Network chemistry patterns in headwater streams – new paper published in PNAS

In a new article published this week in Proceedings of the National Academy of Sciences, we show how high-resolution mapping and analysis of water chemistry throughout a headwater stream network reveals unexpected patterns in how flowing water interacts with the surrounding landscape at multiple spatial scales.  Here’s the abstract and a link to the paper:

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 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- 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.

McGuire KJ, Torgersen CE, Likens GE, Buso DC, Lowe WH, Bailey SW. 2014. Network analysis reveals multiscale controls on streamwater chemistry. Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1404820111

More information on the study can be found here.

About

Dr. Kevin McGuire is an associate professor in the Department of Forest Resources and Environmental Conservation and the associate director for the Virginia Water Resources Research Center in the College of Natural Resources and Environment at Virginia Tech.

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