Impacts of oil palm monocultures on freshwater ecosystems in the Amazon: a case study of dragonflies and damselflies (Insecta: Odonata)

The aim of this study was to investigate the effects of oil palm (Elaeis guineensis) plantations on the water quality and physical structure of streams in the Amazon region and on the diversity of adult odonates (Insecta: Odonata). We tested the hypotheses: (1) that streams draining palm oil monocultures have low water quality and physical integrity and (2) that changes in water quality (local variables) and physical structure (landscape variables) of streams affect the abundance and species richness of the Odonata. A total of 22 streams were studied, of which 15 were in drainage areas used for oil palm plantations and seven were in primary forest areas in the eastern Amazon, Pará State, Brazil. To represent environmental conditions, we selected local variables (e.g., temperature, dissolved oxygen, and turbidity) and landscape variables (e.g., vegetation at 50 and 500 m distance from sampling points) known to be important for the Odonata community. Our results showed that oil palm plantations impact both the physical structure of Amazonian streams and Odonata diversity. The analyses revealed that Odonata abundance and species richness were influenced differently by the variables tested, with dissolved oxygen positively related to Odonata abundance and water temperature and turbidity negatively related to Odonata abundance. Changes in the surrounding vegetation were found to affect the physical structure of streams and influence dragonfly communities. Based on these results, we recommend the implementation of integrated approaches that consider local and landscape factors when monitoring aquatic ecosystems.