Diatom-based dissolved inorganic nitrogen reconstruction in the Changjiang River estuary and its adjacent areas

A five-component weighted average partial least squares(WA-PLS)calibration model was developed by analysing diatom assemblages in 34 surface sediment samples(collected in 2015)from the Changjiang River estuary(CRE)and its adjacent areas to infer dissolved inorganic nitrogen(DIN)concentrations.Eighteen additional sets of surface sediment diatoms and corresponding upper water DIN data(collected in 2012)were used to evaluate the accuracy of the model,and the relationship between observed and diatom-inferred DIN(DI-DIN)values(R2=0.85)illustrated the strong performance of the transfer function,indicating that precise reconstructions of former DIN are possible.The diatom-DIN transfer function was applied to the diatom record from a sediment core DH8-2(1962‒2012)collected in the Fujian-Zhejiang area south of the CRE.The reconstruction based on the DI-DIN model showed a significant DIN increase from 1962-2012,reflecting the influence of human activities on the very large increase in eutrophication.Three distinct periods can be seen from the changes in DIN and diatom taxa.In the 1962-1972 period,the DIN content was relatively low,with an average of 5.94μmol/L,and more than 80%of the diatom species identified were benthic taxa.In the 1972-2004 period,as the impact of human activities intensified,large nutrient inputs caused the DIN content to increase,with an average of 8.25μmol/L.The nutrient inputs also caused a significant change in the nutrient components and a distinct increase in small planktonic taxa.In the 2004-2012 period,the DIN content continued to rise,fluctuating at approximately 10μmol/L.A continuous increase in the frequency of planktonic taxa(up to 65.48%)indicated that eutrophication was further intensified,which was confirmed by the transformation from diatom-induced red tide to dinoflagellate-induced red tide during this period.

Soil resource availability impacts microbial response to organic carbon and inorganic nitrogen inputs

Impacts of newly added organic carbon （C） and inorganic nitrogen （N） on the microbial utilization of soil organic matter are important in determining the future C balance of terrestrial ecosystems. We examined microbial responses to cellulose and ammonium nitrate additions in three soils with very different C and N availability. These soils included an organic soil（ 14.2% total organic C, with extremely high extractable N and low labile C）, a forest soi1（4.7% total organic C, with high labile C and extremely low extractable N）, and a grassland soil（1.6% total organic C, with low extractable N and labile C）. While cellulose addition alone significantly enhanced microbial respiration and biomass C and N in the organic and grassland soils, it accelerated only the microbial respiration in the highly-N limited forest soil. These results indicated that when N was not limited, C addition enhanced soil respiration by stimulating both microbial growth and their metabolic activity, New C inputs lead to elevated C release in all three soils, and the magnitude of the enhancement was higher in the organic and grassland soils than the forest soil. The addition of cellulose plus N to the forest and grassland soils initially increased the microbial biomass and respiration rates, but decreased the rates as time progressed. Compared to cellulose addition alone, cellulose plus N additions increased the total C-released in the grassland soil, but not in the forest soil. The enhancement of total C- released induced by C and N addition was less than 50% of the added-C in the forest soil after 96 d of incubation, in contrast to 87.5% and 89.0% in the organic and grassland soils. These results indicate that indigenous soil C and N availability substantially impacts the allocation of organic C for microbial biomass growth and/or respiration, potentially regulating the turnover rates of the new organic C inputs.

