Showing papers by "Andrew J. Watson published in 1983"

Biological homeostasis of the global environment: the parable of Daisyworld

Abstract: The biota have effected profound changes on the environment of the surface of the earth. At thesame time, that environment has imposed constraints on the biota, so that life and theenvironment may be considered as two parts of a coupled system. Unfortunately, the system istoo complex and too little known for us to model it adequately. To investigate the propertieswhich this close-coupling might confer on the system, we chose to develop a model of animaginary planet having a very simple biosphere. It consisted of just two species of daisy ofdifferent colours and was first described by Lovelock (1982). The growth rate of the daisiesdepends on only one environmental variable, temperature, which the daisies in turn modifybecause they absorb different amounts of radiation. Regardless of the details of the interaction,the effect of the daisies is to stabilize the temperature. The result arises because of the peakedshape of the growth-temperature curve and is independent of the mechanics by which the biotaare assumed to modify the temperature. We sketch out the elements of a biological feedbacksystem which might help regulate the temperature of the earth. DOI: 10.1111/j.1600-0889.1983.tb00031.x

The Influence of Biomineralisation on the Composition of Seawater

Abstract: Elements whose concentration profiles in the deep ocean are characterised by surface depletion and deep water enrichment are incorporated to a significant extent in biologically produced particles. A large proportion of this particulate material results from biomineralisation reactions in the surface layers of the ocean. Five predominant mineral phases have been identified (calcite, aragonite, celestite, barite and opaline silica). These minerals are progressively dissolved from the settling particulate matter and consequently influence the vertical distribution not only of their major constituent elements (Ca, Ba, Sr, C, Si) but also of a range of trace elements (Ge, Se, Zn, Sc, Cr, Be, Cu, Ni). The extent to which the biomineralisation process contributes to the final removal of these trace elements from the ocean is uncertain although the settling mineral fragments might provide sites for the precipitation of insoluble hydrous metal oxides which are known to scavenge a wide range of trace elements from sea water.

Evaluation of a deltamethrin formulation as a back-line treatment of sheep for the control of the sheep body louse (Damalinia ovis)

Abstract: A formulation containing 1% deltamethrin was tested for efficacy against the sheep body louse. It was applied as a back-line treatment at a rate of 1 m1/5 kg bodyweight (2 mg/kg) to sheep either immediately after shearing or 3 weeks later. The formulation killed all observable lice within a day when applied off-shears to sheep which were subsequently confined overnight. When sheep were treated 3 weeks after shearing, and not subsequently confined, all lice were killed within 2–7 days. About 10 weeks protection from reinfestation was provided by off-shears treatment, and about 15 weeks by treatment 3 weeks after shearing. Breakdown in protection occurred when deltamethrin levels in the wool fell to about 1 μg/g greasy wool. Although the results suggest high efficacy, residue data indicate that the spread of insecticide was much less even than with plunge dipping in deltamethrin. A method for determining deltamethrin levels in wool is recorded.