Ecotoxicology https://doi.org/10.1007/s10646-020-02224-1 The impact of lime additions on mercury dynamics in stream chemistry and macroinvertebrates: a comparison of watershed and direct stream addition management strategies Geoffrey D. Millard 1,3 ● Karen Riva-Murray 2 ● Douglas A. Burns 2 ● Mario R. Montesdeoca 1 ● Charles T. Driscoll 1 Accepted: 27 April 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract Acid deposition has declined across eastern North America and northern Europe due to reduced emissions of sulfur and nitrogen oxides. Ecosystem recovery has been slow with limited improvement in surface water chemistry. Delayed recovery has encouraged acid-neutralization strategies to accelerate recovery of impaired biological communities. Lime application has been shown to increase pH and dissolved organic carbon (DOC), which could also drive increased mobilization of mercury (Hg) to surface waters. A four-year study was conducted within Honnedaga Lake’s watershed in the Adirondack region of New York to compare the effects of watershed and direct channel lime additions on Hg in stream water and macroinvertebrates. All treatments sharply increased stream pH and DOC concentrations, but large differences in the duration of impacts were apparent. The watershed treatment resulted in multi-year increases in concentrations and loads of total Hg (150%; 390%), DOC (190%; 350%) and nutrients, whereas total Hg and DOC increased for short periods (72–96 h) after channel treatments. No response of Hg in macroinvertebrates was evident following the watershed treatment, but a potential short-term and spatially constrained increase occurred after the channel treatment. Our observations indicate that both treatment approaches mobilize Hg, but that direct channel liming mobilizes considerably less than watershed liming over any period longer than a few days. During the final study year, increased methyl Hg concentrations were observed across reference and treated streams, which may reflect an extended dry period, highlighting that climate variation may also affect Hg dynamics. Keywords Mercury ● Methylmercury ● Stream ● Macro-invertebrates ● Calcium carbonate ● Remediation Introduction Long-term inputs of acid deposition in the northeastern United States of America (US) have resulted in a depletion of available base cations from forest soils and surface water acidification. In the northeastern US, streams are showing limited rates of acid-neutralizing capacity (ANC) recovery of <1 μeq L -1 y -1 (Burns et al. 2006; Lawrence et al. 2011; Likens and Buso 2012; Strock et al. 2014; Fuss et al. 2015), and episodic acidification continues to occur during high flow conditions (Fuss et al. 2015). In a 2003–2005 study in the western Adirondack region of New York, over half of stream reaches experienced episodic acidification suffi- ciently intense to mobilize toxic concentrations of alumi- num (Al; Lawrence et al. 2008), and models predict ecosystem recovery will take multiple decades (Waller et al. 2012; Fakhraei et al. 2014; Shao et al. 2020). Addition of acid-neutralizing substances to soils and surface waters has been explored as an approach to accel- erate ecosystem recovery from acid deposition. Previous studies have shown that calcium (Ca) additions in the form of wollastonite (CaSiO 3 ) and lime (CaCO 3 ) accelerate the * Geoffrey D. Millard millard.geoffrey@epa.gov 1 Department of Civil and Environmental Engineering, Syracuse University, Syracuse, NY 13244, USA 2 U.S. Geological Survey New York Water Science Center, Troy, NY 12180, USA 3 Present address: National Risk Management Research Laboratory, US Environmental Protection Agency, Cincinnati, OH 45244, USA Supplementary information The online version of this article (https:// doi.org/10.1007/s10646-020-02224-1) contains supplementary material, which is available to authorized users. 1234567890();,: 1234567890();,: