Total Nitrogen Mass Research Articles

Organic Nitrogen Retention in the Atchafalaya River Swamp

Freshwater diversions from the lower Mississippi River into the region’s wetlands have been considered an alternative means for reducing nitrogen loading. The Atchafalaya River Swamp, the largest freshwater swamp in North America, carries the entire discharge of the Red River and 30% of the discharge of the Mississippi River, but it is largely unknown how much nitrogen actually can be retained from the overflowing waters of the Mississippi–Atchafalaya River system. Nitrogen discharge from the upper Mississippi River Basin has been implicated as the major cause for the hypoxia in the Northern Gulf of Mexico, which threatens not only the aquatic ecosystem health, but also Louisiana’s fishery industry, among other problems. This study was conducted to determine the change in organic nitrogen mass as water flows through the Atchafalaya River Swamp and into the Gulf of Mexico. By utilizing the river’s long-term discharge and water quality data (1978–2002), monthly and annual organic nitrogen fluxes were quantified, and their relationships with the basin’s hydrologic conditions were investigated. A total Kjeldahl nitrogen (TKN) mass input–output balance between the upstream (Simmesport) and downstream (Morgan City and Wax Lake Outlet) locations was established to examine the organic nitrogen removal potential for this large swamp. The results showed that on average, TKN input into the Atchafalaya was 200 323 tons year−1 and TKN output leaving the basin was 145 917 tons year−1, resulting in a 27% removal rate of organic nitrogen. Monthly TKN input and output in the basin were highest from March to June (input vs. output: 25 000 vs. 18 000 tons month−1) and lowest from August to November (8000 vs. 6000 tons month−1). There was a large variation in both annual and inter-annual organic nitrogen removals. The variability was positively correlated with the amount of inflow water at Simmesport, suggesting that regulating the river’s inflow at the Old River flood control structures may help reduce nitrogen loading of the Mississippi River to the Gulf of Mexico. Furthermore, the in-stream loss of organic nitrogen indicates that previous studies may have overestimated nitrogen discharge from the Mississippi–Atchafalaya River system.

The effect of fire spatial scale on Bison grazing intensity

To determine whether fire spatial and temporal scales affect foraging behavior and grazing intensity by Bison (Bison bison), we burned three different patch sizes (225, 900, and 3600 m 2 ) across an otherwise homogeneous grassland landscape. We then monitored grazing intensity for the succeeding 14 months. During the first 5 months after the burn (August-January), the Bison grazing intensity pattern was affected by whether a plot was burned and only marginally affected by plot size. During the next 5 months (January-June), grazing intensity was unaffected by plot size, but was greatest in the unburned 225 and 3600-m 2 plots. The final 4 months (June-October), grazing intensity was unaffected by treatments other than being higher in the unburned 3600-m 2 plots. By the final sampling date, biomass was significantly greater in the burned plots and grazing intensity appeared to be responding to the amount of biomass present and the total amount of N present. The pattern displayed within the first 5 months after the burn is congruent with the expectations of optimal foraging theory with overmatching in the smallest plot size of 225 m 2 (BioScience 37 (1987) 789-799). The next two sampling periods displayed a matching aggregate response relative to biomass availability (Oecologia 100 (1999)107-117) and total nitrogen mass (g m -2 ). The temporal shift that we found in Bison response to burn patch size is, to our knowledge, the first such examination of both spatial and temporal responses by Bison to landscape heterogeneity. We now have quantitative evidence of how native herbivores can alter their foraging responses to changes in landscape structure over time.

