Julieta Massaferro

Lake Maggiore (N. Italy) trophic history: fossil diatom, plant pigments, and chironomids, and comparison with long-term limnological data

Abstract 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. Diatom assemblages in the sediment cores precisely reflect the pelagic diatom development for approximately the last century. Prediction of total algal biomass from the profile of the ubiquitous β-carotene and some algal groups in certain period of lake development (e.g. diatoms, Cryptophyta, cyanobacteria) was good, whereas the comparison of taxa-specific carotenoids and algal biomass standing stocks (as cell biovolume) in some case revealed poor correspondence. Selective carotenoid losses, taxa production, and mechanisms controlling pigment sedimentation are factors that biased the comparison. However, pigment concentrations and algal biovolumes are different units but equally valid. The use of fossil pigments complements other studies and provides more detailed information on algal development. A sub-fossil chironomid profile agrees well with the general trophic reconstruction as inferred from the pigment and diatom data, adding more details on changes in littoral substratum, water-level fluctuation and flood events. Models to infer primary productivity and total phosphorus concentration in lake water from sedimentary pigments and diatom assemblages are tested: in the case of the TP reconstruction, reliable results were obtained in this case for the period of high trophic state and for the last decade. During the recovery phase of the 1980s, unexpected high abundance of Stephanodiscus minutulus leads to strong overestimation of TP concentrations. Similarly, the reconstructed primary productivity only disagrees with the experimental data for some years in the last decade. Sensitivity of the sedimentary pigment model as well as the relatively reduced sampling dates likely explains this discrepancy. Similarities are also evident in the temporal diatom assemblage variations of an additional three sub-alpine Italian lakes. As well, the palaeolimnological reconstruction for Lake Maggiore parallels that for Lake Constance, another large sub-alphine lake located north of the Alps.

Late Pleistocene and early Holocene ecological response of Lake El Trébol (Patagonia, Argentina) to environmental changes

Stratigraphy of Lake El Trébol (41°S 71°W, 758 m a.s.l.) described from an 11 m long sediment core provided a continuous record of patecenvironmental changes occurred during the last 14,000 years in southern South America east of the Andes. Located in an ecotonal area within a strong humidity gradient, this lake offers a unique opportunity to develop paleolimnological studies. Using a geochemical approach that includes elemental analysis, bulk organic matter, major nutrients and pigments combined with chironomids and pollen analysis, three zones were identified in the sedimentary record of this take. The oldest one (between 680 and 1,100 cm) corresponds to the late Glacial period. During that time, clayish laminated sediments were formed in a proglacial environment. Low organic matter, biogenic silica and nitrogen contents and the absence of pigments, pollen and chironomids characterise this period. At the end of this period, ca. 14,000 yr BP, a sharp increase in phosphorus concentrations predates major changes in limnological parameters. The transition zone (between 560 and 680 cm) is related to major changes in the drainage system that started soon after ca. 14,000 yr BP and continued to ca. 10,500 yr BP. The chemical composition of the sediments was affected by an increase in physical weathering mechanisms almost coincident with the increase in the regional volcanic activity that produced suspended volcanic detritus. The increase of mainly coarser detritical components may indicate a reorganisation of the fluvial system by that time. Simultaneously, an increase in the productivity of the lake accompanied by a gradual replacement of open vegetation with Nothofagus, Poaceae and Ericaceae, by Nothofagusforest, was observed. In the last zone (between 0 and 560 cm) the productivity of Lake El Trébol achieves maximum values. The trends in geochemical and biological indicators observed at Lake El Trébol can be up to some extent, correlated to those registered in Lake Mascardi. The results support earlier paleoctimatic scenarios from southern South America.

Evidence for short-lived oscillations in the biological records from the sediments of Lago Albano (Central Italy) spanning the period ca. 28 to 17 k yr BP

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.

HEAVY METAL CONTAMINATION IN SEDIMENTS OF LAKE NAHUEL HUAPI, NAHUEL HUAPI NATIONAL PARK, NORTHERN PATAGONIA, ARGENTINA

Trace metals (Sb, As, Br, Cs, Co, Cr, Ag and Hg), rare earth elements (Ce, Eu, La, Lu, Sm, Tb and Yb), and Sc. were analysed in suspended load and in two sediment cores from Lake Nahuel Huapi, Nahuel Huapi National Park, Patagonia, Argentina, by using Instrumental Neutron Activation Analysis. The core activity profiles of 210Pb and 137Cs were measured to estimate the age of the sediments. Silver was enriched in the upper layers of both cores, and correlated with the strong growthof the population of Bariloche City in the last 50 yr. Concentrations are higher in the core sampled near Bariloche, andindicate some transport in the water body. Silver concentrationsmeasured in the suspended load were 4.58±0.36 and 3.46±0.40 μg g-1 in the southern margin of the lake, near San Carlos de Bariloche City, whereas in the northern margin the concentrations were 1.68±0.18 and 1.88±0.23 μg g-1. Concentration ratio for silver in suspended load and upper core layers were equal in both sampling points. These facts suggest that Ag contents correspond to inputs associated with human activities. Bromine concentrations show a strong increase abovebase line values, similar to silver. In contrast, caesium, chromium, and cobalt concentrations do not differ from base linevalues. The metalloids antimony and arsenic show little variationwith regard to base line concentration. Noticeable, the mercurycontents found in the suspended load.

