Annual production and drift of the stream amphipod Gammarus pseudolimnaeus in Valley Creek, Minnesota1

Abstract

Annual production and drift of Gammarus pseudolimnaeus were measured in a 100‐m section of Valley Creek for the 5‐year period 1968–1973. Production was estimated by the procedure previously termed the “Hynes method,” herein proposed to be termed the “size‐frequency method.” Annual production was 271 and 231 kg·ha⁻¹ (dry wt) in the first 2 years but declined subsequently to a low of 64 kg·ha⁻¹, apparently the result of a severe siltation. Annual mean daily drift corresponded, being high at 41 and 46 g·d⁻¹·m⁻³ s⁻¹ in the first 2 years, but only about 7 and 11 in the last 2 years. Mean annual standing stock was also high in the first 2 years (47 and 35 kg·ha⁻¹) but substantially lower n the last 2 years (11 and 17); mean annual density was 7,176 and 6,849·m⁻² in the first 2 years and 1,586 and 2,363·m⁻² in the last 2 years. Annual P:B ratios were 5.7–6.6 over the 5‐year period, with an average of 6.0.