Beet‐Based Deicers Interfere With Early Stage Decomposition of Labile Leaf Litter

ABSTRACT Salinization threatens water quality in freshwater ecosystems during the winter in urban areas where road salt is applied to maintain safe driving conditions. To minimise salinization from road salt, some municipalities have shifted to ‘eco‐friendly’ alternatives, such as a mixture of beet molasses and salt brine for deicing. While the reduction in chloride application has been the motivation to shift to beet‐brine, few studies have explored the effects on ecosystem function in freshwater ecosystems that receive beet‐brine runoff. Our study compared the effects of beet‐brine versus traditional chloride salts on leaf litter decomposition using replicated recirculating stream mesocosms. We quantified respiration of leaf associated microbial communities (hereafter, biofilms), leaf toughness and decomposition (as mass loss) over a two‐week period for a labile (sugar maple; Acer saccharum ) and recalcitrant (post oak; Quercus stellata ) leaf species under five treatments: control (+0 g L −1 Cl − ), low‐beet (+0.15 g L −1 beet‐brine), high‐beet (+1.5 g L −1 beet‐brine), low‐salt (+0.21 g L −1 Cl − ) and high‐salt (+2.1 g L −1 Cl − ). Our results indicate that high beet‐brine application decreased initial (< 7d) decomposition rates for sugar maple leaves (high‐beet‐brine k = 0.017 d −1 , control k = 0.026 d −1 ), which was likely driven by the addition of labile beet‐based carbon. However, we did not observe effects of beet‐brine on mass loss after the first 7 days of decomposition. We found that oak leaf toughness decreased in each of our deicing treatments, likely due to added Cl − . We observed that the beet‐brine addition had a larger effect on leaf litter decomposition and respiration than the equivalent concentration of traditional road salts. We did not observe differences between low salt and high salt treatments in any of our response metrics. Our findings indicate that managers should practice caution when using “eco‐friendly” products and emphasise the need to reduce the application of all deicing products. Future research is needed to quantify the inputs and residence time of beet‐brine products in freshwater ecosystems.