Geochemistry, Fossil Pigments and Temperature Time-Series Analyses

Journal of Limnology, 2000

The palaeoenvironmental history of Lake Candia, a small, shallow, eutrophic lake in Northern Italy, is described for the last ca 2000 years. Sediment samples from a sediment core collected in autumn 1995 were analysed for a range of palaeolimnological indicators, which included the principal algal and sulphur photosynthetic bacterial pigments, as well as magnetic susceptibility, organic matter, carbonates, organic carbon, total nitrogen, total sulphur and various forms of phosphorus. An accurate sediment chronology was determined using 210 Pb, 137 Cs and 14 C. The results show that throughout a first, long phase of the history of this period (from ca AD 100 to 1830; zone 1) the sediments have an organic carbon content of ca 10% d.w. and low concentrations of algal pigments, suggesting a moderately productive environment. Sedimentary carotenoids unique to anaerobic photosynthetic bacteria indicate a seasonally hypolimnetic anoxia during the whole ca 2000 year period. Clear effects of climate changes on lake productivity were inferred from the carotenoid, ß-carotene, okenone and organic carbon estimates. Values were higher in the warm periods before AD ca 660 and during the so-called Little Optimum of the Medieval Warm Epoch (AD ca 1100-1300), and lower during cold moist periods, such as the main phase of the Little Ice Age (AD ca 1550-1700). After AD ca 1830 (zone 2), anthropogenic impacts resulted in a sharp increase in lake trophic state, leading first to a decoupling of the trophic state from natural (climate) variability, and then to "cultural" eutrophication. The onset of this latter process in the Turin area has been set around 1830, when a sharp increase of sedimentary sulphur concentration took place.

2001

A combined bulk and detailed geochemical study of the sedimentary organic matter in Lake Albano, central Italy, provides critical data to track the response of this aquatic system to the environmental changes of variable amplitude that occurred during the Holocene. Rock-Eval pyrolysis of this predominantly laminated, organic carbon-rich sedimentary sequence shows changes in hydrogen and oxygen indices that are related to variations in the dominance of the primary producers. These variations are further confirmed by the pigments and the carbon isotopic composition of bulk organic matter showing that cyanobacteria dominated the lake waters during the early and late Holocene whereas diatoms have been the main producers during the middle Holocene. Sharp decreases in productivity, 2-3 centuries long, are identified at ca. 8.2, 6.4 and 3.8 ka. B.P. Changes in temperature and/or effective moisture are suggested as the most probable causes, although human impact cannot be ruled out for the latest part of the Holocene. *This is one of a series of papers to be published in Journal of Paleolimnology that were contributed from the keynote speakers at the

SIL Proceedings, 1922-2010, 1988

Journal of Limnology, 2001

The first sediment core analyses were carried out in 1958, but it is only from 1985 onward that a modern palaeolimnological approach was applied to the study of Lake Orta, a large and deep lake in North Italy, heavily polluted by ammonia and copper for about 50 and 30 years, respectively. Thus, we summarise those studies from a variety of sediment cores, collected in different years and sites, using both published and unpublished data. Changes in algal pigments (mainly chlorophyll derivatives, total and single carotenoids), inorganic geochemistry, especially heavy metals (e.g. Cu), diatoms, Cladocera, and thecamoebians were studied and related to the stressed environment. The whole picture reveals a close relationship between modifications in algal biomass, density, taxonomic composition and organisms size on the one hand, and water chemistry changes on the other hand. Long-term history of this lake over 7-8 centuries, including invertebrate and terrestrial vegetation dynamics (pollen stratigraphy), reveals close relationship with natural (climate) and anthropogenic forces.

