Variation In Nitrogen Content Research Articles

Effect of Saturated Zone on Nitrogen Removal Processes in Stormwater Bioretention Systems

The introduction of a saturated zone (SZ) has been recommended to address the issue of nitrogen removal fluctuation in the bioretention system, which is one of the most versatile low-impact development facilities for urban stormwater management. Nine experimental columns were used to characterize the nitrogen concentration variations over the outflow during wetting periods and in SZ during the antecedent drying periods (ADPs), as well as compare removal efficiencies of various nitrogen species in systems with different SZ depths under alternate drying and wetting conditions. Results indicated that NO3−-N concentrations in the outflow showed quasi-logistic curve-shaped variations over time: being low (<0.5 mg/L) in the early process, sharply increasing thereafter, and finally flattening around 3.0 mg/L with NO3− leaching; NH4+-N and organic nitrogen (ON) concentrations were consistently low around 0.5 mg/L and 1.8 mg/L, respectively during the wetting periods. NH4+ removal efficiency in bioretention systems was consistently high around 80%, not varying with the increasing SZ depth; ON removal efficiency had a slight rise from 57% to 84% and NO3− removal efficiency was significantly enhanced from −23% to 62% with the SZ depth increasing from 0 to 600 mm. Deeper SZ could store more runoff and promote more denitrification of NO3− and mineralization of ON during the ADPs, providing more “old” water with low NO3− and ON concentrations for water exchange with “new” inflow of higher NO3− and ON concentrations during the wetting periods. The total nitrogen (TN) removal, a combined result of the instantaneous removal through adsorption and retention in the upper soil layer during the wetting periods and the gradual removal via denitrification and mineralization in SZ during the ADPs, was also improved by increasing the SZ depth; TN removal efficiency was elevated from 35% to 73% when the SZ depth increased from zero to 600 mm.

Wood carbonization as a protective treatment on resistance to wood destroying fungi

Wood, as a typical natural material, is crucial to extend its service lifetime through preservative treatments against both biological and abiotic processes. Conventional wood protective treatment methods have major disadvantages by utilization of toxic chemicals. In this study, a physical treatment approach against wood biodeterioration was tested via the carbonization treatment technique. Both Pinus sylvestris and poplar were systematically prepared under different conditions of carbonization treatments to analyze the mechanism of carbonization protective treatment and then the performance against biodeterioration. Variations of nitrogen contents, thiamine (Vitamin B1), inorganic salts, pH, moisture content and the mass loss of wood were investigated after the different carbonization treatments. Indigenous wood decay fungi were destroyed by the carbonization treatments to decrease the opportunity for initiation of destruction from inside the wood. The results also illustrated that significant change of pH and moisture content in wood were also remarkable, but the wood nitrogen contents, thiamine (Vitamin B1) and inorganic salt were not influenced much after carbonization treatments. Since the indigenous microflora and also their favourable conditions for growth were eliminated or further restricted, further protection can be extended for the service life of wood against fungal colonization and biodeterioration under selective conditions.

Denitrogenation model for vacuum tank degasser

Nitrogen in steel is both beneficial and detrimental depending on grade of steel and its application. To get desired low nitrogen during vacuum degassing process, VD parameters namely vacuum level, argon flow rate and holding time has to optimized depending upon initial nitrogen level. In this work a mathematical model to simulate nitrogen removal in tank degasser is developed and how various VD parameters affects nitrogen removal is studied. Ladle water model studies with bottom purging have shown two distinct flow regions, namely the plume region and the outside plume region. The two regions are treated as two separate reactors exchanging mass between them and complete mixing is assumed in both the reactors. In the plume region, transfer of nitrogen to single bubble is simulated. At the gas-liquid metal interface (bubble interface) thermodynamic equilibrium is assumed and the transfer of nitrogen from bulk liquid metal in the plume region to the gas-metal interface is obtained using mass transport principles. The model predicts variation of Nitrogen content in both the reactors with time. The model is validated with industrial process and the predicted results were found to have fair agreement with the measured results.