Nutrient removal by a constructed wetland treating subsurface drainage from grazed dairy pasture

Nitrogen and phosphorus budgets over two annual periods are presented for an establishing surface-flow constructed wetland treating subsurface drainage from rain-fed, dairy cattle grazed pasture in the North Island of New Zealand. Drainage flows to the wetland (occupying ∼1% of the catchment area) were highly pulsed, associated with rainfall and soil water status, and differed between years (305 and 197 mm drainage). Flow-proportional sampling of inflow and outflow concentrations were combined with continuous flow records to calculate mass balances for the wetlands. Influent nitrate concentrations were high (median 11 g m−3) in both years, but transient loads of organic N were also an important form of N in the first year. Mass removal of total nitrogen (TN) and its main constituent forms nitrate/nitrite and organic N was recorded for all seasons over both annual periods studied. TN mass removal efficiency of 79% (841 g m−2 per year) in the first year, declined to 21% (40 g m−2 per year) in the second year, associated with changes in the magnitude, speciation and seasonal pattern of N export from the catchment. Ammoniacal N (NH4-N), which comprised <0.5% of TN loadings to the wetland, was generated in small amounts during passage through the wetland in both years. Total phosphorus (TP) in the drainage waters occurred at median concentrations of 0.1–0.2 g m−3, mainly in dissolved reactive forms (DRP 92% by mass). TP export rose by 101% (5.0 g m−2 per year) after passage through the wetland in the first year, but decreased by 12% (0.2 g m−2 per year) in the second year. The results show that constructed wetlands comprising ∼1% of catchment area can markedly reduce N export via pastoral drainage, but may be net sources of NH4-N, DRP and TP during establishment. Performance of the wetland appeared to be affected by both establishment/maturation factors and year-to-year climatic variations. Longer-term studies, supplemented by process-based laboratory and mesocosm investigations, are required to evaluate sustainable nutrient removal rates over a range of climatic conditions, and identify the key factors regulating performance.

A simple model of nitrogen retention in reservoirs

The total nitrogen mass balance was studied over a two-year period in two reservoirs located in south-eastern Poland. Theobserved nitrogen retention (Nret) inthe reservoirs ranged from 0.18 to 2.12g m-2d-1 (mean 0.83g m-2d-1) in case of theRzeszow Reservoir and from -0.02 to0.41 g m-2d-1 (mean 0.13g m-2d-1) in case of the SolinaReservoir, while the percentage retention(Nret) ranged from 7 to 42% (mean22%) and -15 to 73% (mean 35%),respectively. A good relationship betweenNret and nitrogen loads was observedfor the Solina Reservoir. The data obtainedby the author and collected from theresearches of 6 other reservoirs located insouthern Poland were used to develop anempirical model suitable to predict thenitrogen seasonal dynamics in a reservoir.The model allows for the determination ofboth the annual mean Nret value andits seasonal variation in a reservoir.

Effectiveness of groundwater nitrate removal in a river riparian area: the importance of hydrogeological conditions

Riparian areas are often considered important ecological ecotones that decrease the nitrate load of groundwater discharging into rivers. In this paper, the effectiveness of nitrogen removal from groundwater in a riparian area has been evaluated. We used a quantitative hydrogeological approach which delimited homogeneous stream tubes based on the water table contour. We constructed water and mass balances and used the results to estimate the mass of nitrogen removed by biological processes. Nitrogen removal effectiveness was calculated as the ratio of nitrogen removed to the total nitrogen mass flowing through the riparian area. This approach requires knowledge of the hydrogeological settings and coverage of an area larger than the study site. The removal we observed was seasonally variable, ranging between 2.2 and 7.6 mg N m −2 day −1, and represented up to 95% of the total nitrogen mass entering the riparian area in late summer. Removal effectiveness was only 27–38% in winter, due to the combination of a high nitrogen input and a low plant uptake. Nitrogen removal was highest in spring, but effectiveness was about 60% because the input was as high as in winter. Rainwater infiltrating the riparian area could represent almost the same quantity as groundwater input. Under such conditions, the dilution effect is very important in riparian areas that are not nitrate sources and it is essential to maintain this non-nitrate-emissive use. This study showed that the effectiveness of nitrogen removal in a riparian area is highly dependent on the pathway of water movement through its biologically active layers.

