Drifting plankton from a reservoir subsidize downstream food webs and alter community structure

Abstract

Subsidy between ecosystems has been considered in many natural ecosystems, and should alter food webs and communities in human-impacted ones. We estimated how drifting plankton from a reservoir contribute to downstream food webs and showed that they alter community structures over a 10-km reach below the dam. To estimate the contribution of the drifting plankton to macroinvertebrates, we used C and N isotopes and an IsoSource mixing model. In spring and autumn, contributions of plankton to collector-filterer species were highest 0.2 km downstream of the dam, and clearly decreased from 0.2 to 10 km. At 0.2 km, the contribution of plankton to a predator stonefly was remarkably high. These results indicated that drifting plankton from a dam reservoir could subsidize downstream food webs and alter their energy base, but the importance of this subsidy decreased as distance from the reservoir increased. The general linear models indicated that the abundance of collector-filterers and predators was related positively to zooplankton density in stream water. Thus, food source alteration by drifting plankton also influenced the community structures downstream of the dam.

The effects of dams on longitudinal variation in river food webs

“…Shannon et al (2001) observed enrichment of 13 C in benthic algae, macroinvertebrates and fish up to 350 km downstream of Glen Canyon Dam but no longitudinal trends in d 15 N for the same groups. Doi et al (2008) used isotope signatures of phytoplankton to suggest that they contributed to the downstream food webs for up to 10 km. Overall, while these studies evaluated differences in energy flow between regulated and unregulated rivers, they did not generally account for potential longitudinal patterns in stable isotope composition.…”

Changes in particulate organic matters and plankton populations in nature-like fishways: role of nature-like fish ways in water treatment

“…Moreover, suspension-feeding, filter-feeding, or net-spinning macrozoobenthic organisms could also reduce zooplankton abundance (Czerniawski et al, 2016). Even within a short section of a productive river that includes zooplankton, phytoplankton, and drift food sources, macroinvertebrates and fishes could play an important role in consuming and removing the drifting particles Doi et al, 2008). According to Kim et al (2015) and Park (2015), many fish species were found in Baekjae nature-like fishway and Sejong nature-like fishway during the survey for fish utilization of constructed nature-like fishways.…”

“…The assimilation of dissolved organic substances and nutrients in the water by bacteria, plants, and animals, as well as dilution and mixing processes are designed to self-purify (Heidenwag et al, 2001). In particular, the uptake of drifting organic matter by macroinvertebrates and fishes also plays an important role in self-purification Doi et al, 2008). Therefore, it can be expected that a nature-like fishway with a variety of benthic organisms has the capacity for selfpurification.…”

Downstream effects of hydropower production on aquatic macroinvertebrate assemblages in two rivers in Costa Rica

“…Previous studies have found that changes in hydrology and disruptions of the stream's natural connectivity affect the transportation of nutrients, energy, and sediments to sites below the dam, with effects on macroinvertebrate assemblages (Ward & Stanford, 1983;Petts, 1984;Petts, Armitage & Castella, 1993;Ligon, Dietrich & Trush, 1995;Finer & Jenkins, 2012). Increases in the abundance of collector-filterers below dams are often a consequence of increased transport of phytoplankton and zooplankton from the reservoir through the hydroelectric facility to the river downstream, creating a lake-derived subsidy for food webs below the dam (Ward & Stanford, 1983;Doi et al, 2008;Foto Menbohan et al, 2012). This increase in plankton availability could explain the observed shift from communities dominated by Baetodes, a collector-gatherer-scraper, above dams in our study, to assemblages with higher relative abundance of collector-filterers in sites below the dams.…”

“…Streams affected by large dams can have decreased macrophyte total biomass, as well as macroinvertebrate abundance, richness, and biomass (Troelstrup & Hergenrader, 1990;Dejalon & Sanchez, 1994;Vinson, 2001). Additionally, due to changes in food sources and substrate, the composition of macroinvertebrate functional groups changes downstream from hydroelectric dams, favoring functional groups that can exploit plankton drifting from the reservoir, and that prefer habitats with low sediment deposition (Dejalon & Sanchez, 1994;Doi et al, 2008;Katano, Negishi, Minagawa, Doi, Kawaguchi & Kayaba, 2009). Furthermore, species assemblages of invertebrates and fish are also affected below dams, favoring organisms that are tolerant to the physicochemical characteristics imposed by hydroelectric production (Dejalon & Sanchez, 1994;Vinson, 2001;Foto Menbohan et al, 2012).…”