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A Late Holocene Model of Watershed Erosionand Floodplain Development in Relation to Climate Change and Landscape Modification in Northcentral Puerto Rico
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Soil Erosion Research Under a Changing Climate, January 8-13, 2023, Aguadilla, Puerto Rico, USA .(doi:10.13031/soil.23071)Authors: Lara M. Sánchez-Morales, Timothy Beach
Keywords: Climate Change, Floodplains, Geoarchaeology, Late Holocene, Paleosols.
Abstract
In the last decades, mounting paleoenvironmental and archaeological evidence recovered from the Caribbean have provided critical new insights into the relationship between early human niche construction and climate change in the archipelago starting ca. 8,000 years ago. In Puerto Rico, initial colonization and long-term settlement during the pre-colonial period (5,500 – 450 yrs. cal BP) went hand-in-hand with the introduction of a suite of landscape modification practices to ensure subsistence acquisition such as foraging of local plants, field preparation for low-level cultivation of exotic and domesticated crops (Rodríguez Ramos et al., 2013), and eventually – during times of population growth and increased social complexity – the development of extensive agricultural plots in the upper and lower catchments.
Lowland alluvial valleys are highly susceptible to changes in local precipitation, sea level rise, and land cover, among others. Thus, floodplain sequences are well-suited to investigate how these long-term socio-environmental processes have unfolded; especially in Puerto Rico where human settlement has been continuous from 5,000 years ago to the present. In a time when Puerto Rican–and Caribbean communities more broadly–are again facing new challenges stemming from shifting seasonal patterns, recurring droughts, and intense and frequent storm activity, we expect that the results from this investigation will contribute a deep-time perspective on the confluence between societies and catchments. We show the first stage of analysis of this project by focusing on the sedimentary aspects of our watershed erosion/sedimentation model. Our model of watershed erosion and lower-catchment sedimentation captures differences in downstream sedimentation rates, sediment provenance, and soil development over sequences capturing the last 6,000 years based on particle size, magnetic susceptibility, organic matter and carbonate content, x-ray fluorescence, x-ray diffraction, and AMS-dates. We provide new data collected systematically from the Río Grande de Arecibo (RGA) and Río Grande de Manatí (RGM) floodplains via core and exposure sampling to evaluate: 1) how catchment land cover and hydrology might have changed over time, 2) how landscape modification practices at various degrees of intensity might have contributed to these overall changes, 3) how lower catchment ‘soilscapes‘ constitute “ecological legacies” inherited over generations, and 4) how present-day communities are still adapting to these cumulative legacies, and what this means for future decisions regarding land use in these catchments. We also include preliminary analyses of a sediment sequence from Laguna Tortuguero (Burney et al., 1994), a coastal lagoon east of the RGM that contains a long-term sedimentary record of forest burning, as a comparative case for our floodplain models.
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