3 years ago

Dynamics and fluxes of organic carbon and nitrogen in two Guiana Shield river basins impacted by deforestation and mining activities

Alain Laraque, Jean-Michel Martinez, Abrahan Mora, Antoine Gardel, Eric Beaucher, Marjorie Gallay, Jean-Claude Doudou, Max Sarrazin, Christelle Lagane
Deforestation and mining activities have proven to be very damaging to rivers because these activities disturb the environmental characteristics of rivers. Thus, the concentrations of dissolved organic carbon (DOC), particulate organic carbon (POC), particulate nitrogen (PN) and Chlorophyll-a (Chl-a) were measured monthly during two hydrological years in the Maroni and Oyapock rivers to assess the dynamics and fluxes of organic carbon and nitrogen in these two Guiana Shield basins, which have been strongly (Maroni) and weakly (Oyapock) impacted by deforestation and mining activities. The two-year time series show that DOC, POC, PN and Chl-a concentrations vary seasonally with discharge in both rivers, indicating a hydrologically dominated control. Temporal patterns of DOC, POC and PN indicate that these variables show maximum concentrations in rising waters due to the yield of organic matter and nitrogen accumulated in soils, which are incorporated into the rivers during rainfall. However, the Chl-a concentrations were at a maximum during low water stages. The C/N and C/Chl-a ratios also showed a seasonal trend, with lower values during the low water periods due to an increase in algal biomass. During high water, the POC in both rivers is the result of terrestrial organic matter, whereas during low water autochthonous organic matter can reach up to 34% of the POC. The mean annual fluxes of TOC and PN were higher (4.56 x 105 TonC yr-1 and 1.77 x 104 TonN yr-1, respectively) in the Maroni River than those (1.84 x 105 TonC yr-1 and 0.54 x 104 TonN yr-1, respectively) in the Oyapock River. However, the specific fluxes of DOC, POC and PN from both basins were nearly the same. Although gold mining activities are performed in both basins, there is no conclusive evidence regarding the impact of these activities on the dynamics of organic matter and particulate nitrogen in the Maroni and Oyapock rivers.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/hyp.11394

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