title: Network analysis reveals multiscale controls on streamwater chemistry.
abstract: By coupling synoptic data from a basin-wide assessment of streamwater chemistry with network-based geostatistical analysis, we show that spatial processes differentially affect biogeochemical condition and pattern across a headwater stream network. We analyzed a high-resolution dataset consisting of 664 water samples collected every 100 m throughout 32 tributaries in an entire fifth-order stream network. These samples were analyzed for an exhaustive suite of chemical constituents. The fine grain and broad extent of this study design allowed us to quantify spatial patterns over a range of scales by using empirical semivariograms that explicitly incorporated network topology. Here, we show that spatial structure, as determined by the characteristic shape of the semivariograms, differed both among chemical constituents and by spatial relationship (flow-connected, flow-unconnected, or Euclidean). Spatial structure was apparent at either a single scale or at multiple nested scales, suggesting separate processes operating simultaneously within the stream network and surrounding terrestrial landscape. Expected patterns of spatial dependence for flow-connected relationships (e.g., increasing homogeneity with downstream distance) occurred for some chemical constituents (e.g., dissolved organic carbon, sulfate, and aluminum) but not for others (e.g., nitrate, sodium). By comparing semivariograms for the different chemical constituents and spatial relationships, we were able to separate effects on streamwater chemistry of (i) fine-scale versus broad-scale processes and (ii) in-stream processes versus landscape controls. These findings provide insight on the hierarchical scaling of local, longitudinal, and landscape processes that drive biogeochemical patterns in stream networks.
authors.affiliation: Virginia Water Resources Research Center and Department of Forest Resources and Environmental Conservation, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061; kevin.mcguire@vt.edu likensg@ecostudies.org.
authors.forename: Kevin J
authors.identifier: http://orcid.org/0000-0001-5751-3956
authors.initials: KJ
authors.lastname: McGuire
authors.affiliation: US Geological Survey, Forest and Rangeland Ecosystem Science Center, Cascadia Field Station, and School of Environmental and Forest Sciences, University of Washington, Seattle, WA 98195;
authors.forename: Christian E
authors.initials: CE
authors.lastname: Torgersen
authors.affiliation: Cary Institute of Ecosystem Studies, Millbrook, NY 12545;Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT 06269; kevin.mcguire@vt.edu likensg@ecostudies.org.
authors.forename: Gene E
authors.initials: GE
authors.lastname: Likens
authors.affiliation: Cary Institute of Ecosystem Studies, Hubbard Brook Forest Station, North Woodstock, NH 03262;
authors.forename: Donald C
authors.initials: DC
authors.lastname: Buso
authors.affiliation: Division of Biological Sciences, University of Montana, Missoula, MT 59812; and.
authors.forename: Winsor H
authors.initials: WH
authors.lastname: Lowe
authors.affiliation: US Forest Service, Northern Research Station, Hubbard Brook Experimental Forest, North Woodstock, NH 03262.
authors.forename: Scott W
authors.initials: SW
authors.lastname: Bailey
mesh_terms: D002244:Carbon / Q000032:analysis; D002947:Cities; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods*; D005618:Fresh Water / Q000737:chemistry; D006801:Humans; D008962:Models, Theoretical; D045483:Rivers / Q000737:chemistry*; D012822:Silicon Dioxide / Q000032:analysis; D012964:Sodium / Q000032:analysis
chemical_list: D002244:Carbon; D012822:Silicon Dioxide; D012964:Sodium
keywords: autocorrelation; biogeochemistry; heterogeneity; hydrologic connectivity; watershed
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