Costa Rica has hundreds of lakes, many of which have never been described or sampled by limnologists. Here we summarize initial observations of five small (0.2–1.7ha) lakes located at low elevation (365–490m) in the cantón of Buenos Aries. We collected basic limnological data and samples during visits in 2013 and 2014, and compiled environmental and archaeological data for their surroundings as a contribution to the documentation of lake diversity in Costa Rica, and to support parallel investigations of indicators of environmental history preserved in the sediments of the lakes. Lagunas Carse, Los Mangos, Danta, and Ojo de Agua all appear to owe their origin to landslide events, while Laguna Junquillo is an artificial impoundment. Radiocarbon dates on plant macrofossils near the bases of sediment cores from three of the natural lakes provide minimum ages for lake formation; results indicate that Laguna Los Mangos formed over 4 100 years ago, while Laguna Danta formed prior to 1 320 CE and Laguna Carse formed ca. 1 550 CE, near the time of the Spanish Conquest. More than two dozen archaeological sites are located within 1–3Km of the natural lakes, documenting pre-Columbian human occupation and likely use of lake resources. Lake water temperatures and water chemistry were in keeping with observations at lakes throughout Costa Rica. All five lakes are probably polymictic lakes that turn over frequently; none evinced stratification. The surface lake sediments showed similar organic matter content (22,1–28,8%), with values falling near the middle of the range of lakes previously sampled in Costa Rica. Phytoplankton samples included taxa previously reported from small lowland lakes, but differed between lakes and included dominant taxa that were subdominant or uncommon at other lakes surveyed. Our investigation adds to knowledge of lake characteristics and diversity in Costa Rica, and provides benchmarks for assessing future changes in these lakes and their watersheds resulting from human activity, natural disturbances, and regional and global climate change.

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Thin-section (micromorphological) analysis of samples from the upper 1.5 m of a core obtained in 2007 from Anderson Pond, Tennessee, reveals a coherent but discontinuous record of late Pleistocene and Holocene climate change that supports some interpretations from previous pollen and charcoal analyses but indicates a revised Holocene chronology for this classic pollen site. Legacy sediments recording anthropogenic disturbance compose the upper 65 cm of the core (<160 cal yr BP) and are characterized by mixed, darker-colored, and coarser-grained deposits containing reworked soil aggregates, which sharply overlie finer-grained and lighter-colored, rooted middle Holocene sediments interpreted as a paleosol. These mid-Holocene sediments (95–65 cm; 7100–5600 cal yr BP) record extensive warm-dry subaerial soil conditions during the middle Holocene thermal maximum, manifested by illuviated clay lining root pores, and also contain abundant charcoal. Late Pleistocene sediments (150–95 cm), dark-colored and organic-rich, record open-water conditions and include siliceous aggregate grains at 143–116 cm (14,300–13,900 cal yr BP), recording intense fires. Thin sections are not commonly used in studies of paleoclimate from Quaternary lacustrine sediments, but we advocate for their inclusion in multianalytical approaches because they enhance resolution of depositional and pedogenic processes.

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