Inorganic nitrogen removal of toilet wastewater with an airlift external circulation membrane bioreactor

Removal of inorganic nitrogen （inorganic-N） from toilet wastewater, using a pilot-scale airlift external circulation membrane bioreactor （AEC-MBR） was studied. The results showed that the use of AEC-MBR with limited addition of alkaline reagents and volumetric loading rates of inorganic-N of 0.19-0.40 kg inorganic-N/（m^3·d） helped achieve the desired nitrification and denitrification. Furthermore, the effects of pH and dissolved oxygen （DO） on inorganic-N removal were examined. Under the condition of MLSS at 1.56-2.35 g/L, BODs/ammonia nitrogen （NH4＋-N） at 1.0, pH at 7.0-7.5, and DO at 1.0-2.0 mg/L, the removal efficiencies of NH4^＋-N and inorganic-N were 91.5% and 70.0%, respectively, in the AEC-MBR. The cost of addition of alkaline reagent was approximately 0.5-1.5 RMB yuan/m^3, and the energy consumption was approximately 0.72 kWh/m^3 at the flux of 8 L/（m^2-h）.

Effects of live rock on removal of dissolved inorganic nitrogen in coral aquaria

Maintaining stable water quality is one of the key processes for recirculating coral aquaculture. Traditional aquarium systems which mainly utilized a nitrification of nitrifying bacteria attached to the surface of massive artificial filter material are difficult to maintain the oligotrophic conditions necessary for coral aquaculture. This study investigated the removal effects of dissolved inorganic nitrogen（ammonia and nitrate） by live rock（LR）, a key component in the ＂Berlin system＂ coral aquarium. The expression levels of bacterial functional genes, AOA3,amo A and nos Z, were measured on the exterior and interior of LR. The nitrifying and denitrifying bacterial abundance on LR was quantified and the nitrogen nutrient regulatory effects of LR were evaluated. The results demonstrated that LR mainly removed ammonium（NH_4~＋） from the water with a mean efficiency of 0.141 mg/（kg·h）, while the removal of nitrate（NO_3~–） was not significant. Bacterial diversity analysis showed that ammonia-oxidizing bacteria（AOB） were the most common bacteria on LR, which accounted for 0.5%–1.4% of the total bacterial population, followed by denitrifying bacteria, which accounted for 0.2% of the total population, and the ammonia-oxidizing archaea（AOA） were the least common type（〈0.01%）. The low abundance of denitrifying bacteria may be responsible for the poor nitrate（NO_3~–） removal of LR. Thus, other biological filtration methods are needed in coral aquaria to control nitrates generated from nitrification or biological metabolism.

Seasonal variation of transport pathways and potential source areas at high inorganic nitrogen wet deposition sites in southern China

This study attempts to identify the dominant transport pathways,potential source areas,and their seasonal variation at sites with high inorganic nitrogen(IN)wet deposition flux in southern China.This is a long-term study(2010-2017)based on continuous deposition measurements at the Guangzhou urban site(GZ)and the Dinghushan Natural Reserve site(DHS)located in the Pearl River Delta(PRD)region.A dataset on monthly IN concentration in precipitation and wet deposition flux were provided.The average annual fluxes measured at both sites(GZ:33.04±9.52,DHS:20.52±10.22 kg N/(ha·year))were higher,while the ratios of reduced to oxidized N(GZ:1.19±0.77,DHS:1.25±0.84)were lower compared with the national mean level and the previous reported level throughout the PRD region.The dominant pathways were not always consistent with the highest proportional trajectory clusters.The transport pathways contributing most of deposition were identified in the north and northnortheast in the dry season and in the east-southeast,east,and south-southwest in the wet season.A weighted potential source contribution function(WPSCF)value>0.3 was determined reasonably to define the potential source area.Emission within the PRD region contributed the majority(≥95%at both sites)of the IN deposition in the wet season,while the contribution outside the region increased significantly in the dry season(GZ:27.86%,DHS:95.26%).Our results could help create more effective policy to control precursor emissions for IN fluxes,enabling reduction of the ecological risks due to excessive nitrogen.

