Carbon storage reservoirs in watersheds support stream food webs via periphyton production

Abstract

We measured the natural abundances of radiocarbon (delta14C) in macroinvertebrates, fishes, and their potential food sources, collected from the upper and lower reaches of six temperate streams in Lake Biwa basin (central Japan), three of which flow on limestone bedrock. Several carbon storage reservoirs in the watersheds show distinctive delta14C signatures (e.g., ancient carbonate rocks, -1000 per thousand; modern atmospheric CO2, +50 per thousand). Our analyses showed that the delta14C values for periphytic algae range from -361 per thousand to +21 per thousand, reflecting 14C-depleted signals from watershed storage reservoirs (carbonate rocks and/or soils). In contrast, the delta14C values for coarse particulate organic matter (CPOM) range from -6 per thousand to +62 per thousand, reflecting 14C-enriched signals from modern atmospheric CO2. The periphyton from streams on limestone bedrock was more 14C-depleted than that from streams in non-limestone areas, although the delta14C values for periphyton from the latter were less than modern atmospheric 14CO2 concentration. The delta14C values for most of the consumers were between those for periphyton and CPOM. Based on a delta14C two-source mixing models, the results suggested that the grazers rely on periphyton, while the carbon source for collectors and predators shifts from CPOM in the upper reaches of streams to periphyton in the lower reaches. The delta14C signature can trace carbon from watershed storage reservoirs to benthic production, which suggests that stream food webs are composed of mixtures of carbon originating from various sources of different ages.

Terrestrial‐aquatic linkage in stream food webs along a forest chronosequence: multi‐isotopic evidence

“…In this process, one-half of the HCO 3 − originates from soil CO 2 and the other one-half from carbonate. This is expected because the δ 13 C values of terrestrial litter are controlled by relatively constant isotopic fractionation during C 3 photosynthesis (Peterson and Fry 1987), while the Δ 14 C values of litter are identical to those of modern atmospheric CO 2 (Ishikawa et al 2014). On the other hand, the Δ 14 C value of carbonate is extremely low (approximately −1000‰).…”

“…The FFGs depend to varying degrees on aquatic primary producers (e.g., periphytic algae attached to rock surfaces; hereafter, periphyton) and terrestrial primary producers (e.g., leaf litter of riparian plants; hereafter, terrestrial litter). The Δ 14 C values of periphyton, being derived from ancient sources of inorganic carbon such as bedrocks and soils, are relatively low, while the Δ 14 C values of terrestrial litter, being derived from modern atmospheric CO 2 , are relatively high (Ishikawa et al 2014). Isotopic compositions of bulk periphyton can represent those of periphytic algae (Ishikawa et al 2015b).…”

Use of Multi-Carbon Sources by Zooplankton in an Oligotrophic Lake in the Tibetan Plateau

“…The negative ∆ 14 C combined with the δ 13 C-DIC of ~0‰ might reflect a contribution of limestone bedrock weathering within the lake watershed [32]. DIC from carbonate rock weathering can then be incorporated into the carbon cycling of the lake food webs via primary production and trophic transfer [33].…”

Radiocarbon isotopic evidence for assimilation of atmospheric CO<sub>2</sub> by the seagrass <i>Zostera marina</i>

“…The natural abundance of radiocarbon ( 14 C) has recently been used to assess food web structures (Ishikawa et al, 2014) and the origin and components of organic-matter pools (Goñi et al, 2013), as carbon sources have specific 14 C concentrations ( 14 C). The 14 C of inorganic carbon also has specific values depending on the source, such as DIC or C air .…”

“…The 14 C of inorganic carbon also has specific values depending on the source, such as DIC or C air . The 14 C of DIC generally differs from that of atmospheric CO 2 because of the longer residence time of carbon in aquatic ecosystems than in the atmosphere (Ishikawa et al, 2014;Stuiver and Braziunas, 1993). Moreover, the calculation of 14 C by internal correction using δ 13 C values eliminates any effects from isotopic fractionation (Stuiver and Polach, 1977), overcoming one of the major uncertainties in the conventional δ 13 C approach.…”