Dissolved Organic Nitrogen Content Research Articles

The impact of dissolved organic nitrogen (DON) retention in the vadose zone on nitrogen leaching losses

Leaching of dissolved organic nitrogen (DON) is a significant pathway for nitrogen (N) loss in agricultural ecosystems. The excessive application of N for enhanceing agricultural productivity often results in the leaching of N into groundwater. Yet not well understood, the extent of retention in the vadose zone has critical implications for risk management and remediation strategies. This study aims to advance simulation techniques for modelling the transport process of reactive DON within a heterogeneous vadose zone. Through a combination of laboratory experiments and numerical simulations, the study firstly examines the extent of DON retention in the vadose zone and quantitatively analyse groundwater contamination risk from this kind of accumulation. Our findings indicate that heavy N fertilizer application and high-intensity rainfall events led to elevated contents of DON in the vadose zone and increased DON leaching fluxes into groundwater. Besides, intensifier rainfall reduced the N storage more quickly in scenarios devoid of DON application with higher mineralization rate, while DON slowly mineralized to other forms, largely accumulated in the top layer and migrated deeper with intensifier rainfall after input of urea. In our scenarios, DON accounted for a substantial portion (33–68%) of the total dissolved nitrogen (TDN) leaching fluxes, with exogenous DON content contributing significantly (25–85%) to the overall DON leaching into the aquifer. These results underscore the need for effective strategies to mitigate groundwater contamination risks associated with agricultural N use.

Effects of long-term no-tillage and different stover mulching amounts on soil carbon and nitrogen contents and enzyme activities of carbon and nitrogen cycle in Mollisols.

To understand the effects of different stover mulching amounts in no-tillage on soil carbon and nitrogen contents and enzyme activities, finding a stover mulching amount which can meet the requirement of soil carbon and nitrogen accumulation while maximizing economic benefits, we conducted a long-term conservation tillage field experiment since 2007 in Mollisols area of Northeast China. We analyzed soil carbon and nitrogen contents, enzyme activities and economic benefits under conventional tillage (Control, CT), no-tillage without stover mulching (NT0), no-tillage with 33% stover mulching (NT33), no-tillage with 67% stover mulching (NT67), and no-tillage with 100% stover mulching (NT100) before planting in May 2020. The results showed that compared with CT, NT0 did not affect soil organic carbon (SOC) and total nitrogen (TN) contents, but increased soil organic carbon recalcitrance and decreased the availability of dissolved organic nitrogen (DON) and ammonium nitrogen. Compared with NT0, no-tillage with stover mulching significantly increased SOC contents in 0-10 cm layer and increased with the amounts of stover. In addition, NT67 and NT100 significantly increased SOC stocks, facilitating the accumulation of soil organic matter. The effects of different stover mulching amounts on soil nitrogen content in 0-10 cm layer were different. Specifically, NT33 increased DON content and DON/TN, NT67 increased DON content, while NT100 increased TN content. Compared with CT, NT0 decreased peroxidase (POD) activity in 0-10 cm layer. Compared with NT0, NT33 increased β-glucosidase (βG), cellobiase (CB), 1,4-β-N-acetylglucosaminidase (NAG), polyphenol oxidase (PPO) and POD activities, while NT67 only increased CB, NAG and POD activities in 0-10 cm soil layer, both alleviated microbial nutrient limitation. NT100 increased PPO activity in 10-20 cm layer. NT33 increased carbon conversion efficiency of stover compared with NT100, and had the highest economic benefit. In all, no-tillage with 33% stover mulching was the optimal strategy, which could promote nutrient circulation, boost stover utilization efficiency, improve the quality of Mollisols, and maximize guaranteed income.

Temporal and spatial distribution characteristics and source analysis of dissolved organic nitrogen in the surface sediment of the Caohai Lake, southwest China.

Caohai Lake is a typical natural lake-type karst plateau wetland, which is sensitive to environmental changes, and the release of dissolved organic nitrogen (DON) in sediment is a potential factor of nitrogen pollution in this lake. Therefore, we aimed to reveal the temporal and spatial distribution characteristics and source analysis of DON in karst lake sediment. Surface sediment samples were collected from Caohai Lake in southwest China, and the sample locations were distributed across almost the entire wetland area, during both the wet and dry seasons. The DON content and fluorescence spectroscopy were determined and analysed using a three-dimensional fluorescence-parallel factor analysis (3DEEM-PARAFAC) model. The mean DON content in the sediment during the dry season (67.79 ± 42.96 mg/kg) was higher than that in the wet season (28.57 ± 20.97 mg/kg). There were four fluorescent components of DON in the sediment: C1 (tyrosine-like protein), C2 (terrestrial humus), C3 (tryptophan-like protein) and C4 (terrestrial humus). The DON in the surface sediment of Caohai Lake was influenced by terrestrial sources and biological activities. These findings help reveal the circulation mechanism of endogenous nitrogen in the lake and provide theoretical support for the prevention and control of nitrogen pollution in Caohai Lake.

