Evaluation of Natural Processes and Human Inputs on Riverine Sediments at Nahuel Huapi National Park, Argentina†

EVALUATION OF NATURAL PROCESSES AND HUMAN INPUTS ON RIVERINE SEDIMENTS AT NAHUEL HUAPI NATIONAL PARK, ARGENTINA† G. Román Ross*, S. Ribeiro Guevara, M.A. Arribére and A.J. Kestelman Laboratorio de Análisis por Activación Neutrónica Centro Atómico Bariloche. Comisión Nacional de Energía Atómica 8400 Bariloche. Río Negro. Argentina. *CONICET, Argentina ABSTRACT River bed sediment and suspended load samples were collected from pristine and human disturbed areas at Nahuel Huapi National Park, North-Western Patagonia, Argentina. The aim of the present work is to obtain baseline heavy metal concentration values in the region and to study the impact of human activities in the riverine systems. The identification of the origin of the sediments was achieved by studying the rare earth and other immobile elements behavior. The elemental concentration determinations were performed by means of Instrumental Neutron Activation Analysis (INAA) at RA-6 Research Reactor, complemented by Atomic Absorption Spectrophotometry (AAS). A leaching study with HCl 0.5 N and 3.5 N was performed to discriminate the total non residual (TN-R) of the following heavy metals: Cu, Pb, Ni, Zn, Mn and Fe. Speciation procedures were applied for fluvial sediments determining adsorbed metals, those associated with the organic matter and with Fe and Mn oxides. Cu and Pb are mainly associated to Fe and Mn oxides; although Pb maintains this behavior along the river (except in one urban sampling point in which it is associated strongly with organic matter), Cu increases its association with organic matter while approximating to the river mouth in the urban areas. Heavy metal enrichment factors were calculated for rivers and streams flowing in urban and periurban areas, showing values of Cr, Cu, Pb and Zn factors above the baseline. I. INTRODUCTION studies have pointed sediments as optimal sampling material because they reflect the biological, chemical and In later years there has been a marked increase in physical conditions of an ecosystem [1]. the number of studies devoted to establish the behavior of The evaluation of the effects of urbanization, some elements in the earth crust, and also to monitor the industrialization and sprawling settlements around coastal contaminants introduced by human activities into water areas, is achieved by applying different analytical streams and in the atmosphere. procedures. Some of the most popular are: total metal Waters and aquatic sediments are the main determinations, extraction of total non-residual (TNR) receptacles of heavy metals produced by anthropogenic heavy metals and, more recently, sequential extractions to discharges into waterbodies. The interaction water- determine heavy metal speciation. Several authors have sediment is highly complex due to different factors that discussed about their advantages and disadvantages [2-4], affect the behavior of trace elements in this environment. but some controversies still remain. During transport, the most important changes are To assess provenance, transport and weathering of controlled by the hydrological sorting and the sediments we used extended normalized patterns including environmental parameters. Due to the influence of currents rare earth, immobile and mobile elements. This graphical and point and diffuse discharges in water sampling, some † This study is an integral part of a project carried out within the framework of the IAEA Research Contract N°8409/RB. tool is very useful to identify natural processes in [8]. This technique provides a rapid evaluation of the sedimentary environments [5, 6, 7]. pollution and was successfully used to assess total non- The aim of the present work is to study areas residual (TNR) heavy metal concentrations in coastal affected by contamination due to human activities, and sediments [8] and in stream sediments [9]. Fe, Mn, Ni, Cu, compare the results with those obtained in unpolluted Zn and Pb were analyzed by direct aspiration of the areas. solution in an atomic absorption spectrophotometer (A.A.S.). The sediments also were subjected to sequential extractions following the heavy metal speciation technique II. SAMPLING AND METHODS described by Salomons and Förstner [10]. Total sample concentrations were determined by Study area and sampling. Nahuel Huapi National Park is Instrumental Neutron Activation Analysis (INAA) in the located in northern Patagonia, Argentina (71° W, 41° S). RA-6 Bariloche research reactor. The measurements were In this study, we have selected the Upper Manso River, a performed with a 67 cm3 ORTEC HPGe intrinsic-N pristine watershed, and the southern area of Lake Nahuel coaxial detector which has an efficiency of 12.3 % relative Huapi where Bariloche city is settled (Fig. 1). Also, we to a 7.6 x 7.6 cm NaI(Tl) crystal at 1.33 MeV and 25 cm considered the Limay