scholarly journals Modeling Nitrate Export from a Mesoscale Catchment Using StorAge Selection Functions

2020 ◽  
Author(s):  
Tam V. Nguyen ◽  
Rohini Kumar ◽  
Stefanie R. Lutz ◽  
Andreas Musolff ◽  
Jie Yang ◽  
...  
Keyword(s):  
Nitrate Export

scholarly journals Disparate Seasonal Nitrate Export from Nested Heterogeneous Subcatchments Revealed with StorAge Selection Functions

2021 ◽  
Author(s):  
Tam Van Nguyen ◽  
Rohini Kumar ◽  
Andreas Musolff ◽  
Stefanie Rayana Lutz ◽  
Fanny Sarrazin ◽  
...  
Keyword(s):  
Nitrate Export

scholarly journals Active layer slope disturbances affect seasonality and composition of dissolved nitrogen export from High Arctic headwater catchments

2017 ◽  
Vol 3 (2) ◽  
pp. 429-450 ◽  
Author(s):  
Melissa J. Lafrenière ◽  
Nicole L. Louiseize ◽  
Scott F. Lamoureux
Keyword(s):  
Active Layer ◽  
High Arctic ◽  
Rainfall Runoff ◽  
Headwater Catchments ◽  
Dissolved Nitrogen ◽  
Total Dissolved Nitrogen ◽  
Nitrate Export ◽  
Limiting Nutrient ◽  
Seasonal Discharge ◽  
The Impact

This study investigates the impacts of active layer detachments (ALDs) on nitrogen in seasonal runoff from High Arctic hillslope catchments. We examined dissolved nitrogen in runoff from an undisturbed catchment (Goose (GS)) and one that was disturbed (Ptarmigan (PT)) by ALDs, prior to disturbance (2007) and 5 years after disturbance (2012). The seasonal dynamics of nitrogen species concentrations and fluxes were similar in both catchments in 2007, but the mean seasonal nitrate concentration and mass flux from the disturbed catchment were on the order of 30 times higher relative to the undisturbed catchment in 2012. Stormflow yielded 45% and 60% of the 2012 total dissolved nitrogen flux in GS and PT, respectively, although rainfall runoff provided less than 25% of seasonal discharge. Results support that through the combined effects of increased disturbance and rainfall, climate change stands to significantly enhance the export of nitrate from High Arctic watersheds. This study highlights that the increase in the delivery of nitrate from disturbance is especially pronounced late in the season when downstream productivity and the biological demand for this often limiting nutrient are high. Our results also demonstrate that the impact of ALDs on nitrate export can persist more than 5 years following disturbance.

scholarly journals Changes in discharge and solute dynamics between hillslope and valley-bottom intermittent streams

2012 ◽  
Vol 16 (6) ◽  
pp. 1595-1605 ◽  
Author(s):  
S. Bernal ◽  
F. Sabater
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Stream Water ◽  
Valley Bottom ◽  
Solute Fluxes ◽  
Nitrate Export ◽  
Carbon And Nitrogen Dynamics ◽  
Reactive Solutes ◽  
Monthly Discharge ◽  
Solute Dynamics

Abstract. To gain understanding on how alluvial zones modify water and nutrient export from semiarid catchments, we compared monthly discharge as well as stream chloride, carbon, and nitrogen dynamics between a hillslope catchment and a valley-bottom catchment with a well-developed alluvium. Stream water and solute fluxes from the hillslope and valley-bottom catchments showed contrasting patterns between hydrological transitions and wet periods, especially for bio-reactive solutes. During transition periods, stream water export decreased >40% between the hillslope and the valley bottom coinciding with the prevalence of stream-to-aquifer fluxes at the alluvial zone. In contrast, stream water export increased by 20–70% between the hillslope and valley-bottom catchments during wet periods. During transition periods, stream solute export decreased by 34–97% between the hillslope and valley-bottom catchments for chloride, nitrate, and dissolved organic carbon. In annual terms, stream nitrate export from the valley-bottom catchment (0.32 ± 0.12 kg N ha−1 yr−1 [average ± standard deviation]) was 30–50% lower than from the hillslope catchment (0.56 ± 0.32 kg N ha−1 yr−1). The annual export of dissolved organic carbon was similar between the two catchments (1.8 ± 1 kg C ha−1 yr−1). Our results suggest that hydrological retention in the alluvial zone contributed to reduce stream water and solute export from the valley-bottom catchment during hydrological transition periods when hydrological connectivity between the hillslope and the valley bottom was low.

scholarly journals Assessing winter cover crop nutrient uptake efficiency using a water quality simulation model