Organic Matter in Riverbank Sediments and Fluvisols from the Flood Zones of Lower Vistula River

The research objective of this study was to determine whether and to what extent the form of use of Fluvisols (arable soil and grassland) of a Lower Vistula floodplain valley (Fordonska Valley, Poland) determined their relative organic matter properties, as compared with nearby riverbank sediments. Riverbank sediments were sampled from a depth of 0–20 cm, and soil samples from 0 to30 cm, all in three replicates. Basic physico-chemical soil properties were determined: texture, pH, and the contents of total organic carbon (TOC), total nitrogen (TN), dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). Humic acids (HAs) were extracted by the Schnitzer method and analysed to assess their spectrometric parameters in the UV–VIS range and hydrophilic and hydrophobic properties. Riverbank sediment samples contained significantly lower TOC and TN contents than Fluvisols, regardless of land-use type. The TOC, TN, DOC and DON contents and properties of humic acids in the Fluvisol surface layer depended on land-use type, because the arable soils had significantly lower TOC, TN, DOC and DON contents than the grasslands, despite having a similar grain size (texture). Based on the A2/4, A2/6, A4/6 ratios, it was found that HA molecules isolated from the humus horizon of arable soils had a higher degree of maturity than HAs isolated from grassland soil samples. The spectrometric properties of humic acids isolated from riverbank sediments showed a higher degree of maturity than those from Fluvisols. This research showed that the properties of humic acids in Fluvisols are determined by the quantity and quality of organic matter transported in suspended matter that accumulates annually in flood valleys during flood events. The current land-use type of Fluvisols significantly influenced the properties of organic matter, and thus of humic acids. Therefore, these properties can be used to evaluate the transformation of organic matter that occurs in Fluvisols depending on the type of use.

A protocol for nitrogen isotopic measurement of dissolved organic nitrogen with a combination of oxidation-denitrification and gas phase diffusion methods

ABSTRACT Isotopic tracing technique is one of the most effective methods to identify nitrogen source and fate in aquatic environments. Although dissolved organic nitrogen (DON) is a key component in nitrogen cycles, information on nitrogen stable isotope ratios in DON (δ 15N-DON) is limitedly available for its low recovery through a direct measurement. Indirect measurement is based on mass balance calculations and easy to use with high recovery of DON. However, in theory, the result from mass balance calculation is sensitive to the level of DON content, and its applicability remains to be examined for waters containing a variety of DON content in total dissolved nitrogen (TDN). In this study, we established a protocol for indirect measurement of δ 15N-DON values based on the combination of multiple analytical methods. Precision and accuracy in the measurement were assessed by varying the composition of DON and dissolved inorganic nitrogen, and quantitation thresholds were presented at different acceptable levels. The results illustrated an advantage of the developed protocol possibly applicable to water samples particularly with low DON content that is commonly detected in freshwater. This method is expected to expand the use of isotope tracing techniques for understanding the nitrogen cycle in water environments.

Seasonal variations of nitrogen in permafrost-affected soils of the Qinghai-Tibetan Plateau

The largest permafrost area in China is on the Qinghai-Tibetan Plateau (QTP), and the nitrogen biogeochemical cycles in this area have received significant attention. However, there is insufficient knowledge of the available soil nitrogen and microbial biomass nitrogen (MBN) dynamics in this region, which hinders our understanding of the changes in the ecosystem and the effects of climate change on the nitrogen dynamics in the future. In this study, we determined the monthly changes in ammonium nitrogen, nitrate nitrogen, dissolved organic nitrogen (DON), and MBN contents of the topsoil (at depths of 0–20 cm) from April 2016 to March 2017 in the permafrost region on the QTP. The results show that soil NH4+-N and DON contents decreased during the growing season, while soil NO3–-N content increased during the growing season and in the middle of the winter. The soil MBN contents increased at the beginning of the growing season and decreased during peak growth period, despite significant variations among the different sites. The soil temperature was positively correlated with soil NO3–-N content but it was negatively correlated with the NH4+-N and DON contents. The soil moisture was positively correlated with the soil NO3–-N, DON, and MBN contents. The primary factor affecting the seasonal patterns in soil NO3–-N and DON contents was soil moisture. Soil moisture and plant growth also affected soil MBN via nutrient competition. The nutrient uptake by plants overwhelmed effect of temperature on the MBN in growing season. These findings improve our understanding of the nitrogen biochemical cycles and their response to future climate change.

