Denitrification in bottomland hardwood wetland soils of the Cache River (original) (raw)
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Nitrogen mineralization, nitrification and denitrification in upland and wetland ecosystems
Oecologia, 1991
Nitrogen mineralization, nitrification, denitrification, and microbial biomass were evaluated in four representative ecosystems in east-central Minnesota. The study ecosystems included: old field, swamp forest, savanna, and upland pin oak forest. Due to a high regional water table and permeable soils, the upland and wetland ecosystems were separated by relatively short distances (2 to 5 m). Two randomly selected sites within each ecosystem were sampled for an entire growing season. Soil samples were collected at 5-week intervals to determine rates of N cycling processes and changes in microbial biomass. Mean daily N mineralization rates during five-week in situ soil incubations were significantly different among sampling dates and ecosystems. The highest annual rates were measured in the upland pin oak ecosystem (8.6 g N rn -2 yr-1), and the lowest rates in the swamp forest (1.5 g N m -2 yr-1); nitrification followed an identical pattern. Denitrification was relatively high in the swamp forest during early spring (8040 btg N20-N m -2 d -1) and late autumn (2525 gg N20-N m -2 d-l); nitrification occurred at rates sufficient to sustain these losses. In the well-drained uplands, rates of denitrification were generally lower and equivalent to rates of atmospheric N inputs. Microbial C and N were consistently higher in the swamp forest than in the other ecosystems; both were positively correlated with average daily rates of N mineralization. In the subtle landscape of east-central Minnesota, rates of N cycling can differ by an order of magnitude across relatively short distances.
Nitrate attenuation in a small temperate wetland following forest harvest
Forest Ecology and Management, 2010
Elevated nitrate concentrations in streams and groundwater are frequently observed following forest harvest. In addition to depleting nutrients available for forest regeneration, elevated nitrate export following harvest can have deleterious effects on downstream aquatic ecosystems. As part of a forest harvest experiment conducted at the Turkey Lakes Watershed, Ontario, Canada, stable isotope techniques were employed to investigate nitrate attenuation in a natural wetland receiving high concentrations of nitrate as a result of clear-cutting in the catchment. Isotopic analysis of nitrate (␦ 18 O, ␦ 15 N) and vegetation (␦ 15 N) demonstrated that both denitrification and plant uptake of nitrate resulted in significantly lower nitrate concentrations in wetland outflow compared to incoming stream water. Although the 0.2-ha forested swamp (4% of catchment by area) was too small to be featured on standard topographic maps, the wetland remove 65-100% of surface water nitrate inputs, thereby protecting downstream aquatic habitats from the full effect of N release from forest harvest. The ␦ 15 N enrichment factor associated with nitrate attenuation in wetland surface water was lower than typically observed during denitrification in groundwaters, suggesting that nitrate removal is complete in some areas of the wetland. Plant assimilation of nitrate was also partially responsible for the low observed enrichment factor. Wetland plants recorded the high ␦ 15 N associated with denitrification activity in portions of the wetland. Apportionment of nitrate sources using ␦ 18 O-NO 3 − at the outlet weir was unaffected by the wetland nitrate attenuation under pre-and post-harvest conditions due to the mid-catchment position of the wetland. Future forest management practices designed to recognize and preserve small wetlands could reduce the potentially detrimental effects of forest harvest on aquatic systems.
1998
The transformations of applied (100 kg N ha 1) 15 N labelled NO3 and NH4 in Mississippi River deltaic plain swamp forest soil which receives agriculture runoff from adjacent sugarcane fields were determined. Using an isotopic dilution technique, the rates of NO3 production (nitrification) and reduction in the 15 NO3 treated soil-water-columns were approximately 240 and 2,320 g N ha 1 d 1 , whereas NH4 production (mineralization) and removal rates in the 15 NH4 treated soil-water-columns were 270 and 2160 g N ha 1 d 1 , respectively. It was shown that if nitrification and NH4 assimilation were the primary processes responsible for NH4 removal, average NH4 assimilation would be 145 g N ha 1 d 1. Based on labelled N2-emission, denitrification was 3 fold greater in the NO3 treatment compared to the NH4 treated soil water-columns with rates of 818 and 266 g N ha 1 d 1 respectively. Even though the rate was lower in the NH4 treatment, results show that nitrification-denitrification of NH4 is a significant process. Nitrogen losses determined by 15 N2 emissions were 20.4 and 6.4% and N2O emissions were 0.10 and 0.03% of the applied NO3-N and NH4-N, respectively, over 32 days of incubation. Fertilizer loss through N2O emission was only of minor significance compared to the fertilizer loss through N2 evolution. Nitrous oxide fluxes from the control soil-water-columns averaged 9.4 g N ha 1 d 1. Addition of NO3-N to the columns increased N2O production 56% as compared to a 15% increase from the NH4-N addition. Results show that this wetland soil has a large capacity to process inorganic nitrogen entering the system as a result of agriculture runoff .
