Recent Eutrophication in the Southern Basin of Lake Petén Itzá, Guatemala: Human Impact on a Large Tropical Lake

Abstract

A 210Pb-dated sediment core from a small bay in the southern basin of Lake Peten Itza, Guatemala documents recent cultural eutrophication. Increased sediment accumulation beginning ∼1930 A.D. coincided with catchment population growth and was a consequence of watershed deforestation and increased surface run-off. At the same time, geochemical records from the Lake Peten Itza sediment core indicate increased phosphorus loading and organic matter accumulation. High nutrient concentrations after 1965 A.D. coincided with lower sediment C/N ratios, suggesting an increase in the relative contribution of phytoplankton to the organic matter pool. This inference is confirmed by the dominance of eutrophic and hypereutrophic diatom species. Organic matter δ13C values decreased after 1965 A.D., seemingly contradicting other indicators of recent eutrophication in the southern basin of Lake Peten Itza. Relatively depleted δ13C values in recent sediments, however, may reflect a contribution from 13C-depleted sewage effluent. Increased δ15N of organic matter after 1965 A.D. indicates changes in the dissolved inorganic nitrogen delivered to the lake. The relatively small increase in δ15N (∼0.6‰ ) is less than might be expected with nitrate loading from sewage and soils, and might be offset by the presence of nitrogen-fixing cyanobacteria with low δ15N values.