GUIA PARA LA IDENTIFICACIÓN DE TANYTARSINI SUBFOSILES (DIPTERA: CHIRONOMIDAE: CHIRONOMINAE) DE LA PATAGONIA

Abstract. A GUIDELINE FOR THE IDENTIFICATION OF SUBFOSSIL TANYTARSINI (DIPTERA: CHIRONOMIDAE: CHIRONOMINAE) FROM PATAGONIA. This paper presents a key for the identification of nine subfossil morphotypes of the Tribe Tanytarsini (Subfamily Chironominae), described for Argentinean and Chilean Patagonia, from 39° to 54°S. The key is structured based on the head capsules, which is the only material preserved in the sedimentary record. Tribe Tanytarsini is of particular importance as it includes species with high environmental importance, especially climatic. The material collected in Argentinean and Chilean Patagonia allowed the classification of nine morphotypes, distinguished mainly by four easily observables characteristics; (1) the spur shape of the antennal pedestal, (2) presence and shape of post-occipital plate, (3) number of premandible teeth, and (4) mentum and ventromental plates. The main goal of this contribution is to bring together the very sparse and limited knowledge on Tanytarsini from southern South America, in a simple and practical key helping the identification and separation of morphotypes, especially useful for scientists working with fossil chironomids from the Quaternary of Patagonia and other regions of the Southern Hemisphere.

First human impacts and responses of aquatic systems: A review of palaeolimnological records from around the world:

Lake sediments constitute natural archives of past environmental changes. Historically, research has focused mainly on generating regional climate records, but records of human impacts caused by land use and exploitation of freshwater resources are now attracting scientific and management interests. Long-term environmental records are useful to establish ecosystem reference conditions, enabling comparisons with current environments and potentially allowing future trajectories to be more tightly constrained. Here we review the timing and onset of human disturbance in and around inland water ecosystems as revealed through sedimentary archives from around the world. Palaeolimnology provides access to a wealth of information reflecting early human activities and their corresponding aquatic ecological shifts. First human impacts on aquatic systems and their watersheds are highly variable in time and space. Landscape disturbance often constitutes the first anthropogenic signal in palaeolimnological records. While the effects of humans at the landscape level are relatively easily demonstrated, the earliest signals of human-induced changes in the structure and functioning of aquatic ecosystems need very careful investigation using multiple proxies. Additional studies will improve our understanding of linkages between human settlements, their exploitation of land and water resources, and the downstream effects on continental waters.

Quaternary Fossil Insects from Patagonia

Publisher Summary Fossil insects are often abundant in a wide range of Quaternary deposits. Several orders of insects can be found in fluvial and lacustrine sediments. This chapter focuses on remains of midges and beetles from the Quaternary period, especially the Late Pleistocene and Holocene, for the paleoenvironmental studies. Chironomidae belong to the Order Diptera: Nematocera and they are colloquially known as “non-biting midges.” The distribution of the different chironomid taxa is restricted by environmental conditions. Their remains are of special interest in paleolimnology because their strongly sclerotized larval head capsules are preserved in sediment deposits. There are several reasons for chironomids to be considered important in paleolimnology: (1) they are sensitive to environmental variables such as temperature, pH, trophic conditions, and dissolved oxygen; (2) they have relatively short life cycles; (3) the adult are mobile; (4) the larvae possess chitinous head capsules that are well preserved in lake sediments; and (5) they are abundant, diverse, and readily identifiable to generic and species-group level, enabling high resolution studies. Past chironomid stratigraphies can be reconstructed and readily used to infer environmental conditions at the time of deposition.

Assessing the performance of macroinvertebrate metrics in the Challhuaco-Ñireco System (Northern Patagonia, Argentina)

Seven sites were examined in the Challhuaco-Nireco system, located in the reserve of the Nahuel Huapi National Park, however part of the catchment is urbanized, being San Carlos de Bariloche (150,000 inhabitants) placed in the lower part of the basin. Physico-chemical variables were measured and benthic macroinvertebrates were collected during three consecutive years at seven sites from the headwater to the river outlet. Sites near the source of the river were characterised by Plecoptera, Ephemeroptera, Trichoptera and Diptera, whereas sites close to the river mouth were dominated by Diptera, Oligochaeta and Mollusca. Regarding functional feeding groups, collector-gatherers were dominant at all sites and this pattern was consistent among years. Ordination Analysis (RDA) revealed that species assemblages distribution responded to the climatic and topographic gradient (temperature and elevation), but also were associated with variables related to human impact (conductivity, nitrate and phosphate contents). Species assemblages at headwaters were mostly represented by sensitive insects, whereas tolerant taxa such as Tubificidae, Lumbriculidae, Chironomidae and crustacean Aegla sp. were dominant at urbanised sites. Regarding macroinvertebrate metrics employed, total richness, EPT taxa, Shannon diversity index and Biotic Monitoring Patagonian Stream index resulted fairly consistent and evidenced different levels of disturbances at the stream, meaning that this measures are suitable for evaluation of the status of Patagonian mountain streams.

