Quantifying natural GHG sources and sinks: The role of regional small water bodies

Ponds located in Seqwater catchment areas occupy a surface area over 120 km2 which is in excess of the largest raw water storage, Lake Wivenhoe. Mean methane emission rates ranged from 17 to 2,493 mg m-2 d-1 and bubbling was the dominant emission pathway. Over 67,000 individuals ponds were identified in SEQ region with annual methane emissions over 280,000 t CO2 eq y-1. Weir emission rates were significantly higher compared with all other pond types suggesting Seqwater owned weirs should be included in future greenhouse gas monitoring programs. Seqwater has the opportunity to develop whole catchment mitigation strategies that will be relevant to all artificial water bodies within the catchment area

Accurately measuring the abundance of benthic microalgae in spatially variable habitats

Although many studies measure the abundance of benthic microalgae (BMA), at the meters squared scale, comparing these studies is difficult due to the variety of sampling, extraction, and analysis techniques. This difficulty is exacerbated by the fact that BMA abundance has high spatial and temporal variability, at all spatial scales. A suitable standard sampling regimen would reduce variation in estimates due to different sample collection and processing greatly facilitating comparisons between studies. This study examined the effect of varying the volume of extraction solvent, sampling core diameter, and sample replication on BMA biomass estimates. Key findings, applicable to all spatial scales, to accurately determine biomass were the use of a minimum sediment to extraction solvent ratio of 1:2 and use of a sampling core diameter of 19 mm. Across a wide range of sediment types, at the meters squared scale and using spectrophotometric techniques, a minimum replication number of 8 was found to be appropriate. We report the significant effect coring depth and units of expression have on BMA biomass estimates across a range of sediment types, highlighting the potential pitfalls when comparing studies

Primary production of lake phytoplankton, dominated by the cyanobacterium Cylindrospermopsis raciborskii, in response to irradiance and temperature

We present the first data on the interacting effect of temperature and light on primary production of the toxic cyanobacterium Cylindrospermopsis raciborskii in situ. C. raciborskii can be a dominant component of the phytoplankton community in tropical and subtropical lakes and reservoirs. We examined the interacting effects of a range of light (0, 2, 7, 17, 30, and 100% of ambient light) and temperature (20, 24, 28, and 32 °C) conditions, in terms of primary production rate and primary production irradiance model parameters, for a C. raciborskii-dominated phytoplankton community in a subtropical reservoir. Based on 13C-uptake experiments, phytoplankton preconditioned to temperatures between 24 and 26 °C had highest maximum primary production rates (2.25 ± 0.45 µg C µg Chl-a-1 h-1) at 28 °C and lowest at 32 °C (0.58 ± 0.13 µg C µg Chl-a-1 h-1). Temperature also had an effect on the response to light conditions. Phytoplankton preconditioned to a shallow euphotic depth (~2.3 m deep) had the lowest half saturation of primary production, Ik, at 28 °C and highest at 32 °C, while the highest temperature treatment also had the highest level of photoinhibition at 100% of ambient light. This suggests that the cyanobacterial community is adapted to a low light environment under optimal temperature conditions for primary productivity. These conditions are consistent with other studies showing that C. raciborskii is highly adapted to low light conditions. This work demonstrates the importance of considering temperature when comparing calibrated primary production parameters

Terrestrial–marine connectivity: patterns of terrestrial soil carbon deposition in coastal sediments determined by analysis of glomalin related soil protein

Glomalin, an arbuscular mycorrhizal protein component of soil, can be used as an indicator of terrigenous-derived carbon. We measured glomalin in sediments using the terrestrial end-member as a reference in four coastal settings: (1) intertidal seagrass meadows distributed over a rainfall gradient, (2) sediments inshore and offshore from the mouth of a river, (3) coastal coral reefs at various distances from the shore, and (4) intertidal wetlands with varying levels of groundwater influence. Across the rainfall gradient, glomalin in seagrass meadow sediments increased at sites with high mean annual rainfall during the wet season (r(2) = 0.27; F-1,F-29 = 5.75; p = 0.029). Glomalin decreased in inshore river sediments (terrestrial) to offshore (marine) sediments (r(2) = 0.81; F-1,F-17 = 71.7;

A cost-efficient seabed survey for bottom-mounted OWC on King Island, Tasmania, Australia

This paper presents results from a site assessment for a gravity foundation Oscillating Water Column (OWC) Wave Energy Converter (WEC) designed by Wave Swell Energy (WSE), an Australian wave energy developer. A potential candidate site for this device is the west coast of King Island, Tasmania in relatively shallow water (~ 10 m LAT). The survey included geotechnical data obtained by sub-bottom profiles, seabed imagery, benthic samples and cores with the aid of SCUBA diving as well as short-term deployment of hydromechanics instruments. Our results show that the device can be placed in an area with enough sand coverage and sufficient bearing capacity. However, the location exhibits evidence of scour and an active sediment regime, which requires a more detailed analysis of the long-term sediment transport processes and associated environmental impacts on a gravity foundation structure

Sampling considerations and assessment of Exetainer usage for measuring dissolved and gaseous methane and nitrous oxide in aquatic systems

