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We present a lake-sediment record of pre-Columbian agriculture and fire history from the lowlands of southern Pacific Costa Rica that captures the arrival of maize agriculture at ca. 3360 cal yr BP in the Diquís subregion of the Gran Chiriquí archeological region. Our 4200-year record from Laguna Los Mangos begins 1000 to 2000 years earlier than other lake records from the region and provides the first microfossil and geochemical evidence of vegetation and fire prior to the establishment of maize agriculture. This early portion of the record shows evidence of fire events associated with land clearance or field preparation and maintenance for subsistence activities. Alternatively, these were wildfires ignited unintentionally by people or naturally by lightning or volcanism. Evidence of early maize by ca. 3200 cal yr BP was found at Laguna Zoncho in the southeastern section of the Diquís subregion. Our discovery of early maize agriculture at ca. 3360 cal yr BP in the Laguna Los Mangos watershed in the northwestern portion of the Diquís subregion indicates a rapid adoption of maize agriculture in the region after initial introduction. Pre-Columbian agriculture and fire activity at Los Mangos is nearly continual until historic times, but with a decline after ca. 1170 cal yr BP, coincident with the early Terminal Classic Drought (TCD). We infer a pronounced drying of the lowland environment at Laguna Los Mangos based on a depositional hiatus in the record at ca. 950 during late TCD. Agricultural proxies indicate reduced watershed activity during the ‘Little Ice Age’ following Spanish contact in southern Central America until the 20th century.
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Response of diatom communities to climate and human disturbance: A 4200-year record from Costa Rica
This study integrates diatom analysis with existing records of pollen, charcoal, elemental composition, and stable light isotopes to expand upon the 4200-year history of human activity and climate change from Laguna Los Mangos in southern Pacific Costa Rica. We counted diatoms in peroxide-treated samples and analyzed community composition using cluster analysis, revealing four distinct assemblage zones with diatom variability most closely correlated with phosphorus, titanium, and organic content. The earliest assemblage (Zone D, 4150–3430 cal yr BP) was dominated by Encyonema silesiacum and Nitzschia incognita and aligned with a period of deforestation, erosion, and abundant macrophytes. Gomphonema affine proliferated in Zone C (3430–2450 cal yr BP), reflecting increased pH and productivity likely caused by agriculture-induced nutrient loading. We attributed the preservation gap from 3290 to 2970 cal yr BP in Zone C to silica depletion and erosional deposition that induced decline in diatom abundance by diluting valve concentrations in lake sediments. Nitzschia incognita and G. affine became the dominant taxa in Zone B (2450–1400 cal yr BP), likely reflecting eutrophy, increasing conductivity, and drying climate. Dominance of Diadesmis confervacea indicated reduced lake level in Zone A (1400 cal yr BP–modern) at the onset of the Terminal Classic Drought (TCD). A hiatus in the record indicates lake desiccation from 950 to 450 cal yr BP. During the Little Ice Age (LIA), diatoms reflect conditions similar to Zone B indicating increased lake level, circumneutral pH, and eutrophy. Refilling of the lake indicates increased precipitation during the LIA despite evidence of severe regional drought reported at other sites. Variable precipitation during this period likely resulted from the combined effects of Spanish contact, agricultural collapse, forest recovery, and shifts in Atlantic and Pacific climate forcing mechanisms. Overall, the Los Mangos diatom record reflects shallow, slightly alkaline, eutrophic conditions influenced by nutrient enrichment, erosion, and deforestation associated with maize agriculture.
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- Award ID(s):
- 1660185
- PAR ID:
- 10485402
- Publisher / Repository:
- Sage
- Date Published:
- Journal Name:
- The Holocene
- Volume:
- 33
- Issue:
- 12
- ISSN:
- 0959-6836
- Page Range / eLocation ID:
- 1534 to 1546
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1177/09596836231197775
