Nitrogen Transformation Processes Research Articles

Isotopic and elemental indicators of nutrient sources and status of coastal habitats in the Caribbean Sea, Yucatan Peninsula, Mexico

Nutrient inputs associated with coastal population growth threaten the integrity of coastal ecosystems around the globe. In order to assess the threat posed by rapid growth in tourism, we analyzed the nutrient concentrations as well as the δ 15N of NO 3 − and macrophytes to detect wastewater nitrogen (N) at 6 locations along a groundwater-dominated coastal seagrass bed on the Caribbean coast of Mexico. We predicted that locations with greater coastal development would have higher concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (P), as well as δ 15N of NO 3 −, reflecting wastewater sources of N. However, concentrations of NO 3 − were not significantly different between developed (3.3 ± 5.3 μM NO 3 −) and undeveloped (1.1 ± 0.7 μM) marine embayments. The most important control on DIN concentration appeared to be mixing of fresh and salt water, with DIN concentrations negatively correlated with salinity. The δ 15N of NO 3 − was elevated at an inland pond (7.0 ± 0.42‰) and a hydrologically-connected tide pool (7.6 ± 0.57‰) approximately 1 km downstream of the pond. The elevated δ 15N of NO 3 − at the pond was paralleled by high δ 15N values of Cladophora sp., a ubiquitous green alga (10 ± 1‰). We hypothesize that inputs of nitrogen rich (NO 3 − > 30 μM) groundwater, characterized by 15N enriched signatures, flow through localized submarine groundwater discharges (SGD) and contribute to the elevated δ 15N signatures observed in many benthic macrophytes. However, changes in nitrogen concentrations and isotope values over the salinity gradient suggest that other processes (e.g. denitrification) could also be contributing to the 15N enrichments observed in primary producers. More measurements are needed to determine the relative importance of nitrogen transformation processes as a source of 15N to groundwaters; however, it is clear that continued inputs of anthropogenic N via SGD have the potential to severely impact ecologically and economically valuable seagrass meadows and coral reefs along the Caribbean coast of Mexico.

Nitrate pollution of groundwater in the Yellow River delta, China

Nitrate pollution of groundwater in the Yellow River delta, China is an important issue related not only to nitrate dispersion and health concerns but also to mass transport and interactions of groundwater, sea, and river waters in the coastal area. The spatial distribution of nitrate, nitrate sources, and nitrogen transformation processes were investigated by field surveys and geochemical methods. Nitrate occurred mainly in shallow layers and had a spatial distribution coinciding with geomorphology and land/water use. Irrigation water from the Yellow River and anthropogenic waste are two main nitrogen sources of nitrate in the delta, and both denitrification and mixing processes could take place according to characteristics identified by ionic and isotopic data.

New Aspects of Microbial Nitrogen Transformations in the Context of Wastewater Treatment – A Review

AbstractOver the past few years, new technologies for nitrogen removal have been developed mainly because of the increasing financial costs of the traditional wastewater treatment technologies. Newly discovered pathways, like the anaerobic oxidation of ammonium (ANAMMOX), and uses for nitrogen removal technologies are under discussion. Processes and technologies such as: Partial nitrification; Single reactor systems for High Ammonium Removal Over Nitrite (SHARON); Anammox; Aerobic/anoxic deammonification; Oxygen Limited Autotrophic Nitrification‐Denitrification (OLAND); Completely Autotrophic Nitrogen Removal Over Nitrite (CANON); wetland based systems, all have a high potential for nitrogen removal. However, the pathways of nitrogen transformation processes are very complex. An understanding of how various environmental factors affect these processes and a sound knowledge of existing, worldwide experience pertaining to these novel technologies are the key if the nitrogen removal rates are to be improved and success is to be realized in full‐scale applications. This review describes the present knowledge of the new treatment technologies for wastewater with high nitrogen loads. Special emphasis is given to the influence of environmental factors and the reactor configuration on the nitrogen transformation process and microbial activity.

