The effects of carp, Cyprinus carpio L., on water quality and functioning of aquatic systems were investigated in two experiments in ponds (-90 cm deep) outdoors at Griffith, New South Wales. The experiments represented contrasting conditions of high and low impact, defined by stocking density and food availability, with stocking densities chosen to be above and below 450 kg ha-', the stocking density suggested as a critical threshold for damage. Under high impact conditions, carp had a significant effect on water quality, habitat structure and pond physical characteristics. Turbidity increased from approximately 7 NTU to 26 and 73 NTU by Day 4, there was a complete loss of two out of five plant species tested (Charafibrosa and Vallisneria sp.) by Day 6, and surface water temperature in ponds with carp was significantly greater by Day 7. Plant loss was attributed to uprooting rather than herbivory, as sometimes reported. Under low impact conditions the uprooting rate of Vallisneria was reduced to a third. Contrary to the results of previous studies, there was no evidence of increased nutrients or greater algal biomass in ponds with carp, but this may have been because the sediments were relatively low in phosphorus. A crude nutrient budget based on water concentrations and tissue analysis showed substantial growth of carp in 20 days that could be accounted for only by considering either sediments or terrestrial inputs (ponds were not covered) as an important food source.

Sixteen artificial billabongs on the floodplain of the River Murray, New South Wales, were surveyed over a 14-month period to observe the effect of different hydrological regimes on the development of aquatic macrophyte communities. The billabongs were initially planted with Vallisneria sp. and Myriophyllum papillosum Orch. in November 1994, then flooded. The 16 billabongs were divided into four treatments: summer flood, spring flood, permanent inundation, and a control treatment that was initially flooded and then allowed to vary in depth with rainfall and evaporation. The plant communities were surveyed on six occasions between April 1995 and June 1996, and percentage cover was estimated on each sampling occasion. Fourteen aquatic macrophyte taxa were recorded over the study period. Billabongs in the permanent and summer treatments exhibited less plant diversity than did billabongs in the control or spring treatments. Terrestrial plants germinated on the exposed areas in both spring and control treatments, but not in the other treatments.

Profile conditions were examined in both small experimental and pilot scale sub-surface flow wetlands. The study systems differed in their hydraulic design. The experimental systems had a vertical up-flow design whereas the pilot system was a horizontal flow trench design. Both systems were found to have significant physical, chemical and biological gradients within the sub-surface profile. System age and plant root density appear to be important factors in determining profile differentiation within the experimental systems. Root densities were found to be partitioned between the upper and lower layers on a 70%/30% split, respectively. However, in the experimental systems as the systems aged and root densities increased beyond 112-251 g.m−2 chemical water quality differentiation in the profile disappeared. Pilot scale systems were found to have physical gradients within the profile as evidenced by hydraulic short-circuiting. Vertical root density distribution is proposed as a major cause of this condition in horizontal flow systems.

Investigating habitat use and preferences of a threatened species can be challenging, especially if wild populations have decreased to such low numbers that they occupy only fractions of their former natural range. Hence, assessing habitat suitability of a potential release site for a threatened species before a reintroduction attempt can be difficult because frequently no comparable baseline data are available. In these instances, post-release monitoring data can inform about habitat use and preferences of a reintroduced species. Here, we use monitoring data of an endangered endemic island bird, the Chatham Island black robin Petroica traversi, to investigate habitat preferences and the temporal change in distribution patterns across 26 years following a reintroduction. We show that densities and distribution of black robin pairs at the reintroduction site have changed significantly over the years. Spatial distribution of pairs is clustered, and this clustering has intensified as the population increased. We used the maximum entropy method MaxEnt to model habitat suitability on the island, showing that black robins clearly prefer forested areas inland that are within 70 m to the forest edge at lower elevations (<40 m a.s.l.) and on slopes that have a N-NE aspect. The model also identified one area on the island that comprises suitable habitat, but is currently uninhabited. Applying maximum observed densities to the available area of each suitability class, carrying capacity is estimated as 170 nesting pairs across the island, highlighting the need to find further appropriate habitat urgently. Overall, these topographical and habitat preferences considerably restrict this species' potential distribution, a constraint that has serious conservation implications for future population growth of current populations and (re)introductions to new locations. This study demonstrates that post-release data can reveal relevant limitations to habitat use of highly threatened species.

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