Three cores from two crater lakes in central Italy, Lake Albano and Lake Nemi , collected as part of the interdisciplinary PALICLAS project, are discussed here. Core PALB 94-1E (13.875 m long, taken at a depth of 70 m) covers the last ca 30 kyr years, PALB 94-6B (8.40 m, at 30 m depth) spans from ca 17-26 kyr BP,15 m at 30 m depth) from ca 11 kyr BP to the present. These were analysed for organic matter, CaCO 3 , biogenic silica, carbon, nitrogen, preserved pigments, diatoms and chrysophytes. Primary productivity was reconstructed from pigments (all cores) and total phosphorous from diatom assemblages . In pre-Holocene sequences from Lake Albano there are several well-defined high productivity events in full generally oligotrophic glacial conditions, as inferred from pigments and diatom assemblages and supported by other proxies. The balance of all the evidence about these basal oscillations is strongly towards a climatic forcing. Trends in productivity are similar for many proxies in the Holocene records of Lake Albano and Lake Nemi . The early Holocene is characterised by very high productivity at both sites. Trophic levels throughout much of the period of human activity are lower but remain relatively high and stable at both lakes. It is only in most recent times that inferred productivity levels exceeding those of the early Holocene are found. These proxy records show great internal consistency in their response to distinct, but inter-related, aspects of the lake-catchment system, and reflect major changes in these systems since the late Pleistocene, particularly in lake productivity. This study demonstrates the value and necessity for a multi-proxy, multi-core approach in resolving complex palaeolimnological questions of both anthropogenic and natural environmental change.

Quaternary International, 2004

The availability of long-term series of chemical and biological data and the eutrophication/oligotrophication history of Lake Maggiore allows an attempt to correlate the registered changes with sedimentary records in several sediment cores. Documentary and palaeolimnological data were used to calibrate two important suites of sedimentary indicators of phytoplankton, diatoms and algal pigments.

Quaternary International, 2002

Three cores from two crater lakes in central Italy (Albano and Nemi) spanning the last ca. 11 kyr BP are discussed here. They were analysed for organic matter, dry density, algal and photosynthetic bacteria pigments, diatoms and Cladocera. These palaeolimnological records show great internal consistency in their response to distinct, but inter-related, aspects of the lakecatchment system, and reflect major changes in these systems particularly in lake productivity. The early Holocene was characterised by very high productivity at both sites. Trends in productivity are similar for many proxies in the Holocene records of Lake Albano and Lake Nemi. Trophic levels throughout much of the period of human activity (ca. 4000 yr BP onward) are lower but have remained relatively high and stable at both lakes. It is only in the last few decades that inferred productivity levels have exceeded those of the early Holocene. Statistical analysis (CONstrained Incremental Sum of Square cluster analysis, CONISS) showed five distinct periods during the Holocene characterised by major variations in the abundance and community structure of biological remains and geochemistry. A comparison of results from the different taxonomic groups has enabled the reconstruction of phases of increased productivity and the recognition of signals of anthropogenic impact on the lakes and their catchments. From published pollen diagrams, nine major deforestation events are recognised during the Holocene. These events, in particular the one which occurred in both lakes at 1800 yr BP and identifies the Roman Period, plus another at 3000-3500 yr BP related to agricultural activity during the Bronze Age, produced profound changes in the pelagic community structure of diatoms and Cladocera, which in some cases were even more marked than the accelerated eutrophication seen in recent times. The mid-Holocene climatic transition is also clearly evident and is characterised by a strong decrease in the concentrations of the biological proxies. Most of the observed lacustrine environmental changes are almost synchronous in the two lakes indicating the importance of regional rather than local changes. r

Palaeogeography Palaeoclimatology Palaeoecology, 2009

Exceptional preservation of fossils in so-called Konservat-Lagerstätten requires specific depositional regimes excluding disturbance of bottom sediments by either wave actions and currents or by benthic fauna. We here describe a depositional model for the Eocene "Pesciara di Bolca" Konservat-Lagerstätte based on sedimentological, paleoecological, and detailed organic geochemical results. Sediments were deposited in a lagoonal-like basin with stagnant bottom waters located on an extended carbonate platform that was sheltered from open marine waters by a submarine threshold. Run-off from nearby land areas provided nutrients to support an algal community dominated by diatoms. No fossil diatom shells have been identified, but evidence for their presence is given by the high abundance of highly branched isoprenoids in extractable bitumens. Influx of terrigenous organic matter into the lagoon occurred in particular during deposition of the basal fish-bearing level L1. Here not only plant macrofossils, amber, spores and pollen but also the lipid composition indicated notable input of land plants via the presence of n-C 24 to n-C 32 carboxylic acids, long-chain n-alkanes (n-C 27 , n-C 29 , n-C 31 ) and angiosperm wax triterpenoids. The redox regime in general was strongly reducing as evidenced by the high concentration of sulfur vs. organic carbon, excellent kerogen preservation as shown by high hydrogen indices, and low pristane/phytane but high phytane/n-C 18 ratios. The water column was highly stratified with anoxic saline bottom and fresh surface waters. Euxinic conditions with free reduced sulfur present in the photic zone could only be detected in sediments from the L1 horizon via traces of aromatic carotenoids derived from green sulfur bacteria (chlorobiaceae), which utilize H 2 S in anoxygenic photosynthesis. The depositional regime is thus comparable to the lithographic limestones of Solnhofen but based on biomarker evidence lacks the high salinities postulated for the latter. Biomarker composition indicates that best preservation conditions prevailed in the basal part of the studied section (0-7 m above datum) but declined upon deposition of the upper part. We interpret the body of the Pesciara as a parasequence of the 4th order (0.01-0.5 Ma), with the lower part representing a relative sea-level lowstand and the upper part a relative sea-level highstand.

