Longitudinal Variability in Hydrochemistry and Zooplankton Community of a Large River: A Lagrangian‐Based Approach

Abstract

The variability in water quality and zooplankton community structure during downstream transport was investigated in the Po river (Italy) using for the first time a Lagrangian sampling approach. Two surveys were conducted, one in spring under relatively high discharge levels, and one at low flows in summer. Twelve stations along a 332‐km stretch of the river's lowland reach and four major tributaries were sampled. A hydrodynamic modelling system was used to determine water transport time along the river, with a satisfying fit between simulated and observed discharge values. No clear downstream trend in phosphorus and nitrogen concentrations was found. Conversely, a marked longitudinal decrease in dissolved silica supports the hypothesis of increasing downstream silica limitation during the phytoplankton growing season. In spring, at low residence time, no apparent plankton growth was observed during downstream transport. In summer, higher temperatures and lower turbulence and turbidity associated with longer residence time stimulated algal growth and in‐stream reproduction of fast‐growing rotifer taxa, with the gradual downstream development of a truly potamal assemblage and the increase of the ratio of euplanktonic to littoral/epibenthic rotifer taxa. Crustacean zooplankton density was generally low. The importance of biotic interactions within the zooplankton in driving community abundance and composition appeared to increase in the downstream direction, paralleled by a decrease in the influence of physical forcing. Tributary influence was especially evident where severe anthropogenic alterations of river hydrology and trophic status resulted in enhanced plankton growth, ultimately affecting zooplankton structure in the main river. Copyright © 2016 John Wiley & Sons, Ltd.

Evaluating spatiotemporal variation in water chemistry of the upper Colorado River using longitudinal profiling

“…Although a network of fixed monitoring sites situated along a stream reach, or distributed throughout a network (i.e., synoptic sampling sites), can be used to compare measurements across space (e.g., Bertani, Del Longo, Pecora, & Rossetti, ), these sites are typically situated at least tens of kilometres apart, substantially limiting the resolution of detectable spatial variation. Thus, although it is often possible to discern broad spatial changes in water chemistry, the specifics about where, how, and ultimately why these changes occur are often obscured.…”

Spatial variability of the Po River food web and its comparison with the Danube River food web

“…The abstracts were screened, from which only 7 articles were found to be relevant. After reviewing these selected papers, two articles had data on rotifer predator-prey interactions [30,31]; two papers had detailed species list, but lacking diet information [32,33]; and three papers had information on plankton and macroinverterbrate community composition [34][35][36]. Therefore, it was not possible to obtain data for the Po River food web based only on white literature.…”