricultural land use). Comparison of the positive and negative C flux processes involved suggests that if the C sequestration processes are important, they likely will be so during the next few decades, gradually being counteracted by the C release processes. Based only on tabulating known or predicted C flux effects of these processes, we could not determine if the earth will act as a significant C source from dominance by natural C cycle processes, or as a C sink made possible only by excellent earth stewardship in the next 50 to 100 yrs. Our subsequent analysis concentrated on recent estimates of C release from forest replacement by increased agriculture. Those results suggest that future agriculture may produce an additional 0.6 to 1.2 Pg yr^?1 loss during the 50 to 100 years to CO₂ doubling if the current ratio of farmed to potentially-farmed land is maintained; or a greater loss, up to a maximum of 1.4 to 2.8 Pg yr^?1 if all potential agricultural land is farmed.     

莱州湾南岸滨海湿地的氮、磷循环过程及调控对策

在莱州湾南岸滨海湿地的生物地球化学循环过程中,N、P元素主要来源于通过河流输入的工业废水、城市生活污水、农田地表径流、灌溉余水和海水养殖池养殖废水,通过潮上带、潮间带湿地最终被输送到潮下带近海湿地,引起潮下带近海湿地水体N、P含量的不断升高,2000年通过河流输入到莱州湾南岸的N总量为46271.1t,P总量为2092.1t.潮上带、潮间带自然湿地的底质、土壤和植物对N、P元素有显著的吸收、净化作用.以2000年为例,若不考虑自然湿地的吸收、净化作用,仅靠水体交换、扩散稀释,输送到潮下带近海湿地的N、P在海水中的含量为6.74mg·L-1、0.299mg·L-1,而当年潮下带近海湿地水体N、P含量实测值分别为0.086mg·L-1、0.029mg·L-1,计算值分别是实测值的78.4倍、10.3倍;说明自然湿地对输入的N、P有明显的吸收净化效应.为降低莱州湾南岸潮下带近海湿地海水中的N、P含量,提出了发展循环经济,减小莱州湾南岸滨海湿地的N、P输入通量,对自然湿地进行有效的保护和生态恢复,建设人工湿地、提高湿地的环境净化功能等调控措施.     

The role of sediment microorganisms in the productivity, conservation, and rehabilitation of mangrove ecosystems: an overview

Mangrove communities are recognized as highly productive ecosystems that provide large quantities of organic matter to adjacent coastal waters in the form of detritus and live animals (fish, shellfish). The detritus serves as a nutrient source and is the base of an extensive food web in which organisms of commercial importance take part. In addition, mangrove ecosystems serve as shelter, feeding, and breeding zones for crustaceans, mollusks, fish of commercial importance, and resident and migratory birds. Although mangroves in the United States are protected, the systematic destruction of these ecosystems elsewhere is increasing. Deforestation of mangrove communities is thought to be one of the major reasons for the decrease in the coastal fisheries of many tropical and subtropical countries. There is evidence to propose a close microbe-nutrient-plant relationship that functions as a mechanism to recycle and conserve nutrients in the mangrove ecosystem. The highly productive and diverse microbial community living in tropical and subtropical mangrove ecosystems continuously transforms nutrients from dead mangrove vegetation into sources of nitrogen, phosphorus, and other nutrients that can be used by the plants. In turn, plant-root exudates serve as a food source for the microorganisms living in the ecosystem with other plant material serving similarly for larger organisms like crabs. This overview summarizes the current state of knowledge of microbial transformations of nutrients in mangrove ecosystems and illustrates the important contributions these microorganisms make to the productivity of the ecosystems. To conserve the mangrove ecosystems, which are essential for the sustainable maintenance of coastal fisheries, maintenance and restoration of the microbial communities should be undertaken. Inoculation of mangrove seedlings with plant-growth-promoting bacteria may help revegetate degraded areas and create reconstructed mangrove ecosystems.     

