NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- This thesis examines phytoplankton dynamics and the influences of
environmental variables on them in the Hunter River, New South Wales. The
environmental variables of flow (discharge), water velocity, water temperature,
turbidity, electrical conductivity (conductivity), pH and nutrients (ammonia,
oxidized nitrogen, reactive phosphorus, reactive silica, total nitrogen and total
phosphorus) were examined. Dominance in phytoplankton and periodic
succession and the application of the Intermediate Disturbance Hypothesis to
the Hunter River were also investigated.
The environmental variables of conductivity, turbidity and nutrients appear to be
particularly influenced by flow at several sites, with increased flow causing
increases in turbidity and nutrient levels. Baseline nutrients are, however, still
high with all nutrients exceeding the ANZECC guideline concentrations for
natural waters. These concentrations are also considered high enough to give
the river a trophic status of eutrophic, with inputs into the system from local land
uses of farming, irrigation, mining and town sewage treatment plants.
The phytoplankton communities are dominated by diatoms, with subdominant
populations of Chlorophyceae with periodic succession showing transitions from
true r-strategists (e.g. Cyclotella meneghiniana and Oocystis spp.) to true K-strategists
(e.g. Ceratium spp. and Closterium spp.) through a dominance of
intermediate strategists of the pennate diatoms.
While the Hunter River was dominated throughout by Fragilaria spp., Navicula
spp. and Oocystis spp., the river is divided distinctly into two sections, an upper
and lower section which are characterized by different successional dominance,
notably by large populations of Cyclotella meneghiniana and Melosira varians in
the lower section and dominant populations of Closterium spp. and Ceratium
spp. in the upper section.
The trophic status of the Hunter River shows phytoplankton similarities to
mesotrophic and eutrophic lakes. Due to Fragilaria spp., Navicula spp. and
Oocystis spp. dominating, and the lack of cyanobacterial populations, the
Hunter River appears to be predominantly bordering on eutrophic, with changes
back to mesotrophic during the summer periods in the lower Hunter, when
Cyclotella meneghiniana becomes dominant.
Flow appears to determine the overall residence time of phytoplankton in the
river and has an overall influencing effect, as it is highly correlated with many
other influences such as turbidity, conductivity and nutrients. Water temperature
in the Hunter River appeared to influence seasonality of the phytoplankton
communities. Other than this no individual influence on phytoplankton species
The lack of stratification and low water velocities resulted in only small
populations of cyanobacteria in the upper Hunter River sites, and rarely
observed populations in the lower Hunter River sites. The average water
velocity ranged from 0.599 m/s (upper site) to 0.031 m/s (lowest site). Liddell
Weir however experienced an average velocity of 0.0307 m/s and, under
favourable environmental conditions, increased growth of cyanobacteria could
be possible if this velocity was maintained for extended periods.
Turbidity in the Hunter showed peaks during major flow events, and increases
in the populations of the diatoms Fragilaria spp. and Navicula spp. showed that
benthic/periphytic assemblages contributed to the phytoplankton within these
highly turbid periods.
Conductivity and pH overall showed no influence individually on phytoplankton,
but together with flow and nutrients, conductivity has an influence with a change
in dominance from Chlorophyceae to diatoms shown at Glenbawn Weir.
Nutrients in the Hunter River appear to be non-limiting to phytoplankton growth.
From the observations of the Hunter River, the Intermediate Disturbance
Hypothesis tends to apply to the phytoplankton and environmental conditions.
• Generally disturbances of intermediate intensities tended to promote
higher diversities during, or after, the disturbance event.
• In periods of equilibrium and during disturbances of high and low
intensities, phytoplankton diversity generally decreases.