Effects of pulsed flows on nuisance periphyton growths in rivers: a mesocosm study

Abstract

Rivers regulated by dams are typically characterized by altered biotic communities and habitat structure in downstream reaches. In the Jackson River (Alleghany Co., VA), a relatively constant flow regime below Gathright Dam and anthropogenic nutrient loading have apparently contributed to nuisance levels of periphyton (>300 mg chlorophyll a m À2). These nuisance growths cause low dissolved oxygen concentrations in the water column and altered benthic habitats in the Jackson River. The use of periodic pulsed flows has been suggested as a restoration practice that could potentially reduce periphyton biomass. We investigated the effects of increased flow on periphyton chlorophyll a (chl a), ash-free dry mass (AFDM), % organic matter (%OM) using streamside channels in which periphyton-colonized tiles were subjected to near-bed velocities ranging from 20 (control) to 240 cm s À1. Analysis of variance (ANOVA) and regression were used to examine periphyton responses to velocity treatments. There was a significant decrease in chl a and AFDM, and significant increase in %OM in velocity treatments of 150, 180 and 240 cm s À1 ( p < 0.001), but not in lower velocity channels. Regression analyses showed a significant positive relationship with %OM (r 2 ¼ 0.88) and significant negative relationship with chl a (r 2 ¼ 0.77) and AFDM (r 2 ¼ 0.63). Algal taxa were dominated by Cladophora glomerata, Melosira varians and Pleurosira laevis. There was a significant positive relationship between treatment velocity and % C. glomerata ( p ¼ 0.007, r 2 ¼ 0.87) as diatoms were differentially removed with increasing treatment velocity. Our results demonstrate that pulsed flows can reduce periphyton standing crops in the Jackson River, but the discharge required to achieve this reduction would probably need to produce near-bed velocities >100 cm s À1. Further study is needed to establish specific flow targets and evaluate the direct and indirect effects of pulsed flows on ecological conditions in the Jackson River.

Responses of epibenthic algal assemblages to water abstraction in Hong Kong streams

“…In such cases elsewhere, especially where nutrient supply is high. Such conditions can give rise to excessive or nuisance growths (Flinders & Hart, 2009). …”

Short-term effects of flooding on bacterial ­community structure and nitrogenase activity in microbial mats from a desert stream

“…Unlike the benthic phototrophs, an increase in the green alga Spirogyra was triggered after flooding at most sites, an observation that is consistent with previous reports (Power & Stewart 1987, Biggs & Close 1989, Stevenson 1990). The stimulation of algal productivity has been shown to be due to the high loading of dissolved nutrients by the flood water and/or the reduction in grazing pressure by macroinvertebrates (Grimm & Fisher 1986a, Hamilton & Duthie 1987, Flinders & Hart 2009). The multivariate plots based on ARISA data and pigment distibution were congruent and supported a separation between the microbial community clusters before and after the flood.…”

Nonlinear Relationship of Near-Bed Velocity and Growth of Riverbed Periphyton

“…In this analysis, second-order terms were also included a priori (Equation (5), i.e., RSM) because periphyton growth shows nonlinear responses over time and velocity [46]:…”

“…These results indicate that periphytic growth under low nearbed water velocity conditions stopped after 15 days. This might be due to the limited diffusional acquisition of substrates [13,46]. Correlation between independent variables (incubation time and water velocity) and Chl-a using response surface methodology (i.e., Equation (6)) (solid dots represent experimental conditions).…”

“…These results indicate that periphytic growth under low near-bed water velocity conditions stopped after 15 days. This might be due to the limited diffusional acquisition of substrates [13,46].…”