Long-term analysis of aquatic macrophyte diversity and structure in the Paraguay river ecological corridor, Brazilian Pantanal wetland

Abstract

Spatial and temporal variation in limnological variables, as well as local changes in the hydrological pattern, may affect inundation hydrology and alter biotic interactions and functional diversity of aquatic macrophyte communities in the Pantanal. The objectives of this research in the floodplain along the Paraguay River were to: 1) examine changes in the diversity of aquatic macrophyte communities over a ten-year period based on surveys taken in 2008 and 2018; and 2) evaluate the possible indirect relation of changes in rainfall patterns, which in turn affect lateral hydrological connectivity and limnological variables that directly affect the composition and productivity of the aquatic macrophyte community. Comparison of data taken in 2008 and 2018 revealed a change in the timing and a reduction in the number of rainy days. These changes in rainfall patterns coincided with limnological changes, including increases in transparency, pH, dissolved oxygen, ammonium, nitrate, total nitrogen, orthophosphate, and total phosphorus, as well as decreases in water temperature and connectivity. Species richness of aquatic macrophyte communities in three ecological zones of the Paraguay River floodplain increased between 2008 and 2018, with increases in emergent grasses, emergent non-grasses, and amphibious life forms, showing a trend that favors species that are more adapted to drought conditions. The seasonal pattern of inundation and desiccation, as well as dissolved oxygen and temperature, where correlated with macrophytes communities variations. The colonization and expansion of rooted emergent macrophytes over this period could be a response to local anthropogenic activities, hydrological trends, or may reflect interannual rainfall variability.