Dissolved organic and inorganic carbon in small streams in Eastern Amazonia
Costa, Embrapa Amaz˘nia Oriental, email@example.com
Figueiredo, Embrapa Amaz˘nia Oriental, firstname.lastname@example.org
Markewitz, The University of Georgia, DMARKE@warnell.uga.edu
Davidson, The Woods Hole Research Center, email@example.com
We conducted this study in streams situated in Paragominas and IgarapÚ-ašu counties, in Parß state, Eastern Amazonia during the year of 2005. The streams in Paragominas were: Cinquenta e Quatro (Cq), Sete (St) e Paje˙ (Pj). In all three catchments, the dominant soil type is clay Oxisols. Remnant forests are common in the headwater areas and other land use (pastures, crops, and secondary vegetation) dominate downstream. The stream in IgarapÚ-ašu was Cumaru, where the soils are sandy and small farms are the most important land use class, with areas of headwaters protected by secondary vegetation. The objective of this work was to evaluate the dynamics of dissolved organic and inorganic carbon (DOC and DIC) in these water bodies and its relationships with land use, identifying sources that contribute to the aquatic ecosystem and the seasonality of their concentrations. The maximum values in the Paragominas streams sampling stations were (Cq, St and Pj, respectively): pH (6.30; 4.66 and 4.82), conductivity (59.8; 32.7 and 75.8 ÁS cm-1) and dissolved oxygen (DO) (6.32; 7.94 and 7.35 mg L-1). The minimum values were: pH (4.23; 4.05 and 4.04), conductivity (25.5; 26.2 and 30.5 ÁS cm-1) and DO (2.14; 4.10 and 1.83 mg L-1). In these streams the concentrations of DOC varied between 0.24 and 9.84 mg L-1, and DIC ranged from 0.33 to 8.43 mg L-1. At Cumaru stream, in IgarapÚ-ašu, the maximum and minimum values were: pH (6.22 and 3.62 - headwater; 6.11 and 3.85 - main channel), conductivity (62.0 and 3.7 ÁS cm-1 - headwater; 39.7 and 7,7 ÁS cm-1 - main channel) and DO (8.60 and 2.00 mg L-1 - headwaters; 8.70 and 3.30 mg L-1 - main channel). DOC varied between 0.01 and 15.13 mg L-1 (headwaters) and 0.56 and 16.00 mg L-1 (main channel). The highest DOC concentrations are related to higher discharges in both regions (Paragominas and IgarapÚ-ašu). Higher DOC concentrations in IgarapÚ-ašu compared with Paragominas data point to larger organic carbon leaching in sandy soils than in clay soils. Other conclusions can be reached after the finalization of the complementary studies that focus on the differences in land use, especially agriculture, the characteristics of the soils, leaching and overland flow processes.