Disentangling the influence of hydroclimatic patterns and agricultural management on river nitrate dynamics from sub-hourly to decadal time scales

Dupas, Rémi; Jomaa, Seifeddine; Musolff, Andreas; Borchardt, Dietrich; Rode, Michael

doi:10.1016/j.scitotenv.2016.07.053

Cited by 113 publications

(144 citation statements)

References 64 publications

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“…6). In addition to this lateral differentiation of NO − 3 , DOC and SRP sources, a vertical distribution has previously been observed (e.g., Musolff et al, 2016a) or hypothesized (e.g., Dupas et al, 2016b) for NO − 3 , with higher NO − 3 concentrations in the uppermost soil layers compared to deeper soil layers, leading to higher NO − 3 concentrations in the stream during the wet season due to activation of shallow flow pathways. The hypothesis of a vertical differentiation of concentrations controlling seasonal variations in concentrations cannot apply to DOC and SRP because these two elements are also expected to be present in higher concentrations in the uppermost soil layers and this should therefore lead to seasonal DOC and SRP variations similar to NO − 3 .…”

Section: Land-to-stream Transfermentioning

confidence: 58%

“…In contrast to DOC and SRP, NO − 3 storm dynamics exhibited a majority of dilution patterns in LS-Agr and a combination of dilution and accretion pattern in US-Agr. This suggests that soil NO − 3 concentrations in LS-Agr were lower than in the subsoil, due to plant uptake in the soil and presence of legacy NO − 3 in the subsoil of LS-Agr (Outram et al, 2016), whereas soil NO − 3 concentrations in US-Agr could be lower or higher than in the subsoil according to seasonal variability in soil NO − 3 availability and possibility lateral difference between non-cultivated riparian soils and cultivated upslope soils (Dupas et al, 2016b). Therefore, both lateral and vertical gradients of N sources can explain variability in NO − 3 storm responses.…”

Section: Land-to-stream Transfermentioning

confidence: 99%

“…Second, to quantify the overall variability of discharge (daily) and concentration data (grab sampling), the coefficients of variation (CV) for both discharge and concentrations were calculated for each study catchment and for each year. The coefficient of variation, defined as the ratio of the standard deviation to the mean of a variable, has been used for the same purpose in previous water quantity (Botter et al, 2013) and water quality studies (Dupas et al, 2016b;Musolff et al, 2015;Thompson et al, 2011). Finally, correlation coefficients were calculated between solute concentrations and discharge and between pairs of solute concentrations.…”

Section: Discharge and Concentration Variabilitymentioning

confidence: 99%

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Carbon and nutrient export regimes from headwater catchments to downstream reaches

et al. 2017

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Abstract. Excessive amounts of nutrients and dissolved organic matter in freshwater bodies affect aquatic ecosystems. In this study, the spatial and temporal variability in nitrate (NO − 3 ), dissolved organic carbon (DOC) and soluble reactive phosphorus (SRP) was analyzed in the Selke (Germany) river continuum from three headwaters draining 1-3 km 2 catchments to two downstream reaches representing spatially integrated signals from 184-456 km 2 catchments. Three headwater catchments were selected as archetypes of the main landscape units (land use × lithology) present in the Selke catchment. Export regimes in headwater catchments were interpreted in terms of NO − 3 , DOC and SRP land-to-stream transfer processes. Headwater signals were subtracted from downstream signals, with the differences interpreted in terms of in-stream processes and contributions from point sources. The seasonal dynamics for NO − 3 were opposite those of DOC and SRP in all three headwater catchments, and spatial differences also showed NO − 3 contrasting with DOC and SRP. These dynamics were interpreted as the result of the interplay of hydrological and biogeochemical processes, for which riparian zones were hypothesized to play a determining role. In the two downstream reaches, NO − 3 was transported almost conservatively, whereas DOC was consumed and produced in the upper and lower river sections, respectively. The natural export regime of SRP in the three headwater catchments mimicked a point-source signal (high SRP during summer low flow), which may lead to overestimation of domestic contributions in the downstream reaches. Monitoring the river continuum from headwaters to downstream reaches proved effective to jointly investigate land-to-stream and instream transport, and transformation processes.

