Deconstructing the Effects of Flow on DOC, Nitrate, and Major Ion Interactions Using a High‐Frequency Aquatic Sensor Network

Abstract

Streams provide a physical linkage between land and downstream river networks, delivering solutes derived from multiple catchment sources. We analyzed high‐frequency time series of stream solutes to characterize the timing and magnitude of major ion, nutrient, and organic matter transport over event, seasonal, and annual timescales as well as to assess whether nitrate ( NO3−) and dissolved organic carbon (DOC) transport are coupled in catchments, which would be expected if they are subject to similar biogeochemical controls throughout the watershed. Our data set includes in situ observations of NO3−, fluorescent dissolved organic matter (DOC proxy), and specific conductance spanning 2–4 years in 10 streams and rivers across New Hampshire, including observations of nearly 700 individual hydrologic events. We found a positive response of NO3− and DOC to flow in forested streams, but watershed development led to a negative relationship between NO3− and discharge, and thus a decoupling of the overall NO3− and DOC responses to flow. On event and seasonal timescales, NO3− and DOC consistently displayed different behaviors. For example, in several streams, FDOM yield was greatest during summer storms while NO3− yield was greatest during winter storms. Most streams had generalizable storm NO3− and DOC responses, but differences in the timing of NO3− and DOC transport suggest different catchment sources. Further, certain events, including rain‐on‐snow and summer storms following dry antecedent conditions, yielded disproportionate NO3− responses. High‐frequency data allow for increased understanding of the processes controlling solute variability and will help reveal their responses to changing climatic regimes.

Effects of instream processes, discharge, and land cover on nitrogen export from southern Appalachian Mountain catchments

“…DIN concentration changes during storms were highly variable (Figure S2), which is consistent with other studies showing that the relationship between nitrate or DIN and discharge varies both temporarily and spatially (e.g., Carey et al, ; Jiang et al, ; Lloyd, Freer, Johnes, & Collins, ; Shields et al, ). The stream with the highest DIN concentration, Crawford Branch, frequently exhibited dilution, which is typical of solutes in many urban and suburban streams (e.g., Barco et al, ; Koenig, Shattuck, Snyder, Potter, & McDowell, ; Rose, ; Shields et al, ). The streams with the lowest DIN concentration (Ball Creek and Ray Branch) had the most complex patterns, probably because there was little difference between baseflow and stormflow DIN concentrations in these streams.…”

“…In most streams, both DIN concentration and discharge were low in fall. This was also observed in several forested streams studied by Koenig et al () and probably results from high instream uptake just after leaf fall and typically low fall discharge. If we do not consider the data from this time of year, then the relationship between DIN concentration and discharge for the most forested catchments (Ball Creek and Ray Branch) is essentially chemostatic for both baseflow and storms.…”

Monitoring the riverine pulse: Applying high‐frequency nitrate data to advance integrative understanding of biogeochemical and hydrological processes

“…While clockwise hysteresis in NO 3 − concentrations is reported more frequently than anticlockwise hysteresis (Bowes et al, ; Duncan, Band, et al, ; Lloyd, Freer, Johnes, & Collins, ; Thomas, Abbott, Troccaz, Baudry, & Pinay, ; Vaughan et al, ), patterns can vary within the same watershed as governed by factors such as season, antecedent climatic conditions, and storm magnitude (Baker & Showers, ; Dupas et al, ; Eludoyin et al, ; Fovet et al, ). Rotational patterns also may vary among nearby sites, driven by differences in the presence of artificial drainage and point sources, land use, geology, and soil drainage properties (Bowes et al, ; Koenig, Shattuck, Snyder, Potter, & McDowell, ; Outram et al, ; Vaughan et al, ).…”

Downstream evolution of wastewater treatment plant nutrient signals using high‐temporal monitoring

“…Bowes et al (2015) used distinct patterns in hysteresis plots of nutrients and flow to characterize different sources of nutrients including remobilized bed sediments, WWTPs, and diffuse inputs. Koenig, Shattuck, Snyder, Potter, and McDowell (2017) Questions still remain about the relationship between nutrients and in-stream processing in anthropogenic systems. High-temporal sensors have been used to evaluate N patterns in agricultural streams, with low concentrations observed in the afternoon and high concentrations in the early morning due to higher assimilation during photosynthesis than denitrification at night (Jones, Kim, Wilton, Schilling, & Davis, 2018).…”