New approaches for aquatic biomonitoring in southern Chile based on benthic macroinvertebrates community

Abstract

This work aims to show diversity quantification within biomonitoring context. It was carried out in the lower part of two small catchment basins, representative units of riverscape scenarios, contrasting with respect to their ecological, territorial and land-use characteristics. These catchment basins are found in Valdivian lakes ecoregion (between 39° to 41° S lat.), called Quimán and Llancahue, sampling only low-order stream habitats. Within Quimán there is a run-of-river hydroelectricity, aquaculture of salmonids activity and land use transformation (establishment of meadows and croplands), in south of Mocho Choshuenco stratovolcano. While Llancahue is almost entirely evergreen template forest, managed by Universidad Austral de Chile as a conservation area, surrounded by forest plantations, located eight kilometers to Valdivia city. The diversity quantifications evaluated come specifically from well differentiated analyses. Specifically, they correspond mainly to total biomass (mg/m2), mean biomass (mg*m-2 ind-1), linear regression slope of weight versus body length, mean squared error of the model and coefficient of determination. As for the analysis of phylogenetic inference that is based as such of a consensus tree (from cladistic analysis), they are phylogenetic diversity, mean pairwise distance, mean nearest neighbor distance, number of nodes, taxonomic distinction, smaller distance, larger distance, among other quantifications. Specimens used were the same in both analyses, macroinvertebrates were captured from all accessible habitats. Subsequently, the organisms were freezedried for organic preservation and facilitation of taxonomic determination. According to the results, traditional diversity index reveals greater diversity in Llancahue, as do other metrics such as taxa richness, phylogenetic diversity, number of pairs and nodes of the phylogenetic trees obtained. Total, mean and predator’s biomass were also higher in Llancahue, the allometry in most organisms was negative (pending the regression curve less than 3), with Llancahue samples having the highest number of taxa with positive allometry. In Quimán, metrics related to phylogenetic distances (average pair distance, smallest distance and longest distance) were quantitatively higher. The scenario in Llancahue is a high endemism of the sampled community, while in Quimán prevails discovery of macroinvertebrates related to a poor ecological state. In both scenarios there are organisms from which there is an incomplete taxonomic, ecological and biological knowledge. This work evidenced a set of quantifications, which follow a differential trend when compared between the two basins under study. The diversity complexity is difficult to express in discrete quantitative indicators, due to its multiplicity of scopes and significances, however, it is acceptable under the perspective of biomonitoring programs that must have simple application and interpretation. It is recommended to treat new criteria and evaluate new factors and variables, in addition to applying them to a statistically significant number of sites, in order to effectively test the diversity patterns shown, and to make them formally adaptable to practical biomonitoring programs and designs.