Temporal variability in potentially toxic elements (PTE’s) and benthic Foraminifera in an estuarine environment in Puerto Rico Michael Martínez-Colón1, Pamela Hallock2, Carlos R. Green-Ruíz3 and Joseph M. Smoak4 1
2
School of the Environment, Florida A&M University, Tallahassee, FL, USA College of Marine Science, University of South Florida, St. Petersburg, FL, USA 3 Unidad Académica Mazatlán, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Mazatlán Sinaloa, México 4 Environmental Science, University of South Florida, St. Petersburg, FL, USA email: michael.martinez@famu.edu
ABSTRACT: Bulk concentrations of PTEs (potentially toxic elements) were assessed and compared with foraminiferal assemblages from core sediments from TL (Torrecillas Lagoon), on the north coast of Puerto Rico. Temporal distributions of mud, Fe, Al (proxy for terrigenous sedimentation), and rhenium (proxy for anoxia) reflected changes in land use within the drainage basin associated with human activities over the past century. The mud-dominated sediments provided a major “sink” for PTEs, while Fe oxides and sulfides served as a secondary “sinks”. Temporal variability of Re revealed intervals of aerobic vs anaerobic conditions in the lagoon. The dominant foraminiferal taxa, Ammonia beccarii, Quinqueloculina rhodiensis, Quinqueloculina seminula, and Ammobaculites agglutinans, coupled with low foraminiferal densities and species diversities, as well as barren samples, are characteristic of stressed estuarine environments. Overall bulk concentrations of Cu and Zn negatively correlated with foraminiferal absolute/relative abundances, diversity indices and incidences of test deformities. However, there are no correlations with the assumed bioavailable counterparts (F2Tess-Cu and F2Tess-Zn) were observed. These results indicate that fractionation of PTEs need to be considered in relation to their biological significance to foraminiferal ecology, which may differ substantially from bioavailability to metazoans that ingest sediments. The application of the acid-soluble F2Tess is not recommended in environmental studies using foraminifers as bioindicators, as PTEs in this fraction are likely not bioavailable to these protists. Keywords: Heavy metals, Foraminiferal Ecology, Fractionation, Bioavailability, Hypoxia
INTRODUCTION
Estuaries are unique ecotones that provide habitat for numerous organisms, as well as ecosystem services including nursery and feeding grounds for developmental stages of neritic and coastal marine species. Unfortunately, in addition to natural stressors, these coastal ecotones receive copious amounts of pollutants as a consequence of industrialization and coastal urbanization (Balachandran et al. 2006; Zitello et al. 2008; Seshan et al. 2010; many others). Numerous studies worldwide have assessed estuarine resiliency in response to stressors such as sewage (Abu-Zeid et al. 2013) and PTEs (Martínez-Colón et al. 2009, 2018). Estuarine environments are well known as sinks of PTEs, organic pollutants, and more recently, microplastics (e.g., Ling et al. 2017; Sharma and Chatterjee 2017). In addition, PTE (re)mobilization and potential bioaccumulation are dependent upon solubility in seawater, salinity, type of organic matter among other factors (e.g., Martínez-Colón et al. 2009). The impacts of PTEs on macro-/microbiota are highly dependent on bioavailability, concentration, and duration and timing of exposure (Pinto 2003). As PTEs have long lasting effects on the overall health of an estuary, they impact the diversity and abundance of benthic foraminifers (Yanko et al. 1998; Martins et al. 2015), thereby providing useful bioindicators of such pollution.
The TL (Torrecillas Lagoon) in northern Puerto Rico is influenced by many point and nonpoint sources of pollution (e.g., sewage discharge, boat marinas, etc.) (text-fig. 1). Several studies have characterized and documented the presence of PTEs in sediments, water or tissue samples (fish, clams, etc.) along with anoxic conditions, high fecal coliform counts and excess of nutrients (Ellis and Gómez-Gómez 1976; Ellis 1976; Webb and Gómez-Gómez 1998; SJBE 2000; SJBE 2009; Martínez-Colón and Hallock 2010; and Martínez-Colón et al. 2018). Only two studies have documented organic pollutants (e.g. PCBs, Dieldrin, etc.) from surface and core sediments of TL (San Juan Bay Estuary 2000; Webb and Gómez-Gómez 1998). For example, Vistamar, Villa Carolina, and Round Hills sewage treatment plants discharged into Quebrada Blasina until 1986, when the effluents were redirected towards the Carolina Regional Sewage Treatment Plant (SJBE 2000). Raw sewage from the Vistamar collection system occasionally reaches TL due to overflow (SJBE 2000). Ecological indicators allow assessment of environmental conditions and trends over time (Dale and Beyel 2001). Bioindicators of environmental stress in estuarine environments can be very useful in identifying sources of pollution (Pinto et al. 2009; Bouchet et al. 2012; Emrich et al. 2017). Over the past 50 years,
Micropaleontology, vol. 63, no. 6, text-figures 1–9, table 1, appendices A–H, pp. 357–381, 2017
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