Denitrification Rate Constant Research Articles

Nitrate denitrification rate response to temperature gradient change during river bank infiltration.

Nitrate attenuation during river bank infiltration is the key process for reducing nitrogen pollution. Temperature is considered to be an important factor affecting nitrate attenuation. However, the magnitude and mechanism of its impact have not been clear for a long time. In this study, the effects of temperature and temperature gradient on the nitrate denitrification rate were investigated via static batch and dynamic soil column simulation experiments. The results showed that temperature had a significant effect on the denitrification rate. Temperature effects were first observed in denitrifying bacteria. At low temperatures, the microorganism diversity was low, resulting in a lower denitrification rate constant. The static experimental results showed that the denitrification rate at 19°C was approximately 2.4 times that at 10°C. The dynamic soil column experiment established an exponential positive correlation between the nitrate denitrification decay kinetic constant and temperature. The affinity of denitrifying enzymes for nitrate in the reaction substrate was ordered as follows: decreasing temperature gradient (30°C → 10°C) > zero temperature gradient (10°C) > increasing temperature gradient condition (0°C → 10°C). This study provides a theoretical basis for the biogeochemical processes underlying river bank infiltration, which will help aid in the development and utilization of groundwater resources.

Denitrification kinetics during aquifer storage and recovery of drainage water from agricultural land

An aquifer storage transfer and recovery (ASTR) system was studied in which tile drainage water (TDW) was injected with relatively high NO3 (about 14 mg/L) concentrations originating from fertilizers. Here we present the evolution of denitrification kinetics at 6 different depths in the aquifer before, and during ASTR operation. First-order denitrification rate constants increased over time before and during the first days of ASTR operation, likely due to microbial adaptation of the native bacterial community and/or bioaugmentation of the aquifer by denitrifying bacteria present in injected TDW. Push-pull tests were performed in the native aquifer before ASTR operation. Obtained first-order denitrification rate constants were negligible (0.00–0.03 d−1) at the start, but increased to 0.17–0.83 d−1 after a lag-phase of about 6 days. During the first days of ASTR operation in autumn 2019, the arrival of injected TDW was studied at 2.5 m distance from the injection well. First-order denitrification rate constants increased again over time (maximum >1 d−1). Three storage periods without injection were monitored in winter 2019, fall 2020, and spring 2021 during ASTR operation. First-order rate constants ranged between 0.12 and 0.61 d−1. Denitrification coupled to pyrite oxidation occurred at all depths, but other oxidation processes were indicated as well. NO3 concentration trends resembled Monod kinetics but were fitted also to a first-order decay rate model to facilitate comparison. Rate constants during the storage periods were substantially lower than during injection, probably due to a reduction in the exchange rate between aquifer solid phases and injected water during the stagnant conditions. Denitrification rate constants deviated maximally a factor 5 over time and depth for all in-situ measurement approaches after the lag-phase. The combination of these in-situ approaches enabled to obtain more detailed insights in the evolution of denitrification kinetics during AS(T)R.

Transport Modelling In Jakarta Groundwater Basin using QSWATMOD

The Jakarta groundwater basin is constructed by tertiary, Pleistocene and resent rock consisting of sedimentary rocks, volcanic activities and alluvial. There are three very potential aquifer layers found in this basin i.e. shallow aquifers, upper confined aquifers, and lower confined aquifers bounded by several aquitard. High economic and development activities cause high vulnerability to polluted aquifers such as nutrients. Previous research mentioned the presence of nutrients in groundwater in urban areas can be caused by high anthropogenic activity. Nutrient contamination in groundwater can be a threat to ecosystems in coastal areas. The purpose of this paper is to understand nutrient transport patterns through groundwater hydrogeology systems in the Jakarta groundwater basin, so that the amount of groundwater contribution to the nutrient flux in the Jakarta bay can be estimated. To get the transport nutrient model, QSWATMOD tools in QGIS Software were used. The parameters used in transport nutrient modeling are the definition of subbasins in the SWAT hydrology model, Hydrological Response Unit (HRU), rivers, aquifer thickness, hydraulic conductivity, specific storage, specific yield, hydraulic head, porosity, longitudinal dispersivity, and denitrification rate constant. The sub-basins and river constraints used are the Ciliwung Watersheds fill the Jakarta groundwater basin. The result show Leached Nitrate at the study area was 42 kg/ha and total P loss were 5 kg/ha. However the higher groundwater recharge in the study area increased the risk of groundwater contaminant by nitrate.

