East African soil erosion recorded in a 300 year old coral colony from Kenya

Fleitmann, Dominik; Dunbar, Robert B.; McCulloch, Malcolm T.; Mudelsee, Manfred; Vuille, Mathias; McClanahan, Tim R.; Cole, Julia E.; Eggins, Stephen

doi:10.1029/2006gl028525

Cited by 122 publications

(99 citation statements)

References 29 publications

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“…Studying fossil plants (e.g., pollen grains and macrofossils) allows scientists to reconstruct the history of forest loss [15], and river sediments to provide insights into erosion rates over several centuries [16]. Still, there is a paucity of data on early forest cover and practically no data on historical soil fertility in SSA (even from this last century).…”

Section: Time Horizonsmentioning

confidence: 99%

“…In sum, these studies indicate that rates of soil degradation vary through time (are non-linear) and that not all indicators behave the same way. The longest study is the best example of this, which uses coral barium to calcium ratios from the Malindi reef to evaluate sediment transport (erosion) from the Sabaki river basin in Kenya [16]. Sediment flux was relatively low and consistent from 1700 to 1905, but rises after 1905, corresponding to the start of British settlement and land clearing, and periodic spikes that can be traced back to historical changes in land management.…”

Section: Longitudinal Studiesmentioning

confidence: 99%

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The State of Soil Degradation in Sub-Saharan Africa: Baselines, Trajectories, and Solutions

et al. 2015

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Abstract:The primary cause of soil degradation in sub-Saharan Africa (SSA) is expansion and intensification of agriculture in efforts to feed its growing population. Effective solutions will support resilient systems, and must cut across agricultural, environmental, and socioeconomic objectives. While many studies compare and contrast the effects of different management practices on soil properties, soil degradation can only be evaluated within a specific temporal and spatial context using multiple indicators. The extent and rate of soil degradation in SSA is still under debate as there are no reliable data, just gross estimates. Nevertheless, certain soils are losing their ability to provide food and essential ecosystem services, and we know that soil fertility depletion is the primary cause. We synthesize data from studies that examined degradation in SSA at broad spatial and temporal scales and quantified multiple soil degradation indicators, and we found clear indications of degradation across multiple indicators. However, different indicators have different trajectories-pH and cation exchange capacity tend to decline linearly, and soil organic carbon and yields non-linearly. Future research should focus on how soil degradation in SSA leads to changes in ecosystem services, and how to manage these soils now and in the future. OPEN ACCESS

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Section: Time Horizonsmentioning

confidence: 99%

Section: Longitudinal Studiesmentioning

confidence: 99%

The State of Soil Degradation in Sub-Saharan Africa: Baselines, Trajectories, and Solutions

et al. 2015

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“…Scleractinian corals can live for hundreds of years and continuously record changes in the marine environment in their aragonitic skeletons. Annual density banding in corals allows accurate time control on reconstructions (Knutson et al, 1972), and many studies have utilized corals for paleoclimatic and paleoenvironmental reconstruction, measuring stable isotopes (Dunbar et al, 1994;Cobb et al, 2003, Marion et al, 2005 and metals that substitute into the CaCO 3 matrix (Smith et al, 1979;Hanna and Muir, 1990;Bastidas and Garcia, 1999;Fallon et al, 2002;David, 2003;McCulloch et al, 2003;Ramos et al, 2004;Fleitmann et al, 2007;Lewis et al, 2007;Prouty et al, 2008). Although the coral calcification mechanism and therefore the exact pathway of metal substitution in the aragonite matrix are still under debate (Cohen and McConnaughey, 2003), empirical studies have shown that corals appear to faithfully record relative metal concentrations in the surrounding seawater (Runnalls and Coleman, 2003;Correge, 2006).…”

Section: Introductionmentioning

confidence: 99%

Century-scale records of land-based activities recorded in Mesoamerican coral cores

