Nutrient dynamics in an oligotrophic arctic stream monitored in situ by wet chemistry methods

Abstract

Diurnal trends in hydrochemical components of stream and river water, especially nutrients, is growing in interest as instrumentation capable of measuring at fine time scales becomes increasingly available. In this growing body of work, there are few studies that simultaneously report the dynamics of the major nutrients nitrate, phosphate, and ammonium through time. We used an in situ nutrient autoanalyzer to simultaneously measure nitrate, phosphate, and ammonium concentrations with wet chemistry methods in an arctic headwater stream. We operated the analyzer under two sampling regimes: (1) time interval (hourly) sampling to examine fine time scale nutrient dynamics and (2) continuous sampling (1 s data) to evaluate nutrient uptake from a pulse solute addition experiment. Hourly sampling showed inverse diurnal oscillating trends of nitrate and ammonium concentrations for several days during base flow conditions. We propose that this trend is a result of in-stream nutrient processing (autotrophic demand and nitrification) combined with increased lateral inputs of water from the active (thawed) soil layer at night, after evapotranspiration (ET) has ceased. Pulse additions of ammonium resulted in rapid increases in nitrate concentration, confirming potential magnitude of nitrification in this system. Phosphate concentrations were usually at or below detection limits, consistent with results from previous manual sampling of this stream. We conclude that as studies examining fine time scale nutrient trends in streams and rivers increase, the ability to examine the behavior of multiple nutrients simultaneously will be pertinent to assess the underlying mechanisms driving those trends.

Seasonal patterns of soil nitrogen availability in moist acidic tundra

“…However, McNamara et al (2008) reported increases in North Slope Alaska stream NO 3 − in early fall in some, but not all, years, with similar seasonal timing as our reported decrease in soil NO 3 − . Water sampled from the outlet of Toolik Lake continuously into early September in 2006 did not show a similar peak in NO 3 − (Snyder and Bowden 2014), although in 2011, local stream NO 3 − increased in mid-September (W.B. Bowden, personal communication), coinciding with the described decrease in soil NO 3 − in this study.…”

Seasonality of dissolved nitrogen from spring melt to fall freezeup in Alaskan Arctic tundra and mountain streams

“…As previously mentioned, the small size of the Imnavait watershed limits the time that waters are subjected to instream photochemical and microbial processing compared to the other study sites. Reduced channelized water transit times likely limit potential instream nitrification of available NH 4 + [ Wollheim et al ., ; Snyder and Bowden , ]. As such, we would expect NO 3 − concentrations to increase and NH 4 + concentrations to decrease further downstream from our Imnavait sampling locating, consistent with the patterns observed at the other larger study sites.…”

“…Photooxidation may account for 70-95% of total DOC processed in the water column of lakes and rivers in the region [Cory et al, 2013;Cory et al, 2014]. Similarly, photoammonification of DON [Bushaw et al, 1996;Grzybowski, 2002;Sereda et al, 2012], followed by immobilization or nitrification [Peterson et al, 1997;Wollheim et al, 2001;Snyder and Bowden, 2014], may be an important DON loss mechanism in these systems. Moreover, partial photooxidation stimulates microbial remineralization of otherwise recalcitrant DOC [Cory et al, 2014], and may promote additional DON microbial remineralization postsnowmelt as well.…”

Emerging Tools for Continuous Nutrient Monitoring Networks: Sensors Advancing Science and Water Resources Protection

“…At the watershed-scale, continuous nitrate monitoring is proving useful for both calculating nutrient loading to downstream waters (Pellerin et al, 2014), as well as understanding the drivers of changes in water quality (Hensley et al, 2014). High frequency measurements are also critical to adequately characterize the variability in surface water nitrate and orthophosphate concentrations at some sites, especially during hydrologic events (Pellerin et al, 2012;Bende-Michl et al, 2013;Ferrant et al, 2013;Carey et al, 2014;Outram et al, 2014;Bowes et al, 2015;Sherson et al, 2015) and during periods when instream biological processing or other factors produce, consume, or alter nutrients prior to downstream export (Pellerin et al, 2009;Heffernan and Cohen, 2010;Cohen et al, 2013;Hensley et al, 2014;Snyder and Bowden, 2014). For example, diurnal nitrate patterns similar to those observed in the Potomac River (Figure 2) have been used to estimate rates and drivers of primary productivity in both freshwater (Heffernan and Cohen, 2010;Cohen et al, 2013) and coastal environments (Johnson et al, 2006;Collins et al, 2013).…”