LAKES AS INDICATORS OF ENVIRONMENTAL CHANGE

Lakes respond to environmental changes over time. These can be observed directly or reconstructed in the past from the sediment natural archive using proxy data. Closed-basin lakes indicate precipitation: evaporation balance by changes in water level, detectable by former shorelines, sediment transects from shallow to deep water associated with changes in aquatic macrophyte distribution, and by salinity changes inferred from, for example, diatoms and sediment chemistry.

Lake biota respond to changes in water chemistry. diatom analysis reveals changes in pH and dissolved organic carbon resulting from acid rain. eutrophication is indicated by changes in sediment composition, chemistry (e.g. C, N, P, pigments, lipids) and organism fossils (e.g. chironomids, cladocera, diatoms, other algae, cyanobacteria, aquatic macrophytes). heavy-metal concentrations in sediment indicate metal pollution levels. Lakes also respond to temperature changes. indicator species and stable isotopes in lake sediments provide a record of water and air temperature, ice cover, light penetration, productivity, etc. (e.g. chironomids, cladocera, coleoptera, diatoms).

Lake sediments also contain evidence of catchment changes. minerogenic sediment input reflects erosion. This may be climatic (e.g. younger dryas stadial, glacier variations), catastrophic (e.g. avalanches, debris flows, floods, fire frequency) or human-induced soil erosion (from deforestation, agriculture, modification of the landscape) exacerbated by aridity or irrigation. Lakes indicate terrestrial ecosystem changes through sedimentary records of terrestrial biota.

[See alsobeetle analysis, chironomid analysis, cladocera analysis, diatom analysis, lacustrine sediments, lake-level variations, limnology, multiproxy approach, palaeolimnology, plant macrofossil analysis, pollen analysis, sediment, sedimentological evidence of environmental change]