Temperature and dissolved oxygen have
often been cited as crucial parameters limiting
the survival of aquatic invertebrates in inter-
mittent streams when flow reduces or stops
during summer (Boulton & Lake 1992b; Wil-
liams 2006). The spot measurements in
our study did not capture the critical daily
and seasonal periods of minimum oxygen and
maximum temperature [e.g. small, unshaded
streams in similar climates may experience
diurnal temperature fluctuations of up to
108C (Quinn & Wright-Stow 2008) and dis-
solved oxygen fluctuations of up to 6 mg/l
(Wilcock et al. 1998)]. However, they did
indicate that in summer, oxygen levels at
several sites reached critically low levels (e.g.
B1 mg/l) that very likely reduce the survival of
sensitive insects (Nebeker 1972). Other studies
(e.g. Quinn & Wright-Stow 2008) show that
unshaded headwater streams in similar climates
in New Zealand may reach 308C during mid-
summer, exceeding the temperature tolerances
of many insect taxa (Quinn et al. 1994). Thus
the lower dissolved oxygen and higher tem-
peratures in P than NF sites are likely to be
partly responsible for differences in the inverte-
brate communities among land use types.