Yellow Perch (Perca flavescens) Mercury Unaffected by Wildland Fires in Northern Minnesota

Abstract

Wildland fire can alter mercury (Hg) cycling on land and in adjacent aquatic environments. In addition to enhancing local atmospheric Hg redeposition, fire can influence terrestrial movement of Hg and other elements into lakes via runoff from burned upland soil. However, the impact of fire on water quality and the accumulation of Hg in fish remain equivocal. We investigated the effects of fire-specifically, a low-severity prescribed fire and moderate-severity wildfire-on young-of-the-year yellow perch () and lake chemistry in a small remote watershed in the Boundary Waters Canoe Area Wilderness in northeastern Minnesota. We used a paired watershed approach: the fire-affected watershed was compared with an adjacent, unimpacted (reference) watershed. Prior to fire, upland organic horizons in the two study watersheds contained 1549 μg Hg m on average. Despite a 19% decrease in upland organic horizon Hg stocks due to the moderate severity wildfire fire, fish Hg accumulation and lake productivity were not affected by fire in subsequent years. Instead, climate and lake water levels were the strongest predictors of lake chemistry and fish responses in our study lakes over 9 yr. Our results suggest that low- to moderate-severity wildland fire does not alter lake productivity or Hg accumulation in young-of-the-year yellow perch in these small, shallow lakes in the northern deciduous and boreal forest region.

Origin, Reactivity, and Bioavailability of Mercury in Wildfire Ash

“…Our current findings suggest that wildfire ash could play an important role in global Hg cycling and the Hg biogeochemistry of terrestrial and aquatic ecosystems. For example, wildfire ash itself may decrease or have little effect on Hg contamination in downstream ecosystems (e.g., fish Hg accumulation) due to the less reactive nature of Hg within ash. It should also be recognized that in the burned watersheds other factors such as postburn alteration of food web structures in aquatic ecosystems may lead to subsequent changes in MeHg accumulation in fish .…”

It’s Complicated and It Depends: A Review of the Effects of Ecosystem Changes on Walleye and Yellow Perch Populations in North America

“…Two of the three studies on Walleye identified negative relationships between mercury content of tissues and water clarity in inland lakes (Parks et al 1994; Simonin et al 2008), although a positive correlation was documented in the Laurentian Great Lakes (Lepak et al 2018). Mercury concentrations in Yellow Perch were negatively correlated with water clarity in two studies on Minnesota lakes (Riggs et al 2017; Kolka et al 2019) but were not related in New York lakes (Simonin et al 2008).…”

“…Water level effects on mercury concentrations in Yellow Perch were inconsistent. Sorensen (2019) reported higher mercury concentrations at higher water levels across Minnesota, contrary to findings by Riggs et al (2017). The relationship between water levels and mercury concentrations in Yellow Perch was inconsistent even within a single system (Larson et al 2021).…”

Fire and rain: A systematic review of the impacts of wildfire and associated runoff on aquatic fauna

“…Longer term investigations reveal that aquatic taxa can be sensitive to wildfire ash (Garcia & Carignan, 2005; Ré et al, 2020; Riggs et al, 2017). In a 7‐day bioassay, freshwater clam Corbicula fluminea were resilient to short‐term exposures (1–3 days) of wildfire ash extracts (aqueous extract of ashes, AEA) but mortality climbed to above 45% after 7 days of exposure (Silva et al, 2016).…”