Poplar plantations in coastal China: towards the identification of the best rotation age for optimal soil carbon sequestration

Poplar plantations are an important resource in China, which possess significant potential to offset carbon (C) emissions through the sequestration of atmospheric carbon dioxide (CO₂) within biomass and soil. The traditional rotation age of poplar plantations is determined by maximizing the economic return from timber production. However, the optimal rotation age that results in the highest level of carbon sequestration within the soil remains unclear. In this study, we examined the total C, nitrogen (N) and microbial biomass (SMB) content of soils, as well as other properties in 0–10, 10–25 and 25–40 cm soil profiles along a 0‐ to 20‐yr chronosequence in a coastal region of Eastern China. Soil C stocks were determined for 1 m soil profiles, and the stand biomass in poplar plantations of different ages was investigated. We found that C concentrations within soils increased with plantation age, primarily in the topsoil layers. The periodic annual increment of C in soils peaked between stand ages of from 6 to 10 yr (0.71 t/ha/yr) and then decreased considerably at 17.5 yr, while the mean annual increment of C in soils was the highest at 15 yr (0.573 t/ha/yr). Soil C accumulation (i.e. soil C sequestration) was positively correlated with poplar biomass, soil N and SMB, and negatively correlated with soil potassium (K), calcium (Ca), magnesium (Mg) and sodium (Na), but not with sulphur (S) or phosphorus (P). Our results suggest that a rotation age of 15 yr is optimal for the sequestration of atmospheric CO₂ in poplar plantations in the coastal region of Eastern China. The C sequestration capacity of soil was primarily controlled by poplar biomass, soil N and SMB.     

Ontogenetic niche shifts in the American Alligator establish functional connectivity between aquatic systems

Individual animals undergoing ontogenetic shifts in habitat use may establish a mobile link between discrete ecosystems via movement of energy, nutrients and matter, as well as through impacts on ecosystem and habitat structure. The American Alligator (Alligator mississippiensis) is a model species for studying ecological implications of ontogenetic niche shifts, because they grow in size by several orders of magnitude, and they play a critical role as both top predators and ecosystem engineers. We used equal trapping effort, radio telemetry and nest surveys to document ontogenetic habitat shifts of alligators between hydrologically isolated, seasonal wetlands and riverine systems. To estimate the degree of functional connectivity between systems, we quantified alligator biomass and nutrient excretion in both systems. Seasonal wetlands provided nesting and nursery sites for adult females and juveniles, which constituted 0.78 g/m² biomass and excreted 0.05 g/m²/yr N, P, Ca, Mg, Na and K in that system. In contrast, the riverine system provided non-nesting habitat for adults and sub-adults of both sexes, totaling 0.18 g/m² biomass and excreting 0.01 g/m²/yr of nutrients. Furthermore, sub-adults and adult females were documented moving across the terrestrial matrix, while adult males spent the duration of the study in the creek. Our results demonstrated that ontogenetic niche shifts in alligators establish connectivity between seasonal wetlands and riverine systems and with the surrounding terrestrial matrix. These findings have implications for the definition of jurisdictional wetlands under the US Supreme Court’s 2001 SWANCC decision and highlight the importance of ecological, as well as hydrological, connectivity.     

Workshop summary statement: Terrestrial bioshperic carbon fluxesquantification of sinks and sources of CO2

Understanding the role of terrestrial ecosystems in the global carbon (C) cycle has become increasingly important as policymakers consider options to address the issues associated with global change, particularly climate change. Sound scientific theories are critical in predicting how these systems may respond in the future, both to climate change and human actions. In March 1993, 60 scientists from 13 nations gathered in Bad Harzburg, Germany, to develop a state-of-the-science assessment of the present and likely future C fluxes associated with the major components of the earth's terrestrial biosphere. In the process, particular emphasis was placed on the potential for improving C sinks and managing long-term C sequestration. The majority of the week's work was conducted in eight working groups which independently considered a particular biome or subject area. The working groups considered: the Global Carbon Cycle; Boreal Forests and Tundra; Temperate Forests; Tropical Forests; Grasslands, Savannas and Deserts; Land and Water Interface Zones; Agroecosystems; and Biomass Management. This paper presents a brief overview of their major conclusions and findings. In addition, Table 1 brings together the best estimates from each group as to the current magnitude and estimated future direction of changes in the terrestrial C fluxes.     

