Abstract
The spatial distribution and behavior of limnological variables were studied in a fluvial-lacustrine system, in northern Rio de Janeiro State, Brazil. Physical (e.g. temperature, transparency), physico-chemical (e.g. pH, conductivity), chemical (e.g. inorganic nutrients, dissolved oxygen, particulate and dissolved organic carbon), biochemical (water-soluble carbohydrates – SCHO, total proteins – TPROT, chlorophyll a – Chl a and carotenoids – CAR) and biological (phytoplankton taxa composition) variables were assessed in water-column. Results from dissolved and particulate phases varied considerably among sampling sites. The studied variables indicated some relationships, in limnetic zone, between inorganic compounds and organic products (biochemical). In comparison to lake and outflow (channel) waters, the main inflow (stream) body water was characterized by lower concentrations of particulate biochemical variables and higher concentrations of dissolved inorganic-N. Gross biochemical composition of POC and DOC indicated spatial variation in the fluvial-lacustrine system with the minor participation of TPROT-C (total protein carbon) and SCHO-C (water-soluble carbohydrate carbon) in the center of the lake. At the horizontal space of the lacustrine system, at the ends of the lake, it was also observed a shift between the relative participation of TPROT-C and SCHO-C in POC. Ecophysiological state and nature of particulate matter were also evaluated through photosynthetic pigment concentrations, light microscope analysis, (C:N)a, C:Chl a, SCHO:TPROT, TPROT:Chl a and SCHO:Chl a ratios. Spatial variations were recognized in the fluvial-lacustrine system and were linked to a variety of factors such as the nature (detrital vs. living plankton algae) and origin (allochthonous vs. autochthonous) of the suspended particulate matter, hydrological characteristic of the environments (lotic vs. lentic), phytoplankton metabolical responses induced by nitrogen deficiencies, and wind stress. Additionally, based on the present concentrations of Chl a and the high proportion of the cyanobacterium Cylindrospermopsis raciborskii (∼ 90%) in Cima Lake phytoplankton composition we point out that the lacustrine system has suffered profound limnological changes from the last 10 years.
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