Diatom responses to Holocene environmental changes in a small lake in northwest Spain

The Holocene history of Lagoa Grande (1360 m a.s.l; northwest Spain) has been investigated through the analyses of diatom remains found in a sediment core. Changes in the lake have been interpreted in terms both of climatic variability and major changes in the catchment area. The diatom record begins at about 9800 yr BP and exhibits three marked changes at 8200, 6000, 4200 and at 2600 yr BP, which are interpreted as responses to climatic changes detected by marine and other terrestrial palaeoclimatic records. The initial lake was shallow and Aulacoseira species characteristic of acidic and oligotrophic waters were dominant. The early Holocene is characterised by the presence of Aulacoseira ambigua, which suggests an increase in water depth and nutrient levels. Throughout the Holocene, diatom assemblages underwent several changes linked to fluctuating limnological conditions. These changes in lake characteristics coincide with the regional succession of vegetation, suggesting that climate forcing initiated these limnological changes. During the last 2000 years catchment processes appear to be the major factor controlling lake characteristics in Lagoa Grande site. Diatom responses reflected the progressive peatland development and growth of littoral vegetation in the lake, and not only a change in the regional environment.