Nitrogen Cycle

Immunoblot analyses performed with three monoclonal antibodies (MAbs) that recognized the nitrite oxidoreductase (NOR) of the genus Nitrobacter were used for taxonomic investigations of nitrite oxidizers. We found that these MAbs were able to detect the nitrite-oxidizing systems (NOS) of the genera Nitrospira, Nitrococcus, and Nitrospina. The MAb designated Hyb 153-2, which recognized the alpha subunit of the NOR (alpha-NOR), was specific for species belonging to the genus Nitrobacter. In contrast, Hyb 153-3, which recognized the beta-NOR, reacted with nitrite oxidizers of the four genera. Hyb 153-1, which also recognized the beta-NOR, bound to members of the genera Nitrobacter and Nitrococcus. The molecular masses of the beta-NOR of the genus Nitrobacter and the beta subunit of the NOS (beta-NOS) of the genus Nitrococcus were identical (65 kDa). In contrast, the molecular masses of the beta-NOS of the genera Nitrospina and Nitrospira were different (48 and 46 kDa). When the genus-s...

Ideal bacterial support medium for fixed film denitrification processes/bioreactors must be inexpensive, durable and possess large surface area with sufficient porosity. The present study has been focussed on removing nitrate nitrogen at two different nitrate nitrogen loading rates (60 (NLR I) and 120 (NLR II) mg l-1) from simulated aquaculture wastewater. Coconut coir fibre and a commercially available synthetic reticulated plastic media (Fujino Spirals) were used as packing medium in two independent upflow anaerobic packed bed column reactors. Removal of nitrate nitrogen was studied in correlation with other nutrients (COD, TKN, dissolved orthophosphate). Maximum removal of 97% at NLR-I and 99% at NLR – II of nitrate nitrogen was observed in with either media. Greater consistency in the case of COD removal of upto 81% was observed at NLR II where coconut coir was used as support medium compared to 72% COD removal by Fujino Spirals. The results observed indicate that the organic support medium is just as efficient in nitrate nitrogen removal as conventionally used synthetic support medium. The study is important as it specifically focuses on denitrification of aquaculture wastewater using cheaper organic support medium in anoxic bioreactors for the removal of nitrate nitrogen; which is seldom addressed as a significant problem.

Agricultural nutrient balances have been receiving increasing attention in both historical and nutrient management research. The main objectives of this study were to further develop balance methodologies and to carry out a comprehensive assessment of the functioning and nutrient cycling of 1950s agroecosystems in Portugal. Additionally, the main implications for the history of agriculture in Portugal were discussed from the standpoint of soil fertility. We used a mass balance approach that comprises virtually all nitrogen (N), phosphorus (P) and potassium (K) inputs and outputs from cropland topsoil for average conditions in the period 1951-56. We found a consistent deficit in N, both for nationwide (-2.1 kg.ha(-1).yr(-1)) and arable crops (-1.6 kg.ha(-1).yr(-1)) estimates, that was rectified in the turn to the 1960 decade. P and K were, in contrast, accumulating in the soil (4.2-4.6 kg.ha(-1).yr(-1) and 1.0-3.0 kg.ha(-1).yr(-1), respectively). We observed that the 1950s is the ver...

Due to their boom and bust population dynamics and the enormous biomasses they can attain, jellyfish and ctenophores can have a large influence on the cycling of carbon (C), nitrogen (N) and phosphorus (P). This review initially summarises the biochemical composition of jellyfish, and compares and contrasts the mechanisms by which non-zooxanthellate and zooxanthellate jellyfish acquire and recycle C, N

To detect soil changes related to vegetation and fertility restoration in a long fallow agricultural system of the Venezuelan Andes, 32 soil (A horizon, 0–15cm depth) and litter characteristics were studied in plots at different stages of the fallow-cultivation cycle. Four sectors of the valley were sampled, each one including seven plots: recently ploughed after a long fallow period; 1

Plasma technology is considered a sustainable and clean technology for the conversion of naturally abundant compounds (i.e., water (H2O) and nitrogen gas (N2)) into energy-abundant compounds (e.g., hydrogen gas (H2), ammonia (NH3)) or chemical feed molecules (e.g., nitric oxide (NO)). Here, we report a plasma catalyst-integrated system for sustainable ammonia production, which can facilitate massive, localized ammonia production. This study demonstrates the single-step cogeneration of H2 and nitric oxides (NOx) from H2O in the nitrogen discharge used for ammonia production, which proceeded via the catalytic reduction of NOx by H2. The proposed plasma technique yields higher NO and H2 concentrations than conventional plasma methods, which were used to obtain an ammonia concentration of ∼0.84% with a selectivity of ∼95% and a production rate of 120 μmol/s. These promising results provide a breakthrough in the transition toward sustainable and environmentally friendly ammonia production.

