Global climate change can alter the flux of materials and energy between ecosystems.  One such example is the increased export of dissolved organic carbon (DOC) from terrestrial to aquatic ecosystems.  This phenomenon has been observed around the globe, and is referred to as the “browning” of inland waters.  Food web and ecosystem theory predict that such donor-controlled inputs should influence the stability of recipient ecosystems. We tested these predictions by creating a gradient of terrestrial DOC loading in a series of experimental ponds.  After the DOC gradient had been established, we perturbed each pond with a pulse addition of inorganic nutrients (nitrogen and phosphorus).  Over the course of the experiment, we measured a suite of microbial, food web, and ecosystem response variables.  Using Dynamic Linear Modeling (DLM), we quantified stability (sensitivity and return time) of the ponds in response to the nutrient pulse as a function of terrestrial DOC loading. 

Results/Conclusions

Terrestrial DOC loading had a strong, non-linear effect on pond stability in response to the pulse nutrient perturbation. Specifically, phosphorus (P) uptake was much more rapid in ponds with low DOC loading than ponds with high DOC loading. Using a combination of simulation modeling and reciprocal transplant experiments, we conclude that terrestrial DOC inputs reduce ecosystem stability via light limitation of phytoplankton. Although terrestrial DOC inputs subsidized heterotrophic bacteria to some degree, microbes remained carbon limited and were thus incapable of compensating for episodic increases in P availability. Our results suggest that aquatic ecosystems may become less resilient to nutrient perturbations in the future given the observed trends of increasing DOC around the globe.  These results have implications for the understanding land-water interactions, food web dynamics, and eutrophication under future climate change scenarios.