Increasing content of lipid in tropical microalgae Chlorella sorokiniana and Closterium sp. with variation of nitrogen content and extraction temperature

This research was aimed to obtain algae biofuels as an alternative energy which comes from tropical microalgae biomass Chlorella sorokiniana and Closterium sp. The cultivation was performed at a controlled room in batch culture photobioreactor, temperature 27°C, pH 6, aeration with air flow rate of 150 mL/sec, and light intensity at 2400 lux. These nutrient sources used artificial PHM with KNO3 variation as a nitrogen source of 0 grams; 0.25 grams; 0.5 grams; 1 gram. The research involved microalgae lipid extraction with Blight & Dyer method and also carried out support of alcohol, chloroform and distilled water (1:1:1) with optimum temperature 30oC. Oil yields that obtained were analyzed with Gas Chromatography Mass Spectrometry (GC-MS) method, dry weight with a gravimetric method and cell density with spectrophotometry. The result showed that the reduction of KNO3 materials (0,25 gr) can produce biomass and highest total lipid content at 0,41 g/L and 20,31 %/(w/w). The results showed that KNO3 decreased the amount of biomass which was not significant but the total lipid content of microalgae was increased. Lipid content and fatty acids extracted from Blight & Dyer showed oil content that could potentially be the raw material of biodiesel.

Temporal-spatial variations and influencing factors of nitrogen in the shallow groundwater of the nearshore vegetable field of Erhai Lake, China.

Nitrogen export from the nearshore vegetable field of Erhai Lake seriously threatens the water quality of Erhai Lake, which is the second largest highland freshwater lake in Yunnan Province, China. Among the nitrogen flows into Erhai Lake, shallow groundwater migration is a major pathway. The nitrogen variation and influencing factors in the shallow groundwater of the nearshore vegetable field of Erhai Lake are not well documented. A 2-year field experiment was conducted to determine the concentrations of nitrogen species in the shallow groundwater and their influencing factors in the nearshore vegetable field of Erhai Lake. The results showed that concentrations of TN, NO3--N, and NO2--N gradually increased with increasing elevation and distance from Erhai Lake, but the opposite was observed for NH4+-N in the shallow groundwater. The concentrations of nitrogen species in the rainy season were greater than those in the dry season. NO3--N accounted for more than 79% of total nitrogen in shallow groundwater. Redundancy analysis showed that more than 70% of the temporal and spatial variations of nitrogen concentrations in the shallow groundwater were explained by shallow groundwater depth, and only approximately 10% of variation was explained by the factors of soil porosity, silt clay content of soil, and NH4+-N and NO3--N concentrations of soil (p < 0.05). The shallow groundwater depth had more notable effects on nitrogen concentrations in the shallow groundwater than other factors. This result will strongly support the need for further research regarding the management practices for reducing nitrogen concentrations in shallow groundwater.

Nitrogen absorption behaviors of ZrVFe and related alloys

For the future use of hydrogen storage alloys for ammonia synthesis, nitrogen absorption behaviors of ZrVFe, ZrVFe (Ti) and ZrVFe (Ti-Al), where the elements in parentheses were added or substituted, were volumetrically investigated by successively adding nitrogen at selected temperatures between 593 and 653 K. Nitrogen contents of ZrVFe (Ti-Al) were the highest among the tested three alloys and reached 5.4 mass% under 1 MPa of nitrogen at 653 K. Variations of nitrogen contents with nitrogen pressures showed plateau-like features, that is, the nitrogen contents rapidly increased with the pressures maintained at around 0.01 MPa. Only ZrVFe (Ti-Al) showed additional plateau-like features under approximately 0.0001 MPa. Supplementary addition of aluminum brought about nitrogen absorption ability under very low pressures to maximize the nitrogen absorption capacity of ZrVFe (Ti-Al). While X-ray diffraction peaks from ZrVFe and ZrVFe (Ti) did not substantially change on nitrogenation, those from nitrogenated ZrVFe (Ti-Al) shifted to the lower angles, became broad and contained the peaks from separated phases. Supplementary addition of aluminum would impart thorough nitrogen absorption ability to ZrVFe. Absorbed nitrogen would exist on the surfaces or in the vicinity of the surfaces of the alloys, and significant pulverization of ZrVFe (Ti-Al) during proposed activation treatment would provide reactive surfaces to absorb large amounts of nitrogen.

