Declines in soil-water nitrate in nitrogen-saturated watersheds

2006 ◽  
Vol 36 (8) ◽  
pp. 1931-1942 ◽  
Author(s):  
Pamela J Edwards ◽  
Karl WJ Williard
Keyword(s):  
Organic Carbon ◽  
Soil Water ◽  
Nitrogen Saturation ◽  
Stream Water ◽  
Soil Leachate ◽  
Forested Watersheds ◽  
Central Appalachians ◽  
Soil Ecosystems ◽  
Nitrogen Inputs ◽  
Nitrate Concentrations

Two forested watersheds (WS3 and WS9) in the central Appalachians were artificially acidified with ammonium sulfate fertilizer. WS9 was treated for 8 years, whereas WS3 has been treated for approximately 15 years. Soil leachate was collected from a depth of 46 cm (B horizon) in WS9 and below the A, B, and C horizons in WS3. Nitrate concentrations from WS3 increased for approximately 10–12 years (depending upon horizon) and then did not increase from 2000 through 2003 despite continued fertilizer treatments. Nitrate concentrations in WS9 soil water increased for the first 3 years of fertilization, and then declined for another 2 years. After that time, the concentrations remained relatively constant at approximately 15 µequiv.·L–1; this period of low nitrate concentrations included 2.3 years of fertilization followed by 8.2 years of no fertilization. Stream-water nitrate concentrations from both watersheds indicate they were in stage 2 of nitrogen saturation; however, the soil-water nitrate behavior observed within the setting of continued elevated nitrogen inputs is at odds with responses predicted in current nitrogen saturation theory. We believe that the cessation of nitrate increases in at least the B and C horizons were due primarily to abiotic retention, with recalcitrant forms of dissolved organic carbon providing the carbon needed to induce retention. These results show that nitrogen cycling in forest soil ecosystems is more complex than current nitrogen saturation theory suggests.

Elucidating sources and pathways of dissolved organic carbon in a small, forested catchment – A qualitative assessment of stream, soil and shallow groundwater

2021 ◽  
Author(s):  
Katharina Blaurock ◽  
Phil Garthen ◽  
Benjamin S. Gilfedder ◽  
Jan H. Fleckenstein ◽  
Stefan Peiffer ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Soil Water ◽  
Riparian Zone ◽  
Stream Water ◽  
Shallow Groundwater ◽  
Drinking Water Treatment ◽  
Base Flow ◽  
Qualitative Assessment ◽  
Fluorescence Characteristics

<p>Dissolved organic carbon (DOC) constitutes the biggest portion of carbon that is exported from soils. During the last decades, widespread increases in DOC concentrations of surface waters have been observed, affecting ecosystem functioning and drinking water treatment. However, the hydrological controls on DOC mobilization are still not completely understood.</p><p>We sampled two different topographical positions within a headwater catchment in the Bavarian Forest National Park: at a steep hillslope (880 m.a.s.l.) and in a flat and wide riparian zone (770 m.a.s.l.). By using piezometers, pore water samplers (peepers) and in-stream spectrometric devices we measured DOC concentrations as well as DOC absorbance (A<sub>254</sub>/A<sub>365</sub> and SUVA<sub>254</sub>) and fluorescence characteristics (fluorescence and freshness indices) in soil water, shallow ground water and stream water in order to gain insights into the DOC source areas during base-flow and during precipitation events.</p><p>High DOC concentrations (up to 80 mg L<sup>-1</sup>) were found in soil water from cascading sequences of small ponds in the flat downstream part of the catchment that fill up temporarily. The increase of in-stream DOC concentrations during events was accompanied by changing DOC characteristics at both locations, for example increasing freshness index values. As the freshness index values were approaching the values found in the DOC-rich ponds in the riparian zone, these ponds seem to be important DOC sources during events. Our preliminary results point to a change of flow pathways during events.</p>

scholarly journals Regional Comparison of Nitrogen Export to Japanese Forest Streams

2001 ◽  
Vol 1 ◽  
pp. 572-580 ◽  
Author(s):  
Hideaki Shibata ◽  
Koichiro Kuraji ◽  
Hiroto Toda ◽  
Kaichiro Sasa
Keyword(s):  
Comparative Studies ◽  
N Mineralization ◽  
Surface Soil ◽  
Stream Water ◽  
N Deposition ◽  
N Saturation ◽  
Atmospheric N Deposition ◽  
Forested Watersheds ◽  
Nitrate Concentrations ◽  
Forest Streams

