High-frequency nutrient monitoring to infer seasonal patterns in catchment source availability, mobilisation and delivery

Abstract

S. (2017). High-frequency monitoring of catchment nutrient exports reveals highly variable storm event responses and dynamic source zone activation. Abstract Storm events can drive highly variable behavior in catchment nutrient and water fluxes, yet short-term event dynamics are frequently missed by low-resolution sampling regimes. In addition, nutrient source zone contributions can vary significantly within and between storm events. Our inability to identify and characterize time-dynamic source zone contributions severely hampers the adequate design of land use management practices in order to control nutrient exports from agricultural landscapes. Here we utilize an 8 month high-frequency (hourly) time series of streamflow, nitrate (NO 3-N), dissolved organic carbon (DOC), and hydroclimatic variables for a headwater agricultural catchment. We identified 29 distinct storm events across the monitoring period. These events represented 31% of the time series and contributed disproportionately to nutrient loads (42% of NO 3-N and 43% of DOC) relative to their duration. Regression analysis identified a small subset of hydroclimatological variables (notably precipitation intensity and antecedent conditions) as key drivers of nutrient dynamics during storm events. Hysteresis analysis of nutrient concentration-discharge relationships highlighted the dynamic activation of discrete NO 3-N and DOC source zones, which varied on an event-specific basis. Our results highlight the benefits of high-frequency in situ monitoring for characterizing short-term nutrient fluxes and unraveling connections between hydroclimatological variability and river nutrient export and source zone activation under extreme flow conditions. These new process-based insights, which we summarize in a conceptual model, are fundamental to underpinning targeted management measures to reduce nutrient loading of surface waters.

Continuous nutrient observations capture fine-scale estuarine variability simulated by a 3D biogeochemical model

“…Our experiences were comparable to those reported by Bende-Michl et al (2013) who operated a similar system in the Duck River, northern Tasmania, for 2 years. In both rivers, nutrient data showed a seasonal decline in concentration from spring to summer attributed to in-stream assimilation.…”

Nutrient Dynamics of the Delta: Effects on Primary Producers

“…Collection of nutrient data at frequent intervals in aquatic systems has in almost all cases revealed much higher temporal variability than was evident in less frequent discrete sample collection (Bende-Michl et al 2013;Pellerin et al 2009Pellerin et al , 2011Pellerin et al , 2014Wild-Allen and Rayner 2014). These data also revealed patterns in nutrient dynamics that occur at yearly, seasonal, diurnal, tidal, and individual-event time-scales, which are difficult if not impossible to detect using lowerresolution data (Bende-Michl et al 2013;Bowes et al 2009;Cohen et al 2012Cohen et al , 2013Pellerin et al 2009Pellerin et al , 2011Pellerin et al , 2014Wild-Allen and Rayner 2014).…”

“…We are aware of few studies that report results from in situ high-frequency ammonium analyzers, and-not surprisingly-these studies found that ammonium, nitrate, and phosphate variability are not necessarily linked (Bende-Michl et al 2013;Gilbert et al 2013). Although there are no published studies from the Delta using in situ measurements of ammonium and phosphate, data collected by the USGS on the Sacramento River at Walnut Grove demonstrates their variability and the complex relationship they share with nitrate ( Figure 11).…”

“…Although most high-frequency nutrient studies to date involve nitrate sensors, adoption of commercially available in situ analyzers for phosphate and prototype sensors for ammonium is growing (Rozemeijer et al 2010;Cassidy and Jordan 2011;Bende-Michl et al 2013;Cohen et al 2013;Gilbert et al 2013;Outram et al 2014;Bowes et al 2015). We are aware of few studies that report results from in situ high-frequency ammonium analyzers, and-not surprisingly-these studies found that ammonium, nitrate, and phosphate variability are not necessarily linked (Bende-Michl et al 2013;Gilbert et al 2013).…”

Statistical analysis of the influence of major tributaries to the eco-chemical status of the Danube River

“…Analysis of variance (ANOVA) and the other tests that we have chosen are not very demanding in this matter (Lloyd et al 2014) because they do not require data with very high resolution such as data produced by continual monitoring. Highly frequent measurements can be very important for proper exploration of dynamics and patterns which is well illustrated in the research of the nutrients preformed by Bende-Michl et al (2013).…”