H umans have long been fascinated by the dynamism of free-flowing waters. Yet we have expended great effort to tame rivers for transportation, water supply, flood control, agriculture, and power generation. It is now recognized that harnessing of streams and rivers comes at great cost: Many rivers no longer support socially valued native species or sustain healthy ecosystems that provide important goods and services (Naiman et al. 1995, NRC 1992).

/pdf/the-natural-flow-regime-3j2upj9j41.pdf

The Natural Flow Regime

Impatti, adattamento e vulnerabilita Le cause e le responsabilita dei cambiamenti climatici sono state trattate sul numero di ottobre della rivista Cda. Approfondiamo l’argomento presentando il documento: “Cambiamenti climatici 2007: impatti, adattamento e vulnerabilita” votato ad aprile 2007 dal secondo gruppo di lavoro del Comitato Intergovernativo sui Cambiamenti Climatici (Intergovernmental Panel on Climate Change). Si tratta del secondo di tre documenti che compongono il quarto rapporto sui cambiamenti climatici.

/pdf/climate-change-2007-impacts-adaptation-and-vulnerability-31xc1cf4d3.pdf

Climate Change 2007: Impacts, Adaptation and Vulnerability.

The global decline in estuarine and coastal ecosystems (ECEs) is affecting a number of critical benefits, or ecosystem services. We review the main ecological services across a variety of ECEs, including marshes, mangroves, nearshore coral reefs, seagrass beds, and sand beaches and dunes. Where possible, we indicate estimates of the key economic values arising from these services, and discuss how the natural variability of ECEs impacts their benefits, the synergistic relationships of ECEs across seascapes, and management implications. Although reliable valuation estimates are beginning to emerge for the key services of some ECEs, such as coral reefs, salt marshes, and mangroves, many of the important benefits of seagrass beds and sand dunes and beaches have not been assessed properly. Even for coral reefs, marshes, and mangroves, important ecological services have yet to be valued reliably, such as cross-ecosystem nutrient transfer (coral reefs), erosion control (marshes), and pollution control (mangroves). An important issue for valuing certain ECE services, such as coastal protection and habitat-fishery linkages, is that the ecological functions underlying these services vary spatially and temporally. Allowing for the connectivity between ECE habitats also may have important implications for assessing the ecological functions underlying key ecosystems services, such coastal protection, control of erosion, and habitat-fishery linkages. Finally, we conclude by suggesting an action plan for protecting and/or enhancing the immediate and longer-term values of ECE services. Because the connectivity of ECEs across land-sea gradients also influences the provision of certain ecosystem services, management of the entire seascape will be necessary to preserve such synergistic effects. Other key elements of an action plan include further ecological and economic collaborative research on valuing ECE services, improving institutional and legal frameworks for management, controlling and regulating destructive economic activities, and developing ecological restoration options.

https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1890/10-1510.1

The value of estuarine and coastal ecosystem services

Grain size analysis is an essential tool for classifying sedimentary environments. The calculation of statistics for many samples can, however, be a laborious process. A computer program called GRADISTAT has been written for the rapid analysis of grain size statistics from any of the standard measuring techniques, such as sieving and laser granulometry. Mean, mode, sorting, skewness and other statistics are calculated arithmetically and geometrically (in metric units) and logarithmically (in phi units) using moment and Folk and Ward graphical methods. Method comparison has allowed Folk and Ward descriptive terms to be assigned to moments statistics. Results indicate that Folk and Ward measures, expressed in metric units, appear to provide the most robust basis for routine comparisons of compositionally variable sediments. The program runs within the Microsoft Excel spreadsheet package and is extremely versatile, accepting standard and non-standard size data, and producing a range of graphical outputs including frequency and ternary plots. Copyright © 2001 John Wiley & Sons, Ltd.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/esp.261

GRADISTAT: a grain size distribution and statistics package for the analysis of unconsolidated sediments

