Adequate protection of groundwater dependent vegetation (GDV) at the landscape scale (>10(4)km(2)) is often hampered as their extent is poorly mapped. Remote sensing data sets have previously been used to delineate GDV by analysing both actual and changes, in green biomass over space and time. The rationale behind such approaches is based on the phenological characteristics of GDV, which often retain greater mean green biomass during dry periods, in comparison to vegetation with access to soil moisture only. However, such methods are hampered by inadequate knowledge about how average annual precipitation, seasonality, and differing water regimes of vegetation communities within a landscape influence green biomass. Therefore, we aimed to test for amount of foliage projective cover (FPC) and variation in FPC as indicators of GDV presence. We assessed differences in the FPC of GDV at 3 sites across a 1,500mm(-1)year(-1) precipitation gradient, ranging from arid inland to humid coastal environments in Southern Queensland, Australia. Overall, we found that average annual precipitation had the largest influence on predicting FPC followed by seasonality. During winter in the semi-arid and humid environments (season with least precipitation), FPC for non-GDV was higher than subsurface GDV. For our study area, GDV delineation on the basis of higher green biomass than surrounding vegetation was effective when average annual precipitation was less than similar to 600mm(-1)year(-1).

Tropical floodplains are one of the most productive ecosystems on earth. Studies on floodplain productivity have primarily focused on trees and macrophytes, rather than algae, due to their greater biomass. However, epiphyton—algae and bacteria attached to the submerged portion of aquatic macrophytes—is a major source of energy in many tropical floodplains. Epiphyton productivity rates are unknown for most tropical floodplain wetlands, and spatial variability is not well understood. In this study, we measured primary productivity of epiphyton in Kakadu National Park in northern Australia. We estimated the relative contribution of epiphyton to aquatic production (epiphyton, + phytoplankton + macrophytes). We sampled sites dominated by different macrophyte structural types: vertical emerging grasses, horizontal emerging grasses, submerged macrophytes, and macrophytes with floating leaves. Epiphyton productivity was highly influenced by the structural type of the macrophyte. Highest potential productivity per weight was measured from epiphyton growing on macrophytes with floating leaves and horizontal grasses (1.52 ± 0.53 and 1.82 ± 0.61 mgC/dw g epiphyton/h, respectively) and lowest in submerged macrophytes and vertical grasses (0.57 ± 0.26 and 0.66 ± 0.47 mgC/dw g epiphyton/h, respectively). When considering the areal biomass of the macrophyte and the amount of epiphyton attached, epiphyton on horizontal grasses and submerged macrophytes had productivity values approximately ten times higher (45–219 mgC/m 2 /d) compared to those on vertical grasses and macrophytes with floating leaves (2–18 mgC/m 2 /d). Epiphyton contributed between 2 to 13 percent to the aquatic production of these tropical floodplain wetlands.

Food web subsidies from external sources (“allochthony”) can support rich biological diversity and high secondary and tertiary production in aquatic systems, even those with low rates of primary production. However, animals vary in their degree of dependence on these subsidies. We examined dietary sources for aquatic animals restricted to refugial habitats (waterholes) during the dry season in Australia’s wet–dry tropics, and show that allochthony is strongly size dependent. While small-bodied fishes and invertebrates derived a large proportion of their diet from autochthonous sources within the waterhole (phytoplankton, periphyton, or macrophytes), larger animals, including predatory fishes and crocodiles, demonstrated allochthony from seasonally inundated floodplains, coastal zones or the surrounding savanna. Autochthony declined roughly 10% for each order of magnitude increase in body size. The largest animals in the food web, estuarine crocodiles (Crocodylus porosus), derived ~80% of their diet from allochthonous sources. Allochthony enables crocodiles and large predatory fish to achieve high biomass, countering empirically derived expectations for negative density vs. body size relationships. These results highlight the strong degree of connectivity that exists between rivers and their floodplains in systems largely unaffected by river regulation or dams and levees, and how large iconic predators could be disproportionately affected by these human activities.

Wetlands have been extensively modified by human activities worldwide. We provide a global-scale portrait of the threats and protection status of the world's inland wetlands by combining a global map of inundation extent derived from satellite images with data on threats from human influence and on protected areas. Currently, seasonal inland wetlands represent approximately 6% of the world's land surface, and about 89% of these are unprotected (as defined by protected areas IUCN I-VI and Ramsar sites). Wetland protection ranges from 20% in Central and 18% in South America to only 8% in Asia. Particularly high human influence was found in Asia, which contains the largest wetland area of the world. High human influence on wetlands even within protected areas underscores the urgent need for more effective conservation measures. The information provided here is important for wetland conservation planning and reveals that the current paradigm of wetland protection may be inadequate.