Spatial and temporal variation of nitrous oxide and methane flux between subtropical mangrove sediments and the atmosphere

We quantified spatial and temporal variations of the fluxes of nitrous oxide (N 2O) and methane (CH 4) and associated abiotic sediment parameters across a subtropical river estuary sediment dominated by grey mangrove ( Avicennia marina). N 2O and CH 4 fluxes from sediment were measured adjacent to the river (“fringe”) and in the mangrove forest (“forest”) at 3-h intervals throughout the day during autumn, winter and summer. N 2O fluxes from sediment ranged from an average of −4 μg to 65 μg N 2O m −2 h −1 representing N 2O sink and emission. CH 4 emissions varied by several orders of magnitude from 3 μg to 17.4 mg CH 4 m −2 h −1. Fluxes of N 2O and CH 4 differed significantly between sampling seasons, as well as between fringe and forest positions. In addition, N 2O flux differed significantly between time of day of sampling. Higher bulk density and total carbon content in sediment were significant contributors towards decreasing N 2O emission; rates of N 2O emission increased with less negative sediment redox potential ( E h). Porewater profiles of nitrate plus nitrite (NO x −) suggest that denitrification was the major process of nitrogen transformation in the sediment and possible contributor to N 2O production. A significant decrease in CH 4 emission was observed with increasing E h, but higher sediment temperature was the most significant variable contributing to CH 4 emission. From April 2004 to July 2005, sediment levels of dissolved ammonium, nitrate, and total carbon content declined, most likely from decreased input of diffuse nutrient and carbon sources upstream from the study site; concomitantly average CH 4 emissions decreased significantly. On the basis of their global warming potentials, N 2O and CH 4 fluxes, expressed as CO 2-equivalent (CO 2-e) emissions, showed that CH 4 emissions dominated in summer and autumn seasons (82–98% CO 2-e emissions), whereas N 2O emissions dominated in winter (67–95% of CO 2-e emissions) when overall CO 2-e emissions were low. Our study highlights the importance of seasonal N 2O contributions, particularly when conditions driving CH 4 emissions may be less favourable. For the accurate upscaling of N 2O and CH 4 flux to annual rates, we need to assess relative contributions of individual trace gases to net CO 2-e emissions, and the influence of elevated nutrient inputs and mitigation options across a number of mangrove sites or across regional scales. This requires a careful sampling design at site-level that captures the potentially considerable temporal and spatial variation of N 2O and CH 4 emissions.

Modeling Nitrogen Movement in Rice Irrigated Using Sewage Water

A numerical model is described to simulate water and nitrogen transport and transformations under transient soil water flow conditions. The nitrogen transformation processes considered were nitrification, denitrification, immobilization, mineralization, and ionic exchange of ammonium. The model was evaluated using experimental data from a lysimetric study. Two sets of lysimeters were irrigated with sewage water, whereas, one set was irrigated with tubewell water. Each set had four lysimeters having depths of 1.2, 1.5, 1.8, and 2.0m. Soil and leachate samples were collected and analyzed at regular intervals for NH; -N and N03-N. Model predictions of NH4+-N and N03-N were in close agreement with the observed values except for 37th day observations for NH4+-N and II Oth day observations in case ofN03-N. To evaluate the model performance a paired t test and root mean square error (RMSE) methods were applied. The RMSE values ranged from 0.1 to 3.9 and 0.05 to 2.55 for the ammonium and nitrate distributions, respectively.

