Contamination Alters the Physicochemical and Textural Characteristics of Clays in the Sediments of the Peri Urban Reconquista River, Affecting the Associated Indigenous Microorganisms

Ana E Tufo,María Celeste Grimolizzi,Mauricio Sica,María Belén Prados,Gustavo Curutchet,Susana Vázquez,Natalia F Porzionato

doi:10.3390/min11030242

Abstract

The physicochemical and textural characteristics of river sediments and, essentially, their clays, are at the center of a network of biological and geochemical factors that are mutually modifying. Therefore, the contamination, the characteristics of the clays, and the associated microorganisms strongly influence each other. In this work, sediments from two sites of the urban Reconquista River, near Buenos Aires City, Argentina, exposed to different environmental contexts were characterized. The huge differences in the organic matter content in the vertical profile between both sediments strongly evidenced the polluted status of San Francisco (SF) site as opposed to the Dique Roggero (DR) site. Thorough physicochemical and textural characterization of the sediments and their clay fraction performed by pH, Oxidation-reduction potential (ORP), spectrophotometry, XRD, laser diffraction, N2 adsorption–desorption isotherms, EDS, and SEM measurements revealed that organic matter (DR: 41 ± 5 g kg−1; SF: 150 ± 30 g kg−1) intervened in the retention of heavy metals (DR: 5.6 mg kg−1 Zn, 7 mg kg−1 Cu, 3.1 kg−1 Cr; SF: 240 mg kg−1 Zn, 60 mg kg−1 Cu, 270 mg kg−1 Cr) and affected the level of association and the formation of mineral–organic aggregates (DR: 15 ± 3 μm; SF: 23 ± 4 μm). This can be decisive in the surface interaction required for the establishment of bacterial assemblages, which determine the biogeochemical processes occurring in sediments and have a key role in the fate of contaminants in situ and in the remediation processes that need to be applied to restore the anoxic contaminated sediments.

Highlights

The biogeochemical processes that occur in river sediments are mainly determined by the type of substrate, the electron acceptors, and other environmental parameters that together shape the indigenous microbial communities
The concentrations of inorganic ions measured in both superficial waters confirmed the differences between both sites: nitrate, phosphate, potassium, and calcium were higher at San Francisco (SF), whereas sulfate, sodium and magnesium were higher at the uncontaminated site Dique Roggero (DR)
We found important differences between two 24-km distant sites, DR and SF, of the urban Reconquista River concerning the quality of the surface waters and, mainly, the sediments

Summary

Introduction

The biogeochemical processes that occur in river sediments are mainly determined by the type of substrate, the electron acceptors, and other environmental parameters that together shape the indigenous microbial communities These processes are responsible for ecosystem health and are affected by human activity, which introduces pollution into the waters. Studying the interaction of microorganisms with the sediment clays and of both, in turn, with the contaminants, contributes to the understanding of the self-purification processes and the fate of the different pollutants discharged into the river These pollutants (i.e., heavy metals, polycyclic aromatic hydrocarbons (PAHs), organic chlorine pesticides, phenols, inorganic N compounds) are composed of untreated domestic and industrial effluents [1,2,3,4,5,6]. It is important to know how contamination affects the textural properties of the sediment, especially clays, and how this modifies the adherence of microorganisms, especially bacteria, for the initial formation of biofilms, which are relevant to the riverine biogeochemical cycles

Objectives

Methods

Results

Conclusion