2014 ◽  
Vol 18 (12) ◽  
pp. 5239-5253 ◽  
Author(s):  
I.-Y. Yeo ◽  
S. Lee ◽  
A. M. Sadeghi ◽  
P. C. Beeson ◽  
W. D. Hively ◽  
...  
Keyword(s):  
Water Quality ◽  
Nitrate Leaching ◽  
Cover Crops ◽  
Cover Crop ◽  
Watershed Scale ◽  
Source Areas ◽  
Winter Cover Crop ◽  
Nitrate Export ◽  
Winter Cover ◽  
Winter Cover Crops

Abstract. Winter cover crops are an effective conservation management practice with potential to improve water quality. Throughout the Chesapeake Bay watershed (CBW), which is located in the mid-Atlantic US, winter cover crop use has been emphasized, and federal and state cost-share programs are available to farmers to subsidize the cost of cover crop establishment. The objective of this study was to assess the long-term effect of planting winter cover crops to improve water quality at the watershed scale (~ 50 km2) and to identify critical source areas of high nitrate export. A physically based watershed simulation model, Soil and Water Assessment Tool (SWAT), was calibrated and validated using water quality monitoring data to simulate hydrological processes and agricultural nutrient cycling over the period of 1990–2000. To accurately simulate winter cover crop biomass in relation to growing conditions, a new approach was developed to further calibrate plant growth parameters that control the leaf area development curve using multitemporal satellite-based measurements of species-specific winter cover crop performance. Multiple SWAT scenarios were developed to obtain baseline information on nitrate loading without winter cover crops and to investigate how nitrate loading could change under different winter cover crop planting scenarios, including different species, planting dates, and implementation areas. The simulation results indicate that winter cover crops have a negligible impact on the water budget but significantly reduce nitrate leaching to groundwater and delivery to the waterways. Without winter cover crops, annual nitrate loading from agricultural lands was approximately 14 kg ha−1, but decreased to 4.6–10.1 kg ha−1 with cover crops resulting in a reduction rate of 27–67% at the watershed scale. Rye was the most effective species, with a potential to reduce nitrate leaching by up to 93% with early planting at the field scale. Early planting of cover crops (~ 30 days of additional growing days) was crucial, as it lowered nitrate export by an additional ~ 2 kg ha−1 when compared to late planting scenarios. The effectiveness of cover cropping increased with increasing extent of cover crop implementation. Agricultural fields with well-drained soils and those that were more frequently used to grow corn had a higher potential for nitrate leaching and export to the waterways. This study supports the effective implementation of cover crop programs, in part by helping to target critical pollution source areas for cover crop implementation.

Disentangling the impact of catchment heterogeneity in a meso-scale catchment on nitrate export dynamics across time scales

2020 ◽  
Author(s):  
Carolin Winter ◽  
Stefanie Lutz ◽  
Andreas Musolff ◽  
Michael Weber ◽  
Jan H. Fleckenstein
Keyword(s):  
Time Scales ◽  
Delayed Response ◽  
Nitrogen Surplus ◽  
Retention Capacity ◽  
Transit Times ◽  
Nitrate Concentrations ◽  
Nitrate Export ◽  
Shallow Soils ◽  
The Impact

<p>High nitrate concentrations in groundwater and surface water are a long-known but still widespread problem. To most efficiently reduce nitrate pollution, a detailed understanding of catchment organization and the catchment internal processes that drive nitrate mobilization, transport and storage across time scales is needed. Especially in mesoscale catchments (10<sup>1</sup> – 10³ km²), spatial heterogeneity adds another layer of complexity to these processes compared to headwater catchments. To address this issue, we analyzed seasonal long-term trends (1983 – 2016) and high frequency event dynamics (2010 – 2016) of nitrate concentrations, loads and the concentration-discharge relationship (CQ-slope) in three nested catchments within the Selke catchment (Germany). Transit time distributions (TTDs) were calculated for each nested catchment to analyze the response of nitrate export to changes in nitrogen surplus. The upper part of the Selke catchment is dominated by forests with only little agriculture and an overall lower nitrogen surplus, while the lower Selke is dominated by agriculture and a higher nitrogen surplus. Surprisingly, we found a disproportionally high contribution to nitrate loads from the forest-dominated upper Selke (64% of average annual load at the Selke outlet), caused by high nitrate concentrations during wet seasons ( average of 2.5 mg-N L<sup>-1</sup> during winter and spring) while dry season nitrate concentrations are relatively low (average of 1.1 mg-N L<sup>-1</sup> during summer and autumn). These seasonally high concentrations can be explained by the sub-catchment characteristics such as shallow soils and steeper slopes that lead to a low retention capacity and short effective transit times (peak of TTD after 2 years, indicating a fast response to changes in nitrogen surplus). The increase of nitrate concentrations with discharge resulted in a positive CQ-slope that was consistently observed in long-term dynamics and during events. In the lower Selke, nitrate concentrations are relatively constant across seasons (around 3.1 mg-N L<sup>-1</sup>). This dynamic is caused by deeper aquifers, long effective transit times (peak of TTD at the Selke outlet after 14 years, indicating a delayed response to changes in nitrogen surplus) and legacy stores of nitrate that constantly release into the Selke River. Consequently, the lower Selke dominates nitrate concentrations and loads exported during dry seasons and is characterized by lower CQ-slopes compared to the upper Selke. Our study shows that the contribution of different sub-catchments to elevated nitrate concentrations can vary greatly between seasons, flow conditions and in their response to changes in nitrogen surplus. It is, therefore, not enough to focus on areas of highest nitrogen surplus – such as the upper Selke; instead, an assessment of all characteristic sub-catchments, their temporally variable contribution to nitrate export and their specific TTDs is needed to place reduction measures most effectively and to estimate realistic time scales for their success.</p>