Carilli

Prouty

Hughen

et al. 2009

Marine Pollution Bulletin

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The Mesoamerican Reef, the second-largest barrier reef in the world, is located in the western Caribbean Sea off the coasts of Mexico, Belize, Guatemala, and Honduras. Particularly in the south, the surrounding watersheds are steep and the climate is extremely wet. With development and agricultural expansion, the potential for negative impacts to the reef from land-based runoff becomes high. We constructed annually resolved century-scale records of metal/calcium ratios in coral skeletons collected from four sites experiencing a gradient of land-based runoff. Our proxy data indicate that runoff onto the reef has increased relatively steadily over time at all sites, consistent with land use trends from historical records. Sediment supply to the reef is greater in the south, and these more exposed reefs will probably benefit most immediately from management that targets runoff reduction. However, because runoff at all sites is steadily increasing, even distal sites will benefit from watershed management.

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“…Suspended sediments (clays) carry adsorbed barium and other river-born trace elements that are desorbed in the low-salinity estuarine mixing zone and subsequently behave as conservative dissolved constituents of the ambient seawater in which the corals thrive (Sinclair and McCulloch 2004). Consequently, Ba/Ca and luminescence are used to reconstruct sediment and humic acid runoff, respectively in tropical catchments, where both have been shown to co-vary with the changing magnitude of precipitation and river flow (Fleitmann et al 2007). As Madagascar weather data are scarce (Dewar and Wallis 1999;Dewar and Richard 2007), novel spectral luminescence ratios and conventional luminescence intensities are paired with Ba/Ca to validate the method, supported by rainfall data from a nearby weather station.…”

Section: Introductionmentioning

confidence: 99%

River runoff reconstructions from novel spectral luminescence scanning of massive coral skeletons

et al. 2010

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Inshore massive corals often display bright luminescent lines that have been linked to river flood plumes into coastal catchments and hence have the potential to provide a long-term record of hinterland precipitation. Coral luminescence is thought to result from the incorporation of soil-derived humic acids transported to the reef during major flood events. Corals far from terrestrial sources generally only exhibit dull relatively broad luminescence bands, which are attributed to seasonal changes in coral density. We therefore tested the hypothesis that spectral ratios rather than conventional luminescence intensity provide a quantitative proxy record of river runoff without the confounding effects of seasonal density changes. For this purpose, we have developed a new, rapid spectral luminescence scanning (SLS) technique that splits emission intensities into red, green and blue domains (RGB) for entire cores with an unprecedented linear resolution of 71.4 lm. Since humic acids have longer emission wavelength than the coral aragonite, normalisation of spectral emissions should yield a sensitive optical humic acid/aragonite ratio for humic acid runoff, i.e., G/B ratio. Indeed, G/B ratios rather than intensities are well correlated with Ba/Ca, a geochemical coral proxy for sediment runoff, and with rainfall data, as exemplified for coral records from Madagascar. Coral cores also display recent declining trends in luminescence intensity, which are also reported in corals elsewhere. Such trends appear to be associated with a modern decline in skeletal densities. By contrast, G/B spectral ratios not only mark the impact of individual cyclones but also imply that humic acid runoff 123Coral Reefs (2010) 29:579-591 DOI 10.1007/s00338-010-0629-y increased in Madagascar over the past few decades while coral skeletal densities decreased. Consequently, the SLS technique deconvolves the long-term interplay between humic acid incorporation and coral density that have confounded earlier attempts to use luminescence intensities as a proxy for river runoff.

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East African soil erosion recorded in a 300 year old coral colony from Kenya

Cited by 122 publications

References 29 publications

The State of Soil Degradation in Sub-Saharan Africa: Baselines, Trajectories, and Solutions

The State of Soil Degradation in Sub-Saharan Africa: Baselines, Trajectories, and Solutions

Century-scale records of land-based activities recorded in Mesoamerican coral cores

River runoff reconstructions from novel spectral luminescence scanning of massive coral skeletons

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