Implications of the annual macrophyte growth cycle on habitat in rivers

Abstract

The continuity equation, Manning's equation and an empirically determined relationship between channel roughness and the biomass of macrophytes were used to simulate the effects of weed growth in contrasting channels. Two indices of wetted available habitat, velocity and depth were chosen to illustrate the role of macrophyte in maintaining and modifying instream habitat with particular reference to chalk streams. Plant growth maintained depth within the channels and its effect was modified by channel shape and slope. Weed cutting resulted in very sudden changes in depth and velocity and the loss of a large volume of water from the river. The results indicate that macrophyte growth could be used to maintain wetted habitat while allowing more abstraction, but more data are required on the long-term effects of implementing such policies.

Retention of particulate matter by macrophytes in a first-order stream

“…This study was very short-term, so I most probably missed potential long-term effects of macrophytes in the Breitenbach. Long-term changes in streams caused by macrophyte removal includes noticeable increases in depth, velocity and subsequent changes in discharge (Hearne and Armitage, 1993). Analogously, increasing macrophyte biomass in the Breitenbach may cause opposite changes.…”

Instream and riparian implications of weed cutting in a chalk river

“…Although increased conveyance is desirable to mitigate flood risk it may result in low water levels where abstractions are high (Hearne and Armitage, 1993) or where drought conditions prevail. Therefore, the presence of macrophytes may be important in maintaining acceptable water levels.…”

Fine‐grained bed sediment storage within the main channel systems of the Frome and Piddle catchments, Dorset, UK

“…In addition, increasing evidence of the important role of fine sediment deposition in the transfer and fate of nutrients (House and Warwick, 1999;House, 2003;Evans et al, 2004;Collins et al, 2005) and contaminants (Rees et al, 1999;Rice, 1999;Kronvang et al, 2003;Collins et al, 2005) serves to emphasize its wider significance in non-point pollution problems. Land-use change and intensification associated with the expansion of arable agriculture (Richards et al, 1993) or commercial forestry (Murphy and Milner, 1997) and the resulting higher fine sediment loadings, increased groundwater abstraction (Bickerton et al, 1993) and periodic channel management activities (Hearne and Armitage, 1993) have all been implicated as enhancing river-bed sedimentation.…”