Restoration of riparian vegetation may reduce nutrient and sediment contamination of waterways while potentially enhancing stream channel complexity. Accordingly, the present study used a paired-site approach to investigate the effects of mature regrowth riparian vegetation on river channel morphology and soil nutrients (i.e. nitrogen and phosphorus), comparing four sites of degraded (pasture) and reforested reaches. A revised rapid assessment of riparian condition (RARC) was used to validate the site pairings. Riparian soil nutrient and elemental geochemistry were compared between paired sites, along with two parameters of channel width complexity and two for channel slope complexity. The RARC analysis confirmed the validity of the paired site design. The elemental geochemistry results indicated that underlying geology may affect the paired site analyses. Reaches with mature regrowth vegetation had greater channel width complexity but no difference in their riverbed slope complexity. In addition, degraded reaches had higher soil nutrient (i.e. nitrogen and phosphorus) concentrations, potentially indicative of the greater nutrient retention of pasture grass sites compared with mature regrowth forested reaches with less ground cover. Overall, the present study indicates that restoring mature regrowth riparian vegetation may increase river channel width complexity, although it may require canopy management to optimise the nutrient retention potential necessary to maximise the effect of riparian restoration strategies on freshwater environments.

•This study explores relationships between spatial complexity and form of aquatic macrophytes, and epiphytic algal on a tropical floodplain.•Our study indicates greater algae biomass on macrophytes with high structural complexity.•Our results also suggest shape and alignment of macrophytes, rather than surface area or biomass, result in greater epiphytic attachment.•Water quality conditions within patches is influenced by the structure and density of the dominant macrophyte type.•A layer of submerged macrophyte below the clear water surface, function in a similar way to the littoral zone to boosts epiphyte algal production.

Supratidal mudflats are a poorly understood habitat adjacent to coastal areas and are under pressure from human development and climate change. These habitats are only inundated infrequently but may be important contributors to coastal productivity. This study determined nutrient release and primary productivity (PP) on a large, pristine supratidal mudflat in the wet-dry tropics of Australia. Results of experimental studies on nutrient release and PP upon freshwater inundation were incorporated into a simple model of supratidal mudflat inundation based on remote sensing data and long-term river height data. The model was used to hind-cast potential annual primary production and nutrient release for a period capturing high and low inundation years. Our experimental studies measured a rapid release of nitrate, ammonium and phosphate in the first 2 d after inundation. Some days later there was measurable algal growth. Incorporating this data into the model showed that the main driver for the whole-system PP rates was the areal extent of inundation, rather than the duration of inundation, provided that inundation lasted longer than the minimum period for primary production to occur. The same was true for nutrient release although a shorter period of inundation was needed for release to occur. Future changes in flow and associated flooding, as a result of climate change and/or water resource development, could therefore have significant effects on productivity in these coastal systems.

Isotope studies of freshwater aquatic habitats have shown that epiphytic algae in the form of periphyton provides much of the source material for the biomass of secondary aquatic producers. Consequently, methods that can quantify the seasonal abundance of periphyton are important spatial inputs for wetland management and conservation planning processes for tropical floodplains. In this study, estimation of the seasonal spatial variability in floodplain macrophyte and periphyton abundance was made for the floodplains of the Kakadu region in northern Australia. Statistical modelling, using remotely sensed information, was applied to predict the seasonal distributions of macrophyte structural types, which were then combined with the field measurements of periphyton biomass to produce seasonal distributions of floodplain periphyton biomass per unit area. The seasonal spatial distribution of periphyton was strongly influenced by the seasonal variation in macrophyte abundance. Vertical emergent macrophytes (mainly aquatic grasses), covering 70% of the floodplain in May, had the lowest periphyton abundance. Submerged macrophytes, covering 10–15% of the floodplains, had the greatest periphyton abundance. The submerged macrophytes occupied open water areas, mainly in the deeper backswamp areas on the edges of the floodplains, and these areas maintained high periphyton abundance into the dry season. This study provides explicit spatial representation of the seasonal dynamics of tropical floodplain macrophyte and periphyton abundance and presents an approach that can be applied to map ‘hotspots’ of floodplain periphyton abundance. Copyright © 2016 John Wiley & Sons, Ltd.

