The Relationship of Benthic Macroinvertebrate Assemblages to Water Surface Flow Types in British Lowland Rivers

Surface Flow Types (SFTs), distinctive patterns of disturbance on the surface of flowing water resulting from the interaction between flow and channel shape, were used to delimit meso-scale in-channel habitats in eight British lowland rivers to determine whether SFT mesohabitats were capable of being mapped, and were physically and biologically distinct. Five different SFTs - No Perceptible (NP), Smooth (SM), Rippled (RP), Unbroken wave (UW) and Upwelling (UP) - were investigated, a further three rare types (Chute, Broken wave and Confused) were mapped but not investigated further.
Identification and mapping the extent of SFTs of was shown to be practical by estimating SFT mesohabitat extent onto large scale plans of the stream channel supported by differential Global Positioning Satellite technology. Mesohabitats were drawn as they existed, giving a large degree of variability in relation to channel shape and improving over several current rapid habitat mapping methods.
The physical distinctiveness of five SFT mesohabitats was examined using data collected from 596 mesohabitats over a wide range of discharges. Mean column velocity and substrate grain size (dominant and sub-dominant) increased from NP, through SM and RP to UW. Velocity, substrate size and embeddedness of fine particles were significantly different (ANOVA and Pair-wise) between the five SFTs investigated. Substrate size was positively associated with increasing velocity, depth and embeddedness were negatively associated with velocity. PCA showed that substrate opposes embeddedness and velocity opposes depth. The degree of distinctiveness was diminished by data ranges which encompassed several SFTs.
Macroinvertebrates were collected in 375 samples from 139 SFTs, using one-minute kick samples and identified to Biological Monitoring Working Party family level. ANOVA and Pair-wise analysis of Lotic-invertebrate Index for Flow Evaluation Velocity Group shows significant differences between 80% of SFT combinations with UP least distinct. Mean relative abundance and taxonomic richness increased from NP, through SM and RP to UW and were positively related to velocity. ANOVA showed significant differences between relative abundance and richness in SFTs, whilst Pair-wise analysis shows that adjacent SFTs, in relation to velocity, were less different than those further away. Thus NP is similar to SM and different to UW. Diversity and Equitability between SFTs were less distinct. Thirteen macroinvertebrate family groups were significantly associated (X2 Test) with particular Surface Flow Types, e.g. Ancylidae with UW; Chironomidae with NP. Biological distinctiveness was not established, although general trends were identified
One mesohabitat – UP - is rare, being physically related to NP and SM in depth and substrate, and to SM and RP in velocity and embeddedness. It is biologically less distinct than the other four SFTs.
The research shows that the extents of NP, SM, RP and UW mesohabitats in British lowland rivers are capable of being mapped. There are significant trends in their physical distinctiveness which are linked to increasing downstream velocity although is not strong. The macroinvertebrate relationship is weaker, with abundance and richness increasing with velocity.