Water Quality Impacts of Three Biofilter Designs in Recirculating Aquaculture Systems

Nine recirculating aquaculture systems utilizing three biofilter types were placed on line and stocked with yellow perch, Percaflavescens, fingerlings. Biofilter type differed among systems, and included upflow pulsed bed bead filter, packed tower trickling filter, and rotating biological contactor. Following filter acclimation, a comparative analysis of biofilter performance was conducted, involving measurement of temperature, pH, dissolved oxygen, total ammonia-nitrogen, nitrite­ nitrogen, nitrate-nitrogen, alkalinity, total hardness, carbonaceous biochemical oxygen demand, dissolved organic carbon, and total suspended solids. Filter bed emergence promoted effective carbon dioxide stripping, pH maintenance, and consistent nitrification performance in trickling filters and rotating biological contactors. Higher total ammonia nitrogen mass removal rates were observed in trickling and rotating biological contactor filters than in bead filters. Low total ammonia nitrogen mass removal rates and nitrification efficiencies for all filters resulted from relatively high carbonaceous biological oxygen demand loadings. Analysis of areas under mass removal curves showed that RBC filters were surface area limited. Foam formation in trickling filters effectively removed total suspended solids from the culture water. Filter type did not have a significant effect on median

NUTRIENTS DISCHARGED TO THE MISSISSIPPI RIVER FROM EASTERN IOWA WATERSHEDS, 1996.19971

ABSTRACT: The introduction of nutrients from chemical fertilizer, animal manure, wastewater, and atmospheric deposition to the eastern Iowa environment creates a large potential for nutrient transport in watersheds. Agriculture constitutes 93 percent of all land use in eastern Iowa. As part of the U.S. Geological Survey National Water Quality Assessment Program, water samples were collected (typically monthly) from six small and six large watersheds in eastern Iowa between March 1996 and September 1997. A Geographic Information System (GIS) was used to determine land use and quantify inputs of nitrogen and phosphorus within the study area. Streamliow from the watersheds is to the Mississippi River. Chemical fertilizer and animal manure account for 92 percent of the estimated total nitrogen and 99.9 percent of the estimated total phosphorus input in the study area. Total nitrogen and total phosphorus loads for 1996 were estimated for nine of the 12 rivers and creeks using a minimum variance unbiased estimator model. A seasonal pattern of concentrations and loads was observed. The greatest concentrations and loads occur in the late spring to early summer in conjunction with row‐crop fertilizer applications and spring nmoff and again in the late fall to early winter as vegetation goes into dormancy and additional fertilizer is applied to row‐crop fields. The three largest rivers in eastern Iowa transported an estimated total of 79,000 metric tons of total nitrogen and 6,800 metric tons of total phosphorus to the Mississippi River in 1996. The estimated mass of total nitrogen and total phosphorus transported to the Mississippi River represents about 19 percent of all estimated nitrogen and 9 percent of all estimated phosphorus input to the study area.

Elevated CO2 increases nitrogen fixation and decreases soil nitrogen mineralization in Florida scrub oak

SummaryWe report changes in nitrogen cycling in Florida scrub oak in response to elevated atmospheric CO2 during the first 14 months of experimental treatment. Elevated CO2 stimulated above‐ground growth, nitrogen mass, and root nodule production of the nitrogen‐fixing vine, Galactia elliottii Nuttall. During this period, elevated CO2 reduced rates of gross nitrogen mineralization in soil, and resulted in lower recovery of nitrate on resin lysimeters. Elevated CO2 did not alter nitrogen in the soil microbial biomass, but increased the specific rate of ammonium immobilization (NH4+ immobilized per unit microbial N) measured over a 24‐h period. Increased carbon input to soil through greater root growth combined with a decrease in the quality of that carbon in elevated CO2 best explains these changes. These results demonstrate that atmospheric CO2 concentration influences both the internal cycling of nitrogen (mineralization, immobilization, and nitrification) as well as the processes that regulate total ecosystem nitrogen mass (nitrogen fixation and nitrate leaching) in Florida coastal scrub oak. If these changes in nitrogen cycling are sustained, they could cause long‐term feedbacks to the growth responses of plants to elevated CO2. Greater nitrogen fixation and reduced leaching could stimulate nitrogen‐limited plant growth by increasing the mass of labile nitrogen in the ecosystem. By contrast, reduced nitrogen mineralization and increased immobilization will restrict the supply rate of plant‐available nitrogen, potentially reducing plant growth. Thus, the net feedback to plant growth will depend on the balance of these effects through time.

