The Entomostraca of the Weeds of a Moorland Pond

Abstract

Wise Een Tarn (Nat. Grid Ref. 34/370975) lies on Claife Heights, a low range of hills to the west of Windermere, at an altitude of 650 ft. (199 m.). It is surrounded by typical moorland vegetation and was made by the building of a dam about 1900. Its surface area is 52,700 sq. yd. (44,500 sq.m.), its maximum depth, near the outflow is about 10 ft.; over much of its area the depth does not exceed 3 ft.; as no survey of the tarn has been made, these depth figures are only approximate. Two streams flow into it; one enters at the south-east corner and drains a neighbouring pond, Scale Tarn; the other drains high ground to the south-west of the tarn and enters it on the side opposite to the dam. In the summer and winter of 1947 the alkalinity (as mg. CaCO3/l.) was 9-0 and 6-6 respectively; the corresponding calcium concentrations were 4-9 and 3-7 mg./ll. No survey of the rooted aquatic vegetation has been made; the common water plants were Carex rostrata, Equisetumfluviatile, Potamogeton natans and Juncus bulbosus forma fluitans. In summer, the water-level often fell appreciably, but the extent of the fall was not measured; in winter, the tarn was usually frozen over for a few weeks at least. Between April and October, collections were made at weekly intervals, but in the winter months when few animals were caught, intervals of 3 or 4 weeks separated the sampling dates. Twelve tow-nettings were made in mid-tarn between March and June 1950 for comparison. At each visit, the water temperature was taken and general weather conditions were noted. Forty-two collections (between April 1949 and June 1950) were made at five marginal stations selected so that all weed-beds would be sampled. These five stations are shown in Fig. 1 by Roman numerals. Carex was common at all five stations, and because it grew nearest the water edge was generally completely exposed during dry periods in summer. Offshore the emergent stems of Equisetum and the floating leaves of Potamogeton were the characteristic features of each weedbed, except at Station V where there was no Potamogeton. At both Stations I and IV a bed of Equisetum overlapped somewhat with an adjoining bed of Potamogeton; at Station II Equisetum was more abundant than at Stations I and IV, and formed a thick fringe enclosing and encroaching on a rather small amount of Potamogeton; at Station III Potamogeton was more abundant than at any other station and was screened by a thin fringe of Equisetum on its border nearest the open water of the tarn. Juncus bulbosus was not abundant except at Station V where Equisetum was as abundant as at Stations I and IV. Taking the depth to which the human leg sinks in as a rough measure of the amount of detritus at each station, Station II had more detritus than J. Anim. Ecol. 2I I MAY 1952