Walker Branch NEON / WALK

Walker Branch Watershed (WALK) is an aquatic field site located in the Cumberland Plateau within Roane County, Tennessee. The site is located on the U.S. Department of Energy’s (DOE’s) Oak Ridge Reservation. WALK is managed by the DOE, specifically by the Oak Ridge National Laboratory’s Multiple Research Division. Walker Branch is a wadeable stream that drains a 1.1 km² (270 acre) watershed and is surrounded by deciduous forest. The region's rivers and streams harbor some of the largest variety of fish and mollusk species in the U.S. WALK is part of NEON Domain 07 - Appalachians & Cumberland Plateau, which includes eastern Tennessee, most of Kentucky, southern Ohio, and parts of North Carolina, Georgia, Indiana, and Illinois. The Domain hosts four other NEON field sites, three terrestrial and one aquatic, three of which are located in Tennessee. WALK is colocated with the ORNL terrestrial field site. [1] [2] [3] [4] [5]

The climate at WALK is characterized by moderately large variations in temperature and abundant precipitation. In particular, WALK has hot and humid summers and cool, mild winters. The mean annual average temperature is 14.4°C (58°F) and mean average precipitation is 1340vmm (53 in.). The site is occasionally subjected to high wind events, thunderstorms, droughts, flooding and rare wildfires. Summer afternoon thunderstorms are common, and winters will see occasional snow accumulation which melts shortly afterwards (depending on elevation and sun exposure). [7] [8]

WALK is part of the Chase Group. The parent materials at the ORNL site are residuum, colluvium, and local alluvium derived from Cambrian and Lower to Middle Ordovician geologies. [6]

Forest soils found within the WALK watershed are acidic (pH 3.5 to 4.6), very cherty, infertile, and highly permeable. They are considered ancient and are part of the soil series Fullerton cherty silt loam (5-12% slopes), within the subgroup Typic Paleudults. Other relatively common soils found in the area are Montevallo, Bodine, Minvale, Sunlight, and Etwoah. [4] [6]

WALK is a wadeable, first-order stream with eleven springs flowing into it. [1]

WALK's canopy consists of a dense hardwood forest dominated by oaks and hickories. At and around WALK, there is a mixture of deciduous species in the valleys with patches of shortleaf pine (Pinus echineta) and Virginia pine (Pinus virginiana) on the ridges. Mixed hardwoods at the site include chestnut oak (Quercus prinus), tulip poplar (Liriodendron tulipifera), red maple (Acer rubrum), white oak (Quercus alba), and American beech (Fagus grandifolia). It is 90% closed canopy when leaves are out, and the understory is mostly leaves and groundcover. [1] [2] [6]

The area surrounding WALK hosts about 60 species of fish and 60 species of reptiles and amphibians, ~200 species of migratory, transient and resident birds, and 35 species of mammals, as well as many invertebrate species. Among these, 17 were identified as federally- or state-listed (endangered, threatened, or in need of management) in surveys done in the 2000s. Some common water-loving mammals that can be found at WALK include beaver (Castor canadensis), mink (Mustela vison), and muskrat (Ondatra zibethica). The two most common fish species sampled at WALK are blacknose dace (Rhinichthys atratulus) and banded sculpin (Cottus carolinae). There are two threatened fish species that live in the region: blue sucker (Cycleptus elongatus) and spotfin chub (Erimonax monachus). The area also sees an abundance of semi-aquatic migratory birds and aquatic and semi-aquatic salamander species. [9] [10]

The Walker Branch watershed has a long history of research. In 1942, the United States government selected the rural area for the development of nuclear weapons and materials for the Manhattan project. Originally called the Clinton Engineering Works, the Oak Ridge Reservation includes three facilities: Oak Ridge National Laboratory, Y-12 National Security Plant and the Gaseous Diffusion Plant, now known as the East Tennessee Technology Park (ETTP). In 1943, the reservation housed the world's first operational nuclear reactor, used for the production of plutonium during World War II. After World War II, the U.S. government dissolved the Manhattan Project and established the Atomic Energy Commission to produce and control nuclear energy for military and civilian applications during peace time. In the 1960s, research at the reservation focused on environmental research such as energy efficiency, renewable energy technologies and nuclear technologies and systems. In 1989, the U.S. Department of Energy’s Environmental Management (DOE-EM) and National Nuclear Security Administration began to oversee nuclear clean up activates at the site. Today, the Oak Ridge National Laboratory continues to take part in cutting edge scientific research, Y-12 National Security Complex continues to be used for nuclear weapons processing and materials storage, and the East Tennessee Technology Park (ETTP) is considered a sensitive area with national security concerns.

The NEON site WALK has a long history of environmental research in particular. Intensive environmental research at the Walker Branch site began in the late 1960s following major funding from the DOE Office of Science Biological and Environmental Research Program (BER), Terrestrial Ecosystem Science (TES). The project initially focused on the geological and hydrologic processes that control the amounts and chemistry of water moving through the watershed. Over the next 40 years, research at the watershed focused on hydrological, biogeochemical and ecological studies that examined the impacts of climate variability and change in the region. This research has been headed by various agencies and groups, including the Atmospheric Turbulence and Diffusion Division, Air Resources Laboratory, National Oceanic and Atmospheric Administration in Oak Ridge, Tennessee, and many visiting university researchers. [11] [13] [14] [15]

The Department of Energy (DOE) currently oversees Walker Branch. The DOE strives to ensure America's future by overcoming energy, environmental, and nuclear challenges through scientific research. These projects have all contributed to a more complete understanding of how forest watersheds function and have provided insights into the solution of energy-related problems associated with air pollution, contaminant transport, and forest nutrient dynamics. This is one of a few sites in the world characterized by long-term, intensive environmental studies. Despite some of the long-term research projects being phased out, this type of research still continues to be an important activity in the watershed as NEON will collect data ecological data there for 30 years. [12]

WALK was established as a NEON field site in November 2014. It was trial tested in late 2015 and AOS and AIS operations were up and running early 2016. Data collection from the tower began in early 2015.