Distinctive effects of allochthonous and autochthonous organic matter on CDOM spectra in a tropical lake
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 i...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-05-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/15/2931/2018/bg-15-2931-2018.pdf |
| Summary: | 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 <i>a</i>) 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 <i>a</i>, nutrients, total suspended solid
concentrations (TSM) and spectral CDOM absorption were monitored every 3
days. CDOM quality was characterized by spectral indices
(<i>S</i><sub>250–450</sub>, <i>S</i><sub>275–295</sub>, <i>S</i><sub>350–450</sub>,
<i>S</i><sub>R</sub> and SUVA<sub>254</sub>). 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 (<i>S</i><sub>250–450</sub> and <i>S</i><sub>R</sub>) 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. |
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| ISSN: | 1726-4170 1726-4189 |