Evidence of temperature-controlled dissolved inorganic nitrogen distribution in a shallow lake

Dissolved inorganic nitrogen(DIN) plays an important role in aquatic ecosystems as an available source of nitrogen(N). Despite recent advances in our understanding of the effects of climate change on DIN in coastal waters, shallow high-latitude lakes exposed to large seasonal temperature differences have received limited research attention. Therefore,in the present study, Baiyangdian Lake(BYDL) was selected as the study area, as a typical high latitude shallow lake in North China. Based on water and sediment samples collected in spring, summer and winter seasons, DIN accumulation in sedimentary pore water and DIN diffusion fluxes at the sediment-water interface were quantified under different temperature conditions. Correlation analysis was used to establish the effects of temperature on DIN concentration and diffusion in different media. Results show that the diffusion of DIN at the lake sediment-water interface exhibited a strongly positive relationship with temperature, suggesting that high temperature conditions lead to greater DIN release from sediments. Cold temperatures cause DIN accumulation in sedimentary pore water, providing sufficient substrate for N-related bacteria in the sediment under cold temperature conditions. Temperature controls the vertical distribution of DIN by affecting its migratory diffusion and transformation at the sediment-water interface. These findings are valuable for understanding the impact of climate change on the distribution of N in inland shallow lakes,especially in high latitude shallow lakes subjected to large seasonal temperature differences throughout the year.

Spatial distribution and driving factors of sediment net nitrogen mineralization in riparian zone of the Three Gorges Reservoir

Inorganic nitrogen(N)loss through sediment N mineralization is important for eutrophication surrounding riparian zone.Sediment physicochemical properties have been changed at water-level elevation in riparian zone of the Three Gorges Reservoir(TGR)due to differences in hydrological stress and human activity intensity.However,spatial distribution and driving factor of net N mineralization rate(Nmin)and its temperature sensitivity(Q10)based on the changes in sediment physicochemical properties are still unclear at waterlevel elevation in the riparian zone.A total of 132 sediment samples in the riparian zone were collected including 11 transections and 12 water-level elevations on basin scale of the TGR during drying period,to conduct a 28-day incubation at 15℃,22℃,29℃and 36℃.Nmin,total N(TN)and substrate quality(SQ)increased with water-level elevation,while Q10 showed an opposite trend(P<0.001).Results of the structural equation model showed that water-level elevation had direct positive effects on TN and SQ(P<0.01).In addition,TN was the major factor that had a direct positive effect on Nmin,and SQ was the crucial factor that had a direct negative effect on Q10(P<0.001).In conclusion,increases in TN and SQ were major driving factors of Nmin and its Q10 at water-level elevation,respectively,in riparian zone of the TGR during drying period.

Effect of Biochar and Inorganic Fertilizer on Soil Biochemical Properties in Njoro Sub-County, Nakuru County, Kenya

Declining soil fertility is a major constraint to potato farming, the second most important food crop in Kenya. The objective of the study was to determine the effect of different rates of biochar and inorganic fertilizer on some soil properties;soil pH, soil phosphomonoesterases, inorganic nitrogen and extractable phosphorus. The study was conducted for two seasons (short and long rains) at two locations (Egerton University agricultural field and farmer’s field in Mau Narok) using a split-plot design in a randomized complete block (RCBD) arrangement with variety as the main plot and soil amendments as the subplot. Biochar and Diammonium Phosphate (DAP) at 0, 5, and 10 t⋅ha−1 and 0, 250, and 500 kg⋅ha−1 respectively, were applied, resulting in nine treatment combinations. Two potato varieties (Shangi and Destiny) were used in the study. A combination of 5 t⋅ha−1 biochar and 500 kg⋅ha−1 DAP and sole application of biochar at 5 t⋅ha−1 resulted in an increase of 1.25, 2.54 units in soil pH in two seasons, respectively. Similarly, a combination of 5 t⋅ha−1 biochar and 250 kg⋅ha−1 DAP increased soil available phosphorus by 105 units from 30.7 mg⋅kg−1 to 136 mg⋅kg−1. The application rate of 5 t⋅ha−1 biochar with 250 or 500 kg⋅ha−1 DAP significantly increased soil nitrate by 102.11 and 116.14 units, respectively. Soils amended with biochar at 5 t⋅ha−1 combined with 500 kg⋅ha−1 DAP, 10 t⋅ha−1 of biochar combined with either 250 kg or 500 kg of DAP gave the highest alkaline enzymes (mM pNP × kg−1 × h−1). However, the highest acid soil phosphomonoesterases were obtained under the sole application of DAP at 500 ha−1. Thus, using biochar with chemical fertilizer seems a plausible option to ameliorate the declining nutrient base of farmland in Kenya, which could sustainably support potato growth.

