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Floodplain wetlands provide an important subsidy for riverine food webs as sites of high algal production. However, this subsidy depends on the degree of landscape connectivity during flood pulses, which provides the opportunity for movement of higher order consumers between rivers and floodplains to access these productive habitats. Changes in floodplain inundation extent and duration, due to variable wet season flows or water resource development (WRD), can impact landscape connectivity and ultimately the magnitude of the food web subsidy.We explored landscape connectivity using graph theory and derived four new metrics to measure how different flow scenarios can affect connectivity and algal production. We considered a historic scenario with the present level of water resource development in our study area, the Mitchell River, and a WRD scenario with the inclusion of three new dams in the catchment. We generated 240 unique daily spatial graphs, using surface water inundation maps across 40‐day flood events to compare a dry year (2006), an average flow year (2001) and a wet year (2009) with and without a WRD scenario.Drier years and WRD scenario resulted in floodplain fragmentation, potentially constraining the movement of higher order consumers. Changes in connectivity due to WRD resulted in predicted reductions of up to 26% of algal production on the floodplain that was otherwise connected to the main river channels.Synthesis and applications. The approach developed in this study provides new metrics to identify how changes in floodplain surface water extent due to water resource development and climatic variation may impact ecosystem function such as connectivity that facilitates access of higher order consumers to primary production in floodplain wetlands. With a direct link to river flow alteration, these metrics can inform catchment planning and management to ensure that the conservation of floodplain ecosystem functions is adequately considered in water resource management decisions. [ABSTRACT FROM AUTHOR]

Studies of tropical floodplains have shown that algae are the primary source material for higher consumers in freshwater aquatic habitats. Thus, methods that can predict the spatial variation of algal productivity provide an important input to better inform management and conservation of floodplains. In this study, a prediction of the spatial variability in algal productivity was made for the Mitchell River floodplain in northern Australia. The spatial variation of aquatic habitat types and turbidity were estimated using satellite remote sensing and then combined with statistical modelling to map the spatial variation in algal primary productivity. Open water and submerged plants habitats, covering 79% of the freshwater flooded floodplain extent, had higher rates of algal production compared to the 21% cover of emergent and floating aquatic plant habitats. Across the floodplain, the predicted average algal productivity was 150.9 ± 95.47 SD mg C m−2 d−1 and the total daily algal production was estimated to be 85.02 ± 0.07 SD ton C. This study provides a spatially explicit representation of habitat types, turbidity, and algal productivity on a tropical floodplain and presents an approach to map 'hotspots' of algal production and provide key insights into the functioning of complex floodplain–river ecosystems. As this approach uses satellite remotely sensed data, it can be applied in different floodplains worldwide to identify areas of high ecological value that may be sensitive to development and be used by decision makers and river managers to protect these important ecological assets. [ABSTRACT FROM AUTHOR]

• Introduced a cloud-based framework to assess changes in floodplain productivity. • Upstream flows drive floodplain inundation and aquatic plant biomass accumulation. • Local rainfall has limited impact on the productivity of downstream catchment. • Climate variability is a key constraint to changes in floodplain productivity. • Flows are primary drivers of floodplain inundation in the Mitchell catchment. Rivers in tropical systems across the world are well known for their strong connections with floodplain wetlands. However, increased water needs and changing climate could drive water-management policy that leads to major changes in flow or surface water availability. These changes could have deleterious effects on ecological functions and ecosystem services provided by these freshwater ecosystems (e.g., groundwater recharge, food sources for fish, etc.). In this study, we introduce a cloud-based monitoring framework using multi-resolution satellite observations (2007 - 2020), historical surface inundation (1984 - 2015), and gauge data to better understand these connections in a large river catchment in tropical Queensland (Mitchell River catchment). A key driver and indicator of floodplain productivity, surface water inundation and aquatic biomass distribution respectively, are investigated to provide insight that underpins the prioritization of future surface water developments in this region. Results show that the characteristics of floodplain inundation; loss, persistence, gain and frequency, vary in time and space, and are driven by climate variability. The largest gain (7200 Ha) and persistence (8437 Ha) in total surface inundation were observed in the wet seasons during the periods of 2007 - 2019 , respectively. In the downstream catchment, permanent water surface area was approximately 4.5% (of the total downstream region) compared to the upstream region (2.7%). There is a higher proportion of new permanent water features (16.8%) and new seasonal (30%) surface water classes in the upstream are in contrast to the downstream section (0.7% and 9.6%, respectively). Using multivariate statistics, floodplain productivity was linked to inter-annual changes in flow and rainfall. A partial least squares regression (PLSR) model shows upstream flows drive changes in total floodplain inundation (observed vs predicted, r = 0.95 , p = 0.000). Flows and local rainfall accounted for approximately 60% (r = 0.77 , p = 0.005) and 25% (r = 0.50 , p = 0.120) of the variability in total floodplain inundation, respectively. Different PLSR modelling scenarios confirmed that upstream flows are primary drivers of floodplain inundation and substantial lost in total surface inundation could happen if flows are altered. Just as local rainfall has limited impact on total floodplain inundation (r = 0.92 , p = 0.000 ; for model excluding local rainfall), aquatic plant biomass accumulations are also strongly associated with upstream flows (e.g., r = 0.82). Given the dependence of downstream water level (r = 0.89) and floodplain inundation on upstream flows, sustainable management of river flows in the Mitchell River is fundamentally important to floodplain productivity. [ABSTRACT FROM AUTHOR]