Site Characterization

Site characterization will be performed to choose optimal locations for NGEE Arctic field studies, to coordinate development of field site infrastructure and installation of key instrumentation, and to facilitate archiving and integration of the foundational datasets collected across the NGEE Arctic project. This activity will benefit from and coordinate with “Landscape Characterization and Identification of Geomorphological Features” tasks).

S. Hubbard (LBNL), who has extensive experience in field experimentation and shallow subsurface characterization using remote datasets, will lead this team and will lead and will participate in several associated tasks.

J. Rowland (LANL), who has extensive expertise in land surface dynamics and hydrology; he will lead the NGEE landscape characterization tasks and participate in several hydrology/Geomorphology tasks.

F. Hoffman (ORNL), who is a computational scientist with extensive experience working with global datasets relevant to climate, will lead the representative and scaling tasks.

K. Williams (LBNL) and J. Ajo-Franklin (LBNL) will work with the NGEE team and with Hubbard.

Site Characterization Goal: Coordinate infrastructure development, ensure safe data acquisition, and archive multiscale, multitype datasets needed for integrated site selection, process understanding, scaling, and model parameterization.

Barrow sampling strategy and first intensive field study site. Field studies in the first few years of the project will focus on study sites located within the BEO. Concurrent efforts will focus on identifying a suitable scaling construct and associated sampling plan for other prospective NGEE Arctic field study regions, which are likely to have geomorphic controls that are different from those of the Arctic coastal plain region.

The terrestrial landscape of the Barrow Peninsula is a mosaic of thaw lakes, DTLBs, and interstitial polygonal regions (Hinkle et al. 2007, Figure 1a). Given the low topographic relief, low hydraulic gradient, and shallow depth (< 1m) to the top of the permafrost in this

region, the polygonal landforms greatly influence the microtopography, and in turn, the hydrological stocks and fluxes of the region. Low-centered polygons often have standing water during the growing season (Liljedhal 2012) whereas the middle regions of high-centered polygons are typically well drained. The microtopographically controlled moisture distribution plays a significant role in biogeochemical cycling in this region, as troughs surrounding polygons can serve as pathways for water and nutrients (Woo and Guan 2006) and the depth of the water table below ground surface influences where anaerobic vs aerobic respiration processes dominate (e.g., Zona et al. 2011, Lipson et al. 2012). Indeed, Zuleta et al. (2011) documented that near Barrow, interstitial polygonal regions had a similar CO₂ flux signature as did old and ancient DTLBs, together representing ~59% of the regional flux. They further found that medium and young DTLBs had similar signatures and together represented ~35% of the regional flux (the rest stemming from thaw lakes). These studies highlight the potential power of using a geomorphic-based construct to guide Barrow site characterization and the NGEE Arctic hierarchical scaling framework.

Early NGEE Arctic field efforts will include both intensive and synoptic studies conducted within the BEO. Synoptic studies will be performed in the first two years to provide spatially extensive but sparse baseline datasets associated with key geomorphic features in the BEO, including DTLBs of different ages and interstitial polygonal regions. These synoptic campaigns will lay the groundwork for the more intensive subsequent studies. In the first year of the NGEE Arctic project, intensive field studies will also be initiated, where co-located measurements will be conducted to characterize and monitor vegetation dynamics, soil biogeochemistry, energy and hydrothermal processes, and their couplings as are described in detail later. While in Phase 1, it will not be possible to fully characterize the role of landscape heterogeneity in the evolution of Arctic ecosystems, the sampling approach that we have adopted provides an opportunity to advance process understanding as well as to initialize, parameterize, and validate the NGEE Arctic hierarchical scaling framework.

The first Barrow intensive site (“Site 1”) will be developed within an interstitial polygonal region, a prevalent landform in the Arctic tundra. Figure 1b shows the location of the Poly1 study site, which is located to the southwest of the medium-aged DTLB, where many NSF Biocomplexity investigations have been performed (e.g., Zona et al. 2011). Site 1 encompasses an existing eddy covariance tower, and the site soils are classified as aquiturbals. Four study plots have been identified within Site 1 (Figure 1c), each of which has different geomorphic and hydrological conditions (Table 1). Sampling within the plots and along transects that connect these plots will permit exploration of permafrost degradation pathways. Importantly, it will also permit quantification couplings between vegetation dynamics, soil biogeochemistry, hydrology, permafrost dynamics, and energy balance and their influence on greenhouse gas dynamics under different environmental conditions. For example, working between Site 1C and Site 1D will allow us to explore degradation pathways and fluxes associated with low centered polygons under different moisture conditions. Similarly, working between Site 1A and Site 1C will allow exploration of the impact of polygon age on GHG dynamics. As data from synoptic studies conducted within nearby DTLBs become available, additional NGEE Arctic intensive sites will be developed.

Field site infrastructure and installation of key instrumentation. Site infrastructure is needed to enable the acquisition of field measurements in a safe and efficient manner with minimal disturbance to the fragile ecosystem. Examples of site infrastructure include trail mats/boardwalks, instrument site huts, and field power. Access to nearby laboratories and storage containers must also be considered. Many of these components are already established at the Site 1, and infrastructure will be developed for other intensive sites as they are identified through synoptic studies. As is briefly described below, field instrumentation will vary depending on the stage of the site development.

• Synoptic site instrumentation will include acquisition and analysis of remote-sensing data and surface geophysical measurements (electromagnetic and ground-penetrating radar) as well as limited characterization of carbon stock/age, active layer thickness, water levels and aqueous geochemistry, soil texture, and soil gas at select locations along the geophysical transects.
• Intensive study site instrumentation will include eddy covariance system(s) to quantify latent heat flux, sensible heat flux, advection, and CO₂ and CH₄ fluxes at the scale of tens to hundreds of meters. These sites will also include co-located micrometeorology stations to monitor radiation fluxes, temperatures, and atmospheric conditions. A surface and subsurface monitoring and lysimeter sampling network will be installed for hydrological and aqueous biogeochemical sampling, vegetation will be sampled and characterized, high-resolution geophysical transects will be collected within and between detailed study plots, and soil cores will be collected in and around polygonal features for laboratory analysis and experimentation. Various additional observational measurements and sampling will co-occur within and along transects between plots as part of the hydrogeomorphology, biogeochemistry, vegetation dynamics and energy research.

Assemblage of site characterization data. This task will entail assembling newly collected NGEE Arctic data as well as existing datasets to construct a spatially and temporally explicit database of parameters critical for assessing terrestrial ecosystem processes and feedbacks to climate in and around the NGEE Arctic study sites. Primary existing data inputs will include physiographic data layers at all relevant and available resolutions (including microtopography; geomorphology, soil texture, geochemistry, active layer depth, hydrological and thermal properties, and vegetation); weather and climate data; geophysical transects; and multiscale and multitemporal remote-sensing observations. This repository will evolve as new observations are collected through NGEE Arctic research. The NGEE Arctic data management system, which is expected to serve as a resource for both the NGEE Arctic project team and the community, will take advantage of, connect, and augment existing DOE database tools.

Phase 1 Deliverables

• Field environment, safety, and health (ES&H) protocols for NGEE investigators and collaborators.
• Development of field site infrastructure at two intensive sites at the BEO.
• Synoptic characterization within all key/representative geomorphic units at the BEO.
• Intensive characterization of NGEE Site 1.
• Assembly and archiving of existing and new NGEE Arctic datasets that are critical for assessing terrestrial ecosystem processes and feedbacks to climate and are associated with the BEO study sites.