Extreme drought with seasonal timing consistently promotes CH_(4) uptake through inconsistent pathways in a temperate grassland, China

Methane(CH_(4))is a potent greenhouse gas that has a substantial impact on global warming due to its substantial influence on the greenhouse effect.Increasing extreme precipitation events,such as drought,attributable to global warming that caused by greenhouse gases,exert a profound impact on the intricate biological processes associated with CH_(4) uptake.Notably,the timing of extreme drought occurrence emerges as a pivotal factor influencing CH_(4) uptake,even when the degree of drought remains constant.However,it is still unclear how the growing season regulates the response of CH_(4) uptake to extreme drought.In an effort to bridge this knowledge gap,we conducted a field manipulative experiment to evaluate the impact of extreme drought on CH_(4) uptake during early,middle,and late growing stages in a temperate steppe of Inner Mongolia Autonomous Region,China.The result showed that all extreme drought consistently exerted positive effects on CH_(4) uptake regardless of seasonal timing.However,the magnitude of this effect varied depending on the timing of season,as evidenced by a stronger effect in early growing stage than in middle and late growing stages.Besides,the pathways of CH_(4) uptake were different from seasonal timing.Extreme drought affected soil physical-chemical properties and aboveground biomass(AGB),consequently leading to changes in CH_(4) uptake.The structural equation model showed that drought both in the early and middle growing stages enhanced CH_(4) uptake due to reduced soil water content(SWC),leading to a decrease in NO_(3)–-N and an increase in pmoA abundance.However,drought in late growing stage primarily enhanced CH_(4) uptake only by decreasing SWC.Our results suggested that seasonal timing significantly contributed to regulate the impacts of extreme drought pathways and magnitudes on CH_(4) uptake.The findings can provide substantial implications for understanding how extreme droughts affect CH_(4) uptake and improve the prediction of potential ecological consequence under future climate change.

Long-term impacts of land-use change on dynamics of tropical soil carbon and nitrogen pools

Land-use changes, especially the conversion of native forest vegetation to cropland and plantations in tropical region, can alter soil C and N pools and N availability for plant uptake. Deforestation, followed by shifting cultivation and establishment of rubber tree plantation, is a common land-use change in Xishuangbanna, southwest China. However the influence of this kind of land-use change on soil C and N dynamics in this region remains poorly understood. This study was conducted to assess the effects of land-use change on soil C and N pools. Soil samples were collected on five adjacent plots, which belong to three land-use types including secondary forest-an acuminate banana(Musa itinerans) secondary forest and a male bamboo(Dendrocalamus membranaceae) secondary forest, shifting cultivation, and rubber tree (Hevea brasiliensis (H.B.K.) Muell. Arg.) plantation(one plot is 3-year-old, and another is 7-year-old). We measured soil bulk density (BD), pH value, moisture content and concentrations of soil organic carbon(SOC), total soil nitrogen(TSN), and inorganic N(NO - 3-N and NH + 4-N ) at 0—3, 3—20, 20—40 and 40—60 cm depths, and calculated C and N pools in 0—20, 20—40, 40—60, and 0—60 cm soil layers. Compared with the adjacent secondary forests, shifting cultivation and establishment of rubber tree plantations resulted in significant decline in concentrations and stocks of SOC and TSN in 0—20 and 0—60 cm soil layers, and increase in pH and bulk density at 0—3, 3—20, and 20—40 cm depths. Soil moisture content decreased only in 0—20 cm surface soils in shifting cultivation and plantations. The dynamics of mineral N was much more complex, which had different trends among depths and ecosystems. Compared with the secondary forests, SOC stocks in 0—20 cm surface soils in shifting cultivation and rubber tree plantations(3-year-old plantation and 7-year-old plantation) decreased by 34.0%, 33%, and 23%; and TSN stocks decreased by 32 2%, 20.4%, and 20.4%, respectively, whereas the decreases of SOC and TSN stocks in 0—60 cm soil layers were much less. The results indicated that C and N losses were mainly occurred in 0—20 cm surface soil, followed by 20—40 cm layer.

