DNA molecules originating from animals and plants can be retrieved directly from sediments and have been used for reconstructing both contemporary and past ecosystems. However, the extent to which ...such ‘dirt’ DNA reflects taxonomic richness and structural diversity remains contentious. Here, we couple second generation high‐throughput sequencing with 16S mitochondrial DNA (mtDNA) meta‐barcoding, to explore the accuracy and sensitivity of ‘dirt’ DNA as an indicator of vertebrate diversity, from soil sampled at safari parks, zoological gardens and farms with known species compositions. PCR amplification was successful in the full pH range of the investigated soils (6.2 ± 0.2 to 8.3 ± 0.2), but inhibition was detected in extracts from soil of high organic content. DNA movement (leaching) through strata was evident in some sporadic cases and is influenced by soil texture and structure. We find that DNA from the soil surface reflects overall taxonomic richness and relative biomass of individual species. However, one species that was recently introduced was not detected. Furthermore, animal behaviour was shown to influence DNA deposition rates. The approach potentially provides a quick methodological alternative to classical ecological surveys of biodiversity, and most reliable results are obtained with spatial sample replicates, while relative amounts of soil processed per site is of less importance.
In order to measure dust＇s nutrient input on farmland in different agro-ecological zones, Harmattan dust was sampled by mats with plastic straw in Ghana between 2002-2006. The inputs of total ...nutrients by Harmattan dust in Ghana per Harmattan period were about 1-2 kg Ca ha-1, 0.5-2 kg K ha-1, 0.5-1.5 kg Mg ha-1 and less than 0.5 kg P ha-1. Compared with the annual input of nutrients by precipitation, the dust accounted for 10% or less of Ca, Mg and K but approximately 20%-40% of P. The input of nutrients by dust was only valid for areas with vegetation, because in areas with none or sparse vegetation, loss of soil due to wind erosion and hereby loss of nutrients might be significant. In farmland areas with bare and vegetated fields there seemed to be an internal redistribution of the nutrients and not a net gain of nutrients from outside the area （long-range transported dust）. The input of P by dust might be of some importance in the traditional shifting cultivation systems, while the inputs of other three nutrients of Ca, Mg and K were so low that they must be considered insignificant. In the intensive agriculture systems with huge inputs of manures and fertilizers the nutrient input by dust is insignificant and could be neglected.
Field process measurements and OSL/AMS-dating methods were employed in combination to examine the Holocene evolution of the Keta Sand Spit, east of the Volta River delta in Ghana, as well as the ...hydrodynamic processes driving present spit dynamics. Large-scale changes in shoreline configuration, with far-field implications for sediment supply to downdrift coasts along the Bight of Benin, have been rooted in river mouth switches, which are dated at approximately 5–7000 yr BP and 2500 yr BP. The most recent barrier stage is the present Keta Sand Spit, which originated about 2500 yr BP. The spit migrates slowly in an easterly direction due to gradients in longshore sediment transport induced by morphodynamic interactions between wave-induced currents and shoreline orientation. These autochthonous longshore transport gradients are the major reason for the large coastal erosion rates in the lee of the Sand Spit, rather than a decreased sediment supply caused by damming of the Volta River.
•OSL-datings near the Volta River delta reveal a complex depositional history of the area.•Delta switches likely occurred about 6000 yrs BP and 2500 yrs BP.•Present coastal erosion is driven by internal morphodynamic feedbacks of the Keta Sand Spit.•The Akosombo Dam is not the main cause for the coastal erosion in eastern Ghana.
The limited information on change in shifting cultivation systems of small islands of the Pacific stands in contrast to increasing evidence of this farming system's demise in other parts of the ...tropics. Here, we assess changes in agricultural activities during the past 40 years of Bellona Island, Solomon Islands, where shifting cultivation is still maintained in the traditional way. Fallow length has increased despite population growth due to redistribution of the cultivated area, migration-induced extensification and changes in crops. Productivity of the farming system remains high although there are indications of soil degradation in the centre of the island. However, there are no signs that the traditional shifting cultivation system in Bellona may become unsustainable in the near future and extreme land use transformations seen in other Pacific islands are not found here.