Modeling Nitrate Export at the Catchment Scale using StorAge Selection Functions

2020 ◽  
Author(s):  
Tam Nguyen ◽  
Rohini Kumar ◽  
Stefanie R. Lutz ◽  
Andreas Musolff ◽  
Jan H. Fleckenstein
Keyword(s):  
Time Distribution ◽  
Root Zone ◽  
Hydrologic Model ◽  
Distributed Model ◽  
Nitrate Transport ◽  
Catchment Scale ◽  
Near Surface ◽  
Soil Zone ◽  
Different Ages ◽  
Nitrate Export

<p>Catchments store and release water of different ages. The time of a water parcel remaining in contact with the catchment subsurface affects the solute dynamics in the catchment and ultimately in the stream. Catchment storage can be conceptualized as a collection of different water parcels with different ages, the so-called residence time distribution (RTD). Similarly, the distribution of water ages in streamflow at the catchment outlet, which is sampled from the RTD, is called the travel time distribution (TTD). The selection preferences for discharge can be characterized by StorAge selection (SAS) functions. In recent years, numerical experiments have shown that SAS functions are time-variant and can be approximated, for example, by the beta distribution function. SAS functions have been emerging as a promising tool for modeling catchment-scale solute export.</p><p>In this study, we aim to integrate the SAS-based description of nitrate transport with the mHM-Nitrate model (Yang et al., 2018) to simulate solute transport and turnover above and below the soil zone including legacy effects. The mHM-Nitrate is a grid based distributed model with the hydrological concept taken from the mesoscale Hydrologic Model (mHM) and the water quality concept taken from the HYdrological Predictions for the Environment (HYPE) model. Here, we replaced the description of nitrate transport in groundwater from the original mHM-Nitrate with time-variant SAS-based modeling, while we kept the detailed description of turnover of organic and inorganic nitrogen in the near-surface (root zone) from mHM-Nitrate. First-order decay was used to represent biogeochemical (denitrification) processes below the root zone and in the stream. The proposed model was tested in a mixed agricultural-forested headwater catchment in the Harz Mountains, Germany. Results show that the proposed SAS augmented nitrate model (with the time-variant beta function) is able to represent streamflow and catchment nitrate export with satisfactory results (NSE for streamflow = 0.83 and for nitrate = 0.5 at the daily time step). Overall, our combined model provides a new approach for a spatially distributed simulation of nitrogen reaction processes in the soil zone and a spatially implicit simulation of transport pathways of nitrate and denitrification in the entire catchment.</p><p><span>Yang, X.</span>, <span>Jomaa, S.</span>, <span>Zink, M.</span>, <span>Fleckenstein, J. H.</span>, <span>Borchardt, D.</span>, & <span>Rode, M.</span> ( <span>2018</span>). <span>A new fully distributed model of nitrate transport and removal at catchment scale</span>. <em>Water Resources Research</em>, <span>54</span>, <span>5856</span>– <span>5877</span>.</p>

Insect defoliation enhances nitrate export from forest ecosystems

Oecologia ◽  
1981 ◽  
Vol 51 (3) ◽  
pp. 297-299 ◽  
Author(s):  
W. T. Swank ◽  
J. B. Waide ◽  
D. A. Crossley ◽  
R. L. Todd
Keyword(s):  
Forest Ecosystems ◽  
Insect Defoliation ◽  
Nitrate Export
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