Riverine habitat heterogeneity: the role of slackwaters in providing hydrologic buffers for benthic microfauna

Abstract

Slackwater habitats within lowland rivers support abundant biotic communities and provide these communities with a refuge from increases in discharge. These refuges allow biota to persist as discharges, vary and provide a source of colonists for slackwaters further downstream. In order to investigate the response of slackwater benthic microfaunal communities to changes in discharge, artificial slackwaters were created within the main channel of a lowland river and benthic microfaunal communities were sampled over a 60-day period. Benthic microfauna within the artificial and reference slackwaters were recorded in higher richness and abundance than in the main river channel. Within days the communities in the artificial slackwaters were similar to those in the reference slackwaters. The rapid speed of colonisation suggests that initial colonisation of slackwaters is likely to occur via active or passive dispersal of biota and that these systems and communities are resilient to changes in discharge.

Potamozooplankton communities in three different outlets from mesotrophic lakes located in lake-river system

“…Therefore, the values of all hydrological parameters were increased, including the depth, which according to CCA also positively influenced the zooplankton biomass. More water with greater width and depth causes floodplains and slack waters, which are a source of zooplankton in the river current (Saunders & Lewis 1998, Nielsen et al 2010. Thus, the more slack waters connected with a river, the more quantity of zooplankton in the river current.…”

Reduction of zooplankton communities in small lake outlets in relation to abiotic and biotic factors

“…The richest sources of zooplankton are lakes, reservoirs, floodplains, and ponds (Ejsmont-Karabin & Węgleńska 1996, Lair 2006, Chang et al 2008, Czerniawski & Pilecka-Rapacz 2011. Much less productive sources of zooplankton in rivers are wetlands and slackwaters (Richardson 1992, Nielsen et al 2010. Irrespective of the source, after reaching the main watercourse over a certain section of the river zooplankton suffers qualitative and quantitative reduction, which is most pronounced for large crustaceans (Armitage & Capper 1972, Walks & Cyr 2004.…”

Summer zooplankton in small rivers in relation to selected conditions

“…River plankton ecologists are also interested in how the river zooplankton community in the main channel is modified by the inflow from the slackwaters [4,16], floodplains [28] connected reservoirs [24,29,30] and tributaries [8]. How much the zooplankton communities are reduced between upstream and downstream sections, especially below lake outlets, [3,5,9,29] is another major point of interest.…”

“…The greater the width and depth of the river, the more small floodplains and slackwaters there are, which play a very important role in zooplankton reproduction. These small water bodies also help move the zooplankton to the main channel [1,15,16]. Nielsen et al [16] have observed that the abundance of adult microcrustaceans even exceeded 180 ind.…”

“…The difference in the trophic status of lake outlets may also similarly affect the abundance of zooplankton [9]. However, many authors indicate that the river regime mainly determines the structure of the zooplankton community in rivers [14][15][16].…”