Reservoir Floodplains Support Distinct Fish Assemblages

Abstract

Reservoirs constructed on floodplain rivers are unique because the upper reaches of the impoundment may include extensive floodplain environments. Moreover, reservoirs that experience large periodic water level fluctuations as part of their operational objectives seasonally inundate and dewater floodplains in their upper reaches, partly mimicking natural inundations of river floodplains. In four flood control reservoirs in Mississippi, USA, we explored the dynamics of connectivity between reservoirs and adjacent floodplains and the characteristics of fish assemblages that develop in reservoir floodplains relative to those that develop in reservoir bays. Although fish species richness in floodplains and bays were similar, species composition differed. Floodplains emphasized fish species largely associated with backwater shallow environments, often resistant to harsh environmental conditions. Conversely, dominant species in bays represented mainly generalists that benefit from the continuous connectivity between the bay and the main reservoir. Floodplains in the study reservoirs provided desirable vegetated habitats at lower water level elevations, earlier in the year, and more frequently than in bays. Inundating dense vegetation in bays requires raising reservoir water levels above the levels required to reach floodplains. Therefore, aside from promoting distinct fish assemblages within reservoirs and helping promote diversity in regulated rivers, reservoir floodplains are valued because they can provide suitable vegetated habitats for fish species at elevations below the normal pool, precluding the need to annually flood upland vegetation that would inevitably be impaired by regular flooding. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Evidence for Serial Discontinuity in the Fish Community of a Heavily Impounded River

“…Moreover, reservoirs impounded on the low ends of rivers may include in their riverine upper reaches extensive floodplains periodically inundated by fluctuating reservoir water levels that to a degree mimic natural inundations. These upper reaches can support distinct and speciose fish assemblages that benefit from periodic connections between the reservoir, the floodplain environments and associated wetlands (Buckmeier et al, 2014;Miranda et al, 2014). Such connectivity may also benefit riverine species whose juveniles require access to floodplains.…”

Assessing Establishment and Growth of Agricultural Plantings on Reservoir Mudflats

“…These barren mudflats created within reservoir embayments support distinct fish communities relative to those occurring in floodplains with natural vegetation (Miranda et al. ). Restoration of degraded ecosystems, such as floodplains or reservoir mudflats, is a primary goal of habitat management (Pegg and Chick ; Carmignani and Roy ).…”

Functional Age as an Indicator of Reservoir Senescence

“…Over time this promotes erosion and homogenization of once diverse littoral habitats (Allen and Tingle 1993). Well-established riparian zones and wetlands that provide key ecological services to natural lakes and the original river are generally limited to upper reaches near the entrance of tributaries but often degrade due to unnatural water level fluctuations (Miranda et al 2014). Lack of woody debris deposition in the littoral zone, limited access to backwaters and wetlands, and lack of seed banks and stable water levels to promote native aquatic plants characterize barren littoral habitats in many reservoirs (Miranda 2008).…”