Nitrogen uptake by rhizomes of the clonal sedge Carex bigelowii: a previously overlooked nutritional benefit of rhizomatous growth

Studies on the rhizomatous clonal sedge Carex bigelowii, at a fellfield site in subarctic Swedish Lapland examined the ecological potential of rhizomes as nitrogen uptake systems. Direct application of a solution of 15NH415NO3 to the rhizomes of C. bigelowii significantly enriched the 15N content of the plant tissue. The pattern of enrichment indicated movement of labelled nitrogen into rhizomes and adjoining tissue (including roots and shoots), showing both uptake and translocation via the rhizome system. There was a gradient of decreasing 15N enrichment with increasing distance from the point of labelling, and estimation of the total mass of nitrogen taken up via labelled rhizomes showed low levels and rates of uptake. Quantification of the size of rhizome and root systems of C. bigelowii at the study site indicates that 80% of the living biomass may be below ground, and that the surface area of the rhizome system of C. bigelowii is approx. two‐thirds that of the roots. The rhizome system of C. bigelowii can therefore act as a route for nitrogen uptake, with the potential to exploit almost as great a volume of soil as the root system. This mechanism of nitrogen uptake may play an important role in the Arctic, where many species have a clonal, rhizomatous growth form. In addition, plant growth in many arctic ecosystems is limited by low soil nutrient availability, a result of low temperatures (leading to slow soil decomposition rates) and patchy resource distribution. Nitrogen uptake via rhizomes may provide plants with the capacity to take advantage of transient nutrient supplies, and may partly compensate for the cost of developing and maintaining persistent rhizome networks in ecosystems where nutrient resources are in short supply.

Nitrogen cycling in the tropical rain forest of French Guiana: comparison of two sites with contrasting soil types using δ15N

The natural '5N abundance method for estimating symbiotic biolo- gical N2-fixation was tested on legume trees from two rain forests on contrasting soils (oxisols and spodosols) in Frenich Guiana. When possible, the siglnificance of N2-fixing species in the plant community was evaluated in terms of density, bio- mass and contribution of N2-fixation to the building up of the total nitrogen mass in the leaves. Of the two sites, the rain forest on spodosols was the less favourable for application of the 6'5N method: the available soil nitrogen was isotopically similar to fixed-N2. Hence, the results showed that a reliable estimate of N2- fixation could not be obtained. A substantial contribution of fixed-N2 to the nitro- gen nutrition of legumes was found on oxisols, with an average value of 54 % Ndfa (Nitrogen derived from the atmosphere). The contribution of the N2-fixing leg- umes to the biomass of the stand was estimated to be 2 t ha-' for the leaf biomass and 136 t ha-' for the total above-ground plant biomass. With 7.5 % of trees in the stand able to fix N2 (462 out of 6156), N2-fixation was estimated to be 7 kg ha-' y-'. These results are the first use of the 6'5N method to estimate nitrogen input by N2-fixing legumes to a natural rain forest. The inter-site variability observed in the 6'5N of the non-fixing plants suggested different nitrogen-cycling processes in the two soils. The 6'5N of the non-N2-fixing plants could be related to the soil nitrogen availability and be used as an indicator of efficient or non-efficient nitro- gen-cycling rain forests. The spatial variability of the 6'N in the plant-available soil nitrogen pool and the nitrogen balance in tropical rain forests are discussed.

Nitrogen transport and transformations in a shallow aquifer receiving wastewater discharge: A mass balance approach

