The influence of sediment supply on the channel morphology of upland streams: Howgill Fells,Northwest England

Previous work on stream channels in upland areas of Britain has demonstrated a close control over channel morphology and stability by the rate of coarse sediment supply from the hillslopes of the catchment. Streams fed by large amounts of coarse sediment develop unstable, wide, often braided channels, whereas those with limited coarse sediment supply develop stable, much narrower, often meandering channels. The sediment supply from hillslopes is controlled by thresholds of hillslope stability, storm event frequency, and the coupling between the hillslopes and the channel. Climatically-induced changes in any of these three factors may have implications for channel morphology and stability. This paper examines these implications in British upland fluvial systems, with particular reference to the Howgill Fells, Cumbria, in the contexts of the adjustment of stream channels to sediment supply from erosional gully systems, and their response to and recovery from major flood events.     

Novel prebiotic model systems: interactions of nucleosides and nucleotides with aqueous micellar sodium dodecanoate

The partition coefficients, K-values, of adenosine, guanosine, cytidine, uridine, 5¹-adenylic acid (AMP), 5¹-guanylic acid (GMP), 5¹-cytidylic acid (CMP), and 5¹-uridylic acid (UMP) between water and aqueous sodium dodecanoate has been determined by gel filtration on Sephadex G-25. Below the critical micelle concentration of the surfactant, K-values for all nucleotides and nucleosides are similar. Differential uptake of the four nucleotides and nucleosides is observed, however, by micellar sodium dodecanoate. K-values for adenosine, AMP; guanosine, GMP; cytidine, CMP; and uridine, UMP are 6.16·10³, 9.52·10³; 12.0·10³, 14.6·10³; 19.6·10³, 19.6·10³, 34.2·10³ and 40.3·10³. Similar K-values for corresponding pairs of nucleotides and nucleosides imply that the predominant interaction is between the pyrimidine or purine rings of the substrates and the charged Stern layer of the surfactant. Prebiotic significance of these results is discussed.