Response of the flora and macroinvertebrate fauna of a chalk stream site to changes in management

Abstract

SUMMARY 1. Temporal changes in a series of habitats and their macroinvertebrate assemblages were examined on a 50‐m section of a chalk stream in Berkshire, England between June 1975–79 and June 1997–2001. 2. The site was part of a trout fishery in 1975–79, when river management included instream weed cutting together with control of bankside trees and riparian vegetation. Management ceased in the 1980s and by 1997–2001, the site was heavily shaded by trees and riparian vegetation. 3. The mean area of instream macrophytes decreased by 50% between the first and second sampling period. In contrast, gravel and silt increased and invading marginal vegetation formed a new habitat. 4. Changes in macroinvertebrate family richness between sampling periods were scale dependant. Although there were, on average, significantly more families in individual replicates in 1975–79 than in 1997–2001, total family richness for the site in each year did not differ significantly between sampling periods. 5. Sixty families of macroinvertebrates were recorded during the study, 50 in both sampling periods, 53 in 1975–79 and 57 in 1997–2001. This small increase in site family richness may be due to the invading marginal plants. 6. Total macroinvertebrate abundance was significantly lower in the second sampling period. A major drought in 1976 resulted in significantly higher densities of macroinvertebrates, partly through the exploitation of epiphytic diatoms by chironomid larvae. A drought in 1997 failed to elicit a similar response because of the limited macrophytes and diatoms under heavy shading by trees and marginal vegetation. 7. Significant increases in important shredders and decreases in some scrapers between the early and later sampling years largely reflected changes in available food resources. 8. Whereas macroinvertebrate family richness has been conserved under the recent ‘no management’ regime, the site is now less attractive as a fishery because of poor access and lower densities of some macroinvertebrates taken by brown trout.

Impact of major changes in flow regime on the macroinvertebrate assemblages of four chalk stream sites, 1997–2001

“…As expected, the Lambourn at Bagnor differed from the three Kennet sites, not only because it was on a tributary of the Kennet but also due to the heavy shading (Wright et al, 2003). Ephemerellidae, Baetidae and frequently Chironomidae were less abundant at Bagnor, whereas Glossosomatidae occurred at higher densities.…”

“…Some of the major differences (see Appendix) included higher densities of Baetidae and Ephemerellidae on the three unshaded Kennet sites than on the equivalent habitat at the heavily shaded Bagnor site. However, shading does appear to favour Glossosomatidae at Bagnor (Wright et al, 2003). A number of families including Simuliidae and Chironomidae, in addition to Baetidae and Ephemerellidae, generally occurred at higher densities on macrophytes compared to gravel, irrespective of site.…”

Macrophyte communities of European streams with altered physical habitat

“…Previous investigations demonstrated that the spatial distribution of macrophytes in lowland stream reaches changes in response to physical degradation or impact (Baattrup-Pedersen et al, 2002;Wright et al, 2003). The STAR sampling methodology (MTR & RHS) does not allow distribution changes within reaches to be examined.…”

Exploring the interactions between flood defence maintenance works and river habitats: the use of River Habitat Survey data

“…Conversely, excessive macrophyte growth in lowland catchments, particularly within unshaded reaches and those affected by agricultural runoff and sewage effluent, can represent a significant flood risk and exceed optimum levels of plant growth for river biota (Haslam, 1978;Wright et al, 2003). Different plant morphologies have different impacts on the flow environment (Naden et al, 2006), but overall aquatic macrophytes are observed to increase hydraulic roughness, modify velocity patterns and promote deposition of fine sediments (Gregg and Rose, 1982;Gurnell et al, 2006;Wharton et al, 2006).…”