Trace metal concentrations in soil-plant complex in rocky shore salt marshes of Central Patagonia

Highlights

• Metals on marshes of the Nuevo Gulf tend to accumulate on the southern coastal edge.

• Cd, Pb, Cr and Ni showed anthropic enrichment and the other metals a natural origin.

• Fe and Al were higher in soil than in plant, and Pb, Cu and Zn were all similar.

• Cr and Ni were abundant as pseudototal and showed a high bioaccumulation in roots.

• Cd was scarce in the soil and was mostly concentrated in Spartina’ roots.

Abstract

Population growth and industrialization involve environmental problems, such as metal pollution, and coastal environments are particularly susceptible to such issues. Within this framework, we aimed: (i) to determine the levels of trace metals in soils and Spartina densiflora tissues in rocky shore marshes of Central Patagonia; (ii) to relate metal concentration patterns in the different soil-plant complex fractions to environmental conditions; and (iii) to investigate whether geographical metal concentration patterns can be explained with anthropogenic influences and sources and/or by local prevailing biogeochemical processes. For this purpose, soil samples and associated vegetation were collected in five rocky shore marshes located at different distances from an urban or industrial area. The concentration of Al, Cd, Cr, Cu, Fe, Ni, Pb, and Zn in soils (pseudototal and bioavailable) and in plants (roots and shoots) was determined. Then the enrichment factor, bioaccumulation and translocation factor were calculated. The soil mineralogy and the behavior of these metals according to different soil variables were discussed. The results showed different behavior and level of anthropic impact according to the metal considered. Salt marshes located on the southern edge of the Nuevo Gulf showed the highest concentrations of metals. Fe, Al, Cu and Zn showed mostly a natural origin. Fe and Al were mainly in soils rather than in plants, while Cu and Zn were similarly distributed in both matrixes. Although Cd in soils showed enrichment, it would have a natural origin. Also, it was scarce in the soil and was mostly concentrated in Spartina’ roots. Pb, Cr and Ni showed anthropic enrichment too, being mainly derived from the port and industrial activities. Pb had significant representation in all soil-plant subsystems and showed the highest bioavailability in soils. Cr and Ni, were found in high concentration in the soil and showed a high bioaccumulation in roots. The human impact level in rocky shore marshes of the Nuevo Gulf in Central Patagonia associated to the trace metals pollution varies from being scarce to significantly important, with the marshes located in its southern margin showing the worst scenarios.

Introduction

Salt marshes are considered one of the most valuable environments due to several ecosystem services that are provided, such as food, shelter, refuge, a place of reproduction for several animal species, coastal protection, water purification through the filtering of nutrients and other pollutants, carbon sequestration, as well as a variety of touristic, recreational and educative uses (Barbier et al., 2011). Such circumstances have led to a notable worldwide increase in research activity for these ecosystems, not excluding the Argentinian’ salt marshes (Alberti et al., 2007; Botté et al., 2008; Daleo et al., 2011; Negrin et al., 2016; among others) and in particular, Patagonian’ salt marshes which were oblivious to this trend during the last few decades. Most of these Patagonian studies were focused on ecological patterns and processes (e.g., Alberti et al., 2007; Daleo and Iribarne 2009; Idaszkin et al., 2011; Sueiro et al., 2011, 2012; Firstater et al., 2016), while others were interested in deleterious effects pursuing environment-related issues, for example, biological invasions (Schwindt et al. 2009, 2020; Mendez et al., 2012; Sueiro et al., 2013) or pollution (Marinho et al., 2013, 2017; Idaszkin et al., 2014, 2015, 2017a,b,c; Pollicelli et al., 2018).

Trace metals are natural components of ecosystems that can be augmented through anthropogenic activities, and inclusively reaching toxic levels for the organism that inhabit there (Kabata-Pendias and Pendias 2000). As intertidal environments, salt marshes, are susceptible to trace metal pollution, being that pollutants wasted in the sea could spread into the intertidal zone during each high tide period (Hung and Chmura 2007). In this way, these environments can capture trace metals of the sea, and depending on the metal and the physico-chemical features of the environment (pH, organic matter content, clay fraction content, mineralogical composition, salinity, redox potential, among others), they could remain in the soil or be absorbed by the biota (Reboreda and Caçador 2007). Also, plants inhabiting salt marshes play an essential role in the behavior of trace metals, by reducing tidewater flow favoring the sedimentation of transported particles and associated trace metals, and/or for being able to produce chemical changes in the soil, affecting metals' mobility, speciation, bioavailability and distribution (Duarte et al., 2010). Depending on soil condition, the metal and the plant species, salt marsh plants can absorb the metals accumulating them in the roots or through translocation metals accumulations are found in their aerial structures (Weis and Weis 2004). In fact, several studies have indicated that salt marsh plants have a crucial role in metal dynamics in these environments by affecting the biogenic cycle of metals (e.g., Almeida et al., 2006; Reboreda and Caçador 2007; Cambrollé et al., 2008; Duarte et al., 2010).

There is a complex of rocky shore salt marshes of little expansion in the vicinity of the city of Puerto Madryn, Chubut, Argentina (Bortolus 2010), all located on the Nuevo Gulf coast (~81000 inhabitants in 2010; INDEC) where the most important industrial activities are related to aluminium production. These industries are located inside the city leading to significant port activity. Tourism and fisheries are also important in this city, which also implies port movement. All these activities are potential sources of pollutants, that could be transported in the seawater or the air spreading from close areas to long distances before being deposited (Alloway 2010). Previous studies showed that sediments of the port zone have high concentrations of total aliphatic and aromatic hydrocarbons (Commendatore and Esteves 2007; Bigatti et al., 2009) as well as of trace metals (Gil et al., 1999; Primost et al., 2017). However, these substances can also reach nearby salt marshes and can accumulate in both soil and plants. These salt marshes are mainly inhabited by the cordgrass Spartina densiflora, which demonstrate a high tolerance and a capacity to accumulate vast amounts of different metals in their tissues, mainly in the roots (Cambrollé et al., 2008; Redondo-Gómez 2013; Idaszkin et al. 2014, 2015). Accordingly, the aims of this work were: (i) to determine the levels of trace metals in soils and Spartina densiflora tissues in rocky shore marshes of Central Patagonia; (ii) to relate metal concentration patterns in the different soil-plant complex fractions to environmental conditions; and (iii) to investigate whether geographical metal concentration patterns can be explained with anthropogenic influences and sources and/or by local prevailing biogeochemical processes.