Multiproxy palaeoecological data for lake Dallund S0, Denmark, were synthesized to explore the link between changes in the terrestrial environment (from pollen, and sediment physical properties) with those in the aquatic environment (from diatom, macrofossil, zooplankton and Pediastrum data) since the introduction of agriculture c. 6000 years ago. The lake was relatively insensitive to catchment disturbance during the Neolithic (3870-1700 BC) and Early Bronze Age (1700-1000 BC) periods but was dramatically impacted by environmental changes associated with a major deforestation phase at the transition from the Late Bronze Age (1000-500 BC) to the Pre-Roman Iron Age (500 BC-AD 0). A major eutrophication of the lake took place as a result of a changing agricultural system and also the retting of flax and hemp during the Mediaeval period (AD 1050-1536). Analyses of the data sets representing the terrestrial and aquatic environments demonstrate that human activities over thousands of years have not only impacted and shaped the Danish landscape but have also played a major role in lake development.

Diatom, macrofossil, pollen, Pediastrum and biogenic silica analyses were carried out on an 1 --m sediment sequence from the Danish lake Dallund S0, demonstrating major changes in the aquatic ecosystem over the last 7000 years. A diatom-phosphorus calibration model was applied to the fossil diatom record to reconstruct in-lake total phosphorus (TP) concentrations over this period. Prior to the introduction of agriculture to the region, c. 6000 years ago, the lake was relatively deep and had low diatom-inferred TP concentrations (c. 20 jg TP/L), with limited macrophyte growth. Moderate nutrient enrichment of the lake was inferred during the Bronze Age (1700-500 Bc) and Iron Age (500 BC -AD 1050) periods and evidence for water-level lowering was observed. Marked eutrophication of the lake (reconstructed TP levels consistently > 100 gg/L) was associated with major changes in agriculture during the Mediaeval period (AD 1050-1536) and continued to the present day. These data document the long-term anthropogenic impact on Dallund S0, a lake in an area with a long history of human activity.

1. A weighted averaging (WA) regression and calibration model for diatoms and total phosphorus (TP) was developed from a dataset of 45 surface‐sediment samples from Swedish lakes. Jack‐knifed error statistics were comparable with those for similar diatom–TP datasets: r2jack=0.47, root mean squared error of prediction (RMSEP)=0.24 log10μg TP L–1 and mean bias=–0.002 log10 μg TP L–1 for the simple WA model; r2jack=0.36, RMSEP=0.27 log10 μg TP L–1 and mean bias=0.017 log10 μg TP L–1 for WA with tolerance downweighting. 2. The model was used to estimate TP concentrations for the Ekoln basin of Lake Mälaren using a 210Pb‐dated sediment core record. Highly eutrophic conditions developed in the basin in the 1960s as a result of nutrient inputs from cultivated land and the city of Uppsala. A reduction in the supply of phosphorus from sewage outlets in the late 1960s resulted in less eutrophic conditions. 3. The model results indicated levels of 50–60 μg TP L–1 prior to 1900. The rapid eutrophication of the lake basin after the 1950s and the subsequent recovery were evident from the diatom data. 4. Diatom‐inferred TP (DI–TP) values were validated by comparison with monitored data for the period 1966–95. The diatom model tended to underestimate TP at high levels (> 80 μg L–1) but overestimate at lower concentrations. 5. A good agreement was observed between the trends in TP concentration and the DI–TP concentration and the timing of the maximum was well reflected by the diatom‐based reconstruction. A significant correlation (r2=0.69, P < 0.01) was found between DI–TP and measured TP at this site.

SUMMARY 1. Seasonal phosphorus variability may be considerable in eutrophic lakes and patterns are influenced by internal, as well as external, nutrient loading. The strong seasonality of planktonic diatoms, with main growth periods in the spring and also in the autumn in meso‐ to eutrophic lakes, means that the measure of total phosphorus (TP) that is most relevant for diatom ecology may not be adequately assessed by single or few measurements during the year. 2. The diatom species assemblage of surface sediments can be used to infer in‐lake nutrient concentrations. Weighted averaging (WA) and weighted averaging partial least squares (WAPLS) regression and calibration models for diatoms and annual mean TP were developed for a 29‐site data set of Danish lakes based on (a) all diatom species and (b) planktonic species only. Jack‐knifed error statistics were: =0.37, root mean squared error of prediction (RMSEP)=0.28 log10μg TP L−1 and mean bias=0.04 log10μg TP L−1 for the WAPLS 2‐component model based on all species; =0.23, RMSEP= 0.32log10μg TP L−1 and mean bias=0.07 log10μg TP L−1 for the WA model with tolerance downweighting based on planktonic species only. These are comparable with similar, published data sets. 3. A subset of 23 sites was used to develop models based on seasonal TP measurements. Mean spring TP concentrations gave only slightly improved RMSEP values for models based on all species and plankton‐only (0.24 log10μg TP L−1 and 0.29 log10μg TP L−1, respectively). 4. Weighted averaging models derive environmental optima, for individual species, which are not necessarily of ecological relevance. However, good water chemistry data are required to model species' responses adequately and to develop calibration data sets.