River Research and Applications, 2013
ABSTRACT Overbank flooding is thought to be a critical process controlling nitrogen retention and cycling. Yet, studies aimed at quantifying these effects, specifically nitrification, are relatively few. In this study, we investigated the effects of season and flood frequency on soil nitrification rates in forested floodplains of Upper Mississippi River, Pool 8. Samples were collected from three plots within each site in April, August and November 2006. Plots were equally divided among three flood frequency categories as follows: rare, moderate and frequent based on elevation and flood probability model. We found a significant difference in nitrification rates among flood frequency categories as follows: rare > moderate > frequent (F = 4.49, p < 0.01) and over season: spring > summer > autumn (F = 8.88, p < 0.01). Regression for all samples showed that elevation, NH4-N, bulk density and soil temperature explained a moderate amount of variation in nitrification rates (R2 = 0.29, p < 0.01). Models for moderately flooded, spring, summer and autumn samples improved when analysed individually. The absence of a correlation between nitrification rates and hydrology limits our ability to predict rates based on hydrology alone. The model based on elevation and season allows us to estimate nitrification rates with moderate confidence (R2 = 0.27, p < 0.01). A rough calculation of forest floodplain nitrification rates suggests that 473 mt of NO3-N are produced annually, about 0.5% of Pool 8 total annual NO3-N budget. Copyright © 2013 John Wiley & Sons, Ltd.
Denitrification in Riparian Wetlands Receiving High and Low Groundwater Nitrate Inputs
Journal of Environmental Quality, 1994
Wetlands potentially remove a high percentage of the groundwaterborne nitrate (NO~) that moves from upland environments before it reaches streams. It is important to determine how much of the NO~ that enters wetlands is actually removed from the ecosystem by denitrifleation (conversion of NO~-into N2 gas) rather than cycled between plants and soil. We measured denitrifieation in riparian forests with upland to wetland transition zones (moderately well drained and somewhat poorly drained soils) and red maple (Acer rubrum L.) swamps (poorly and very poorly drained soils) on two sides of a stream. Soils on the two sides were similar, but the upland land use on one side was a high density, unsewered residential development (enriched site), while the upland on the other side was undeveloped (control site). Denitrification was measured using an acetylene-based intact core (0-15 cm) technique under unnmended, water amended, and water plus nitrate-amended conditions. Denitrification (both unamended and amended rates) and soil and groundwater NO~ levels were consistently higher in soils on the enriched site. Estimates of annual denitrifieation ranged from <5 kg N ha-1 yr-~ on the moderately well drained control site soil to nearly 40 kg N ha-~ yr-t on the very poorly drained enriched site soil. Stimulation of surface soil denitrification by subsurface NO~ enrichment requires a complex interaction between hydrology, plant uptake of NO~-, and movement of plant N into soil NO~ pools through iitterfail, mineralization, and nitrification. Comparison of measured denitrification rates with estimates of groundwater NO~ loading suggested that denitrification may have removed up to 50% of the groundwater NO~ that entered the enriched site.
Soil Biology & Biochemistry, 2010
In the small, agricultural, artificially drained Orgeval watershed d 15 N values of leached nitrates and soil organic nitrogen were found to be significantly higher than the primary nitrogen (N) sources from which they are derived, namely, synthetic fertilizers, atmospheric deposition, and symbiotic or nonsymbiotic N 2 fixation (all with d 15 N close to zero). In vertical soil profiles, the d 15 N of organic N increased with depth, reaching higher values (up to 8&) particularly at stations that were frequently waterlogged as judged from ochre iron traces, such as downhill field sites or in riparian buffer strips. Nitrification, volatilization, and denitrification are the main fractionating processes able to modify the isotopic composition of soil N. Using a newly designed algorithm for calculating the equilibrium isotopic composition of all soil N species, resulting from the average annual balance of their transformations, we show that the observed trends can be explained by the action of denitrification. We suggest that the isotopic composition of soil organic N can be used as a semiquantitative indicator of the intensity of denitrification integrated over century-long periods.