Effects of Nitrogen Forms on Carbon and Nitrogen Accumulation in Tomato Seedling

Utilization of organic nitrogen （N） is an important aspect of plant N assimilation and has potential application in sustainable agriculture. The aim of this study was to investigate the plant growth, C and N accumulation in leaves and roots of tomato seedlings in response to inorganic （NH4^＋-N, NO3^-N） and organic nitrogen （Gly-N）. Different forms of nitrogen （NH4^＋-N, NO3^--N, Gly-N） were supplied to two tomato cultivars （Shenfen 918 and Huying 932） using a hydroponics system. The plant dry biomass, chlorophyll content, root activity, total carbon and nitrogen content in roots and leaves, and total N absorption, etc. were assayed during the cultivation. Our results showed that no significant differences in plant height, dry biomass, and total N content were found within the first 16 d among three treatments; however, significant differences in treatments on 24 d and 32 d were observed, and the order was NO3^--N 〉 Gly-N 〉 NH4^＋-N. Significant differences were also observed between the two tomato cultivars. Chlorophyll contents in the two cultivars were significantly increased by the Gly-N treatment, and root activity showed a significant decrease in NHa^＋-N treatment. Tomato leaf total carbon content was slightly affected by different N forms; however, total carbon in root and total nitrogen in root and leaf were promoted significantly by inorganic and organic N. Among the applied N forms, the increasing effects of the NH4^＋-N treatment were larger than that of the Gly-N. In a word, different N resources resulted in different physiological effects in tomatoes. Organic nitrogen （e.g., Gly-N） can be a proper resource of plant N nutrition. Tomatoes of different genotypes had different responses under organic nitrogen （e.g., Gly-N） supplies.

Effects of elevated atmospheric CO2 and nitrogen fertilization on nitrogen cycling in experimental riparian wetlands

Studies on the relationship between plant nitrogen content and soil nitrogen reduction under elevated CO2 conditions and with different nitrogen additions in wetland ecosystems are lacking. This study was meant to assess the effects of elevated CO2 concentrations and inorganic nitrogen additions on soil and plant nitrogen cycling. A cultured riparian wetland, alligator weeds, and two duplicated open top chambers （OTCs） with ambient （380μmol/mol） and elevated （700 μmol/mol） CO2 concentrations at low （4 mg/L） and high （6 mg/L） nitrogen fertilization levels were used. The total plant biomass increased by 30.77% and 31.37% at low and high nitrogen fertilization levels, respectively, under elevated CO2 conditions. Plant nitrogen content decreased by 6.54% and 8.86% at low and high nitrogen fertilization levels, respectively. The coefficient of determination （R2） of soil nitrogen contents ranged from 0.81 to 0.96. Under elevated CO2 conditions, plants utilized the assimilated inorganic nitrogen （from the soil） for growth and other internal physiological transformations, which might explain the reduction in plant nitrogen content. A reduction in soil dissolved inorganic nitrogen （DIN） under elevated CO2 conditions might have also caused the reduction in plant nitrogen content. Reduced plant and soil nitrogen contents are to be expected due to the potential exhaustive use of inorganic nitrogen by soil microorganisms even before it can be made available to the soil and plants. The results from this study provide important information to help policy makers make informed decisions on sustainable management of wetlands. Larger-scale field work is recommended in future research.

