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Previous studies on the relationship between ecosystem productivity, size and food-chain length have been restricted to comparisons between locations. We examined the effect of temporal variability in productivity on trophic structure of a floodplain ecosystem, hypothesising that during the wet-flood pulses, the increased resource availability might lead to higher food-chain lengths. We examined multiple common sampling locations and species during a severe El Niño drought which followed a consecutive series of historically wet La Niña years, comparing trophic position and dietary sources. While carbon stable isotopes showed no significant difference between the two phases, nitrogen stable isotopes indicated that most species were feeding higher in the food chain in the wet phase. The results suggest that oscillations in climate phase-driven changes have effects on food-chain lengths through changes in productivity, without the introduction of new sources of carbon or changes to the composition of higher-order predators.

Quantifying carbon storage in coastal wetland environments is important for identifying areas of high carbon sequestration value that could be targeted for conservation. This study combines remote sensing and sediment analysis to identify spatial variation in soil carbon storage for Currambene Creek, New South Wales, Australia to establish whether vegetation structure influences soil carbon storage in the upper 30 cm. Wetland vegetation was delineated to capture structural complexity within vegetation communities using Light detection and ranging (Lidar) point cloud data and aerial imagery with an object-based image analysis approach. Sediment cores were collected and analysed for soil carbon content to quantify below-ground carbon storage across the site. The total soil carbon storage in the upper 30 cm for the wetland (59.6 ha) was estimated to be 3933 ± 444 Mg C. Tall mangrove were found to have the highest total carbon storage (1420 ± 198 Mg C), however are particularly sensitive to changes in sea-level as they are positioned lowest in the intertidal frame. Conservation efforts targeted at protecting areas of high carbon sequestration, such as the tall mangrove, will lead to a greater contribution to carbon mitigation efforts.

The high cost of fish feed is an impediment to the sustainability and growth of the aquaculture industry in Papua New Guinea (PNG). In order to develop cost-effective feeding strategies for Genetically Improved Farmed Tilapia (GIFT), an understanding of this species’ dietary requirements, and how they can be met in a pond system, is essential. The contribution of formulated feed and natural food to the growth of GIFT is poorly understood in PNG. Consequently, feeding strategies are currently not based on scientific knowledge on the contributions of different nutritional inputs in the farming systems. Stable isotopes, in combination with standard growth measurements and stomach content analysis, may provide more insight into the role of different sources of nutrients in the growth of GIFT. A 90-day feeding experiment was conducted to estimate the relative contributions of different food sources in the diet of GIFT. The overall aim of the research was to determine the role of different nutrient sources to underpin future work on modified feeding strategies that can reduce the cost of fish farming in PNG. The feeding experiment was a 2 x 3 completely randomized design (CRD) as it was appropriate for smaller trials with fewer replicates or experimental units. Locally formulated fish feed (Goroka Mini Mill) was the single factor considered in this CRD experiment at two treatment levels: daily feeding (T1) and weekly feeding (T2), with three replicate units for each treatment.Additionally, the ponds were fertilised weekly using a mixture of organic (chicken manure) and inorganic (urea & TSP) fertilisers throughout the experiment. These are commonly used fertilisers in PNG. Ponds were stocked with juvenile GIFT of 10cm total length (TL) and 16g body weight (BW) at 3 fish/m2. The fish were fed three times daily for six days (T1) and weekly (T2) with locally formulated fish feed (28 % CP) based on 5% BW but later reduced to 4%. Growth was measured every 21 days, while pond w

Environmental water allocations are used to improve the ecological health of wetlands. There is now increasing demand for allocations to improve ecosystem productivity and respiration, and enhance carbon sequestration. Despite global recognition of wetlands as carbon sinks, information regarding carbon dynamics is lacking. This is the first study estimating carbon sequestration for semiarid Phragmites australis reedbeds. The study combined aboveground biomass assessments with stable isotope analyses of soils and modeling of biomass using Normalized Digital Vegetation Index (NDVI) to investigate the capacity of environmental water allocations to improve carbon storage. The study considered relationships between soil organic carbon (SOC), carbon sources, and reedbed persistence in the Macquarie Marshes, a regulated semiarid floodplain of the Murray-Darling Basin, Australia. SOC storage levels to 1 m soil depth were higher in persistent reedbeds (167 Mg ha−1) than ephemeral reedbeds (116-138 Mg ha−1). In situ P. australis was the predominant source of surface SOC at persistent reedbeds; mixed sources of surface SOC were proposed for ephemeral reedbeds. 13C enrichment with increasing soil depth occurred in persistent and ephemeral reedbeds and may not relate to flow characteristics. Despite high SOC at persistent reedbeds, differences in the rate of accretion contributed to significantly higher rates of carbon sequestration at ephemeral reedbeds (approximately 554 and 465 g m−2 yr−1) compared to persistent reedbeds (5.17 g m−2 yr−1). However, under current water regimes, rapid accretion at ephemeral reedbeds cannot be maintained. Effective management of persistent P. australis reedbeds may enhance carbon sequestration in the Macquarie Marshes and floodplain wetlands more generally.

Suzzi, A. L., Gaston, T. F., McKenzie, L., Mazumder, D., & Huggett, M. J. (2022). Tracking the impacts of nutrient inputs on estuary ecosystem function. Science of The Total Environment, 811, article 152405. https://doi.org/10.1016/j.scitotenv.2021.152405