Louisa Bridge warm spring. Co. Kildare

Survey site description

This site is located approximately 2 km north-west of Leixlip town in Co. Kildare. The warm spring is located close to the top of the River Rye valley in an area of calcareous grassland terracing. Several springs and seepages are found as you travel downhill from the site towards the river channel at valley floor level. This is the only warm spring in Ireland located in a designated Special Area of Conservation (SAC, site code 0001398, Rye Valley/Carton) under the 1992 Habitats Directive of the Council of the EU.

(photo: sweep sampling in Louisa Bridge warm spring - note large volumes of litter)

Louisa Bridge warm spring is located close to the Royal Canal and was uncovered during canal construction in 1794. By the end of the 18th century the site had been developed as a spa but by the late 19th century the site was failing to attract visitors and fell into disrepair. Development of this spring as a spa involved the construction of a hexagonal stone well chamber with a series of steps descending towards the centre and this structure remains relatively intact today. The chamber is approximately 0.7 m deep at the centre and is fed from a single point inflow towards the back wall. The substratum in the chamber was primarily highly organic sulphurous black mud. Water levels in the chamber fluctuated during the year, however the surface area remained relatively constant, measuring approximately 50 m2. Land adjacent to the chamber was a mixture of calcareous grassland and scrub. Approximately one quarter of the chamber's external circumference was bordered by a high stone wall from the original canal construction. Heavy pollution has been a problem at this site (Terry Doherty, NPW wildlife ranger, pers. comm.) and domestic refuse dumping and general neglect which has resulted in severe degradation in both water and general ecological quality at this site was observed on all visits to this site.

Macroinvertebrate survey 

The spa at Louisa Bridge was sampled in Spring (March 2003), Summer (July 2003) and Autumn (October 2003). In the spring, the water louse Asellus aquaticus were the most abundant organisms and dominated the fauna, with only one specimen each of the water bug Velia caprai and the mollusc Lymnaea peregra recorded. Asellus sp. was also the dominant species in the summer, although the abundance of this species decreased in the autumn survey. Dipteran larvae, Chironomidae, Pedicia sp., and the beetle Brychius sp. were recorded in the summer. Oligochaetes (which were not recorded in the spring or summer) were the most abundant taxa in the autumn. The abundance of molluscs recorded (Lymnaea peregra) increased gradually over the survey. Beetle larvae (Haliplus sp.) were found in autumn samples amongst surface algae and the increase in their numbers coincided with an increase in algal growth.

Species richness at this site increased in summer and autumn, but was generally relatively low (3-7 species/higher taxa). The total number of organisms found did not differ greatly between the three surveys (ranging between 62 and 84). Many of the invertebrates were recorded as solitary specimens only, such as the snails Lymnaea stagnalis, the dipteran Tipula sp. and the mayfly Ephemerella ignita.

Physico-chemistry 

Water temperature remained relatively constant (ranging between 16 and 16.4 oC) over the sampling period. The pH value ranged between 7.15 and 7.6, while conductivity was recorded at relatively high levels (ranging between 1602 - 1637 µS/cm). Oxygen concentrations were generally very low at this site, however they were higher in autumn (1.4 mg/l) compared with spring (0.6 mg/l) and summer (0.02 mg/l). The water level increased by approximately 40 cm from spring to autumn.

Aquatic macrophyte survey 

The number of plant species or higher taxa recorded in this spring ranged between two (spring and autumn) and three. The community was dominated by the filamentous algal species Cladophora however Charophytes were recorded as occasional in both spring and summer but increased in abundance in the autumn. The Duckweed (Lemna minor) was recorded from this site only in summer. The algal content in water increased substantially over the course of the sampling period.

Other notable features 

Tufa was not apparent other than a light patchy deposition in places on the chamber wall near the spring discharge point. The substratum at this site was composed of a thick layer of highly anoxic (foul smelling) black organic mud. Large volumes of litter were present in the spa chamber on all visits and dumping of larger objects (washing machine, shopping trolleys etc.) had also occurred. A strong water flow was present above the main discharge point at the back of the chamber, with suspended sediments flowed quickly away in the water current. Groundwater gas bubbles issued at several points near the discharge point.

© Ecological Consultancy Services Ltd 2003