Promoting effects of corn straw and exceed sludge as carbon sources on denitrification of constructed wetlands

As the low C/N ratio of effluent from wastewater treatment plant, the advanced treatment of constructed wetlands (CWs) on the effluent is often unsatisfactory, especially for the removal of N. In order to increase the N removal efficiency, this paper tested three kinds of carbon sources acid and alkali treated straw, alkali treated straw and exceed sludge for promoting the denitrification of CWs. The results showed that alkali treated straw performed the strongest carbon release ability (0.43mg?g-1?h-1) and the maximum C/N ratio (27.3). While acid and alkali treated straw’s carbon release ability and C/N ratio were 0.37 mg?g-1?h-1 and 12.8, exceed sludge’s carbon release ability and C/N ratio were 0.37 mg?g-1?h-1 and 8.4. In order to improve the C/N ratio in CWs to 5/1, 450g alkali treated straw and exceed sludge were added into tide flow wetlands (TFCWs) and subsurface flow wetlands (SSFWs) respectively to test the improvement of denitrification. Compared with the control groups, the N removal of CWs with carbon sources were significantly improved. CWs with alkali treated straw showed better removal effects of N than CWs exceed sludge. The analysis results of the first-order kinetic process suggested that the denitrification rate constants of TFCW control group, TFCW with exceed sludge and TFCW with alkali treated straw were 0.126, 0.262 and 0.345, respectively. The denitrification rate of TFCW with alkali treated straw was 2.74 times of TFCW control group, and 1.32 times of TFCW with excess sludge. This study has contributed to understand the possibility of straw and exceed sludge as the carbon sources to strengthen the denitrification in CWs.

The influence mechanism of temperature on solid phase denitrification based on denitrification performance, carbon balance, and microbial analysis

In this work, the influence mechanism of temperature on solid phase denitrification (SPD) was investigated using a pilot-scale reactor supported with polycaprolactone (PCL). The results showed that under nitrate loads of ~31.5 mg N/(L·h), as temperature decreased from 30 °C to 13 °C, the nitrate removal efficiency declined from 94% to 57%. Furthermore, denitrification rate constants were input into Arrhenius equation and the resulting temperature coefficient was 1.04. Significantly nitrite accumulation and less effluent COD residue occurred at low-temperatures. Via stoichiometry, the sludge yield coefficient and COD demand for nitrate removal both increased as a function of increasing temperature; and were calculated at 20 °C as 0.069 g MLVSS/(g COD·d) and 3.265 g COD/g N, respectively. Carbon balance analysis indicated that the COD release rate (υ) at 30 °C was twice that at 13 °C. LEfSe analysis demonstrated that Desulfomicrobium, Desulfovibrio, and Meganema were abundant at low-temperature, while Simplicispira, Aquabacterium, and Acidovorax were enriched at high-temperature. Besides, carboxylesterase (PCL depolymerase) was more abundant at high-temperature, implying an association with a fast υ. Moreover, nar was enriched at low-temperature, while nir was depleted, which led to nitrite accumulation. These results provide reference for SPD design parameter estimation and/or optimal operation strategy.

Understanding urban stormwater denitrification in bioretention internal water storage zones.

