Vegetation (Floating River Vegetation) - Office of Public Works

3.5 Parameters affecting species distribution
As described in the habitat classification of Water Courses of Plain to Montane Levels with
Aquatic Vegetation EU 3260 a characteristic of watercourses supporting floating river vegetation is
the periodic rise and fall in water level in winter and summer, respectively. Low water levels in
summer provide aquatic plant species an opportunity to flower and also an opportunity for
terrestrial species to colonise aquatic environments. Low water levels reduce the competitive
advantage aquatic plants possess in aquatic environments.
The following dataset is a correlation between the physical parameters observed on-site at
each sampling point with that of floating river vegetation. Survey sites containing floating river
vegetation have been highlighted in blue in the tables in Appendix E.
During the survey of the Owenriff River square the majority of the watercourses surveyed
were found to be in flood. Not alone was the water flowing at a fast rate but it also had a brown peat
colour similar in colour to peat (probably surface run-off from surrounding habitats, see table 2.3).
Those watercourses not in flood did possess floating river vegetation. It is highly probable that the
gravel base of the Owenriff River would support floating river vegetation but the shade recorded at
some of the sites surveyed would not favour aquatic growth.
Floating river vegetation was recorded in all but one watercourse in the Clare River square.
All watercourses in this survey square are maintained by the Office of Public Works and are not
shaded. Depth and river base did vary between survey sites. The survey site in the middle of a bog
(section 2.3) was the only site without floating river vegetation. Recent work on the watercourse
and the acidity of the surrounding bog habitat may have prevented floating river vegetation growth.
As with the River Clare square floating was recorded in all but one watercourse. All
watercourses in this survey square are maintained by the Office of Public Works and are not
excessively shaded. A selection of riverbed substrates and water depth was recorded. Site 2 was the
only site where water was not evident as the channel was colonised by a selection of tall aquatic
vegetation growth. The presence of water parsnip would indicate that still and / or shallow water
was present. Colonisation of site 3 with scrub vegetation such as willow would not favour aquatic
species and was the only site that did not support floating river vegetation.
Shade appeared to be a significant parameter influencing the growth of floating river
vegetation. Although partial shade was noted for site 1 and site 3, considerably less light (morning
eastern sun) was available at site 1. This was reflected in the growth of moss only as opposed to
water crowfoot, Ranunculus, and moss recorded at site 3. Site 4 comprised of a small cascading
stream that collected in pools. The watercourse was surrounded with tall woodland trees providing
constant shade. No aquatic vegetation was recorded at the site, not even moss as observed in site 1
(section 3.2). Though slight turbidity was noted due to the cascading water it unlikely that this
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