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Abstract

Effects of plant removal on habitat conditions, stream metabolism and benthic invertebrates were studied in two macrophyte-rich streams (Chriesbach, Mühlibach) of the Swiss Plateau. We monitored a control reach (no treatment) and two impact reaches (removal of plants by cutting or dredging) in each stream. Sampling was conducted during a 2-4 month period before and a 9 month period after the removal of 84-94% of the plant biomass. Oxygen concentrations were continuously recorded for 3-4 months. Plant removal decreased water depth and increased current velocity. The total number of invertebrates decreased by about 65%. Plant cutting mainly affected taxa that used macrophytes as habitat. Highly mobile taxa and taxa living on or within the bed sediment were less affected. Invertebrate densities recovered within 4-6 months. The removal of plants resulted only in a moderate increase in nocturnal oxygen concentrations. In the stream where plants were cut in spring, macrophytes recovered within the same growing season. In the other stream, where plant growth started later, plants were cut in summer and no recovery of plants occurred until the following spring.

Evaluating effects of weed cutting on water level and ecological status in Danish lowland streams

“…Flow resistance associated with aquatic plants is the main reason for active maintenance of aquatic plant populations in streams (Dawson & Robinson, 1984;Naden, Rameshwaran, Mountford, & Robertson, 2006;Pitlo & Dawson, 1990), and maintenance is performed regularly in many lowland streams to increase the discharge capacity (e.g. Baattrup-Pedersen et al, 2009;Caffrey, 1993;Fox & Murphy, 1990;Kaenel & Uehlinger, 1999;Vereecken, Baetens, Viaene, Mostaert, & Meire, 2006;Wiegleb, Br€ oring, Filetti, Brux, & Herr, 2014). Maintenance methods include simple weed cutting involving removal of aquatic plant biomass or removal of selected species using a scythe or boat mounted with knives (Baattrup- Pedersen, Larsen, & Riis, 2003;Old et al, 2014;Schwarz & Snelder, 1999) and dredging of the total macrophyte biomass and associated accumulated sediments using an excavator (Caffrey, 1993;Sabbatini & Murphy, 1996a, 1996b.…”

“…Old et al, 2014). This is surprising considering that maintenance has a tremendous effect on the ecology of the streams (Armitage, Blackburn, Winder, & Right, 1994; Baattrup-Pedersen, G€ othe, Riis, & O'Hare, 2016;Baattrup-Pedersen et al, 2003;Dawson, Clinton, & Ladle, 1991;Kaenel & Uehlinger, 1999). Instead, maintenance is performed under the assumption that removal of aquatic plant biomass improves flood protection and runoff from agricultural land if applied regularly (Bach et al, 2016;Old et al, 2014;Vogelsang, 2016).…”

Impact of partial removal of the invasive macrophyte Lagarosiphon major (hydrocharitaceae) on invertebrates and fish

“…This rapid recolonization by lagarosiphon occurred despite the complete clearance of any residual stem material. Similar experiments on vegetation removal with other macrophytes indicate that rapid recovery is a common outcome (Fox and Murphy, 1990;Unmuht et al, 1998;Kaenel and Uehlinger, 1999). Furthermore, the availability of free space in the clear-cut channels, abundant light, protection from wave action by the channel walls formed by lagarosiphon stems, and lastly lateral encroachment from the channel walls probably facilitated the recolonization process.…”

“…However, there was no detectable impact on other chemical or physical water parameters. Reasons for this might include the comparatively narrow nature of weed beds in this part of the lake preventing the build-up of deoxygenated zones in the macrophyte beds and a change in pH through photosynthetic activity as seen in other dense macrophyte beds (Scott and Osborne, 1981;Cardinale et al, 1997;Kaenel and Uehlinger, 1999). Additionally, there is a noticeable downstream water current in this part of the hydro-lake enhancing the exchange of water between the macrophyte beds and surrounding open water.…”

“…There is considerable information available on the impact of different degrees of macrophyte management and methods on fish communities, abundance, biomass and fecundity (Bailey, 1978;Maceina et al, 1991;Bettoli et al, 1993;Valley and Bremigan, 2002;Sammons et al, 2003), but very little on the impacts of control on invertebrates (but see: Kaenel and Uehlinger, 1999). Generally, moderate macrophyte cover can provide spatial diversity and is beneficial for fish diversity and sport fish production in contrast to excessive cover and a lack of macrophytes (Crowder and Cooper, 1979;Wiley et al, 1984;Killgore et al, 1998;Bickel and Closs, 2008).…”