TRADE-OFFS: What drives pelagic GPP across lake ecosystems?

It is well-known and accepted that light and nutrients are the main controls on pelagic primary production in lakes. However, widespread and ongoing environmental change are altering nutrient loads and the light environment in lakes through processes like brownification. While substantial research in drivers of pelagic primary production in lakes has been conducted over the last few decades, the responses are often context-dependent. In 2018, Kelly et al. published a paper in Ecosystems that proposes a predictive model that can investigate these responses.The model predicts a "hump shaped" relationship between GPP and DOC when nutrient and DOC loads are correlated in space and time. The magnitude of the peak is determined by the stoichiometry of the DOC to nutrient load, while the location of the peak along the x-axis is mainly determined by lake area. It is predicted that when nutrients are provided in greater supply relative to DOC, primary productivity should be high. In large lakes, light limitation for primary producers should occur at a lower DOC concentration relative to smaller lakes due to the positive relationship between lake area and epilimnion depth. We propose a data synthesis of GLEON lakes in which we test this newly developed theory. Specifically we will ask:

1. How does pelagic GPP vary as a function of incoming DOC & nutrient load stoichiometry, in-lake light climate, and lake size?
2. Does a model developed in the north temperature lakes hold for other lake regions of the world?

Would you like to contribute data? If you missed the data call on the GLEON list-serv, please refer to THIS DOCUMENT to read more about what we are looking for.