02269nas a2200205   4500008004100000245005300041210005300094300001300147490000700160520164700167653003501814653002201849653003001871653001901901653001801920653002501938100001801963700001601981856006601997       2008                        eng d00aHeadwater influences on downstream water quality0 aHeadwater influences on downstream water quality  a367 -3770 v413 a<p>We investigated the influence of riparian and whole watershed land use as a function of stream size on surface water chemistry and assessed regional variation in these relationships. Sixty-eight watersheds in four level III U.S. EPA ecoregions in eastern Kansas were selected as study sites. Riparian land cover and watershed land use were quantified for the entire watershed, and by Strahler order. Multiple regression analyses using riparian land cover classifications as independent variables explained among-site variation in water chemistry parameters, particularly total nitrogen (41%), nitrate (61%), and total phosphorus (63%) concentrations. Whole watershed land use explained slightly less variance, but riparian and whole watershed land use were so tightly correlated that it was difficult to separate their effects. Water chemistry parameters sampled in downstream reaches were most closely correlated with riparian land cover adjacent to the smallest (first-order) streams of watersheds or land use in the entire watershed, with riparian zones immediately upstream of sampling sites offering less explanatory power as stream size increased. Interestingly, headwater effects were evident even at times when these small streams were unlikely to be flowing. Relationships were similar among ecoregions, indicating that land use characteristics were most responsible for water quality variation among watersheds. These findings suggest that nonpoint pollution control strategies should consider the influence of small upland streams and protection of downstream riparian zones alone is not sufficient to protect water quality.</p>10ageographic information systems10aHeadwater streams10aNonpoint source pollution10aRiparian zones10awater quality10aWatershed management1 aDodds, W., K.1 aOakes, R.M.  uhttps://link.springer.com/article/10.1007%2Fs00267-007-9033-y