Conventional free-draining bioretention systems promote nitrate production and continual leaching to receiving waters. In this study, laboratory tests demonstrated the efficacy of an internal water storage zone (IWSZ) to target nitrate removal via denitrification. Experimental results confirmed that the carbon substrate characteristics (Willow Oak woodchip media) and the hydraulic retention time of nitrified stormwater affected nitrate removal performance. A 2.6-day batch treatment time reduced 3.0mg-N/L to <0.01mg/L, corresponding to a first-order denitrification rate constant of 0.0011min-1 . Under various flow conditions, the associated hydraulic retention time may be used as a predictive measurement of nitrate removal performance. Scanning electron microscopy and 16S rRNA analysis of the woodchips showed that biofilms were present that could be responsible for anaerobic lignocellulose degradation and denitrification. This knowledge, along with evaluation of the biofilm community composition, reinforced the notion of a heterogeneous structure due to nutrient availability and hydrodynamic conditions. PRACTITIONER POINTS: Denitrification can occur using woodchips in a bioretention internal water storage zone. The denitrification rate is slow and may be limited during field-scale applications. A woodchip pretreatment did not provide long-term enhancement to the denitrification rate. Denitrification bacteria were found in the internal water storage zone.

Denitrification Kinetics of High‐Strength Nitrate in Granular Sludge Reactors

Biological denitrification of high‐strength nitrate is challenging due to building‐up of toxic nitrite to high levels. In this study, denitrification kinetics of high‐strength nitrate is investigated in a granular sludge reactor operated in sequencing batch mode. The nitrate concentrations are increased from 677, 1355, 2032, 2710, 3387, 4065–4742 mg L−1 NO3N in the reactor. Carbon and an electron source (acetate) are supplied at a fixed acetate‐carbon to nitrate‐nitrogen ratio of 1.5. At steady state, complete denitrification of 4742 mg L−1 NO3N in the feed is observed within the first 20 h of sequencing batch reactor (SBR) cycle. High denitrification rate constants are observed for NO3N concentrations from 677 to 2032 mg L−1. However, a decrease in denitrification rate constants is observed for nitrate‐N concentrations of 2710–4742 mg L−1, due to inhibition caused by transient accumulation of high levels of nitrite. Denitrifying biomass formed in the SBR is predominantly consisted of granular sludge, containing cocci, and rod‐shaped microorganisms. Cultivation of nitrite‐tolerant, denitrifying microbial community in granular sludge will help in the development of high rate reactors needed for process application.

Numerical Simulation and Sensitivity Analysis for Nitrogen Dynamics Under Sewage Water Irrigation with Organic Carbon

This study is focused on investigating the impacts of organic carbon on the denitrification process of nitrogen transformation and transport. A numerical model, Nitrogen-2D, is modified by considering the impact of organic carbon in the denitrification equation. The modified model is used to simulate the soil nitrogen (including nitrate and ammonium) dynamics under the primary and secondary sewage water irrigation with different organic carbon concentrations. The simulated results of accumulated drainage water amount, soil nitrogen concentration, and nitrogen concentration in the drainage water show that the simulations and measurements are consistent. The comparison of results from the original and improved models shows the necessity to consider the impact of organic carbon. The nitrogen mass balance is calculated to analyze the nitrogen transformation processes quantitatively under different input organic carbon sources. Furthermore, the effect of different input organic carbon sources on the soil nitrogen dynamics is investigated by using the modified Nitrogen-2D model with the calibrated parameters. The input organic carbon source helps to speed up the mineralization and denitrification, which contributes to the slight increase of ammonium concentration and the decrease of nitrate concentration in the shallow soil. Since a large number of soil water and nitrogen transformation and transport parameters are needed when setting up the model, a local sensitivity method is conducted to evaluate the input parameters by the sewage water irrigation case. The results show that the drainage water amount is very sensitive to the exponent n and the coefficient α of the soil water retention function and that the ammonium concentration is very sensitive to the first-order nitrification rate constant, the decomposition rate coefficient in humus pool, and the soil ammonium adsorption coefficient. The nitrate concentration is sensitive to more parameters, especially to the exponent n and the coefficient α in the soil water retention function and to the denitrification rate constant.

Coupled Nitrification-Denitrification Caused by Suspended Sediment (SPS) in Rivers: Importance of SPS Size and Composition.