Dynamics of the nitrogen transformation in a shallow stream and possible interventions

This paper presents the assessment of the efficiency of the main biological nitrogen transformation processes in a shallow well-oxygenated river and conditions under which they are active and stabilise. The process dynamics was studied with the help of mathematical modelling of 2 years on-line data series measured in a reach of the Toess River, Switzerland. The algal nitrogen uptake was very stable and unaffected by most but frequent flood events. Daylight photosynthetic nitrogen uptake stabilised at 6 mgN mstreambed(-2) h(-1) (15 degrees C), dark uptake on storage products at rates of 0.5-2.5 mgN mstreambed(-2) h(-1). Nitrogen uptake by heterotrophic bacteria in the hyporheic zone was relatively constant at a level of 1.5-3.5 mgN mstreambed(-2) h(-1). Streambed nitrification could establish only during periods with average an daily concentration of at least 0.3 g(NH4-N) m(-3) in river water for several weeks. The maximum nitrification rate was 35 mgN mstreambed(-2) h(-1) for 3 g(NH4-N) m(-3). The effects of reduced nitrification in the WWTP and of river banks shading on a sudden ammonium peak were simulated. A river reach endangered by ammonium spills should be kept open to sun to favour ammonium uptake by algae. In-stream nitrification reduces ammonium peaks efficiently but leads to toxic nitrite concentrations.

Determination of respiration, gross nitrification and denitrification in soil profile using BaPS system

A facility of BaPS (Barometric Process Separation) was used to determine soil respiration, gross nitrification and denitrification in a winter wheat field with depths of 0—7, 7—14 and 14—21 cm. N 2O production was determined by a gas chromatograph. Crop root mass and relevant soil parameters were measured. Results showed that soil respiration and gross nitrification decreased with the increase of soil depth, while denitrification did not change significantly. In comparison with no-plowing plot, soil respiration increased significantly in plowing plot, especially in the surface soil of 0—7 cm, while gross nitrification and denitrification rates were not affected by plowing. Cropping practice in previous season was found to affect soil gross nitrification in the following wheat-growing season. Higher gross nitrification rate occurred in the filed plot with preceding crop of rice compared with that of maize for all the three depths of 0—7, 7—14 and 14—21 cm. A further investigation indicated that the nitrification for all the cases accounted for about 76% of the total nitrogen transformation processes of nitrification and denitrification and the N 2O production correlated with nitrification significantly, suggesting that nitrification is a key process of soil N 2O production in the wheat field. In addition, the variations of soil respiration and gross nitrification were exponentially dependent on root mass ( P<0.001).

Correlation between the nitrogen content of soil and element uptake of maize in a pot experiment

Introduction The nitrogen content of the soil serves as a permanent nitrogen source for plants. Since a significant part of the nitrogen in the soil can be found partly in the humus materials and partly in other organic materials, plant and animal residues and in organic bounds in microorganisms, mineral nitrogen forms that are available for plant uptake account for only a few percentages of the total content. Most of the biogeochemical nitrogen transformation processes occur in the humus-rich layer of the soil between the natural vegetation and the crops via the contribution of the organisms living in the soil. The humus balance and nitrogen management of soils closely correlate. ROSSWALL (1976) estimated the nitrogen turnover of the microorganisms and the plant system to be 95% (cit. NEMETH, 1995). The transformation of organic matter in the soil is performed by the organisms living in the soil, the activity of which is largely determined by the ecological and agrotechnical factors. In our pot experiment, the changes in the soil nitrogen forms and in the biomass and nitrogen uptake of maize were determined in soils from a long-term fertilization experiment.

The hydrology of riparian buffer zones; two case studies in an ephemeral and a perennial stream