Pre-evacuated Exetainers are commonly used as measurement vials for the determination of methane (CH4) and nitrous oxide (N2O) concentrations in liquid and gaseous samples from aquatic environments. The impact of residual air in these Exetainers on measurement accuracy is assessed. Residual air pressure in commercially available, pre-evacuated Exetainers varied between 0.071 +/- 0.008 atm and 0.180 +/- 0.031 atm in examined batches. This background contamination can lead to large errors when determining dissolved and gaseous CH4 and N2O concentrations particularly at low concentrations. A method for Exetainer pretreatment is suggested and verified, to reduce the residual CH4 and N2O. Vials are flushed (needle 30 G 3 0.5 '', 0.3 mm) with nitrogen gas (N-2) for 5 min, which reduces the background CH4 and N2O concentrations to 0.092 +/- 0.008 ppm and 0.016 +/- 0.001 ppm, respectively, approximately 3-4% of their respective concentrations in air. To avoid an alteration of sample concentration by variable residual gas levels left during a pre-evacuation step, liquid and gaseous samples are injected into the N-2 filled Exetainers. For gaseous samples where large volumes of gas are available, Exetainers can alternatively be flushed with 100 mL of sampling gas. For gaseous samples, measured CH4 and N2O concentrations of standard gases were statistically identical to their known concentrations. For liquid samples, measured CH4 and N2O concentrations of liquid standard dilution series showed strong linear correlations with theoretically calculated concentrations (slope CH4: 1.04, slope N2O: 1.12). Sample concentrations remained constant over a minimum storage period of 6 weeks

The importance of small artificial water bodies as sources of methane emissions in Queensland, Australia

Emissions from flooded land represent a direct source of anthropogenic greenhouse gas (GHG) emissions. Methane emissions from large, artificial water bodies have previously been considered, with numerous studies assessing emission rates and relatively simple procedures available to determine their surface area and generate upscaled emissions estimates. In contrast, the role of small artificial water bodies (ponds) is very poorly quantified, and estimation of emissions is constrained both by a lack of data on their spatial extent and a scarcity of direct flux measurements. In this study, we quantified the total surface area of water bodies <105m2 across Queensland, Australia, and emission rates from a variety of water body types and size classes. We found that the omission of small ponds from current official land use data has led to an underestimate of total flooded land area by 24%, of small artificial water body surface area by 57% and of the total number of artificial water bodies by 1 order of magnitude. All studied ponds were significant hotspots of methane production, dominated by ebullition (bubble) emissions. Two scaling approaches were developed with one based on pond primary use (stock watering, irrigation and urban lakes) and the other using size class. Both approaches indicated that ponds in Queensland alone emit over 1.6 Mt CO2 eq. yr−1, equivalent to 10% of the state's entire land use, land use change and forestry sector emissions. With limited data from other regions suggesting similarly large numbers of ponds, high emissions per unit area and under-reporting of spatial extent, we conclude that small artificial water bodies may be a globally important missing source of anthropogenic greenhouse gas emissions

Winners and losers as mangrove, coral and seagrass ecosystems respond to sea-level rise in Solomon Islands

A 2007 earthquake in the western Solomon Islands resulted in a localised subsidence event in which sea level (relative to the previous coastal settings) rose approximately 30-70 cm, providing insight into impacts of future rapid changes to sea level on coastal ecosystems. Here, we show that increasing sea level by 30-70 cm can have contrasting impacts on mangrove, seagrass and coral reef ecosystems. Coral reef habitats were the clear winners with a steady lateral growth from 2006-2014, yielding a 157% increase in areal coverage over seven years. Mangrove ecosystems, on the other hand, suffered the largest impact through a rapid dieback of 35% (130 ha) of mangrove forest in the study area after subsidence. These forests, however, had partially recovered seven years after the earthquake albeit with a different community structure. The shallow seagrass ecosystems demonstrated the most dynamic response to relative shifts in sea level with both losses and gains in areal extent at small scales of 10-100 m. The results of this study emphasize the importance of considering the impacts of sea-level rise within a complex landscape in which winners and losers may vary over time and space

Tidal energy in Australia – Assessing resource and feasibility to Australia’s future energy mix

This paper presents an overview and progress of a recently commenced three year project funded by the Australian Renewable Energy National Agency led by the Australian Maritime College, (University of Tasmania), in partnership with CSIRO and University of Queensland. The project has a strong industry support (OpenHydro Ltd, Atlantis Resources Limited, MAKO Tidal Turbines Ltd, Spiral Energy Corporation Ltd and BioPower Systems Ltd) and aims at assessing the technical and economic feasibility of tidal energy in Australia, based on the best understanding of resource achievable. The project consists of three interlinked components to support the emerging tidal energy sector. Component 1 will deliver a National Australian high-resolution tidal resource assessment; in Component 2, case studies at two promising locations for energy extraction will be carried out; lastly, Component 3 will deliver technological and economic feasibility assessment for tidal energy integration to Australia’s electricity infrastructure. The outcomes of this project will provide considerable benefit to the emerging tidal energy industry, the strategic-level decision makers of the Australian energy sector, and the management of Australian marine resources by helping them to understand the resource, risks and opportunities available