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Abstract The extent to which terrestrial organic matter supports aquatic consumers remains uncertain because factors regulating resource flows are poorly understood. We sampled 12 lakes throughout the Sierra Nevada (California, USA) spanning large gradients in elevation and size to evaluate how watershed attributes and lake morphometry influence resource flows to lake carbon pools and zooplankton. We found that the size and composition of carbon pools in lakes were often more strongly determined by watershed or lake features rather than by elevational position. Using three different tracers of resource origin (δ13C, Δ14C, C:N ratio), we found terrestrial contributions to most lake resource pools (dissolved organic carbon, particulate organic matter (POM), sediments) and pelagic consumers (zooplankton) were more strongly related to local‐scale watershed features such as vegetation cover or watershed area: lake area rather than to elevation. Landscape patterns in multiple tracers indicated consistent contribution of within‐lake C sources to bulk resource pools across elevations (POM, sediments, zooplankton). δ13C‐enrichment of lake C pools and overlap with δ13C of terrestrial resources can arise due to reduced fractionation of13C by phytoplankton under CO2limitation, therefore we recommend careful consideration of potential environmental drivers when interpreting among‐lake patterns in δ13C. Our findings emphasize the importance of local‐scale variation in mediating terrestrial contributions to lake food webs.
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Aquatic biomass is a major source to particulate organic matter export in large Arctic rivers
Arctic rivers provide an integrated signature of the changing landscape and transmit signals of change to the ocean. Here, we use a decade of particulate organic matter (POM) compositional data to deconvolute multiple allochthonous and autochthonous pan-Arctic and watershed-specific sources. Constraints from carbon-to-nitrogen ratios (C:N), δ 13 C, and Δ 14 C signatures reveal a large, hitherto overlooked contribution from aquatic biomass. Separation in Δ 14 C age is enhanced by splitting soil sources into shallow and deep pools (mean ± SD: −228 ± 211 vs. −492 ± 173‰) rather than traditional active layer and permafrost pools (−300 ± 236 vs. −441 ± 215‰) that do not represent permafrost-free Arctic regions. We estimate that 39 to 60% (5 to 95% credible interval) of the annual pan-Arctic POM flux (averaging 4,391 Gg/y particulate organic carbon from 2012 to 2019) comes from aquatic biomass. The remainder is sourced from yedoma, deep soils, shallow soils, petrogenic inputs, and fresh terrestrial production. Climate change-induced warming and increasing CO 2 concentrations may enhance both soil destabilization and Arctic river aquatic biomass production, increasing fluxes of POM to the ocean. Younger, autochthonous, and older soil-derived POM likely have different destinies (preferential microbial uptake and processing vs. significant sediment burial, respectively). A small (~7%) increase in aquatic biomass POM flux with warming would be equivalent to a ~30% increase in deep soil POM flux. There is a clear need to better quantify how the balance of endmember fluxes may shift with different ramifications for different endmembers and how this will impact the Arctic system.
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- PAR ID:
- 10444805
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 120
- Issue:
- 12
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1073/pnas.2209883120
