GEOMORPHOLOGY OF STEEPLAND HEADWATERS: THE TRANSITION FROM HILLSLOPES TO CHANNELS1

Headwater streams comprise 60 to 80 percent of the cumulative length of river networks. In hilly to mountainous terrain, they reflect a mix of hillslope and channel processes because of their close proximity to sediment source areas. Their morphology is an assemblage of residual soils, landslide deposits, wood, boulders, thin patches of poorly sorted alluvium, and stretches of bedrock. Longitudinal profiles of these channels are strongly influenced by steps created by sediment deposits, large wood, and boulders. Due to the combination of small drainage area, stepped shallow gradient, large roughness elements, and cohesive sediments, headwater streams typically transport little sediment or coarse wood debris by fluvial processes. Consequently, headwaters act as sediment reservoirs for periods spanning decades to centuries. The accumulated sediment and wood may be episodically evacuated by debris flows, debris floods, or gully erosion and transported to larger channels. In mountain environments, these processes deliver significant amounts of materials that form riverine habitats in larger channels. In managed steepland forests, accelerated rates of landslides and debris flows resulting from the harvest of headwater forests have the potential to seriously impact the morphology of headwater streams and downstream resources.     

Accuracy assessment of land surface temperature retrievals from Landsat 7 ETM + in the Dry Valleys of Antarctica using iButton temperature loggers and weather station data

The McMurdo Dry Valleys of Antarctica are the largest snow/ice-free regions on this vast continent, comprising 1 % of the land mass. Due to harsh environmental conditions, the valleys are bereft of any vegetation. Land surface temperature is a key determinate of microclimate and a driver for sensible and latent heat fluxes of the surface. The Dry Valleys have been the focus of ecological studies as they arguably provide the simplest trophic structure suitable for modelling. In this paper, we employ a validation method for land surface temperatures obtained from Landsat 7 ETM + imagery and compared with in situ land surface temperature data collected from four transects totalling 45 iButtons. A single meteorological station was used to obtain a better understanding of daily and seasonal cycles in land surface temperatures. Results show a good agreement between the iButton and the Landsat 7 ETM + product for clear sky cases. We conclude that Landsat 7 ETM + derived land surface temperatures can be used at broad spatial scales for ecological and meteorological research.     

SPATIAL AND TEMPORAL DYNAMICS OF WOOD IN HEADWATER STREAMS OF THE PACIFIC NORTHWEST1

This paper synthesizes information on the spatial and temporal dynamics of wood in small streams in the Pacific Northwest region of North America. The literature on this topic is somewhat confused due to a lack of an accepted definition of what constitutes “small” streams and what is the relative size of woody debris contained within the channel. This paper presents a matrix that defines woody debris relative to channel size and then discusses the components of a wood budget. Headwater streams are in close proximity to wood sources and, in steeplands, are often tightly constrained by steep hillslopes. Special consideration is given to ecosystem characteristics and to management practices that affect the wood dynamics in this context. Knowledge gaps and uncertainties that can be used to guide future research are identified. Very little is currently known about the role of mass wasting in wood recruitment and storage relative to other processes, such as bank erosion and mortality, in larger streams. Further, very little work has addressed the relative importance of different wood depletion processes, especially those associated with wood transport. The effect of other ecosystem variables on wood dynamics locally across a watershed (from valley bottom to mountaintop) and regionally across the landscape (from maritime to continental climates) is not addressed. Finally, the scientific community has only begun to deal with the effects of management practices on wood quantity, structure, and movement in small streams.     

Cleaning of water contaminated by heavy metals using beetroot fibers as biofilter

We report for the first time the use of beetroot fibers to eliminate heavy metals from polluted water. This biomass is used to remove lead, copper and zinc ions. The kinetics and beetroot fibers fixation capacities of lead, zinc and copper according to various physico‐chemical parameters such as pH, and the concentration of metal solutions were studied. The experiments were carried out in a laboratory column with fixed bed. For kinetic studies, samples of metal solutions were taken at regular intervals and measured by atomic absorption spectrometry. pH at 6.6 shows a maximum retention of the above cited metals by beetroot fibers (98%, 92%, 90% respectively). Quantity of cations retained by this biomass in simple and mixture solution is respectively estimated to be 23.6, 14.02 and 14.64 mg/g. Results indicate the usefulness of this biomass in the remediation of water contaminated by heavy metals by a rapid, practical and efficient method.     

