Climate and productivity affect total mercury concentration and bioaccumulation rate of fish along a spatial gradient of subarctic lakes

Abstract

Climate change is resulting in increased temperatures and precipitation in subarctic regions of Europe. These changes are extending tree lines to higher altitudes and latitudes, and enhancing tree growth enabling intensification of forestry into previously inhospitable subarctic regions. The combined effects of climate change and land-use intensification extend the warm, open-water season in subarctic lakes and increase lake productivity and may also increase leaching and methylation activity of mercury within the lakes. To assess the joint effects of climate and productivity on total mercury (THg) bioaccumulation in fish, we conducted a space-for-time substitution study in 18 tributary lakes of a subarctic watercourse forming a gradient from cold pristine oligotrophic lakes in the northern headwaters to warmer and increasingly human-altered mesotrophic and eutrophic systems in the southern lower reaches. Increasing temperature, precipitation, and lake productivity were predicted to elevate length- and age-adjusted THg concentrations, as well as THg bioaccumulation rate (the rate of THg bioaccumulation relative to length or age) in muscle tissue of European whitefish (Coregonus lavaretus), vendace (Coregonus albula), perch (Perca fluviatilis), pike (Esox lucius), roach (Rutilus rutilus) and ruffe (Gymnocephalus cernua). A significant positive relationship was observed between age-adjusted THg concentration and lake climate-productivity in vendace (r = 0.50), perch (r = 0.51), pike (r = 0.55) and roach (r = 0.61). Higher climate-productivity values of the lakes also had a positive linear (pike; r = 0.40 and whitefish; r = 0.72) or u-shaped (perch; r = 0.64 and ruffe; r = 0.50) relationship with THg bioaccumulation rate. Our findings of increased adjusted THg concentrations in planktivores and piscivores reveal adverse effects of warming climate and increasing productivity on these subarctic fishes, whereas less distinct trends in THg bioaccumulation rate suggest more complex underlying processes. Joint environmental stressors such as climate and productivity should be considered in ongoing and future monitoring of mercury concentrations.

Increasing temperature and productivity change biomass, trophic pyramids and community‐level omega‐3 fatty acid content in subarctic lake food webs

“…Differences in lake productivity originate predominantly from variation in vegetation and land‐use practices within the catchment (Jussila et al., 2014). The northernmost lakes are situated near pristine areas with anthropogenic impacts limited to nature tourism and reindeer herding, and from the timberline southwards industrial forestry activities including large‐scale clear‐cut areas, site preparation and intensive ditching (Ahonen et al., 2018; Hayden et al., 2017; Jussila et al., 2014; Table S1). Catchment area characteristics and land‐use variables were derived with the Finnish Environment Institute VALUE‐tool combining catchment and CORINE‐database and open map data (Ahonen et al., 2018; Hayden et al., 2017).…”

“…The northernmost lakes are situated near pristine areas with anthropogenic impacts limited to nature tourism and reindeer herding, and from the timberline southwards industrial forestry activities including large‐scale clear‐cut areas, site preparation and intensive ditching (Ahonen et al., 2018; Hayden et al., 2017; Jussila et al., 2014; Table S1). Catchment area characteristics and land‐use variables were derived with the Finnish Environment Institute VALUE‐tool combining catchment and CORINE‐database and open map data (Ahonen et al., 2018; Hayden et al., 2017). Lake location (coordinates, altitude), morphometrical data (area, depth, mean depth, volume) and water physical‐chemistry (nutrients, light) were derived from the Finnish Environment Institute (HERTTA‐database) and National Survey of Finland, or from our own sampling (Table S1).…”

Improved Environmental Status: 50 Years of Declining Fish Mercury Levels in Boreal and Subarctic Fennoscandia

“…Arctic charr, brown trout, perch and roach are generalist species that may forage across both pelagic and littoral habitats. The coldwater adapted Arctic charr and brown trout are present in oligotrophic lakes; the cool-water species perch is often the dominating species in mesotrophic lakes, and the warm-water species roach are abundant in eutrophic lakes 33 . Arctic charr, brown trout and perch undergo ontogenetic dietary shifts from invertebrates to fish prey, but roach feed exclusively on invertebrate prey 32,34 .…”

“…To examine such differences between fish species, and to disentangle the cause for the different magnitude of decreases in fish Hg concentrations over time, data on age 45 and trophic level indicators (i.e. stable isotopes of nitrogen, N 64 ) would be necessary 32,33 .…”

Influence of Thermal Pollution on the Physiological Conditions and Bioaccumulation of Metals, Metalloids, and Trace Metals in Whitefish (Coregonus lavaretus L.)

“…Mercury biomagnifies to higher trophic levels in food webs and methylmercury (MeHg), accounting for 91% of the mercury found in the whitefish (Coregonus clupeaformis) from Northern Lake Huron [40]. In Fennoscandian, an increase in the muscle Hg concentration in 6 fish species and Hg bioaccumulation rate in whitefish (Coregonus lavaretus) was observed, according to the temperature gradient from the cold pristine oligotrophic lakes in the north to the warmer and increasingly human-altered mesotrophic and eutrophic systems in the south, where, apparently, mercury methylation is more intensive [41]. Methylmercury is absorbed effectively (>90%) from the gut and enters tissues as a cysteine-bound conjugate that mimics the amino acid methionine, moving freely into cells via amino acid transport proteins [7].…”