The main focus of my research is the development of new instrumentation and techniques for field-based measurements in aquatic ecosystems. These portable sensors are used to provide insight into some of the most pressing problems facing these ecosystems: ocean acidification and eutrophication.
Since the industrial revolution, the oceans have absorbed about 1/3 of the anthropogenic CO2 released to the atmosphere. While this has reduced the effect of CO2 emissions on climate change, it has also led to a 0.1 unit reduction in the pH of the world's oceans.
When CO2 is absorbed by seawater it forms carbonic acid (H2CO3) which dissociates to H+ and bicarbonate (HCO3-). The H+ reacts with carbonate ions (CO32-), forming additional bicarbonate. The net reaction, referred to as ocean acidification, is to increase the concentration of H+ (decreasing the seawater pH) and to reduce the concentration of carbonate.
Our group is interested measuring these changes to the relative inorganic carbon concentrations. The figure below, modified from the IPCC 4th Assessment Report (2007) Figure 7.3, shows the size of each carbon reservoir on Earth and how it has changed since the industrial revolution.
Figure: A comparison of the preindustrial (blue circles) and modern (red circles) carbon reservoirs shows significant changes (black circles) since the industrial revolution. The size of the carbon reserviors are given as Gt C. (1 Gt = 1,000 million tons, i.e. billion tons); change is expressed as % change.
Our group is developing new field-deployable sensors to measure fine-scale changes in carbonate chemistry and to study ocean acidification's impact on the structure of vulnerable calcifying organisms.
Phosphate is a limiting nutrient in aquatic environments and plays a vital role in the growth of plankton and aquatic plants. However, when a water system becomes over-enriched, it can lead to excessive plant growth and algal blooms, a process known as eutrophication. In addition to being toxic, the algal blooms can shade higher plants, deplete the water's oxygen supply, and lead, in extreme cases, to the disappearance of entire fish populations. When the closure of fisheries and loss of tourism dollars are considered, the economic impact of eutrophication can be substantial. Therefore, there is great interest in identifying the sources of phosphate and understanding movement through the environment. Our group is developing low-cost, field-portable sensors which allow fine-scale measurements of phosphate and help to identify sources and sinks.
In regions with unregulated mining, water pollution from runoff can have severe environmental and health consequences. Our group is developing sensors for community-based monitoring of pollution in water systems affected by mining. The sensors incorporate low-cost ion-selective electrodes into a versatile new platform for the rapid measurement of heavy metals in water.
The field-deployable sensors are calibrated using a non-linear Bayesian approach. This approach significantly extends limits of detection and provides realistic estimate of measurement precision. Tutorials and software (for R and OpenBUG) are available.
C.L. Hurd, C. Cornwall, K. Currie, C.D. Hepburn, C.M. McGraw, K.A. Hunter, P.W. Boyd, (2011). Metabolically-Induced pH Fluctuations by Some Coastal Calcifiers Exceed Projected 22nd Century Ocean Acidification: A Mechanism For Differential Susceptibility? In press, Global Change Biology.
C. Cornwall, C.D. Hepburn, D. Pritchard, K. Currie, C.M. McGraw, K.A. Hunter, C.L. Hurd, (2011). Differential Responses of Macroalgae with Various Carbon-Use Strategies to Ocean Acidification. In press, Journal of Phycology.
V. Cummings, J.Hewitt, A. Van Rooyen, K. Currie, S. Beard, S. Thrush, J. Norkko, N. Barr, P. Heath, N J. Halliday, R. Sedcole, A. Gomez, C. McGraw, V. Metcalf (2011) Ocean Acidification at High Latitudes: Potential Effects on Functioning of the Antarctic Bivalve Laternula elliptica. PLoS ONE, 6(1): e16069.
C.M. McGraw, C. Cornwall, M.R. Reid, K. Currie, C.D. Hepburn, P.W. Boyd, C.L. Hurd, K.A. Hunter (2010). An Automated pH-Controlled Culture System for Laboratory-Based Ocean acidification Experiments. Limnology & Oceanography: Methods, 8: 686-694.
C.M. McGraw, G. Khalil, J.B. Callis (2008). Comparison of time and frequency domain methods for luminescence lifetime measurement. Journal of Physical Chemistry C, 112 (21):8079-8084.
C.M. McGraw, A. Radu, C. Slater, D. Diamond, (2008). Pb2+-selective polymer-membrane electrodes for deployable devices. Electroanalysis, 20 (3):340-346.