Ecosystem respiration: Drivers of daily variability and background respiration in lakes around the globe

Abstract

We assembled data from a global network of automated lake observatories to test hypotheses regarding the drivers of ecosystem metabolism. We estimated daily rates of respiration and gross primary production (GPP) for up to a full year in each lake, via maximum likelihood fits of a free-water metabolism model to continuous highfrequency measurements of dissolved oxygen concentrations. Uncertainties were determined by a bootstrap analysis, allowing lake-days with poorly constrained rate estimates to be down-weighted in subsequent analyses. GPP and respiration varied considerably among lakes and at seasonal and daily timescales. Mean annual GPP and respiration ranged from 0.1 to 5.0 mg O 2 L 21 d 21 and were positively related to total phosphorus but not dissolved organic carbon concentration. Within lakes, significant day-to-day differences in respiration were common despite large uncertainties in estimated rates on some lake-days. Daily variation in GPP explained 5% to 85% of the daily variation in respiration after temperature correction. Respiration was tightly coupled to GPP at a daily scale in oligotrophic and dystrophic lakes, and more weakly coupled in mesotrophic and eutrophic lakes. Background respiration ranged from 0.017 to 2.1 mg O 2 L 21 d 21 and was positively related to indicators of recalcitrant allochthonous and autochthonous organic matter loads, but was not clearly related to an indicator of the quality of allochthonous organic matter inputs.Gross primary production (GPP) and respiration are perhaps the two most fundamental processes in ecosystems. At the cellular or organismal level, they describe biochemical pathways that make organic carbon molecules and energy available to cells. When these cellular processes are integrated across an entire ecosystem, the result-ecosystemlevel GPP, ecosystem respiration, or collectively ecosystem metabolism-describes biogeochemical and trophic processes occurring at the system level.There is substantial interest in understanding the controls on ecosystem metabolism in aquatic (Mulholland et al.

Intra- and inter-annual variability in metabolism in an oligotrophic lake

“…Advances in high-frequency dissolved oxygen sensor technology (e.g., Staehr et al 2012;Weathers et al 2013), increased metabolism model complexity, and use of parametric statistical techniques (van de Bogert et al 2007;Hanson et al 2008) have improved the spatial and temporal resolution of metabolism estimates. These advances have enabled new discoveries about the role of lakes in the global C cycle (e.g., Solomon et al 2013), controls on metabolism (Hoellein et al 2013), and spatial variability of metabolism within lakes (Van de Bogert et al 2012). Furthermore, these rapidly-developing techniques have facilitated investigation of the variability of metabolism at finely-resolved spatial (Klug et al 2012; Van de Bogert et al 2012) and temporal (Hanson et al 2008;Solomon et al 2013) scales.…”

“…These advances have enabled new discoveries about the role of lakes in the global C cycle (e.g., Solomon et al 2013), controls on metabolism (Hoellein et al 2013), and spatial variability of metabolism within lakes (Van de Bogert et al 2012). Furthermore, these rapidly-developing techniques have facilitated investigation of the variability of metabolism at finely-resolved spatial (Klug et al 2012; Van de Bogert et al 2012) and temporal (Hanson et al 2008;Solomon et al 2013) scales.…”

“…Further, due to subtle diel variation in oxygen concentrations in oligotrophic lakes, physical processes may overwhelm the biological signal. For example, in a global survey of metabolic rates across 25 lakes, two oligotrophic systems, Lake Sunapee, New Hampshire, USA and Sparkling Lake, Wisconsin, USA, had many days with near-zero estimates of GPP and R (Solomon et al 2013). Traditional openwater metabolism models may need modification to capture diel fluctuations in GPP and R in lakes with low productivity (McNair et al 2015).…”

“…To date, most lake metabolism studies using these techniques have focused on temporal variation based on measurements made in the epilimnion and restricted to one year time periods (e.g., Carignan et al 2000;Sadro et al 2011;Klug et al 2012;Solomon et al 2013;Morales-Pineda et al 2014), in part because the deployment of high-frequency sensors is a recent phenomenon (Weathers et al 2013). In the few studies when metabolism was estimated across multiple years in lakes, rivers, or estuaries, metabolic rates were linked to anthropogenic nutrient loading (Uehlinger 2006) and climatic variation (Roberts et al 2007;Staehr and Sand-Jensen 2007;Einola et al 2011;Laas et al 2012;Caffrey et al 2014;Roley et al 2014).…”

“…We asked three questions: (1) How do GPP, R, and NEP vary at both intra-and inter-annual time scales in this oligotrophic lake? We predicted that GPP and R would generally be strongly coupled and low relative to rates estimated in mesotrophic and eutrophic lakes (Solomon et al 2013) and that NEP would usually be negative, given low algal production (Hanson et al 2004;Solomon et al 2013). (2) What are the effects of storms on metabolic rates?…”