Aquatic Planting Project

Introduction

Selection of Planting Sites

Planting Sites

Attention was now turned to obtaining more diverse species to continue the project. In the previous year (2000), growths of Myriophyllum and other species were identified in a tributary of the Ouse at Walstead, and the riparian owner was willing to donate some samples. However, an inspection of the stream in July 2001 showed it to be completely devoid of sub–aquatic vegetation. A substantial amount of housing development has taken place at the headwaters of this stream near Haywards Heath, and the riparian owner said that there were now more frequent and severe spates due to surface water runoff which were scouring the bed of the stream on a regular basis, denuding it of resident vegetation.

2002

Fig.1

Shortly after this planting there was a moderate spell of rain with consequent increase in current volume and velocity. An inspection of the site indicated that none of the planted material had survived. Experience has shown that establishing new plant communities in this stream is difficult with the exception of Ranunculus fluitans. This plant takes root quickly and having done so grows rapidly. It is resistant to fragmentation from increased current velocity and turbulence and even if the emergent growth is denuded, new growth takes place from the rootstock. The roots of this plant appear to stabilize the streambed creating areas resistant to erosion.

The original plantings in 2000 were now large enough to divide and provide samples for further distribution, with likelihood of successful establishment. A comprehensive programme of distribution has been undertaken throughout the section of the stream from its confluence with Plumpton Mill Stream to Clapper's Bridge. There is now no doubt that this species should survive and flourish.

During the spring and summer of 2002 further attempts have been made to introduce Callitriche spp. This plant can be found in certain places on the River Ouse and is often abundant in adjacent ditches. However, it is relatively fragile and susceptible to fragmentation. It appears to take longer to root than R. fluitans, does not grow as quickly and its root systems do not significantly contribute to the stability of the substrate. Heavy rainfall during the spring and early summer of 2002 contributed to many failures. Experience has shown that selected sites in proximity to established Ranunculus fluitans are more likely to succeed. (See fig. 1). It remains to be seen if these survive the winter spates of 2002/03.

2003

Fig.2

2003 was not a good year for this project. With very high summer temperatures and prolonged drought conditions from the beginning of May to the end of September, water levels in the stream were extremely low. Many riffle areas supporting growths of Ranunculus became almost stagnant pools. Without agitation from a robust flow, algal deposits covered the vegetation with a slimy brown film, inhibiting photosynthesis and growth mechanisms. (See fig.2).

Some planting of Ranunculus at other sites was undertaken in the spring, but few if any of these survived. The situation will be reviewed in the spring of 2004.

2004

Ranunculus Fluitan flourishing after the drought of 2003

Fig.3

The damage to the submerged vegetation in the stream caused by the prolonged drought conditions of the 2003 summer was not as devastating as it appeared. In the late spring of 2004 most of the species were seen to regenerate with the maintained rate of flow. There is now no doubt that Ranunculus fluitans is permanently established in the watercourse and scattered colonies of Callitriche and Sparganium emersum are also present.

The project has proved successful in adding to the biodiversity of the stream and this work will be continued on other streams in the catchment.
(See Fig.3)