INFLUENCE OF SUBSTRATE TYPE AND PHYSICOCHEMICAL CONDITIONS ON MACROINVERTEBRATE FAUNAS AND BIOTIC INDEXES OF SOME LOWLAND WAIKATO, NEW-ZEALAND, STREAMS
Kj. Collier et al., INFLUENCE OF SUBSTRATE TYPE AND PHYSICOCHEMICAL CONDITIONS ON MACROINVERTEBRATE FAUNAS AND BIOTIC INDEXES OF SOME LOWLAND WAIKATO, NEW-ZEALAND, STREAMS, New Zealand Journal of Marine and Freshwater Research, 32(1), 1998, pp. 1-19
Lowland streams in agricultural areas are often considered degraded be
cause of high turbidity, high biomass of adventive macrophytes, and a
predominance of fine bed substrates. Invertebrate faunas in these stre
ams are being increasingly used in biomonitoring, and an understanding
of factors affecting their distribution and abundance is important fo
r interpreting the results of these studies. We measured physicochemic
al parameters and sampled macroinvertebrate faunas on inorganic substr
ates, wood, and macrophytes to investigate factors influencing inverte
brate distribution and abundance in Waikato, New Zealand, lowland stre
ams, and to evaluate six biotic indices and a rapid bioassessment prot
ocol for lowland stream environments. At most sites, invertebrate faun
as were dominated numerically on all substrate types by the hydrobiid
snail Potamopyrgus antipodarum (Gray), the eusirid amphipod Paracallio
pe, and Diptera (mostly the chironomid Neonella forsythii Boothroyd an
d the blackfly Austrosimulium spp.). Stepwise regression analyses indi
cated that densities of some common taxa on inorganic substrates (0.1
m(-2)) and macrophytes (gl wet weight) were correlated with combinatio
ns of reach water depth, percentage of bed covered by macrophytes or s
and/silt, and water quality factors including conductivity, water temp
erature, and measures of dissolved oxygen (DO) concentration and magni
tude of diel fluctuation. These factors and also the amount of wood pr
esent explained 36-87% of the variation in several of the biotic indic
es examined on different substrate types. Some taxonomic (no. of taxa)
and compositional (% dominant taxon) indices appeared sensitive to me
asured habitat conditions, and this may affect their utility for detec
ting water quality impacts in lowland streams. Percent Ephemeroptera,
Plecoptera, and Tricoptera (EPT), and the Macroinvertebrate Community
Index (MCI) and its quantitative analogue (QMCI) reflected factors tho
ught to be more associated with direct and indirect effects of riparia
n and catchment land use on water quality (DO, conductivity, temperatu
re, macrophyte cover). Comparison of indices derived from intensive an
d rapid bioassessment sampling yielded significant regressions with sl
opes that were not significantly different to 1 for % EPT and MCI. The
se indices appear to be particularly useful for rapid bioassessment of
lowland stream environments.