Baseline water quality and nutrient dataset from the Almada River Watershed under the potential influence of the West-East Integration Railway (FIOL), Bahia, Brazil

This dataset supports the manuscript entitled "Nutrient Assessment in a river under the potential influence of a planned railway: establishing an environmental baseline." It provides baseline water quality and nutrient data collected in the Almada River Watershed (Bahia, northeastern Brazil), an area potentially influenced by the construction of the West-East Integration Railway (FIOL) and the planned Porto Sul port complex. The dataset includes measurements obtained during six sampling campaigns conducted between June 2022 and January 2023 at seven monitoring sites. Variables comprise geographic coordinates, sampling dates, physicochemical water parameters (temperature, pH, electrical conductivity, dissolved oxygen), total suspended solids, chlorophyll-a, dissolved inorganic nitrogen species (NO₃⁻, NO₂⁻ and NH₄⁺), dissolved organic nitrogen (DON), dissolved total nitrogen (DTN), particulate organic nitrogen (PON), dissolved inorganic phosphorus (orthophosphate), dissolved organic phosphorus (DOP), dissolved total phosphorus (DTP), and particulate organic phosphorus (POP). The repository includes the complete dataset used in the study, a data dictionary describing all variables and measurement units, metadata for the sampling sites, and a README file documenting the dataset organization and analytical procedures. These data establish a pre-impact environmental baseline and may support future environmental monitoring, environmental impact assessments, watershed management, comparative before-and-after studies, and investigations of nutrient biogeochemistry and eutrophication in tropical freshwater ecosystems.