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

Abstract

In the Tennessee River, USA, we examined lengthwise patterns in fish community structure and species richness within and among nine reservoirs organized in sequence and connected through navigational locks. Within reservoirs, the riverine, transition and lacustrine zones supported distinct, although overlapping, nearshore fish assemblages; differences were also reflected in measures of species richness. Spatial patterns were most apparent for rheophilic species, which increased in species richness and representation upstream within each reservoir and downstream across the chain of reservoirs. This pattern resembled a sawtooth wave, with the amplitude of the wave peaking in the riverine zone below each dam, and progressively higher wave amplitude developing downstream in the reservoir chain. The observed sawtooth pattern supports the serial discontinuity concept in that the continuity of the riverine fish community is interrupted by the lacustrine conditions created behind each dam. Upstream within each reservoir, and downstream in the chain of reservoirs, habitat characteristics become more riverine. To promote sustainability of rheophilic fishes and maintain biodiversity in impounded rivers, conservation plans could emphasize maintenance and preservation of riverine environments of the reservoir's upper reaches, while remaining cognizant of the broader basin trends that provide opportunities for a lengthwise array of conservation and management policy. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Temporal changes in fish diversity in lotic and lentic environments along a reservoir cascade

“…The lentic environment (also called the lacustrine zone) is the area in the reservoir that is deeper and wider, where water current is generally unnoticeable and thermal stratification may occur. The environment presents low nutrient concentrations in relation to upstream reaches, but since more light is available due to the settling of fine sediments, primary production is higher (Agostinho, Pelicice, & Gomes, ; Miranda & Dembkowski, ). The lotic environment (also called riverine zone) refers to the upper reaches of the reservoir that features higher current velocity, low water residence time, higher turbity and nutrient levels, and lower light penetration, limiting primary production (Agostinho et al., ; Miranda & Dembkowski, ).…”

“…The environment presents low nutrient concentrations in relation to upstream reaches, but since more light is available due to the settling of fine sediments, primary production is higher (Agostinho, Pelicice, & Gomes, ; Miranda & Dembkowski, ). The lotic environment (also called riverine zone) refers to the upper reaches of the reservoir that features higher current velocity, low water residence time, higher turbity and nutrient levels, and lower light penetration, limiting primary production (Agostinho et al., ; Miranda & Dembkowski, ). The lotic environment may connect to the next upstream dam or to fluvial upstream stretches, thus lotic and lentic environments may alternate along a reservoir cascade system (Ward & Stanford, ).…”

“…The evaluation of long‐term effects on fish diversity is better understood for single dams than for a series of dams in a cascade (Castello & Macedo, ; Cheng, Li, Castello, Murphy, & Xie, ). Reservoir cascades present longitudinal shifts in physical and biological parameters, which drives changes in biodiversity that can vary in intensity and direction depending on the longitudinal position of the impoundment (Miranda & Dembkowski, ; Miranda, Habrat, & Miyazono, ; Stanford & Ward, ; Ward & Stanford, ). Cumulative effects of multiple dams on fish assemblages are expected to be much stronger than those caused by a single dam alone (Castello & Macedo, ; Cheng et al., ).…”

“…When there are no lotic remnants between reservoirs built in series along a river (this varies according to the water level of the next reservoir in the cascade), the possibilities to compare lotic and lentic environments in a cascade are more limited. Nevertheless, a few studies have demonstrated fish diversity impacts in lotic stretches between dams in a reservoir cascade (Ferrareze, Casatti, & Nogueira, ; Ferrareze, Nogueira, et al., ; Miranda & Dembkowski, ; Miranda et al., ; Silva et al., ). Moreover, there are indications that lotic stretches associated with lentic environments are important for the maintenance of fish diversity (Agostinho et al., ; Marques et al., ; Miranda & Dembkowski, ; dos Santos et al., ).…”

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

“…() described three main zones within a reservoir: fluvial, transitional and lacustrine. As expected and found in our results, the predicted longitudinal discontinuity in environmental features determines different groups of species along this gradient, according to the particular requirements of each species (Okada et al ., ; Agostinho et al ., ; Miranda and Debkowski, ). Although remarkable, these longitudinal differences in the fish assemblage structure were not decisive for different effects of water level variation among the reservoir regions.…”