Shoring up the foundations of production to respiration ratios in lakes

Abstract

The ratio of primary production to ecosystem respiration rates (P:R ratio) is an ostensibly simple calculation that is used to characterize lake function, including trophic status, the incorporation of terrestrial organic carbon into lacustrian food webs, and the direction of carbon dioxide (CO 2 ) flux between a lake and the atmosphere. However, many predictive links between P:R ratios and lake ecosystem function stem from a historically plankton-centric perspective and the common use of the diel oxygen curve approach. We review the evolution of the use of P:R ratios and examine common assumptions underlying their application to (1) eutrophication, (2) carbon flux through lake food webs, and (3) the role of lakes in the global carbon budget. Foundational P:R studies have been complicated principally by the following: most P:R ratios were calculated from mid-lake measurements and failed to incorporate nonplanktonic dynamics; there has been confusion regarding the food web implications when P:R ≠ 1; and CO 2 fluxes between lakes and the atmosphere are influenced by nonmetabolic processes. We argue for a re-assessment, or shoring up, of several fundamental assumptions that continue to guide metabolism research in lakes by accounting for mixing, benthic-littoral processes, groundwater fluxes, and abiotic controls on gas dynamics to better understand lake food webs and accurately integrate lake ecosystems into landscape-scale carbon cycling models.

Long‐term change in metabolism phenology in north temperate lakes

“…Within‐lake spatial heterogeneity may account for some differences observed in metabolism phenology, especially in the northern lakes. Our model does not explicitly account for littoral‐benthic metabolic processes and likely biases the planktonic‐offshore DO measurements (Brothers and Vadeboncoeur 2021). Any contributions of littoral planktonic, periphyton and submerged macrophyte activity to pelagic DO dynamics, via lateral flow processes, are subsumed in our general metabolism analysis and evaluation.…”

“…Such a two‐layer DO model for lakes that accounts for dynamic shifts between mixed conditions in the fall to spring to stratified conditions in the summer builds a more holistic and comprehensive representation of pelagic DO concentrations and metabolic fluxes, and—although simplified—can be used for the quantification of long‐term changes of pelagic DO and metabolism. An important caveat is that spatial heterogeneity in DO can be high (van de Bogert et al 2007) due to spatial variability in metabolism (Brothers and Vadeboncoeur 2021) and the influence of mixing and lateral flow on observed DO patterns (MacIntyre and Melack 1995; Staehr et al 2010).…”

Trophic Transfer Efficiency in Lakes

“…Gross primary production (GPP) rates in lakes are commonly measured using the diel oxygen curve technique (Staehr and others 2010;Hoellein and others 2013), though phyto-plankton production was historically estimated using 14 C with both methods yielding similar results (Lottig and others 2022). Littoral-benthic GPP is often under-represented in assessments of lake primary production rates (reviewed by Brothers and Vadeboncoeur 2021), but can be accounted for by measuring oxygen dynamics or 14 C incorporation in sealed light/dark or multi-depth chambers (Devlin and others 2016) as well as modelling approaches (Vadeboncoeur and others 2008;Brothers and others 2016) incorporating fluorescence-based rapid light curve measurements (Jassby and Platt 1976).…”

Filamentous Algae Blooms in a Large, Clear-Water Lake: Potential Drivers and Reduced Benthic Primary Production

“…There is no universal standardized protocol for the measurement of GPP in benthic periphyton communities. All methods for measuring aquatic metabolism rates are associated with some errors [31,32], and research focusing on benthic metabolism in particular has generally been more recent than research on planktonic dynamics [33]. Nevertheless, in situ measurements of changes in oxygen concentrations in sealed transparent benthic chambers or domes are a common method for assessing periphyton metabolism rates both in marine [34] and freshwater [35,36] environments.…”

“…Littoral-benthic resources are an important support for aquatic food webs [21,67,68], including those in Bear Lake, where phytoplankton production is minimal [69]. Elevated CR rates in the non-FAB treatment compared to the FAB treatment (Figure 4C) indicate that a large fraction of the carbon fixation in these assemblages likely fuels microbial production and respiration, although it cannot be taken for granted that such carbon is effectively transferred up the food web to higher trophic levels [70], as variable bacterial growth efficiencies can also result in a loss of carbon as respiration to the water column ( [32] and references therein, [71]). However, during these sampling periods, the measured NEP tended to be positive at the non-FAB site and negative at the FAB site (Figure 4D), indicating that an active surplus of organic matter at non-FAB rocks may be available to benthic consumers at higher trophic levels.…”