Biodegradability of Dissolved Organic Carbon in the Rio Piedras watershed, Puerto Rico

Urbanization strongly impacts stream ecosystems and little information is known about how it affects DOC in rivers and how consequently it affects tropical rivers. The importance of DOC is that it is the basis of the food chain in many rivers. This project focuses on changes in DOC biodegradability along a tropical urban river in Puerto Rico. The Rio Piedras runs through the heart of the San Juan Metropolitan Area, making it susceptible to human impacts. The headwaters are less urbanized therefore surrounded by riparian forests whereas downstream, urbanization increases and riparian vegetation decreases. Water samples were collected at seven sites along the river during the months of June, November and January 2008. Samples were incubated for five days at 20 ºC and analyzed for BOD₅. To measure the organic carbon (Particulate + Dissolved Organic Matter) quality, the biodegradability constant (k) was computed for each sample using the Thomas graphing method. Although the k constant seems to be elevated in the headwaters (1.809d^-1; SD = 1.3172) and near the mouth (1.420 d^-1; SD = 4.2879) and decreased in the middle (3.641 d^-1; SD = 8.2969), after concluding a t-test these differences did not prove to be significant (p˃0.05). This demonstrates that urban watersheds do not seem to portray patterns regarding biodegradability of organic carbon.