Our main objective was to investigate the effect of Spartina anglica stems on hydrodynamics, sediment dynamics and their influence on seasonal morphological changes on the upper shore and salt marsh of an intertidal mudflat in the Tavy estuary (southwest England). On an intertidal transect, the greatest seasonal changes in sediment levels occurred at the seaward edge and lower part of the salt marsh, and on the lower shore mudflat, while the smallest changes occurred on the mid-and upper-shore mudflat. Flume studies demonstrated flow attenuation with increasing Spartina stem density, but this was accompanied by an increase in turbulent kinetic energy and bed shear stress (τ 0 ). The critical erosion threshold (τ e ), however, remained relatively constant at 0.12 Pa. Field measurements showed that τ 0 was well below τ e under calm conditions. During periods of windwave activity, when daily mean wind speeds were > 8 m s -1 , τ 0 was greater than τ e in the lower salt marsh for brief periods at the beginning and end of tidal inundation. At the seaward edge of the salt marsh, τ 0 increased to 1.0 Pa and τ 0 was greater than τ e throughout the inundation period, causing significant sediment erosion. Wind-induced wave activity was the major driver of sediment erosion on soft muddy shores and this was enhanced by the interaction with S. anglica stems. The number of days per month with mean daily wind speeds > 8 m s -1 was inversely related to changes in sediment levels at the seaward edge of the salt marsh. During the summer, winds were below this threshold, and there was gradual accretion. Results are discussed in the context of climate changes involving increased storminess leading to increased erosion. We show that the S. anglica salt marsh should not be considered a 'bio-stabiliser' of fine muddy sediment.

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This study was undertaken to determine the present ecological state of rivers and streams in the Buffelspoort Valley Conservancy (BVC), against which later potential changes in, and impacts on, water quality could be measured. After very brief training, all field work, including site selection and sample collection, was carried out by the members of the Conservancy. All samples collected by the members of the Conservancy were of an adequate quality for analysis and yielded meaningful results. This study demonstrates that there is great potential for the use of diatoms in community monitoring programmes, mainly due to the ease and rapidity with which samples can be collected. The participation of communities is also vital in gaining a more complete overview of the diatom species occurring in South Africa.