Characterization and concentrations of polycyclic aromatic hydrocarbons in emissions from different heating systems in Damascus,Syria

Traffic has long been recognized as the major contributor to polycyclic aromatic hydrocarbon (PAH) emissions to the urban atmosphere. Stationary combustion sources, including residential space heating systems, are also a major contributor to PAH emissions. The aim of this study was to determine the profile and concentration of PAHs in stack flue gas emissions from different kinds of space heaters in order to increase the understanding of the scale of the PAH pollution problem caused by this source. This study set out to first assess the characteristics of PAHs and their corresponding benzo[a]pyrene equivalent emissions from a few types of domestic heaters and central heating systems to the urban atmosphere. The study, enabled for the first time, the characterization of PAHs in stationary combustion sources in the city of Damascus, Syria. Nine different types of heating systems were selected with respect to age, design, and type of fuel burned. The concentrations of 15 individual PAH compounds in the stack flue gas were determined in the extracts of the collected samples using high-performance liquid chromatography system (HPLC) equipped with ultraviolet–visible and fluorescence detectors. In general, older domestic wood stoves caused considerably higher PAH emissions than modern domestic heaters burning diesel oil. The average concentration of ΣPAH (sum of 15 compounds) in emissions from all types of studied heating systems ranged between 43?±?0.4 and 316?±?1.4 μg/m³. Values of total benzo[a]pyrene equivalent ranged between 0.61 and 15.41 μg/m³.     

SEDIMENT TRANSPORT AND CHANNEL MORPHOLOGY OF SMALL,FORESTED STREAMS1

This paper reviews sediment transport and channel morphology in small, forested streams in the Pacific Northwest region of North America to assess current knowledge of channel stability and morphology relevant to riparian management practices around small streams. Small channels are defined as ones in which morphology and hydraulics may be significantly influenced by individual clasts or wood materials in the channel. Such channels are headwater channels in close proximity to sediment sources, so they reflect a mix of hillslope and channel processes. Sediment inputs are derived directly from adjacent hillslopes and from the channel banks. Morphologically significant sediments move mainly as bed load, mainly at low intensity, and there is no standard method for measurement. The larger clastic and woody elements in the channel form persistent structures that trap significant volumes of sediment, reducing sediment transport in the short term and substantially increasing channel stability. The presence of such structures makes modeling of sediment flux in these channels — a potential substitute for measurement — difficult. Channel morphology is discussed, with some emphasis on wood related features. The problem of classifying small channels is reviewed, and it is recognized that useful classifications are purpose oriented. Reach scale and channel unit scale morphologies are categorized. A “disturbance cascade” is introduced to focus attention on sediment transfers through the slope channel system and to identify management practices that affect sediment dynamics and consequent channel morphology. Gaps in knowledge, errors, and uncertainties have been identified for future research.     

SUSPENDED SEDIMENT DYNAMICS IN SMALL FOREST STREAMS OF THE PACIFIC NORTHWEST1

This paper reviews suspended sediment sources and transport in small forest streams in the Pacific Northwest region of North America, particularly in relation to riparian management. Mass movements, reading and yarding practices, and burning can increase the supply of suspended sediment. Sediment yields recovered to pre‐harvest levels within one to six years in several paired catchment studies. However, delayed mass movements related to roads and harvesting may produce elevated suspended sediment yield one or more decades after logging. There is mixed evidence for the role of streamside tree throw in riparian buffers in supplying sediment to streams. Harvesting within the riparian zone may not increase suspended sediment yield if near stream soils are not disturbed. Key knowledge gaps relate to the relative roles of increased transport capacity versus sediment supply, the dynamics of fine sediment penetration into bed sediments, and the effects of forest harvesting on suspended sediment at different scales. Future research should involve nested catchments to examine suspended sediment response to forest practices at multiple spatial scales, in combination with process‐based field studies.