Nitrogen (N) emissions in Asian countries are predicted to increase over the next several decades. An understanding of the mechanisms that control temporal and spatial fluctuation of N export to forest streams is important not only to quantify critical loads of N, N saturation status, and soil acidification N dynamics and budgets in Japanese forested watersheds is not clear due to the lack of regional comparative studies on stream N chemistry. To address the lack of comparative studies, we measured inorganic N (nitrate and ammonium) concentrations from June 2000 to May 2001 in streams in 18 experimental forests located throughout the Japanese archipelago and belonging to the Japanese Union of University Forests. N concentrations in stream water during base flow and high flow periods were monitored, and N mineralization potential in soil was measured using batch incubation experiments. Higher nitrate concentrations in stream water were present in central Japan, an area that receives high rates of atmospheric N deposition. In northern Japan, snowmelt resulted in increased nitrate concentrations in stream water. The potential net N mineralization rate was higher in surface soil than in subsurface soil, and the high potential for N mineralization in the surface soil partly contributed to the increase in nitrate concentration in stream water during a storm event. Regional differences in the atmospheric N deposition and seasonality of precipitation and high discharge are principal controls on the concentrations and variations of nitrates in stream water in forested watersheds of Japan.

scholarly journals Effect on nitrate concentration in stream water of agricultural practices in small catchments in Brittany: II. Temporal variations and mixing processes

2002 ◽  
Vol 6 (3) ◽  
pp. 507-514 ◽  
Author(s):  
L. Ruiz ◽  
S. Abiven ◽  
C. Martin ◽  
P. Durand ◽  
V. Beaujouan ◽  
...  
Keyword(s):  
Land Use ◽  
Nitrate Concentration ◽  
Stream Water ◽  
Agricultural Practices ◽  
Temporal Variations ◽  
Base Flow ◽  
Seasonal Patterns ◽  
Annual Variations ◽  
Nitrogen Inputs ◽  
Nitrate Concentrations

Abstract. In catchments with impervious bedrock, the nitrate concentrations in streamwater often show marked seasonal and small inter-annual variations. The inter-annual trends are usually attributed to changes in nitrogen inputs, due to changes in land use or in nitrogen deposition whereas seasonal patterns are explained in terms of availability of soil nitrate for leaching and of seasonality of nitrogen biotransformations. The companion paper showed that inter-annual variations of nitrogen in streamwater are not directly related to the variations of land use. The aim of this study is to describe nitrate concentration variations in a set of very small adjacent catchments, and to discuss the origin of the inter-annual and seasonal trends. Data from four catchments at the Kerbernez site (South Western Brittany, France) were used in this study. Nitrate concentrations in streamwater were monitored for eight years (1992 to 1999) at the outlet of the catchments. They exhibit contrasting inter-annual and seasonal patterns. An extensive survey of agricultural practices during this period allowed assessment of the amount of nitrogen available for leaching. The discharges measured since 1997 show similar specific fluxes but very different seasonal dynamics between the catchments. A simple, lumped linear store model is proposed as an initial explanation of the differences in discharge and nitrate concentration patterns between the catchments. The base flow at the outlet of each catchment is considered as a mixture of water from two linear reservoirs with different time constants. Each reservoir comprises two water stores, one mobile contributing to discharge, the other, immobile, where nitrate moves only by diffusion. The storm flow, which accounts for less than 10% of the annual flux, is not considered here. Six parameters were adjusted for each catchment to fit the observed data: the proportion of deep losses of water, the proportion of the two reservoirs and the size and initial concentration of the two immobile stores. The model simulates the discharge and nitrate concentration dynamics well. It suggests that the groundwater store plays a very important role in the control of nitrate concentration in streamwater, and that the pattern of the seasonal variation of nitrate concentration may result from the long term evolution of nitrogen losses by leaching. Keywords: nitrate, diffuse pollution, groundwater, seasonal variations, agricultural catchment, simulation model

scholarly journals Export flux of unprocessed atmospheric nitrate from temperate forested catchments: A possible new index for nitrogen saturation

2018 ◽  
Author(s):  
Fumiko Nakagawa ◽  
Urumu Tsunogai ◽  
Yusuke Obata ◽  
Kenta Ando ◽  
Naoyuki Yamashita ◽  
...  
Keyword(s):  
Soil Water ◽  
Nitrogen Saturation ◽  
Weighted Average ◽  
Deposition Flux ◽  
Forested Catchments ◽  
Export Flux ◽  
Stable Isotopic ◽  
Nitrate Concentrations ◽  
Atmospheric Nitrate ◽  
Stream Nitrate

