Maycira Costa (PI, UVic)
Evlyn Novo (INPE - Brazil)
Kevin Telmer (SEOS - UVic)
Felipe Lobo (PhD. Student, UVic)
The characterization of transmission of solar energy in the water column is essential for understanding several water processes such as phytoplankton distribution and primary productivity, the ecology, and chemistry of the upper water column. Changes in transmission of light in water are mostly due to variability of water optical constituents, which in the Amazon are strongly affected by seasonal riverine stream flow, regional geology, and upland processes. Anthropogenic use of the Amazonian uplands could have major regional effects on the seasonal distribution of optical constituents in the water, and subsequently affect the quantity and quality of light in the water column.
Preliminary results showed that the quantification of hyperspectral downwelling vertical attenuation coefficient (Kd) and irradiance (Ed) in the euphotic depth (Zeu) in 2005 (falling) and 2006 (rising waters) in Amazonian waters showed that Kd is higher in the blue (5-9 m-1), decreasing towards the green (4-7 m-1) and red (3-5 m-1) part of the spectra. Further, Kds are generally higher in white waters than in black and clear waters. A stepwise multiple regression analysis showed that when all the data is polled together, TSS and acdom are the main drivers of spectral Kds (R2 ~ 0.65; p<0.005). However, when analyzing only black and clear waters Chla also explains the variability of Kds (R2 ~ 0.96; p<0.005). The selective attenuation by the optical constituents result in maximum light reaching Zeu of 1.0 to 0.5 m (white waters) is dominantly at 685nm, Zeu of 1.8 to 3.0 m (black) is at 695nm, and Zeu of 4.0 to 3.0 m (clear) is at 590nm.This research will provide the first baseline information about quality and quantity of light under water in the Amazon rivers, and how this may change in rivers under the influence of small-scale gold mining.