Chironomids as Indicators of Paleoproductivity in the Pampa Region, Argentina.

MONTES DE OCA, MF; MARTIN,R.; MASSAFERRO, J.; LAPRIDA, CECILIA

Mendoza

Congreso; 4th International paleontological congress; 2014

IPA

The subfossil assemblages of chironomids are broadly utilized in mid latitudes of South America as biological proxy to reconstruct at high resolution the paleotemperature. Most of these researchers were conducted in the South of Argentina. On the other hand, subfossil chironomids provide information to reconstruct the trophic status of lakes, their assemblages respond rapidly to changes that occur in concentrations of nutrients (N, P), presence of heavy metals, increase of organic matter, etc. However, in Argentina this insect group is scarcely used in paleolimnology studies as an indicator of paleoproductivity. The subfossil chironomids of the Pampa region would provide an opportunity for an interesting case study because most Pampean lakes show changes in their trophic state (productivity). These changes are related to regional climatic fluctuations and anthropic activities that alter drainage in the catchment area (for example, intensive soy harvest with fertilizer application). In this study, preliminary result of chironomids assemblages analyses from ten lakes of Pampa region, Argentina (36°S, 62°W), are presented. We also reveal the potential of Pampean chironomids as biological proxy in order to provide evidence of changes in lakes productivity in the Pampa region. We analyzed superficial sediments samples of 10 lakes from Pampa region. These samples were collected in the summer 2014, using a dredge or short corer. Samples for chironomid analysis (3gr wet) were disaggregated in warm 10% KOH solution and sieved. All chironomid head capsules were picked under a binocular microscope and mounted on slides using Hidromatrix©solution. A minimum of 35 head capsule were mounted. The chironomid head capsules were identified using taxonomic keys. Preliminary result revealed that assemblage Polypedilum/Chironomus/Goeldochironomus/Dicrotendipes could be associated to hipereutrophic conditions lakes. The ultimate goal is to retrieve more ecological information about the subfossil chironomids taxa present in the Pampa region and recognizing these taxa as reflecting of productivity. We will expect to the Pampean chironomid assemblages allow recognizing and separate the climatic of anthropic signal. The subfossil assemblages of chironomids are broadly utilized in mid latitudes of South America as biological proxy to reconstruct at high resolution the paleotemperature. Most of these researches were conducted in the Southern South America (Argentina and Chile). On the other hand, subfossil chironomids provide information to reconstruct the trophic status of lakes, their assemblages respond rapidly to changes that occur in concentrations of nutrients (N, P), increase of organic matter, etc. However, in Argentina this insect group is scarcely used in paleoproductivity of lakes studies. The subfossil chironomids of the Pampas would provide an opportunity for an interesting case study because most Pampean lakes show changes in their trophic state (productivity). These changes are related to regional climatic fluctuations and anthropic activities that alter drainage in the catchment area (for example, intensive soy harvesting with fertilizer application). In this study, we present a preliminary result of subfossil chironomids from ten lakes of Pampa region, Argentina (36°S, 62°W. This study reveals the potential of Pampean chironomids as paleoproductivity biological proxy The ultimate goal is to retrieve more ecological information about the subfossil chironomids taxa present in the Pampa region and recognizing these taxa as reflecting of productivity. We will expect to the Pampean chironomid assemblages allow recognizing and separate the climatic of anthropic signal. We analyzed superficial sediments samples of 10 lakes from Pampa region. These samples were collected in the summer 2014, using a dredge or short corer. Samples for chironomid analysis (3gr wet) were disaggregated in warm 10% KOH solution and sieved. All chironomid head capsules were picked under a binocular microscope and mounted on slides using Hidromatrix© solution. A minimum of 35 head capsule were mounted and identified using taxonomic keys (Walker 2001, Cranston, 1997). Our preliminary results show the appearance of Polypedilum/Chironomus/Goeldochironomus/Dicrotendipes assemblage in most of the hipereutrophic lakes. The hypereutrophic state of these lakes could be related to a marked increase (near 1990) in agricultural activity that developed in the catchment area, with intensive soybean production with the widespread use of pesticides and fertilizer (Scuffed et al., 2012 Viglizzo et al. 2002). We then can interpret the occurrence of that assemblage as related to high productivity conditions.