Effects of freezing intensity on soil solution nitrogen and microbial biomass nitrogen in an alpine grassland ecosystem on the Tibetan Plateau,China

The change of freeze-thaw pattern of the Tibetan Plateau under climate warming is bound to have a profound impact on the soil process of alpine grassland ecosystem;however,the research on the impact of the freeze-thaw action on nitrogen processes of the alpine grassland ecosystem on the Tibetan Plateau has not yet attracted much attention.In this study,the impact of the freezing strength on the soil nitrogen components of alpine grassland on the Tibetan Plateau was studied through laboratory freeze-thaw simulation experiments.The 0–10 cm topsoil was collected from the alpine marsh meadow and alpine meadow in the permafrost region of Beilu River.In the experiment,the soil samples were cultivated at –10℃,–7℃,–5℃,–3℃ and –1℃,respectively for three days and then thawed at 2℃ for one day.The results showed that after the freeze-thaw process,the soil microbial biomass nitrogen significantly decreased while the dissolved organic nitrogen and inorganic nitrogen significantly increased.When the freezing temperature was below –7℃,there was no significant difference between the content of nitrogen components,which implied a change of each nitrogen component might have a response threshold toward the freezing temperature.As the freeze-thaw process can lead to the risk of nitrogen loss in the alpine grassland ecosystem,more attention should be paid to the response of the soil nitrogen cycle of alpine grasslands on the Tibetan Plateau to the freeze-thaw process.

Temperature Sensitivity of Nitrogen Dynamics of Agricultural Soils of the United States

Soil temperature controls gaseous nitrogen losses through nitrous oxide (N2O) and ammonia (NH3) fluxes. Eight surface soils from agricultural fields across the United States were incubated at 10°C, 20°C, and 30°C, and N2O and NH3 flux were measured twice a week for 91 and 47 d, respectively. Changes in cumulative N2O and NH3 flux and net N mineralization at three temperatures were fitted to calculate Q10 using the Arrhenius equation. For the majority of soils, Q10 values for the N2O loss ranged between 0.23 and 2.14, except for Blackville, North Carolina (11.4) and Jackson, Tennessee (10.1). For NH3 flux, Q10 values ranged from 0.63 (Frenchville, Maine) to 1.24 (North Bend, Nebraska). Net soil N mineralization-Q10 ranged from 0.96 to 1.00. Distribution of soil organic carbon and total soil N can explain the variability of Q10 for N2O loss. Understanding the Q10 variability of soil N dynamics will help us to predict the N loss.

Nitrogen absorption by alpine forage species based on 15N tracer technique in a hydroponic culture

Based on 15N tracer technique,absorption of different concentrations of ammonium nitrogen(N-NH^(4+)),nitrate nitrogen(N-NO^(3-))and glycine(NGly)by root of six species of alpine forage(Puccinellia tenuiflora,Poa crymophila,Festuca sinensis,Elymus nutans,Elymus sibiricus and Bromus inermis)was studied in a hydroponic culture.The uptake kinetic parameter was analyzed according to Michaelis-Menten equation.The Michaelis-Menten equation represents the velocity equation for the relationship between the initial rate of an enzymatic reaction and the substrate concentration.The result showed that the absorption range of ammonium nitrogen,nitrate nitrogen and glycine by root of six species of alpine plant were 1.1-20.9μmol·g^(-1)·h^(-1),0.4-3.4μmol·g^(-1)·h^(-1) and 0.1-3.7μmol·g^(-1)·h^(-1),which accounts for 68.8%-74.7%,12.0%-27.0%and 4.3%-13.4%of total absorptivity,respectively.The six kinds of P.tenuiflora,P.crymophila,F.sinensis,E.nutans,E.sibiricus and B.inermis showed significant difference in nitrogen absorption.At the same concentration,the absorption of nitrogen in different forms of the same herbage is different.The absorptive amount of ammonium nitrogen was the highest among them,then the glycine,the nitrate nitrogen was least absorbed.The results could provide a theoretical basis for nitrogen utilization in alpine forages.For example,P.tenuiflora showed a much higher ability of absorbing nitrogen nutrition in a high salt environment and could be a more suitable herbage to be planted in saline-alkali soil in the Qinghai-Tibet Plateau as compared with E.nutans.