Responses of soil active carbon and nitrogen to short-term warming in alpine treeline of west Sichuan, China.

Alpine treeline ecosystem is more sensitive to global warming under low temperature limitation with the aggravation of greenhouse effect, which may directly affect plant growth and soil carbon and nitrogen processes. We expected that climate warming would change soil active carbon and nitrogen content in alpine ecosystems. This experiment was conducted in long-term research station of alpine forest ecosystems, in Lixian County, Sichuan Province. The open top camber (OTC) was used to simulate warming, intact soil core (soil organic layer and mineral soil layer) of OTC and CK were collected in April, July and October 2017. Soil dissolved organic carbon (DOC), soil microbial biomass carbon (MBC), dissolved organic nitrogen (DON) and soil microbial biomass nitrogen (MBN) were measured. The results showed that average temperature increased by 0.88 ℃ for air, 0.48 ℃ for soil organic layer and 0.23 ℃ for mineral soil layer. The simulated warming did not significantly change soil organic matter and water content, but significantly increased pH of mine-ral soil layer, and significantly reduced DOC and DON contents of mineral soil layer in non-growing season. There was significant seasonal variation for the contents of DOC, DON and MBN in the two layers, but not for MBC. The MBC and MBN contents of soil organic layer were significantly higher than that of mineral soil layer. There was a significant positive correlation between active carbon and nitrogen with soil organic matter and water content. There was a significant positive correlation between MBC, MBN and soil pH, whereas MBN was negatively correlated with soil temperature.

Algal uptake of dissolved organic nitrogen in wastewater treatment plants

The algal uptake of dissolved organic nitrogen (DON) in the anaerobic–anoxic–oxic (A2O) process was investigated in this study. Anaerobic, aerobic and effluent DON samples from two wastewater treatment plants (WWTPs) were separated into hydrophilic and hydrophobic fractions using a DAX-8 resin coupled with an anion exchange resin and a nanofiltration (NF) pretreatment. Hydrophilic DON accounted for 66.66%–88.74% of the entire DON for the two plants evaluated. After a 15-day incubation, 16.95%–91.75% DON was bioavailable for algal growth, and untreated samples exhibited higher DON bioavailability, with 52.83% DON average uptake rates, compared with the hydrophilic and hydrophobic fractions (45.53% and 44.40%, respectively) because the pretreatment caused the inorganic salt to be resistant to algae. Anaerobic untreated samples, hydrophilic fractions and hydrophobic fractions showed higher DON reduction rates and higher biomass accumulation compared with the other DON fractions due to the decomposition of resistant organics by anaerobic and anoxic bacteria. DON in aerobic and effluent samples of plant A was more bioavailable than that of plant B with usages of 27.49%–55.26% DON. DON bioavailability in the anaerobic–anoxic–oxic process decreased in the following order: anaerobic>effluent>aerobic. The DON contents were reduced after anaerobic treatment in the two plants. The EEM-PARAFAC model identified three DON components, including two humic acid-like substances and one protein-like substance in plant A and two protein-like substances and one humic acid-like substance in plant B.

Effect of long-term fertilization on soil aggregate-associated dissolved organic nitrogen on sloping cropland of purple soil

To investigate the effect of fertilization practice on dissolved organic nitrogen (DON) in aggregates, the study was conducted and involved four fertilization treatments: no fertilizer; mineral fertilizer (MF); pig manure matched with mineral fertilizer (MFP) and crop straw matched with mineral fertilizer (MFR). The results showed that DON content and storage were the highest in > 5 mm aggregates and were the lowest in < 0.25 mm aggregates. Compared with MF, MFP and MFR significantly increased DON contents in > 5 mm by 404.7% and 184.4%. In comparison with MFR, DON content and storage in > 5 mm aggregates for MFP were significantly enhanced by 77.5% and 75.0%. A significantly positive linear correlation relationship between DON content and microbial biomass carbon content was observed in aggregates (R<sup>2</sup> = 0.84; P < 0.01). The results suggest that pig manure matched with mineral fertilizer is a preferred strategy for retaining DON nutrient due to enhanced microbial biomass in aggregates on sloping upland of purple soil.

