Evaluation of nutrients and major ions in streams-implications of different timescale procedures.

Small watersheds are characterized by a high degree of sensitivity to changes observed in their environment, making them important sampling and management units. Due to this high sensitivity, several studies have shown that intensive collecting may be more effective in these systems compared to other timescale procedures. The aim of this study was to evaluate the concentration of organic and inorganic nutrients and major ions dissolved in two small watersheds with different land uses to determine whether there are differences between these watersheds with different levels of impact and to identify the most appropriate timescale procedure for the variables under analysis. Therefore, monthly, daily, and hourly samples were taken in the two streams in the northeast of Brazil. One of the streams is located in an undisturbed area (environmental protected area) (S1) and one in a disturbed area (S2). The results showed significant differences for conductivity, temperature, pH, dissolved oxygen (%), sodium (Na(+)), and chloride (Cl(-)) ions and higher values presented in the anthropogenic stream. Dissolved inorganic nitrogen (DIN) in S2 mainly comprised ammonium (NH4 (+)), while nitrate (NO3 (-)) predominated in S1. The considerable increase in the concentration of NO3 (-) and dilution of Na(+) and Cl(-) after rain in April in S1 shows how precipitation may change the chemical composition of the water in a 1-day period. No changes were observed in the concentrations of major ions and nutrients that could be related to the cyclical variation of the hours during the day in both small watersheds. Daily collections allow better monitoring of the dynamics of streams and greater robustness of the data.