Multi-proxy studies are becoming increasingly common in palaeolimnology. Eight basic requirements and challenges for a multi-proxy study are outlined in this essay – definition of research questions, leadership, site selection and coring, data storage, chronology, presentation of results, numerical tools and data interpretation. The nature of proxy data is discussed in terms of physical proxies and biotic proxies. Loss-on-ignition changes and the use of transfer functions are reviewed as examples of problems in the interpretation of data from multi-proxy studies. The importance of pollen analysis and plant macrofossil analysis in multi-proxy studies is emphasised as lake history cannot be interpreted without knowledge of catchment history. Future directions are outlined about how multi-proxy studies can contribute to understanding biotic responses to environmental change.

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Multi-proxy studies in palaeolimnology

Diatoms as indicators of lake eutrophication

Past occurrences of hypoxia in the Baltic Sea and the role of climate variability, environmental change and human impact

Increases in atmospheric temperature and nutrients from land are thought to be promoting the expansion of harmful cyanobacteria in lakes worldwide, yet to date there has been no quantitative synthesis of long-term trends. To test whether cyanobacteria have increased in abundance over the past ~ 200 years and evaluate the relative influence of potential causal mechanisms, we synthesised 108 highly resolved sedimentary time series and 18 decadal-scale monitoring records from north temperate-subarctic lakes. We demonstrate that: (1) cyanobacteria have increased significantly since c. 1800 ce, (2) they have increased disproportionately relative to other phytoplankton, and (3) cyanobacteria increased more rapidly post c. 1945 ce. Variation among lakes in the rates of increase was explained best by nutrient concentration (phosphorus and nitrogen), and temperature was of secondary importance. Although cyanobacterial biomass has declined in some managed lakes with reduced nutrient influx, the larger spatio-temporal scale of sedimentary records show continued increases in cyanobacteria throughout the north temperate-subarctic regions.

Acceleration of cyanobacterial dominance in north temperate-subarctic lakes during the Anthropocene.

Late Quaternary Lake-Level Record from Northern Eurasia

SUMMARY (1) The history of Diss Mere, Norfolk, U.K. was reconstructed by diatom and pigment analysis of a sediment core, with emphasis on the influence of changing vegetation and land-use on lake history. (2) The lake was mildly nutrient-rich (mesotrophic) early in its history. (3) The lower part of the core shows large variations in diatom concentrations and distinct lithological changes, including broad bands of silt and short sections of laminated sediments, which suggest fluctuating lake levels in the early Holocene. (4) Increased concentrations of the blue-green algal pigment oxcillaxanthin indicate the expansion of Oscillatoria about 6000 years B.P., probably in response to increased stabilization of the water column. (5) The subsequent preservation of over 3 m of laminated sediments in the midHolocene and extremely high pigment concentrations indicate a long period of moderate water levels and seasonal hypolimnetic oxygen depletion. (6) Increased pigment concentrations and percentages of diatom taxa characteristic of moderately enriched lakes correlate with pollen evidence of Neolithic and Bronze Age forest disturbance. (7) The termination of the laminated sediments and a transition from a Cyclotelladominated diatom assemblage to one dominated by Stephanodiscus spp. correlate with pollen evidence of widespread deforestation. Thus rapid and sustained eutrophication of the mere probably resulted from increased nutrient inputs caused by forest clearance. (8) The mere remained eutrophic throughout the remainder of its history, and subsequent shifts in the diatom community indicate limnological responses to agricultural practices associated with Cannabis cultivation and later to the growth of a town around the mere.

S. C. Fritz

Papers

Lake development and limnological response to prehistoric and historic land-use in diss, norfolk, u.k.