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  • 1. Farahbakhshazad, Neda
    A constructed vertical macrophyte system for the retention of nitrogen in agricultural runoff2000In: Environmental technology, ISSN 0959-3330, E-ISSN 1479-487X, Vol. 21, no 2, p. 217-223Article in journal (Refereed)
    Abstract [en]

    Recent evidence for the importance of luxury rhizome accumulation of N by the common reed Phragmites australis opens the possibility for N retention in constructed vertical wetlands. The removal of nutrients (N and P) from agricultural runoff was investigated in columns planted with P. australis in a sand bed. Nitrate demonstrated a Linear removal with detention time (60-300 min) and was accounted for by membrane-Limited root uptake. Ammonia was effectively removed from agricultural runoff, with nitrate removed at longer detention times. Detention time based on a targeted nitrate removal therefore represents a suitable design parameter for a vertical macrophyte system. On the other hand, ammonia was more effectively removed at low concentrations, but ineffectively removed at higher concentrations. Nitrogen is effectively accumulated in rhizomes which could be mechanically ground, composted and returned to agriculture.

  • 2. Farahbakhshazad, Neda
    Ammonia removal from oil refinery effluent in vertical upflow macrophyte column systems2002In: Water, Air and Soil Pollution, ISSN 0049-6979, E-ISSN 1573-2932, Vol. 135, no 1-4, p. 237-247Article in journal (Refereed)
    Abstract [en]

    Constructed vertical macrophyte systems, for nitrogen removal from oil refinery wastewater, were investigated. Detailed studies were carried out in laboratory columns (diameter, 0.06 m; depth, 0.5 m; operating volume, 0.6 L) planted with common reed, Phragmites australis. Through a vertical flow format, collected oil refinery wastewater was supplied directly to the columns. Wastewater quality varied through the experimental period with initial ammonia concentrations ranging from 3 to 20 mg N L-1. Effective ammonia removal was obtained for the planted columns with a hydraulic detention time of 5 hr. Removal efficiencies above 90% was obtained for high (above 6 mg N L-1) ammonia inflow concentrations. A satisfactory ammonia removal was obtained at shorter detention times for the low initial concentrations. Longer detention times also provided organic nitrogen removal. Recirculation of the flow, which provides the same total detention time but a higher hydraulic loading, provides the possibility to adjust the flow rate and the inflow ammonia concentration with detention time to achieve a target outflow concentration.

  • 3. Farahbakhshazad, Neda
    Modeling nitrate leaching with a biogeochemical model modified based on observations in a row-crop field in Iowa2006In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 196, no 1-2, p. 116-130Article in journal (Refereed)
    Abstract [en]

    Prediction of nitrate leaching from cropland is crucial for preventing surface or ground water degradation. Accurate modeling of nitrate leaching requires simulations of both soil hydrological and biogeochemical processes. This paper reports an attempt to improve an existing biogeochemical model, Denitrification-Decomposition or DNDC, for estimation of nitrate leaching from crop fields with tile drainage system. DNDC was equipped with detailed biogeochemical processes of nitrogen turnover but a simple module for one-dimensional movement of soil water. Observations from nine drainage tiles with three different fertilizer treatments in 4 years (1996-1999) at an experimental field in Iowa were used for model modifications. Preliminary comparisons with observed tile discharge flow indicated that the original DNDC lacked the water leaching recession character. To correct this deviation, new water retention features were added to DNDC by: (1) adopting a recession curve to regulate the gravity drainage flow in the explicitly simulated soil profile (0-50 cm) and (2) introducing a virtual water pool for the space between the bottom of the modeled soil profile (50 cm) and the tile lines depth of placement (145 cm) to control the tile discharge flow. With these modifications, model prediction of water leaching fluxes from the tile drainage lines was improved. An adsorbed N pool was created in DNDC to simulate the buffering effect of soil on the amount of nitrate available for leaching. The Langmuir equation was adopted to simulate adsorption and desorption of ammonium ions on the soil absorbents. This modification enhanced the model capacity for simulating free ammonium dynamics, nitrification, and nitrate leaching. Sensitivity tests of the modified DNDC showed that the modeled impact of differences of precipitation, soil texture, soil organic carbon content, and fertilizer application rates on nitrate leaching rates were consistent with observations reported by other researchers. This study indicated that a biogeochemical model with limited modifications in hydrology could serve nitrate leaching prediction and be useful for sustainable agricultural management.

  • 4. Farahbakhshazad, Neda
    Nutrient removal in a vertical upflow wetland in Piracicaba, Brazil2000In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 29, no 2, p. 74-77Article in journal (Refereed)
    Abstract [en]

    Vertical upflow wetland systems have shown high nutrient removal efficiencies. The removal of nutrients (N and P) from wastewater was investigated in a vertical upflow wetland system in Piracicaba, Brazil. The concentration removal was 93% for phosphate, 78% for nitrate and 50% for ammonia. Effective phosphate removal was observed in the top soil layer which has a high surface adsorption area. Nitrate was removed satisfactory at low loading rates due to plant uptake and denitrification. Removal of ammonia was concentration dependent and decreased at high inflow concentrations. Spatial sampling through the bed showed that the treatment efficiency was not uniform. The possibility of the recycling of nutrients as a soil improver or animal feed is an important feature of this type of vertical flow wetland system.