Effects of Nitrate and Labile Carbon on Denitrification of Southern Temperate Forest Soils
Chilean journal of agricultural research, 2010
The pressure for anthropogenic land use changes and logging of temperate forests in southern Chile is rapidly increasing, with its potentially high impacts on the capacity of soils to retain important limiting elements. We tested the hypotheses that logging increases the denitrification rates and nitrate and C limitation of denitrifiers activity would be higher in soils of unlogged, old-growth forests than in soils of logged forests. Potential denitrification rates were estimated by the acetylene inhibition assay in intact soil cores in laboratory short-term aerobic incubations using the following treatments: 0.7 mmol NO 3-N addition, the same nitrate addition plus 23.3 mmol C-glucose, and controls (no additions) with and without 10% v/v acetylene. Forest logging did not significantly change soil nitrate content and C lability (e.g. soil C/N ratio). A nested two-factor ANOVA for repeated measures showed that denitrification was enhanced by nitrate plus labile C additions in both forests, suggesting that in both logged and unlogged forests labile C and nitrate limit denitrifiers activity. Increases were up to one order of magnitude when glucose was added to nitrate treated soils; from 373 ± 113 to 3 353 ± 451 µg N 2 ON m-2 d-1 in the unlogged, oldgrowth forest and from 1 369 ± 941 to 12 192 ± 7 474 µg N 2 ON m-2 d-1 in the logged forest. We conclude that, denitrification would be enhanced in logged forests in the longer term due to a greater nitrate and labile C availability of both in disturbed soils.
Increased rates of denitrification in nitrogen-treated forest soils
Forest Ecology and Management, 2000
The effect of increased nitrogen deposition (30 kg N ha À1 per year as NH 4 NO 3 ) on nitrogen losses by denitri®cation was studied in a Norway spruce (Picea abies) forest in Central Switzerland. Denitri®cation and potential controlling variables were measured on ®ve replicate areas, treated with a solution of NH 4 NO 3 (N-treated plots), or only moistened with rain water for comparison (control plots).
Soil Biology & Biochemistry, 2013
Microbial nitrification and denitrification both can emit nitrous oxide (N 2 O), a major greenhouse gas, and the relative contribution of each pathway depends strongly on soil moisture conditions. We conducted a stable isotope tracer experiment to determine the contribution of nitrification and denitrification to N 2 O and dinitrogen (N 2 ) fluxes in coastal plain wetlands, and to determine the response of these processes to changing soil moisture. We added 15 N-labeled nitrate (NO À 3 ) or ammonium (NH þ 4 ) to intact soil cores collected from an agricultural field, a restored wetland, and a preserved forested wetland, and subjected the cores to a drying or wetting hydrologic manipulation. Across all soils and treatments, the combined fluxes of N 2 O and N 2 ranged widely, between 0.23 and 2900 mg N m À2 h À1 , and N 2 O accounted for as little as 0% to as much as 43% of the total gaseous nitrogen (N) fluxes. Fluxes of both gases increased with increasing soil moisture in all soils and tracer treatments, but the relative enhancement of the two gases varied by soil type and N source. The N 2 O yields [N 2 O/(N 2 O þ N 2 )] derived from both nitrification and denitrification were low (1e3%) in five of eight soils in each tracer experiment. Surprisingly, nitrification-derived N 2 O yields were highest (13e31%) in soils with the highest organic matter and soil moisture (restored wetland under simulated rain and forested wetland under drained and simulated rain), while denitrification-derived N 2 O yields (12e36%) were highest under simulated rain in the two mineral soils (agricultural field and mineral soils of the restored wetland), and under drained conditions in the forested wetland. These results are consistent with field-measured N 2 O fluxes in our previous work in these sites. We suggest that nitrification plays an important and underappreciated role in contributing to N 2 O fluxes from freshwater wetlands with often-saturated, acid-organic soils, while incomplete denitrification is the likely source of N 2 O following rain events in agricultural soils in southeastern U.S. coastal plain wetlands.