[1] We use the Total Ozone Mapping Spectrometer (TOMS) sensor on the Nimbus 7 satellite to map the global distribution of major atmospheric dust sources with the goal of identifying common environmental characteristics The largest and most persistent sources are located in the Northern Hemisphere, mainly in a broad “dust belt” that extends from the west coast of North Africa, over the Middle East, Central and South Asia, to China There is remarkably little large-scale dust activity outside this region In particular, the Southern Hemisphere is devoid of major dust activity Dust sources, regardless of size or strength, can usually be associated with topographical lows located in arid regions with annual rainfall under 200–250 mm Although the source regions themselves are arid or hyperarid, the action of water is evident from the presence of ephemeral streams, rivers, lakes, and playas Most major sources have been intermittently flooded through the Quaternary as evidenced by deep alluvial deposits Many sources are associated with areas where human impacts are well documented, eg, the Caspian and Aral Seas, Tigris-Euphrates River Basin, southwestern North America, and the loess lands in China Nonetheless, the largest and most active sources are located in truly remote areas where there is little or no human activity Thus, on a global scale, dust mobilization appears to be dominated by natural sources Dust activity is extremely sensitive to many environmental parameters The identification of major sources will enable us to focus on critical regions and to characterize emission rates in response to environmental conditions With such knowledge we will be better able to improve global dust models and to assess the effects of climate change on emissions in the future It will also facilitate the interpretation of the paleoclimate record based on dust contained in ocean sediments and ice cores

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2000RG000095

Environmental characterization of global sources of atmospheric soil dust identified with the nimbus 7 total ozone mapping spectrometer (toms) absorbing aerosol product

Aeolian dust and dust deposits

The Nature and Importance of Aeolian Sand Research.- The Nature of Airflow.- Characteristics of Windblown Sediments.- Mechanics of Aeolian Sand Transport.- The Formation of Sand Seas and Dune Fields.- Aeolian Bed Forms.- Internal Sedimentary Structures of Aeolian Sand Deposits.- Post-Depositional Modification of Dune Sands.- Management and Human Use of Sand Dune Environments.- Aeolian Research Techniques.

Aeolian sand and sand dunes

The nature, origin and accumulation of loess

Although contemporary dust storms are frequent in arid and semi-arid areas, desert loess deposits are poorly developed. Much of the World's loess occurs in mid-latitude areas which experienced glaciation during the Pleistocene. Ocean core evidence indicates that dust transport from sub-tropical deserts increased during cold stages of the Pleistocene, but loess formed only on certain desert margins, for reasons which have not been fully explained. This paper re-examines the mechanisms of dust transport and deposition, and the circumstances leading to the accumulation of thick loess. Typical loess is composed mainly of medium silt grains which are transported in short-term suspension a few metres above the ground. Significant thicknesses of loess form only when dust is trapped within a limited area, often relatively close to the source. Dust particles finer than 20 μm are transported mainly in long-term suspension over a greater height range and may be widely dispersed.

The availability of silt and the frequency, magnitude and direction of dust-transporting winds are important factors governing the potential for loess formation, but the existence of a suitable dust trap is particularly important. Traps may be formed by topographic obstacles, areas of moist ground, or vegetated surfaces. Vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid-latitudes during the Pleistocene. Dust blown during glacial periods from certain deserts, notably in Sinai, Soviet Central Asia and China, accumulated as loess in neighbouring semi-arid regions. On the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps. During most of the Holocene net dust deposition rates in all desert-marginal areas have been too low for significant loess accumulation. This is mainly due to a reduction in silt availability and a tendency towards landscape stability. Reported dust storm frequencies during the past 50 years over-estimate the longer-term Holocene dust flux due to the effects of human activities. Much modern dust owes its origin to erosion of cultivated soils in semi-arid areas and is finer than typical loess.

Kenneth Pye

Papers

GRADISTAT: a grain size distribution and statistics package for the analysis of unconsolidated sediments

Aeolian dust and dust deposits

Aeolian sand and sand dunes

The nature, origin and accumulation of loess

Dust transport and the question of desert loess formation