During our brushing out activity on the Bevern Stream a distinct lack of submerged aquatic vegetation was apparent. In the riffle and pool systems, which are characteristic of this watercourse upstream from Clappers Weir, the only species detected were water mosses (fontinalis antipyretica and eurhynchium riparoides).
These are found in some of the fast water areas on large stones and boulders. The deeper pools where there is a silt substrate and slow current do not appear to support any submerged vegetation of note.
A similar situation also pertains to the Northend Stream.
It is difficult to understand why these two streams suffer from this deprivation when the main river and other tributaries contain an abundance of submerged flora of varying species. Factors such as instability of the stream bed in spate conditions, herbicide pollution etc. may be involved, but these are not factors peculiar to these two streams alone. There may just be a lack of seeding of appropriate species.
It has been demonstrated that the number of invertebrates present is greatly enhanced by the presence of submerged flora. A survey carried out by Percival and Whitehead on the rivers Aire, Nidd and Wharfe found a mean of 3,316 invertebrates per sq. m. in loose stones compared with 243,979 in areas with submerged vegetation on stones. It would therefore seem reasonable to assume that an increase in the variety and amounts of submerged water plants in the streams would improve the habitat for invertebrates and enhance the ecology.
It was therefore decided to implement an experimental planting project in the Bevern Stream with continuous monitoring of the results, subject to Environment Agency and riparian owner consents. These consents were obtained and valuable advice was given by Jane Cecil the Environment Agency Fisheries and Ecology Manager for the Sussex area. A donor site was identified on the River Ouse at Sharpsbridge where prolific growths of starwort (callitriche sp.), water crowfoot (ranunculus fluitans) and strapweed (sparganium emersum) were available. Permission to harvest in this area was kindly given by the riparian owner Mr. John Sclater.
The sites for planting were selected to maximise the chances of successful establishment. Factors considered were stability of the stream bed in maximum flow conditions, adequate light, and freedom from disturbance such as by cattle or human activity. The exercise was also timed to allow optimum conditions for the successful establishment of the plants, but avoiding disturbance to fish breeding activity. Four sites were chosen where access is reasonably easy for monitoring purposes.
The first two sites are at North Barns Farm by kind permission of Mr. G. Awbery. One is in the Plumpton Mill Stream just above its confluence with the Bevern, map ref. TQ 374159, the other in the Bevern Stream about 200 metres downstream from the confluence map ref. TQ376158. Plumpton Mill Stream has a chalk spring source and is bounded by little if any arable land. There are no significant effluent discharges into this water. The Bevern Stream at this point carries effluent from Ditchling Sewage Treatment Works, Streat Golf Course Works and possible herbicide contamination from this and surrounding arable land. The proximity of these two sites with different water compositions facilitates a comparative study.
The next site is downstream at Hurst Barns Farm map ref. TQ 384157, by kind permission of Lady Marina Bury. The surrounding land is organically farmed and therefore free from direct herbicide spray drift.
The final site is at Knowlands Farm map ref. TQ 415165, by kind permission of Mr. & Mrs. N. Lear. This is surrounded by improved grassland which is subject to herbicide spraying from time to time it is also downstream from the Barcombe STW outfall and therefore in the most polluted section.