An assessment of the effects of climatic change on agriculture

This paper summarizes some of the results and conclusions of an international project funded by IIASA and UNEP on the effects of climatic variations on agriculture. An overall goal of the project was to improve our understanding both of first-order effects of climatic variations on agricultural productivity and of higher-order effects on regional and national economies. Two broad types of experiments are described: (i) impact experiments, which provide estimates of first-order and higher-order effects of climatic variations on farming systems, and which assume that no adjustments are put in place, and (ii) adjustment experiments, which evaluate a number of adjustments available at the farm or government level to offset or mitigate these effects.The results from case studies in cool temperate and cold regions in Saskatchewan (Canada), Iceland, Finland, northern European U.S.S.R. and Japan] are described here. Findings from a parallel set of IIASA/UNEP case studies in semiarid regions, which examine the effects of a different set of climatic scenarios, are reported elsewhere (Parry et al., 1988b).     

Magnetization of immobilized particle dispersions with two distinct particle sizes

The magnetic properties of specimens containing dispersed magnetic particles, at low concentrations, containing two distinct size ranges, have been measured. The results have been used to evaluate the effectiveness of several parameters which have been used to discriminate the type of particles in a dispersion. The location of the point representing the properties of a specimen on a graph of $\text{M}{}_{\mathrm{<mtext>RS</mtext>}}\text{M}{}_{\mathrm{<mtext>S</mtext>}}$ and $\text{H}{}_{\mathrm{<mtext>R</mtext>}}\text{H}{}_{\mathrm{<mtext>c</mtext>}}$ indicates a possible particle dispersion which would produce a model with equivalent magnetic properties. The behaviour of dispersions of titomagnetic is also considered and these produce ambiguities in the interpretation of the graph. The possibility of modelling a dispersion which has equivalent properties to specimens from a single lava is considered.     

The piezomagnetic effect in rocks: a comparison of measurements in high and low fields

There are some puzzling features of the stress-dependence of magnetic susceptibility in rocks, although the behaviour in high fields appears to be well understood. As a test for the factors that cause low-field behaviour to differ from current theories we have made both high- and low-field torquemeter measurements of the stress-induced magnetic anisotropies of a number of rocks. Ratios of low- and high-field torques differing from expectation by factors up to 4 or so have been found in some rocks, although others conform well to expectation. A comprehensive study of magnetic and microscopic properties was undertaken to seek the cause(s) of the discrepancies. Stress sensitivity of susceptibility becomes particularly high in titanomagnetite with composition parameter x ≈ 0.6, at which the intrinsic anisotropy vanishes, and some other high values appear to be related to the presence of sulphide. It is concluded that current theory is satisfactory if but only if the magnetic minerals in a rock are simple titanomagnetites with x ? 0.4.     

Progress in isotope paleohydrology using lake sediment cellulose

Recent advances in sample preparation techniques and mass spectrometry have fostered more routine oxygen isotope analysis of aquatic cellulose in lake sediment cores, a proxy for lake water oxygen isotope history. These methodological developments have significantly increased the feasibility of incorporating this approach into high-resolution, multi-site, and multi-proxy studies, which are frequently necessary to answer complex hydrological, hydroecological and hydroclimatic questions requiring a paleoenvironmental perspective. Direct translation of lake sediment aquatic cellulose oxygen isotope composition into lake water oxygen isotope composition offers appreciable opportunity for quantitative paleohydrological reconstructions, as evidenced by studies conducted over the past 15 years that span Holocene and pre-historical timescales.     

Geochemistry of hydrothermal alteration at the Roosevelt hot springs thermal area,Utah

Hot spring deposits in the Roosevelt thermal area consist of opaline sinter and sintercemented alluvium. Alluvium, plutonic rocks, and amphibolite-facies gneiss have been altered by acidsulfate water to alunite and opal at the surface, and alunite, kaolinite, montmorillonite, and muscovite to a depth of 70 m. Marcasite, pyrite, chlorite, and calcite occur below the water table at about 30 m.The thermal water is dilute (ionic strength 0.1–0.2) sodium-chloride brine. The spring water now contains 10 times as much Ca, 100 times as much Mg, and up to 2.5 times as much SO₄ as the deep water. Although the present day spring temperature is 25°C, the temperature was 85°C in 1950.A model for development of the observed alteration is supported by observation and irreversible mass transfer calculations. Hydrothermal fluid convectively rises along major fractures. Water cools by conduction and steam separation, and the pH rises due to carbon dioxide escape. At the surface, hydrogen and sulfate ions are produced by oxidation of H₂S. The low pH water percolates downward and reacts with feldspar in the rocks to produce alunite, kaolinite, montmorillonite, and muscovite as hydrogen ion is consumed.     

Titanomagnetites prepared at different oxidation conditions: Influence of magnetite-rich inclusions

Synthetic titanomagnetites prepared at 1300°C at different oxidation potentials, although giving only spinel-type X-ray reflections, were found to contain a small amount of included material with a Curie point above that for the bulk material. Specimens, comprising either dispersed sized grains, or polycrystalline spherical aggregates of grains, develop thermoremanent moments which are dependent upon the presence of the inclusions. The magnetization of the inclusions is revealed by thermal demagnetization experiments, and the experimental results are compared with the effects expected to arise from magnetic shielding by the matrix titanomagnetite.     

Earth albedo and the orbit of Lageos

The long-period perturbations in the orbit of Lageos satellite due to the earth's albedo have been found using a new analytical formalism. The earth is assumed to be a sphere whose surface diffusely reflects sunlight according to Lambert's law. Specular reflection is not considered. The formalism is based on spherical harmonics; it produces equations which hold regardless of whether the terminator is seen by the satellite or not. Specializing in the case of a realistic zonal albedo shows that Lageos' orbital semimajor axis changes periodically by only about a centimeter and the eccentricity by two parts in 10⁵. The longitude of the node increases secularly by about 6×10^–4 arc sec yr^–1. The effect considered here can explain neither the secular decay of 1.1 mm day^–1 in the semimajor axis nor the observed along-track variations in acceleration of order 2×10^–12 ms^–2.     

Use of Sonication for Enhanced Sampling of Attached Microbes from Groundwater Systems

The vast majority of microorganisms in aquifers live as biofilms on sediment surfaces, which presents significant challenges for sampling as only the suspended microbes will be sampled through normal pumping. The use of a down-well low frequency sonicator has been suggested as a method of detaching microbes from the biofilm and allowing rapid sampling of this community. We developed a portable, easy to use, low-frequency electric sonicator and evaluated its performance for a range of well depths (tested up to 42 m below ground level) and casing types. Three sonicators were characterized in laboratory experiments using a 1 m long tank filled with pea gravel. These included a commercially available pneumatic sonicator, a rotating flexible shaft sonicator, and the prototype electric sonicator. The electric sonicator detached between 56 and 74% of microbes grown on gravel-containing biobags at distances ranging between 2 and 50 cm from the sonicator. The field testing comprises of a total of 55 sampling events from 48 wells located in 4 regions throughout New Zealand. Pre- and post-sonication samples showed an average 33 times increase in bacterial counts. Microbial sequence data showed that the same classes are present in pre- and post-sonicated samples and only slight differences were seen in the proportions present. The sampling process was rapid and the significant increases in bacterial counts mean that microbial samples can be quickly obtained from wells, which permits more detailed analysis than previously possible.