title: Whole-lake carbon-13 additions reveal terrestrial support of aquatic food webs.
abstract: Ecosystems are supported by organic carbon from two distinct sources. Endogenous carbon is produced by photosynthesis within an ecosystem by autotrophic organisms. Exogenous carbon is produced elsewhere and transported into ecosystems. Consumers may use exogenous carbon with consequent influences on population dynamics, predator-prey relationships and ecosystem processes. For example, exogenous inputs provide resources that may enhance consumer abundance beyond levels supported by within-system primary production. Exogenous fluxes of organic carbon to ecosystems are often large, but this material is recalcitrant and difficult to assimilate, in contrast to endogenously produced organic matter, which is used more easily. Here we show, by the experimental manipulation of dissolved inorganic (13)C in two lakes, that internal primary production is insufficient to support the food webs of these ecosystems. Additions of NaH(13)CO(3) enriched the (13)C content of dissolved inorganic carbon, particulate organic carbon, zooplankton and fish. Dynamics of (13)C indicate that 40-55% of particulate organic carbon and 22-50% of zooplankton carbon are derived from terrestrial sources, showing that there is significant subsidy of these ecosystems by organic carbon produced outside their boundaries.
authors.affiliation: Institute of Ecosystem Studies, Millbrook, New York 12545, USA. pacem@ecostudies.org
authors.forename: Michael L
authors.initials: ML
authors.lastname: Pace
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Cole
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Carpenter
authors.forename: James F
authors.initials: JF
authors.lastname: Kitchell
authors.forename: James R
authors.initials: JR
authors.lastname: Hodgson
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Van De Bogert
authors.forename: Darren L
authors.initials: DL
authors.lastname: Bade
authors.forename: Emma S
authors.initials: ES
authors.lastname: Kritzberg
authors.forename: David
authors.initials: D
authors.lastname: Bastviken
mesh_terms: D000818:Animals; D002244:Carbon / Q000378:metabolism*; D002247:Carbon Isotopes; D003621:Daphnia / Q000378:metabolism*; D005399:Fishes / Q000378:metabolism; D020387:Food Chain; D005618:Fresh Water / Q000737:chemistry / Q000469:parasitology*; D008824:Michigan; D015048:Zooplankton / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D002244:Carbon