Abstract
Aim: The importance of land use patterns on the occurrence and magnitude of eutrophication-related variables (total phosphorus, total nitrogen, chlorophyll-a and total suspended solids) was assessed for three tropical rivers located in the same watershed (Ribeira do Iguape watershed, Sao Paulo State, Brazil); Methods: To obtain the percentages of land use by sub-basin, thematic maps were carefully analyzed and a Planimeter was used. Land use patterns were classified as: forest, agriculture, pasture, water, urban area, grassland and others (e.g. clouds and shadows). Samples for determination of Total Phosphorus (TP), Total Nitrogen (TN), Chlorophyll-a (Chl-a) and Total Suspended Solids (TSS) were collected from the three Brazilian rivers; Results: Canha River, more preserved (about 70% of its catchment area is covered by forests), presented some sites characterized as oligotrophic and others as mesotrophic. Pariquera-Acu River in turn showed great oscillation in TSI (Trophic State Index) and Jacupiranguinha River was the most influenced by the eutrophication (TSI results were characteristic of hypereutrophic systems). In this river, the concentrations of total phosphorus reached 124 mg.L–1 in the sample site that reflects the impacts suffered by the aquatic environment due to the discharge of an industrial effluent; Conclusions: The results suggested that the trophic level of the rivers was associated with land use found in their drainage areas and with the specific characteristics of each lotic system, such as presence or absence of riparian vegetation, for instance. It is expected that these results contribute to the advancement of Limnology and serve as stimulus and basis for the beginning of plans and programs to revitalize the studied aquatic ecosystems of Baixo Ribeira do Iguape watershed (SP, Brazil).
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