Riparian zones can provide a protective buffer between streams and adjacent land-based activities by removing nitrate from shallow groundwater flowing through them. Hydrological factors are an important influence on the effectiveness of riparian buffer zones in reducing pollutant loads delivered to streams. In this paper, we present results from a study of the hydrology of two riparian buffers belonging to an ephemeral and a perennial stream, which are part of a research project to study nitrogen transport and transformation processes in shallow groundwater in South-East Queensland, Australia. The investigation at the ephemeral site has shown that a shallow perched water table forms shortly after stream flow commences as a result of lateral flow from the stream to floodplain; it resides within the carbon-rich root zone and drains off after stream flow ceases. The low head gradient of 1% results in a low flow rate of about 6 cm/day along the floodplain, slow enough to allow effective removal of nitrate via denitrification to occur. The investigation at the perennial site has shown that water table dynamics within the floodplain are dissociated from the up-slope area except during over-bank flood events. During non-event conditions, there is low streamward gradient that results in a base flow component to the stream; the water table depth is about 3.5 m, hence missing most of the carbon-rich soils located close to the soil surface. During flood events, a reverse gradient towards the floodplain is formed; the streamward gradient is re-established after the flood wave passes. The water table fluctuates between 1.8 and 3.5 m under these conditions thus having a higher chance of interacting with more active floodplain sediments. Water stored in the floodplain has a residence time of 2–10 days, providing an opportunity for denitrification to reduce nitrate concentrations prior to water draining back to the stream.

Modelling Oxygen Transport in a Reedbed-constructed Wetland Purification System for Dilute Effluents

This paper describes a simple model of oxygen supply to aerobic microorganisms in a horizontal reedbed-constructed wetland. The model simulates oxygen transport through the water by diffusion and convection, and via the macrophyte plants to the microorganisms that reside on their roots. The model also describes nitrogen (N) transformation processes for organic material with high biological oxygen demand (BOD), ammonium and nitrate. Some of these transformation processes are aerobic and therefore constrained if the oxygen supply is inadequate. Parameter values have been selected for equations describing oxygen transport and N transformation rates to fit data from a functioning reedbed processing sewage from a rural community. This reedbed achieves a large reduction in ammonium concentration in the effluent. Since it is unlikely that so much ammonium could have been lost by volatilisation alone, this implies rapid transport of oxygen to the microorganisms to convert the ammonium to nitrate. This rate is substantially higher than that which can be explained by diffusion and convection through the water alone, suggesting an important role for oxygen transport via the plants to the roots.

Relationships between culturable soil microbial populations and gross nitrogen transformation processes in a clay loam soil across ecosystems

The size and quality of the soil organic matter (SOM) pool can vary between ecosystems and can affect many soil properties. The objectives of this study were to examine the relationship between gross N transformation rates and microbial populations and to investigate the role that SOM plays in these factors. In our study, culturable microbial and actinomycete populations were positively correlated with gross mineralization and ammonium (NH4+) consumption rates over time in both ecosystems. These correlations provide evidence that microbial plate counts could be a good representation of all microbes responsible for gross mineralization and gross NH4+ consumption. Rates of gross mineralization, nitrification and NH4+ consumption were significantly greater in forest soil than old-field soil. These greater rates in forest soil could be due to the presence of higher levels of readily transferable substrates in SOM. Gross nitrification rates were considerably lower than gross mineralization and NH4+ consumption rates over the experimental period, indicating heterotrophic uptake of NH4+ rather than use by autotrophic nitrifiers under soil and environmental conditions in this study. Additionally, microbial populations were significantly (p<0.01) greater in forest soil than in old-field soil, which could also be related to the higher level of SOM in the forest soil. Net mineralization and nitrification rates were similar between ecosystems. Results also showed that net rates were highly correlated to each other, but were not correlated with culturable microbes or gross N transformation rates, indicating the isolation of net rates in relation to fundamental controlling factors.

Modelling nitrogen removal in a coupled HRP and unplanted horizontal flow subsurface gravel bed constructed wetland