An exergy modeling and optimization of an industrial ammonia unit based on steam methane reforming (SMR) process is presented. The base-case unit produces about 1000 t NH3/day [1], as well as power and steam, with no auxiliary exergy use. Some critical operation parameters are analyzed and the base-case and optimal operating conditions of the major components are compared. Since the ammonia synthesis process is highly exothermic, higher per-pass conversions in industrial adiabatic reactors are often achieved by using various sequential catalyst beds, where a near-optimum profile of reaction rate vs temperature can be attained by regulating the inlet temperature of each bed. This is performed via internal heat recovery, either by preheating reactor feed gas or by using waste heat boilers, which results in an increase of the steam production and a smaller fuel consumption. But, although such near-optimum operation conditions may lead to higher reaction rates and, thus, lower catalyst volumes could be required, it is found that the optimal design of the ammonia loop is rather determined by the performance of each component and their interdependencies. Moreover, since the proposed objective function (exergy destruction minimization) is very sensitive to specific process variables, the convergence of the solution algorithm is sometimes hindered. The exergy destruction breakdown shows that the ammonia converter and the refrigeration system are together responsible for more than 71e82% of the total exergy destruction in the ammonia loop, which in turn varies between 25.6 and 38.8 MW for optimal and base-case operation conditions, respectively.

This review presents progress made over the last decades in the understanding of the metabolic capabilities of nitrifying and denitrifying microorganisms for the biotransformation of nitrogen, sulfur, and carbon compounds present in wastewaters. There are nowadays still many discoveries to be made about the metabolism, phylogeny and ecological behavior of bacteria that play an important role in the nitrogen cycle. The interest of the scientific community in the biological nitrogen cycle is at present very high, because it can be linked to either sulfur or carbon cycles. The connection of biological cycles is of the utmost technological relevance as it has allowed the simultaneous elimination of reduced sulfur and phenolic compounds under nitrifying or denitrifying conditions. The environmental factors affecting the nitrification and denitrification biological processes are described in this review.

Management practices, such as tillage, crop rotation, and N fertilization, may affect net global warming potential (GWP) and greenhouse gas intensity (GHGI), but their global impact on cropland soils under different soil and climatic conditions need further evaluation. Available global data from 57 experiments and 225 treatments were evaluated for individual and combined effects of tillage, cropping systems, and N fertilization rates on GWP and GHGI which accounted for CO 2 equivalents from N 2 O and CH 4 emissions with or without equivalents from soil C sequestration rate (ΔSOC), farm operations, and N fertilization. The GWP and GHGI were 66 to 71% lower with no-till than conventional till and 168 to 215% lower with perennial than annual cropping systems, but 41 to 46% greater with crop rotation than monocroppping. With no-till vs. conventional till, GWP and GHGI were 2.6-to 7.4-fold lower when partial than full accounting of all sources and sinks of greenhouse gases (GHGs) were considered. With 100 kg N ha-1 , GWP and GHGI were 3.2 to 11.4 times greater with partial than full accounting. Both GWP and GHGI increased curvilinearly with increased N fertilization rate. Net GWP and GHGI were 70 to 87% lower in the improved combined management that included no-till, crop rotation/perennial crop, and reduced N rate than the traditional combined management that included conventional till, monocop-ping/annual crop, and recommended N rate. An alternative soil respiration method, which replaces ΔSOC by soil respiration and crop residue returned to soil in the previous year, similarly reduced GWP and GHGI by 133 to 158% in the improved vs. the traditional combined management. Changes in GWP and GHGI due to improved vs. traditional management varied with the duration of the experiment and inclusion of soil and climatic factors in multiple linear regressions improved their relationships. Improved management practices reduced GWP and GHGI compared with traditional management practices and combined management practices were even more effective than individual management practices in reducing net GHG emissions from cropland soils. Partial accounting overestimated GWP and GHGI values as sinks or sources of net GHGs compared with full accounting when evaluating the effect of management practices.

This article outlines the isotope systematics of processes in the ocean nitrogen (N) cycle and their impact on the isotopic compositions of the major N forms, with an eye toward how the N isotopes may record current N fluxes and past changes. The dominant dynamic is of kinetic isotope discrimination, in which the light isotope of N (14N) is preferentially converted from substrate to product, leaving the substrate enriched in 15N. The strength of the isotopic signal increases with the amplitude of the isotope discrimination in a given N conversion, and it is also affected by the degree to which that conversion consumes its substrate, with a higher degree of consumption strengthening the signal in the substrate but weakening it in the product.

Aspects of the electrochemical reduction of nitrogen and carbon dioxide at molecular and heterogeneous catalysts are discussed. We focus on recent advances in the field and discuss some of the remaining challenges in the production of solar fuels from N2 and CO2 with a direct, integrated solar fuel device. We propose metrics of catalyst assessment for non-H2 solar fuels.

