Sensors capable of unattended pCO2 measurements, as well as high spatial/temporal resolution flow-through pCO2 analyzers have become increasingly cost effective tools in aquatic science. These technologies greatly extend the reach of water-quality monitoring projects, for which we present 3 examples. First, a flow-through CO2 analyzer was added to the suite of instruments used in a long-term estuarine monitoring program, allowing investigation of biogeochemical processes at diel to inter-annual scales. We show that net ecosystem metabolism drives air-water CO2 exchange by directly measuring diel excursions in DIC and pCO2 throughout an entire estuary. Diel variations in pCO2 were large, similar in magnitude to seasonal variability, leading the estuary to transition from sink to source status over diel to seasonal scales. Extreme climatic events like hurricanes and major floods may significantly impact annual C budgets. For example, flooding associated with hurricane Joaquin (2015) caused annual CO2 emissions to increase by 31 and 44% in two North Carolina estuaries. Second, an in-situ CO2 sensor was used to investigate C cycling in hyper-eutrophic Lake Taihu, China. While diel cycles in production and respiration drew down CO2 to limiting levels, storms drove large increases in pCO2, causing the lake to act as a moderate net CO2 source to the atmosphere (0.35 mmol C m-2 hr-1). Finally, an in-situ CO2 sensor was paired with direct measurements of air-water CO2 exchange in a shallow, lagoonal estuary, allowing the physical drivers of gas transfer velocity (GTV) to be investigated. Early findings suggest that GTV parameterizations derived for coastal or oceanic systems may not be applicable in shallow, lagoonal estuaries. Future studies may need to develop unique GTV parameterizations on an estuary-by-estuary basis, due to the system-specific nature of physical forcing in estuaries. With only minor changes between studies, two commonly used CO2 platforms were added to existing projects, allowing a diverse set of biogeochemical questions in lakes and estuaries to be addressed.

Assessing spatial or temporal variability in pCO2 dynamics of estuarine and freshwater ecosystems: Case studies from North Carolina and China demonstrate trade-offs

255th National Meeting (2018)

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