A coupled model was developed that incorporates all the major nitrogen transformation mechanisms influencing nitrogen removal in aquatic systems. The model simulates nitrogen transformation and removal processes in the high rate pond (HRP) and the subsurface constructed wetland unit (SSCW). The model considered organic nitrogen (ON), ammonia nitrogen (NH 3-N), and nitrate nitrogen ( NO 3 - - N ) as the major forms of nitrogen involved in the transformation chains. The influencing transformation mechanisms considered in the model include uptake of inorganic nitrogen by algae and bacteria, mineralization, sedimentation, volatilisation of ammonia and nitrification coupled with denitrification processes. The results showed that improved nitrogen removal occurred with increase in hydraulic time of the HRP unit. It was also revealed that the HRP can effectively be used to promote nitrification and subsurface flow gravel bed constructed wetland can be used as a denitrifying unit. The most efficient mechanisms were determined using a transformation model. The model indicated that nitrification and mineralization were dominant contributing 51.1% and 14.9%, respectively. Denitrification and mineralization were most significant in the SSCW accounting for 43.5% and 16.7%, respectively. Nitrification–denitrification route was observed to be the most significant mechanism for nitrogen removal in the coupled system with an overall contribution of 53%. The model predicted the overall nitrogen removal as 37% compared to 38.4% obtained from field measurements.

Nitrogen transformation in horizontal subsurface flow constructed wetlands I: Model development

In this paper a mathematical model for prediction of nitrogen transformation in horizontal subsurface flow constructed wetlands was developed. Two horizontal subsurface flow constructed wetlands were designed to receive organic loading rate below 50 kg/ha/d and hydraulic loading rate of 480 m 3/ha/d from a primary facultative pond. Two rectangular shaped units each 11.0 m long, 3.7 m wide and 1.0 m deep and bottom slope of 1% were constructed and filled with 6–25 mm diameter gravel pack to a depth of 0.75 m. Each unit was planted with Phragmites mauritianus with an initial plant density of 29,000 plants/ha. The plants were allowed to grow for about four months before sampling for water quality parameters commenced. Samples were collected daily for about three months. Dissolved oxygen, pH and temperature were measured in situ and ammonia, total Kjeldahl nitrogen, nitrates, nitrite and Chemical Oxygen Demand were measured in the laboratory in accordance with Standard Methods. The mathematical model took into account activities of biomass suspended in the water body and biofilm on aggregates and plant roots. The state variables modelled include organic, ammonia, and nitrate–nitrogen, which were sectored in water, plant and aggregates. The major nitrogen transformation processes considered in this study were mineralization, nitrification, denitrification, plant uptake, plant decaying, and sedimentation. The forcing functions, which were considered in the model, are temperature, pH and dissolved oxygen. Stella II software was used to simulate the nitrogen processes influencing the removal of nitrogen in the constructed wetland. One of the two-wetland units was used for model calibration and the second unit for model validation. The model results indicated that 0.872 gN/m 2 d was settled at the bottom of the wetland and on gravel bed and roots of the plants. However, 0.752 gN/m 2 d (86.2%) of the settled nitrogen was regenerated back to the water body, which means that only 13.8% of the settled nitrogen was permanently removed. Denitrification and nitrification were responsible for transformation of 0.436 gN/m 2 d and 0.425 gN/m 2 d, respectively. Uptake of nitrogen by plants was 0.297 gN/m 2 d out of which 0.140 gN/m 2 d was returned to the water body as plants decay. It was found that the major pathways leading to permanent removal of nitrogen in a horizontal subsurface flow constructed wetland system in descending order are denitrification (29.9%), plant uptake (10.2%) and net sedimentation (8.2%). A total nitrogen removal of 48.9% was achieved in this study.

Modelling Nitrogen Transformation in Horizontal Subsurface Flow Constructed Wetlands Planted with Phragmites Mauritianus

