Uptake of Sulfate from Ambient Water by Freshwater Animals
2020
Michael B. Griffith | James M. Lazorchak | Herman Haring
To better understand how the sulfate (SO<sub>4</sub><sup>2−</sup>) anion may contribute to the adverse effects associated with elevated ionic strength or salinity in freshwaters, we measured the uptake and efflux of SO<sub>4</sub><sup>2−</sup> in four freshwater species: the fathead minnow (<i>Pimephales promelas</i>, Teleostei: Cyprinidae), paper pondshell (<i>Utterbackia imbecillis</i>, Bivalvia: Unionidae), red swamp crayfish (<i>Procambarus clarkii</i>, Crustacea: Cambaridae), and two-lined mayfly (<i>Hexagenia bilineata</i>, Insecta: Ephemeridae). Using <i>δ(<sup>34</sup>S/<sup>32</sup>S)</i> stable isotope ratios and the concentrations of S and SO<sub>4</sub><sup>2−</sup>, we measured the SO<sub>4</sub><sup>2−</sup> influx rate (<i>J<sub>in</sub></i>), net flux (<i>J<sub>net</sub></i>), and efflux rate (J<sub>out</sub>) during a 24 h exposure period. For all four species, the means of <i>J<sub>in</sub></i> for SO<sub>4</sub><sup>2−</sup> were positive, and <i>J<sub>in</sub></i> was significantly greater than 0 at both target SO<sub>4</sub><sup>2−</sup> concentrations in the fish and mollusk and at the lower SO<sub>4</sub><sup>2−</sup> concentration in the crayfish. The means of <i>J<sub>out</sub></i> and <i>J<sub>net</sub></i> were much more variable than those for <i>J<sub>in</sub></i>, but several species by target SO<sub>4</sub><sup>2−</sup> concentration combinations for <i>J<sub>out</sub></i> and <i>J<sub>net</sub></i>, were negative, which suggests the net excretion of SO<sub>4</sub><sup>2−</sup> by the animals. The results of our experiments suggest a greater regulation of SO<sub>4</sub><sup>2−</sup> in freshwater animals than has been previously reported.
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