The Effects of Rapid Water Level Changes on Fish Assemblages: The Case of a Spillway Gate Collapse in a Neotropical Reservoir

Abstract

River damming and associated reservoir causes intense and dramatic changes that create new environments, with particular structure and functioning. In these systems, flow control and artificial variations in water level are important determinants of the structure of fish assemblages. Planned reduction in water level (drawdown) is used to manage productivity in reservoirs. However, the effects of non‐planned reductions, such as those related to the collapse of spillway gates, are rarely studied. The objective of this study was to evaluate the effects of a rapid reservoir drawdown, because of the collapse of a gate, on the structure of fish assemblage in a Neotropical reservoir, in Southern Brazil, operated as run‐of‐the‐river. Water level variation because of the collapse reached up to 20 m. A canonical analysis of principal coordinates (CAP) was used to summarize the structure of fish assemblage. Spearman rank correlations were performed between each CAP axes retained for interpretation and fish species abundances, to assess the ones that most contributed to observed patterns. The first CAP axis identified strong variations in the spatial scale, while the third axis identified variations in the time scale (before and after the collapse). The most notable negative effect was the loss of several fish that perished during the reservoir drawdown, probably because of adverse limnological conditions. Results showed significant benefits of water level variation on the entire fish assemblage, and we suggest that, observed some peculiarities, this variation can be used to manage reservoirs, as a tool to enhance fish abundances. Copyright © 2016 John Wiley & Sons, Ltd.

A long-term study on zooplankton in two contrasting cascade reservoirs (Iguaçu River, Brazil): effects of inter-annual, seasonal, and environmental factors

“…This process delays and mitigates flow peaks, which means that, in contrast to rivers, reservoirs do not follow a seasonal pattern (Ravazzani et al, 2014;Ignatius & Rasmussen, 2016). Even run-of-river reservoirs, such as SO, show large changes in their flow regime that are inconsistent with natural regimes (Baumgartner, Baumgartner & Gomes, 2017). Furthermore, the lack of seasonality in the SO reservoir may be closely linked to the operational needs of the upstream SS reservoir, which has a major influence on the flow regime.…”

“…However, a dam significantly alters the riverine ecosystem (Silva et al, 2014;Oliveira et al, 2018) because the reservoir blocks the free flow of the river and creates a semi-lentic or lentic habitat (Baxter, 1977). Important factors, such as the quantity and quality of the water, habitats, nutrient and sediment transport, and water retention time (WRT) can dramatically change (Baumgartner, Baumgartner & Gomes, 2017;Loken et al, 2018). Thus, either directly or indirectly, artificial variations in water level can affect all aquatic organisms, from primary producers (phytoplankton) to consumers (zooplankton, macroinvertebrates, and fish) (Baumgartner et al, 2019).…”

Peer Review #1 of "A long-term study on zooplankton in two contrasting cascade reservoirs (Iguaçu River, Brazil): effects of inter-annual, seasonal, and environmental factors (v0.1)"

“…This process delays and mitigates flow peaks, which means that, in contrast to rivers, reservoirs do not follow a seasonal pattern (Ravazzani et al, 2014;Ignatius & Rasmussen, 2016). Even run-ofriver reservoirs, such as SO, show large changes in their flow regime that are inconsistent with natural regimes (Baumgartner, Baumgartner & Gomes, 2017). Furthermore, the lack of seasonality in the SO reservoir may be closely linked to the operational needs of the upstream SS reservoir, which has a major influence on the flow regime.…”

“…However, a dam significantly alters the riverine ecosystem (Silva et al, 2014;Oliveira et al, 2018) because the reservoir blocks the free flow of the river and creates a semi-lentic or lentic habitat (Baxter, 1977). Important factors, such as the quantity and quality of the water, habitats, nutrient and sediment transport, and water retention time (WRT) can dramatically change (Baumgartner, Baumgartner & Gomes, 2017;Loken et al, 2018). Thus, either directly or indirectly, artificial variations in water level can affect all aquatic organisms, from primary producers (phytoplankton) to consumers (zooplankton, macroinvertebrates, and fish) (Baumgartner et al, 2019).…”

Zooplankton communities and their relationship with water quality in eight reservoirs from the midwestern and southeastern regions of Brazil

“…Dams significantly alters riverside ecosystems because the creating of a reservoir blocks the free flow of the river and creates a semi-lentic or lentic habitat. Thus, important factors such as the quantity and quality of water, habitats, and nutrient transport can change dramatically (Baumgartner et al, 2017;Loken et al, 2018). In addition, artificial variations in the water level can directly and indirectly affect zooplankton communities.…”