Evaluation of Carbon Sequestration Potential in Amla (Emblica officinalis Gaertn.) Orchards in Semi-arid Region of India

Carbon sequestration potential in terms of above and below ground biomass carbon and soil organic carbon in orchards of Emblica officinalis in semi-arid Rajasthan has been estimated. Total carbon stock in soil was calculated using allometric equations. Physico-chemical properties of topsoil and subsoil have been studied using standard methods. Chakaiya variety was found to be most suitable for C sequestration with 66.32 kg/plant above ground biomass out of the three varieties of E. officinalis under study namely chakaiya, kanchan and narendra. The age difference of 2 years between two orchards of the same variety (Chakaiya) had no significant difference in their above ground biomass. Total C stock varied from 19.16 to 19.39 Mg ha−1 in 12 years of old plantations. Variation in nitrogen content in subsoil samples has been observed. But, it remained unchanged in topsoil. From the carbon sequestration potential point of view, E. officinalis is an efficient native genotype with 23.48 Mg ha−1 biomass in 14 years duration in the semi-arid region.

Nitrogen content determinations in different stages of thermal treatment involved in conversion of ammonium diuranate to uranium metal

Determination of nitrogen content in the uranium metal and uranium oxide based reactor fuels is important to meet the requirement of specifications given by fuel designer. Therefore, a systematic study was carried out to determine the variations in nitrogen content during the conversion of ammonium diuranate (ADU) to uranium oxides (UO3 and UO2), and finally to uranium metal by inert gas fusion-thermal conductivity detection (IGF-TCD) technique. To understand the measured nitrogen content variations, the thermal decomposition study of ADU was carried out using thermogravimetry (TG)/differential thermogravimetry (DTG) and differential thermal analysis (DTA) in the temperature range of 25–1073 K. Powder X–ray diffraction (XRD) technique was used to confirm the formation of uranium oxide precursors at different temperature.

Intra-crystal co-variations of carbon isotopes and nitrogen contents in diamond from three North American cratons

Eighteen diamond samples from the A154 South kimberlite pipe (Diavik Mine), Slave Craton, Northwest Territories (Canada); sixteen diamond samples from the Lynx kimberlite dyke, Superior Craton, Quebec (Canada) and twelve diamond samples from the Kelsey Lake kimberlite pipe, Wyoming Craton, Colorado (USA), were cut through the core-zones, polished, imaged by cathodoluminescence (CL), and analyzed by secondary ion mass spectrometry (SIMS) for carbon isotope composition and nitrogen abundance. Twenty Kelsey Lake diamond plates, including the twelve crystals analyzed by SIMS, were analyzed by Fourier transform infrared spectrometry (FTIR) for nitrogen concentration and aggregation state.Diamond samples from Diavik and Kelsey Lake have average δ13CPDB and nitrogen contents (atomic ppm) similar to those found by earlier studies: averaging between −3.9‰ and 486ppm, and −7‰ and 308ppm, respectively. Samples from the Lynx dyke, investigated for the first time, are substantially different, having δ13C=−1.2‰ and nitrogen content=32ppm (averages). All three localities have examples of significant variations in nitrogen content (>100ppm) within single stones. Carbon isotope variation within individual stones is relatively minor (<2‰). In terms of nitrogen aggregation, samples from the Kelsey Lake kimberlite are dominated by zones of Type IaA, but mixed-type and Type IaB (less common) stones also occur. For the majority of samples, overall intra-diamond zonations of nitrogen abundances and carbon isotope ratios are not in agreement with modeled trends for single-event Rayleigh fractionation of diamond from fluid under nitrogen-compatible conditions at 1100°C. The involvement of fluids from subducted crustal reservoirs with exceptionally light, and in the case of Lynx samples, exceptionally heavy δ13CPDB values is necessary to explain the observed growth histories of all the samples studied here.

Assessing changes in thermally upgraded papers with different nitrogen contents under accelerated aging

Thermally upgraded Kraft (TUK) papers prepared from the same batch process but with a different percentage of stabilizing additives (1.2, 2.6 and 4.4% of nitrogen) were studied under accelerated aging at 170 °C. The increment of stabilizing additives in paper with the consequent increment of nitrogen content slows down the rate of molecular chain scission of the cellulose and reduces the paper tensile strength loss rate. However, a progressive reduction in the enhancement of the paper life span by the increment of nitrogenous additives in paper was observed. The cellulose degradation methanol and ethanol markers were found to be reliable and accurate for tracking the aging of TUK papers even with the variation of nitrogen content in paper. A promising correlation between methanol concentration and the paper tensile index with different nitrogen content was determined. This correlation could be used as a basis for developing tools to assess power transformers residual life. FTIR-ATR analyses of dicyandiamide in aged papers showed a rapid reaction and decomposition of dicyandiamide in other compounds that slows down cellulose aging. The nitrogen content of aged paper, measured with the Dumas method, showed a slight variation during the study. This implies that the nitrogen compounds continue to be attached, presumably by polar forces to the paper. Thermogravimetric analysis (TGA) of new and aged Insuldur® paper samples showed that nitrogen additives improve the thermal stability of paper at high temperatures.

