Macroinfaunal Distribution at an Organic-Enriched Estuarine Harbour: Quequén Grande River Inlet, Argentina
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GRAVEL ISSN 1678-5975 Dezembro - 2011 V. 9 – nº 1 57-67 Porto Alegre Macroinfaunal Distribution at an Organic-Enriched Estuarine Harbour: Quequén Grande River Inlet, Argentina Godoy, C.E.1; Isla, F.2 & Elías, R.1 1 Departamento de Ciencias Marinas, Universidad Nacional de Mar del Plata. Funes 3350, Mar del Plata, Argentina ([email protected]). 2 Instituto de Geología de Costas y del Cuaternario, Universidad Nacional de Mar del Plata. Casilla de correo 722, Mar del Plata, Argentina. ABSTRACT Estuarine benthic assemblages are highly sensitive to pollution. At the same time, they are sensitive to chemical and/or physical changes induced by tides or floods. The estuary of the Quequén Grande River is occupied by a harbour with a constant trading of cereals. Benthic communities are best environmental indicators. In order to evaluate the health of the harbour, a limited sampling of infaunal benthic community was carried out. Nematodes and Capitella "capitata" sp. were the most common species. As the harbour is enriched in organic matter derived from the cities of both margins and the jetties inhibit wave or wind action on the bottom, anoxic conditions prevail almost all year. Therefore, the disposal of the anoxic muds dredged is matter of concern in relation to resort beaches. Peak discharges of the river, constant dredging and the enrichment with organic matter are explaining the present distribution and abundance of these communities. Palavras chave: macrobenthos, Quequén Harbour, multivariate analyses. 58 Macroinfaunal Distribution at an Organic-Enriched Estuarine Harbour: Quequén Grande River Inlet, Argentina INTRODUCTION De Ferrera, 1998; Cortizo & Isla, 2000; Perillo et al., 2004). The area was also of concern in Benthos is particularly sensitive to any type relation to urban sewage disposals (Polizzi, of substrate (Elías et al., 2004), but in coastal 2006). To the headlands of the harbour there are areas and estuaries the salinity becomes the most recreational activities related to nautical sports important conditioning factor. Pollution can be and fishing facilities. The watershed is another significant variable affecting highly asymmetric receiving water from the left populated and industrialized areas (Estacio et margin. River discharge usually increases during al., 1997), increasing in low-energy sectors. summer months between a minimum of 6 to a Organic matter derived from domestic wastes is maximum of 167 m3/s (Teruggi et al., 2005). a common pollutant in highly populated areas In this paper, the distribution of subtidal (Méndez, 2002); the increase in nutrients leads macrobenthic community from a harbour to euthrophication. Marine benthic communities, located at the outer marine sector of the especially the macrobenthic infauna (>0.5 mm Quequén estuary was analyzed. Its distribution in body length), have been widely regarded as is related to environmental variables of water bioindicator for monitoring coastal pollution. (salinity, temperature, pH, turbidity) and Sessile infauna is sensitive to environmental sediment (grain size and organic-matter changes such as nutrient and oxygen content). concentration. The principal effects of organic wastes when is incorporated to the sediments are MATERIALS AND METHODS hypoxia (low content in oxygen), anoxia (lack of oxygen) and alteration of the benthic structure Study area (composition, diversity, abundance). The communities become qualitative and structurally The Quequén Grande River is located to the simpler, been the opportunistic k-strategic south of Buenos Aires Province (38º40'S; species replaced by the r-strategic species. 58º45'W), flows to the south of the Tandilia Benthos respond quickly to environmental Range. In its meandering reaches the width is changes, frequently showing an ecological slightly variable between 150 and 200 m and succession. Such changes are within the depth fluctuates between 2 and 4 m (Piccolo & community rather than between communities Perillo, 1997). The construction of the Quequén (Pearson & Rosenberg, 1978). Sensitive species Harbour sued, in addition to the construction of disappear, and only few species can tolerate it jetties, the dredging of the last 2 km of the and eventually proliferate. In an extreme estuary (Fig. 1). Accordingly, in harbour the situation the macrobenthos community can depth reaches 10 – 12 m and the circulation is disappear. Benthic organisms are also of special very low. Sea water dominates at the bottom concern to analyse the results of dredging during common tides; however this pattern may activities, involving not only grain-size be completely altered after peak discharges variations but also total organic carbon (TOC) (Perillo et al., 2004). The magnitude of flooding effects (US Army Corps of Engineers, 1996). is important because they are significant and Harbours from the Southern Hemisphere are fairly frequent. One of the largest occurred in poorly known in terms of their infaunal 1980 with peaks of 200 m3/s that destroyed the communities. There are only some rapid three major bridges of the estuarine area (Perillo characterisation of the sewage outlets at the et al., 2004). The major sources of ports of Montevideo (Danulat et al., 2002; contamination are the urban outfalls of Muñiz et al., 2004) and Mar del Plata (Rivero et Necochea and Quequén that discharge their al., 2005). Dealing with the Quequén Harbour, wastes directly into the system (Polizzi, 2006). foraminifera, gastropods and bivalves At the harbour, there are also illegal sewer distributions were related to the salinity regime disposals. Necochea has a Combined Sewer (Boltovskoy & Boltovskoy, 1968; Wright, 1968; Outfall (CSO) to the estuary for storm events. Lopez-Gappa et al., 1990; De Francesco & Isla, Quequén harbour is subject to common 2003; Adami et al., 2004). The physics of the accidental dumping of cereal grains (Perillo et estuary is clearly related to the tidal and fluvial al., 2004) and, the Power Plant discharges water effects (Piccolo & Perillo, 1997; 1999; Campo 5-7ºC higher than the estuary (Wright, 1968). GRAVEL Godoy et al. 59 Figure 1. Location map and of sampling stations. Sampling was performed on 15 May, 2007 Multivariate analyses were performed by with a Pomar type grab (0.025 m2). Sampling means of the PRIMER program (Plymouth design include 10 sites within the harbour, and Marine Laboratory, UK) analyzing changes in four outside sites (as reference). However only 5 abundance and species composition. The stations could be sampled, with three replicates ordination was carried out with the each (2 in station 5). Station 1 was located in the multidimensional scaling (MDS) on the inner harbour, called “Broken Bridge”, adjacent untransformed abundance of all benthic species to a discharge of an outfall of Necochea (CSO). and the similarity percentage analysis (SIMPER) The subsequent sampling sites were located to discriminate the species that most contributed towards the inlet: stations 2 and 4 in the vicinity to differentiate stations. The average of the of the docks and, station 3 in the centre of the species richness (S), the mean abundance (A), port. Station 2 was front of Silos (cereals the Shannon diversity index (Shannon & deposits). Station 5 is almost in front of the Weaver, 1963) and the evenness index (Pielu, discharge of the cooling waters of the 1969), were calculated for each station. A one- Thermoelectric Power Plant. way ANOVA test was carried out with these Environmental variables in the water column parameters in order to establish differences (salinity, temperature, pH, turbidity and depth) among stations (Zar, 1984). were measured in situ using a water-quality checker Horiba U-10. Sediment samples in each RESULTS station were obtained for grain size analysis and organic matter content. The cereal seeds find A total of 2,137 individuals representing 15 into the sediment were also counted. The taxa were determined (Tab. 1). More than 97% samples were sieved through a 0.5 mm mesh, of the total abundance corresponded to only 4 and the retain organisms fixed with 5% taxa: Nematods, Capitella "capitata" sp., Alitta neutralized formaldehyde on board. In succinea and Onuphis dorsalis. laboratory the material was transferred to alcohol 70% after the identification and Multivariate analysis quantification of specimens under stereoscopic microscope. Sediment samples were also sieved The multidimensional scaling analysis through a mesh of 0.0625 mm to separate sand (MDS) of the average abundance (stress= 0) did from mud (silt and clay). The titration method of not clearly discriminate groups, although Walkley & Black (1970) was used to quantify represent almost exactly the spatial sampling the organic matter content in sediments, and pattern (Fig. 2). expressed in percent of mud and sand. GRAVEL 60 Macroinfaunal Distribution at an Organic-Enriched Estuarine Harbour: Quequén Grande River Inlet, Argentina Table 1. Abundance of specimens collected in all simples. Taxa Abundance (%) Nematods 74,400 Capitella "capitata" sp. 20,960 Alitta succinea 1,450 Onuphis dorsalis 0,840 Laeonereis culveri 0,560 Paraonidae indet. 0,470 Polychaete indet. 0,420 Pelecypod indet. 0,280 Syndesmia sp. 0,190 Glycera americana 0,140 Cyrtograpsus angulatus 0,046 Parandalia tricuspis 0,046 Lumbrineris tetraura 0,046 Tellina sp. 0,046 Nucula puelcha? 0,046 (CSO), dominated exclusively by Nematods; b) Stations 2 and 4, located in the docks, dominated by Nematods and Capitella "capitata" sp., accompanied by Alitta succinea; c) Stations