Shifts in the seasonality of riverine Si concentrations are driven by changing climate and hydrology

The seasonal behavior of fluvial dissolved silica (DSi) concentrations, termed DSi regime, mediates the timing of DSi delivery to downstream receiving waters and thus governs river biogeochemical function and the condition of aquatic communities. Previous work identified five distinct regimes identified across rivers spanning the Northern Hemisphere, with many rivers exhibiting multiple regimes over time. Several drivers of DSi regime behavior have been identified at small scales, including climate, land cover, and lithology, yet large scale spatiotemporal controls on DSi regimes remain unclear. Here, we evaluate the role of several environmental variables on the behavior of average and annual DSi regimes in over 200 rivers across North America. Our models were better able to predict annual DSi regime behavior (correctly classifying > 80% of regimes), compared to average regime behavior (correctly classifying > 55% of regimes). Climate, primary productivity, temperature, evapotranspiration, and discharge were important predictors of regime behavior. This presentation will focus on our investigation of shifting regime behavior over 18 years of record at 159 sites with long-term records. Many sites exhibited shifting regime membership over time, especially sites exibiting spring trough regimes. Together, these results indicate that DSi behavior is more strongly controlled by climate, ecosystem productivity, and hydrology than static watershed characteristics, and demonstrate that fluctuations in climate and hydrology may alter the temporal availability of DSi to rivers.

Primary Presenter: Keira Johnson, Oregon State University (johnkeir@oregonstate.edu)

Authors:

Keira Johnson, Oregon State University  (johnkeir@oregonstate.edu)

Joanna Carey, Babson College  (jcarey@babson.edu)

Kathi Jo Jankowski, USGS  (kjankowski@usgs.gov)

Lienne Sethna, Science Museum of Minnesota  (lsethna@smm.org)

Sidney Bush, Oregon State University  (bushsi@oregonstate.edu)

Diane McKnight, University of Colorado Boulder  (Diane.Mcknight@colorado.edu)

William McDowell, University of New Hampshire  (Bill.McDowell@unh.edu)

Adam Wymore, University of New Hampshire  (Adam.Wymore@unh.edu)

Pirkko Kortelainen, Finnish Environment Institute  (pirkko.kortelainen@syke.fi)

Jeremy Jones, University of Alaska Fairbanks  (jbjonesjr@alaska.edu)

Nicholas Lyon, National Center for Ecological Analysis and Synthesis  (lyon@nceas.ucsb.edu)

Hjalmar Laudon, Swedish University of Agricultural Sciences  (Hjalmar.Laudon@slu.se)

Amanda Poste, Norwegian Institute for Nature Research  (amanda.poste@nina.no)

Pamela Sullivan, Oregon State University  (Pamela.Sullivan@oregonstate.edu)