scholarly journals Timescales of C turnover in soils with mixed crystalline mineralogies, Kruger National Park, South Africa

2016 ◽  
Author(s):  
Lesego Khomo ◽  
Susan Trumbore ◽  
Carleton R. Bern ◽  
Oliver A. Chadwick
Keyword(s):  
South Africa ◽  
Organic Matter ◽  
National Park ◽  
Large Fraction ◽  
Turnover Time ◽  
Kruger National Park ◽  
Surface Soils ◽  
Organic C ◽  
Soil C

Abstract. Organic matter-mineral associations stabilize much of the carbon stored globally in soils. Metastable short-range-order (SRO) minerals such as allophane and ferrihydrite provide one mechanism for long-term stabilization of organic matter in soil. However, ancient and highly weathered soils that cover a large fraction of land area lack SRO minerals. Here we evaluate the role of different minerals on the amount and turnover time (TT) of carbon in a field setting designed to minimize the role of SRO by taking advantage of multiple lithologies in Kruger National Park, South Africa. Density separation demonstrated that most of the C was associated with minerals, even in surface soils. A parallel separation of clay-sized material demonstrated that 9–47 % of the organic C in these soils was stabilized by clays. Organic C associated with clay-sized material had average TT of 1020 ± 460 years in surface soils. The mean TT of this clay-associated C increased with depth and with fraction of total clay that was smectite. Because the C associated with smectite clay was so old, the amount of smectite (2 : 1 clays) controlled the age of bulk soil C across Kruger landscapes. The TT of the majority of soil C – not stabilized by clays – was much shorter, 190 ± 190 years in surface horizons. We suggest that this faster component reflects timescales of weaker C stabilization by crystalline Fe and Al oxyhydr)oxides and kaolinite (1 : 1) clays, as well as LF fractions not associated with minerals. Thus, bulk or HF carbon integrates C stabilized by mechanisms with inherently different TT, something that is often inferred from radiocarbon measurements. While SRO mineral concentrations were very low in these soils, the soils with most SRO had very high C content but also very young C. In other environments, SRO can be very stable and sorb C on very long timescales. We hypothesize that the seasonal wetting and drying in the KNP may reduce the age of SRO minerals as well as the C associated with them. Across the varying lithologies and a precipitation gradient found in the KNP, we found mineralogy to be the most important explanatory factor for C content (related to crystalline Fe) and turnover time (related to the amount of smectite).

Stem mortality of Acacia nigrescens induced by the synergistic effects of elephants and fire in Kruger National Park, South Africa

2008 ◽  
Vol 24 (6) ◽  
pp. 655-662 ◽  
Author(s):  
Glenn R. Moncrieff ◽  
Laurence M. Kruger ◽  
Jeremy J. Midgley
Keyword(s):  
South Africa ◽  
National Park ◽  
Synergistic Effects ◽  
Kruger National Park ◽  
Field Surveys ◽  
Natural Fires ◽  
Large Trees ◽  
Low Levels ◽  
Stem Mortality

Abstract:One manner in which elephants utilize trees is by removing their bark. This type of utilization is concentrated on the largest trees in the landscape. The role of bark removal in increasing the vulnerability of large trees to fire and the mechanism through which fire damage is mediated were investigated in Kruger National Park, South Africa, by experimentally removing bark and burning Acacia nigrescens stems with diameters ranging between 30 and 68 mm. Also, field surveys were conducted subsequent to natural fires in order to investigate mortality patterns of large trees with dbh greater than 15 cm with bark removed by elephants. An increasing probability of mortality was associated with increasing amounts of bark removal but only if trees were burned. When trees had bark removed but were not burnt, simulating damage only to cambium and phloem, none of the 12 treated stems died in the 4-mo period over which the experiment ran. Moreover, low levels of cambium damage were detected in large burned stems. This suggests that bark removal increases fire-induced xylem damage and that this damage contributes towards stem mortality. In a survey of 437 large trees, bark removal by elephants was frequent on large stems (44%) and larger trees have greater amounts of bark removed. Post-fire mortality of large trees was significantly associated with increasing bark removal and stem diameter. These results indicate that bark removal by elephants increases the vulnerability of stems to fire, resulting in mortality of large stems otherwise protected from fire.

scholarly journals Timescales of carbon turnover in soils with mixed crystalline mineralogies

SOIL ◽  
2017 ◽  
Vol 3 (1) ◽  
pp. 17-30 ◽  
Author(s):  
Lesego Khomo ◽  
Susan Trumbore ◽  
Carleton R. Bern ◽  
Oliver A. Chadwick
Keyword(s):  
Organic Matter ◽  
Arid Zone ◽  
Turnover Time ◽  
Bulk Soil ◽  
Humid Climate ◽  
Mineral Contents ◽  
Organic C ◽  
Soil C ◽  
Fe Oxyhydroxides ◽  
The Mean

