Resistindo, apesar de tudo? Efeito dos múltiplos usos do solo nas comunidades de macrófitas em ecossistemas aquáticos amazônicos.

Abstract

Land-use is considered the most severe driver of biodiversity change. Biomes, such as tropical forests, and ecosystems, such as freshwaters, have been damaged by land use, and this is concerning, since they are important to global biodiversity maintenance. Aquatic macrophytes are sensitive to changes that occur on their physical habitat, and they respond at different scales to the effects of land use. This study's main objective was to evaluate the effects of multiple land-use on macrophyte diversity. Our hypotheses were that: i) macrophyte species richness increases in multiple land-use gradients and ii) macrophyte species composition changes along a multiple land-use gradient. For that, we surveyed, in July 2017, 30 aquatic ecosystems (streams, lakes and ponds) located in Paragominas, Pará, Brazil. Species richness was sampled by taking notes of ali species that occurred in a 150m transect of each site. We sampled composition data with a lm2 quadrat, giving a percentage of cover to each species inside it. The predictive variables consisted of the local environmental variables (water parameters and canopy cover), and the landscape variables, which consisted of the percent of land-use and land cover classes present on each sampling site, that were obtained using geoprocessing techniques. To test hypothesis (i), Generalized Additive Mixed Models were used. To test hypothesis (ii), we used a distance-based redundancy analysis. Additionally, a Threshold Indicator Taxa Analysis was performed to identify which species are indicators of the land-use classes used on this study. We recorded 49 macrophyte species, and one of those was considered invasive. Species richness was affected positively by landuse, and negatively by canopy cover, corroborating hypothesis (i). Altered sites could provide more microhabitats, favoring more species, due to increased light incidence, sediment load, and nutrient input. Species composition was affected negatively by canopy cover, and positively related to pH and land-use, partially corroboration hypothesis (ii). More altered sites can provide habitat heterogeneity and increase life-form diversity. Three species were selected as indicators of land-use change: Cabomba aquatica, Eleocharis interstincta and Utricularia sp. Macrophyte communities could be experiencing an early stage of succession, in which the appearing of invasive species could be the start of a decrease in diversity as the consequences of land-use become abrasive. Those results point macrophytes as indicators of altered conditions, reinforcing their potential use to be considered on freshwater assessments on Amazônia.