Impact of regulated releases on periphyton and macroinvertebrate communities: The dynamic relationship between hydrology and geomorphology in frequently flooded rivers.

Abstract

Flood-type disturbances affect both periphyton and macroinvertebrate communities depending on their frequency, magnitude and duration, but some impacts can be mitigated by geomorphic constraints. We studied four rivers in the Adirondack Mountains; the Indian River experienced regulated flow releases creating bank-full floods four times/week whereas other study sites provided a continuum of control conditions for comparison. We sampled periphyton and macroinvertebrate communities in each river along with channel hydrology, hydraulics and geomorphology. Periphyton abundance varied seasonally and among rivers depending on nitrate concentrations and scour. Flow releases created a static mosaic of patches consisting of heavily scoured bed sediment in the thalweg (high shear stress areas-HSS) which had very low periphyton abundance; boulders and rocky shoals created low shear stress areas (LSS) supporting mats of filamentous algae. Macroinvertebrate densities were highest in HSS areas whereas LSS areas had lower macroinvertebrate densities that were more similar to reference rivers, although both LSS and HSS areas had the lowest species diversity and richness. Macroinvertebrate composition in HSS areas was dominated by filter-feeders, whereas LSS areas had more gatherers and scrapers. While all rivers had high boulder densities, the Indian River could be considered geomorphically moribundits substrate was immobile and the channel experienced no adjustments in spite of high flood frequencies. These physical characteristics help mitigate the severe hydrologic conditions that releases create because the static mosaic of low and HSS patches allow certain macroinvertebrates adapted to this level of disturbance to persist. This static mosaic is different from the shifting mosaic pattern often observed in streams following flood-type disturbances. Geomorphically moribund rivers may lack ecological sensitivity to hydrologic disturbances, and decisions to limit flow modification (e.g. recreational flow releases, hydropower generation) should consider whether assumed ecological impacts are likely to occur given local geomorphic conditions and constraints.

Effects of hydropeaking on benthic invertebrate community composition in two central Norwegian rivers

“…Similar to the situation in the Bævra and Lundesokna, increasing invertebrate densities with increasing distance from shore downstream plants of hydropeaking rivers have also been recorded by others (Fisher & LaVoy, ; Troelstrup & Hergenrader, 1990; Jones, ). In agreement with our findings, Fuller et al () recorded higher invertebrate densities in high shear stress areas than low shear stress areas and argued that ecological impacts may be mitigated by geomorphic constraints. They found that the substrate in the high shear stress area was immobile and channel experienced no adjustments in spite of high flood frequencies.…”

“…In both rivers, gatherers/collectors were the dominating functional feeding group in the ramping zone. This is in agreement with Fuller et al (), but they also found that grazers dominated low shear stress areas. Troelstrup and Hergenrader () found that gatherers/collectors together with predators were the predominating FF‐groups in areas subjected to diel flow fluctuations.…”

Food resources and cyprinid diet in permanent and temporaryMediterranean rivers with natural and regulated flow

“…Places with low streamflow variability and without flood pulses changing the available habitat can maintain a higher concentration of resources, especially organic matter and plant material, which are easily consumed (Piana et al 2006). Diet diversity was constant in the nonregulated river but significantly decreased during spring in the regulated one, which can be explained by the absence of natural spring high flows, which reduces the effect that substrate scour has on invertebrate diversity, while facilitating detritus accumulation (Fuller et al 2011), contributing to a reduction in barbel dietary breadth. Within the southern system, the regulated river presented a higher abundance of macrophytes and invertebrates in the environment, which may result from the hypolimnetic discharge by the upstream dam in the end of spring, which is usually eutrophic, deoxygenated and of bad quality, benefiting plant growth and affecting less tolerant animal species, reducing, for example, invertebrate diversity and increasing the abundance of taxa adapted to harsh environments (Brittain & Saltveit 1989;Cortes et al 2002).…”

“…Diet diversity was constant in the nonregulated river but significantly decreased during spring in the regulated one, which can be explained by the absence of natural spring high flows, which reduces the effect that substrate scour has on invertebrate diversity, while facilitating detritus accumulation (Fuller et al. ), contributing to a reduction in barbel dietary breadth.…”

Fluvial lateral environments in Río de La Plata basin: effects of hydropower damming and eutrophication

“…In sites associated to free-flowing rivers a lower biomass would be associated to the influence of floods, frequent water level fluctuations and higher turbidity (Uehlinger et al, 2003;Fuller et al, 2011).…”