Environmental control of mesozooplankton community structure in the Hangzhou Bay, China

A quarterly study of mesozooplankton community structure and environmental variables in the Hangzhou Bay was conducted to examine the response of mesozooplankton community to the variation of water mass and environmental condition. The southeast coast of China is a typical region under the intensive influence of Asia monsoon and freshwater discharge from rivers. The water mass and environmental condition of the Hangzhou Bay, which were influenced by the interaction of currents, freshwater discharge of the Qiantang River and Changjiang River Plume, showed significant seasonal variation. Our results showed that both biomass and abundance were significantly higher in summer（（247.7±148.8） mg/m^3 and（350.9±215.6） ind./m^3, respectively）than those in other seasons. Four eco-geographical regions were divided based on the cluster analysis of zooplankton community of the Hangzhou Bay throughout the year, except for winter. Monsoon and the dissolved inorganic nitrogen（DIN） input from freshwater discharge of the Qiantang River and Changjiang River resulted in temporal and spatial variations of environmental gradient in the Hangzhou Bay, which significantly influenced the structure of mesozooplankton community. Redundancy analysis（RDA） indicated that the mesozooplankton community structure was strictly correlated with the DIN gradient, while salinity gradient showed a weak influence in the Hangzhou Bay.

Denitrification in Qi'ao Island coastal zone,the Zhujiang Estuary in China

Samples of sediments and the overlying water were collected in the Qi＇ao Island coastal zone,the Zhujiang（Pearl River） Estuary（ZE）.Denitrification rates,sediment oxygen demand（SOD）,and fluxes of inorganic nitrogen compounds were investigated with N2 flux method,using a self-designed continuous flow through and auto-sampling system.The results indicate that the denitrification rates varied between 222 and 908 μmol/（m2·h） with an average of 499 μmol /（m2·h）.During incubation,the sediments absorbed dissolved oxygen in the overlying water with SOD ranging from 300 to 2 363 μmol/（m2·h）.The denitrification rates were highly correlated with the SOD（r2=0.77） regardless of the NO-3＋NO-2 concentrations in the overlying water,organic carbon contents in sediments and water temperature,suggesting that the SOD was probably the main environmental factor controlling the denitrification in the Qi＇ao Island coastal zone.There was a net flux of NO-3＋NO-2 into the sediments from the overlying water.The NH＋4 flux from sediments into water as the result of mineralization was between 12.3 and 210.3 μmol/（m2·h）,which seems limited by both organic carbon content in sediment and dissolved oxygen concentration in the overlying water.

Salt-tolerant Microbiota Enhancing Contaminants Removal from Mariculture Wastewater Containing Sulfamethoxazole in an A/O-MBBR