A mathematical model was developed to permit dynamic simulation of nitrogen interaction in a pilot horizontal subsurface flow constructed wetland receiving effluents from primary facultative pond. The system was planted with Phragmites mauritianus , which was provided with root zone depth of 75 cm. The root zone was packed with gravel of 6 to 25 mm diameter in uniform proportions. Stella II software was used to simulate nitrogen transformation processes. The results show that the most influential nitrogen transformation processes were nitrification, denitrification, plant uptake, decomposition and accretion of organic nitrogen. Volatilisation played a negligible role in reducing nitrogen at the typically neutral pH levels found in subsurface wetland systems. Denitrification process, which ensures the permanent removal of nitrogen, accounted for 0.219 g/m 2 .d, which was only 15.0% of incoming nitrogen load (1.458 gN/m 2 .d). Harvesting of plants removed 0.195 gN/m2.d (13.4%) from the system. Accretion of organic nitrogen was a major pathway accounting for 0.279 g/m 2 .d, which is 19.2% of all the influent nitrogen. The accumulation of ammonia nitrogen was found to be high compared to other water phase state variables (organic nitrogen and nitrate nitrogen). Journal of Civil Engineering Research and Practice Vol.1(2) 2004: 1-15

Handbook of processes and modeling in the soil-plant system

Handbook of processes and modeling in the soil-plant system

A coupled soil water and nitrogen balance model for flooded rice fields in India

Quantification of nitrate losses is important for devising measures to ensure sustainability of soil fertility and groundwater resources and for the development of crop nutrient management protocols. Hence, in the present study a simple model for assessing concentration of nitrate in water percolating out of the flooded rice (Oryza Sativa) fields is presented. The model considers all the important nitrogen (N) transformation processes that take place in flooded rice fields such as urea hydrolysis, volatilization, nitrification, mineralization, immobilization, denitrification, crop uptake and leaching. It is based on coupling of soil water and N-balance models. The coupled model also accounts for weather, and timings and amounts of water and fertilizer applications. All the N-transformations except plant uptake and leaching are considered to follow first-order kinetics. A heuristic procedure is developed for selection of the rate constants of the transformation processes for different soil and environmental conditions. The model is evaluated by comparing simulation results with published data of three field experiments conducted at two locations namely G.B. Pant University Farm, Pantnagar, UP and IARI Research Farm, New Delhi of India, respectively. The simulation results show that urea hydrolysis is completed within 7 days of fertilizer application. It was also observed that the volatilization loss of N varies from 25 to 33% of the applied fertilizer and 75% of the total volatilization loss occurs within 7 days of urea application. The modeled leaching losses from the field experiments varied from 20 to 30% of the applied N. The N-uptake by the crop increased immediately after the application of fertilizer and decreased at 60 days after transplanting. The model is sufficiently general to be used in a wide range of conditions for quantification of nutrient losses by leaching and developing water and fertilizer management strategies for rice in irrigated areas.

Water quality modeling of the Cahaba River, Alabama

The Cahaba River, a sixth-order stream, tributary to the Mobile-Alabama River, is one of the few free-flowing rivers in Alabama. The Cahaba River lies in north-central Alabama and its watershed includes a variety of land uses from forested and agricultural to urban. Water quantity and quality modeling of the Cahaba River using several modules of the hydrologic simulation program FORTRAN (HSPF) and the nonpoint source model (NPSM) using the GIS-based BASINS package showed good agreement with measured flow data for low- and high-flow years but poor agreement with total nitrogen concentrations in the water column. Disparities between modeling and measured water quality data are attributed to the limited point source data available for nitrogen inputs to the stream and the lack of nitrogen-transformation process modeling with the NPSM. Future simulations should include use of models with detailed nitrogen transformation modules.

Effect of ammonium and oxygen on methane and nitrous oxide fluxes across sediment–water interface in a eutrophic lake

