Dissolved organic carbon (DOC) is a key component of the carbon cycle in aquatic systems, and understanding the dynamics of DOC is essential for understanding aquatic ecosystem metabolism and functioning. However, recent increases in the atmospheric deposition of DOC is causing staining, or browning to occur in freshwater systems. This impacts the gross primary production (GPP), as browning interferes with light dependent biological processes. Chromophoric or colored dissolved organic material (CDOM) can be used to explain the optical properties of organic carbon. It is known for having a strong relationship with total DOC in many systems, and has been used as a proxy for DOC in other studies. The objectives of this study were to determine the range in DOC and CDOM quantity in streams and lakes, and to assess any differences in trends between the two system types. Sampling a variety of stained and unstained systems, we predicted a wide range in DOC and CDOM with a positive relationship between the two parameters. We expected that this relationship would be stronger in lakes, since closed systems allow for longer retention of nutrients and greater decomposition of less-colored DOC with low molecular weight. Surface water grab samples were taken from 54 streams and lakes across the northern highlands region of Wisconsin and the upper peninsula of Michigan.
Results/Conclusions
In addition to DOC and CDOM, spectrophotometric properties of water samples were analyzed for color at 456nm, specific ultraviolet absorption at 254nm (SUVA254), spectral slope at 275-295nm and 350-370nm (S275-295, S350-370), and spectral ratio (Sr). Overall, DOC ranged from 3.01-25.01 mg/L and CDOM ranged from 4.25-32.29 mg/L. In both streams and lakes, the relationship between DOC and CDOM was highly linear, and spectrophotometric properties exhibit a strong relationship with DOC and CDOM. As expected, these relationships were tighter for lake samples than stream samples. Additionally, various samples possessed high values for color relative to DOC and CDOM quantity, which can be caused by the presence of other dissolved materials present in the system. Iron analyses will be done, as its presence in the system could explain this trend.