Suspended sediment (SPS) is ubiquitous in rivers, and SPS with different particle sizes and compositions may affect coupled nitrification-denitrification (CND) occurring on SPS significantly. However, there is no related research report. In this work, 15N isotope tracer technique was adopted to explore the CND in systems containing SPS (8 g L-1 and 1 g L-1) collected from the Yellow River with various particle sizes, including <2, 2-20, 20-50, 50-100, and 100-200 μm. The results showed that the CND occurred on SPS and the CND rate was negatively related to particle size; both nitrification and denitrification rate constants increased with decreasing SPS particle size. For instance, SPS (8 g L-1) with a particle size below 2 μm had the highest 15N2 emission rate of 1.15 mg-N/(m3·d), which was 2.9 times that of 100-200 μm. This is because SPS with a smaller particle size had a larger specific surface area and a higher organic carbon content, which is beneficial for bacteria growth. Both the nitrifying and denitrifying bacteria population were positively correlated with CND rate (p < 0.05). Different from the 15N2 production, 15N2O emission rate did not decrease with increasing SPS particle size. For the system containing 8 g L-1 SPS, 15N2O emission rate reached the highest of 1.05 μg-N/(m3·d) in the 50-100 μm SPS system, which was 17.5 times that of 100-200 μm. Similar results could be found from the system with 1 g L-1 SPS. This is due to the fact that the oxygen concentration at the SPS-water interface increased with SPS particle size, and the oxygen conditions might be most suitable for the production of N2O in the 50-100 μm system. This study suggests that SPS size and composition play an important role in nitrogen cycle of river systems, especially for the production of N2O.

Drainage and Nitrate Leaching from Artificially Drained Maize Fields Simulated by the Precision Nitrogen Management Model.

Environmental nitrogen (N) losses (e.g., nitrate leaching, denitrification, and ammonia volatilization) frequently occur in maize ( L.) agroecosystems. Decision support systems, designed to optimize the application of N fertilizer in these systems, have been developed using physically based models such as the Precision Nitrogen Management (PNM) model of soil and crop processes, which is an integral component of Adapt-N, a decision support tool providing N fertilizer recommendations for maize production. Such models can also be used to estimate N losses associated with particular management practices and over a range of current climates and future climate projections. The objectives of this study were to update the PNM model to include an option for simulating soil-water processes in artificially drained soils, and to calibrate the revised PNM model and test it against multiyear field studies in New York and Minnesota with different soils and management practices. Minimal calibration was required for the model. Denitrification rate constants were calibrated by minimizing the error between simulated and observed nitrate leaching for each study site. The normalized root mean squared error of cumulative daily drainage for the validation sets ranged from 10 to 23%. For cumulative daily nitrate leaching, the normalized root mean squared error ranged from 11 to 28% for the validation sets. The minimal calibration required and relatively simple data inputs make the PNM model a broadly applicable tool for simulating water and N flows in maize systems.

Application of half-order kinetics to sulfur-utilizing autotrophic denitrification for groundwater remediation

The kinetics of sulfur-utilized autotrophic denitrification of groundwater was evaluated in batch tests to obtain kinetic parameters. Experiments were performed in media bottles containing varying NO3 −-N concentrations (20, 44, and 77 mg/L) with 4.0–4.75 mm-sized sulfur particles. Alkalinity was set as a constant in all experimental containers at 850 mg/L as CaCO3. The half-order kinetic model was found to adequately describe the process efficiently, yielding denitrification rate constants of 4.36, 5.51, and 6.91 mg-N1/2/L1/2 · h in the presence of NO3 −-N at 20, 44, and 77 mg/L, respectively. The rate of denitrification increased with the increasing initial NO3 −-N concentrations.