Eutrophication has decreased the O 2 content and increased the NH 4 + availability in freshwaters. These changes may affect carbon and nitrogen transformation processes and the production of CH 4 and N 2O, which are important greenhouse gases. We studied release of CH 4 and N 2O from a eutrophic lake sediment under varying O 2 and NH 4 + conditions. Intact sediment cores were incubated in a laboratory microcosm with a continuous anoxic or oxic water flows containing 0, 50, 500, 5000, or 15 000 μM NH 4 +. With the anoxic flow, the sediment released CH 4, up to 7.9 mmol m −2 d −1. With the oxic flow, the CH 4 emissions were small indicating limited CH 4 production and/or effective CH 4 oxidation. Addition of NH 4 + did not affect sediment CH 4 release, evidence that the CH 4 oxidizing bacteria were not disturbed by the extra NH 4 +. The release of N 2O from the sediment was highest, up to 7.6 μmol m −2 d −1, with the oxic flow without NH 4 + addition. Oxygen was the key factor regulating the production of NO 3 −, which enabled denitrification and production of N 2O. However, the highest NH 4 + addition increased nitrification and associated O 2 consumption causing a decrease in sediment O 2 content and in accumulation of NO 3 − and N 2O, which were effectively reduced to N 2 in denitrification. In summary, sediment CH 4 and N 2O dynamics are regulated more by the availability of O 2 than extra NH 4 +. Anoxia in eutrophic lakes favouring the CH 4 production, is the major contributor to the atmospheric consequences of water eutrophication.

Soil Acidification Induced by Ammonium Sulphate Addition in a Norway Spruce Forest in Southwest Sweden

The contributions of different acidifying processes to the total protonload (TPL) of the soil in control plots (C) and ammonium sulphate treatedplots (NS) were studied in a Norway spruce stand in Southwest Sweden during 1988–1998. The annual deposition of inorganic nitrogen and sulphate was on average 18 kg N and 20 kg S ha-1. In addition the NS treated plots received 100 kg N and 114 kg S ha-1 annually. The amounts of nutrients added to the ecosystem by wet and dry deposition and the leaching at 50 cm depth were calculated. The net atmosphericproton load, the proton load by nitrogen transformations in the soil, the sulphate sorption/desorption in the soil and the excess base cation accumulation in biomass were calculated. There was no leaching of inorganic nitrogen from control plots during the study period. The net atmospheric proton deposition, originating from sulphuric and nitric acid deposition, was the main contributor to TPL in control plots. The addition of ammonium sulphate increased the leaching of ammonium, nitrate, sulphate, magnesium and calcium but not of potassium. The TPL in NS plots was about ten times that in control plots. The nitrogen transformation processes were the main contributors to TPL to NS soil, in the beginning by ammonium uptake and later also by nitrification. The pH decreased by 0.4 units in the mineral soil. The between-year variation in TPL during the eleven year period in C plots (200–1500 molc ha-1 yr-1) and in NS plots (1000–13000 molc ha-1 yr-1) was mainly dependent on the sorption or release of sulphate. Both in C and NS, the TPL was buffered mainly by dissolving solid aluminium compounds, most probably some Al(OH)3 phase.

Characterization of the microbial community and nitrogen transformation processes associated with moving bed bioreactors in a closed recirculated mariculture system

The microbial consortium of a moving bed bioreactor (MBB) connected to a marine recirculating aquaculture system was examined by denaturing gradient gel electrophoresis (DGGE) of amplified 16S rRNA gene fragments. Both ammonia and nitrite oxidizers, Nitrosomonas cryotolerans and Nitrospira marina, respectively, were found associated with the marine system as well as a number of heterotrophic bacteria, including Pseudomonas sp. and Sphingomonas sp. In addition, two Planctomycetes sp. were detected in the system suggesting the capability for anaerobic ammonia oxidation (anammox). The potential for carrying out different nitrogen transformation processes—nitrification, denitrification and anammox—by the bead consortium in both low and high organic load MBBs was measured by short-term batch incubation. Beads with a high organic load exhibited a lower nitrification rate (25 mg NH 3–N/m 2/h) than low organic load beads (31.5 mg NH 3–N/m 2/h) as well as the ability to carry out denitrification and anammox processes. The potential of using MBBs to induce different nitrogen transformation processes was evaluated, and it was found that this type of bioreactor has the capability to serve as a platform for mediating desired anoxic processes such as denitrification and anammox.