Decadal Time Frames Research Articles

Carbon Dioxide Emissions from Exhumed Petrocalcic Horizons

The second largest pool of terrestrial carbon is soil CaCO3 In addition to being an important sink of atmospheric CO2, soil carbonate is potentially an important source of atmospheric CO2 The cemented form of soil carbonate—the petrocalcic horizon—develops in geomorphically stable soil in arid, semiarid, and some subhumid climates. In many of these dryland areas, such as the Chihuahuan Desert of North America, erosion has stripped away overlying soil and exhumed the petrocalcic horizon, thereby exposing it to a weathering zone above the calcification zone where it normally forms. This research tested the hypothesis that soil type 1 (eroded Aridisols with exhumed petrocalcic horizons) will emit more CO2 than soil type 2 (noneroded Aridisols with petrocalcic horizons) or soil type 3 (Entisols formed in sandy, noncalcareous sediments). We tested this hypothesis by comparing the amount of CO2 and the δ13C of CO2 released from the three soil types. Using a randomized complete block design, CO2 emissions were measured using NaOH and soda lime traps from June 2002 to October 2003. Neither the NaOH traps nor soda lime traps detected any statistical difference in cumulative CO2 emissions from the three soil types at the α = 0.05 level. Moreover, the isotopic analysis of CO2 did not match the isotopic values of pedogenic carbonate, nor were there any statistical differences (α = 0.05) in δ13C of CO2 among the three soil types. We conclude, therefore, that exhumed petrocalcic horizons are not actively emitting CO2 at a rate significantly greater than adjacent soils, and thus carbon stored in petrocalcic horizons can be considered a recalcitrant reservoir within the decadal timeframe pertinent to carbon sequestration policies.

Short-term Periglacial Processes, Vegetation Succession, and Soil Development within Sorted Patterned Ground: Jotunheimen, Norway

Small (1 ≤ m diameter) sorted patterned ground features were studied on the Little Ice Age forelands of three Jotunheimen glaciers. Patterned ground appears to be most active near the ice margins, declining in intensity of activity with distance from the glaciers. Vegetation and soil development are negligible within patterned ground that is “Recent” (decadal time frame). Significant (P < 0.05) fine scale differences in vegetation and soil development occur within patterned ground on terrain ∼70 yr in age, with patterned ground borders having higher values of vegetation cover and thicker soils than that in patterned ground centers. With increasing age of terrain and patterned ground, soil development and vegetation encroach inward toward patterned ground centers, implying that a short-term, active periglacial zone exists near the ice margin, decaying with time and glacier retreat. Specifically, terrain that has been deglaciated for ∼70 years and is approximately ∼350–500 m from the ice margin shows a significant decline in frost activity, allowing for the initiation of pedogenesis and vegetation colonization.

Allocation of river flows for restoration of floodplain forest ecosystems: a review of approaches and their applicability in Europe.

Floodplain forests are flood-dependent ecosystems. They rely on well-timed, periodic floods for the provision of regeneration sites and on tapered flood recession curves for the successful establishment of seedlings. These overbank flood events are described as "regeneration flows." Once floodplain forest trees are established, in order to grow they also require adequate, although variable, river stage levels or "maintenance flows" throughout the year. Regeneration flows are often synonymous with flood flows and only occur periodically. There is a disparity between this need for varied interannual flows over the decadal time frame and the usual annual cycle of flow management currently used by most river management agencies. Maintenance flows are often closer to established minimum flows and much easier to provide by current operational practices.A number of environmental flow methodologies, developed in North America, Australia, and South Africa are described in this review. They include the needs of the floodplain environment in the management and allocation of river flows. In North America, these methodologies have been put into practice in a number of river basins specifically to restore floodplain forest ecosystems. In Australia and South Africa, a series of related "holistic approaches" have been developed that include the needs of floodplain ecosystems as well as in-channel ecosystems. In most European countries, restoration of floodplain forests takes place at a few localized restoration sites, more often as part of a flood-defense scheme and usually not coordinated with flow allocation decisions throughout the river basin. The potential to apply existing environmental flow methodologies to the management of European floodplain forests is discussed.

