Seasonality and extreme flooding can override the effects of debris dam removal on riverine species: a case study of macroinvertebrates

Debris dam removal serves as a conservation strategy to enhance landscape connectivity. However, we still do not know the joint effects of debris dam removal and seasonality on riverine species. Using multi-year data in a monsoonal stream, we examined the response of macroinvertebrate communities to the removal of one debris dam using a Before-After-Control-Impact design (BACI). We found that the debris dam removal did not affect organic matter quantity, invertebrate abundance and diversity, and community structure, except for the abundance of invertebrate filter-feeders. On the other hand, seasonality influences nearly all of the ecological metrics which suggests that seasonality can override debris dam removal as the main driver of these ecological metrics. Moreover, extreme flooding during the wet season affects the abundance of invertebrates, suggesting that the seasonal life cycle of invertebrates after recovering from the dry season, may not fully compensate for the impact of extreme flooding. Evaluating the ecological impacts of debris dam removal in monsoonal areas with dynamic weather conditions could benefit the decision-making of using debris dam removal as conservation practices by restoring freshwater habitat with minimal impact on riverine species (e.g., macroinvertebrates) as far as freshwater ecosystem, especially with the occurrence of extreme floods.