Efficiency of crustacean zooplankton in transferring allochthonous carbon in a boreal lake.

Guillaume Grosbois,Milla Rautio,Dominic Vachon,Paul A. del Giorgio

doi:10.1002/ecy.3013

Abstract

Increased incorporation of terrestrial organic matter (t-OM) into consumer biomass (allochthony) is believed to reduce growth capacity. In this study, we examined the relationship between crustacean zooplankton allochthony and production in a boreal lake that displays strong seasonal variability in t-OM inputs. Contrary to our hypotheses, we found no effect of allochthony on production at the community and the species levels. The high-frequency seasonal sampling (time-for-space) allowed for estimating the efficiency of zooplankton in converting this external carbon source to growth. From the daily t-OM inputs in the lake (57-3,027kg C/d), the zooplankton community transferred 0.2% into biomass (0.01-2.36kg C/d); this level was of the same magnitude as the carbon transfer efficiency for algal-derived carbon (0.4%). In the context of the boundless carbon cycle, which integrates inland waters as a biologically active component of the terrestrial landscape, the use of the time-for-space approach for the quantifying of t-OM trophic transfer efficiency by zooplankton is a critical step toward a better understanding of the effects of increasing external carbon fluxes on pelagic food webs.

Highlights

The high abundance of lakes in the boreal landscape creates dynamic land–water interactions that enhance matter and energy fluxes from the drainage basin toward these waterbodies (Lehner and Do€ll 2004, Polis et al 2004)
This study presents a detailed seasonal pattern of crustacean zooplankton use of terrestrial organic matter from which two main results emerge
At the ecosystem scale, we found that zooplankton were able to transfer the terrestrial organic matter (t-OM) into their biomass with a transfer efficiency that was in the same range of magnitude as their efficiency of transferring algal carbon

Summary

Introduction

The high abundance of lakes in the boreal landscape creates dynamic land–water interactions that enhance matter and energy fluxes from the drainage basin toward these waterbodies (Lehner and Do€ll 2004, Polis et al 2004). The incoming fluxes are materialized by terrestrial organic matter (t-OM) inputs into lakes, which have increased during the last decades—a process called browning (Monteith et al 2007, Creed et al 2018, Wauthy et al 2018). Terrestrial OM has long been considered an unimportant resource for pelagic aquatic food webs and has been often excluded from the calculations of carbon flux supporting primary and secondary consumers. A complete understanding of lake carbon cycles is highly dependent on all seasons, all other seasons but summer remain little explored in limnology, and direct evidence regarding terrestrial carbon impacts on aquatic food webs at an annual scale have remained elusive. Inputs of t-OM in lakes are highly variable in time and strongly dependent on seasonal or weatherrelated events (Lambert et al 2013). Extreme storm events can have a major impact on the amount of t-OM entering the lake and on the entire lake carbon cycle

Methods

Results

Conclusion