DOI: 10.5061/dryad.wh70rxx0d
title: Old methane fuels modern river food web

description: Dominant ecological paradigms provide theoretical frameworks for two basal
 sources of carbon to riverine food webs: carbon fixed by algae and
 submerged macrophytes (autochthonous) and carbon fixed by terrestrial
 vascular plants that enter aquatic ecosystems as litter (allochthonous).
 An additional, less studied, pathway for carbon to enter rivers is as
 methane that is produced in small quantities via methanogenesis by
 anaerobic methanogenic archaea. Because rivers are generally well
 oxygenated, methane is not often recognised as a substantial contributor
 to riverine carbon budgets. However, methane may also enter rivers via
 natural gas macro–seeps where underground deposits connect to the surface
 via fissures and fractures. We explored the contribution of methane from
 natural gas macro–seeps to food webs by comparing δ13C values of animals
 and their foods from reaches rich in dissolved methane with reaches where
 methane concentrations were at background levels. Animals
 collected from river reaches with natural gas macro–seeps had
 significantly depleted δ13C values compared to animals from reference
 reaches. Within natural gas macro–seep reaches, methane served as the
 principal basal carbon source for mayfly primary consumers (Tasmanocoenis
 spp.), contributing up to 55% of their total carbon budget.
 Methane–derived carbon persisted across multiple trophic levels of the
 natural gas macro–seep food web, subsidising up to 19% of the carbon in
 Decapoda and 28% in carnivorous fish. Among Decapoda, carbon of
 terrestrial origin dominated biomass contributions, supplying up to 55% of
 carbon to Macrobrachium australiense and 56% to Parataya
 australiensis. Autochthonous carbon contributions were highest among
 zooplankton, with up to 33% of their carbon fixed by algae. Our
 findings establish the prevalence of a natural gas derived
 methane–methanotrophic bacteria–primary consumer pathway. We emphasise its
 significance as a potentially dominating energy conduit in rivers with
 high concentrations of dissolved methane, demonstrating feeding preference
 redundancy at low trophic levels. Additionally, we provide useful
 information for the incorporation of different sources of carbon in
 riverine food webs.
description: # Old methane fuels modern river food web Dataset DOI:
 [10.5061/dryad.wh70rxx0d](10.5061/dryad.wh70rxx0d) ## Description of the
 data and file structure Here we provide the data we used to complete our
 stable isotope analyses. Please refer to the manuscript methods for
 details of our analyses. We provide 4 csv files that include data for
 river discharge, d13C values of sources and consumers, and trophic
 discrimination factors. **1) combined_methane_descrimination.csv**:
 trophic discrimination factors used in the MixSiar model for each animal
 taxon. * Consumer: identity of each animal taxa - Source: potential
 sources of carbon * Meand13C: mean delta 13C values - SDd13C: standard
 deviation of delta 13C values * Mean15N: mean delta 15N values - SDd15N:
 standard deviation of delta 15N values **2) Discharge_DS_Chinchilla.csv**:
 daily river discharge in the Condamine River * Date: date of observation
 (dd/mm/yy) - Q: discharge (ML/day) **3) methane_consumers.csv**: delta 13C
 values of animals used in the MixSiar model * Date: date of observation
 (dd/mm/yy) - Trip: day of observation (1-6) corresponding to date * Site:
 location of observation taken within methane seep zone - Grouped_organsim:
 identity of each animal taxa * deltaC: delta 13C values **4)
 methane_sources.csv:** delta 13C values of end-members used in the MixSiar
 mixing model * Source: potential sources of carbon - Site: location of
 observation taken within methane seep zone * zone: discrimination of the
 reach treatment (methane) or reference - Mean13C: mean delta 13C values *
 SDd13C: standard deviation of mean 13C values - n: number of samples used
 for analyses