IIMYC   23581
INSTITUTO DE INVESTIGACIONES MARINAS Y COSTERAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Non-pollen palynomorphs, plant macrofossils and associated fauna as complementary indicators of the trophic status of shallow lakes from southern South America
Autor/es:
SÁNCHEZ VUICHARD, G.; TONELLO, M; GONZÁLEZ SAGRARIO M. A.; FONTANA, S.; STUTZ, S.; NAVARRO D.
Lugar:
Salvador, Bahía
Reunión:
Congreso; XIV INTERNATIONAL PALINOGICAL CONGRESS; 2016
Resumen:
Different fossil groups reflect different aspects of the system strengthening palaeoenvironmental interpretations. In lacustrine sediments the analysis of non-pollen palynomorphs (NPP), plant macrofossils and associated fauna are complementary to the pollen analysis. NPP comprehend mycelium and spores of fungi, cyanobacteria and clorophycean algae remains (cenobia, zygospores, colonies, akinetes, heterocysts and sheaths), cysts of dinoflagellates, testate rhizopod (thecamoebian), invertebrates remains (exoskeleton fragments, resting eggs, rotifer loricas, microturbellarian oocystes, gemmula and spicules of freshwater sponges, spines of leaves, among others). Plant macrofossils and associated fauna include seeds, fruits, spores, leaves, buds, bud-scales, flowers, tissue fragments, fragments and resting eggs of invertebrates. All these represent planktonic, benthic and plant communities of obligate aquatic organisms, as well as those living in the lakeshore area. We present results of the analysis of these fossils from eight shallow lakes located in Pampa plain (33º-39ºS; 57º- 66ºO), Argentina. Pollen, NPP and plant macrofossils and associated fauna analyzed in lacustrine sediment sequences revealed the occurrence of alternating macrophyte-dominated clear and phytoplankton-dominated turbid phases during the Holocene. At the beginning of the Holocene the abundance of Chara (gyrogonites) indicated that these lakes were clear and shallow. During the middle Holocene the presence of Chara (gyrogonites and oospores) and high amount of Peridinium cyst, denote that these lakes were clear and brackish. This condition persisted until ca. 2000 cal yrBP, when others macrophytes appeared (Tolypela oospores, Myriophyllum mericarps, Zanichellia and Ruppia fruits, Potamogeton seeds and Ceratophyllum spines), indicating a more diverse community due to a higher nutrient level. Towards ca. 700-500 cal yrBP the lakes turned to a turbid phase dominated by phytoplankton species like Pediastrum, Scenedesmus, Tetraedron (cenobia) and Gloetrichia (sheats) and became eutrophic. Cladocera (zooplankton) increased their abundance denoted by the occurrence of resting eggs (ephippia) of Daphnia, Ceriodaphnia, Simocephalus and Bosmina. The existence of turbid phase indicators as well as the presence of Nitella (oospores) and others macrophytes indicate clear phases alternating with the general turbid phase. In this multi-proxy analysis, NPP, and plant macrofossils and associated fauna in conjunction with pollen, provided an adjusted interpretation of the evolution of lakes. Also, it contributes to a better understanding of the complex network of interactions in these ecosystems, helping unravel the potential causes of the observed patterns.