The impacts of land surface heterogeneity on the atmospheric boundary layer processes have been the subject of several investigations over the past few decades as the exchange of mass and energy between the surface and the atmosphere over flat and homogeneous surfaces is relatively well understood. One of the issues in addressing surface heterogeneity arises from the fact that the relationship between land surface characteristics and surface fluxes is typically non-linear. While a number of studies focused on surface-atmosphere exchanges over heterogeneous forest ecosystems, little attention has been paid to an environment both affected by urban land management and rural forest canopy. In this study eddy covariance techniques have been used at the Howard University Beltsville site that is located in Beltsville, Maryland, where a 31-m flux tower is installed over a grassland, surrounded by mixed deciduous and coniferous forests, but is also influenced by urban infrastructure to the west and north of the site, to investigate the mechanisms that govern the partitioning of the surface energy balance over the site during three seasons of 2006. Results showed strong responses of surface fluxes to the seasonal variability of net radiation, surface albedo, which resulted from the change in phenological stage experienced by the vegetation canopy, and the balance between soil moisture availability and atmospheric evaporative demand. Sensible and latent heat fluxes measured at the site were strongly controlled by the land use types within a distance of 1100m upwind of the site.