Rg. Young et al., EFFECTS OF AGRICULTURAL-DEVELOPMENT ON PROCESSING OF TUSSOCK LEAF-LITTER IN HIGH COUNTRY NEW-ZEALAND STREAMS, Freshwater Biology, 32(2), 1994, pp. 413-427
1. We compare the rates and mechanisms of processing of tussock (Chion
ochloa spp.) leaf litter in six New Zealand streams draining grassland
catchments that contrast in the extent to which they have been develo
ped for pasture. 2. Rates of processing, measured as rate of weight lo
ss of leaf packs and rate of leaf softening, were at the slow end of t
he spectrum for vascular plant processing. Processing was faster at de
veloped sites, mediated mainly through the influence of oxidized nitro
gen concentration on microbial activity. 3. Few invertebrate shredders
colonized leaf packs and it is unlikely that invertebrates had an app
reciable effect on leaf processing in our study streams, which do not
effectively retain leaf litter. Very small headwater tributaries appea
r to retain leaf litter and possess a more abundant shredder community
. 4. Measures of leaf processing in our six streams were significantly
correlated with Petersen's (1992) RCE score of stream condition. We d
iscuss the potential for using rate of leaf litter processing as a met
hod of bioassessment. 5. Even the most degraded stream in our study is
classed as 'good' using the RCE inventory system. Human impact in the
Taieri River is relatively small compared with the degradation observ
ed in some parts of the world.