Description:
Lakes are an important source and sink of atmospheric CO2, and thus are a vital component of the global carbon cycle. However, with scarce data on potentially important subtropical and tropical areas for whole continents such as Australia, themagnitude of large-scale lake CO2 emissions is unclear. This study presents spatiotemporal changes of dissolved inorganic carbon and water—to—air interface CO2 flux in the two of Australia's largest connected, yet geomorphically different freshwater lakes (Lake Alexandrina and LakeAlbert, South Australia), during drought (2007 to September—2010) and post-drought (October 2010 to 2013). Lake levels in the extreme drought were on average approximately 1 m lower than long-term average (0.71 m AHD). Drought was associated with an increase in the concentrations of dissolved inorganic species, organic carbon, nitrogen, Chl-a and major ions, aswell aswater acidification as a consequence of acid sulfate soil (ASS) exposure, and hence, had profound effects on lake pCO2 concentrations. Lakes Alexandrina and Albert were a source of CO2 to the atmosphere during the drought period, with efflux ranging from0.3 to 7.0mmol/m2/d. The lake air–water CO2 flux was negative in the post-drought, ranging between−16.4 and 0.9mmol/m2/d. The average annual CO2 emission was estimated at 615.5 × 106 mol CO2/y during the drought period. These calculated emission rates are in the lower range for lakes, despite the potential for drought conditions that shift the lakes from sink to net source for atmospheric CO2. These observations have significant implications in the context of predicted increasing frequency and intensity of drought as a result of climate change. Further information on the spatial and temporal variability in CO2 flux from Australian lakes is urgently warranted to revise the global carbon budget for lakes.
Description:
The Gippsland Lakes hold significant environmental, cultural, and social importance, it holds Ramsar status, contains significant Indigenous heritage, and is valued by industries and communities for its natural resources and tourism. However, since establishing a tidal inlet, the Gippsland Lakes have become progressively more susceptible to salinization. This increased marine association has resulted in the formation of a migrating salinity gradient where formerly freshwater wetlands are subject to increased sulfate availability. The research presented here investigates the implications of salinization with respect to the development of acid sulfate soils (ASS) and investigates whether past salinization exacerbated sulfide formation. The study draws upon a variety of methods, it conducts sediment incubations to simulate and understand how acidification rates change at different ionic strengths and explores whether diatoms can reveal the aquatic conditions that preceded acidification and metal sulfide formation. Furthermore, based upon the electrical properties of sediments, the study assesses whether geophysical methods can map the distribution of sulfuric and sulfidic products. By manipulating the water source used when incubating sediments, the study simulates and compares acidification rates under both fresh and brackish conditions. Trends suggest that despite its alkalinity (100 mg/L CaCO3), sediments incubated with brackish water experienced accelerated acidification and became pH 0.30 – pH 0.23 more acidic than equivalent freshwater treatments. These results are complemented by diatom data that suggest brackish conditions preceded acidification. In the early diatom record, the occupation of alkaline/saline species correlate with sulfide accumulation, while a subsequent shift to acidobiontic taxa correlates with pH decline and the development of sulfuric conditions. The results from diatom analysis and soil incubation tests are further supported by electrical resistivity tomography (ERT) where a positive relationship is observed between acidification, elevated ionic strength, and a decline in electrical resistivity. These results support the premise that in wetlands subject to ASS oxidation, the influx of H+ and SO42- contributes to increasing electrolytic conduction, and compared to sulfidic and monosulfidic environments, will ultimately lead to a decline in electrical resistivity.
Description:
The Gippsland Lakes hold significant environmental, cultural, and social importance, it holds Ramsar status, contains significant Indigenous heritage, and is valued by industries and communities for its natural resources and tourism. However, since establishing a tidal inlet, the Gippsland Lakes have become progressively more susceptible to salinization. This increased marine association has resulted in the formation of a migrating salinity gradient where formerly freshwater wetlands are subject to increased sulfate availability. The research presented here investigates the implications of salinization with respect to the development of acid sulfate soils (ASS) and investigates whether past salinization exacerbated sulfide formation. The study draws upon a variety of methods, it conducts sediment incubations to simulate and understand how acidification rates change at different ionic strengths and explores whether diatoms can reveal the aquatic conditions that preceded acidification and metal sulfide formation. Furthermore, based upon the electrical properties of sediments, the study assesses whether geophysical methods can map the distribution of sulfuric and sulfidic products. By manipulating the water source used when incubating sediments, the study simulates and compares acidification rates under both fresh and brackish conditions. Trends suggest that despite its alkalinity (100 mg/L CaCO3), sediments incubated with brackish water experienced accelerated acidification and became pH 0.30 – pH 0.23 more acidic than equivalent freshwater treatments. These results are complemented by diatom data that suggest brackish conditions preceded acidification. In the early diatom record, the occupation of alkaline/saline species correlate with sulfide accumulation, while a subsequent shift to acidobiontic taxa correlates with pH decline and the development of sulfuric conditions. The results from diatom analysis and soil incubation tests are further supported by electrical resistivity tomography (ERT) where a positive relationship is observed between acidification, elevated ionic strength, and a decline in electrical resistivity. These results support the premise that in wetlands subject to ASS oxidation, the influx of H+ and SO42- contributes to increasing electrolytic conduction, and compared to sulfidic and monosulfidic environments, will ultimately lead to a decline in electrical resistivity.