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Network analysis reveals multiscale controls on streamwater chemistry

Proceedings of the National Academy of Sciences

By:
, , , , , and
DOI: 10.1073/pnas.1404820111

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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.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Network analysis reveals multiscale controls on streamwater chemistry
Series title:
Proceedings of the National Academy of Sciences
DOI:
10.1073/pnas.1404820111
Volume
111
Issue:
19
Year Published:
2014
Language:
English
Publisher:
United States National Academy of Sciences
Contributing office(s):
Forest and Rangeland Ecosystem Science Center
Description:
6 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Proceedings of the National Academy of Sciences
First page:
7030
Last page:
7035
Number of Pages:
6