New Zealand Journal of Marine and Freshwater Research abstracts

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Processing of willow leaves in two suburban streams in Christchurch, New Zealand

K. J. COLLIER
M. J. WINTERBOURN

Department of Zoology University of Canterbury Private Bag, Christchurch New Zealand

Abstract Breakdown of willow leaves (Salix babylonicd) enclosed in mesh bags (3 and 0.2 mm mesh) was investigated in Cashmere Stream and Avon River, Christchurch, New Zealand. Leaves lost weight faster in 3 mm than in 0.2 mm mesh bags and weight losses in 3 mm mesh bags were faster in Cashmere Stream. Calculated decay coefficients (-k), for 3 and 0.2 mm mesh bags respectively, were 0.0154 and 0.0114 (Avon River) and 0.0173 and 0.0117 (Cashmere Stream). Faster breakdown in 3 mm mesh bags could be in part the result of feeding activities of macroinverte-brates, especially Potamopyrgus antipodarum and Physa acuta. The significantly faster leaf processing in Cashmere Stream can be attributed to the presence of larvae of the shredder Triplectides obsoleta which were found in small numbers. Densities of invertebrates (predominantly P. antipodarum) per gram of leaf (dry weight) peaked in bags which had been immersed for 41 days (Cashmere Stream) and 58 days (Avon River). At these times the amount of initial leaf biomass left was 45 and 38% respectively. Results of this and overseas studies on willow leaf breakdown suggest that leaves of Salix spp. are most palatable to stream invertebrates when 35-45% of initial leaf biomass remains.

Keywords Salix babylonica L.; willow; Cashmere Stream; Avon River; decomposition; decay coefficient; microbial conditioning; invertebrate feeding Received 3 January 1986; accepted 14 April 1986

New Zealand Journal of Marine and Freshwater Research, 1986, Vol. 20: 575-582 Received 3 January 1986; accepted 14 April 1986

PDF file of entire paper: medium quality (1070K); (scanned from paper original: notes about this process)

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