Agriculture impairs stream ecosystem functioning in a tropical catchment.

The expansion of agriculture is particularly worrying in tropical regions of the world, where native forests are being replaced by crops at alarming rates, with severe consequences for biodiversity and ecosystems. However, there is little information about the potential effects of agriculture on the functioning of tropical streams, which is essential if we are to assess the condition and ecological integrity of these ecosystems. We conducted a litter decomposition experiment in streams within a tropical catchment, which were subjected to different degrees of agricultural influence: low (protected area, PA), medium (buffer area, BA) and high (agricultural area, AA). We quantified decomposition rates of litter enclosed within coarse-mesh and fine-mesh bags, which allowed the distinction of microbial and detritivore-mediated decomposition pathways. We used litter of three riparian species representing a gradient in litter quality (Alnus acuminata > Ficus insipida > Quercus bumelioides), and examined detritivore assemblages through the contents of litterbags and benthic samples. We found that the increasing agricultural influence promoted microbial decomposition, probably due to nutrient-mediated stimulation; and inhibited detritivore-mediated and total decomposition because of reduced detritivore numbers, most likely caused by pesticides and sedimentation. Effects were evident for Alnus and Ficus, but not for Quercus, which was barely decomposed across the gradient. Our study provides key evidence about the impact of agriculture on tropical stream ecosystem functioning, which is associated to changes in stream assemblages and may have far-reaching repercussions for global biochemical cycles.

Effects of multiple stressors associated with agriculture on stream macroinvertebrate communities in a tropical catchment.

Tropical forests are declining at unprecedented rates in favour of agriculture, and streams can be severely impacted due to effects of multiple stressors that have rarely been considered together in tropical studies. We studied the effects of multiple stressors associated with agricultural practices (pesticide toxicity, nutrient enrichment and habitat alteration-quantified as TUmax, soluble reactive phosphorus concentration and sedimentation, respectively) on macroinvertebrate communities in a tropical catchment in Panama (13 stream sites sampled in 20 occasions from 2015 to 2017, with 260 samples in total). We examined how macroinvertebrate abundance, taxonomic richness, community composition and biotic indices (SPEAR and BMWP/PAN, which were specifically designed to detect pesticide toxicity and nutrient enrichment, respectively) varied depending on the studied stressors, considering their single and combined effects. Our analyses revealed significant effects of the studied stressors on macroinvertebrate communities, with two particular results that merit further attention: (1) the fact that pesticide toxicity affected BMWP/PAN, but not SPEAR, possibly because the former had been adapted for local fauna; and (2) that most stressors showed antagonistic interactions (i.e., lower combined effects than expected from their individual effects). These results highlight the need for toxicity bioassays with tropical species that allow adaptations of biotic indices, and of observational and manipulative studies exploring the combined effects of multiple stressors on tropical macroinvertebrate communities and ecosystems, in order to predict and manage future anthropogenic impacts on tropical streams.

Comparación de dos aproximaciones para la estimación de la incertidumbre en análisis de residuos de plaguicidas mediante cromatografía de gases / Comparison of two approaches to estimate the uncertainty for pesticide residue analysis by gas cromatography / Comparação de dois métodos para a estimativa da incerteza análise de resíduos por cromatografia gasosa