The Kinetic Difference of Denitrification and Sulfate Reduction Conducted by Anaerobic Microbes

For investigating the competitive ability of denitrifying bacteria and sulfate reducing bacteria on the substrate in the anaerobic environment, denitrification and sulfate reduction experiments were conducted under the conditions of different carbon content and different nitrate/sulfate ratio, and the kinetic difference of denitrification and sulfate reduction was also analyzed. The experimental results showed that denitrification could essentially be completed in 7~9 h at the same condition of carbon source content, but sulfate reduction was completed after 12 h. Denitrification rate constant of the microbes was over one time larger than that of sulfate reduction. When the carbon source was enough (C/N ratio and C/S ratio more than 3), denitrification efficiencies all surpassed 98%, while that of sulfate reduction only reached 84%. Under the same condition, the nitrate reduction ability of microbes was stronger than that of sulfate reduction, and the process of nitrate reduction had much more superiority.

Acceleration of Denitrification in Turbid Rivers Due to Denitrification Occurring on Suspended Sediment in Oxic Waters

High suspended sediment (SPS) concentration exists in many rivers of the world. In the present study, the effects of SPS concentration on denitrification were investigated in airtight chambers with sediment samples collected from the Yellow River which is the largest turbid river in the world. Results from the nitrogen stable ((15)N) isotopic tracer experiments showed that denitrification could occur on SPS in oxic waters and the denitrification rate increased with SPS concentration; this was probably caused by the presence of low-oxygen microsites in SPS. For the water systems with both bed-sediment and SPS, the denitrification kinetics fit well to Logistic model, and the denitrification rate constant increased linearly with SPS concentration (p < 0.01). The denitrification caused by the presence of SPS accounted for 22%, 38%, 53%, and 67% of the total denitrification in systems with 2.5, 8, 15, and 20 g L(-1) SPS, respectively. The activity of denitrifying bacteria in SPS was approximately twice that in bed-sediment, and the denitrifying bacteria population showed an increasing trend with SPS concentration in both SPS and bed-sediment, leading to the increase of denitrification rate with SPS concentration. Furthermore, the denitrification in bed-sediment was accelerated by increased diffusion of nitrate from overlying water to bed-sediment under agitation conditions, which accompanied with the presence of SPS. When with 8 g L(-1) SPS, approximately 66% of the increased denitrification compared to that without SPS was attributed to denitrification on SPS and 34% to agitation conditions. This is the first report of the occurrence of denitrification on SPS in oxic waters. The results suggest that SPS plays an important role in denitrification in turbid rivers; its effect on nitrogen cycle should be considered in future study.

Effect of Dissolved Oxygen Tension and Agitation Rates on Sulfur-Utilizing Autotrophic Denitrification: Batch Tests

The effect of dissolved oxygen (DO) and agitation rate in open and closed reactors was examined for sulfur-utilizing autotrophic denitrification. The reaction rate constants were determined based on a half-order kinetic model. Declining denitrification rate constants obtained for open reactors those of 8.46, 8.03, and 2.18 for 50 mg NO(3) (-)-N/L, while 11.12, 9.14, and 0.12 mg(1/2)/L(1/2) h were for 100 mg NO(3) (-)-N/L at agitation speeds of 0, 100, and 200 rpm. In closed reactors, the ever-increasing denitrification rates were 10.13, 22.56, and 37.03, whereas for the same nitrate concentrations and speeds the rates were 13.17, 15.63, and 26.67 mg(1/2)/L(1/2) h. The rate constants correlated well (r ( 2 ) = 0.89-0.99) with a half-order kinetic model. In open reactors, high SO(4) (2-)/N ratios (8.02-75.10) while in closed reactors comparatively low SO(4) (2-)/N ratios (6.10-13.39) were obtained. Sulfur oxidation occurred continuously in the presence of DO, resulting in mixed cultures acclimated to sulfur and nitrate. SO(4) (2-) was produced as an end product, which reduced alkalinity and lowered pH over time. Furthermore, DO inhibited sulfur denitrification in open reactors, while agitation in closed reactors increased the rate of denitrification.

