Spatial variability of chromophoric dissolved organic matter in a large floodplain river: control factors and relations with phytoplankton during a low water period

Abstract

Chromophoric dissolved organic matter (CDOM) affects ecological processes in freshwater environments. Few studies assessed its spatial variability and relations with phytoplankton in floodplain rivers. Therefore, these topics were examined in a hydrological connectivity gradient in the Middle Paraná system. Absorption coefficients at 250 and 365 nm were measured to estimate CDOM concentration and molecular weight (MW), to find their explanatory limnological variables (Redundancy Analysis, RDA), and to assess their contribution to the explanation of phytoplankton structure (Canonical Correspondence Analysis, CCA). Conductivity and turbidity explained CDOM significantly. Increased conductivity from the main channel to floodplain lakes was associated with increased CDOM concentration. The lake indirectly connected to the river showed the highest turbidity associated with high-MW-CDOM, while the isolated lake showed the highest conductivity associated with low-MW-CDOM. Phytoplankton structure was significantly explained by conductivity, turbidity, and high-MW-CDOM (CCA). Environments directly connected to the river (with the lowest conductivity) were associated with diatoms. Phytoflagellates were associated with turbidity and high-MW-CDOM in the lake indirectly connected to the river, whereas Cyanobacteria were associated with conductivity and low-MW-CDOM in the isolated lake. The combined effect of physical factors and CDOM explained the highest fraction of species variation (partial CCA). As a conclusion: (1) CDOM increases as hydrological connectivity with the river decreases; (2) lake sediment resuspension is linked to an increase of high-MW-CDOM; (3) lake isolation from the river corresponds to an increase in low-MW-CDOM; and (4) CDOM explains phytoplankton structure significantly and should be considered as an important variable in studies of microalgal assembly.

Phytoplankton dynamics in the Congo River

“…This is quite different from most reports on phytoplankton composition in large tropical rivers, particularly of South America (e.g. Garcia de Emiliani, ; Lewis et al ., ; Davies et al ., ; Devercelli et al ., ; O'Farrell & Izaguirre, ) but also from Africa (Prowse & Talling, ; Talling & Rzόska, ): one would have expected dominance of diatoms during both discharge conditions, owing to light limitation resulting from the TSM concentration in the mainstem and large tributaries, and from high DOC in the blackwater tributaries (Mayora, Devercelli & Frau, ). Indeed, considering a mean daily surface irradiance of 750 μE m −2 s −1 , calculated from continuous recordings during the cruises, the mean light exposure of phytoplankton would have been on average 35 μE m −2 s −1 in FW versus 71 μE m −2 s −1 in HW (Table ).…”

A trait‐based approach predicting community assembly and dominance of microbial invasive species

“…Samples were taken bimonthly in six occasions (January 2013-March 2014), including littoral and open water sites (n = 12). The Miní Lake is located within the Paraná River floodplain, it is permanently connected to the river with a residence time between 1 and 10 days, and modulated by hydrological and sedimentological pulses of the fluvial system (Mayora et al 2013(Mayora et al , 2016. In Miní Lake, samplings were carried out approximately fortnightly from November 2009 to December 2010, and from January to December 2012 (n = 38).…”

“…High flushing rates in Miní Lake hinder C. furcoides local growth and precludes it from negatively affect the local community. Further, a high degree of native species connectivity constitutes a mechanism that diminishes the negative effects of invasion (Howeth 2017) and increase total phytoplankton richness (Devercelli et al 2014, Mayora et al 2016. The analysis of invasion processes explicitly including network effects should be conducted to determine the relative contribution of dispersal versus local effects.…”

Spatio‐temporal variability in underwater light climate in a turbid river‐floodplain system: Driving factors and estimation using Secchi disc

“…Previous studies have shown a decrease in suspended particulate matter and an increase in CDOM and phytoplankton biomass from the main channel (MC) towards the most isolated floodplain water bodies (Mayora, Devercelli, & Frau, ; Unrein, ; Zalocar de Domitrovic, Devercelli, & García de Emiliani, ). The spatial differences are more evident during isolation periods due to the effects of local driving forces (Maine, Suñe, & Bonetto, ; Roberto, Santana, & Thomaz, ; Thomaz, Bini, & Bozelli, ).…”