After the Kyoto Protocol: Can soil scientists make a useful contribution?*

Abstract. Over 170 countries have ratified the UN Framework Convention on Climate Change (UNFCCC) which aims at ‘the stabilisation of greenhouse gases in the atmosphere at a level that will prevent dangerous anthropogenic interference with the climate system’. The Kyoto Protocol, signed in 1997, commits the developed (‘Annex 1′) countries to a reduction in gaseous emissions. The global increase in atmospheric CO₂, the main greenhouse gas, comes mainly from fossil fuels (6.5 Gt C yr^?1), together with about 1.6 Gt C yr^?1 from deforestation. The atmospheric increase is only 3.4 Gt C yr^?1, however, due to a net sink in terrestrial ecosystems of about 2 Gt C yr^?1, and another in the oceans. Increasing net carbon sequestration by afforestation of previously non-forested land is one way of reducing net national emissions of CO₂ that is permitted under the Kyoto Protocol. Future modifications may also allow the inclusion of carbon sequestration brought about by other forestry and agricultural land management practices. However, associated changes in net fluxes of two other greenhouse gases identified in the Protocol — nitrous oxide (N₂O) and methane (CH₄) — will have to be taken into account. Growth of biomass crops can increase N₂O emissions, and drainage of wetlands for forestry or agriculture also increases them, as well as emissions of CO₂, while decreasing those of CH₄. The problems of how to quantify these soil sources and sinks, to maximize soil C sequestration, and to minimize soil emissions of CH₄ and N₂O, will present a major scientific challenge over the next few years — one in which the soil science community will have a significant part to play.     

The Mississippian Paleosols in the Brontsy Quarry,Kaluga region

A chronosequence of five Visean (Aleksinian–Venevian interval, C1v, 326–336 Mya) paleosols on the territory of Moscow calcareous sedimentary basin (Brontsy quarry, Kaluga region) was studied in detail. Two lowermost paleosols are coastal peat-bearing paleosols developed under mangrove vegetation. Three upper paleosols develop pedocomplexes, in which the lower part is the marine limestone altered to different degrees by weathering/pedogenesis with the formation of eroded Rendzina-type soil. It is overlain by paleosols developed from terrigenous sediments of playa origin. They are characterized by elevated concentrations of Fe, Mg, Ti, Ga, and some other elements; the formation of secondary micritic carbonates, iron oxides, and smectites; and increased values of geochemical indexes (such as CIA-K). Smectite (low-charged beidellite) predominates in these paleosols. Iron oxides are represented by goethite and lepidocrocite attesting to the predominance of oxygenic environments. Pedocomplex at the Mikhaylovian/Venevian boundary is overlain by non-marine palustrine deposits known as “black rhizoidal limestone.” The paleoclimate reconstruction based on the chemical composition data attests to its polycyclic character. The Mikhaylovian time was most humid was (~1000 mm/yr). Later, starting from Venevian, gradual aridization of the climate began and annual precipitation decreased to 750 mm/yr and less.     

Mangroves as indicators of coastal change

In view of the unique biological characteristics of mangroves, it is interesting to assess the extent to which these ecosystems can be used as indicators of coastal change or sea-level rise. From recent studies of mangrove mortality at several locations (including Guiana, Gambia, Côte d'Ivoire, Kenya, India and Bangladesh), it appears that these coastal ecosystems are so specialized that any minor variation in their hydrological or tidal regimes causes noticeable mortality. Each species of mangrove (but particularly those belonging to the genera Rhizophora, Bruguiera, Sonneratia, Heritiera and Nypa) occurs in ecological conditions that approach its limit of tolerance with regard to salinity of the water and soil, as well as the inundation regime. If the duration of daily immersion were to be modified by tectonic, sedimentological or hydrological events, the species either readjusts to the new conditions or succumbs to unsuitable conditions. Consequently, the use of remote sensing data for mangrove ecosystems offers excellent potential as a tool for monitoring coastal change.