Colloids and organic matter complexation control trace metal concentration-discharge relationships in Marshall Gulch stream waters

Kyle D. Trostle, J. Ray Runyon, Michael A. Pohlmann, Shelby E. Redfield, Jon Pelletier, Jennifer McIntosh, Jon Chorover

Research output: Contribution to journalArticlepeer-review

21 Scopus citations

Abstract

This study combined concentration-discharge analyses (filtration at 0.45 μm), cascade filtrations (at 1.2, 0.4, and 0.025 μm) and asymmetrical flow field flow fractionation (AF4) to probe the influence of colloidal carriers (dissolved organic matter and inorganic nanoparticles) on observed concentration-discharge relationships for trace metals in a 155 ha forested catchment of the Santa Catalina Mountains Critical Zone Observatory (SCM CZO), Arizona. Many major elements (Na, Mg, Si, K, Ca) show no colloidal influence, and concentration-discharge relationships for these species are explained by previous work. However, the majority of trace metals (Al, Ti, V, Mn, Fe, Cu, Y, REE, U) show at least some influence of colloids on chemistry when filtered at the standard 0.45 μm cutoff. Concentration-discharge slopes of trace metals with modest colloidal influence are shallow (∼0.3) similar to that measured for dissolved organic carbon (DOC, 0.24), whereas elements with greater colloidal influence have steeper concentration-discharge slopes approaching that of Al (0.76), the element with the largest colloidal influence in this study (on average 68%). These findings are further supported by AF4 measurements that show distinct and resolvable pools of low hydrodynamic diameter DOC-sized material coexistent with larger diameter inorganic colloids, and the ratio of these carriers changes systematically with discharge because the DOC pool has a concentration-discharge relationship with shallower slope than the inorganic colloidal pool. Together these data sets illustrate that positive concentration-discharge slopes of trace metals in stream waters may be explained as the relative partitioning of trace metals between DOC and inorganic colloids, with contributions of the latter likely increasing as a result of increased prevalence of macropore flow.

Original languageEnglish (US)
Pages (from-to)7931-7944
Number of pages14
JournalWater Resources Research
Volume52
Issue number10
DOIs
StatePublished - Oct 1 2016

Keywords

  • C-Q relationships
  • DOC complexation
  • colloids
  • trace metals

ASJC Scopus subject areas

  • Water Science and Technology

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