Abstract. To clarify the biological processing of nitrate within temperate forested catchments using unprocessed atmospheric nitrate exported from each catchment as a tracer, we continuously monitored stream nitrate concentrations and stable isotopic compositions including 17O-excess (Δ17O) in three forested catchments in Japan (KJ, IJ1, and IJ2) for more than two years. The catchments showed varying flux-weighted average nitrate concentrations: 58.4, 24.4, and 17.1 µmol L−1 in KJ, IJ1, and IJ2, respectively. In addition to stream nitrate, nitrate concentrations and stable isotopic compositions in soil water were determined for comparison in the most nitrate-enriched catchment (the KJ site). While 17O-excess of nitrate in soil water showed significant seasonal variation, ranging from +0.1 to +5.7 ‰, stream nitrate showed small variation, from +0.8 to +2.0‰ in KJ, +0.7 to +2.8 ‰ in IJ1, and +0.4 to +2.2‰ in IJ2. We concluded that the major source of stream nitrate in each forested catchment was nitrate in groundwater, which buffered the seasonal variations in soil water nitrate. The estimated annual export flux of unprocessed atmospheric nitrate accounted for 9.4 ± 2.6 %, 6.5 ± 1.8 %, and 2.6 ± 0.6 % of the annual deposition flux of atmospheric nitrate in KJ, IJ1, and IJ2, respectively. The export flux of unprocessed atmospheric nitrate relative to the deposition flux showed a clear normal correlation with the flux-weighted average concentration of stream nitrate, indicating that reductions in the biological assimilation rates of nitrate in forested soils, rather than increased nitrification rates, are likely responsible for the enrichment of stream nitrate, probably due to nitrogen saturation. The export flux of unprocessed atmospheric nitrate relative to the deposition flux in each forest ecosystem is applicable as an index for nitrogen saturation.

scholarly journals Temperature controls production but hydrology regulates export of dissolved organic carbon at the catchment scale

2020 ◽  
Vol 24 (2) ◽  
pp. 945-966 ◽  
Author(s):  
Hang Wen ◽  
Julia Perdrial ◽  
Benjamin W. Abbott ◽  
Susana Bernal ◽  
Rémi Dupas ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Groundwater Flow ◽  
Soil Water ◽  
Reactive Transport ◽  
Stream Water ◽  
Catchment Scale ◽  
High Discharge ◽  
Doc Production ◽  
Doc Concentration

Abstract. Lateral carbon flux through river networks is an important and poorly understood component of the global carbon budget. This work investigates how temperature and hydrology control the production and export of dissolved organic carbon (DOC) in the Susquehanna Shale Hills Critical Zone Observatory in Pennsylvania, USA. Using field measurements of daily stream discharge, evapotranspiration, and stream DOC concentration, we calibrated the catchment-scale biogeochemical reactive transport model BioRT-Flux-PIHM (Biogeochemical Reactive Transport–Flux–Penn State Integrated Hydrologic Model, BFP), which met the satisfactory standard of a Nash–Sutcliffe efficiency (NSE) value greater than 0.5. We used the calibrated model to estimate and compare the daily DOC production rates (Rp; the sum of the local DOC production rates in individual grid cells) and export rate (Re; the product of the concentration and discharge at the stream outlet, or load). Results showed that daily Rp varied by less than an order of magnitude, primarily depending on seasonal temperature. In contrast, daily Re varied by more than 3 orders of magnitude and was strongly associated with variation in discharge and hydrological connectivity. In summer, high temperature and evapotranspiration dried and disconnected hillslopes from the stream, driving Rp to its maximum but Re to its minimum. During this period, the stream only exported DOC from the organic-poor groundwater and from organic-rich soil water in the swales bordering the stream. The DOC produced accumulated in hillslopes and was later flushed out during the wet and cold period (winter and spring) when Re peaked as the stream reconnected with uphill and Rp reached its minimum. The model reproduced the observed concentration–discharge (C–Q) relationship characterized by an unusual flushing–dilution pattern with maximum concentrations at intermediate discharge, indicating three end-members of source waters. A sensitivity analysis indicated that this nonlinearity was caused by shifts in the relative contribution of different source waters to the stream under different flow conditions. At low discharge, stream water reflected the chemistry of organic-poor groundwater; at intermediate discharge, stream water was dominated by the organic-rich soil water from swales; at high discharge, the stream reflected uphill soil water with an intermediate DOC concentration. This pattern persisted regardless of the DOC production rate as long as the contribution of deeper groundwater flow remained low (<18 % of the streamflow). When groundwater flow increased above 18 %, comparable amounts of groundwater and swale soil water mixed in the stream and masked the high DOC concentration from swales. In that case, the C–Q patterns switched to a flushing-only pattern with increasing DOC concentration at high discharge. These results depict a conceptual model that the catchment serves as a producer and storage reservoir for DOC under hot and dry conditions and transitions into a DOC exporter under wet and cold conditions. This study also illustrates how different controls on DOC production and export – temperature and hydrological flow paths, respectively – can create temporal asynchrony at the catchment scale. Future warming and increasing hydrological extremes could accentuate this asynchrony, with DOC production occurring primarily during dry periods and lateral export of DOC dominating in major storm events.

