Effects of land use on sediment composition in low-order tropical streams

Effects of Environmental Variables and Habitat Integrity on the Structure of the Aquatic Insect Communities of Streams in the Cerrado-Caatinga Ecotone in Northeastern Brazil

Alterations in the environmental gradients of streams have a direct influence on the structure of the insect communities of the orders Ephemeroptera, Plecoptera, and Trichoptera (EPT), which are extremely sensitive to changes in habitat. The present study evaluated how habitat integrity in streams influence the composition of EPT genera, by testing three hypotheses: (i) the composition of the EPT genera is modified along the gradient of environmental disturbance; (ii) the composition of the EPT genera is more homogeneous in gradients with a higher degree of anthropogenic disturbance, and (iii) the greatest degree of environmental disturbance along the gradient results in the reduction of the richness and abundance of EPT genera. The study focused on 14 tributaries of the middle Itapecuru River, within an area of ecotone between the Brazilian Cerrado and Caatinga biomes. Data on the structure and physicochemical traits of the streams were collected between September 2014 and July 2015, a period that covers both the dry and rainy seasons in the study region. The results of the present study indicate that the composition of the EPT genera is modified in accordance with the variation in the habitat integrity, although, in contrast with expectations, more impacted areas had a more heterogeneous composition than undisturbed ones. The areas with more integrated landscapes contribute positively to the richness and abundance of EPT genera of the streams of the Cerrado-Caatinga ecotone. Given this, habitat integrity provide an important predictor of EPT diversity in the streams of the Cerrado-Caatinga ecotone.

Functional responses of stream fish communities to rural and urban land uses

Abstract We tested the effects of ruralization and urbanization on the functional diversity indices and the composition of functional traits of Neotropical stream fish communities. The study was carried out in 24 streams of the Pirapó, Piquiri, Paraná III and Iguassu river basins. Land use in the watershed was categorized as percentages of native vegetation, rural occupation and urban occupation. Statistical tests revealed negative bivariate correlations between functional dispersion and the proportion of native vegetation in the watershed. The results indicate that a higher percentage of rural or urban occupation is associated with increased functional dispersion. In the analyzes of trait composition, significant alterations were observed in response to urbanization while only the increase in herbivory responded to ruralization. As the area of native vegetation is reduced by urbanization, the trait composition changes, with reduced proportions of species with intolerance to hypoxia, migratory reproductive behavior, external fertilization, and subterminal mouth, and increased proportions of species with parental care, detritivory, internal fertilization, and an upper mouth. Therefore, fish species that have these specific characteristics are more likely to disappear from streams as urbanization progresses. In summary, urbanization was related to a greater change in the composition of functional traits than ruralization.

Unified Multimetric Index for the Evaluation of the Biological Condition of Streams in Southern Brazil Based on Fish and Macroinvertebrate Assemblages

We developed MMI models that combine responses of fish and benthic macroinvertebrates for the evaluation of the biotic integrity of streams. The MMI was developed using a dataset covering stream sampling sites in the South of Brazil. Reference streams were identified based on the physical and chemical conditions and riparian vegetation. Thirty-four metrics were calculated and evaluated for their range, redundancy, and responsiveness to the environmental perturbation. We applied a robust approach to select the most sensitive metrics and MMI models based on the complexity and ability of the index in distinguishing impacted and reference sites. The four best MMI models selected are composed of different combinations of the eight metrics: % fish herbivorous, fish evenness, fish abundance, % macroinvertebrate shredder; % macroinvertebrate predator; % macroinvertebrate tolerant, % macroinvertebrate swimmer, and % macroinvertebrate burrower. All of the MMI models selected presented good performance in distinguishing reference streams from those impacted by different forms of land use. This study is one of the few attempts to use more than one biological assemblage in a single-multimetric index. Accordingly, we believe that the unified MMI we developed could be a useful tool to assist in the conservation and management of water resources in Neotropical regions, specially, in the implementation of ecological integrity tools more cost-effectively.