Soil erosion in the Falkland Islands: an assessment

Observations and data concerning soil erosion on clay-rich, sand-rich and organic soil materials are reported for the Falkland Islands, South Atlantic, where soil erosion is both widespread and currently active, though rather uneven in its distribution. The most extensively eroded areas are located on coastal sand deposits and where sandy soils occur at inland sites. There is evidence that some erosion is natural and was initiated before the Islands were settled; other erosion is of more recent origin and can be associated with land management practices, principally grazing management, stocking rates, and the frequency and intensity of pasture burning. The impact of soil erosion on the agricultural economy of the Islands appears to be negligible and it is not perceived to be an important environmental issue. This lack of concern probably arises because the on-farm and off-farm costs of erosion have never been determined and there are no data relating to rates of erosion. It is suggested that a research programme be established aimed at monitoring erosion rates, assessing land use practices that initiate erosion, and assessing the costs of erosion. Furthermore, guidelines for soil conservation should be established. If pasture burning is to continue, a recommended code of practice should be drawn up. Given the importance of the sheep industry to the Falkland Islands, it is desirable that the grazing potential be maintained.     

Origin of the northern Atlantic's Heinrich events

As first noted by Heinrich, 1988, glacial age sediments in the eastern part of the northern Atlantic contain layers with unusually high ratios of ice-rafted lithic fragments to foraminifera shells. He estimated that these layers are spaced at intervals of roughly 10 000 years. In this paper we present detailed information documenting the existence of the upper five of these layers in ODP core 609 from 50° N and 24° W. Their ages are respectively 15 000 radiocarbon years, 20 000 radiocarbon years, 27 000 radiocarbon years, about 40 000 years, and about 50 000 years. We also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers. Although we are not of one mind regarding the origin of these layers, we lean toward an explanation that the Heinrich layers are debris released during the melting of massive influxes of icebergs into the northern Atlantic. These sudden inputs may be the result of surges along the eastern margin of the Laurentide ice sheet.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

The North American datum of 1983: Project methodology and execution

A new adjustment of the geodetic control networks in North America has been completed, resulting in a new continental datum—the North American Datum of 1983 (NAD 83). The establishment ofNAD 83 was the result of an international project involving the National Geodetic Survey of the United States, the Geodetic Survey of Canada, and the Danish Geodetic Institute (responsible for surveying in Greenland). The geodetic data in Mexico and Central America were collected by the Inter American Geodetic Survey and validated by the Defense Mapping Agency Hydrographic/Topographic Center. The fundamental task ofNAD 83 was a simultaneous least squares adjustment involving 266,436 stations in the United States, Canada, Mexico, and Central America. The networks in Greenland, Hawaii, and the Caribbean islands were connected to the datum through Doppler satellite and Very Long Baseline Interferometry (VLBI) observations. The computations were performed with respect to the ellipsoid of the Geodetic Reference System of 1980. The ellipsoid is positioned in such a way as to be geocentric, and its axes are oriented by the Bureau International de l'Heure Terrestrial System of 1984. The mathematical model for theNAD readjustment was the height-controlled three-dimensional system. The least squares adjustment involved 1,785,772 observations and 928,735 unknowns. The formation and solution of the normal equations were carried out according to the Helmert block method. [Authors' note:This article is a condensation of the final report of the NAD 83 project. The full report (Schwarz,1989) contains a more complete discussion of all the topics.]     

Fatty acids and sterols of particulate matter in a brackish and seasonally anoxic coastal salt pond

Particulate matter and interfacial sediment from a seasonally anoxic coastal salt pond were analyzed for fatty acids and sterols to examine variations in organic sources, and compositional changes across the oxic-anoxic interface in the water column and at the sediment-water interface. Fatty acid distributions in suspended particles varied seasonally and as a function of depth. Fatty acids of algal origin (e.g. 16:3, 16:4, 18:3, 18:4) were abundant in particles in oxic surface waters, but these labile components were depleted in particles from the anoxic zone which instead were enriched in bacterial fatty acids (e.g. 16:1Δ⁹, 18:1Δ¹¹, anteiso-C₁₅). Sterol distributionsvaried less than fatty acid distributions and particles throughout the water column reflected an upper water algal source with little in situ alteration. There was evidence for an in situ conversion of Δ⁵-stenols to 5(α)H-stanols in suspended particles in the anoxic zone. Sinking particles and the interfacial sediment were compositionally similar to each other, but different from suspended particles. These data reflect differences in particle source, transport and transformation processes occuring in the water column.     

A Holocene paleoenvironmental history of Lake Alexandria,South Australia

An investigation of Holocene sediments within Lake Alexandrina, a shallow coastal lake at the mouth of the Murray River, South Australia, is presented based on a multidisciplinary approach.¹⁴C and²¹⁰Pb radiometric dating methods are used to establish a geochronological framework for the last 7000 yr BP, and diatoms, sand-siltclay ratios, organic carbon, phosphorus and copper concentrations are used to infer paleoenvironmental changes.The diatom assemblages indicate a change from marine-brackish to oligosaline-freshwater conditions between 7000 and 6000 yr BP, with sea-level stabilisation and continuous barrier formation across the Murray mouth. Sand pulses after 2300 yr BP document sand spit formation in the lake and the commencement of extensive lacustrine sedimentation.In the past 100 years which include the advent of European settlement in the region, the short-term²¹⁰Pb-based mass accumulation rate of 0.063 g cm^–2 yr^–1 is greater than that of the longer-term mean¹⁴C-based rate (0.023 g cm^–2 yr^–1), and high concentrations of phosphorus and copper correspond to historical records of blue-green algal blooms.This is the fifth in a series of papers published in this issue on the paleolimnology of aric regions. These papers were presented at the Sixth International Paleolimnology Symposium held 19–21 April, 1993 at the Australian National University, Canberra, Australia. Dr A. R. Chivas served as guest editor for these papers.     

Gut contents of common mummichogs,Fundulus heteroclitus L., in a restored impounded marsh and in natural reference marshes

We examined the gut contents of mummichogs, Fundulus heteroclitus L., entering and leaving ditches in three marsh regions within the Barn Island Wildlife Management Area in Connecticut: a restored impounded valley marsh, a marsh below the impoundment dike (Headquarters Marsh), and an unimpounded valley marsh (Davis Marsh). On the Headquarters Marsh and at certain times on the other two marshes, fish entered the ditches on the flooding tide with relatively little food in their guts and left them on the following ebbing tide with considerably more food in their guts. Since the high tides did not flood the surface of the high marsh, it appears that the ditches are important foraging areas. Major components of the gut contents were detritus, algae, amphipods, tanaids, copepods, and insects. During the summer, fish in the restored impounded marsh consumed less food per unit body weight than did fish inhabiting the other marsh regions.     

Evidence suggesting anaerobic oxidation of the bisulfide ion in Chesapeake Bay

Upper Chesapeake Bay bottom waters are stratified in the summer. In the water column below the pycnocline, anoxic and sulfidic conditions exist. Hydrogen sulfide concentrations approach 60 μM or greater and elemental sulfur is also present. Water samples brought on board ship, exposed to light, and not treated with formaldehyde show rapid sulfide decomposition which is significantly faster than sulfide oxidation by molecular oxygen. The data presented show evidence for anaerobic, sulfide oxidation. The kinetics of the decomposition are consistent with possible biological mediation. Hydrogen, peroxide produced by microorganisms may be the chemical oxidant responsible for the oxidation. Alternately, solid metal oxides such as colloidal manganese oxide phases may be reponsible.