Investigation of micro climate and energy balance along a stream

This sub-project of the ACRP project Bio_Clic deals first with the experimental characterisation of the riparian micro climate and of the energy balance of the stream. In a second step the experimental data are used to validate a stream energy balance model. To determine the above stream microclimate and the inherent microclimate in the riparian vegetation plots, routine measurements of air temperature and air humidity, wind speed, shortwave and longwave radiation balance (ingoing and outgoing radiation flux) will be performed. To characterize the stream surface energy exchange following parameters will be measured: firstly the river will be characterized by measuring stream flow, stream depth and width and surrounding riparian vegetation. Secondly routine measurements of water temperature in three different depths and of the bed sediment temperature (to determine sediment heat exchange) will be performed. The data of the CR1000 datalogger (4Mb storage capacity) will be read out regularly (every 3 months) at the site. On this occasion some additional measurements of water transmissivity and measurements to characterize the inhomogeneities of the measured parameters (water temperature, solar radiation and wind) will be performed. The stream energy balance modelling will be performed with the program HEATSOURCE. The total net heat flux into or out of a stream is the sum of the shortwave radiation balance, of the longwave radiation balance, of the latent heat flux, of the convection heat flux at the air water interface and of the streambed conduction. The radiation balance code needs firstly to account for the influence of riparian vegetation on shortwave and longwave radiation balance. Two different approaches will be compared for this radiation subroutine: 1) a gap light analyzer technique and 2) a canopy shade factor approach which requires the exact dimensions of the surrounding canopy as well as the angle of the horizon at all sky directions. The radiation code will be validated using the radiation measurements and fish eye photographs performed within the field surveys. The stream energy balance model will be tested using different approaches for the calculation of evaporative heat loss, sensible heat loss and water absorption. For calculation of the evaporative heat loss a Penman type method will be compared with a mass transfer method and an energy budget method. Sensible heat will be calculated using a bowen ratio method and a temperature gradient method. The stream energy balance model also includes the water absorption calculated using some empirical equation obtained with measurements, and it also takes into account the streambed heat conduction.