  • 5. Farahbakhshazad, Neda
    Phosphorus removal in a vertical upflow constructed wetland system2003In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 48, no 5, p. 43-50Conference paper (Refereed)
    Abstract [en]

    Mechanisms for P removal in a vertical upflow macrophyte system were studied in controlled laboratory columns filled with sand and planted with Phragmites australis. Substrate P removal was shown to increase with flow rate, a parameter which can be enhanced through effluent recirculation. An alternative substrate (leca, light expanded clay aggregate) provided improved equilibrium adsorption characteristics, but uncrushed and within the kinetic constraints of a macrophyte system gave no improvement for P adsorption over sand. Intermittent loading of the sand based macrophyte system permitted control of the P concentration, with lower effluent peak concentrations for increased resting interval (no P inflow). Where P loading was targeted, continuous flow provided the optimum mass removal conditions.

  • 6. Farahbakhshazad, Neda
    et al.
    Dinnes, Dana L.
    Li, Changsheng
    Jaynes, Dan B.
    Salas, William
    Modeling biogeochemical impacts of alternative management practices for a row-crop field in Iowa2008In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 123, no 1-3, p. 30-48Article in journal (Refereed)
    Abstract [en]

    The management of contemporary agriculture is rapidly shifting from single-goal to multi-goal strategies. The bottleneck of implementing the strategies is the capacity of predicting the simultaneous impacts of change in management practices on agricultural production, soil and water resources and environmental safety. Process-based models provide an opportunity to quantify the impacts of farm management options on various pools and fluxes of carbon (C) and nitrogen (N) in agroecosystems. The denitrification-decomposition or DNDC model was recently modified for simulating N cycling for the U.S. Midwestern agricultural systems. This paper reports a continuous effort on applying the model for estimating the impacts of alternative management practices (e.g., no-till, cover crop, change in fertilizer rate or timing) on agroecosystems in the Midwestern U.S. A typical row-crop field in Iowa was selected for the sensitivity tests. The modeled results were assessed with a focus on four major indicators of agro-ecosystems, namely crop yield, soil organic carbon (SOC) sequestration, nitrate-N leaching loss and nitrous oxide (N2O) emissions. The results indicated that no-till practice significantly increased SOC storage and reduced nitrate-N leaching rate, but slightly decreased crop yield and increased N2O emissions. By modifying the methods of fertilizer application in conjunction with the no-till practice, the disadvantages of no-till could be overcome. For example, increasing the fertilizing depth and using a nitrification inhibitor could substantially reduce N2O emissions and increase crop yield under the no-till conditions. This study revealed the complexity of impacts of the alternative farming management practices across different climate conditions, soil properties and management regimes. Process-based models can play an important role in quantifying the comprehensive effects of management alternatives on agricultural production and the environment.

  • 7. Norman, Josefine
    et al.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
    Farahbakhshazad, Neda
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Butterbach-Bahl, Klaus
    Li, Changsheng
    Klemedtsson, Leif
    Simulation of NO and N2O emissions from a spruce forest during a freeze/thaw event using an N-flux submodel from the PnET-N-DNDC model integrated to CoupModel2008In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 216, no 1, p. 18-30Article in journal (Refereed)
    Abstract [en]

    The amount of nitrogen gases (N2O, No and N-2) emitted from forest soils depends on interactions between soil properties, climatic factors and soil management. To increase the understanding of nitrogen processes in soil ecosystems, two dynamic models, CoupModel (coupled heat and mass transfer model for soil-plant-atmosphere systems) and the denitrification-decomposition (DNDC) model were selected. Both are dynamic models with different submodels for soil, vegetation, hydrology and climate system. CoupModel has a higher degree of detail on soil physical and abiotic components, whereas the DNDC model contains details of microbiological processes involved in production of nitrogen gases. To improve the previous simple submodel of nitrogen emission in CoupModel, we included a submodel corresponding to the forest version of DNDC containing photosynthesis/evapotranspiration-nitrogen (PnET-N-DNDC model). The nitrogen (N) and carbon

  • 8. van Oijen, M.
    et al.
    Cameron, D. R.
    Butterbach-Bahl, K.
    Farahbakhshazad, Neda
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Kiese, R.
    Rahn, K. -H
    Werner, C.
    Yeluripati, J. B.
    A Bayesian framework for model calibration, comparison and analysis: Application to four models for the biogeochemistry of a Norway spruce forest2011In: Agricultural and Forest Meteorology, ISSN 0168-1923, E-ISSN 1873-2240, Vol. 151, no 12, p. 1609-1621Article in journal (Refereed)
    Abstract [en]

    Four different parameter-rich process-based models of forest biogeochemistry were analysed in a Bayesian framework consisting of three operations: (1) Model calibration, (2) Model comparison, (3) Analysis of model-data mismatch. Data were available for four output variables common to the models: soil water content and emissions of N(2)O, NO and CO(2). All datasets consisted of time series of daily measurements. Monthly averages and quantiles of the annual frequency distributions of daily emission rates were calculated for comparison with equivalent model outputs. This use of the data at model-appropriate temporal scale, together with the choice of heavy-tailed likelihood functions that accounted for data uncertainty through random and systematic errors, helped prevent asymptotic collapse of the parameter distributions in the calibration. Model behaviour and how it was affected by calibration was analysed by quantifying the normalised RMSE and r(2) for the different output variables, and by decomposition of the MSE into contributions from bias, phase shift and variance error. The simplest model, BASFOR, seemed to underestimate the temporal variance of nitrogenous emissions even after calibration. The model of intermediate complexity. DAYCENT, simulated the time series well but with large phase shift. COUP and MoBiLE-DNDC were able to remove most bias through calibration. The Bayesian framework was shown to be effective in improving the parameterisation of the models, quantifying the uncertainties in parameters and outputs, and evaluating the different models. The analysis showed that there remain patterns in the data - in particular infrequent events of very high nitrogenous emission rate - that are unexplained by any of the selected forest models and that this is unlikely to be due to incorrect model parameterisation.

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