Effects of sediment resuspension on the oxidation of acid-volatile sulfides and release of metals (iron, manganese, zinc) in Pescadero estuary (CA, USA)

Abstract

Bar-built estuaries are unique ecosystems characterized by the presence of a sandbar barrier, which separates the estuary from the ocean for extended periods and can naturally reopen to the ocean with heavy rainfall and freshwater inflows. The physical effects associated with the transition from closed to open state, specifically water mixing and sediment resuspension, often indirectly worsen water quality conditions and are suspected to drive near-annual fish kills at the Pescadero estuary in northern California. The effects of sediment acid-volatile sulfide (AVS) oxidation, specifically oxygen depletion, acidification, and metal release, are believed to aggravate water conditions for fish but remain poorly understood. We performed slurry incubations containing sediment from 4 sites in the Pescadero estuary, representing a gradient from the Pacific Ocean to freshwater tributaries. We measured near-maximum rates of aqueous hydrogen sulfide oxidation, sediment AVS oxidation, sulfate production, and acidification, as well as near-maximum release rates of iron (Fe), manganese (Mn), and zinc (Zn) to the water column. We estimated AVS oxidation rates of 8 to 21 mmol S kg d , which were 3 orders of magnitude higher than aqueous hydrogen sulfide oxidation rates, 6 to 26 μmol S kg d . We suggest that aqueous hydrogen sulfide cannot be responsible for the observed kills because of low concentrations and minimal oxidative effects on pH and metal concentrations. However, the oxidative effects of AVS are potentially severe, decreasing pH to strongly acidic levels and releasing aqueous Fe, Mn, and Zn concentrations up to 11.2 mM, 0.46 mM, and 88 μM, respectively, indicating a potential role in worsening water conditions for fish in the Pescadero estuary. Environ Toxicol Chem 2018;37:993-1006. © 2017 SETAC.

Effect of overlying water pH, temperature, and hydraulic disturbance on heavy metal and nutrient release from drinking water reservoir sediments

“…Then, Fe was gradually re-adsorbed by the sediments after 15 days. Richards et al, (2018) found that a considerable amount of Fe from oxides was released at low pH values. However, in this study, the initial overlying water pH values were set as 6.5, 8, and 9.…”

Particle aggregation, pH changes and metal behaviour during estuarine mixing: review and integration

“…The formation of iron (hydr)oxides is effective for the removal of trace metals under oxidising conditions, whereas the formation of sulfides can be conducive to the removal of trace metals under reducing conditions (Duan et al 2019). Resuspension and oxidation of solid FeS phases can also release dissolved Fe and other metals (Richards et al 2018). Pb has also been found predominantly in the particulate (including colloidal) fraction of rivers and estuaries (Erel et al 1991;Benoit et al 1994;Benoit 1995;Tanguy et al 2011).…”

“…The potential role of pH changes in estuaries leading to desorption of Zn from particles (non-conservative addition) is discussed and modelled further below. There can also be dynamic production of different-sized colloids, sediment : water fluxes, resuspension and sorption-desorption reactions that can affect the concentration of Zn and other metals (Benoit et al 1994;Wen et al 1999;Richards et al 2018). Duan et al (2019) found that the dynamics of Cu and Zn were primarily controlled by Fe and Mn diagenesis, and that sediment fluxes were a significant source of trace metals in the water column.…”

“…DIC isotope measurements have been found to be useful in tracing internal alkalinity sources (Atekwana et al 2003), with calcium and strontium isotopes also useful for tracing carbonate precipitation and dissolution (Shao et al 2018). Eutrophication, anoxia and elevated pCO 2 due to climate change have been implicated in observations of increased acidification in some estuaries (Cai et al 2017;Shen et al 2019), as has resuspension of volatile sulfide phases (Richards et al 2018). Spatial and temporal changes in pH in estuaries could greatly affect the sorption of trace metals and ligands to particle surfaces (Dzombak and Morel 1990), which is assessed further below.…”

“…Following deposition, mixing and redistribution of sediment phases and associated metals can occur (Reese et al 2019). Flux of metals to the water column from the sediment arises due to diffusion or resuspension and oxidation of sulfide phases (Richards et al 2018;Duan et al 2019).…”