Lethal and sub‐lethal effects of acid, aluminium and lime onGammarus pulexduring repeated simulated episodes in a Welsh stream

SUMMARY.1. A soft‐water stream in upland mid‐Wales was dosed with sulphuric acid, aluminium sulphate and limestone slurry to produce a zone of aluminium at low pH. and one of aluminium, low pH and added lime. 2. Three episodes of 24‐h duration were induced, each separated by a 12‐h inter‐dosing period, and the responses of the crustaceanGammarus pulexmonitored throughout. 3.G. pulexparasitized by the acanthocephalanPomphorhynchus laeviswere significantly more sensitive than unparasitized individuals. 4. Liming significantly reduced mortality during dosing but postexposure deaths were greatest for animals which had been exposed in the time zone. 5. The disruption of precopulalory behaviour inG. pulexwas rapid and liming did not mitigate this response.