Phytoplankton gross primary production increases along cascading impoundments in a temperate, low-discharge river: Insights from high frequency water quality monitoring

Abstract

Damming alters carbon processing along river continua. Estimating carbon transport along rivers intersected by multiple dams requires an understanding of the effects of cascading impoundments on the riverine metabolism. We analyzed patterns of riverine metabolism and phytoplankton biomass (chlorophyll a ; Chl a ) along a 74.4-km river reach intersected by six low-head navigation dams. Calculating gross primary production (GPP) from continuous measurements of dissolved oxygen concentration, we found a maximum increase in the mean GPP by a factor of 3.5 (absolute difference of 0.45 g C m −3 d −1 ) along the first 26.5 km of the study reach, while Chl a increased over the entire reach by a factor of 2.9 (8.7 µg l −1 ). In the intermittently stratified section of the deepest impoundment the mean GPP between the 1 and 4 m water layer differed by a factor of 1.4 (0.31 g C m −3 d −1 ). Due to the strong increase in GPP, the river featured a wide range of conditions characteristic of low- to medium-production rivers. We suggest that cascading impoundments have the potential to stimulate riverine GPP, and conclude that phytoplankton CO 2 uptake is an important carbon flux in the river Saar, where a considerable amount of organic matter is of autochthonous origin.

The phytoplankton community as a descriptor of environmental variability: a case study in five reservoirs of the Paraná River basin

“…The RT presented by a reservoir interferes directly with the development of the phytoplankton community so that increasing RT is one the main drivers of biomass increment (Soares et al, 2008;Perbiche-Neves et al, 2011;Engel et al, 2019). In our study, reservoirs R1, R2 and R3 presented low RT, between 7 and 48 days, due to the high water flow of the Paraná River.…”

“…In this study, reservoirs constructed in series in the Paraná River (R1, R2 and R3) presented, for most sampling events, lower values for richness and biomass the phytoplankton and a tendency reduction of these values along the longitudinal gradient of the river, from reservoir R1 to R2 and then to R3. This is probably because the downstream reservoir is strongly influenced by the upstream reservoir, which retains part of the seston that should be exported downstream (Perbiche-Neves et al, 2011;Bovo-Scomparin et al, 2013), altering the quantity and quality of organic carbon that is passively transported downstream in a reservoir cascade (Engel et al, 2019).…”

Photosynthesis, carbon acquisition and primary productivity of phytoplankton: a review dedicated to Colin Reynolds

“…When rivers are regulated, carbon processing is altered along the river continuum. Engel et al (2019) examined the phytoplankton along a 74 km river stretch of the River Saar, Germany to analyse the effect of cascading impoundments (six navigation dams) on riverine metabolism. GPP was calculated from continuous measurements of dissolved oxygen.…”

Intelligent Wide-Area Water Quality Monitoring and Analysis System Exploiting Unmanned Surface Vehicles and Ensemble Learning

“…In recent years, the evolution of high-resolution sensors and Internet of Things (IoT) technologies has significantly improved water quality monitoring technologies [8][9][10]. Various WQMSs have been designed to solve the problems related to the water quality monitoring of lakes [11,12], rivers [13,14], and groundwater [15,16]. Generally, water quality can be accurately determined by laboratory analysis, but spatial resolution and rapid assessment cannot be obtained with efficiency, simultaneously.…”