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Spatio‐temporal variability in underwater light climate in a turbid river‐floodplain system: Driving factors and estimation using Secchi disc
Author(s) -
Mayora Gisela,
Devercelli Melina
Publication year - 2019
Publication title -
river research and applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.679
H-Index - 94
eISSN - 1535-1467
pISSN - 1535-1459
DOI - 10.1002/rra.3429
Subject(s) - floodplain , photosynthetically active radiation , environmental science , colored dissolved organic matter , flood myth , hydrology (agriculture) , atmospheric sciences , ecology , phytoplankton , geology , geography , chemistry , biochemistry , photosynthesis , geotechnical engineering , archaeology , nutrient , biology
The underwater light climate has important effects on primary producers. The aim of this research was to evaluate its variability in a turbid river‐floodplain system. Photosynthetically active radiation (PAR) was measured in the Middle Paraná River during different hydrological phases to (a) analyse the photosynthetically active radiation attenuation coefficient ( k ) and euphotic depth (Z eu ) as well as their associations with optically active components and (b) develop and evaluate indices and regression models based on Secchi disc (SD) measurements to estimate k and Z eu . Values of k were higher in the fluvial system than in the floodplain and during low‐water stage than high‐water stage. Particulate components controlled the light climate variability. Chromophoric dissolved organic matter and chlorophyll‐ a had significant effects during floods. The estimation of k and Z eu was sensitive to temporal but not to spatial variations. The highest prediction accuracy was observed when using specific non‐linear regressions for each hydrological phase, especially for Z eu estimation (low stage: k = 1.76 × SD −0.80 , Z eu = 2.62 × 1/SD −0.80 ; high stage: k = 2.04 × SD −0.53 , Z eu = 2.26 × 1/SD −0.53 ). The indices k × SD and Z eu /SD were significantly different from those proposed for clear water environments. It is concluded that temporal variations should be considered when estimating k and Z eu in turbid river‐floodplain systems because of the temporal heterogeneity in optically active components. Considering that ecological implication of the light climate depends on Z eu :depth ratio, we propose to estimate Z eu instead of k . Finally, indices proposed for clear water environments are not recommended to be applied to turbid environments.