One of the challenges of evaluating existing traditional farming systems is to combine local knowledge and modern scientific methods and terminology. This requires an evaluation of indigenous soil ...classification in modern terms. This paper focuses on an indigenous soil classification system developed by local farmers on the island of Bellona, Solomon Islands. The definitions of the different soil types are described and the principles of the classification system and the applicability of ethnopedology in soil surveys are discussed. Based on interviews with about 20 per cent of the farmers on the island as well as standard soil chemical and physical determinations on main soil types, an evaluation of the soil types for cultivation of various crops is carried out. The soils on Bellona are developed on oolitic or clayey phosphate‐rich deposits forming the basis for the agriculture production on the island. The Bellonese soil classification system is mainly based on the physical properties of the humus‐containing top layer. Subsoil layers are only used for classification if they are very close to the surface and may be mixed with the topsoil. Results show a general agreement among farmers, who perceive the same four out of seven soil types as highly useful for cultivation and rank these soil types similarly according to their suitability for different crops such as yam, watermelon, cassava and sweet potato. It is concluded that the indigenous soil classification is in line with the soil production potential and useful for land evaluation on Bellona.
In the context of major global environmental challenges such as food security, climate change, fresh water scarcity and biodiversity loss, the protection and the sustainable management of soil ...resources in Africa are of paramount importance. To raise the awareness of the general public, stakeholders, policy makers and the science community to the importance of soil in Africa, the Joint Research Centre of the European Commission has produced the Soil Atlas of Africa. To that end, a new harmonised soil map at the continental scale has been produced. The steps of the construction of the new area-class map are presented, the basic information being derived from the Harmonized World Soil Database (HWSD). We show how the original data were updated and modified according to the World Reference Base for Soil Resources classification system. The corrections concerned boundary issues, areas with no information, soil patterns, river and drainage networks, and dynamic features such as sand dunes, water bodies and coastlines. In comparison to the initial map derived from HWSD, the new map represents a correction of 13% of the soil data for the continent. The map is available for downloading.
•A new soil map of Africa at the continental scale•Harmonisation steps from database processing to Google Earth image analysis•Legacy soil data updated according to the WRB soil classification system•The soil map is at the heart of the Soil Atlas of Africa.•The map is available for downloading as a free resource.
Accurate information regarding soil organic carbon (SOC) stocks is crucial to understanding the terrestrial carbon cycle and for setting environmental policies concerning C, such as those governing ...land use conversion and soil management. Soils may act as a sink or source of the greenhouse gas CO
2 through exchange with the atmosphere. As soils contain a very large stock of organic C even small stock changes represent a large CO
2 flux.
The contemporary stocks of SOC in Denmark to 1
m depth were estimated by combining data from two soil and one land use database using four different scaling-up methods, which take into account land use and soil textures. The estimated stocks vary from 563 to 598
Tg
C, with 579
Tg
C as the average, when urban areas, lakes and open fjords are excluded.
Wetland soils have the highest average SOC density (35.6
kg
m
−2), followed by soils under forests (16.9
kg
m
−2), agricultural soils (14.0
kg
m
−2), and soils under natural vegetation (14.4
kg
m
−2). Nationwide, 60% of the total SOC is found within 28
cm depth, which is the median ploughing depth, and 78% within 50
cm depth. Sixty-nine percent of the total SOC stock is under agricultural land and 40% is found in the plough layer.
The Danish CO
2 reduction commitment under the Kyoto Protocol corresponds to 0.57% of the total SOC stocks in Denmark, meaning that verification of C sequestration by C accounting will be difficult over the relatively short period set by the protocol. Adoption of ‘improved best’ management practices and conversion of arable land to forests or wetlands will contribute to increased C sequestration, but the biophysical conditions set finite limits for the amounts of C that can potentially be sequestrated. Additionally, the effects on other greenhouse gas release processes also need to be evaluated.
