Environmental Geochemistry and Health, 1991, Vol. 13(2), page 93

Trace element geochemistry of soils and plants in Kenyan conservation areas and implications for wildlife nutrition John Maskall and lain Thornton Environmental Geochemistry Research Centre for Environmental Technology, Royal School of Mines, Imperial College, London SW7 2BP, UK Abstract Trace element concentrations in soils, plants and animals in National Parks and Wildlife Reserves in Kenya are assessed using geochemical mapping techniques. Soil trace element concentrations are shown to be related to soil parent material and possibly to pedological and hydrological factors. At Lake Nakuru National Park, plant trace element concentrations vary with plant species and the geochemical conditions that influence uptake are discussed. Impala at Lake Nakuru National Park and black rhino at Solio Wildlife Reserve are shown to have a lower blood copper status than animals from other areas. The trace element status of wildlife is assessed also with respect to critical concentrations used for domestic ruminants. It is suggested that at Lake Nakuru National Park, the low soil copper content and high molybdenum content of some plants contributes to the low copper status of impala and may also influence the nutrition of other species.

Introduction

In Kenya, the conservation of wildlife, in particular the black rhinoceros, has become increasingly reliant on the successful operation of small, well protected areas termed sanctuaries. This paper examines trace element concentrations in soils, plants and animals in several National Parks and Wildlife Reserves, some of which have been designated as rhino sanctuaries. The study has four aims: (1) To relate soil trace element concentrations to the local geology and soil type. (2) To examine trace element uptake from soils to plants at Lake Nakuru National Park. (3) To assess the relationship between the trace element status of soils and plants and the trace element status of wildlife. (4) To assess the ability of wildlife sanctuaries to supply trace elements to animals. The relationship between the trace element status of a soil and that of its parent material is strongest for young soils in temperate regions where there has not been marked pedological weathering (Berrow and Mitchell, 1980). Aubert and Pinta (1977) note that the trace element concentrations in tropical soils may depend on their degree of evolution particularly with respect to the intensity of leaching processes. In Kenya, Nyandat and Ochieng (1976) noted that soils underlain by volcanic rocks contained less copper than soils underlain by metamorphic rocks whilst copper concentrations varied greatly in soils underlain by sedimentary rocks. Factors which influence trace element uptake by plants include soil pH, soil moisture and plant genus,

species and variety amongst others (Reith, 1965; Fleming, 1973). In Kenya, Hnkerton (1967) records that neither soil pH nor soil organic matter had any influence on the incidence of copper deficiency in wheat in the Rift Valley. However, Nyandat and Ochieng (1976) found a small but significant correlation between copper uptake in wheat and pH for several Kenyan soils. Increased soil wetness with season has been found to increase the copper content of pastures in the Kenya highlands (Howard et al., 1962) and decrease the selenium concentration in pastures and browse plants in other areas (Mbwiria et al., 1984). Legume and browse species have been shown to contain higher concentrations of wace elements than grasses in tropical regions (Tartour, 1966; Fleming, 1973; Reid et al., 1979). Trace element concentrations of tropical pastures can fall as the plant matures (Gomide et al., 1969) and during periods of rapid growth (Fleming, 1973). The trace element status of wildlife and its relation to that of soils and plants has received little attention. An initial interpretation of soil and plant trace element concentrations at Lake Nakuru National Park has been reported by the authors (Maskall and Thornton, 1989). Associations between trace element concentrations in soils and plants and trace element deficiencies in pastures, crops and livestock have been identified in Kenya. Rift Valley soils developed on ash and pumice have been found to be low in copper (Pinkerton, 1967), EDTA extractable copper (Nyandat and Ochieng, 1976) and acetic acid extractable cobalt (Chamberlain, 1959). These soils have been associated with copper deficiency in wheat (Pinkerton, 1967; Nyandat and Ochieng, 1976), pastures (Howard, 1969) and cattle (Howard, 1970). Berg et al. (1973) consider Rift Valley soils to be

94

Trace element geochemistry

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capable of producing selenium deficiency in animals. "Nakuru-itis", a wasting disease of cattle, identified as cobalt deficiency (Hudson, 1944) was associated with two areas of soil developed on volcanic ashes in the Rift Valley. A disease resembling swayback was reported in goats, sheep and Grant's gazelle in the Kenyan Rift Valley by Hedger et al. (1964). A copper deficiency conditioned by high levels of molydenum and sulphate in plants was suggested as the cause. Copper and cobalt deficiencies have also been reported on Rift Valley soils in Tanzania (Naik, 1965) and Ethiopia (Roeder, 1980). Critical concentrations of trace elements in plants and animal tissues have been established from studies of deficiencies in domestic ruminants. Russell and Duncan (1956) indicated that cases of uncomplicated copper

deficiency in cattle do not normally occur when the level of copper in pastures was above 5 lxg g-1. This concentration was adopted by Howard et al. (1962) and again by Howard (1969) as the value used for assessment of pastures in Kenya. Cunha (1973) found that copper deficiency in cattle usually occurred when the amount of molybdenum in forage exceeded 3 Ixg g-I and the copper level was below 5 I-tg g-1. In England and Wales, molybdenum induced copper deficiency is often found when pastures contain 2 Ixg g-1 molybdenum or more (Thornton, 1977). Naik (1965) identified a level of 0.06 txg g-t cobalt in pasture as necessary to avoid deficiencies in cattle in Tanzania although values ranging from 0.07 txg g-1 to 2 ~tg g-I have been used in other parts of the world (Young, 1979).

J. Maskall and I. Thornton

95

Materials and Methods Geochemical reconnaissance surveys were carried out at three National Parks and four Wildlife Reserves between September 1986 and November 1988. Surface (0-15 cm) and subsurface (15-30 cm) soils were collected on a regular grid where possible. Each surface soil comprised a composite of nine subsamples taken from a 4 x 4 m square using a 2.5 cm diameter soil auger. Subsurface soils comprised three subsamples. Soil pits were excavated on the major soil types at each location to a depth of 2 m Lake Nakuru where possible. Prot-iles were examined for colour, texture and wetness and samples taken from each soil horizon. 'Total' concentrations of trace elements were determined by digesting the 40

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Figure 17 Amboseli National Park. Copper concentration in surface soil.

Figure 18 Amboseli National Park. Cobalt concentration in surface soil.

National Park and of black and white rhinoceros from Solio Wildlife Reserve are presented (Tables 3, 4 and 5). Vitamin B12 concentrations are significantly higher (p

Trace element geochemistry of soils and plants in Kenyan conservation areas and implications for wildlife nutrition.

Trace element concentrations in soils, plants and animals in National Parks and Wildlife Reserves in Kenya are assessed using geochemical mapping tech...
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