Summary The European Water Framework Directive (WFD) requires that all natural European waterbodiesshould be assigned to one of five ecological categories defining the degree to which present-day conditions deviate from those uninfluenced or only negligibly impacted by anthropogenic activities (the reference condition). By 2015, all relevant waterbodies must have obtained 'good' ecological quality. 2. We describe the changes in ecological state in 21 Danish lakes using  1850 as a benchmark for reference conditions. Sediment samples representing 1850, 1900, 1950 and 2000 were analysed for diatom and cladoceran subfossils. Ecological status since 1850 was evaluated using correspondence analysis and dissimilarity measures to assess assemblage changes, and existing transfer functions were applied to infer changes in total phosphorous concentrations from diatoms (DI-TP) and submerged macrophyte coverage (SUB-COV) and benthi-planktivorous fish catch per unit effort (BP-CPUE) from cladoceran subfossils. 3. Eighteen lakes underwent significant changes, most markedly during the past 50-100 years, in either or both diatom and cladoceran community structure. Low floristic and faunal alteration was found only in three lakes; these were, however, already nutrient-rich in 1850. 4. In 1850, most lakes were already characterized by high DI-TP (median of 17 lakes = 86 µg TP L -1 ), high inferred BP-CPUE and low inferred SUB-COV, and these eutrophic conditions still prevail. In addition, the accumulation rate of sediment and cladoceran subfossils and the pelagic dominance of diatoms and cladocerans have increased. 5. When applying the thresholds proposed by a recent WFD classification for Danish lakes to the DI-TP values, only one lake could be described as having a 'good' ecological state with a concurrent low community change since 1850, limited to the cladoceran community, however. This suggests that this lake alone may serve as a potential reference site. 6. Synthesis and applications. Our study, demonstrating the potential of a palaeolimnological approach to assess deviations from reference conditions, suggests that Danish reference lakes may be difficult to find, most probably due to the country's long history of cultural impact. Lake managers consequently face great challenges in their endeavour to ensure 'good' ecological state by 2015. Therefore, further restrictions on land-use and nutrient loading in lake catchments are needed as is the initiation of restoration activities to improve the ecological state of the lakes.

Changes in Faroese land surfaces during the late Holocene reflect intimate interactions between cultural and environmental development. Analyses of fossil wood, pollen and plant macrofossils indicate that the present open landscape replaced shrubby vegetation that was present from c. 6000 BC Up to C. AD 660. Conditions altered during the late Holocene, with loss of woody vegetation and increasing erosion: trends that were initiated prior to human settlement. AMS dating of sub-fossil Betula, Salix and Juniperus found buried in peat profiles from the islands of Su8uroy, Sandoy, Eysturoy, Vagar and Streymoy, revealed that the islands had at least partial woody vegetation cover up to the time of continuous settlement. The settlement horizon, identified in a lacustrine sequence on the island of Eysturoy, dated to c. AD 570. It comprised pollen evidence for the cultivation of Hordeum, cultural macrofossil assemblages, charcoal fragments, diatom assemblage changes indicating lake nutrient enrichment and physical measurements showing increased sedimentation rates. The pollen record showed that heathland development was initiated prior to anthropogenic impact. The ecosystem impacts of settlement were therefore superimposed on landscape changes that began around AD 250. The earlier changes were most likely forced by increased storminess and declining atmospheric temperatures.

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Lake Mälaren is the water supply and recreation area for more than 1 million people in central Sweden and subject to considerable environmental concern. To establish background data for assessments of contemporary levels of trophy and heavy metal pollution, sediment cores from the lake were analyzed. Diatom-inferred lake-water phosphorus concentrations suggest that pre-20th century nutrient levels in Södra Björkfjärden, a basin in the eastern part of Mälaren, were higher (c. 10-20 micrograms TP L-1) than previously assumed (c. 6 micrograms TP L-1). Stable lead isotope and lead concentration analyses from 3 basins (S. Björkfjärden, Gisselfjärden and Asköfjärden) show that the lake was polluted in the 19th century and earlier from extensive metal production and processing in the catchment, particularly in the Bergslagen region. The lake has experienced a substantial improvement of the lead pollution situation in the 20th century following closure of the mining and metal industry. The lead pollution from the old mining industry was large compared to late-20th century pollution from car emissions, burning of fossil fuels and modern industries.