Non-pollen palynomorphs, plant macrofossils and associated fauna as complementary indicators of the trophic status of shallow lakes from southern South America

SÁNCHEZ VUICHARD, G.; GONZÁLEZ SAGRARIO M. A.; STUTZ, S.; TONELLO, M; FONTANA, S.; NAVARRO D.

Congreso; XIV INTERNATIONAL PALINOGICAL CONGRESS; 2016

Differentfossil groups reflect different aspects of the system strengtheningpalaeoenvironmental interpretations. In lacustrine sediments the analysis of non-pollenpalynomorphs (NPP), plant macrofossils and associated fauna are complementaryto the pollen analysis. NPP comprehend mycelium andspores 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, rotiferloricas, microturbellarian oocystes, gemmula and spicules of freshwatersponges, spines of leaves, among others). Plant macrofossils and associatedfauna include seeds, fruits, spores, leaves, buds, bud-scales, flowers, tissuefragments, fragments of invertebrates and resting eggs. All these represent planktonic,benthic and plant communities of obligate aquatic organisms, as well as those livingin the lakeshore area. We present results of theanalysis of these fossils from eight shallow lakes located in Pampaplain (33º-39ºS; 57º- 66ºO),Argentina. Pollen, NPP and plant macrofossils and associated fauna analyzed in lacustrinesediment sequences revealed the ocurrence of alternatingmacrophyte-dominatedclear and phytoplankton-dominated turbid phases during the Holocene. At the beginning ofthe Holocene the abundance of Chara(gyrogonites) indicated that these lakes were clear and shallow. During the middleHolocene the presence of Chara(gyrogonites and oospores) and high amount of Peridinium cyst, denote that these lakes were clear and brakish.This condition persisted until ca. 2000 yrBP, when others macrophytes appeared (Tolypela oospores, Myriophyllum mericarps, Zanichelliaand Ruppia fruits, Potamogeton seedsand Ceratophyllum spines), indicatinga more diverse community due to a higher nutrient level. Towards ca. 700-500 cal yrBP the lakes turned toa turbid phase dominated by phytoplankton species like Pediastrum, Scenedesmus, Tetraedron (cenobia) and Gloetrichia (sheats) and becameeutrophic. Cladocera (zooplankton) increased their abundance denoted by theoccurrence of resting eggs (ephippia) of Daphnia,Ceriodaphnia, Simocephalus and Bosmina. The existence of turbid phaseindicators as well as the presence of Nitella(oospores) and the others macrophytes indicate clear phases alternating withthe general turbid state. In this multi-proxy analysis, NPP, and plant macrofossils andassociated fauna in conjunction with pollen, provided an adjustedinterpretation of the evolution of lakes. Also, it contributes to abetter understanding of the complex network of interactions of these ecosystems,helping unravel the potential causes of the observed patterns.