The effects of acid rock drainage onCarex aquatilis leaf litter decomposition in rocky Mountain fens

Abstract

Fens occur in many Colorado Rocky Mountain watersheds that have historically been affected by metal mining activities. A persistent effect of mining is acid rock drainage (ARD), which flows from mine adits and tailings piles. ARD water has low pH and high concentrations of heavy metals and can pollute surface and ground water supporting fens. There are few floristic differences between polluted and pristine fens, and it is unclear what long-term affects ARD has on fens. We investigated decomposition of native leaf litter and a standard litter for two years in fourCarex aquatilis-dominated subalpine fens. Two of the fens are affected by ARD, and their source waters have pH 6.0 and low metal concentrations. ARD significantly reduced native litter decomposition rates over two years (ANOVA, p <0.01) with 63% of the initial mass of leaf litter remaining at the most pristine site (Peru Creek fen), 47 % at a moderately polluted site (Argentine fen), and 23% at the most pristine site (Deer Creek fen). ARD also reduced the quality of litter produced. Standard litter decomposed more rapidly than native litter at all sites, particularly Peru Creek fen. Site, representing fen environment, and litter origin, representing native vs. standard litter, significantly affected decomposition rates (ANOVA, p < 0.0001) Pristine fens had decomposition rates comparable with boreal rich fens, while polluted fens had decomposition rates comparable with boreal poor fens and bogs. Acid rock drainage causes ecosystem-level responses in organic matter processing, peat accumulation rates, and most likely in nutrient cycling, which could have long-term affects on fen primary and secondary production and other functions.