Browsing by Author "Smith, Valdon R."

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    Field soil respiration rate on a Sub-Antarctic island : its relation to site characteristics and response to added C, N and P
    (Scientific Research Publishing Inc, 2012-06) Lubbe, Andrea; Smith, Valdon R.
    Botanical, soil chemistry and soil microbiology variables were tested as predictors of in situ soil respiration rate in the various terrestrial habitats on sub-Antarctic Marion Island (47oS, 38oE). Inorganic P and total N concentration were the best predictors amongst the chemistry variables and bacteria plate count the best of the microbiology variables. However, while these chemistry and microbiology variables could accurately predict soil respiration rate for particular habitats, they proved inadequate predictors across the whole range of habitats. The best suite of predictors comprised only botanical variables (relative covers of five plant guilds) and accounted for 94% of the total across-habitat variation in soil respiration rate. Mean field soil respiration rates (2.1 - 15.5 mmol CO2 m-2 h-1) for habitats not influenced by seabirds or seals are similar to rates in comparable Northern Hemisphere tundra habitats. Seabird and seal manuring enhances soil respiration rates to values (up to 27.6 mmol CO2 m-2 h-1) higher than found at any tundra site. Glucose, N, P or N plus P were added to three habitats with contrasting soil types; a fellfield with mineral, nutrient-poor soil, a mire with organic, nutrient-poor soil and a shore-zone herbfield heavily manured by penguins and with organic, nutrient-rich soil. Glucose addition stimulated soil respiration in the fellfield and mire (especially the former) but not in the coastal herbfield soil. N and P, alone or together, did not stimulate respiration at any of the habitats, but adding glucose to fellfield soils that had previously been fortified with P or NP caused a similar increase in respiration rate, which was greater than the increase when adding glucose to soils fortified only with N. This suggests that fellfield soil respiration is limited by P rather than N, and that there is no synergism between the two nutrients. For the mire and coastal herbfield, adding glucose to soils previously fortified with N, P or NP did not enhance rates more than adding glucose to soils that had received no nutrient pre-treatment.
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    Nutrient dynamics in the vicinity of the Prince Edward Islands
    (AFRICAN SUN MeDIA, 2008) Smith, Valdon R.; Froneman, P. William
    Nutrient concentrations in the open waters of the Polar Frontal Zone (PFZ) are highly variable, reflecting the region’s complex oceanographic regime. Surface concentrations of nitrate, silicate and phosphate range from 9.5 to 97.5, from 0.2 to 16.5 and from < 0.1 to 16.6 mmol m-3, respectively (Allanson et al. 1985; Duncombe Rae 1989; Ismail 1990; Balarin 2000). Changes in nutrient concentrations coincide with the intrusion of Antarctic surface water from the south and sub-Antarctic surface water from the north (Ansorge et al. 1999; Froneman et al. 1999). Mesoscale features such as far field eddies or the eddies generated by the interaction between the Antarctic Circumpolar Current (ACC) and the South-West Indian Ridge further contribute to the heterogeneity in nutrient concentrations within the surface waters of the PFZ (Ansorge & Lutjeharms 2002, 2003; Ansorge et al. 2004).
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    South African research in the Southern Ocean : new opportunities but serious challenges
    (Academy of Science of South Africa, 2013) Treasure, Anne M.; Moloney, Coleen L.; Bester, Marthan N.; McQuaid, Christopher D.; Findlay, Ken P.; Best, Peter B.; Cowan, Don A.; De Bruyn, P. J. Nico; Dorrington, Rosemary A.; Fagereng, Ake; Froneman, P. William; Grantham, Geoff H.; Hunt, Brian P. V.; Meiklejohn, Ian; Pakhomov, Evgeny A.; Roychoudhury, Alakendra N.; Ryan, Peter G.; Smith, Valdon R.; Chown, Steven L.; Ansorge, Isabelle J.
    South Africa has a long track record in Southern Ocean and Antarctic research and has recently invested considerable funds in acquiring new infrastructure for ongoing support of this research. This infrastructure includes a new base at Marion Island and a purpose-built ice capable research vessel, which greatly expand research opportunities. Despite this investment, South Africa’s standing as a participant in this critical field is threatened by confusion, lack of funding, lack of consultation and lack of transparency. The research endeavour is presently bedevilled by political manoeuvring among groups with divergent interests that too often have little to do with science, while past and present contributors of research are excluded from discussions that aim to formulate research strategy. This state of affairs is detrimental to the country’s aims of developing a leadership role in climate change and Antarctic research and squanders both financial and human capital.
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    Spatial variation in soil chemistry on a Sub-Antarctic island
    (Scientific Research Publishing Inc, 2012-03) Conradie, Everhard Christiaan; Smith, Valdon R.
    On both west and east sides of sub-Antarctic Marion Island (47oS, 38oE), total Na and exchangeable Na, Mg and K concentrations in the soil decline with increasing distance inland and altitude, related to a decrease in the intensity of seaspray deposition. On the east side, the coastal plain is wide and slopes gently up to the mountainous interior and total C, total N and soil moisture content all decrease significantly, whereas bulk density increases significantly, as one moves away from the sea, reflecting a gradual change from organic, wet, low bulk density peats characteristic of low-land coastal regions to mineral, dry, high bulk density volcanic soils characteristic of inland areas. On the west side, the narrow coastal plain is bounded by an escarpment that rises up very steeply to the highland interior. There, sampling was largely restricted to the coastal plain (soils are rare on the escarpment and interior) and did not cover the same transition from organic to mineral soils as on the east side. Hence, total C, total N and bulk density did not change significantly with increasing distance inland on the west side. Most total Mg is in the mineral fraction of the soil, with a lesser contribution by organic, exchangeable and soil solution forms of Mg. On the east side the gradual transition from highly organic peats to very mineral soils results in an increase in total Mg going inland, but on the west, where there was not this change in soil minerality, total Mg decreased with increasing distance inland, reflecting the decreasing intensity of seaspray. Once the between-side differences in the influence of altitude and distance from the sea are accounted for, there are significant differences in soil chemical composition between the two sides of the island. Overall, west side soils are more influenced by both seaspray and the parent volcanic basalts than are east side soils.