Savannas

Grasebene, /. grassy plain, prairie, savanna, grasen, v.i. graze cut grass. 

Tropical forests and savannas are the primary source of C emissions that originate from biomass burning (73, 75). However, temperate forests are also sources of atmospheric carbon. Harmon et al. (77) reported that conversion of primary temperate forests to younger, second-growth forests lead to increases in atmospheric CO2 levels, due to losses in long-term carbon storage within these forests. They ascertained that timber exploitation of 5 million hectares of primaiy forests in the Pacific Northwest of North America during the past century has resulted in the addition of 1,500 Tg of C to the atmosphere. 

Figure 5.1. A simple flow diagram of ratios in a modern savanna system (a), and (b)...

Bridge, B.J., Mott, J.J., Winter, W.H. Hartigan, R.J. (1983). Improvement in soil structure resulting from sown pastures on degraded areas in the dry savanna woodlands of northern Australia. Australian Journal of Soil Research, 21, 83-90. Cionco, R.M. (1972). A wind profile index for canopy flow. Boundary Layer Meteorology, 3, 255-63. 

Rood BE, Gottgens JF, DeUrno JJ, Earle CD, CrismanTL. 1995. Mercury accumulation trends in Florida Everglades and savannas marsh flooded soils. Water Air Soil Pollut 80 981-990. 

Savanna ADA (5) Recreational fishing Sediment to bottom feeders TNT DNT TNB... 

The 5,330 hectare (13,170 acre) Savanna Army Depot Activity, north of Savanna, IL, consists of high ground and Mississippi River flood plain. In the flood plain are 223 hectares of waterways connected to the river about 10 hectares of sediment plain in these waterways are considered potentially contaminated by munitions-related compounds (see Table I). Of these compounds, only TNT has been isolated (0.3 rag/kg in one sediment sample) DNT, TNB, and RDX are associated with TNT in other munitions contexts, hence they were also included. The waterways are fished by a number of activity personnel and retirees. These persons and their families may eat some of their catch, and thereby ingest those compounds that might be present in the fish (predominantly carp and catfish, both bottom-feeders). Acceptable safe sediment level guidance for these compounds was therefore desired. 

Table V. Calculated Values of Acceptable Contaminant Levels in Waterway Sediment (Cg) and Safety Factors (Cw/Cw ) for River-Derived Drinking Water, Savanna Army Depot Activity.

Rosenblatt, D.H. "Environmental Risk Assessment for Four Munitions-related Contaminants at Savanna Army Depot Activity," Technical Report 8110, U.S. Army Medical Bioengineering Research and Development Laboratory, Fort Detrick, Frederick, MD, November 1981, AD A116650. 

Boutton TW, Archer SR, Midwood AJ, Zitzer SF, Bol R (1998) 513C values of soil organic carbon and their use in documenting vegetation change in a subtropical savanna ecosystem. Geoderma 82 5-41... 

Martin A, Mariotti A, Balesdent J, Lavelle P, Vuattoux R (1990) Estimate of organic matter turnover rate in savanna soil by 13C natural abundance measurements. Soil Biol Biochem 22 517-523... 

Stott P (1984) The savanna forests of mainland southeast Asia an ecological survey. Prog Phys Geogr 8 315-335... 

U.S. Army Defense Ammunition Center School, Equipment Division, Savanna, IL 61074-9639... 

Savanna, Tropical Forest Fivi-Plinticic Ferrasols, Fuvisols, Vertisols, Subtropical Rendzinas, Ferralitic Cambisols, Nitosols, Ferralitic Arenosols, Subtropical South Asian 0.3 1.00 0.3... 

The receptors of interest are soils of agricultural (arable lands, grasslands) and non-agricultural (forests, steppes, heath lands, savanna, etc.) ecosystems. In non-agricultural ecosystems, the atmospheric deposition is the only input of heavy metals. Regarding the Forest ecosystems, a distinction should at least be made between Coniferous and Deciduous Forest ecosystems. When detailed information on the areal distribution of various tree species (e.g., pine, fir, spruce, oak, beech and birch) is available, this should be used since tree species influence the deposition and uptake of heavy metals and the precipitation excess. On a world scale, soil types can be best distinguished on the basis of the FAO-UNESCO Soil Map of the World, climate and ecosystem data from NASA database (1989). 

