A comparison of the effect of beaver and human‐made impoundments on stream zooplankton

Abstract

Small human‐made dams and beaver ponds cause significant changes in the environment of small streams. The decreased current velocity and increased water retention time in these impoundments favour the development of limnetic organisms, for example, zooplankton. However, small human‐made reservoirs are regulated, deep and narrow, whereas beavers create relatively large impoundments with numerous shallow patches and their impact on the stream zooplankton communities can be different. We compared the effect of beaver ponds and small reservoirs on the zooplankton communities in streams. Three sample collection sites were established in each stream. Site 1 was approximately 100 m upstream of the water impoundment formed by the dam. Site 2 was at the dam impoundment of the stream water. Site 3 was approximately 300 m below the dam. Beaver ponds have a larger impact on the zooplankton richness and the abundance changes compared with seminatural reservoirs not maintained by people, and a much greater impact than reservoirs regularly cleaned and regulated. Beaver ponds create heterogeneous environment that favour the occurrence of a greater number of zooplankton species compared with small reservoirs. Moreover, the increase in organic matter in the downstream areas could lead to trophic changes in the stream.

Spatial Changes in Invertebrate Structures as a Factor of Strong Human Activity in the Bed and Catchment Area of a Small Urban Stream

“…Hence, even a small dam that created a very shallow reservoir caused a significant difference in the richness and abundance of zooplankton between the upstream and the downstream sections. A similar pattern of the distribution of the zooplankton community was reported in small forest streams and rivers impounded by human-made dams or beaver dams in some studies [7,10,14,21]. We observed that in the impoundment (POND)-the "Słoneczne lake" of Bukówka-the richness and abundance of zooplankton were high, which was comparable to or even exceeded those in the typical temperate limnetic basins (e.g., eutrophic lakes or reservoirs) [22,23].…”

“…It is generally known that zooplankton disperse passively from the outlet of stagnant basins to downstream and can colonize new habitats [27]. Drifting zooplankton can colonize the river if its bed offer zones with low current velocity or with stagnant water (e.g., slack waters, impoundments, and floodplains) [7,10]. The main variables that contribute to the increase in the richness and abundance of zooplankton in the Bukówka stream at the more downstream sites are as follows: a decrease in the current velocity, a longer water retention time or greater areas of open-water zones, higher number of slack water areas, covering of floodplains by macrophytes, and adjacent water bodies [14,28,29].…”

Spatial changes in zooplankton communities in a strong human-mediated river ecosystem

“…Also zooplankton transfer from lakes and reservoirs into the river is well documented (e.g., Basu & Pick, 1997 ; Pourriot, Rougier & Miquelis, 1997 ; Czerniawski & Domagala, 2014 ). Drifting zooplankton can colonize the river if its bed offer zones with low current velocity or with stagnant water e.g., slackwaters, impoundments, floodplains ( Czerniawski & Sługocki, 2017 ; Czerniawski & Sługocki, 2018 ). The Barycz is a kind of impoundment–cascade system in which richness and abundance of zooplankton increase with the number of dams.…”

The Impact of Land Use Transformations on Zooplankton Communities in a Small Mountain River (The Corgo River, Northern Portugal)

“…However, hydrological changes, such as lower current velocity or an increase of nutrient content, and higher temperatures in small rivers provide atypical yet favorable conditions for zooplankton growth. Zooplankton reacts rapidly to the hydrological changes in rivers, increasing its richness and abundance [13,14]. This certainly depends on the reservoir characteristics, and specifically its hydrological conditions, which consequently can change biological conditions and favor the development of planktonic organisms that cannot resist stronger water currents.…”

“…The more severe the changes upstream, the stronger the effects downstream [2]. Zooplankton was one of the indicators for these changes [6,14]. However, the functioning of a small lowland river depends on different values of hydrological factors than that of mountain rivers.…”