The influx of sediments carried by rivers can be measured continuously using a turbidimeter through the indirect relationship between turbidity and suspended sediment concentration (SSC). However, this process is dependent on obtaining water samples with suspended sediments to calibrate the turbidimeter. Sampling can be carried out through different methods, resulting in errors and uncertainties in estimating the SSC. Four different possibilities for the composition of the calibration curve were tested in order to evaluate the effectiveness of the turbidimeter calibration for different sampling strategies. The study was conducted in 2012 and 2013 in two catchments in southern Brazil that had a strong sediment yield impact. The results indicate that sampling during rainfall events generate a significant and representative SSC for the turbidimeter calibration. The use of an integrating sampler for synthetic samples provides an effective calibration, but overestimates SSC compared to calibration from rainfall event sampling. The samples collected at fixed intervals - weekly and daily - generated an insufficient amount of data and are not representative of real sediment concentrations of the catchments.

Aim of study: To develop and measure sustainability indicators for the water-food-energy nexus in the Ibirapuitã river basin production systems in the Brazilian Pampa biome. The research seeks to contribute to the area of agriculture and sustainability along two lines: a) develop a methodology of sustainability indicators that can be applied to farming systems globally; and b) increase understanding of the interrelationship between water, food and energy and how it affects rural areas' sustainability. Area of study: The study was conducted in the Ibirapuitã river basin in the Brazilian Pampa biome. Material and methods: The construction of the indicators was based on the MESMIS methodology (Framework for the Evaluation of Management Systems incorporating Sustainability Indicators). In research, 121 farming systems were sampled. The sustainability indexes of the indicators between and within each dimension were analyzed using analysis of variance (ANOVA) and Tukey's test. Main results: A significant difference was found between the averages of the indices of the dimensions in the production systems of the basin (p<0.05). The water dimension presented the highest level of sustainability, classified as "ideal". The energy dimension presented an intermediate level of sustainability, classified as "acceptable”. Furthermore, the food dimension presented the lowest sustainability index among the nexus, classified as "alert". These indexes contribute to identifying the main action points for improving the systems, being an essential tool for local rural extension. Research highlights: The study consolidated a methodology for measuring sustainability indicators based on farming systems' water, energy, and food production characteristics, capable of being replicated in other realities.