In the tropical moist semi-deciduous forests of West Africa, soil catenas with extremely gravel-rich soil horizons at the summits and upper slopes and largely gravel-free profiles at the lower slope ...are common. Previous investigations have suggested that these gravel layers are the result of macro-invertebrates mining of fine-grained soil material from the subsoil leaving behind the gravel, to build galleries at the surface subsequently exposing it to water erosion transport downslope. We examined the indirect effect of this process on the distribution along a soil catena of crucial base cations (Ca2+, Mg2+, K+) and plant available phosphorous (P), which is often growth-limiting in these tropical ecosystems. We found that the export of fine-grained soil material at the top of the catena reduces the soil stocks (to 1 m) of these elements by up to 60%, while the soil fertility downslope did not change significantly. This important long-term (100–1000 yr scale) reduction in soil fertility at the top of slopes resulting from bioturbation and water erosion is overlooked in contemporary literature, which primarily focus on the beneficial impact termites and ants have on ecosystem functioning in more level savannah landscapes. As the type of catena studied is widespread across tropical environments, this effect is likely ecologically substantial. Future research should aim at understanding such long-term consequences of bioturbation on landscape ecology as well as soil heterogeneity and fertility, so we do not overlook potential negative ecosystem effects.
•Termites increase down slope soil erosion of particles finer than 2 mm.•Consequently, the upslope soil on the catena develops a gravelly layer at the profile surface or at shallow depth.•The gravelly layer decreases the soil nutrient stock up to 60% in the upslope catena members.•The down-slope movement of soil material does not have any significant effect on the nutrient stock at the lower slope.•The overall effect is a net-decrease in soil nutrients.
Soil organic carbon (SOC) in tropical forest soils is typically characterized by fast turnover rates but mineralization might be inhibited resulting in long term organic matter protection. This study ...focuses on SOC trapped in iron oxides in a Paleudult (chromic Acrisol) located in the moist semi-deciduous forest in Ghana by determining the age of the SOC, quantifying the geochemical characteristics of the SOC, and estimating how much of the SOC that is bound so tightly to the oxides that it does not participate in the normal turnover of organic matter in the soil. The SOC has been characterized by using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and 14C dating. The turnover rate of the reactive SOC was determined by basal soil respiration (BSR) and a ratio between the SOC stock in the soil. The investigation shows that SOC associated with iron nodules has a 14C age of more than 21,000years and the absence of CO2 release during BSR measurements reveals that iron nodules have trapped and immobilized ~21% of SOC stored in the top 1m (~3.4kgCm−2). NMR results indicate that trapped SOC in the iron nodules is more decomposed than the organic matter in the topsoil.
•We examine carbon sequestration in relation to iron-oxides in a tropical catena.•We examine recalcitrant soil carbon in iron nodules in tropical soils.•Carbon in iron/organic matter can be more than 20,000years old.•More than 20% of the carbon in the soils may be immobilized.
Soil erosion in forests is often considered negligible or minimal. In some tropical forest ecosystems, however, the combination of continuous surface exposure of fine soil particles at the upper ...slope by soil macrofauna and episodic precipitation can cause considerable downslope soil transport, and the introduction of slash and burn agriculture is often found to speed up soil erosion even more. Here we, for the first time, use OSL dating to quantify the long-term soil erosion rate along a hillslope in the moist semi-deciduous forest zone of Ghana. During the last ~4–5000years about 100cm of sediment has accumulated at an approximately constant rate of ~0.13–0.21mmyear−1 (1.95–3.15tha−1year−1). This is about an order of magnitude higher than literature estimates from similar environments, primarily obtained using short-term experimental setups; this suggests that care should be taken when extrapolating short-term erosion estimates to centennial or millennial timescales. We further deduce that an apparent acceleration in erosion began ~4500years ago. This may be due to the introduction of cultivation in the area, slightly earlier than previously suggested (2800–3500years ago). In this case the erosion rate based on deposition below 100cm (~0.05mmyear−1) can be taken to represent the (natural) erosion rate without human influence; this value is consistent with literature estimates. More retrospective studies of soil erosion rates are needed in order to confirm the validity of our methodology and results, as well as to test the reliability of extrapolated short-term erosion estimates.
•OSL dating is used to quantify the long-term erosion rate in a tropical forest.•About 4500years BP the rate shifted from ~0.05 to ~0.13–0.21mmyear−1.•Our results are an order of magnitude higher than short-term rates from literature.•Care should be taken when extrapolating short-term rates to 102–104year scale.
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