The proportion of areas with different precipitation rates varies from continent to continent. For instance, different arid ecosystems, from Dry Savanna to Extra-Dry Desert, are predominant in India and Australia. To a lesser degree these ecosystems occur in Central and South America. In an equatorial belt of Africa, the distribution of areas with different precipitation is shown in Table 1. 

We can see that the Tropical Rain Green Forest ecosystems occupy about 1/5 of the African equatorial belt, whereas about 1/2 of this area is Woody and Tall Grass Savanna ecosystems. The rest of the area are occupied by various Dry Steppe and Dry and even Extra-Dry Desert ecosystems, like the Sahara, with annual rainfall less than 200 mm. As it has been mentioned above, the amount of precipitation is of high significance for exposure pathways of pollutants. 

The Seasonal Tropical Forest and Woody Savanna ecosystems are common in tropical regions with a short dry period. The characteristic features of soils from these ecosystems are the neutral reaction of soil solution and periodic leaching during wet season. The herbaceous species favor the formation of both sward and humus horizons. 

Different conditions are typical for Dry Tropical Wood, Dry Savanna and Dry Woody Shrub ecosystems in areas with precipitation rates of 400-600 mm and a prolonged dry season. The microbial activity is suppressed during a dry season. The soils of these ecosystems have no even periodic leaching, the formation by transpiration of a biogeochemical barrier in the upper soil layer favors the alkaline reaction and accumulation of soluble salts. This decreases also the intensity of exposure to different pollutants for living organisms. 

Table 3. Content of heavy metals in soils of two Dry Savanna ecosystems from East Africa, ppm (after Dobrovolsky, 1994).

Both of the soils are enriched in various elements, like zirconium, titanium, beryllium, niobium, and strontium, due to their enlarged content in the alkali basalts and phonolites of the East-African Rift. We can see that soils of Tanzanian Dry Savanna ecosystems contain niobium 11 times, beryllium and molybdenum 6 times, and titanium and zirconium 4 times as high as compared to the respective crust concentrations (darks) of these metals. In the Ugandan soils, the chromium content is 7 times higher... 

Table 4. Biogeochemical mass balance for the Tropical Flooded Savanna ecosystems, kg/ha/yr (after Vegas-Vilarrubia et al., 1994).

Table 9 compares the contents of heavy metals in the ash of various grass and tree species from the Savanna ecosystems of East Africa. We can see that nickel, barium, and strontium accumulate in the tree organs (twigs), whereas the accumulation of other metals is pronounced in grasses. 

The aerial parts of grasses in Savanna ecosystems exhibit a high ash content from 6 to 10%. This is partly due to the presence of minute particles of mineral dust, which are discernible under a microscope or, occasionally, even with the naked eye. The exposure to mineral dust accounts for 2-3% of the weight of dry mass of grass aerial parts. We can consider that this dust is responsible for the elevated concentrations of some minerals, like Ga, which has a low Cb value. This element contains in windblown finely dispersed clay particles. Nevertheless, even with allowance made for the silicate dust content, the total sum of ash elements in grasses of savanna ecosystems is twice as much as that of the grasses from Alpine Meadow ecosystems. 

Strontium, barium, manganese, copper, molybdenum, and nickel are elements of strong accumulation in plant species of African Savanna ecosystems, in spite of different content in soils and soil-forming rocks. The Cb values are >1. The other elements, like beryllium, zirconium, titanium and vanadium, are less taken up by plants and their Cb values are less than 0.5. These refer to various exposure pathways to both microbes and plants as links in biogeochemical food webs. 

Table 9. Bio geochemical fluxes and exposure to heavy metals in various plant species of Savanna ecosystems of East Africa (after Dobrovolsky, 1994).

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