River, which acts as water collector distance. Data collection was performed in 4096 channels of Nahuel Huapi drainage area. The main commercial with a Nuclear Data ND76 multichannel analyzer, and activity of Bariloche city is the tourism and it has not analyzed for peak position and intensity in a personnal industrial activities. The geology of the region is mainly computer [11]. composed by volcanic and sedimentary rocks. The most The samples, ranging in mass from 90 to 200 mg, modern deposits include glacial and fluvioglacial were placed in plastic vials with a final disk sample shape accumulations. of 1 cm in diameter and from about 0.10 to 0.20 cm Five samples were taken in the Upper Manso thickness. The filters with the suspended material, plus an River and Lake Mascardi drainage area: VN in the river unused filter, were assembled individually in sealed plastic headwater, CO and PL in two affluent streams, RM close bags. to Mascardi lake and LR after the lake. In the southern The samples were irradiated for 7 to 9 hours in the area of Lake Nahuel Huapi, we sampled the Ñirihuau River reactor core (thermal flux ~ 9.0 x 1012 cm-2 s-1, epithermal (ÑH samples) and two streams: Gutiérrez and Ñireco (GZ flux ~ 3.5 x 1011 cm-2 s-1 ) . The samples were irradiated and ÑC samples) in spring and fall (indicated by 1 and 2 inside an aluminum can together with two sets of two respectively). On the Limay river we also sampled five monitors each set, namely: Co (~1 mg) and 0.112 % Au-Al sites: BL on Nahuel Huapi lake, CF at the confluence of (~ 1 mg). One of these sets was positioned at the bottom of Traful river, NQ at Neuquén city and L1 and L2 in the can, the other set at the top (that is, about 6 cm apart between Traful river confluence and Neuquén. one from the other) to correct for non-uniformity in both the thermal and epithermal fluxes. After irradiation the filters with the suspended material were folded and tightly packed to a final disk shape of 1 to 2 cm in diameter. Two measurements were performed for each sample: the first one after 5 to 9 day decay and the second after 10 to 20 day decay. The thermal and epithermal neutron fluxes were determined with the Co and Au-Al monitors, and the concentrations were determined using absolute methods. The fundamental constants and nuclear parameters were taken from current tables [12-15]. All concentration values reported refer to dry weight samples. To check the quality of the results, standard reference materials (IAEA SOIL-7 and SL-1) where analyzed together with the samples following the same analytical procedure. III. RESULTS AND DISCUSSION Fig. 1: Study area Total non residual (TNR) metals. In the Upper Manso River, the total non-residual metal contents are very low, Analytical methods. The river bed sediments were with higher contents for Zn and Fe. collected by means of plastic spoons, taking special care of In the streams, the concentrations of Cu manifest an not losing the fine fraction. Samples were dried and sieved increase with respect to Upper Manso River samples. A with a 63 µm stainless steel mesh. The < 63 µm material noticeable increase in Pb contents were observed in ÑC2. was subjected to acid leaching with HCl 0.5 N and 3.5 N Zn, Mn and Fe concentrations showed very constant following the methodology used by Chester and Voutsinou values. Seasonal variations were not observed in any of lake. This agree with previous observations by Chester et these watersheds. al. [9] concerning the Pb host fraction, which has been In Limay River, all the elements exhibited a non identified as the oxides in both natural or polluted variable behavior with a gradual increasing trend in Pb, Zn sediments. In the Limay river, the Pb-OM association y Mn concentrations from the headwaters to Neuquén city. increases downstream. The Ñireco stream is the one of the points of interest, because it shows the highest Pb values, especially Heavy metal speciation. The great importance of the close to the mouth, where it flows across Bariloche city. research on heavy metal speciation is due to the fact that a There is an increase in the Pb-OM association compared to change in speciation causes a change in the bioavailability. the Fe and Mn oxides. In order to simplify the analytical requirements, we Zn is highly associated to organic matter in the considered three fractions: adsorbed metals, metals Upper Manso river, however this trend is changed for the associated to Fe/Mn oxides and metals associated with LR sample, where Zn is associated to the Fe and Mn organic matter. The total amount was calculated as the oxides. In the Limay river Zn distribution is uniform along sum of these three fractions. Results are presented in the catchment, with some variations close to Neuquén city. figure 2. The Fe and Mn speciation diagrams show similar The phenomenon of adsorption is developed in fine patterns.

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