Gradiente Longitudinal do Fitoplâncton ao Longo de um Grande Rio Tropical

Abstract

The Paraíba do Sul River supplies more than 20 million inhabitants and is impacted by anthropic activities, with industrial and domestic effluents, electric power generation and irrigation. Among the multiple uses in the system, the generation of energy stands out, since buses have been one of the main causes of changes in aquatic ecosysteμS, whose transformations can be associated to socioeconomic losses and reduction of biodiversity. This work is part of the Cachoeiras Project, a multi-institutional expedition, composed by the National Institute of Space Research, National Center for Natural Disaster Monitoring and Alerts, Rio de Janeiro State University, Federal University of Itajubá (INPE, CEMADEN, UERJ, UNIFEI), which traveled throughout the Paraíba River in kayaks, performing continuous collections in the main channel, from July to September 2015 and made available data on abiotic and chlorophyll-a variables. The objective of this study is to evaluate the interactions between the phytoplankton community and the set of physicochemical factors and the effects of the existing riverbeds on the phytoplankton quantitative and qualitative expressions through the functional groups approach. Phytoplankton samples were analyzed from 219 sampling stations, with emphasis on the responses to the effects of the buses present in the river channel. Functional Groups Based on Morphology (GFBM) and Functional Groups Based on River Morphology (GFBMr) were used to capture phytoplankton relationships with environmental conditions. Canonical Correspondence Analysis (CCA) was used to relate environmental conditions to abundance biovolume) of the functional groups. The values of Phosphorus and Nitrogen were related to the increase of urban agglomerates. Changes in the phytoplankton composition showed that typical groups of lentic environments appear from 30 km upstream of the busses, revealing the phytoplankton's functional response to the change in river flow. These changes were due to the type of bus and the residence time. The anthropic influence of the urban agglomerates, determining nutrient values (NH4 +, NO3 -, PO4-3), and the hydrodynamic change by the bus, were the factors associated to the increase of the phytoplankton functional richness, related to the increase in the supply of resources. The GFBM and GFBMr functional groups approach proved to be a good tool for the analysis of the effects of the lotic-lenotic-lotic transition on spatial dynamics of phytoplankton, with GFBMr groups being more efficient in this discussion