Benthic macroinvertebrate and fish communities in Lake Huron are linked to submerged groundwater vents

Groundwater can be an important source of nutrients and energy to aquatic ecosystems, but quantifying the inputs and biogeochemical importance remains challenging. A series of submerged groundwater vents in northern Lake Huron were examined to determine the linkage between groundwater nutrients and aquatic food webs. We collected samples of key food-web components from groundwater vent and reference habitats and analyzed them for ¹³C, ¹⁵N, and ³⁴S isotopes. Dissolved inorganic carbon (DIC) in the groundwater was depleted in ¹³C, while aqueous sulfate was enriched in ³⁴S (mean differences between groundwater and reference sites were –3.9‰ and +12.0‰, respectively). Benthic primary producers, macroinvertebrates, and benthivorous fish had significantly lower δ¹³C values in groundwater environments, and benthivorous fish were somewhat depleted (–2.5‰) in δ³⁴S at groundwater sites compared to reference sites. However, δ¹⁵N values were not different between groundwater and reference sites, and pelagic components of the ecosystems (plankton and planktivorous and piscivorous fish) were similar in both δ¹³C and δ¹⁵N. These data suggest benthic metazoan communities surrounding groundwater vents are partially linked to groundwater-derived benthic primary production, while planktivorous and piscivorous communities not directly associated with the benthos do not rely on groundwater nutrients.