Aquatic ecosystems are critical to the long-term viability and vibrancy of communities and economies across northern Australia. In a region that supports significant cultural and ecological water values, partnerships between Indigenous and non-Indigenous stakeholders can benefit aquatic ecosystem management. We present, as a case study from the Kimberley region of Western Australia, a collaborative research program that successfully documented Indigenous and Western Scientific knowledge of remote wetlands, using a variety of field-based activities, questionnaires, interviews and workshops. The sharing of knowledge between Indigenous and non-Indigenous research partners facilitated a comprehensive understanding of ecosystem values, threats, processes, management priorities and aspirations. These formed the basis of a management plan and monitoring tools, designed to build the capacity of an Indigenous ranger group to engage in research, monitoring and management of wetlands. The project provides a useful example of the benefits of collaborations in the context of remote-area management where local communities are responsible for environmental management and monitoring, such as is the case in northern Australia and presumably other areas of the world.

Biotic communities are shaped by adaptations from generations of exposure to selective pressures by recurrent and often infrequent events. In large rivers, floods can act as significant agents of change, causing considerable physical and biotic disturbance while often enhancing productivity and diversity. We show that the relative balance between these seemingly divergent outcomes can be explained by the rhythmicity, or predictability of the timing and magnitude, of flood events. By analyzing biological data for large rivers that span a gradient of rhythmicity in the Neotropics and tropical Australia, we find that systems with rhythmic annual floods have higher-fish species richness, more stable avian populations, and elevated rates of riparian forest production compared with those with arrhythmic flood pulses. Intensification of the hydrological cycle driven by climate change, coupled with reductions in runoff due to water extractions for human use and altered discharge from impoundments, is expected to alter the hydrologic rhythmicity of floodplain rivers with significant consequences for both biodiversity and productivity.

The Alligator Rivers region is located in the wet–dry tropics along the coastal zone of northern Australia and contains Kakadu National Park, which is recognized under the Ramsar Convention on Wetlands and is a World Heritage listed site. Multiple anthropogenic stressors increasingly affect the floodplains of this region, and baseline information on floodplain inundation dynamics is necessary to manage these threats and develop adaption strategies for sea level rise. This study uses classification tree modeling to combine microwave (ALOS L-band Synthetic Aperture Radar) and optical (Landsat Thematic Mapper, TM 5) satellite data with field-sampled aquatic vegetation and depth logger data to predict the seasonal and inter-annual dynamics of aquatic plant cover and extent of inundation in the region. The USGS Landsat TM 5 image archive was sampled between 1985 and 2011 using three seasonal samples per year to create a comprehensive long-term time series of seasonal and inter-annual floodplain inundation extents. Classification accuracy for the inundation mapping was estimated at 86% based on seasonal depth logger data. The mean extent of inundation at the end of the wet season (March/April) was 1784km2 (range 2283–1309km2), receding on average to approximately 25% of its extent by August/September. Seasonal inundation patterns exhibit an exponential recession of inundation into ‘backswamp’ areas on the fringes of the floodplains with hydro-periods on the order of 5months. The findings of this work significantly improve our understanding of dynamics in this environmentally and culturally unique area and provide a basis for application in other seasonally flooded environments.

ABSTRACT The rate of erosion of hillside gullies depends both on gully flow characteristics and the resistance offered by the gully soil profile to erosion. This paper describes a method for quantifying a physically‐based resistance measure, illustrated by application to a gully feeding sediment into the Bremer River, southeast Queensland, Australia. The dynamics of discharge down the gully during runoff events is the driver of erosion, but this was unknown. A new method is described whereby this unmeasured flow can be estimated using data on rainfall rate and river gauge monitoring. The data collected on the gully was the increase in dimensions and volume (and so soil loss) over a two year period. This information was obtained from a digital elevation model (DEM) of the catchment, derived from Light Detection and Ranging (LiDAR) observations made at either end of the two year period. The soil profile resistance characteristic evaluated is the energy required to erode a unit mass of soil from the gully walls, a physically‐defined parameter, J , present in flow‐driven erosion theory, which was adapted and applied to predict soil loss from the Bremer River gully. The value of J was evaluated by equating predicted to measured gully soil loss over the two year period using two alternative descriptions of gully cross‐section. Firstly a realistic gully shape description was used, made possible by LiDAR data, yielding J = 405.5 J/kg. Secondly, in order to allow use of more widely‐available aerial photography for such studies, the simplifying assumption of a semi‐circular gully shape was made, yielding J = 455 J/kg. Allowing a ±30% error in estimated effective runoff rate for this ungauged gully, the estimated J value would have an uncertainty of +1%/−7% using the actual gully geometry. The assumptions made in estimating J are discussed, and possible applications of this information listed. Copyright © 2014 John Wiley & Sons, Ltd.