The continental shelf benthic ecosystem: current status, agents for change and future prospects

Continental shelf benthic ecosystems play an important role in the economy of many coastal states through the provision of food, non-living resources and through control of climate. Changes in the status of these ecosystems, through either natural or human-induced environmental drivers can be expected to have important economic and social consequences. Agents that could induce change include climate and oceanography, hydrology (river discharge), land-use and waste disposal practices, fishing, aquaculture and extraction of non-living resources. Trends in all of these drivers, particularly those under human influence, suggest that shelf systems will come under increasing pressure. Attempts to predict the future state of any ecological system are fraught with difficulty, particularly over decadal time-frames. This is, perhaps, especially true for continental shelf ecosystems where data on current status are poor and our understanding of many of the drivers of change somewhat rudimentary. What can be said for certain, however, is that change will occur and, in the short term, many of the signs point towards deterioration in the ecological condition of many shelf systems, but particularly those of developing countries. Trends in land-use practices, with consequences for nutrient, sediment and freshwater input to coastal seas appear to be particularly worrying, but the poor state of many demersal fisheries systems must also be acknowledged. In contrast to the developing world, although challenges undoubtedly remain, particularly with respect to atmospheric inputs resulting from energy production, current trends in environmental management suggest that pressures imposed by land use, waste disposal and fishing will probably decline over the coming decades on the shelves of many developed countries. At the global scale, therefore, the key driver for sustainable use of our continental shelf ecosystems would appear to be intimately linked to the social and economic well-being of poorer nations.

Use of paleo-records in determining variability within the volcanism–climate system

Volcanic eruptions that inject large quantities of sulfur-rich gases into the stratosphere have the capability of cooling global climate by 0.2–0.3°C for several years after the eruption. Equatorial eruptions will impact global climate whereas mid-latitude eruptions can cool climate in the hemisphere of origin. Magnitude of cooling varies by latitude and it is possible for warming to occur in certain regions, primarily during the winter. Although instrumental records have been used to quantify the volcanic impact on climate, they are limited in their temporal and spatial coverage, and the style and magnitude of eruptions occurring over the two centuries of instrumental records is limited. A thorough evaluation of the range of variability in the volcanism–climate system requires a multidisciplinary approach that includes the analysis of ice core records, geological data, atmospheric measurements and visual phenomena, tree-ring records and other proxy data. Evaluation of these longer time series indicates that multiple volcanic eruptions have the potential to force climate over decadal to multi-decadal time frames, especially when these eruptions enhance or extend pre-existing cool conditions. On the other hand, a lack of climatically significant eruptions may result in warmer average temperatures over decadal time frames because the volcanic-cooling component within the climate system is absent. Mega-eruptions, like the Toba eruption of ∼71,000–73,000 yr ago, may impact climate on centennial time frames through positive feedback mechanisms. Evidence exists which indicates that environmental changes associated with rapid climatic fluctuations, such as crustal loading/unloading with glaciation/deglaciation and variability in glacial meltwater loading on ocean basins, may cause an increase in volcanic activity.

Floodplain biogeomorphology

Floodplains are unique ecosystems because of their linear form, the sometimes extreme dynamism of their geomorphology and because they process large fluxes of energy and materials from upstream areas. This article focuses on the importance of hydrological inputs to floodplains through 1) their influence on the arrangement of landforms and vegetation communities and 2) the connections between flooding regimes and the regeneration and turnover time of floodplain vegetation. Many researchers have demonstrated close links between the arrangement of vegeta tion communities and sedimentary landform types, elevation, soil characteristics, tolerance to flooding and availability of soil moisture. It is suggested that plants on floodplains are found along a combined gradient of available moisture and oxygen which can be viewed simultaneously as a flooding frequency gradient and a complex soil moisture gradient. Discussion of experi mental work on floodplains demonstrates the importance of these gradients to a range of flood plain species in different environments. The relationships between these environmental gradients and the apparent high level of overlap between planform patterns of landforms and vegetation communities on floodplains are related to lag times in different parts of vegetation communities. Flood regimes greatly influence the availability of areas suitable for vegetation regeneration from year to year and the age structure of floodplain communities over decadal time frames. Biotic factors also influence biogeomorphological relationships on floodplains and range from sediment- trapping by vegetation to the impacts of beaver and grazing animals on floodplain hydrology and vegetation. Restoration of floodplains is high on the agenda in many countries and it is argued that, for sustainable results, restoration of hydrological pathways is essential. Planned flood releases below dams in several African countries have had varied success rates but the develop ment of models for managing flows to achieve different restoration targets is the start of an integrated approach to restoring complex floodplain ecosystems.