Holocene changes in trophic states of shallow lakes from the Pampa plain of Argentina

Abstract

Changes in trophic status of shallow lakes from the southeastern Pampa plain of Argentina are evaluated based on the relative presence of submerged macrophytes and phytoplankton. The evolution of lake Lonkoy is reconstructed for the last 5000 years, using pollen, non-pollen palynomorphs (NPPs) and macrofossil remain analyses, revealing three main lake stages. A macrophyte-dominated clear lake prevailed until 670 cal yr BP. Afterwards, the lake changed to a turbid phytoplankton-dominated state. Recently, the lake has turned to a turbid phase, caused by resuspended sediment. These results are compared with two other paleolimnological records from the region, lakes Hinojales and Nahuel Rucá, revealing a similar late-Holocene evolution, with a shift from a macrophyte- to phytoplankton-dominated lake, occurring at broadly the same time. The shift of states may be attributed to a shift in climate after 1000 cal. yr BP towards wetter conditions during the Medieval Climate Anomaly.

Mid-late Holocene lake levels and trophic states of a shallow lake from the southern Pampa plain, Argentina

“…Higher values of Fe (Fig. 4) could be related to human disturbance since 1900 AD, in coincidence with the beginning of intense agricultural activities in the area (Stutz et al, 2012). Since ~AD 1950 (Subunit 4.2) there is a shift to a Sc3, when enhanced productivity and thermal stratification of the lake promoted oxygen depletion.…”

“…Tonello and Prieto (2010) pointed out a shift towards more humid conditions since 2000 yr cal BP, in coincidence with the shift to a turbid Sc1 state and high lake levels in Lake La Brava (Unit 3). Frequent fresh water and humid pulses between 1200-670 BP have been also recognized in some shallow pampean lakes (Stutz et al, 2012). Tonello and Prieto (2010) recognized semiarid conditions for the last 500 years.…”

“…According to Quirós et al (2002), the pristine state of small pampean lakes was clear, and most of them became turbid as a consequence of the expansion of the agriculture frontiers. Stutz et al (2012) explored successfully alternative states in shallow pampean lakes in centennial time-scales and provided evidence of changes in trophic states and shift between turbid and clear since 1000 yr BP.…”

“…Few studies have inferred the environmental history of shallow lakes in the southern Pampa plain during the Holocene (Stutz et al, 2002(Stutz et al, , 2006(Stutz et al, , 2012Borel et al, 2003;Fontana, 2005;Valero Garcés, 2009). One of these studies has reconstructed the water level of Lake La Brava over the past 4800 years based on rock magnetic, pollen, and geochemical analysis suggesting periodic climatic changes from cooler to warmer and humid conditions (Irurzún et al, in press).…”

Reconstrucción paleohidrológica de la Salina de Ambargasta(Argentina) durante los últimos 45000 años mediante geoquímica de isótopos estables

“…Durante esta etapa, una expansión de las planicies fangosas capilares con sedimentación siliciclástica dominante (AB-1-A y AB-2-E) indicó una disminución de la precipitación efectiva. Stutz et al (2012) analizaron polen, palinomorfos no polínicos, macrorestos vegetales y fauna asociada en la laguna Lonkoy en la Llanura Pampeana Argentina y encontraron que desde Boletín de la Sociedad Geológica Mexicana / 2017 / 521 DISCUSIÓN / CONCLUSIONES el Holoceno Medio hasta los 2000 años cal. AP existieron fases claras en el ambiente lacustre indicando condiciones más secas que las actuales, fluctuaciones de sequía e inundaciones y/o alta evaporación.…”