Atmospheric water plumes; mapping water transport through the forest canopy using distributed sensor networks

Evapotranspiration provides the primary water loss mechanism from forests, controlling catchment hydrological dynamics, forest productivity and ecosystem biodiversity. Advanced atmospheric simulations have highlighted how forest canopy structures that cluster at a range of spatial scales induce complex spatiotemporal connections and disconnections between the sub canopy and the atmosphere. Such temporal connectivity both restricts the transport of water and induces isolated, temporally discrete plumes from the sub canopy through to the atmosphere. This atmospheric connectivity will be severely impacted by transitions in forest canopy structure as a result of CO2 fertilisation, drought stress, wind throw and forest management activities that will have unknown and/or unintentional impacts on forest ecosystem productivity, biodiversity and hydrology.
Despite advanced model simulations of complex atmospheric water transport pathways, the ability to observe these dynamic conditions has been hampered by the available measurement approaches; approaches that currently integrate water fluxes from throughout a measurement footprint from a single expensive technologically advanced instruments located on an isolated tower. New distributed sensor networks have offered a tantalising glimpse into the spatiotemporal complexity of forest evapotranspiration, measuring the Bowen ratio, air temperature and atmospheric humidity at a decimetre resolution vertically through the forest canopy. However, to date the power of this approach has been limited by the number of available towers necessary to support such spatially explicit measurements through a 3-D canopy. Whilst current measurements are located on a single isolated tower, the 100 towers throughout BIFoR FACE facility combined with the latest distributed temperature sensing technology already installed at Mill Haft offers a truly unique opportunity to directly explore the invisible water transport network and wind flow patterns though the forest canopy.
The project will apply this state-of-the-art approach to map the atmospheric hydroscape, from distributed water sources through the sub canopy and trees, to the integrative atmospheric sink. It will explore how changing canopy structures in space and time (over season and in response to CO2 fertilisation) modify the atmospheric transport. It will assess the extent to which water fluxes are controlled by local scale atmospheric connectivity and provide the experimental foundation to support the state of the art numerical modelling studies to quantify the impact of global environmental change and management approaches on this critical global flux.
Fibre-Optic cables will be installed through the FACE canopy using of CO2 fertilisation towers. Temperatures will be measured at a decimetre spatial scale and sub minute temporal resolution. Wet and dry cable temperature differences will be used to measure atmospheric humidity, and active heating of the cable enables wind speed measurement. Data analysis will build upon approaches applied in current cross-scale high frequency BIFoR FACE networks, from non-linear short-term stream biogeochemistry dynamics to spatial disturbed moisture measurement. Notably, advanced spatial analysis techniques such as Empirical Orthogonal Functions, will determine the principal components of data in space and time.