Quantifying Nitrogen Process Rates in a Constructed Wetland Using Natural Abundance Stable Isotope Signatures and Stable Isotope Amendment Experiments

This study describes the spatial variability in nitrogen (N) transformation within a constructed wetland (CW) treating domestic effluent. Nitrogen cycling within the CW was driven by settlement and mineralization of particulate organic nitrogen and uptake of NO3-. The concentration of NO3- was found to decrease, as the delta15N-NO3- signature increased, as water flowed through the CW, allowing denitrification rates to be estimated on the basis of the degree of fractionation of delta15N-NO3-. Estimates of denitrification hinged on the determination of a net isotope effect (eta), which was influenced byprocesses that enrich or deplete 15NO3- (e.g., nitrification), as well as the rate constants associated with the different processes involved in denitrification (i.e., diffusion and enzyme activity). The influence of nitrification on eta was quantified; however, it remained unclear how eta varied due to variability in denitrification rate constants. A series of stable isotope amendment experiments was used to further constrain the value of eta and calculate rates of denitrification, and nitrification, within the wetland. The maximum calculated rate of denitrification was 956 +/- 187 micromol N m(-2) h(-1), and the maximum rate of nitrification was 182 +/- 28.9 micromol N m(-2) h(-1). Uptake of NO3- was quantitatively more important than denitrification throughoutthe wetland. Rates of N cycling varied spatially within thewetland, with denitrification dominating in the downstream deoxygenated region of the wetland. Studies that use fractionation of N to derive rate estimates must exercise caution when interpreting the net isotope effect. We suggest a sampling procedure for future natural abundance studies that may help improve the accuracy of N cycling rate estimates.

Effective denitrification scales predictably with water residence time across diverse systems

AbstractNitrogen provides a fundamental building block for life. However, some nitrogen species (e.g., NO~3~) cause water quality degradation and contribute to climatic warming as a greenhouse gas (e.g., N~2~O). Denitrification is a central process in the nitrogen cycle, transforming water-soluble nitrogen to gaseous nitrogen, thereby removing nitrogen from the system. The factors controlling denitrification are known, yet the general quantitative comparison of controls on denitrification remains a rich area of study. Understanding the relative importance of various controls over denitrification is critical given its biological importance, role in the Earth system, and the current perturbation of the global nitrogen cycle by human activity. We demonstrate that the 'effective' denitrification rate constant (first-order constant; k~e~ [T^-1^]) and advective water transport (mean residence time; [tau] [T]) scale inversely across diverse systems, ranging from hillslopes and groundwater to large lakes and estuaries. As a result, we observe a relatively constant nitrogen removal across nine orders of magnitude in transport time scales. A central question remains as to why k~e~ scales approximately linearly with [tau]. We suggest that the variability of k~e~ arises from hydrologic masking of an intrinsic denitrification rate constant (k~den~). A two-compartment model shows how k~e~ varies with the amount of advective water, and thus [tau], explaining how denitrification losses in the reactive zone of a system are controlled by mass transfer to that reactive zone. Our finding highlights mean residence time in the advective zone as a primary control on effective rates of denitrification, while other factors (e.g., nitrate and organic carbon concentrations) provide secondary controls. Furthermore, the relationship between k~e~ and [tau] demonstrates the strong coupling of the water and nitrogen cycles.

Bayesian modeling of the assimilative capacity component of nutrient total maximum daily loads

Implementing stream restoration techniques and best management practices to reduce nonpoint source nutrients implies enhancement of the assimilative capacity for the stream system. In this paper, a Bayesian method for evaluating this component of a total maximum daily load (TMDL) load capacity is developed and applied. The joint distribution of nutrient retention metrics from a literature review of 495 measurements was used for Monte Carlo sampling with a process transfer function for nutrient attenuation. Using the resulting histograms of nutrient retention, reference prior distributions were developed for sites in which some of the metrics contributing to the transfer function were measured. Contributing metrics for the prior include stream discharge, cross‐sectional area, fraction of storage volume to free stream volume, denitrification rate constant, storage zone mass transfer rate, dispersion coefficient, and others. Confidence of compliance (CC) that any given level of nutrient retention has been achieved is also determined using this approach. The shape of the CC curve is dependent on the metrics measured and serves in part as a measure of the information provided by the metrics to predict nutrient retention. It is also a direct measurement, with a margin of safety, of the fraction of export load that can be reduced through changing retention metrics. For an impaired stream in western Oklahoma, a combination of prior information and measurement of nutrient attenuation was used to illustrate the proposed approach. This method may be considered for TMDL implementation.

