Lexlip cold spring, Louisa Bridge, Co. Kildare

Survey site description 

Temperatures at Louisa Bridge cold spring have been recorded in the past as ranging between 6 and 14oC (Minerex, 1983). The spring is characterised by a generally low flow rate, with long periods during the summer when there is no flow. With such low flow rates, the water temperature is controlled to some extent by ambient air temperature, accounting for the seasonal variation in water temperatures. The maximum temperatures occur in August and September and minimum recorded in February and March (Minerex, 1983). The spring pool covered a surface area of approximately 20 m2.

Macroinvertebrate / faunal survey 

This cold spring, close to the Louisa bridge warm spring, was sampled in summer and autumn only. Over 20 species / higher taxa were recorded here in both summer and autumn surveys. The most abundant organisms recorded in summer were the snails Lymnaea peregra, the mayfly Caenis horaria and midge larvae, chironomidae. Other organisms which were abundant in summer, included Asellus aquaticus, the mollusc Bithynia sp., the damselfly larvae Enallagma cyatheigerum and the mayfly Centropoleum luteolum. In autumn the most abundant macroinvertebrates recorded were Chironomidae, gastropods Potamopyrgus antipodarum and Lymnaea peregra, bivalves - Sphaeridae., the mayfly Cloeon dipterum and the hemipteran Hydrometra stagnoma. This site was the only spring where a relatively species-rich group of Odonata and Ephemeroptera were recorded.

The damselflies (Zygoptera) consisted of substantial numbers of the damselfly nymph Enallagma cyathiergum and low numbers of Ischura elegans (in summer). Both species are widespread and common in Ireland with larvae that inhabit aquatic vegetation and a life cycle generally completed within one year (Dragonfly Ireland, Nelson and Morrow).

Also recorded in summer, were dragonfly larvae (Anisoptera) Sympetrum striolatum and Brachytron pratense. Sympetrum striolatum is a common and widespread species in Ireland and the most common of its genus. Adults can be seen from mid June to the end of October, and larvae stay amongst vegetation with larval development completed in one year (dragonfly Ireland, 2003).

Brachytron pratense (Muller, 1764), also known as the 'hairy' dragonfly, is a widespread and locally common species. The first of the large dragonflies to emerge each year and adults can be seen from early May to mid July at sheltered lowland lakes, fens and cutover bogs. It is locally common in parts of the midlands, north and west. Larvae are found amongst plant debris and development normally takes 2 years but can occur faster in warmer conditions (Dragonfly Ireland, 2003).

In autumn, the Zygopteran fauna mainly comprised Pyrphasoma nymphula in small numbers and two specimens of Ischura elegans. P. nymphula is common and found throughout Ireland. The larvae are bottom dwellers amongst plant debris and vegetation, feeding on other insect larvae, protozoa, rotifers and microcrustaceans, with larval development taking 2 years and final instar larva in diapause over second winter (Nelson et al, 2000).

One dragonfly species, Orthetrum cancellatum was recorded in autumn. O. cancellatum is uncommon and confined to base-rich loughs in central and western Ireland. Larvae of this species live in pond bottoms partially buried in silt and usually take 2 - 3 years to reach maturity

The Ephemeropteran community at this site were more abundant in summer and comprised Caenis horaria in substantial numbers in addition to many specimens of Cloeon simile and Centropoleum luteolum. Caenis horaria are widespread in Ireland in lakes, ponds and slow flowing water, preferring silty depositing habitats (Kelly-Quinn & Bracken, 2000). Cloeon simile is also common and thought to be encountered in most of the limestone lakes in Ireland (Kelly-Quinn & Bracken, 2000). Temperature is thought to have a strong influence on its life cycle (Whelan, 1980 in Kelly-Quinn & Bracken, 2000). Centroptilum luteolum is ubiquitous in Ireland both in lentic and lotic habitats although thought to have a preference for low gradients and slow currents (Kelly-Quinn & Bracken, 2000).

Physico-chemistry 

Water temperature ranged between 14.4 (summer) and 14.9oC (autumn). pH was recorded as 7.84 on both occasions and conductivity levels were high, ranging between 1470 and 1556 µS/cm. Oxygen concentrations of between 6.9 mg/l, 75% saturation (summer), and 8.2, 81% saturation (autumn) were recorded.

Aquatic macrophyte survey 

The cold spring is located in an area of open marsh which has a rich and diverse plant community including some aquatic and semi-aquatic species. Eight species were recorded directly within or at the edges of the spring. Most species were recorded on both visits (summer and autumn). All species were recorded as either occasional or rare and included the algae Cladophora sp., and the vascular plants Carex sp., Hippuris vulgaris, Typha latifolia, Mentha aquatica, Menyanthes trifoliata, Oenanthe sp. and Scirpus sp. Water levels in the spring did not fluctuate noticeably over the summer to autumn period.

© Ecological Consultancy Services Ltd 2003