Print PageIn aquatic ecosystems, respiration of organic matter to CO2 is a critical ecosystem process linked to food webs, global biogeochemical cycles, and ecosystem trophic state. Models of ecosystem respiration (ER) almost exclusively assume respiration to be constant both night and day. However, respiration rates are likely to vary on hour to minute time scales due to, for example, availability and quality of organic substrates. There are currently only a handful of studies that examine intra-diel patters of ecosystem respiration, and none that have compared these patterns among multiple lakes over a range in biologic and physical characteristics.
We capitalized on the Global Lakes Ecological Observatory Network (GLEON) of autonomous, high-frequency sensor data from 24 globally distributed lakes to investigate patters in nighttime respiration rates. Data were limited to nighttime hours during summer months and analyzed on a daily basis. Dissolved oxygen data were compared to a comprehensive ecosystem metabolism model with five potential mechanisms of ER: no ER, constant ER, linearly decreasing ER, exponentially decreasing ER, and sigmoid changes in ER. The relative support among models was compared to the observed data using information theoretic criteria.
Results/Conclusions
We found significant empirical support for multiple models of ecosystem respiration both among and within lakes. The most parsimonious models were predominantly the relatively simple constant ER and linearly decreasing ER over the nighttime period. However, we also frequently found support for more complex models including exponentially decreasing and sigmoid patterns of ER. The best models of ER were related to intrinsic characteristics of each lake including ecosystem trophic state, temperature regime, and light environment. Similar relationships were also present at the daily scale. With a greater mechanistic understanding of ER over a wide diversity of ecosystem types, we will be better able to predict the ecosystem effects of anthropogenic changes (climate change, eutrophication) to aquatic ecosystems. The continued expansions of global, high-frequency sensor networks will be essential in refining our understanding of what controls this and other critical ecosystem processes.