Nitrogen transport and transformations were followed over the initial 3 years of development of a plume of wastewater‐contaminated groundwater in Cape Cod, Massachusetts. Ammonification and nitrification in the unsaturated zone and ammonium sorption in the saturated zone were predominant, while loss of fixed nitrogen through denitrification was minor. The major effect of transport was the oxidation of discharged organic and inorganic forms to nitrate, which was the dominant nitrogen form in transit to receiving systems. Ammonification and nitrification in the unsaturated zone transformed 16–19% and 50–70%, respectively, of the total nitrogen mass discharged to the land surface during the study but did not attenuate the nitrogen loading. Nitrification in the unsaturated zone also contributed to pH decrease of 2 standard units and to an N2O increase (46–660 µg N/L in the plume). Other processes in the unsaturated zone had little net effect: Ammonium sorption removed &lt;1% of the total discharged nitrogen mass; filtering of particulate organic nitrogen was less than 3%; ammonium and nitrate assimilation was less than 6%; and ammonia volatilization was less than 0.25%. In the saturated zone a central zone of anoxic groundwater (DO ≤ 0.05 mg/L) was first detected 17 months after effluent discharge to the aquifer began, which expanded at about the groundwater‐flow velocity. Although nitrate was dominant at the water table, the low, carbon‐limited rates of denitrification in the anoxic zone (3.0–9.6 (ng N/cm3)/d) reduced only about 2% of the recharged nitrogen mass to N2. In contrast, ammonium sorption in the saturated zone removed about 16% of the recharged nitrogen mass from the groundwater. Ammonium sorption was primarily limited to anoxic zone, where nitrification was prevented, and was best described by a Langmuir isotherm in which effluent ionic concentrations were simulated. The initial nitrogen load discharged from the groundwater system may depend largely on the growth and stability of the sorbed ammonium pool, which in turn depends on effluent‐loading practices, subsurface microbial processes, and saturation of available exchange sites.

Plasma immersion ion implantation (PI3) and r.f. plasma nitriding of a microalloyed steel

Plasma immersion ion implantation (PI3) is a hybrid surface treatment combining high-energy nitrogen implantation with plasma nitriding. More specifically, in PI3 the sample, whilst immersed in a radiofrequency (r.f.) plasma, is negatively biased to the implantation voltage, typically about 45 kV pulses with a duration of 100 μs. The high voltage is responsible for nitrogen implantation. However, it is believed that additional nitrogen would be thermocherm'cally absorbed on the surface during the highvoltage off-period owing to the presence of a d.c. self-bias developed on the sample still immersed in the r.f. plasma. The exact contribution of this self-bias to the total nitrogen mass transfer is not known at this time, but it is suspected to be significant, judging by the fact that the total nitrogen content of steels after PI3 treatment is always many times greater than the nominated implantation dose.In an effort to gain an idea about the extent of thermochemically driven nitrogen absorption, the following investigation was undertaken. Samples of a commercially available microalloyed steel were treated by PI3 and r.f. plasma nitriding under identical conditions. Based on extensive microstructural characterization of nitrided samples, it has been found that the PI3 process produced surface layers with higher hardness and thicker cases than r.f. plasma nitriding.

The response of a freshwater wetland to long-term “low level” nutrient loads - marsh efficiency

Total phosphorus (TP) and nitrogen (TN) mass balances were calculated for Boney Marsh, a subtropical constructed freshwater wetland located along the floodplain of the Kissimmee River in south Florida, USA. River water was diverted through the marsh for a 9-year period (1978–1986). Monthly mean retention rates were 0.03 and 0.41 g m −2 month −1 for TP and TN, respectively, for the period of record. Nutrient retention rates and nutrient loading rates were strongly correlated for TP but not for TN. Total phosphorus removal efficiencies were consistently higher than TN removal efficiencies at all times, and remained relatively unchanged during the entire study period. The subtropical marsh was a net positive sink for TP year-round but not for TN. Boney Marsh nutrient assimilation capacity remained high and invariable for the period of record for TP but not for TN. Our analysis showed that studies which derive nutrient removal estimates from reductions in surface water concentrations, rather than mass balances, may under-represent mass retention by as much as 50 and 100% for TP and TN, respectively. Rainfall contributions to Boney Marsh nutrient budgets could be as high as 99 and 94% for TP and TN, respectively, depending on the season. An apparent net settling velocity for total phosphorus of 9.93 m year −1 provided independent confirmation of settling rates previously estimated for the Water Conservation Areas of southern Florida.