Plasmonic properties of titanium nitride thin films prepared by ion beam assisted deposition

Titanium nitride (TiNx) is regarded as a kind of promising plasmonic material for its high performances. We studied the influence of nitrogen partial pressure pn and deposition temperature Td on the structural and plasmonic properties of the TiNx thin films prepared by ion beam assisted deposition (IBAD). The results show that IBAD is an effective method to tailor the plasmonic properties of TiNx films in visible and near-IR region. The plasmonic properties of the films have significant Td and pn dependence. Higher pn and lower Td can reduce the plasma frequency and the plasmon resonance. Higher pn and higher Td can reduce the optical loss of the samples. The modification of the plasmonic properties is related to the variation of nitrogen content.

Spatial and temporal variation of nitrogen concentration and speciation in runoff and storm water in the Indian River watershed, South Florida

Nitrogen (N) is considered as a key element that triggers algal boom in the Indian River Lagoon (IRL), South Florida. Intensive agriculture may have contributed to increased N input into the IRL. Runoff and storm water samples were collected in representative agricultural fields and along waterways that connect lands to the IRL from April 2013 to December 2014. Concentrations of different N species (particulate N, dissolved organic N, dissolved NH4 (+)-N, and NO3 (-)-N) and related water physical-chemical properties were measured. Total N (TN) concentrations generally decreased from agricultural field furrows to discharging point of the waterways but were generally above the US EPA critical level (0.59mgL(-1)) for surface water. Organic N was the dominant form of dissolved N, followed by NO3 (-)-N, and dissolved NH4 (+)-N. Concentrations and speciation of N in water varied with sites and sampling times but were generally higher in summer and fall and lower in spring and winter, as affected by the seasonality of regional hydrology and agricultural practices. Correlations occurred between N concentration, water physical properties, and rainfall. This information has important implications in the development of best management practices to minimize the impacts of agricultural practice on N loading in the Indian River Lagoon.

Does host plant quality affect the oviposition decisions of an omnivore?

Optimal oviposition theory predicts a positive relationship between female preference for oviposition hosts and offspring performance. Interspecies effects on oviposition preference have been widely investigated, especially for herbivores. However, intraspecies variation, such as nitrogen content, might also influence female preference for oviposition hosts and subsequent offspring performance. To evaluate this possibility, we investigated the oviposition preference of a zoophytophagous omnivore and the development and survival of its nymphs on a single species of host plant that varied in nitrogen content. In choice and no-choice experiments without prey, female omnivores were allowed to oviposit on plants that had been fertilized using 4 rates of nitrogen fertilizer (39, 78, 156, and 311 mg/L nitrogen) for 72 h. After 72 h, the most females were found on tomato plants receiving high concentrations of nitrogen fertilizer and more eggs were laid on those plants. First instar nymphs developed more rapidly on high-nitrogen plants and third instar nymphs developed faster on low-nitrogen plants. Plant nitrogen did not affect nymph survival to the adult stage, or the probability of survival over time. Although female omnivores did discriminate between potential oviposition hosts based on plant nitrogen, their choices did not significantly impact nymph development or survival. This is the first study to show that intraspecies variation in nitrogen content between plants affects the oviposition preference of female omnivores, but not offspring performance.

Land use and topography as predictors of nitrogen levels in tropical catchments in Xishuangbanna, SW China

The conversion of vast tropical forests to cash crops represents a widespread land-use change in tropical regions, and has consequences for soil and water biogeochemical cycles. We examined how the conversion of tropical forest to rubber plantations in Xishuangbanna, southwest China, influenced the nitrogen concentrations in stream water. Water samples were collected between 2008 and 2010 at 35 sites to search for spatial and temporal variations in nitrogen concentrations and for their relationships with environment variables. Streams associated with rubber plantations (“rubber streams”) had significantly higher total N (TN) and total dissolved N (TDN) concentrations than forest streams during all seasons. TN, TDN and nitrate concentrations were observed to be significantly higher in streams associated with mixed land use than in forest streams only in the middle rainy season. The highest TN, TDN and nitrate concentrations were observed in rubber streams, and the lowest were observed in forest streams, indicating that land-use change had a significant effect on N concentrations. Statistically significant seasonal differences in TN, TDN and nitrate concentrations, with the greatest values in the middle rainy season, were observed in rubber and mixed streams, but not in forest streams. Canonical correspondence analysis identified the proportions of rubber plantation and tropical forest land, as well as slope gradient, as primary predictors of nitrogen concentration. Our results indicate that controlling rubber plantation expansion on steep slopes and avoiding single or large areas of rubber plantation within a catchment can mitigate nutrient loss.

