Smaller surface deposit feeding macroinvertebrates probably rely on both rnicroblal and non-living sources of organic matter, but only scant evidence supports the hypothesis that food is limiting to natural populations. Summer declines in deposit feeding populations have been ascribed to food limitation and to the seasonal influx of predators. We used a bioassay approach to test the following hypotheses: ( l ) Sediment supports more population growth in the spring and early summer, relative to the late summer and fall. (2) The nutritive value of sediment declines from spring to early fall, and absorption therefore should decrease. Laboratory tests using the common deposit feeding oligochaete Paranais litoralis partially support both hypotheses. Population growth studies of spring and summer sediment show a relatively nutritionally enriched surface sediment layer, suggesting that the sediment is recharged in the late fall and winter, either by particulate organic matter deposition or microbial transformation of previously unabsorbable material. High summer temperature contributes to the negative effect of poor sediment quality. In Flax Pond. Long Island, New York, field studies show summer declines of several species of deposit feeding invertebrates, but caging studies demonstrate that predation is not a likely cause of the crashes, which proceed at similar rates inside and outside of cages.

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Chromium, manganese, nickel, vanadium and uranium have been determined in inter-tidal sediments collected from locations along the Cumbrian coast. Total concentrations of chromium, nickel and vanadium were determined by electrothermal atomic absorption spectrometry (ETAAS). Manganese was determined by flame AAS and uranium was quantified by alpha particle spectrometry with a surface barrier detector. Two alternative approaches to calibration were investigated in an attempt to obviate the need for routine use of the full standard additions procedure. It was found that the response following a single addition of standard solution, at a concentration 50% of the initial estimate, could be used to correct for the minor interference effects observed. Elevated levels of chromium (39.5 +/- 0.9 mu g g(-1)), vanadium (33.0 +/- 0.6 mu g g(-1)) and uranium (39.0 +/- 1.2 Bq kg(-1)) were observed at Whitehaven, whilst concentrations of manganese were highest in samples from more northerly locations. The uranium enhancement is due to the extraction of phosphates from ore naturally rich in radionuclides at the nearby Albright and Wilson 'Marchon' chemical manufacturing plant. The chromium contamination may also arise from chemical manufacturing, whilst the vanadium is thought to originate from oil spillage. Interferences associated with use of the European Communities Bureau of Reference (BCR) sequential extraction protocol were investigated, and the operationally-defined speciation of chromium, manganese, nickel and vanadium was then determined. Chromium, nickel and vanadium were found mainly in association with the residual sediment phase, except at Whitehaven and Maryport where increases in the oxidizable fractions were apparent. A large proportion of the manganese at all sites was present as exchangeable species, i.e., soluble in 0.11 mol l(-1) acetic acid, and this was not affected by sample drying (at 60 degrees C) nor by storage (for 6 months) prior to extraction

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