Monday, August 8, 2016

Energy Balance of Tundra Landscapes

While the NGEE Arctic project has been interested in the energy balance of high-latitude ecosystems for several years, those measurements have focused on our site near Barrow, AK. We have used a suite of sensors to characterize energy-related processes across ice-wedge polygons and drained thaw lake basins. We have also deployed an instrument package on an automated cart that rides along a 65-m tram that collects data every three hours throughout the season. These systems are the product of our colleagues at LBNL and BNL.

This week Margaret, Bryan, Ori, and Sigrid – all from LBNL – were keen to deploy the portable system at sites near Council, AK on the Seward Peninsula. The suite of instruments included sensors for measuring short- and longwave radiation, incoming and reflected PAR, surface temperature, albedo, PRI, and NDVI. A camera could also be activated to take pictures of vegetation in each of the plots. The system was carried across the tundra and deployed at plots where we characterized community composition. This way we can interpret components of the energy balance and relate those to specific vegetation types. This will ensure that ecotypes are properly parameterized for use in our NGEE Arctic models.

Tasks were divided among the team; Ori prepared stakes for marking plots and she and Margaret picked representative 2.5 x 2.5 m plots along a transect and determined community composition. The transect crossed tussock tundra, several thermokarst features, and then two drained thaw lakes. Once plots were selected, Bryan and Sigrid walked from plot to plot with the sensors and made measurements as they went. A measurement would take 5 minutes with the greatest investment of time and energy spent walking between plots. We repeated measurements over a period of 4 to 5 days.  Ancillary data on thaw depth, soil temperature, and soil water content were also recorded at each plot. Our team had the opportunity to sample across a range of weather conditions; sunny days and rainy days.

It was a great week for deploying the energy balance system, looking at data, talking among our NGEE Arctic colleagues, and envisioning how we could improve the system in the coming months. Right now we are happy with the results and how they will inform models, especially models that explicitly represent vegetation dynamics including shrub expansion in tundra ecosystems.