Relationships between aquatic biotic communities and water quality in a tropical river–wetland system (Ecuador)

Many tropical wetlands threatened by land use changes, or modifications in hydrological regime require effective management policies and implementation to protect them. The Abras de Mantequilla wetland, located in the Guayas River Basin in Ecuador, is subject to two major environmental disturbances, i.e., short-term agriculture (rice, maize) on the land around the wetland and the effects of planned infrastructure works of the Baba dam in the upper catchment. Both activities are expected to be the main constraints for the future wetland health. The objective of this study was to provide an initial characterization of the biotic communities of the river and wetland habitats before the dam starts operating. Plankton, macroinvertebrates, fishes and associated physical and chemical variables were sampled at 12 sites during the wet season (February 2011). Biotic metrics (abundance, taxa richness, diversity and evenness) were computed for the aquatic communities in the wetland and the river. A biotic index (Biological Monitoring Working Party-Colombia/adaptation) was applied to the macroinvertebrate community. Relationships between biotic and abiotic variables indicated nutrients, velocity and sediment type as main drivers. Cluster analysis grouped physico-chemical variables according to river or wetland sites. Similarities regarding the taxa composition among sites were explored with non-metric multidimensional scaling method (NMDS), showing clusters for ichthyoplankton and macroinvertebrates. Higher densities of organisms were recorded in the wetland compared with the river. The wetland is an important area of breeding and reproduction for fish communities, with its lentic habitats promoting the development of high densities of ichthyoplankton. In order to achieve sustainable solutions for integrated river–wetland systems, management options should focus on maintaining natural variation in hydrodynamic conditions throughout the entire catchment, as well as implement good practices in agriculture and reforestation using native species. Local and national authorities should support continuous monitoring programmes, taking account of seasonal variation and of future impacts from flow reduction and nutrient enrichment.