Spatial and temporal variability of light attenuation in large rivers of the Amazon

• Published in: Hydrobiologia Vol. 702; no. 1; pp. 171 - 190
• Main Authors: Costa, M. P. F., Novo, E. M. L. M., Telmer, K. H.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.02.2013; Springer; Springer Nature B.V
• Subjects: Absorption; Animal and plant ecology; Animal, plant and microbial ecology; Biogeochemistry; Biological and medical sciences; Biomedical and Life Sciences; Chlorophyll; Cyanophyceae; Dissolved organic matter; Ecology; Fresh water ecosystems; Freshwater & Marine Ecology; Fundamental and applied biological sciences. Psychology; General aspects; Invisibility; Life Sciences; Light; Nuclear radiation; Photosynthesis; Plankton; Primary Research Paper; Rivers; Sediment, Suspended; Sedimentation & deposition; Suspended sediments; Synecology; Wavelengths; Zoology; South America; America; Amazon Basin; Brazil, Para, Oriximina, Trombetas; Brazil, Para, Tapajos R; ASE, Atlantic, Madeira; Brazil, Para, Trombetas R; South America, Amazon R; Light attenuation; Underwater irradiance; Sediment; Dissolved organic matter; Phytoplankton; Rivers; Amazon; Spatial variability; Tropical zone; Underwater; Environmental factor; Irradiance; Sediments; Freshwater environment; Aquatic environment; Light; Attenuation; Stream
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1007/s10750-012-1319-2

The light field and its relationship with biogeochemical variables were investigated in the Solimões, Negro, Amazon, Madeira, Uatumã, Trombetas, and Tapajós Rivers. In high suspended sediment rivers, total suspended matter is the primary control on light attenuation ( r  = 0.8), with colored dissolved organic matter (CDOM) being secondary ( r  = −0.6) due to scattering and absorption, respectively. Photosynthetically active radiation was the lowest (<100.0 μmol m −2  s −1 at the depth of half Z 1% ) and was limited to depths of less than 1.0 m and confined to red light. In low suspended sediment rivers, CDOM is the primary control on light attenuation ( r  = 0.9). The concentrations of chlorophyll a (Chla) and CDOM cause variations among these rivers. High CDOM rivers, Negro and Uatumã, are depleted (<0.5% of incoming irradiance) of blue and green light at the depth of half Z 1% . The light spectra of low CDOM and higher Chla waters, such as the Tapajós, Uatumã, and Trombetas Rivers at rising water stage, are restricted to green and red wavelengths, and marked by high absorption at 620 and 670 nm, due to the presence of Cyanophyceae.