A Paleohistory of Climate, Vegetation, and Human Land Use in Coastal Peru

The Institute for the Advanced Study of Culture in the Environment (IASCE) at the University of South Florida (USF) recently received a Collaborative Research grant from the National Science Foundation titled “The Ecological Context of Early Settlement in a Southern Peruvian Coastal Valley Circa 5000-1000 BP”.

Working with colleagues from the University of Maine (UMaine), Drs. Alice Kelley and Daniel Sandweiss, the USF IASCE team and UMaine professors and students traveled to study landscape changes in the Chincha Valley in southern Peru in the summer of 2019. The research was designed to assess both the natural changes and those caused by humans in valley over the last 5000 years. This work gives us inherently interesting knowledge about how our ancestors managed their environment and adapted to severe weather events, as well as providing a tool to better predict these catastrophes in the future.

The Chincha Valley, located about 125 miles south of Lima was and remains one of the largest agriculturally productive regions of southern coastal Peru. Previous research identified a rich archaeological history of complex society in the valley, beginning at least in the late 2nd millennium BCE. The earliest settled villages were precursors to the Paracas culture, a widespread political and social entity that began around 800 BCE and continued up to around 100 BCE. Previous field surveys identified dozens of major Paracas period platform mound sites in the valley, making Chincha one of the main centers of development for this early Andean culture.

The Proyecto Arqueológico de Chincha, or PACH, began work in 2011. The project is directed by Professor Charles Stanish, Executive Director of the Institute for the Advanced Study of Culture and the Environment, and Dr. Henry Tantaleán, professor at San Marcos National University in Lima. The collaborative research was built on the impressive work conducted by previous archaeologists, botanists, agronomists, and historians who have worked in the region for over a century.

Coastal Peru is a very dry desert punctuated with rivers that flow west from the Andes Mountains. Scientists who have studied human settlement in Peru over the last 7,000 years have always assumed that the first farmers to work the land, built canals from the large rivers to irrigate the dry, desert plains. During excavations in 2014 in the farm fields in Chincha, Stanish and his team discovered something quite unexpected – the area near the ocean, at least the first three miles, was actually a rich swampland prior to human occupation as farmers.

We discovered this by examining microscopic plant remains in the soil samples that we meticulously collected from layers of rock in the area. We then had carbon samples from the levels dated using Accelerator Mass Spectrometry - an advanced technique used to measure the amount of Carbon-14 in organic materials. This gives us dates with a precision to about +/- 75 years.

The idea that the peoples 4000 or more years ago converted the swamps into a form of sustainable agriculture was quite remarkable. However, the original farmers and their descendants had to deal with the periodic El Niño phenomenon.

El Niños, or technically the warm phase of the El Niño–Southern Oscillation (abbreviated as ENSO), occur when a band of warm water sweeps through the Pacific in the southern Hemisphere. This warm water creates droughts in some parts of the Pacific, but spawns torrential rains on the coast of Peru, normally a place with very little annual rainfall. The ENSO events occur periodically. The mild form has about a four-year cycle, while the extreme events can cause tremendous flooding, mud slides, economic disruptions, famine, and destruction of towns and agricultural infrastructures.

Since the arrival of Europeans in Peru up to the present day, there have been about two dozen or so very serious events of this magnitude. The team’s work promises to help understand the periodicity of the ENSO, as well as the human response to these events. This information will be useful in the future for scientists to predict such powerful climatic events over longer lead times.

Excavations at the site of Pozuelo, one of the oldest agricultural village sites known in the Chincha Valley, by Christine Bergmann, a Department of Anthropology graduate student at USF, has revealed deep strata, or sedimentary rock. Bergmann, a specialist in scientific archaeology, will analyze the sediments from the test units and reconstruct the vegetation and geomorphological history of this particular site.

The study of ancient plants, called paleobotany, utilizes fossilized seeds, pollen, and what we call phytoliths. Phytoliths are microscopic parts of plants that have absorbed silica, and therefore have literally become fossilized. Different kinds of plants can be distinguished by the different phytoliths that they leave. Seeds act in the same way. Seeds and phytoliths can be recovered in very old sediments. If the moisture and pH conditions are right, they can last for tens of thousands of years. Once these plant parts have been collected, they can be combined with preserved shells and animal bones to reconstruct the ancient climate and ecological communities.

A major component of the NSF grant is being used to train students in field and laboratory methods. However, due to the COVID-19 pandemic, research is currently on hold. Once the team is cleared to continue their work, they will host some UMaine students at the USF Tampa campus to work in our paleobotanical lab run by our post-doc, Dr. Christopher Kiahtipes. Likewise, USF students will travel to UMaine to train in their facilities. USF will also host visitors from Peruvian universities to train in the labs on the Tampa campus.

Once international travel resumes, Stanish and his team will continue their research, in which they plan to excavate many more units across the valley. The analysis of the soil geomorphology and the ancient plant remains will give us a comprehensive picture of the vegetation and climate history over the last 5000 years in the Pacific coast of South America. Combined with work in other parts of the Pacific, this information will be useful for refining our predictive models of major ENSO events.

Published on: 6/19/2020