1. In unshaded, nutrient‐rich streams, prolific growth of stream macrophytes often results in flows that over‐top the banks and in high primary production and respiration that may result in extreme diel variations in dissolved oxygen. Consequently, water protection authorities commonly remove macrophytes periodically. 
2. We investigated the effect of plant removal on stream metabolism and oxygen balance in two Swiss streams with a high macrophyte biomass. We monitored the concentration of dissolved oxygen before and after macrophytes were removed by cutting and dredging, and calculated rates of gross primary production and ecosystem respiration by means of diel oxygen curves. 
3. The removal of plants, which had reached a dry biomass of 320–420 g m−2 immediately before plant removal, had a different impact on stream metabolism in the two streams. In the first (plants removed in May), neither primary production nor ecosystem respiration were significantly affected. In the second (plants removed in late July), gross primary production and ecosystem respiration were reduced by about 70%. In this latter stream gross primary production increased in the first 2 weeks after plant removal but never recovered to pre‐disturbance levels. 
4. The removal of plants coincided with only a moderate increase in nocturnal oxygen concentration (+1 mg L−1). This, and the rapid partial recovery of stream metabolism in the second stream, suggests that an increase in the oxygen concentration after plant cutting is transient in unshaded, nutrient‐rich streams.

The effect of aquatic plant removal on benthic invertebrates and their habitat was studied in two macrophyte‐rich streams of the Swiss Plateau. In each stream, habitat conditions (macrophyte biomass, current velocity, water depth) and invertebrate densities were monitored in a control reach and in a reach where plants were removed by cutting. Biological samples were taken and physical parameters measured on three dates before and six dates after plant removal in both reaches. Responses to plant removal were similar in both streams; macrophyte cutting initially decreased mean plant biomass (ca. 85%) and total number of invertebrates (ca. 65%). Variation between replicates was, however, higher in one of the streams, causing fewer effects on plants and invertebrates to be statistically significant. Plant cutting affected mainly taxa that used macrophytes as habitat (e.g. Simuliidae, Chironomidae), whereas highly mobile taxa (e.g. Ephemeroptera) and taxa living on or within the bed sediments (e.g. Trichoptera, Bivalvia) were less affected. Taxa that decreased after plant removal recovered within 4–6 months, although recovery of macrophytes was quite different in both streams. Invertebrate recovery also seemed to be seasonally dependent, with cutting having a less severe impact during summer than spring. Our results suggest that macrophytes in streams should be removed only in summer, preferably leaving some plant beds to act as refugia for phytophilous invertebrates. © 1998 John Wiley & Sons, Ltd.

No 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.

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.