Abstract:
This pilot study sought to provide initial indicators of possible biogeochemical processes and sediment characteristics from Smith’s Lake, a NSW ICOLL, and their relationships with greenhouse gas (GHG) fluxes. It was ultimately hoped to determine Smith’s Lake’s GHG production capacity, and its susceptibility to eutrophication. Aerobic incubation of sediment samples showed small positive fluxes for CO2 and CH4, but a negative flux for N2O (xÌ…CO2= 28.97mg.kg-1.d-1; xÌ…CH4= 20.11µg.kg-1.d-1; xÌ…N2O= -0.58µ.kg-1.d-1). Comparison of sediment properties to GHG seven-day cumulative (SDC) emissions revealed CO2 levels were primarily correlated with organic matter (OM), while although aerobic respiration was important, anaerobic processes were suggested to dominate. CH4 production was less than CO2 but also strongly correlated with available OM. Unexpectedly CH4 also positively correlated with total nitrogen (TN), which indicated most sediment nitrogen could not be denitrification intermediates which inhibit methanogenesis. The negative N2O flux was explained by low TN (xÌ…= 0.02%), nitrogen fixation, and low efficiency or no denitrification. This was the most significant result as it suggested Smith’s Lake had no ability to regulate nitrogen input. This pilot study concluded that although nutrient burden was low, Smith’s Lake could be a contributing source of CO2 and CH4, and due to the long residence times of water in ICOLLs, combined with little evidence for denitrification, was susceptible to eutrophication. Long-term studies accounting for seasonal variation, including analysis of sediment interstitial fluid and anaerobic incubations, are required for sediment biogeochemical properties and GHG production relationships to be properly elucidated for Smith’s Lake.
Capstone