Modelling and evaluation of nitrogen removal performance in subsurface flow and free water surface constructed wetlands

With the aim of protecting drinking water sources in rural regions, pilot-scale subsurface water flow (SSF) and free water surface flow (FWS) constructed wetland systems were evaluated for removal efficiencies of nitrogenous pollutants in tertiary stage treated wastewaters (effluent from the Pasaköy biological nutrient removal plant). Five different hydraulic application rates and emergent (Canna, Cyperus, Typhia sp., Phragmites sp., Juncus, Poaceae, Paspalum and Iris) and floating (Pistia, Salvina and Lemna) plant species were assayed. The average annual NH4-N, NO3-N and organic-N treatment efficiencies were 81, 40 and 74% in SSFs and 76, 59 and 75% in FWSs, respectively. Two types of the models (first-order plug flow and multiple regression) were tried to estimate the system performances. Nitrification, denitrification and ammonification rate constants (k20) values in SSF and FWS systems were 0.898 d-1 and 0.541 d(-1), 0.486 d(-1) and 0.502 d(-1), 0.986 d(-1) and 0.908, respectively. Results show that the first-order plug flow model clearly estimates slightly higher or lower values than observed when compared with the other model.

Nitrogen management in reservoir catchments through constructed wetland systems

In this study, nitrogen removal was investigated in pilot-scale subsurface flow (SSF) and in free water surface flow (FWS) constructed wetlands installed in the campus of TUBITAK-Marmara Research Center, Gebze, near Istanbul, Turkey. The main purposes of this study are to apply constructed wetlands for the protection of water reservoirs and to reuse wastewater. Experiments were carried out at continuous flow reactors. The effects of the type of plants on the removal were investigated by using emergent (Canna, Cyperus, Typhia spp., Phragmites spp., Juncus, Poaceae, Paspalum and Iris.), submerged (Elodea, Egeria) and floating (Pistia, Salvina and Lemna) marsh plants at different conditions. During the study period HLRs were 30, 50, 70, 80 and 120 L m(2)d(-1) respectively. The average annual NH4-N, NO(3)-N, organic N and TN treatment efficiencies in SSF and FWS wetlands are 81% and 68%, 37% and 49%, 75% and 68%, 47% and 53%, respectively. Nitrification, denitrification and ammonification rate constant (k20) values in SSF and FNS systems have been found as 0.898 d(-1) and 0.541 d(-1), 0.488 d(-1) and 0.502 d(-1), 0.986 d(-1) and 0.908 respectively. Two types of the models (first-order plug flow and multiple regression) were tried to estimate the system performances.

EFFECT OF PARAMETER UNCERTAINTY ON DRAINMOD PREDICTIONS: II. NITROGEN LOSS

Reducing nitrate levels in sensitive coastal waters has become a national priority. Agriculture has been targeted as a significant contributor to this problem. Controlled drainage is recognized as one way to reduce nitrate losses from agricultural fields requiring subsurface drainage. The computer–based hydrology model DRAINMOD can be used to predict the effect of drainage design on the rate of subsurface drainage and the water quality related to nitrates in these waters. An uncertainty analysis of the model was conducted to quantitatively assess the variability in the model predictions for average annual nitrate loss through subsurface drainage, surface runoff, and denitrification caused by parameter uncertainty. First–order approximation and Monte Carlo simulation were used to estimate the effect of the uncertainty in the most sensitive parameters (dispersivity, bulk density, % nitrogen uptake by corn, mineralization rate constant, and denitrification rate constant) on the uncertainty in the model objective functions. The denitrification rate constant accounted for greater than 70% of the uncertainty in terms of the variance for all objective functions under both conventional and controlled drainage. Reducing the uncertainty in influential parameters can reduce the uncertainty in DRAINMOD predictions for nitrate loss.