Little Ice Age to Present Paleoenvironmental Reconstruction Based on Multiproxy Analyses from Nahuel Huapi Lake (Patagonia, Argentina)

Abstract. Lakes are ideal sites to study environmental changes since they preserve climatic, anthropogenic, and volcanic signals in their sediments. Brazo Blest is one of the most important ramifications of Lake Nahuel Huapi and it is an interesting site to study climatic variations as it receives direct discharge of heavy suspended sediments loads from Tronador Glacier through the Frías River, as a result of the abrasion of the bedrock and runoff from the surrounding Valdivian Forest. A short sediment core from Brazo Blest was analyzed for chironomid and diatom assemblages and pigments in order to reconstruct environmental changes during the last 100 years in the basin under study. This multiproxy study also included geochemical and physical analyses and reveals changes in the productivity of the lake over time, showing a shift in the 1950s from autochthonous to allochthonous organic matter. This modification is related to the increase of precipitation and the consequent fluvial runoff from two catchments, Frías River and the Blest-Cántaros basin together with the effects ofrising temperatures, which affected Tronador Glacier. Further, it allows us to link volcanic eruptions to a decrease in species richness and number of chironomids and diatoms, as a consequence of reduced light intensities and food availability induced by the high content of suspended sediments in the water column. This study highlights the effectiveness of multiproxy analyses to reconstruct environmental changes.

Multiproxy response to climate- and human-driven changes in a remote lake of southern Patagonia (Laguna Las Vizcachas, Argentina) during the last 1.6 kyr

espanolLaguna Las Vizcachas es un lago remoto situado en la estepa de la Patagonia meridional al este de los Andes, en una zona clave para estudiar efectos del clima, especialmente por el modo y la intensidad de los vientos del oeste (westerlies), que constituyen el factor climatico dominante en la region. En este trabajo se utilizaron registros sedimentarios de polen, diatomeas y quironomidos, combinados con datos sedimentologicos y geoquimicos para reconstruir la historia ambiental de Laguna Las Vizcachas (50° 42’ S; 71° 59’ W; 1100 msnm), desde AD 400 hasta el presente. Nuestros resultados proporcionan evidencia de variabilidad climatica durante los ultimos AD 1600 . Entre los AD 400 a AD 1550, la presencia de polen de Poaceae junto con diatomeas planctonicas y pequenas diatomeas bentonicas, sugiere un aumento gradual de la precipitacion con temperaturas del aire frias y persistentes. Alrededor de los AD 1550, la disminucion de Poaceae y el aumento de diatomeas bentonicas sugieren temperaturas aun mas frias, lo cual es concordante con registros de avances glaciarios en la zona, probablemente asociados a la Pequena Edad de Hielo. La aparicion simultanea de morfotaxa de quironomidos indicadores de temperaturas frias como los Tanytarsini, apoya esta interpretacion. Desde el ano AD 1750 hasta el presente, la aparicion de polen tipo Ranunculaceae, de quironomidos semi-terrestres y litorales y ademas de diatomeas epifitas sugieren la expansion de habitats litorales que indican un descenso en el nivel de agua del lago, con menor precipitacion que los anos previos. Ademas, el aumento de las diatomeas planctonicas, Dicostella y Aulacoseira, y la fuerte disminucion de pequenas diatomeas bentonicas revelarian el inicio de un periodo de calentamiento. Por ultimo, la aparicion de polen de Rumex y Plantago se relaciona con la llegada temprana de los europeos y el posterior aumento de la actividad humana en la zona. EnglishLaguna Las Vizcachas is a remote lake located in the southern Patagonian steppe east of the Andes, in a key area to study the effects of the climate, especially the mode and intensity of the mid-latitude westerlies which are the dominant climate drivers in this region. Pollen, diatom and chironomid records combined with sedimentological and geochemical data are used to reconstruct the environmental history of Laguna Las Vizcachas (50°42´ S; 71°59´ W; 1100 masl) from AD 400 to the present. Our results provide evidence of changing climate conditions during the last 1.6 kyr. From AD 400 to 1550, the presence of Poaceae pollen together with planktonic and small benthic diatoms suggests a gradual increase in precipitation, and persistent cold air temperatures. At ca. AD 1550, the decrease in Poaceae and the high values of small benthic diatoms are interpreted as colder temperatures, which agree with nearby records of glacial advances probably associated with the Little Ice Age. The simultaneous appearance of the cold-tolerant chironomid morpho taxa Tanytarsini supports this assumption. From AD 1750 to the present, the appearance of Ranunculaceae-type pollen, semi-terrestrial and littoral chironomids and epiphytic diatoms suggest the expansion of littoral habitats indicative of lower lake levels; which implies less precipitation than previously. Additionally, the increase of both planktonic diatoms Dicostella and Aulacoseira and the sharp decrease of small benthic diatoms is interpreted as the onset of a warming period. The appearance of Rumex and Plantago pollen is related to the arrival of Europeans and subsequent increasing human activity in the area.