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 super(13)C, super(15)N, and super(34)S isotopes. Dissolved inorganic carbon (DIC) in the groundwater was depleted in super(13)C, while aqueous sulfate was enriched in super(34)S (mean differences between groundwater and reference sites were -3.9ppt and +12.0ppt, respectively). Benthic primary producers, macroinvertebrates, and benthivorous fish had significantly lower [delta] super(13)C values in groundwater environments, and benthivorous fish were somewhat depleted (-2.5ppt) in [delta] super(34)S at groundwater sites compared to reference sites. However, [delta] super(15)N 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 [delta] super(13)C and [delta] super(15)N. 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.