米槠人促更新林与杉木人工林叶片及凋落物溶解性有机物的数量和光谱学特征

PDF HTML阅读 XML下载 导出引用 引用提醒 米槠人促更新林与杉木人工林叶片及凋落物溶解性有机物的数量和光谱学特征 DOI: 10.5846/stxb201306101638 作者: 作者单位: 湿润亚热带山地生态国家重点实验室培育基地,湿润亚热带山地生态国家重点实验室培育基地,湿润亚热带山地生态国家重点实验室培育基地,湿润亚热带山地生态国家重点实验室培育基地,湿润亚热带山地生态国家重点实验室培育基地,湿润亚热带山地生态国家重点实验室培育基地,湿润亚热带山地生态国家重点实验室培育基地 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学青年基金项目（31100467）；国家自然科学基金项目（31070548）；福建省自然科学青年基金项目（2011J05105）；福建师范大学优秀青年骨干教师培养基金项目（fjsdky2012008） Quantities and spectral characteristics of DOM released from leaf and litterfall in Castanopsis carlesii forest and Cunninghamia lanceolata plantation Author: Affiliation: Fujian Normal University,,Cultivation Base of State Key Laboratory of Humid Subtropical Mountain Ecology,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:选取中亚热带米槠人促更新林（CCF）和杉木人工林（CLP）内的鲜叶、未分解层（L层）和半分解层（F层）凋落物为研究对象进行室内淋溶，对其淋溶液中的溶解性有机碳（DOC）、溶解性有机氮（DON）和溶解性有机磷（DOP）含量，紫外吸收值（SUVA），腐殖化指标（HIX）和红外光谱（FTIR）等进行了比较分析，以揭示其淋溶液中溶解性有机物（DOM）的数量和光谱学特征。结果表明：随着淋溶时间的增加，不同样品的DOM含量呈现先上升后下降，或者有波动的上升的趋势，这是因为DOM的释放和反吸附共同控制着DOM的含量。两林分中，F层凋落物DOM的SUVA值显著高于鲜叶和L层凋落物（P < 0.05）；从鲜叶到L层到F层凋落物，其HIX逐渐变大并且三者荧光强度最大值对应的波长由短波向长波移动，这是腐殖化程度越来越高、电子共轭体系逐渐增大的体现。两个林分6种样品的红外光谱显示了5个相似的吸收谱带，但不同样品各吸收带的相对比例不同，强度最大的吸收来自于H键键合的-OH的伸缩振动；同一林分内3种样品之间红外吸收的差异证明了鲜叶到L层再到F层凋落物，其DOM的芳香类物质含量逐渐升高，化学键力常数变小。总体上，与杉木人工林相比，米槠人促更新林的DOM养分含量更高，结构更复杂，因而更有利于有机质的积累。 Abstract:DOM (Dissolved Organic Matter) is the most reactive pool of organic matter in ecosystems. Among others, it is the energy source of most microbial metabolism. It also plays a key role in the biogeochemistry of C/N/P due to its high mobility. In forest ecosystems, the amount of DOM that is respired, accumulated in soils or leached from the ecosystems are highly dependent on its chemical nature, which may differ between types and species of litter. Castanopsis carlesii forest (CCF) and Cunninghamia lanceolata plantation (CLP) are of dominant forest type and distributed widely in Fujian province, mid-subtropical China. While previous work focused on the biomass and carbon storage of the two kinds of stands, information on DOM from fresh leaves and litterfall from the two kinds of stands is rare. In this study, laboratory leaching experiments were carried out for leachates from fresh leaves and litterfall in L and F layers, which are from a 36-year-old Castanopsis carlesii forest (CCF) by artificially promoted regeneration and a 37-year-old Cunninghamia lanceolata plantation (CLP) in Sanming, Fujian province. We examined the quantities and spectral characteristics of DOM in terms of Dissolved Organic Carbon (DOC), Dissolved Organic Nitrogen (DON) and Dissolvd Oganic Phosphorus (DOP) content, Special Ultraviolet-Visible Absorption (SUVA), Humication Index (HIX) and Fourier Transform Infrared (FTIR) spectroscopy. The results showed that during leaching, the DOC, DON and DOP content in different samples either reached their maximum first followed by a decreasement, or showed an increasing valley and peak cycle; this is because that the release and desorption of DOM both controled the content of DOM. The amount of total DOC from CCF is comparable to that from CLP, but the amounts of DON and DOP are much higher than those from CLF. In the two stands, SUVA value of the DOM from F layer were significantly higher than those of fresh leaf and L layer (P < 0.05), suggesting that F layer litter contains more aromatic substances. In the order of fresh leaf, litter in L layer and F layer, the HIX increased gradually and the maximum fluorescence intensity shifted from shorter to longer wavelengths, which can be explained by a higher humification degree and the presence of larger conjugated systems; also, DOM from CCF has higher HIX than that from CLP. Each of the six kinds of samples showed five IR absorption bands in common, i.e., 3758-3058 cm-1, 1630-1600 cm-1, 1420-1400 cm-1, 1080-1020 cm-1, 690-610 cm-1, whose relative intensities differed between samples, with the strongest absorption in all cases arising from stretching vibration of H-bonding hydroxyl groups. DOM from CCF is more carboxylic acid abundant than DOM from CLP. The infrared absorption differences between three kinds of samples in the same stand supported that the aromatic substance content gradually increased and conjugated systems growed larger from the fresh leaves to L layer litter to F layer litter. Overall, DOM from CCF is nutrient richer and bears more complex structures, thus favoring organic matter accumulation, when compared with DOM from CLP. 参考文献 相似文献 引证文献

