CSU Thurgoona:Notebook/Dissolved Iorganic Carbon in headwaters/2009/09/08
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Significance and innovation
The fundamental innovation in this project is the development of a new instrument capable of unattended in situ measurement and logging of DIC and pCO2, exploiting the benefits provided by gas permeable ePTFE tubing. The system is novel in terms of both the type of tubing (silicone tubing has been used with limited success in the past to measure pCO2 in the field) and in the ability for automated, sequential in-line acidification of water samples, thereby, for the first time, enabling unattended, logged measurements of DIC and ambient pCO2 (for comparison with other relevant parameters including temperature, pH, conductivity, pressure, sediment, POC, DOC and water flux). By logging pH and temperature, full DIC speciation can be calculated if this is desired. It is generally the case that new techniques that offer more precise, higher resolution measurements enable a new generation of research questions to be addressed. Therefore the broadest significance of this project is that it will open up new potential for undertaking high-temporal-resolution, long-term field experiments into landscape-scale carbon cycling, integrated with terrestrial studies to a degree that has not been achieved previously. Development of the instrument also will be of general utility in studies of inorganic carbon dynamics in groundwater, soil water, urban and farming systems and the marine environment, though these applications are not pursued as pert of this proposal. The particular significance of the field study proposed here is that no study in the freshwater ecosystems of Australian highlands that has fully accounted for lateral fluxes of carbon in rivers (POC, DOC and DIC). This is an important omission in terrestrial carbon cycle studies as, for example, Bird et al. (2008) have suggested that lateral fluxes may remove significant carbon where vegetation located on steep terrain. Quantifying these lateral fluxes is a requirement for correctly determining sink/source strength of vegetation (e.g. Malhi and Grace, 2000). For obvious logistic reasons there have also been comparatively few studies of ecosystem carbon dynamics in steep highland regions, where eddy covariance techniques cannot be applied, though much of the remaining vegetation in the freshwater ecosystems of Australian highlands is in mountainous terrain precisely because access is difficult. These highlands are potentially of additional significance as the rate of future temperature increase is likely to be faster at higher altitude than lower altitude in the freshwater ecosystems (IPCC, 2007).