scholarly journals Riparian zone processes and soil water total organic carbon (TOC): implications for spatial variability, upscaling and carbon exports

2012 ◽  
Vol 9 (3) ◽  
pp. 3031-3069
Author(s):  
T. Grabs ◽  
K. H. Bishop ◽  
H. Laudon ◽  
S. W. Lyon ◽  
J. Seibert
Keyword(s):  
Organic Carbon ◽  
Spatial Variability ◽  
Total Organic Carbon ◽  
Soil Water ◽  
Riparian Zone ◽  
Stream Water ◽  
Chemical Transformations ◽  
Topographic Wetness Index ◽  
Integration Model ◽  
Groundwater Levels

Abstract. Groundwater flowing from hillslopes through riparian (near stream) soils often undergoes chemical transformations that can substantially influence stream water chemistry. We used landscape analysis to predict total organic carbon (TOC) concentrations profiles and groundwater levels measured in the riparian zone (RZ) of a 67 km2 catchment in Sweden. TOC exported from 13 riparian soil profiles was then estimated based on the riparian flow-concentration integration model (RIM). Much of the observed spatial variability of riparian TOC concentrations in this system could be predicted from groundwater levels and the topographic wetness index (TWI). Organic riparian peat soils in forested areas emerged as hotspots exporting large amounts of TOC. Exports were subject to considerable temporal variations caused by a combination of variable flow conditions and changing soil water TOC concentrations. From more mineral riparian gley soils, on the other hand, only small amounts with relatively time-invariant concentrations were exported. Organic and mineral soils in RZs constitute a heterogeneous landscape mosaic that controls much of the spatial variability of stream water TOC. We developed an empirical regression-model based on the TWI to move beyond the plot scale to predict spatially variable riparian TOC concentration profiles for RZs underlain by glacial till.

scholarly journals A novel analytical approach for the simultaneous measurement of nitrate and dissolved organic carbon in soil water

2021 ◽  
Vol 25 (4) ◽  
pp. 2159-2168
Author(s):  
Elad Yeshno ◽  
Ofer Dahan ◽  
Shoshana Bernstain ◽  
Shlomi Arnon
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Soil Water ◽  
Water Samples ◽  
Agricultural Soils ◽  
Water Solution ◽  
Production Costs ◽  
Natural Soil ◽  
Nitrate Concentrations ◽  
Total Absorbance

Abstract. In this paper, we present a novel approach, enabling the measurement of nitrate concentrations in natural soil porewater containing natural soil dissolved organic carbon (DOC). The method is based on UV absorbance spectroscopy, combined with fluorescence spectroscopy, for simultaneous analysis of DOC and nitrate concentrations. The analytical procedure involves deduction of the absorption caused by the DOC from the total absorbance in the UV range that is attributed to both DOC and nitrate in the water solution. The analytical concept has been successfully tested in soil water samples obtained from five agricultural sites, as well as in water samples obtained from a commercial humus soil mixture. We believe that the new analytical concept can provide a scientific foundation for developing a sensor for real-time nitrate concentration measurements in agricultural soils. As such, it can play a significant role in reducing nitrate pollution in water resources, optimizing input application in agriculture, and decreasing food production costs.

scholarly journals Long cold winters give higher stream water dissolved organic carbon (DOC) concentrations during snowmelt

2010 ◽  
Vol 7 (3) ◽  
pp. 4857-4886 ◽  
Author(s):  
A. Ågren ◽  
M. Haei ◽  
S. Köhler ◽  
K. Bishop ◽  
H. Laudon
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Soil Water ◽  
Stream Water ◽  
Climatic Conditions ◽  
Spring Flood ◽  
Soil Frost ◽  
Winter Climate ◽  
Doc Concentration ◽  
Preceding Winter