Nutrient Dynamics of Estuarine Invertebrates Are Shaped by Feeding Guild Rather than Seasonal River Flow.

This study aimed to determine the variability of carbon and nitrogen elemental content, stoichiometry and diet proportions of invertebrates in two sub-tropical estuaries in South Africa experiencing seasonal changes in rainfall and river inflow. The elemental ratios and stable isotopes of abiotic sources, zooplankton and macrozoobenthos taxa were analyzed over a dry/wet seasonal cycle. Nutrient content (C, N) and stoichiometry of suspended particulate matter exhibited significant spatio-temporal variations in both estuaries, which were explained by the variability in river inflow. Sediment particulate matter (%C, %N and C:N) was also influenced by the variability in river flow but to a lesser extent. The nutrient content and ratios of the analyzed invertebrates did not significantly vary among seasons with the exception of the copepod Pseudodiaptomus spp. (C:N) and the tanaid Apseudes digitalis (%N, C:N). These changes did not track the seasonal variations of the suspended or sediment particulate matter. Our results suggest that invertebrates managed to maintain their stoichiometry independent of the seasonality in river flow. A significant variability in nitrogen content among estuarine invertebrates was recorded, with highest % N recorded from predators and lowest %N from detritivores. Due to the otherwise general lack of seasonal differences in elemental content and stoichiometry, feeding guild was a major factor shaping the nutrient dynamics of the estuarine invertebrates. The nutrient richer suspended particulate matter was the preferred food source over sediment particulate matter for most invertebrate consumers in many, but not all seasons. The most distinct preference for suspended POM as a food source was apparent from the temporarily open/closed system after the estuary had breached, highlighting the importance of river flow as a driver of invertebrate nutrient dynamics under extreme events conditions. Moreover, our data showed that estuarine invertebrates concentrated C and N between 10–100 fold from trophic level I (POM) to trophic level II (detritivores/deposit feeders) and thus highlighted their importance not only as links to higher trophic level organisms in the food web, but also as providers of a stoichiometrically homeostatic food source for such consumers. As climate change scenarios for the east coast of South Africa predict increased rainfall as a higher number of rainy days and days with higher rainfall, our results suggest that future changes in rainfall and river inflow will have measurable effects on the nutrient content and stoichiometry of food sources and possibly also in estuarine consumers.

Nitrogen Solubility in High‐Manganese Steel Grades

The solubility of nitrogen in molten steel depends on temperature and also on the concentration of alloyed elements. In this work, the variation of nitrogen content is investigated as a function of the manganese content at varied nitrogen partial pressures in atmosphere. Previous works are compared to the experimental results of this study. Furthermore, a second order interaction coefficient was determined for nitrogen partial pressures from 60 to 1013 mbar and a [Mn] content up to 30 wt% Those investigations have been carried‐out to receive more data for the design of metallurgical processes concerning the production of the new group of high [Mn]‐steel grades with extraordinary properties combinations like high strength simultaneously with high formability.

Relationship Between Atmospheric Ammonia Concentration and Nitrogen Content in Terricolous Lichen (Cladonia portentosa)

From April 2006 to April 2007, the geo- graphical and seasonal variation in nitrogen content in terricolouslichen(Cladoniaportentosa)andatmospher- ic ammonia concentrations were measuredat fiveheath- land sites. The seasonal variation in the nitrogen content of the lichen was small, even though there was a large seasonal variation in the air concentration of ammonia. A sizable local variation in the nitrogen content of the lichen was found even at the scale of a few kilometres. The nitrogen content in the lichen showed a high corre- lation to the yearly mean value of the measured ammo- nia concentration in air at the different locations. This investigation is part of a larger attempt to incorporate effects of nitrogen in the conservation status of terres- trial habitat types.

Seasonal changes in carbon and nitrogen compound concentrations in a Quercus petraea chronosequence.

