Effects of forest land management on erosion and revegetation after the eruption of Mount St. Helens

The 1980 eruption of Mount St. Helens covered soils with a tephra blanket and killed the forest tree cover in a 550 km² area. After the eruption, rates of sheetwash and rill erosion, and plant cover were measured on tephra-covered hillslopes which had been subject to three land-management practices: grass seeding; scarification, and salvage logging. On rapidly-eroding hillslopes subject to grass seeding, limited plant covers were established only after erosion had declined sharply. Logging of trees downed by the eruption and scarification of previously logged surfaces slowed erosion, although the effect was small because erosion rates had already slowed substantially by the time these two practices were implemented. The factors controlling erosion, revegetation, and their relative timing at Mount St. Helens are similar to those following explosive volcanic eruptions elsewhere, suggesting that grass seeding is not likely to be effective at slowing erosion following most tephra eruptions, and that early mechanical disturbance could be an effective erosion-control measure. The results also indicate that even without deliberate conservation measures, processes which mechanically disturb a surface layer of low hydraulic conductivity (such as frost-action or trampling) can radically reduce runoff and erosion before revegetation has an important effect.     

Particle dislodgement from a flat sand bed by wind

The rate, with respect to area and time, at which grains are dislodged from a sand bed for given wind conditions is an important factor in determining the grain transport rate and the intensity of grain activity in each of the transport modes. The literature of the subject contains little direct information about particle dislodgement. The paper describes a series of experiments in which dyed sand grains, spread on the surface of quartz dune sand in a wind-tunnel, were photographed at five second intervals while the sand was exposed to wind. The data on rate of loss of coloured grains was used, for two of three chosen size fractions, to deduce the dislodgement rate for each size fraction. The variation of this dislodgement rate with shear velocity is shown graphically for values of u_* between 24 cm s^?1 and 50 cm s^?1. Because of the artificial method of distribution of the coloured sand grains, the results should be applied with caution to natural conditions. The interpretation of the observations of dyed grain loss involved the numerical simulation of the process which comprises removal of coloured grains, slightly offset by replenishment as upwind coloured grains settle briefly in the observed zone. An estimation of grain excursion length has to be incorporated in the simulation. This estimation was made by trial, but general corroboration was found from earlier work. Comparisons are made between dislodgement rates obtained thus and rates estimated by Anderson (1986) and by Jensen and Sorensen (1986). Reasonable agreement with the latter is found in the u_* range 30 cm s^?1.     

Vertical Distribution and Partitioning of Chromium in a Glaciof luvial Aquifer

The vertical distribution and partitioning (between the solid and aqueous phase) of chromium in a glaciofluvial aquifer in northeastern Connecticut were assessed. Most of the chromium (99 percent of its mass) is bound to the soil. Retardation is primarily the result of binding to organic matter and adsorption to iron oxide coatings. However, other attenuation mechanisms also appear to be significant. If the degree of chromium binding observed here is representative of other chromium contaminated sites, pump-and-treat remediation will not remove the vast amount of chromium from the subsurface. However, most of the chromium may be immobile, and removal may not be required following the initial pumping to remove the mobile fraction. Further knowledge of the mechanisms that bind chromium to the soil, their reversibility, and their kinetics is essential to developing effective remediation strategies.     

THE PREPARATION OF THREE BASE-METAL REFERENCE MATERIALS: LEAD CONCENTRATE, IGS-42, ZINC CONCENTRATE, IGS-43 AND COPPER MATTE, IGS-44

Three base-metal concentrates, each weighing 25 kg, were ground to -175 mesh (90 μm) and homogenised. They were then sub-sampled into foil-lined envelopes and sealed under argon before being issued to 27 participating laboratories for analysis. Over 4000 analytical results were returned and, after evaluation, a total of 37 elements within the three samples have been given recommended or more cautious probable values. The high standard of precision attained has enabled clear-cut distinctions to be made between methods for the determination of some elements. The most important of these is between titrimetry and electrogravimetry in the determination of copper.     

Green algal ropes: A novel estuarine phenomenon in the gulf of Maine

During late summer and early autumn of both 1984 and 1985 we observed and photographed the development of a green algal bloom on intertidal mudflats in eastern Maine. The bloom culminated in the formation of thick (8–10 cm) mats and long (>50 m) erpentine rope-like structures. The algal mat was polytypic but composed primarily ofEnteromorpha intestinalis L. We describe the probable sequence of events which led to the formation of algal ropes. The processes involved appear to parallel the development of ball-like masses in other algae. Algal ropes developed after mat formation, as prevailing winds and tidal currents rolled individual and entwined strands across the mudflat. The great mass of algae eventually became embedded into the sediment surface producing anoxic conditions in the substrate up to several cm deep. The ecological significance and possible negative effects of this altered environment on a commercially important bivalve species are discussed.     

Archaean crustal evolution in southern West Greenland: A review based on observations in the Buksefjorden region

Thermal, metamorphic and tectonic processes associated with the two major crust-forming events expressed as voluminous generation of Amîtsoq and Nûk tonalitic-granitic gneisses, ca. 3750 Ma and ca. 2800 Ma respectively, in southern West Greenland are reviewed briefly in the light of recent studies in the Buksefjorden region.     

The distribution and stable carbon isotopic composition of dissolved organic carbon in estuaries

The distributions of dissolved organic carbon (DOC) and the natural carbon isotope ratio of DOC (DO¹³C) in estuaries reflect the predominant sources and sinks of organic matter from both allochthonous and autochthonous origins. The traditional view is that DOC in land-margin ecosystems reflects mainly the mixing of land-derived and oceanic DOC. However, this view is not consistent with the bulk of our data from a survey of DOC and DO¹³C distributions in estuaries on the East and Gulf coasts of the USA. While it is accurate that the DOC in estuaries includes material derived from land and from the ocean, the distributions of DOC and DO¹³C in several estuaries reflect additional DOC inputs from estuarine phytoplankton and tidal marshes. Even when DOC concentrations were distributed conservatively, the isotopic composition of the DOC revealed the existence of a dynamic cycle of DOC input and removal in some systems.     

Mineralization of organic material and bacterial dynamics in Mississippi River plume water

Net remineralization rates of organic matter and bacterial growth rates were observed in dark-bottle incubation experiments conducted in July–August and February with water samples collected from sites in the Mississippi River plume of the Gulf of Mexico. Our objectives were to measure site-specific degradation rates of labile dissolved and particulate organic matter, quantify the potential importance of bacteria in these processes, and examine the kinetics of degradation over time. Unfiltered samples, and samples treated to remove (or dilute out) particles larger than bacteria, were enclosed in 9-1 bottles and incubated in the dark for 3–5 d. Respiration rates and inorganic compound accumulation rates were higher in summer than in winter and were highest in unfiltered surface samples at sites of intermediate salinities where phytoplankton were most abundant. The ratio of ammonium accumulation to oxygen removal in summer experiments suggested that the mineralized organic material resembled “Redfield” stoichiometry. Chemical fluxes were greater in bottles containing large (>1–3 μm) particles than in the bottles with these particles removed, but bacterial activities were generally similar in both treatments. These results suggest that particle consumers were an important component of total organic matter degradation. However, these experiments may have underestimated natural bacterial degradation rates because the absence of light could affect the production of labile organic substrates by phytoplankton. In agreement, with this hypothesis, bacterial growth rates tended to decrease over time in summer in surface plume waters where phytoplankton were abundant. In conjunction with other data, our results indicate that heterotrophic processes in the water column are spatially and temporally dependent on phytoplankton production.