Articles | Volume 15, issue 9
Biogeosciences, 15, 2931–2943, 2018
Biogeosciences, 15, 2931–2943, 2018

Research article 16 May 2018

Research article | 16 May 2018

Distinctive effects of allochthonous and autochthonous organic matter on CDOM spectra in a tropical lake

Luciana Pena Mello Brandão1,2, Ludmila Silva Brighenti1, Peter Anton Staehr2, Eero Asmala3, Philippe Massicotte4, Denise Tonetta5, Francisco Antônio Rodrigues Barbosa1, Diego Pujoni1, and José Fernandes Bezerra-Neto1 Luciana Pena Mello Brandão et al.
  • 1Limnea, ICB, Universidade Federal de Minas Gerais, Av. Antonio Carlos, 6627, Pampulha, Belo Horizonte, Minas Gerais, Brazil
  • 2Department of Bioscience, Aarhus University, Frederiksborgvej, 399, 4000 Roskilde, Denmark
  • 3University of Helsinki, Tvärminne Zoological Station, J.A. Palménin tie 260, 10900 Hanko, Finland
  • 4Departament of Biology, University of Laval, Pavillion Alexandra-Vachon 1045, av. De la Medecine, local 2078, Québec, Canada
  • 5Limnos, ECZ, Universidade Federal de Santa Catarina, Campus Universitário Reitor João David Ferreira Lima, Trindade, Florianópolis, Santa Catarina, Brazil

Abstract. Despite the increasing understanding about differences in carbon cycling between temperate and tropical freshwater systems, our knowledge on the importance of organic matter (OM) pools on light absorption properties in tropical lakes is very scarce. We performed a factorial mesocosm experiment in a tropical lake (Minas Gerais, Brazil) to evaluate the effects of increased concentrations of allochthonous and autochthonous OM, and differences in light availability on the light absorption characteristics of chromophoric dissolved organic matter (CDOM). Autochthonous OM deriving from phytoplankton ( ∼  Chl a) was stimulated by addition of nutrients, while OM from degradation of terrestrial leaves increased allochthonous OM, and neutral shading was used to manipulate light availability. Effects of the additions and shading on DOC, Chl a, nutrients, total suspended solid concentrations (TSM) and spectral CDOM absorption were monitored every 3 days. CDOM quality was characterized by spectral indices (S250–450, S275–295, S350–450, SR and SUVA254). Effects of carbon sources and shading on the spectral CDOM absorption was investigated through principal component (PCA) and redundancy (RDA) analyses. The two different OM sources affected CDOM quality very differently and shading had minor effects on OM levels, but significant effects on OM quality, especially in combination with nutrient additions. Spectral indices (S250–450 and SR) were mostly affected by allochthonous OM addition. The PCA showed that enrichment by allochthonous carbon had a strong effect on the CDOM spectra in the range between 300 and 400 nm, while the increase in autochthonous carbon increased absorption at wavelengths below 350 nm. Our study shows that small inputs of allochthonous OM can have large effects on the spectral light absorption compared to large production of autochthonous OM, with important implications for carbon cycling in tropical lakes.

Short summary
Using mesocosms we investigated the effect of the increase in the allochthonous and autochthonous sources of DOM in a tropical lake, in order to simulate its effects on the characteristics of lakes caused by anthropogenic impacts. The seasonal allochthonous input has much larger effects on the lake and, in addition to increasing nutrients, alters the transparency of water and consequently controls the seasonal dynamics of phytoplankton (autochthonous source) and lake ecology.
Final-revised paper