Organic C and N mineralization as affected by dissolved organic matter in paddy soils of subtropical China

In this study, dynamics of dissolved organic matter (DOM) and mineralization of soil organic C and N in subtropical China were investigated. Paddy and upland soils were derived from Tertiary sandstone, Quaternary red clay and river alluvium with low, middle, and high levels of soil fertility. Dissolved organic carbon contents (DOC) varied from 3.8 to 68.7 mg/kg and dissolved organic nitrogen contents (DON) ranged from 2.9 to 18.3 mg/kg, respectively, during the experimental period. Both DOC and DON increased with increasing soil fertility. The content of DOM was characterized by strong seasonal fluctuation in soils, and seasonal patterns showed the maximum value in Nov and the minimum in July. The contribution of DOM to mineralization of C and N was significantly affected by soil types and seasons. DOM removal significantly decreased the cumulative organic C mineralization in soils derived from Tertiary sandstone and River alluvium (by 1.6%–20.3% with an average of 7.1%), while it did not significantly change those in soils derived from Quaternary red clay. Similarly, the cumulative mineralization of N in paddy soils after DOM removal decreased by 6.7%–27.3% over seasons. In this study, DOM played an important role in soil C and N mineralization in subtropical China. It appears that contribution of DOM to minerilization of C and N in paddy soils was possibly related to DOM content and composition.

Formation of organic chloramines during water disinfection – chlorination versus chloramination

Many of the available studies on formation of organic chloramines during chlorination or chloramination have involved model organic nitrogen compounds (e.g., amino acids), but not naturally occurring organic nitrogen in water. This study assessed organic chloramine formation during chlorination and chloramination of 16 natural organic matter (NOM) solutions and 16 surface waters which contained dissolved organic nitrogen (DON). Chlorination rapidly formed organic chloramines within 10 min, whereas chloramination formed organic chloramination much more slowly, reaching the maximum concentration between 2 and 120 h after the addition of monochloramine into the solutions containing DON. The average organic chloramine formation upon addition of free chlorine and monochloramine into the NOM solutions were 0.78 mg-Cl 2/mg-DON at 10 min and 0.16 mg-Cl 2/mg-DON at 24 h, respectively. Organic chloramine formation upon chlorination and chloramination increased as the dissolved organic carbon/dissolved organic nitrogen (DOC/DON) ratio decreased (i.e., DON contents increased). Chlorination of molecular weight (10,000 Da) fractionated water showed that molecular weight of DON would not impact the amount of organic chloramines produced. Comparison of three different disinfection schemes at water treatment plants (free chlorine, preformed monochloramine, and chlorine/ammonia additions) indicated organic chloramine formation could lead to a possible overestimation of disinfection capacity in many chloraminated water systems that add chlorine followed by an ammonia addition to form monochloramine.

