EFFECT OF RIPARIAN LAND-USE ON CONTRIBUTIONS OF TERRESTRIAL INVERTEBRATES TO STREAMS

Since terrestrial invertebrates are often consumed by stream fishes, l and-use practices that influence the input of terrestrial invertebrate s to streams are predicted to have consequences for fish production. W e studied the effect of riparian land-use regime on terrestrial invert ebrate inputs by estimating the biomass, abundance and taxonomic richn ess of terrestrial invertebrate drift from 15 streams draining catchme nts with three different riparian land-use regimes and vegetation type s: intensive grazing - exotic pasture grasses (4 streams), extensive g razing - native tussock grasses (6 streams), reserve - native forest ( 5 streams). Terrestrial invertebrate drift was sampled from replicated stream reaches enclosed by two 1 mm mesh drift nets that spanned the entire channel. The mean biomass of terrestrial invertebrates that ent ered tussock grassland (12 mg ash-free dry mass m(-2) d(-1)) and fores t streams (6 mg AFDM m(-2) d(-1)) was not significantly different (p > 0.05). However, biomass estimated for tussock grassland and forest st reams was significantly higher than biomass that entered pasture strea ms (1 mg AFDM m(-2) d(-1)). Mean abundance and richness of drifting te rrestrial invertebrates was not significantly different among land-use types. Winged insects contributed more biomass than wingless inverteb rates to both pasture and tussock grassland streams. Winged and wingle ss invertebrates contributed equally to biomass entering forest stream s. Land use was a useful variable explaining landscape-level patterns of terrestrial invertebrate input for New Zealand streams. Evidence fr om this study suggests that riparian land-use regime will have importa nt influences on the availability of terrestrial invertebrates to stre am fishes.