Mass Flux Calculations Show Strong Allochthonous Support of Freshwater Zooplankton Production Is Unlikely

Michael T Brett,George B Arhonditsis,Sudeep Chandra,Martin J Kainz,Caroline P Slomp

doi:10.1371/journal.pone.0039508

Abstract

Many studies have concluded terrestrial carbon inputs contribute 20–70% of the carbon supporting zooplankton and fish production in lakes. Conversely, it is also known that terrestrial carbon inputs are of very low nutritional quality and phytoplankton are strongly preferentially utilized by zooplankton. Because of its low quality, substantial terrestrial support of zooplankton production in lakes is only conceivable when terrigenous organic matter inputs are much larger than algal production. We conducted a quantitative analysis of terrestrial carbon mass influx and algal primary production estimates for oligo/mesotrophic lakes (i.e., TP≤20 µg L−1). In keeping with the principle of mass conservation, only the flux of terrestrial carbon retained within lakes can be utilized by zooplankton. Our field data compilation showed the median (inter-quartile range) terrestrial particulate organic carbon (t-POC), available dissolved organic carbon (t-DOC) inputs, and in-lake bacterial and algal production were 11 (8–17), 34 (11–78), 74 (37–165), and 253 (115–546) mg C m−2 d−1, respectively. Despite the widespread view that terrestrial inputs dominate the carbon flux of many lakes, our analysis indicates algal production is a factor 4–7 greater than the available flux of allochthonous basal resources in low productivity lakes. Lakes with high loading of t-DOC also have high hydraulic flushing rates. Because t-DOC is processed, i.e., mineralized or lost to the sediments, in lakes at ≈0.1% d−1, in systems with the highest t-DOC inputs (i.e., 1000 mg m−2 d−1) a median of 98% of the t-DOC flux is advected and therefore is not available to support zooplankton production. Further, advection is the primary fate of t-DOC in lakes with hydraulic retention times <3 years. When taking into account the availability and quality of terrestrial and autochthonous fluxes, this analysis indicates ≈95–99% of aquatic herbivore production is supported by in-lake primary production.

Highlights

There is considerable interest [1,2,3,4,5] and debate [5,6,7] about the role terrestrial organic matter inputs play in supporting the production of invertebrate and fish consumers in lakes
This study focuses on the role terrestrial organic matter inputs may play in invertebrate and fish production in lakes, and especially lakes with high areal terrestrially derived dissolved organic carbon (t-DOC) loading rates, the conclusions of this study are highly relevant to the role lakes play as carbon sinks, conduits or sources in the global carbon cycle [25]
Literature Analysis Previous studies have concluded that terrestrial organic matter strongly supports zooplankton production in a series of upper Midwestern USA lakes [3,5,8,11], hereafter referred to as the UNDERC lakes

Summary

Introduction

There is considerable interest [1,2,3,4,5] and debate [5,6,7] about the role terrestrial organic matter inputs play in supporting the production of invertebrate and fish consumers in lakes. Other field studies concluded that the t-DOC R bacterial production R protozoan pathway is the primary route by which terrestrial inputs support zooplankton [2,4,9]. Field determinations have shown t-POC inputs are only

Methods

Results

Conclusion