Journal of Paleolimnology, 2000

We report the results of analyses of pigments (derived from algae and photosynthetic bacteria), diatoms and invertebrate fossil remains (ostracods, cladocerans, chironomids) in two late Pleistocene sediment cores from Lago Albano, a crater lake in Central Italy. The record contains evidence for oscillations in lake biota throughout the period ca. 28 to 17 k yr BP. The earliest of these are contained in the basal 3.5 m of light olive-gray and yellowish-gray spotted muds sampled in core PALB 94-1E from 70 m water depth. The later oscillations are best represented in the more extended sediment sequence recovered from a second core site, PALB 94-6B, in 30 m water depth. The sediments at site 1E, containing the earlier oscillations (ca. 28-24 k yr BP), predate any sedimentation at the shallower site, from which we infer an initially low lake level rising to permit sediment accumulation at site 6B from ca. 24 k yr onwards. At site 6B, massive silts rich in moss remains are interbedded with laminated silts and carbonates. These sediments span the period ca. 24 to 17 k yr and are interpreted as representing, respectively, times of shallow water alternating with higher lake stands, when the lake was stratified and bottom water was stagnant. A range of mutually independent chronological constraints on the frequency and duration of the oscillations recorded in the lake biota indicate that they were aperiodic and occurred on millennial to century timescales. We interpret them as responses to climate forcing through its impact on lake levels and changing aquatic productivity. The time span they occupy, their frequency and their duration suggest that at least some of these changes may parallel both the Dansgaard-Oeschger events recorded in Greenland Ice Cores and the contemporary oscillations in North Atlantic circulation documented in marine sediment cores.

Journal of Limnology, 2000

A palaeoenvironmental reconstruction for the past 2-3 centuries of eight remote sites from northern to southern Europe was based on a number of palaeolimnological proxies, especially fossil pigments. Most of the lakes studied are located above the timberline and a great effort centred on the creation and analysis of a data-sets of sedimentary records. A chronology for the last century was based on radiometric techniques ( 210 Pb, 241 Am 137 Cs). The accumulation rate of recent sediment was found to vary from 0.041 cm y -1 (Lake Saanajärvi, Finland) to 0.14 cm y -1 (Jezero v Ledvici, Slovenia). During the time-span represented by the cores were the major changes in organic carbon and nitrogen in Nižné Terianske Pleso (Slovakia), Redó (Spain) and Gossenköllesee (Austria). Constant increase of these nutrients from AD 1900 onwards was shown in lakes Saanajärvi, Nižné Terianske Pleso and Hagelseewli (Switzerland). No common trends in sulphur concentrations was evident. There is evidence of an atmospheric input of sulphur in Hagelseewli. This lake shows the highest concentrations, 10 fold higher at surface than the other lakes (ca 6% d.m.) Saanajärvi and Jezero v Ledvici. Except Gossenköllesee (Kamenik et al. 2000, this issue). Significant catchment disturbances are absent in these remote environments, so these increases can be considered to be the result of temperature increase or atmospheric nutrient pollution. Carotenoids belonging to sulphur anaerobic photosynthetic bacteria of the green and red groups (Chlorobiaceae and Chromatiaceae) were found in three lakes, i.e. Jezero v Ledvici, Hagelseewli and Gossenköllesee, implying that these lakes experienced seasonal anoxia in their bottom waters with strong stratification.