Computer Aided Control of Nitrogen Removal in Small Activated Sludge Wastewater Treatment Plants

Extended aeration plants achieve almost complete nitrification, due to their mean solids retention time of more than two weeks. Intelligent control of nitrification and denitrification processes is called for, due to high energy-costs for additional oxygenation, uncontrolled denitrification processes in the final settling tanks (which impair the effluent quality) and lastly, high effluent nitrogen concentrations. Long experience is available from the application of an on-line nitrate monitor; interpretation of this gives detailed information about nitrification and denitrification processes and kinetics under real operating conditions, depending on temperature, MLSS, BOD and total nitrogen mass flow rates. The poor availability and reliability of the nitrate monitor as a control element led to the development of computer aided control of nitrogen removal processes. A common computer system has been completed with electronic filters, A/D converters and relay interfaces to control the functions of a new fine bubble diffusor system and three air blowers. The software is able to calculate the length of aerobic and anoxic intervals in order to realize a saw-tooth like graph of NOx concentration under various conditions. It also surveys the DO level during aeration periods.

Nodulation and nitrogen fixation in Purshia: inoculation responses and species comparisons

Nitrogen fixing trees and shrubs may be useful in revegetation efforts. Speculation that insufficient endophyte populations in surface soils may limit non-leguminous symbiotic nitrogen fixation in marginal land was explored.Purshia tridentata andP. glandulosa seedlings were grown in greenhouse trials using ten soils from nativePurshia sites. Treatments include a control, an inoculated treatment, and six mmole nitrogen amendment. When inoculated with aP.tridentata crushed nodule inoculum, two of five non-nodulating soils and three sparsely nodulating soils produced well nodulated plants. Inoculation also increased nodule mass, total nitrogen, nitrogen content and shoot dry mass in plants from some of the soils. Of the three soils failing to produce nodulated plants when inoculated, one produced plants that responded well to nitrogen additions but failed to nodulate under low nitrogen conditions; another produced severely stunted plants indicating nutritional limitations on the host; and the third produced plants that were not nitrogen deficient. An application of nitrogen completely suppressed nodulation in all but one soil. The twoPurshia species were similar in nodulation, nitrogen fixation and growth, although important exceptions exist that indicate species may differ in adaptability to certain soil conditions.

Runoff Water Quality from Dairy Pastures in the Piedmont Region

ABSTRACT EIGHT (0.012 ha) runoff plots were used to collect seven months of background information on the run-off water quality from a dairy pasture. Following this period, dairy manure (dry and slurry) was applied to the plots and subsequently received weekly artificial rainfalls to determine water quality from the runoff. The total mass of total kjeldahl nitrogen, total solids, phosphorus, and chemical oxygen demand removed from that applied during seven runoff events ranged from 2.7 to 4.1 per-cent, 0.3 to 0.7 percent, 7.0 to 12.2 percent, and 1.2 to 2.6 percent, respectively.

Nitrogen balance during intermittent dialysis therapy of uremia

Daily measurements of nitrogen balance were made at two levels of protein intake in five patients undergoing chronic intermittent dialysis therapy. During ingestion of high (1.4 g/kg of body wt) protein intake, nitrogen balance was positive on nondialysis days and negative on dialysis days, so that cumulative balance for the week of study was not different from zero. During ingestion of low (0.5 g/kg) protein intake, nitrogen balance was approximately zero on nondialysis days but was again negative on dialysis days, so that cumulative balance for this period was negative. The negative nitrogen balance observed on dialysis days was associated with a higher rate of urea nitrogen generation (Gu, g/24 hr, determined by a kinetic model of urea nitrogen in dialysis patients) that was most evident in the hours immediately following dialysis. Net protein catabolic rate (PCR, g/24 hr), derived from total nitrogen mass balance equations, correlated very closely with Gu:Gu = 0.154 PCR - 1.7, r = 0.96. This relationship agreed well with previous observations made in nondialyzed uremic patients under more steady-state conditions. These studies demonstrate that nitrogen balance is negative on dialysis days regardless of protein intake, and that Gu is higher on dialysis days. The negative nitrogen balance could result from amino acid loss in dialysate and from increased protein catabolism stimulated by loss of glucose into dialysate.