Forest productivity declines with tree age. This decline may be due to changes in metabolic functions, resource availability and/or changes in resource allocation (between growth, reproduction and storage) with tree age. Carbon and nitrogen remobilization/storage processes are key to tree growth and survival. However, studies of the effects of tree age on these processes are scarce and have not yet considered seasonal carbon and nitrogen variations in situ. This study was carried out in a chronosequence of sessile oak (Quercus petraea Liebl.) for 1 year to survey the effects of tree age on the seasonal changes of carbon and nitrogen compounds in several tree compartments, focusing on key phenological stages. Our results highlight a general pattern of carbon and nitrogen function at all tree ages, with carbon reserve remobilization at budburst for growth, followed by carbon reserve formation during the leafy season and carbon reserve use during winter for maintenance. The variation in concentrations of nitrogen compounds shows less amplitude than that of carbon compounds. Storage as proteins occurs later, and mainly depends on leaf nitrogen remobilization and root uptake in autumn. We highlight several differences between tree age groups, in particular the loss of carbon storage function of fine and medium-sized roots with tree ageing. Moreover, the pattern of carbon compound accumulation in branches supports the hypothesis of a preferential allocation of carbon towards growth until the end of wood formation in juvenile trees, at the expense of the replenishment of carbon stores, while mature trees start allocating carbon to storage right after budburst. Our results demonstrate that at key phenological stages, physiological and developmental functions differ with tree age, and together with environmental conditions, influence the carbon and nitrogen concentration variations in sessile oaks.

Temporal trends in nitrogen concentrations and losses from agricultural catchments in the Nordic and Baltic countries

Long-term monitoring data from catchments with relatively uniform land use is important in order to cover management needs such as implementation of various EU Directives. This paper in a uniform fashion examines the temporal trends in nitrogen (N) concentrations and losses from agricultural catchments in the Nordic and Baltic countries. Thirty-five (35) catchments (range 0.1–33km2) in Norway (9), Denmark (5), Sweden (8), Finland (4), Estonia (3), Latvia (3) and Lithuania (3) were selected for this study. The longest time series were 23 years (1988–2010), while the shortest one was 10 years (2002–2011). The monthly nitrogen concentration and loss data series were tested for statistical trends (p<0.05; two-sided test) using the partial Mann–Kendall (PMK) test with stream discharge as an explanatory variable.The study results show a large variation in nitrogen concentrations and losses among the studied catchments, with a large interannual variability in all catchments. For nitrogen losses, 11 statistically significant trends were detected. Nine of these were downward (four out of five Danish catchments; four out of eight in Sweden; one out of three in Finland). Upward trends were detected in two catchments (one in Estonia and one in Latvia). For nitrogen concentrations, 13 statistically significant trends were detected. 10 of these were downward. Among the 11 catchments that showed trends in nitrogen losses, nine catchments also showed statistically significant trends in the in-stream concentration series. In addition, three more Swedish catchments showed downward trends in the concentration series, and one Estonian catchment showed an upward trend. These results indicate that targeted strategies towards reduced nitrogen losses from agricultural land (as in the case of Denmark and Sweden) may significantly improve nutrient surface water quality in small agricultural catchments

Comparing litter dynamics of Phragmites australis and Spartina alterniflora in a sub-tropical Chinese estuary: Contrasts in early and late decomposition

Litter decomposition in communities dominated by emergent macrophytes can be considered a two-phased decomposition process, a standing phase followed by decay on the sediment surface. We examined the decomposition and nutrient dynamics in both phases of three structural components (leaves, flowers, stems) of two common emergent macrophytes in the Min River estuary, southeast China. The two species were Phragmites australis, a native species, and Spartina alterniflora an invasive one. Decomposition was slower in the standing phase compared to the sediment surface phase for most structural components of both species. In the standing and sediment surface phase, the exponential breakdown rates (k-value) for all structural components of S. alterniflora were much greater than the corresponding values for P australis. The k-values in different components of P. australis and S. alterniflora ranged from 0.96 to 1.79×10−3d−1 and 1.67 to 4.58×10−3d−1 in the standing phase, and from 1.60 to 5.32×10−3d−1 and 3.05 to 6.93×10−3d−1 in the sediment surface phase, for the two species, respectively. Over the 210 day study, the litter carbon concentrations in three structural components of P. australis fluctuated considerably compared to S. alterniflora. The variations in nitrogen concentration of flower and stem litter in both species experienced a similar pattern throughout the experimental period, in the sediment surface phase, although the nitrogen concentration increased in both species. Litter phosphorus concentration showed a completely different pattern between the two species throughout.