La correcta interpretación de un resultado de medición requiere el conocimiento de la incertidumbre de la medida; de esta manera, se han desarrollado diferentes aproximaciones y guías para realizar el cálculo y la interpretación de la incertidumbre de la medición. En este estudio se comparan dos aproximaciones para la estimación de la incertidumbre de una metodología, de manera rápida y económica basada en el método QuEChERS para el análisis de 15 plaguicidas organofosforados mediante cromatografía de gases con detector de nitrógeno fósforo. El primer método empleado se basa en la aproximación descrita por la guía para la expresión de la incertidumbre de medición (GUM), la cual se apoya en la combinación de las incertidumbres involucradas en los procesos de medición de la metodología. El segundo método utilizado correspondió a la aproximación propuesta por Haslòva y Stêpán, la cual incluye algunos elementos del método de arriba hacia abajo (top down) y se basa en el empleo de los datos de repetibilidad en diferentes etapas del proceso analítico. Los resultados mostraron que al emplear la aproximación de la GUM, los valores de incertidumbre son más bajos que al utilizar el método de Haslòva. Asimismo, mediante la aproximación GUM se encontró que el aporte a la incertidumbre por la preparación de los estándares (peso, dilución y pureza) representa el principal componente. Por otro lado, mediante el método combinado se pudo establecer que la principal fuente de incertidumbre corresponde al proceso de extracción de los analitos, y, en contraste, se halló que la fuente que menor aporta corresponde a la preparación de los estándares. Finalmente, los valores calculados de incertidumbre expandida mediante el método combinado se encontraron entre el 12,7 y el 27,1% de la concentración a la cual se estimó la incertidumbre.

The correct interpretation of a measurement result requires knowledge about its uncertainty. Very different approaches for the estimation of the uncertainty related to measurement results are found in the literature and in published guidelines. In this work two different approaches for uncertainty estimation are compared on an easy, rapid and low-cost sample preparation approach for the determination of pesticide residues in fruits by gas chromatography with nitrogenous phosphorous detector. It was determined the contributions to the uncertainty at each analytical step such as extraction, clean up, evaporation and instrumental analysis. The first method was based on the guide to the expression of uncertainty in measurement (GUM) approach, which derives the uncertainty of a measurement result by combining the uncertainties related to the uncertainty sources of the measurement process. The second method was an approach previously presented by Haslòva and Stêpán, which included some elements of "top-down" estimation in that it included repeatability data generated by fortification experiments at different stages of the method to estimate the contribution of each step to the overall uncertainty. The results showed that when is employing GUM approach the uncertainty values were lowest compared with Haslòva method. Using the GUM approach uncertainty of standard preparation (uncertainties of weighing and diluting standards, uncertainties of purity of standards) was shown to represent the main source of combined standard. On the other hand, when the second method was used, the main source of uncertainty extraction process was identified. By contrast, it was found that the source contributes less to global uncertainty was the standards preparation. Finally, the expanded uncertainties for Haslòva method using a coverage factor of two were between 12.7% and 27.1% of the concentration, which was estimated uncertainty.

A correta interpretação do resultado de uma medição requer o conhecimento da incerteza de medição, assim, diferentes abordagens têm sido desenvolvidos e orientações para o cálculo e interpretação da incerteza de medição. Este estudo compara duas abordagens para estimar a incerteza de uma metodologia, mais rápido, baseado no custo método para analisar QuEChERS 15 pesticidas organofosforados por cromatografia gasosa com detector de nitrogênio e fósforo. O primeiro método utilizado baseiase o procedimento descrito pelo guia para a expressão da incerteza de medição (GUM) que é baseado numa combinação de incertezas envolvidas no processo de medição da metodologia. O segundo método utilizado foi o método proposto pelo Haslòva e Stepan, que inclui alguns elementos de cima para baixo método (de cima para baixo) e baseia-se na utilização de dados de repetibilidade em diferentes fases do processo analítico. Os resultados mostraram que, utilizando a aproximação dos valores de incerteza GUM são inferiores quando se utiliza o método Haslòva. Além disso, através da abordagem de goma foi encontrada para contribuir para a incerteza para a preparação de padrões (diluição de peso e pureza) é o componente principal. Por outro lado, pelo método combinado verificou-se que a principal fonte de incerteza corresponde à extracção de analitos em contraste verificou-se que a fonte fornece corresponde menos para a preparação de padrões. Finalmente, os valores calculados para a incerteza expandida foram entre 12,7% e 27,1% da concentração à qual a incerteza estimada.