Some sources and biogeochemical processes of the nitrogen cycle were studied to determine the existing balance of this nutrient in the first 300 m of the water column of Alfonso Basin. The seasonal variability of microbial planktonic abundances were described, as well as, their association to the carbon assimilation (AC) levels, organic production and physicochemical variables. The dynamics of the thermohaline, during the process of winter mixing and the elevation of deep water due to pumping (April to July) of a cyclonic eddy caused a prolonged period of high levels of oxidized nutrients, which resulted in high planktonic abundances. However, this increase generally was restricted to the uppermost layer, where according to canonical correspondence analysis, the planktonic components were positively associated to dissolved oxygen and temperature. Estimated annual AC values in the euphotic zone (Zeu) were substantially higher (6741 kg C ha-1 yr-1) compared to previous reports for the Gulf of California, where the fraction between 0.4 to 20 μm had a contribution of ~ 63 %. At 150 m depth, AC rates fluctuated between 0.26-3.2 mg C m-3 h-1 which were attributed to both the activity of chemolithotrophic organisms, as well as phytoplankton groups adapted to very low irradiances, which were consistent with their densities distribution. Among the evaluated nitrogen inputs, vertical transport of nitrate due to cyclonic eddy was the most important for the Zeu (63 kg N ha-1 yr-1), followed by biological N2 fixation (FBN) and atmospheric deposition of gas + aerosol (26 and 7 kg N ha-1 yr-1, respectively). FBN registered large values compared to previous measurements for the Gulf of California and other coastal and oceanic systems, as well as detection levels at 150 m depth under high concentration of dissolved inorganic nitrogen suggesting a positive feedback due low nitrogen to phosphorus ratio. Between 100-300 m, nitrogen losses by N2 production via denitrification and ANAMMOX were low compared to observed rates in sites of the Pacific oxygen minimum zones. Likewise, ANAMMOX was predominant (79%) relative to denitrification. This characteristic was attributed mainly to the physiological inhibition by relatively high dissolved oxygen content at the site (0.15-1.72 ml O2 l-1), the presence of denitrification inhibitors (e.g. H2S and HS-), and/or unevaluated production and consumption of intermediate forms such as N2O. Nitrification in the aphotic layer as a mechanism for regeneration of dissolved inorganic forms, showed a high contribution to the mobilization of nitrogen (251 kg N Ha-1 yr-1) compared to other physiological rates, and integrated values were similar to previous estimates of nitrification for the Zeu of the Gulf of California and Mexican Pacific Ocean. However, the temporal variability of these rates was strongly associated with the availability of substrates (e.g. nitrite and ammonium) during periods of high biological production. Indirect calculations of assimilation of dissolved inorganic nitrogen from AC rates corroborate the prevalence of this activity in the mobilization of nitrogen in the Zeu (949 kg N ha-1 yr-1). Indirect calculations of dissolved inorganic nitrogen assimilation through AC rates corroborate the predominance of this activity to the mobilization of nitrogen in the euphotic layer (949 kg N Ha-1 yr-1). The nitrogen budget indicated that external inputs and nitrification in the first 300 m depth barely contributed with 53% of the requirement of this element for phytoplankton growth organisms. This suggests the presence of alternative routes or reservoirs associated with the dissolved organic fraction as a nitrogen supply mechanism for mixotrophic populations. Clearly the results provided by this study indicate a highly dynamic cycle of nitrogen and its potential for positive feedback nitrogen inventory to mitigate the N:P unbalance prevailing in Cuenca Alfonso.

Highlights: Labile nitrogen and carbon soil properties essential for ecological studies are analyzed. Particulate and mineral-associated organic matters that are ecologically meaningful were evaluated. Spectral modeling of Hyperion data in subtropical coastal wetlands of west Florida is feasible. Both Simple Ratio and PLS models of spectral data provided statistically significant results. The narrow bands of the Hyperion image are essential compared to Landsat image data.

Abstract
Abstract

Developing spectral models of soil properties is an important frontier in remote sensing and soil science. Several studies have focused on modeling soil properties such as total pools of soil organic matter and carbon in bare soils. We extended this effort to model soil parameters in areas densely covered with coastal vegetation. Moreover, we investigated soil properties indicative of soil functions such as nutrient and organic matter turnover and storage. These properties include the partitioning of mineral and organic soil between particulate (>53 μm) and fine size classes, and the partitioning of soil carbon and nitrogen pools between stable and labile fractions. Soil samples were obtained from Avicennia germinans mangrove forest and Juncus roemerianus salt marsh plots on the west coast of central Florida. Spectra corresponding to field plot locations from Hyperion hyperspectral image were extracted and analyzed. The spectral information was regressed against the soil variables to determine the best single bands and optimal band combinations for the simple ratio (SR) and normalized difference index (NDI) indices. The regression analysis yielded levels of correlation for soil variables with R2 values ranging from 0.21 to 0.47 for best individual bands, 0.28 to 0.81 for two-band indices, and 0.53 to 0.96 for partial least-squares (PLS) regressions for the Hyperion image data. Spectral models using Hyperion data adequately (RPD > 1.4) predicted particulate organic matter (POM), silt + clay, labile carbon (C), and labile nitrogen (N) (where RPD = ratio of standard deviation to root mean square error of cross-validation [RMSECV]). The SR (0.53 μm, 2.11 μm) model of labile N with R2 = 0.81, RMSECV= 0.28, and RPD = 1.94 produced the best results in this study. Our results provide optimism that remote-sensing spectral models can successfully predict soil properties indicative of ecosystem nutrient and organic matter turnover and storage, and do so in areas with dense canopy cover.