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Section: Land-to-stream Transfermentioning

confidence: 58%

Section: Land-to-stream Transfermentioning

confidence: 99%

Section: Discharge and Concentration Variabilitymentioning

confidence: 99%

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Carbon and nutrient export regimes from headwater catchments to downstream reaches

et al. 2017

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“…Responses of NO 3 -N and DOC concentration dynamics varied between nutrients and between storm events (as discussed in more detail below). NO 3 -N concentrations were typically diluted on the rising limbs of storm hydrographs, most likely due to the rapid delivery of relatively low-concentration water transferred to the stream channel from near-surface soil flow paths in the early stages of each event [Outram et al, 2014;Dupas et al, 2016], whereas patterns in DOC concentrations generally exhibited flushing behavior through storm events. In contrast to the relatively high variability between NO 3 -N and DOC …”

Section: Temporal Dynamics Of Streamflow No 3 -N and Docmentioning

confidence: 99%

High‐frequency monitoring of catchment nutrient exports reveals highly variable storm event responses and dynamic source zone activation

et al. 2017

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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 (NO3‐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 NO3‐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 NO3‐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.

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“…[3]):

L = \frac{K \sum_{i = 1}^{n} C_{i} Q_{i}}{\sum_{i = 1}^{n} Q_{i}} Q_{r}

where C i and Q i are instantaneous high‐frequency concentration and discharge data, L is the load estimate, Q r is the average flow discharge based on the long‐term data, K is a unit conversion factor, and n is the number of concentration measurements. Storm events were detected from 15‐min flow data and defined as events with an increase in discharge of at least 0.2 m 3 s −1 and a decrease in discharge of at least 50% after the peak discharge (Bieroza and Heathwaite, 2015; Dupas et al, 2016). …”

Section: Methodsmentioning

confidence: 99%

Hydrologic Extremes and Legacy Sources Can Override Efforts to Mitigate Nutrient and Sediment Losses at the Catchment Scale

et al. 2019

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Combating eutrophication requires changes in land and water management in agricultural catchments and implementation of mitigation measures to reduce phosphorus (P), nitrogen (N) and suspended sediment (SS) losses. To date, such mitigation measures have been built in many agricultural catchments, but there is a lack of studies evaluating their effectiveness. Here we evaluated the effectiveness of mitigation measures in a clay soil‐dominated headwater catchment by combining the evaluation of long‐term and high‐frequency data with punctual measurements upstream and downstream of three mitigation measures: lime‐filter drains, a two‐stage ditch, and a sedimentation pond. Long‐term hydrochemical data at the catchment outlet showed a significant decrease in P (−15%) and SS (−28%) and an increase in nitrate nitrogen (NO3–N, +13%) concentrations. High‐frequency (hourly) measurements with a wet‐chemistry analyzer (total and reactive P) and optical sensor (NO3–N and SS) showed that the catchment is an abundant source of nutrients and sediments and that their transport is exacerbated by prolonged drought and resuspension of stream sediments during storm events. Lime‐filter drains showed a decrease in SS by 76% and total P by 80% and an increase in NO3–N by 45% compared with traditional drains, potentially indicating pollution swapping. The effectiveness of two‐stage ditch and sedimentation pond was less evident and depended on the prevalent hydrometeorological conditions that drove the resuspension of bed sediments and associated sediment‐bound P transport. These results suggest that increased frequency of prolonged drought due to changing weather patterns and resuspension of SS and sediment‐bound P during storm events can override the generally positive effect of mitigation measures. Core Ideas We assessed the efficiency of catchment mitigation measures to reduce water pollution. At the catchment outlet, concentrations of P and sediments decreased by 15 and 28%. Lime‐filter drains reduced P and sediments by 80% but increased nitrate by 45%. Prolonged drought and resuspension of sediments exacerbated stream nutrient export. High‐frequency data show that legacy sources can override mitigation efforts.

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Disentangling the influence of hydroclimatic patterns and agricultural management on river nitrate dynamics from sub-hourly to decadal time scales

Cited by 113 publications

References 64 publications

Carbon and nutrient export regimes from headwater catchments to downstream reaches

Carbon and nutrient export regimes from headwater catchments to downstream reaches

High‐frequency monitoring of catchment nutrient exports reveals highly variable storm event responses and dynamic source zone activation

Hydrologic Extremes and Legacy Sources Can Override Efforts to Mitigate Nutrient and Sediment Losses at the Catchment Scale

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