Spatiotemporal Variation of Trace Elements and Stable Isotopes in Subtropical Estuaries: II. Regional, Local, and Seasonal Salinity-Element Relationships

Abstract

Trace elements and stable isotopes are commonly used in chronologically formed biominerals as proxies of temperature and/or salinity in estuarine and marine environments. To accurately use the chemistry of biominerals as salinity proxies, understanding the consistency of dissolved element-salinity relationships across spatiotemporal scales is essential. We examined relationships between dissolved Ba:Ca, Sr:Ca, Mg:Ca, Mn:Ca, δ 18 O, and salinity on regional, local, and seasonal scales in the lower portions of subtropical estuaries (salinities 15-42 ppt) of Texas, including locations where seasonal alternations between negative and positive estuaries can occur. Across all spatiotemporal scales, Ba:Ca displayed a negative linear relationship within the sampled salinity range and was elevated at sites furthest from the ocean and lowest at locations closest to the Gulf of Mexico. This pattern remained consistent as the neutral estuary switched from negative to positive after a rain event. On regional scales, δ 18 O displayed a positive linear relationship with salinity and was strongly related to evaporation rates. On local and seasonal scales, evaporation-enriched δ 18 O at upper enclosed estuarine sites and this pattern was consistent over time including periods of reverse estuary conditions. Dissolved Sr:Ca and Mg:Ca varied linearly with salinity on regional scales but displayed minimal variation across temporal scales within an estuary. High variability in dissolved Mn:Ca-salinity relations was found at all spatiotemporal scales, with localized episodic peaks of Mn:Ca possibly due to sediment disturbance. Although dissolved Ba:Ca and δ 18 O were not predictably related to salinity on local scales, consistent up-estuary enrichment and lowerestuary depletion make these two constituents reliable proxies for animal movements across the ocean-estuary gradient as recorded in chronologically formed biominerals.

Fine‐scale variability in elemental composition of estuarine water and otoliths: Developing environmental markers for determining larval fish dispersal histories within estuaries

“…Unlike in other studies (Thorrold et al 1998;Bradbury et al 2008;Mohan and Walther 2015), Sr : Ca did not prove to be a useful element, with no relationship between otolith concentrations and ambient concentrations or salinity. Laboratory experiments using black bream otoliths have shown that otolith concentrations of Sr and Ba are explained by complex interactions between ambient concentrations, salinity and temperature (Elsdon and Gillanders 2002.…”

“…The ability to distinguish between otoliths collected from different regions within an estuary relies on there being variation in physicochemical properties of the water (Campana 1999;Schaffler et al 2014;Mohan and Walther 2015). Estuarine water chemistry is highly variable and closely linked to freshwater flows and tidal movement (Aston 1978;Walther and Nims 2015).…”

Proportions of demersal fish exposed to sublethal hypoxia revealed by otolith chemistry

“…This is similar to the proportion of YOY and Age-1 croaker utilizing estuarine habitats observed by Mohan & Walther (2016) of 29%. Although eutrophication is extensive throughout estuaries bordering the Gulf of Mexico (Bricker et al 1999), estuarine hypoxia may not develop (Mohan & Walther 2015) or may occur in localized areas (Yakupzack et al 1977, Montagna & Froeschke 2009 that are avoidable by croaker (Eby & Crowder 2002;Campbell & Rice 2014). Indeed, Campbell & Rice (2014) observed avoidance of intruding hypoxia by juvenile croaker that occurred over short periods of time (i.e.…”

Estuarine Lago Mare fauna from the Tertiary Piedmont Basin indicates episodic Atlantic/Mediterranean exchange during the final stage of the Mediterranean Salinity Crisis

“…Due to their proximity to rivers, estuaries are more prominently affected by seasonal changes in precipitation, runoff, and evaporation than other marginal marine environments. Prominent seasonal δ 18 O variations in the order of several permil also at salinities b 10 psu are well documented in Miocene and recent estuaries (Surge and Lohmann, 2002;Harzhauser et al, 2011b;Mohan and Walther, 2015). We argue that the spread of δ 18 O data in the time-averaged Moncucco taphocoenosis reflects such changes.…”