Floodplains and their associated wetlands are important features of semiarid and arid landscapes, providing habitat and refugia for native species as well as contributing to human needs for freshwater. Globally, floodplain habitats are some of the most modified ecological communities because of water resource development and land-use changes. However, the hydrological changes that have occurred in highly variable semiarid and arid systems are rarely quantified in a way that helps us understand the consequences for different floodplain habitat types. This study investigated changes in floodplain-river connectivity that have occurred because of water resource development on four floodplain habitat types in the Lachlan River Catchment, Australia: (a) temporary floodplain lakes, (b) intermittent river red gum (Eucalyptus camaldulensis) swamps, (c) intermittent black box (Eucalyptus largiflorens) swamps, and (d) terminal wetlands (wetlands along distributary creeks). Changes to floodplain-river connectivity characteristics were calculated using their commence to fill thresholds and flow scenarios derived from a river hydrology model, enabling comparison of long-term data sets (120 years) encompassing a range of climate conditions. Connection regime metrics have changed significantly in all floodplain habitats except intermittent black box swamps. Temporary floodplain lakes have experienced the greatest reduction in number of connection events (60% reduction), followed by intermittent river red gum swamps (55% reduction). Intermittent black box swamps and terminal wetlands have experienced the least change in number of connection events (35% reduction). The nature of the change in connection suggests a change in vegetation communities will occur in response to long-term hydrological change.

The distribution of plants on flood plains depends on the hydrological regime on the flood plain and the hydrological requirements of the plants. The aims of the present study were to: (1) determine the relationships between germination of tangled lignum (Duma florulenta) and nitre goosefoot (Chenopodium nitrariaceum) and hydrological regime; (2) determine the buoyancy of the seeds of the two species, and hence the ability of the seeds to disperse by water; and (3) inform environmental flow requirements for the two species. Seeds of tangled lignum germinated best on soaked soil and on soil inundated for 20 days. Seeds of nitre goosefoot germinated best on soil inundated for 5 days and on soaked soil. The majority of tangled lignum seeds floated for at least 7 days. The majority of nitre goosefoot seeds sank within 7 days. The results of the present study are consistent with the observed distributions of the species on flood plains. Tangled lignum requires ~20 days of flooding and wet soils following flood recession for optimal germination. Nitre goosefoot requires a few days of flooding and wet soils following flood recession for optimal germination. The inundation requirements for germination of tangled lignum and nitre goosefoot should be considered in the management of environmental flows.

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Environmental flows are increasingly being used to restore degraded floodplain vegetation; however, the type of flow regime required for recovery to healthy condition can vary depending on the extent of degradation before restoration. Regulation of the River Murray has affected floodplain ecosystems at many locations, including Bottle Bend Reserve, in south-western New South Wales, Australia. Within Bottle Bend Reserve, tangled lignum (Duma florulenta) dominates sections of the higher floodplain elevations. Lignum is an important and widely distributed Australian shrub occurring in arid and semiarid river systems within the Murray–Darling and Lake Eyre Basins. In an effort to restore floodplain vegetation, three environmental flows were delivered to Bottle Bend Reserve between 2013 and 2016. Flows varied in magnitude, leading to a mosaic of different regimes across the area. Condition surveys were undertaken over 1 year, namely, before, during and after delivery of the September 2016 environmental flow. This study found that the greatest response occurred in lignum plants with no recent environmental water, although lignum plants with one or two recent environmental flows still responded relative to the control. Lignum was in a better condition at sites that received more environmental flows, demonstrating the value of increased frequency of flows in recovering vegetation health.