Abstract Background Weeds have high spatial variability and show clustering behavior, with heterogeneity in scales that can be evaluated through multifractal analysis. Objective The objective of this study was to evaluate the spatial variability of weeds using multifractal analysis in a no-till area. Methods Sampling was conducted at 1,015 sampling points in an experimental plot with a regular grid of 5 × 5 m (2.38 ha) with no tillage. The area was cultivated with triticale (Triticum secale), and in the summer of 2011, the area was cultivated with soybean (Glycine max). Data were analyzed using descriptive statistics and multifractal analysis using the box-counting method to determine the scaling properties of the variables. Results The predominance of Raphanus raphanistrum was identified in the winter crop and Commelina ssp. during the summer. The singularity spectrum showed greater asymmetry for Raphanus raphanistrum and Commelina ssp. in relation to the category of other weeds (OW). The degree of multifractality varied throughout the study period, showing the ecological patterns of the studied species. Scale heterogeneity was revealed, with different degrees of multifractality that evidenced the processes of dispersion and colonization of the environment by the different weed species evaluated. Conclusions The species Raphanus raphanistrum and Commelina ssp. showed domains of low measurement values, and OW was the most heterogeneous.

Este estudo é parte do esforço para o estabelecimento de um Protocolo de Bioavaliação Rápida (PBR) utilizando macroinvertebrados bentônicos como bioindicadores da qualidade de água de riachos no Sudeste do Brasil. Foi analisada a relação custo/eficácia de procedimentos de coleta freqüentemente utilizados em PBRs, amostradores do tipo Surber e Kick-net, e de três malhas, 125, 250 e 500 µm. Foram coletados e identificados 126.815 macroinvertebrados, representando 57 famílias. As amostras coletadas com Kick-net apresentaram número de taxa e de valores do índice BMWP significativamente maiores do que as coletadas com Surber, sem um aumento significativo no esforço amostral medido em tempo despendido para análise da amostra. Não houve diferenças significativas quanto à relação custo/eficácia entre os coletores. Quanto ao tamanho da malha, em 125 µm e 250 µm foram encontradas maiores abundância de macroinvertebrados e necessário mais tempo para processar as amostras, no entanto sem produzir diferenças significativas no número de taxa e em valores do índice BMWP. Assim, a malha de 500 µm foi considerada mais eficiente do que as malhas mais finas. Portanto, recomenda-se o uso de coletores do tipo kick usando uma malha de 500µm, para PBRs ao nível taxonômico de família em rios de características similares às deste estudo no Brasil.

This study is part of the effort to test and to establish Rapid Bioassessment Protocols (RBP) using benthic macroinvertebrates as indicators of the water quality of wadeable streams in south-east Brazil. We compared the cost-effectiveness of sampling devices frequently used in RBPs, Surber and Kick-net samplers, and of three mesh sizes (125, 250 and 500 µm). A total of 126,815 benthic macroinvertebrates were collected, representing 57 families. Samples collected with Kick method had significantly higher richness and BMWP scores in relation to Surber, but no significant increase in the effort, measured by the necessary time to process samples. No significant differences were found between samplers considering the cost/effectiveness ratio. Considering mesh sizes, significantly higher abundance and time for processing samples were necessary for finer meshes, but no significant difference were found considering taxa richness or BMWP scores. As a consequence, the 500 µm mesh had better cost/effectiveness ratios. Therefore, we support the use of a kick-net with a mesh size of 500 µm for macroinvertebrate sampling in RBPs using family level in streams of similar characteristics in Brazil.