Small streams that drain agricultural landscapes have come under close scrutiny as potentially significant indirect sources of greenhouse gases (GHGs) to the atmosphere. By exploring the stream-ground water connection in three dimensional space (horizontally and vertically beneath the stream channel, and longitudinally along the stream corridor) our results show (1) ground water can be a significant source of greenhouse gases to streams draining agricultural watersheds with concentrations in excess of atmospheric equilibrium by 221 mu mol C L super(-1) carbon dioxide, 0.64 mu mol C L super(-1) methane, and 0.65 mu mol N L super(-1) nitrous oxide (N sub(2)O); (2) changes in the stream-ground water connection can create seemingly erratic [...]