Mayan Urbanism: Impact on a Tropical Karst Environment

Abstract

From the first millennium B.C. through the 9th-century A.D. Classic Maya collapse, nonurban populations grew exponentially, doubling every 408 years, in the twin-lake (Yaxha-Sacnab) basin that contained the Classic urban center of Yaxha. Pollen data show that forests were essentially cleared by Early Classic time. Sharply accelerated slopewash and colluviation, amplified in the Yaxha subbasin by urban construction, transferred nutrients plus calcareous, silty clay to both lakes. Except for the urban silt, colluvium appearing as lake sediments has a mean total phosphorus concentration close to that of basin soils. From this fact, from abundance and distribution of soil phosphorus, and from continuing post-Maya influxes (80 to 86 milligrams of phosphorus per square meter each year), which have no other apparent source, we conclude that riparian soils are anthrosols and that the mechanism of long-term phosphorus loading in lakes is mass transport of soil. Per capita deliveries of phosphorus match physiological outputs, approximately 0.5 kilogram of phosphorus per capita per year. Smaller apparent deliveries reflect the nonphosphatic composition of urban silt; larger societal outputs, expressing excess phosphorus from deforestation and from food waste and mortuary disposal, are probable but cannot be evaluated from our data. Eutrophication is not demonstrable and was probably impeded, even in less-impacted lakes, by suspended Maya silt. Environmental strain, the product of accelerating agroengineering demand and sequestering of nutrients in colluvium, developed too slowly to act as a servomechanism, damping population growth, at least until Late Classic time.

Climate drying and associated forest decline in the lowlands of northern Guatemala during the late Holocene

“…Sediment of Unit U2 (∼ 3000 to ∼1000 cal yr BP) in all cores consists of a thick, detrital inorganic clay unit. This lithology has been identified in other Petén lakes and was designated "Maya Clay" (Deevey et al, 1979;Anselmetti et al, 2007). The sedimentation rate increased in the "Maya Clay" zone to 0.15 cm/yr in 11A, to 0.10 cm/yr in 11B, and to 0.02 cm/yr in 11C.…”

“…This vegetation change was generally interpreted as being exclusively a consequence of ancient Maya activities (e.g. forest clearance, slash and burn agriculture) (Deevey et al 1979;Binford 1983;Vaughan et al 1985;Brenner 1994). In some cases, however, it was not possible to distinguish the relative significance of human-versus climateinduced vegetation change (Islebe et al, 1996;Curtis et al, 1998).…”

Population, resources, and environment: Implications of human behavioral ecology for conservation

“…Other examples, perhaps less detailed, suggest that these problems have existed throughout time. Current work suggests that the abandonment of Mayan cities was related to agricultural failures (Deevey et al 1979, Turner 1982. Ancient Sri Lankans, by forest clearing on mountainous regions, created flooding and reservoir siltation (Lowdermilk 1953), causing serious problems.…”

Evidence disputing deforestation as the cause for the collapse of the ancient Maya polity of Copan, Honduras

“…Investigations in the Maya area have found varying patterns of erosion (37,46,47). Although research on erosion layers around some Maya centers has supported environmental degradation during the Late Classic period, no such evidence can be found at other centers (37).…”

“…2 and 3). The clay levels, in particular, may be a product of the rapid deposition of soil eroded from denuded hillsides during periods of rain and recall the "Maya Clay" layers found in lakebed sediments elsewhere in the Maya area (46,47). The first 3 of these clay levels follow the earliest period of forest clearance preserved in the sediments when the hillsides first may have lost their vegetation (see Figs.…”