Through the dam into troubled waters: Combined effects of stream fragmentation, habitat deterioration, and poor water quality on lowland stream fish distribution

Abstract

This study aimed to distinguish the contribution of stream fragmentation and poor habitat and water quality to the decline in riverine fish species. The species presence was related to the number of barriers between a specific lowland stream section and the main river and to the length of the stream section remaining between two barriers. To investigate the relationship between the absence of fish species and poor ecological water quality, the EQR and stream velocity indices were compared between accessible sites where the fish was either present or absent. 79% of the 1039 km lowland stream length was disconnected from the river Meuse by one or more barriers and 34% by more than 5 barriers, while 28% of all stream sections were shorter than 2.5 km. Only 2% of sites scored a very good water quality, while all study sites were characterized by (very) slow flowing waters (<0.15 m/s). As many fish passages are built to improve connectivity, fish passages do not improve habitat quality. Gudgeon and stone loach were hardly affected by stream fragmentation, and only slightly by too short stream sections. Ide was moderately affected, while the migratory species chub and dace were severely affected by stream fragmentation.Chub and dace were also sensitive to poor habitat and water quality. Distinguishing the effects of stream fragmentation, habitat deterioration, and poor water quality on lowland stream fish distribution increased the understanding of the reasons for the presence and absence of species and may aid effective management and restoration efforts.

Patterns and drivers of water quality changes associated with dams in the Tropical Andes

“…The fish communities downstream of Colombia's Porce III dam -one of the projects with hypoxic tailwater -have shifted, with a loss of some native species and replacement by invasive exotic species (Valencia-Rodríguez et al, 2022). The authors of this study attribute these shifts to habitat fragmentation, but anoxia/hypoxia could be an important factor, as many other studies have commented that the multiple changes and stressors imposed by dams are difficult to disentangle (van Puijenbroek et al, 2021;Young et al, 1976). A review from Brazil indicates that poor oxygen management associated with dams is likely to be a major driver of fish mortality in South American rivers, accounting for roughly 40 % of fish kills covered by the media (Agostinho et al, 2021).…”

“…Colombian regulations stipulate that industrial or commercial activities should not alter water temperatures by more than 5 • C, which is a temperature difference that has been associated with acute responses from tropical biota, such as fish mortality from warm water (Cooper et al, 2019) or disruption to fish reproductive cycles from cold water (King et al, 1998). A more conservative thermal change threshold of ±2 • C may be warranted given that the community composition of macroinvertebrates is highly sensitive to subtle changes in the thermal regime (Eady et al, 2013;Preece and Jones, 2002) and assessments of global climate change effects on fish delimit a 2 • C threshold for impacts (van Vliet et al, 2013). Furthermore, as we are limited (by data availability) to just a few random comparisons for most sites for Colombia, we are unlikely to be capturing the most extreme moments of thermal impact; thus, the precautionary principle would dictate a stricter approach.…”

“…Power plants with data for upstream vs. downstream comparisons are listed first and sorted by surface area. van Vliet et al, 2013;Cooper et al, 2019).…”

Macroinvertebrate conservation in river ecosystems: Challenges, restoration strategies, and integrated management approaches

“…The improvement of fish passage is a critical component of connectivity restoration efforts, as many macroinvertebrate species rely on fish for dispersal, either through attachment to fish or by utilizing the same passageways (Van Puijenbroek et al 2021). Ensuring that fish can effectively move between river habitats can indirectly benefit macroinvertebrate populations by promoting the exchange of individuals and genetic material between populations, thereby enhancing their resilience to environmental disturbances and reducing the risk of local extinctions (Favaro et al 2014;Kimmel & Argent 2016).…”