Global abundance and size distribution of streams and rivers

To better integrate lotic ecosystems into global cycles and budgets, we provide approximations of the size-distribution and areal extent of streams and rivers. One approach we used was to employ stream network theory combined with data on stream width. We also used detailed stream networks on 2 continents to estimate the fraction of continental area occupied by streams worldwide and corrected remote sensing stream inventories for unresolved small streams. Our estimates of global fluvial area are 485 000 to 662 000 km(2) and are +30-300% of published appraisals. Moderately sized rivers (orders 5-9) seem to comprise the greatest global area, with less area covered by low and high order streams, while global stream length, and therefore the riparian interface, is dominated by 1st order streams. Rivers and streams are likely to cover 0.30-0.56% of the land surface and make contributions to global processes and greenhouse gas emissions that may be +20-200% greater than those implied by previous estimates.