A. Haapala et T. Muotka, SEASONAL DYNAMICS OF DETRITUS AND ASSOCIATED MACROINVERTEBRATES IN A CHANNELIZED BOREAL STREAM, Archiv fur Hydrobiologie, 142(2), 1998, pp. 171-189
This study documents various components of detritus dynamics in a chan
nelized third order stream in Central Finland. Total annual litterfall
entering the stream was 310 g AFDM m(-2). Leaf fall, which comprised
86.7% of total input, exhibited a distinct seasonal peak in September-
October, with a maximum daily input rate of 13 g m(-2). The contributi
on of woody detritus to total input was only 5%. The mean annual stand
ing stocks of coarse (23.0 g AFDM m(-2)) and fine (1.76 g AFDM m(-2))
benthic organic matter are among the lowest reported for woodland stre
ams. Macroinvertebrate standing stock peaked in February (1205 mg DW m
(-2)), and the annual minimum (276 mg DW m(-2)) occurred in August. Sh
redding invertebrates did not reach their maximum biomass until March,
although the availability of benthic leaf litter peaked already in Oc
tober. In contrast, FPOM-collectors and predatory invertebrates tracke
d closely the seasonal availability of their food resources. Leaf rele
ase experiments showed that the stream had a low retention capacity: 1
3-40% of 500 artificial leaves were retained within a 50 m experimenta
l section at discharges ranging from 0.46 to 1.52 m(3) s(-1). The stre
am is poorly retentive because it lacks effective retention devices (e
.g. large woody debris). Due to the low retentivity of the stream bed
and fast decomposition rates of the primary litter sources (birch and
alder leaves), shredders probably face a severe springtime food limita
tion in this stream. We suggest that adding retentive devices to strea
m bed is a viable management strategy for restoration of channelized w
oodland streams.