ABSTRACTFloodplain wetlands in the wet–dry tropics are under increasing pressure from water resource development, and there is a need for methods to assess the biophysical dynamics of these extensive and often remote ecosystems. This study assessed the capacity of optical remote sensing methods to monitor the seasonal dynamics of inundation, turbidity, and aquatic vegetation cover for a northern Australian savanna catchment. MODIS data were used to map seasonal flood inundation patterns, and Landsat 5 TM data were used to map dry‐season waterbody dynamics. A network of water‐depth loggers and temperature sensors provided ground observations of surface inundation dynamics, and was used to validate the inundation mapping. Post‐flood waterbody surface area declined by 89% over the dry season, with 70% of the decline occurring for Palustrine (floodplain) waterbodies. All aquatic systems became increasingly disconnected as the dry season progressed. Statistical relationships were developed between seasonal measurements of turbidity, aquatic vegetation cover, and Landsat spectral data. Catchment wide predictions showed that turbidity increased and macrophyte cover decreased for the Palustrine and Lacustrine (lake) systems, while the Riverine systems became less turbid over the dry season. These results show that, for open savanna landscapes where cloud cover does not limit waterbody detection, optical remote sensing methods can be effectively applied to assess seasonal patterns of inundation and accompanying biophysical dynamics. This provides an effective tool to evaluate the impact of river flow regime changes from water resource use or climate change in these regions. Copyright © 2012 John Wiley & Sons, Ltd.

In highly seasonal tropical environments, temporal changes in habitat and resources are a significant determinant of the spatial distribution of species. This study disentangles the effects of spatial and mid to long-term temporal heterogeneity in habitat on the diversity and abundance of savanna birds by testing four competing conceptual models of varying complexity. Focussing on sites in northeast Australia over a 20 year time period, we used ground cover and foliage projected cover surfaces derived from a time series of Landsat Thematic Mapper imagery, rainfall data and site-level vegetation surveys to derive measures of habitat structure at local (1-100 ha) and landscape (100-1000s ha) scales. We used generalised linear models and an information theoretic approach to test the independent effects of spatial and temporal influences on savanna bird diversity and the abundance of eight species with different life-history behaviours. Of four competing models defining influences on assemblages of savanna birds, the most parsimonious included temporal and spatial variability in vegetation cover and site-scale vegetation structure, suggesting savanna bird species respond to spatial and temporal habitat heterogeneity at both the broader landscape scale and at the fine-scale. The relative weight, strength and direction of the explanatory variables changed with each of the eight species, reflecting their different ecology and behavioural traits. This study demonstrates that variations in the spatial pattern of savanna vegetation over periods of 10 to 20 years at the local and landscape scale strongly affect bird diversity and abundance. Thus, it is essential to monitor and manage both spatial and temporal variability in avian habitat to achieve long-term biodiversity outcomes.

Analysis of aerial photographs shows that gully erosion in three catchments in south-east Queensland, Australia, was initiated by post-European settlement. Analysis of historical rainfall and runoff showed that for two of the catchments, gully initiation occurred during wet decadal periods. Historical descriptions of the settlement of south-east Queensland and Moreton Bay detail significant changes in landuse and clearing of vegetation for grazing of domestic animals and urban development since 1842. Historical gully erosion rates varied from 14 to 1826m2yr−1 and erosion rates are positively correlated with catchment area multiplied by slope. Analysis of gully erosion rates showed a linear increase in planemetric area over time. Together, these data show gully initiation in the three catchments is associated with post-European settlement land use practices and above average rainfall and runoff. Initiation of gullying across the region is similar to the previous studies in south-east Australia and highlights the sensitivity of the landscape to vegetation clearing and alternating periods of above average rainfall and drought.