Abstract. Organic matter–mineral associations stabilize much of the carbon (C) stored globally in soils. Metastable short-range-order (SRO) minerals such as allophane and ferrihydrite provide one mechanism for long-term stabilization of organic matter in young soil. However, in soils with few SRO minerals and a predominance of crystalline aluminosilicate or Fe (and Al) oxyhydroxide, C turnover should be governed by chemisorption with those minerals. Here, we correlate mineral composition from soils containing small amounts of SRO minerals with mean turnover time (TT) of C estimated from radiocarbon (14C) in bulk soil, free light fraction and mineral-associated organic matter. We varied the mineral amount and composition by sampling ancient soils formed on different lithologies in arid to subhumid climates in Kruger National Park (KNP), South Africa. Mineral contents in bulk soils were assessed using chemical extractions to quantify Fe oxyhydroxides and SRO minerals. Because of our interest in the role of silicate clay mineralogy, particularly smectite (2 : 1) and kaolinite (1 : 1), we separately quantified the mineralogy of the clay-sized fraction using X-ray diffraction (XRD) and measured 14C on the same fraction. Density separation demonstrated that mineral associated C accounted for 40–70 % of bulk soil organic C in A and B1 horizons for granite, nephelinite and arid-zone gabbro soils, and > 80 % in other soils. Organic matter strongly associated with the isolated clay-sized fraction represented only 9–47 % of the bulk soil C. The mean TT of C strongly associated with the clay-sized fraction increased with the amount of smectite (2 : 1 clays); in samples with > 40 % smectite it averaged 1020 ± 460 years. The C not strongly associated with clay-sized minerals, including a combination of low-density C, the C associated with minerals of sizes between 2 µm and 2 cm (including Fe oxyhydroxides as coatings), and C removed from clay-sized material by 2 % hydrogen peroxide had TTs averaging 190 ± 190 years in surface horizons. Summed over the bulk soil profile, we found that smectite content correlated with the mean TT of bulk soil C across varied lithologies. The SRO mineral content in KNP soils was generally very low, except for the soils developed on gabbros under more humid climate that also had very high Fe and C contents with a surprisingly short, mean C TTs. In younger landscapes, SRO minerals are metastable and sequester C for long timescales. We hypothesize that in the KNP, SRO minerals represent a transient stage of mineral evolution and therefore lock up C for a shorter time. Overall, we found crystalline Fe-oxyhydroxides (determined as the difference between Fe in dithionate citrate and oxalate extractions) to be the strongest predictor for soil C content, while the mean TT of soil C was best predicted from the amount of smectite, which was also related to more easily measured bulk properties such as cation exchange capacity or pH. Combined with previous research on C turnover times in 2 : 1 vs. 1 : 1 clays, our results hold promise for predicting C inventory and persistence based on intrinsic timescales of specific carbon–mineral interactions.

scholarly journals Abstracts of papers from the Rhinoceros Conservation Workshop, Skukuza, Kruger National Park,31 August – 4 September 1988

Koedoe ◽  
1989 ◽  
Vol 32 (2) ◽  
Author(s):  
Editorial Office
Keyword(s):  
South Africa ◽  
National Park ◽  
Kruger National Park ◽  
Illegal Trade ◽  
Black Rhinoceros ◽  
Diceros Bicornis ◽  
Conservation Plan ◽  
And Performance ◽  
Vital Factor

The following abstracts is included: 1.) Finances: the vital factor in rhinoceros conservation 2.) Towards a black rhinoceros Diceros bicornis translocation strategy to meet the aims of the conservation plan for the species in South Africa and the TBVC states 3.) Status, history and performance of black rhinoceros Diceros bicornis populations in South Africa, the TBVS states and Namibia 4.) Distribution and monitoring of black rhinoceros Diceros bicornis populations in Zimbabwe 5.) Census and marking systems for black rhinoceros Diceros bicornis with special reference to Zulu- land game reserves 6.) The Auxiliary Game Guard System in northwestern Namibia and its role in black rhinoceros Diceros bicornis conservation 7.) Black rhinoceros Diceros bicornis capture and translocation techniques as used in Etosha National Park 8.) The role of non-governmental organisations in black rhinoceros Diceros bicornis conservation in Africa 9.) Development of an intelligence/information network to counter poaching and the illegal trade in trophies

scholarly journals Casting Activity ofScherotheca gigasin No-Till Mediterranean Soils: Role in Organic Matter Incorporation and Influence of Aridity

2010 ◽  
Vol 2010 ◽  
pp. 1-6 ◽  
Author(s):  
Paloma Bescansa ◽  
Iñigo Virto ◽  
Oihane Fernández-Ugalde ◽  
María José Imaz ◽  
Alberto Enrique
Keyword(s):  
Organic Matter ◽  
Agricultural Soils ◽  
Nw Spain ◽  
Organic C ◽  
No Till ◽  
Physico Chemical ◽  
C Stocks ◽  
Casting Activity ◽  
Total Organic C

The behaviour of earthworms, their role in organic matter incorporation into the soil, and the influence of aridity in such processes in arid and semiarid regions have scarcely been studied. In this study, physico-chemical analyses of the casts and the surrounding no-till agricultural soils of three experimental sites representing an aridity gradient in Navarre (NW Spain) were done. The casts were formed by the activity of the only anecic species,Scherotheca gigas(Dugès, 1828), ubiquitous in no-till soils in this region. We observed a significant depletion of clay and higher concentration of total organic C and labile C in the form of particulate organic matter (POM) in the casts as compared to the surrounding soil, suggesting selective ingestion of soil byS. gigas. This, together with the observation of increased concentration in POM with increasing aridity, suggests a major role of this species in the observed progressive gains of organic C stocks in no-till soils in the region.

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