. The Canadian field-naturalist. 298 The Canadian Field-Naturalist Vol. 108 LABRADOR. Figure 1. Location of Tolypella glomerata in insular Newfoundland, Canada. have previously occurred receiving runoff and seep- age water from the inland escarpment. It is likely, however, that the macrophytes present were intro- duced since the construction period. The larger pool is approximately 200 m2 in area whereas the smaller pool 100 m to the northeast is only one-third this size. Maximum water depth which measured 25 cm fluctuated somewhat during the summer, but never dropped drastically and the pools
. The Canadian field-naturalist. 298 The Canadian Field-Naturalist Vol. 108 LABRADOR. Figure 1. Location of Tolypella glomerata in insular Newfoundland, Canada. have previously occurred receiving runoff and seep- age water from the inland escarpment. It is likely, however, that the macrophytes present were intro- duced since the construction period. The larger pool is approximately 200 m2 in area whereas the smaller pool 100 m to the northeast is only one-third this size. Maximum water depth which measured 25 cm fluctuated somewhat during the summer, but never dropped drastically and the pools never dried out in the two years of observation (1992-1993) because of frequent rains and inland seepage. It is conceivable that in some years the pools might be subject to partial or total drying for a short period. The firm bed of the pools is of coarse gravel sealed by a fine pale grey calcareous mud and cov- ered by several centimeters of loose organic ooze. Water pH tested with a Cole-Parmer digital meter (pHep+) on 29 August 1992 was and conductivi- ty tested with a Myron L DS Meter (Model EP-10) was 480 umhos/cm. Both these values are among the highest measured in Newfoundland freshwaters reflecting the soluble calcareous substrate as well as the proximity of the pools to the ocean and the effect of salt spray (Kerekes 1978). The pH of inland cal- careous marl ponds rarely rises above with a con- ductivity of 300 umhos/cm In areas of acid rock sub- strate, Newfoundland freshwaters are highly dilute producing conductance values of less than 50 umhos/cm (often less than 25) and mostly ranging in pH from ,to , but with some values falling below pH Besides Tolypella, two aquatic macrophytes occur in the pools, the pondweed Potamogeton filiformis Pers. and the White Water Crowfoot, Ranunculus trichophyllus Chaix. Both of these are readily dis- persed cosmopolitan species of North America, Europe and Asia with tough seed coats resistant to waterfowl digesti
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