Role of abiotic and biotic factors in structuring the metazoan plankton community in a lowland river

Abstract

Water and quantitative zooplankton samples were collected at approximately monthly intervals from June 2000 to June 2002 in the middle section of the Po River (Northern Italy). Highly variable hydrological conditions were observed in the 2 years, with river flow varying approximately between 400 and 9300 m 3 s À1 . Dissolved inorganic nitrogen (DIN) usually decreased at higher river discharges. Autotrophic production was limited by phosphorus availability during the growing period (May-October); no significant adverse effect of zooplankton grazing upon algal biomass was detected. A total of 161 zooplankton taxa were found. The records of the rotifers Lecane incospicua, L. cornuta, Proales sigmoidea, Cephalodella limosa, and of the cladoceran Phrixura leei were new for Italy. Rotifers strikingly were the most abundant group over the entire sampling period. Zooplankton abundance was positively correlated to water temperature and chlorophyll-a concentration, and only in warmer months inversely correlated to river flow. Species of the genus Brachionus were responsible for the two density peaks (>1000 ind L À1 ) of the rotifer taxocoenosis observed in July 2000 and August 2001, coinciding with chlorophyll-a peaks higher than 50 mg L À1 and minima of Shannon equitability index. Water temperature, chlorophyll-a, and soluble reactive phosphorus (SRP) were found to be the most important variables in explaining the observed rotifer assemblages by Canonical Correspondence Analysis. A simple descriptive model is proposed to represent the combined influence of abiotic constraints and biotic interactions on the zooplankton abundance and diversity in the middle reach of the Po River.

Structure of potamoplankton along a gradient of preservation of riparian vegetation in subtropical streams

“…Many studies in stream ecosystems have showed seasonality as the main variable correlated with higher values of algal biomass, chlorophyll-a and species richness (Rodrigues et al 2007, Borges and Train 2009, Rossetti et al 2009, Tavernini et al 2011. In the present study, the higher rainfall recorded during the summer might be the explanation for the higher biomass and diversity observed in the studied streams.…”

Flood‐Pulse Effects on Zooplankton Assemblages in a River‐Floodplain System (Gemenc Floodplain of the Danube, Hungary)

“…Water age should be more important for zooplankton than for phytoplankton due to the longer generation time of zooplankton (BASU and PICK, 1997). On the other hand, in a survey on the Po River (Italy) ROSETTI et al (2009) found significant influences of temperature and trophic conditions, but no direct effects of the hydrological regime on zooplankton. However, the Po River is confined within artificial banks, which results in poor connection between the main arm and its floodplain.…”

Benthic metabolism and denitrification in a river reach: a comparison between vegetated and bare sediments

“…In regulated rivers, the altered hydrology affects solid transport and sedimentation rates and can amplify the effects of nutrient loadings, inducing eutrophication processes (Dodds 2006;Hilton et al 2006;Rossetti et al 2008). Current velocity and water turbulence have also been recognized as prime factors regulating growth and distribution of submerged macrophytes (Madsen et al 2001;Sand-Jensen 2008).…”