The wide application of antibiotics in aquaculture requires an efficient treatment of the wastewater before discharging it into the environment.During the wastewater treatment,the influence of antibiotics on the performance of bioreactor should be well revealed due to their toxicity to the functional microbial community.In this study,the effect of feeding 10-30 mg L−1 sulfamethoxazole(SMX)in influent on the performance of an anoxic/oxic-moving bed biofilm reactor(A/O-MBBR)treating mariculture wastewater and the responding change of biofilm microbial communities was investigated.The COD average removal rate remained at 94.61%-97.34%with the dosage of SMX.Compared with that,the nitrifying removals of NH4+-N and NO2−-N were violently inhibited by 30 mg L−1 SMX and denitrifying removal of the NO3−-N decreased obviously with 20 mg L−1 or more SMX.The microbial community in the successful startup bioreactor was relatively abundant,while the diversity of microbial community decreased with the increase of feeding SMX.The salt-tolerant and SMX-resistant genera Arcobacter,Thiothrix,Desulfuromusa and Nitrosomonas were gradually enriched and finally played a vital role in converting COD and recycling nitrogen and sulfur.Hence,the present A/O-MBBR reactor with the salt-tolerant functional microbiota achieved efficient removal of pollutants in the presence of low concentration(e.g.,10 mg L−1)SMX.

Zai Pit Effects on Selected Soil Properties and Cowpea (<i>Vigna unguiculata</i>) Growth and Grain Yield in Two Selected Dryland Regions of Kenya

Erratic rainfall and temperature regimes, strongly affect agricultural productivity. To address the reduction in production, this study assessed the effect of Zai pit depths on selected soil properties and cowpea growth and grain yield. “Zai” pit technology was tested in two locations falling under Agroecological Zone IV (relatively dry areas) i.e. Katumani in Machakos County and Naivasha in Nakuru County, Kenya, aiming to determine the combined effect of four “Zai” pit depths and two levels of manure (plots with manure and plots without manure) on selected soil properties, growth and yield of cowpea. Experiment was laid out in split plot arrangement, with manure levels as the main plot factor and “Zai” pit depths (Flat: Z0, 30 cm: Z30, 45 cm: Z45 and 60 cm: Z60) as subplot factor, replicated four times. Cowpea (M66 variety) was used as the test crop. Inorganic N and extractable P were significantly (P < 0.05) higher, at 1.37 mg⋅kg−1 for Nin and 80.4 mg⋅kg−1 for Pex in Zai pits compared to flat plots which were at 0.91 mg⋅kg−1 for Nin and 47.1 mg⋅kg−1 for Pex. The values of Nin and Pex also varied depending on depths, with Z45 having highest Nin at 1.17 against the least, at 0.89 in the Z0, while Pex was highest in Z30 at 102.3 mg⋅kg−1 while Z0 having the least Pex of 89.7 mg⋅kg−1. Generally, crops in “Zai” pitted plots were larger in diameter at 0.46 cm than crops in flat plots at 0.42 cm. Better performance was observed in yield, with Z30 yielding 30.5% against 18.2% Flat plots in Machakos while 27.9% in Z30 against 22.5% from Flat plots in Naivasha. This study demonstrated great potential of “Zai” pit technology on crop production, as reflected on improved growth and yield of cowpeas. Combining “Zai” pits with manure increases soil Nin, Pex and is a guarantee of great crop performance in terms of high final yields.

Effects of La^(3+),Ce^(3+) on nitrogen removal in sequencing batch reactor

Batch experiments were conducted to study the short-term biological effects of rare earth ions(La^(3+),Ce^(3+))and their mixture on the nitrogen removal in a sequencing batch reactor(SBR).The data showed that higher NH4+–N removal rate,total inorganic nitrogen removal efficiency,and denitrification efficiency were achieved at lower concentrations of rare earth elements(REEs)(<1 mg/L).In the first hour of the aeration stage of SBR,the presence of REEs increased the total inorganic nitrogen removal efficiency and NH4+–N removal effi-ciency by 15.7%and 10%–15%,respectively.When the concentrations of REEs were higher than 1 mg/L,the total inorganic nitrogen removal efficiency decreased,and nitrate was found to accumulate in the effluent.When the concentrations of REEs was up to 50.0 mg/L,the total inorganic nitrogen removal efficiency was less than 30%of the control efficiency with a high level of nitrate.Lower concentrations of REEs were found to accelerate the nitrogen conversion and removal in SBR.