Lake ecologist Dr Stephen Thackeray considers the possibilities presented by earth observation working alongside traditional monitoring
This month I had the pleasure of attending a combined workshop for the GloboLakes and GLaSS projects at Stirling University, nestled beneath the impressive Wallace Monument. These initiatives have successfully brought together international experts from a wide range of universities, research institutions and private businesses with an ambitious common goal: to establish a satellite-based global observatory to monitor the state of freshwaters, and their responses to environmental pressures such as climate and land-use change. Reflecting back on this meeting, I am excited by the possibilities presented by earth observation, and more convinced than ever of the need for complementary, detailed in situ monitoring.
For those of us used to “traditional” sampling of lake ecosystems, collecting physical, chemical and biological data from on board a boat, and then analysing and processing samples in the lab afterwards, these technologies offer a major change in perspective. Whereas availability of staff time and resources inevitably limit the number of lakes we can monitor, satellite remote sensing data can provide a synoptic picture of water quality change across hundreds to thousands of lakes globally. New scientific insights will surely follow. Not all lakes are the same in terms of structure and functioning, and we are on the brink of being able to monitor change across the full range of this ecological diversity.
Not only that, these technologies allow us to map and understand the spatial “patchiness” that characterises the open water of each and every lake. Such spatial coverage would be difficult to achieve by traditional means. The potential to produce a truly global assessment of the state of lake ecosystems, on which society depends in so many ways, is clear and exhilarating.
"The potential to produce a truly global assessment of the state of lake ecosystems, on which society depends in so many ways, is clear and exhilarating."
As with any technology, great potential also brings important scientific challenges. Many of us will need to get used to working with, analysing and summarising terabytes of satellite data! Importantly the onus to translate these data into practically-useful measures of ecological state and water quality change, to inform regulators and managers, will be placed squarely on the scientific community. However, through regular consultation between researchers and stakeholders, this can no doubt be achieved.
A key theme apparent to me through the workshop, however, was that there is much ongoing technical development in the mathematical routines used to convert “raw” satellite data into measures of phytoplankton biomass, potentially-toxic cyanobacterial blooms, suspended solid concentrations and water colour. This validation process is reliant upon “matching up” in situ, traditional monitoring data with that from satellites passing far overhead. So, while satellite observation provides unprecedented spatial coverage, ongoing monitoring efforts on the ground (or, rather, water) will help us realise this potential.
Furthermore, only in situ monitoring can provide us with important information on community composition, food-web interactions impacting grazers and socio-economically important predators like fish, deep water processes such as oxygen depletion, and the mechanisms behind whole-system phenomena like ecological resilience. Similarly, satellites currently do not have the temporal resolution provided by automatic, high-frequency monitoring buoys that capture the full dynamic nature of lakes and are essential for model development and validation.
All of this suggests that there is great merit in pursuing a tiered approach to the monitoring of freshwaters, that recognises the complementary nature of automatic and manual in situ and satellite monitoring. Satellites provide a global picture of change for a few useful measures of water quality but, embedded in this picture, we require detailed monitoring of a range of ecologically distinct sites that contribute to the ongoing development of this technology, and provide the mechanistic insight needed to underpin our attempts to project future change.
"There is great merit in pursuing a tiered approach to the monitoring of freshwaters, that recognises the complementary nature of automatic and manual in situ and satellite monitoring"
Aligning in situ monitoring, ecological modelling and earth observation will no doubt be a challenging and rewarding endeavour for many years to come.
* MERIS is the Medium Resolution Imaging Spectrometer instrument on board the European Space Agency's now defunct ENVISAT satellite.