Hydrogeomorphic processes influencing alluvial gully erosion were evaluated at multiple spatial and temporal scales across the Mitchell River fluvial megafan in tropical Queensland, Australia. Longitudinal changes in floodplain inundation were quantified using river gauge data, local stage recorders and HEC‐RAS modelling based on LiDAR topographic data. Intra‐ and interannual gully scarp retreat rates were measured using daily time‐lapse photographs and annual GPS surveys. Erosion was analysed in response to different water sources and associated erosion processes across the floodplain perirheic zone, including direct rainfall, infiltration‐excess runoff, soil‐water seepage, river backwater and overbank flood inundation. The frequency of river flood inundation of alluvial gullies changed longitudinally according to river incision and confinement. Near the top of the megafan, flood water was contained within the macrochannel up to the 100‐year recurrence interval, but river backwater still partially inundated adjacent gullies eroding into Pleistocene alluvium. In downstream Holocene floodplains, inundation of alluvial gullies occurred beyond the 2‐ to 5‐year recurrence interval and contributed significantly to total annual erosion. However, most gully scarp retreat at all sites was driven by direct rainfall and infiltration‐excess runoff, with the 24‐h rainfall total being the most predictive variable. The remaining variability can be explained by seasonal vegetative conditions, complex cycles of soil wetting and drying, tension crack development, near‐surface pore‐water pressure, soil block undermining from spalling and overland flow, and soil property heterogeneity. Implications for grazing management impacts on soil surface and perennial grass conditions include effects on direct rainfall erosion, water infiltration, runoff volume, water concentration along tracks, and the resistance of highly dispersible soils to gully initiation or propagation under intense tropical rainfall. Copyright © 2012 John Wiley & Sons, Ltd.

1. Northern Australia is characterised by a tropical wet-dry climate that regulates the distinctive character of river flow regimes across the region. There is marked hydrological seasonality, with most flow occurring over only a few months of the year during the wet season. Flow is also characterised by high variability between years, and in the degree of flow cessation, or intermittency, over the dry season.2. At present, the relatively low human population density and demand for water in the region means that most rivers have largely unmodified flow regimes. These rivers therefore provide a good opportunity to understand the role of natural flow variability in river ecosystem structure and processes.3. This review describes the major flow regime classes characterising northern Australian rivers, from perennial to seasonally intermittent to extremely intermittent, and how these regimes give rise to marked differences in the ecological character of these tropical rivers, particularly their floodplains.4. We describe the key features of these flow regimes, namely the wet and dry seasons and the transitions between these seasons, and how they regulate the biophysical heterogeneity, primary productivity and movement of biota in Australia's wet-dry tropical rivers.5. We develop a conceptual model that predicts the likely hydrological and ecological consequences of future increases in water abstraction (e. g. for agriculture), and suggest how such impacts can be managed so that the distinctive ecological character of these rivers is maintained.

1. Despite implications for top-down and bottom-up control and the stability of food webs, understanding the links between consumers and their diets remains difficult, particularly in remote tropical locations where food resources are usually abundant and variable and seasonal hydrology produces alternating patterns of connectivity and isolation. 2. We used a large scale survey of freshwater biota from 67 sites in three catchments (Daly River, Northern Territory; Fitzroy River, Western Australia; and the Mitchell River, Queensland) in Australia's wet-dry tropics and analysed stable isotopes of carbon (δ(13) C) to search for broad patterns in resource use by consumers in conjunction with known and measured indices of connectivity, the duration of floodplain inundation, and dietary choices (i.e. stomach contents of fish). 3. Regression analysis of biofilm δ(13) C against consumer δ(13) C, as an indicator of reliance on local food sources (periphyton and detritus), varied depending on taxa and catchment. 4. The carbon isotope ratios of benthic invertebrates were tightly coupled to those of biofilm in all three catchments, suggesting assimilation of local resources by these largely nonmobile taxa. 5. Stable C isotope ratios of fish, however, were less well-linked to those of biofilm and varied by catchment according to hydrological connectivity; the perennially flowing Daly River with a long duration of floodplain inundation showed the least degree of coupling, the seasonally flowing Fitzroy River with an extremely short flood period showed the strongest coupling, and the Mitchell River was intermediate in connectivity, flood duration and consumer-resource coupling. 6. These findings highlight the high mobility of the fish community in these rivers, and how hydrological connectivity between habitats drives patterns of consumer-resource coupling.