EDI Data Portal
The enclosed data are results from a series of monthly (May-August) experiments conducted in 2016. We measured changes in five variables (dissolved organic carbon (DOC), dissolved inorganic carbon, dissolved oxygen, the spectral slope ratio, and the DOC specific ultraviolet absorbance at 320 nm). Groundwater samples adjacent to four lakes of varying trophic status were used to assess changes in the above variables due to photodegradation and biodegradation. Three lakes (Lacawac, Giles, and Waynewood) are located in the Pocono region of Pennsylvania. The fourth lake (Annie) is located in Venus, FL. Details of the experiment can be found in Dempsey et al. 2020 (accepted at Biogeosciences). In this study, we used groundwater (terrestrial DOC) to simulate storm water inputs to the surface of a lake. We assessed the relative importance of photodegradation and biodegradation by measuring changes in the above variables. All experiments were conducted on the surface of Lake Lacawac (PA). Here, we provide our raw data from the experiments.
Outgassing of carbon dioxide (CO2) from freshwater ecosystems comprises 12-25% of the total carbon flux from soils and bedrock. This CO2 is largely derived from both biodegradation and photodegradation of terrestrial dissolved organic carbon (DOC) entering lakes from wetlands and soils in the watersheds of lakes. In spite of the significance of these two processes in regulating rates of CO2 outgassing, their relative importance remains poorly understood in lake ecosystems. In this study, we used groundwater from the watersheds of one subtropical and three temperate lakes of differing trophic status to simulate the effects of increases in terrestrial DOC from storm events. We assessed the relative importance of biodegradation and photodegradation in oxidizing DOC to CO2. We measured changes in DOC concentration, colored dissolved organic carbon (SUVA320 and Sr), dissolved oxygen, and dissolved inorganic carbon (DIC) in short-term experiments from May-August, 2016. In all lakes, photodegradation led to larger changes in DOC and DIC concentrations and optical characteristics than biodegradation. A descriptive discriminant analysis showed that in brown-water lakes, photodegradation led to the largest declines in DOC concentration. In these brown-water systems, ~30% of the DOC was processed by sunlight and a minimum of 1% was photo mineralized. In addition to documenting the importance of photodegradation in lakes, these results also highlight how lakes in the future may respond to changes in DOC inputs.