Abstract. We show that long cold winters enhanced the stream water dissolved organic carbon (DOC) concentrations during the following spring flood. Using a 15 year stream record from a boreal catchment, we demonstrate that the interannual variation in DOC concentrations during spring flood was related to the discharge, and winter climate. That discharge is important for DOC concentration agrees with previous studies. By controlling for discharge we could detect that the winter climatic conditions during the preceding winter affected the soil water DOC concentrations, which in turn affected the concentrations in the stream. The results from the stream time-series were also supported by a riparian soil frost experiment, which showed that a long period of soil frost promoted high DOC concentrations in the soil water.

scholarly journals Regulation of stream water dissolved organic carbon (DOC) concentrations during snowmelt; the role of discharge, winter climate and memory effects

2010 ◽  
Vol 7 (9) ◽  
pp. 2901-2913 ◽  
Author(s):  
A. Ågren ◽  
M. Haei ◽  
S. J. Köhler ◽  
K. Bishop ◽  
H. Laudon
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Soil Water ◽  
Annual Variation ◽  
Stream Water ◽  
Memory Effects ◽  
Winter Climate ◽  
Snowmelt Period ◽  
Doc Export

Abstract. Using a 15 year stream record from a northern boreal catchment, we demonstrate that the inter-annual variation in dissolved organic carbon (DOC) concentrations during snowmelt was related to discharge, winter climate and previous DOC export. A short and intense snowmelt gave higher stream water DOC concentrations, as did long winters, while a high previous DOC export during the antecedent summer and autumn resulted in lower concentrations during the following spring. By removing the effect of discharge we could detect that the length of winter affected the modeled soil water DOC concentrations during the following snowmelt period, which in turn affected the concentrations in the stream. Winter climate explained more of the stream water DOC variations than previous DOC export during the antecedent summer and autumn.

scholarly journals From soil water to surface water – how the riparian zone controls element transport from a boreal forest to a stream

2017 ◽  
Vol 14 (12) ◽  
pp. 3001-3014 ◽  
Author(s):  
Fredrik Lidman ◽  
Åsa Boily ◽  
Hjalmar Laudon ◽  
Stephan J. Köhler
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Soil Water ◽  
Riparian Zone ◽  
Stream Water ◽  
Major And Trace Elements ◽  
Organic Soils ◽  
Terrestrial Environment ◽  
Riparian Soils ◽  
Mineral Soils

Abstract. Boreal headwaters are often lined by strips of highly organic soils, which are the last terrestrial environment to leave an imprint on discharging groundwater before it enters a stream. Because these riparian soils are so different from the Podzol soils that dominate much of the boreal landscape, they are known to have a major impact on the biogeochemistry of important elements such as C, N, P and Fe and the transfer of these elements from terrestrial to aquatic ecosystems. For most elements, however, the role of the riparian zone has remained unclear, although it should be expected that the mobility of many elements is affected by changes in, for example, pH, redox potential and concentration of organic carbon as they are transported through the riparian zone. Therefore, soil water and groundwater was sampled at different depths along a 22 m hillslope transect in the Krycklan catchment in northern Sweden using soil lysimeters and analysed for a large number of major and trace elements (Al, As, B, Ba, Ca, Cd, Cl, Co, Cr, Cs, Cu, Fe, K, La, Li, Mg, Mn, Na, Ni, Pb, Rb, Se, Si, Sr, Th, Ti, U, V, Zn, Zr) and other parameters such as sulfate and total organic carbon (TOC). The results showed that the concentrations of most investigated elements increased substantially (up to 60 times) as the water flowed from the uphill mineral soils and into the riparian zone, largely as a result of higher TOC concentrations. The stream water concentrations of these elements were typically somewhat lower than in the riparian zone, but still considerably higher than in the uphill mineral soils, which suggests that riparian soils have a decisive impact on the water quality of boreal streams. The degree of enrichment in the riparian zone for different elements could be linked to the affinity for organic matter, indicating that the pattern with strongly elevated concentrations in riparian soils is typical for organophilic substances. One likely explanation is that the solubility of many organophilic elements increases as a result of the higher concentrations of TOC in the riparian zone. Elements with low or modest affinity for organic matter (e.g. Na, Cl, K, Mg and Ca) occurred in similar or lower concentrations in the riparian zone. Despite the elevated concentrations of many elements in riparian soil water and groundwater, no increase in the concentrations in biota could be observed (bilberry leaves and spruce shoots).

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