Simultaneous colour and DON removal from sewage treatment plant effluent: Alum coagulation of melanoidin

The aim of this study was to detect and characterise melanoidin in sewage treatment plant (STP) effluent, and to study the ability of alum coagulation to remove the colour and dissolved organic nitrogen (DON) associated with melanoidin. The melanoidin is non-biodegradable due to the complex cyclic based structure and thus it directly contributes to effluent nitrogen concentrations from the sewage treatment plant (STP). Lowering of effluent total nitrogen limits and the link between colour and chlorinated disinfection by-products have therefore driven a need to understand the structure, properties and treatability of DON species found in STP effluent. The focus of this paper is the refractory coloured, organic nitrogen compound melanoidin. Wetalla STP effluent has relatively high colour (170 mg-PtCo L −1) and DON (2.5 mg L −1) for a biological nutrient removal STP, owing to an industrial supply of melanoidin containing molasses fermentation wastewater. Alum coagulation jar tests were performed on synthetic melanoidin solution, STP effluent containing melanoidin (Wetalla, Toowoomba, Australia) and STP effluent free of melanoidin (Merrimac, Gold Coast, Australia) to examine the treatability of melanoidin and its associated colour and DON content when present in STP effluent. The removal of melanoidin from STP effluent resulted in significant colour and DON reduction. An alum dose of 30 mg L −1 as aluminium was sufficient to reach maximum removal of colour (75%), DON (42%) and dissolved organic carbon (DOC) (30%) present in melanoidin containing STP effluent. Alum was shown to preferentially remove DON with a molecular weight >10 kDa over small molecular weight DON. Fluorescence excitation-emission matrix examination of the humic compounds present in the STP effluent indicated that melanoidin type humic compounds were more readily removed by alum coagulation than other humic compounds.

Seasonal variability and export of dissolved organic nitrogen in the northwestern Mediterranean Sea

Hydrodynamic and biogeochemical monthly time series were carried out in the Gulf of Lions (northwestern Mediterranean) between 1993 and 1994. Detailed analysis of vertical profiles of dissolved organic nitrogen (DON) revealed an accumulation of nitrogen in the Upper Mixed Layer (UML) above the seasonal thermocline. DON was not corrected for ammonia concentration because of negligible concentrations of this element during the whole year in the studied area. In midwinter (January–February), DON concentrations were quasi‐homogeneous throughout the water column (about 3.5 μM). Subsequently, surface DON concentrations increased up to autumn, with a subsurface maximum greater than 6.0 μM observed in September. During this time, inorganic nutrients became virtually undetectable in the UML. The total DON content (0–1000 m) increased by about 784 mmol m−2 from winter through to the end of summer. At this time, labile and semilabile DON represented a maximum of 20% of the bulk DON. Assuming that DON was essentially removed from surface water by diffusive process during the stratified period and by vertical mixing during the rest of the year, 210 to 723 mmol m−2 a−1 was exported as DON, which represented 40–90% of the total new production. Following this DON export enabled us to balance the nitrogen budget of the area studied over the duration of the experiment.

Concentrations of nitrogen in sandy sediments of a eutrophic estuarine lagoon

Concentrations of sediment organic nitrogen, dissolved inorganic nitrogen (ammonium, nitrite and nitrate), and dissolved organic nitrogen (DON) in sediments were measured at two sites in a eutrophic estuarine lagoon. One is a shallow aerobic site where macrobenthos are abundant and the other is a deep anaerobic site devoid of macrobenthos. Four species of macrobenthos (Bivalvia: Corbicula japonica, Annelida: Notomastus sp., Neanthes japonica and Oligochaeta sp.) were found in 8 sandy sediment cores collected at a shallow site in three succcessive summers. DON (170–1500 μg atom N l-1) was the major constituent of dissolved nitrogen with 10 times greater concentration than ammonium (55–180 μg atom N l-1) and 1000 times greater than nitrate (0.14–5.9 μg atom N l-1) and nitrite (0.21–1.4 μg atom N l-1). The ammonium content in anaerobic muddy sediments at the deep site (210–350 μg atom N l-1) was higher than in aerobic sandy sediments, whereas DON was higher in aerobic sediments than anaerobic sediments (90–240 μg atom N l-1). In aerobic sediments, depth profiles of DIN were nearly constant whereas DON was mostly highest at the surface. On the other hand, the increase of DON and ammonium was observed where macrobenthos was found. The occurrence of macrobenthos and high content of DON and ammonium content in the layers of sediment may suggest the influence of macrobenthos in the partitioning of nitrogen species through their motion and excretion.