16 THE ESSEX NATURALIST
Nucula nucleus and Abra alba were recorded from further up the
estuary than had been observed since the cold winter of 1962/63
and Macropodia has returned to the Blackwater.
INTRODUCTION and METHODS
In an earlier paper (Barnes and Coughlan, 1971), the authors
presented the results of a general survey of the Blackwater
Estuary, Essex. This survey was designed to assess the extent
to which the estuary had recovered from the severe winter of
1962/63 and to present a general picture of the distribution pat-
terns of the dominant macrofauna. In May 1970 and again in
June 1971, the authors investigated in more detail a limited area
of this estuary around the cooling water intakes and outfalls of
Bradwell Nuclear Generating Station. Here the emphasis was
placed upon a determination of the differences, if any, manifested
by the faunas adjacent to the intakes on the one hand and to the
outfalls on the other. These two culvert systems are sited on
opposite sides of a 250 m sheet-steel "barrier" or "baffle" wall
aligned along the long axis of the estuary and designed to separ-
ate the inflowing and outflowing water masses. The outflowing
water at source is from 8 to 10°C above the ambient tempera-
ture and hence if the discharge of heated effluent from the power
station has any effect upon the macroscopic benthic fauna of the
Blackwater, it is surely in the immediate area of the outfall cul-
verts that any such effects should be manifested (Fig. 1).
Fig. 1. Sketch-map of the mouth of the Blackwater Estuary showing the
area surveyed