Suction-controlled triaxial testing: Laboratory procedures in relation to resistance envelope methods

In certain tropical slopes it appears possible that soil suction may play a significant role in maintaining stability. This communication outlines a laboratory suction-controlled triaxial test that can be undertaken to validate the threshold suction predicted by resistance envelope methods. It is shown that for two sites examined in St. Lucia, West Indies, the results from such a test confirm results obtained by use of resistance envelopes.     

The contribution of throughflow to storm runoff: An evaluation of a chemical mixing model

The contribution of throughflow to storm runoff is examined using a chemical mixing model. The results predict that throughflow is an important component of storm runoff particularly during the period of stream recession. Supporting hydrological data suggests that a major throughflow input occurs coincident with the stream discharge peak. The two sets of results therefore conflict in the predicted timing of the throughflow response.     

Concentration,vertical flux,and remineralization of particulate uranium in seawater

Concentrations and fluxes of particulate U were measured throughout the water column at several locations in the Atlantic and Pacific Oceans with in situ filtration systems and sediment traps. The results indicate that dissolved U is fixed to particles in surface seawater. Organic matter appears to be the carrier phase. Formation of particulate authigenic U below the surface waters could not be detected. Authigenic U is remineralized within the bathypelagic layers at the open ocean sites studied. In the Panama Basin, an upwelling area with high biological productivity, remineralization of authigenic U in the deep water column was not observed. The rate of remineralization of authigenic U in the deep sea is insufficient to produce a measurable concentration gradient between surface and deep waters within the mixing time of the oceans. Formation of authigenic U in the water column in areas such as the Panama Basin is not a significant sink for U on an ocean wide basis.     

Verteilung und Herkunft der Sedimente in Lotkernen von der Island-Färöer-Schwelle (Nordatlantik)

The components from nine sediment cores in the region of the Iceland-Faeroe-Ridge have been analysed. In this region, characterized by very complicated hydrographical and glacial conditions, only the Arctic slope of the ridge shows comparatively clear conditions which make it possible to correlate different parts of the cores. The sedimentation on the Atlantic slope, on the contrary, seems to be less clearly differentiated due to reworking processes. The components of the sand- and pebble-fraction can be divided into an autochthonous group of basalt- and shale-pebbles, derived from the ridge itself, and an allochthonous group, transported over large distances, with quartz, crystalline rocks, sandstone, flint, and chalk as main components. Whereas the autochthonous group shows parts of the cores which can be correlated with each other based on different sedimentation rates, the distribution of allochthonous group varies so strongly that it is impossible to recognize any regularity in sedimentation. Only the flint and the chalk occur in well-defined levels and thus make possible to correlate the cores. The Iceland-Faeroe-Ridge was supplied with allochthonous components from a broad source area which was, however, homogeneous with respect to both its horizontal distribution and the time-span representend in the sediment cores. Maxima of sedimentation were subsequently blurred by reworking processes on both slopes of the ridge. During the periods of glaciation the hydrographic conditions in the North Atlantic area were completely different from those of to-day.     

Autoxidation of N(III), S(IV), and other Species in Frozen Solution – A Possible Pathway for Enhanced Chemical Transformation in Freezing Systems

The chemistry of glycolaldehyde (hydroxyacetaldehyde) relevant to the troposphere has been investigated using UV absorption spectrometry and FTIR absorption spectrometry in an environmental chamber. Quantitative UV absorption spectra have been obtained for the first time. The UV spectrum peaks at 277 nm with a maximum cross section of (5.5± 0.7)×10^–20 cm² molecule^–1. Studies of the ultraviolet photolysis of glycolaldehyde ( = 285 ± 25 nm) indicated that the overall quantum yield is > 0.5 in one bar of air, with the major products being CH₂OH and HCO radicals. Rate coefficients for the reactions of Cl atoms and OH radicals with glycolaldehyde have been determined to be (7.6± 1.5)×10^–11 and (1.1± 0.3)×10^–11 cm³ molecule^–1 s^–1, respectively, in good agreement with the only previous study. The lifetime of glycolaldehyde in the atmosphere is about 1.0 day for reaction with OH, and > 2.5 days for photolysis, although both wet and dry deposition should also be considered in future modeling studies.     

Paleolimnological assessment of human impacts on an urban South African lake

North End Lake is a polluted and eutrophic freshwater system located in Port Elizabeth, South Africa. Since the lake is expected to be used for recreational/tourist purposes by 2010, a rehabilitation program will have to be designed. For this reason, we retrieved a sediment core from the central region of the lake to decipher the effect of historical human impacts on the water body. Pre-disturbance paleolimnological inferences indicate that the lake was likely mesotrophic. After ∼1831, when sheep farming activities were undertaken in the catchment, increases in trophic state and changes in sediment composition were observed. After ∼1937, increases in trace metal levels, organic matter, spheroidal carbonaceous particles (SCP) and changes in sediment composition were recorded. The system became eutrophic as indicated by the dominance of the diatom Actinocyclus normanii, a cosmopolitan species often observed in systems where water quality has been dramatically degraded. The conditions worsened after 1986 because of the construction of a storm-water retention system, which intentionally channeled storm-water runoff into the lake. Because of this, extremely high values of fecal coliforms (i.e. 2 × 10⁶ every 100 ml) have been measured in the water column. The paleolimnological information identified the sharp increase in organic content in the uppermost section of the core, and this could be correlated to the operation of the storm-water retention system. Therefore, as an immediate management measure, we suggest that the storm-water retention system should either no longer be utilized, or the storm-water runoff should be treated before disposal into the lake. In addition, an effective sewage system has to be constructed.