Spatial distribution of bioavailable nitrogen in surface sediment of Isahaya Bay (Japan) and its relation to drainage from a reclaimed freshwater reservoir

To reveal the diverse occurrence forms and spatial distribution characteristics of nitrogen in the surface sediments of Ming Lake, a sequential leaching method was employed to determine the nitrogen in the surface sediments of Ming Lake. The results show that the total Nitrogen (TN) of the surface sediments of Ming Lake are between 383.23 and 3270.38 ug/g, and the spatial distribution is generally shown as southwest>middle>southeast>west of the lake. The results indicate the nutrient level of the whole lake is not very high. However, for some local areas a risk of high eutrophication pollution may exist due to excessive content; the average TTN is 638.77 ug/g which occupying 36 % of the lake; the spatial distribution is the same with TN; the average (NTN) is 928.61 ug/g that occupied 61 % of TN. With the exception of SAEF-N, every occurrence form of nitrogen was positive with TOM, indicating that the content and spatial distribution of organic matter in the surface sediments of Minghu Lake are the main controlling factors for the content and spatial distribution characteristics of various forms of nitrogen in the sediments.

为探究湖泊水体悬浮颗粒物和沉积物有机碳、氮来源及水质指示意义，分析了2013-2014年洱海悬浮颗粒物和表层沉积物有机碳同位素（δ¹³C）、氮同位素（δ¹⁵N）和C/N比值时空变化特征及与水质的关系.结果表明：①洱海悬浮颗粒物δ¹³C、C/N、δ¹⁵N在旱、雨季差异显著（P<0.05），旱季变化范围分别为-31.75‰~-18.21‰（均值-25.34‰±4.14‰）、9.1~16.9（均值13.3±2.7）、4.9‰~7.4‰（均值6.4‰±1.3‰），雨季变化范围分别为-14.7‰~-23.8‰（均值-20.2‰±3.3‰）、4.6~8.9（均值7.1±1.6）、7.4‰~10.8‰（均值9.3‰±1.8‰）.悬浮颗粒物有机碳来源在旱季以陆源C3植物为主（46.0%±6.9%），转变为雨季以浮游植物为主（43.3%±6.1%）；氮来源在旱季以陆源植物为主（40.7‰±6.5%），转变为雨季以湖内水生植物和浮游植物为主（39.9%±6.6%）.表层沉积物δ¹³C（-24.0‰~-14.6‰（均值为-18.7‰±4.7‰））和C/N（9.1~15.5（均值为12.1±3.3））均无显著季节差异（P>0.05），δ¹⁵N在旱、雨季差异显著（P<0.05），变化范围分别为1.9‰~4.9‰（均值为3.6‰±1.5‰）和0.7‰~7.8‰（均值为4.2‰±1.8‰）.表层沉积物有机碳来源在旱、雨季均以陆源C4植物为主（48.2%±19.1%），氮来源旱季以陆源植物为主（44.3%±10.1%），转变为雨季以化肥为主（30.3%±6.8%）.两者有机碳与氮来源差异揭示水生和浮游植物来源的有机碳与氮易降解，对水质影响较大，而陆源C4植物和土壤来源的有机碳和化肥来源氮易沉积，对水质影响相对较小.②随机森林回归分析表明，悬浮颗粒物有机质（POM）来源差异（δ¹³C、C/N）、氧化还原电位和水温（WT）是影响水体多营养循环指标的重要因子，重要度为4.0%~6.9%；POM、C/N和WT是影响叶绿素a的重要因子，重要度为9.3%~10.7%，说明POM来源特征结合水环境因子显著影响水质，而表层沉积物有机质来源相对稳定，对水质无显著影响.为防控洱海水质持续下降，除了加强外源控制，雨季还应重点采取控藻措施.;In order to explore the sources of organic carbon and nitrogen in suspended particles (SP) and sediments, and their implication for water quality, the spatiotemporal variation characteristics of stable isotopic carbon (δ¹³C), nitrogen (δ¹⁵N) and C/N in SP and surface sediments of Lake Erhai were determined in 2013-2014, and their effects on water quality were analyzed. The results showed that, ① The δ¹³C, C/N and δ¹⁵N of SP were significantly different between dry and wet seasons (P<0.05), and varied in the range of -31.75‰ to -18.21‰(the mean was -25.34‰±4.14‰), 9.1 to 16.9(13.3±2.7) and 4.9‰ to 7.4‰(6.4‰±1.3‰) in the dry season, and -23.8‰ to -14.7‰(-20.2‰±3.3‰),4.6 to 8.9(7.1±1.6) and 7.4‰ to 10.8‰(9.3‰±1.8‰) in the wet season, respectively. The end-member mixing model showed, the sources of organic carbon in SP transformed from the terrestrial C3 plants dominated (46.0%±6.9%) in the dry season to phytoplankton dominated (43.3%±6.1%) in the wet season; the nitrogen sources in SP transformed from the terrestrial plants dominated (40.7%±6.5%) in the dry season to aquatic plants and phytoplankton dominated (39.9%±6.6%) in the wet season. There were no significant differences in δ¹³C and C/N in surface sediments between dry and wet seasons (P>0.05), and the δ¹³C and C/N varied in the range of -24.0‰ to -14.6‰(-18.7‰±4.7‰)) and 9.1 to 15.5(12.1±3.3), respectively. The δ¹⁵N of surface sediments was significantly different between dry and wet seasons(P<0.05), and varied in the range of 1.9‰ to 4.9‰(3.6‰±1.5‰) and 0.7‰ to 7.8‰(4.2‰±1.8‰), respectively. The organic carbon in surface sediments in dry and wet seasons mainly originated from the terrestrial C4 plants, which contributed 48.2%±19.1% of the total organic carbon, and the nitrogen sources in surface sediments transformed from the terrestrial plants dominated (44.3%±10.1%) in the dry season to fertilizers dominated (30.3%±6.8%) in the wet season. The different sources of organic carbon and nitrogen between SP and surface sediments revealed that the organic carbon and nitrogen from phytoplankton were easily degraded, leading to the deterioration of water quality; while the organic carbon from terrestrial C4 plants and soil erosion and nitrogen from fertilizer are easy to deposit, which had little effect on water quality. ② Correlation analysis and random forest regression analysis showed that the source difference of particulate organic matter(POM) (δ¹³C and δ¹⁵N), oxidation-reduction potential and water temperature (WT) in SP were key indicators in the multi-nutrient cycling index for lake water with the importance for 4.0% to 6.9%, while POM, C/N and WT in SP were key indicators in chlorophyll-a for lake water with the importance for 9.3% to 10.7%, which indicated that the source characteristics of POM combining with environmental factors had a significant effect on water quality. However, the source characteristics of organic carbon and nitrogen in surface sediments have no significant effect on water quality. For the protection of Lake Erhai, in addition to further strengthening the control of external loads, the phytoplankton biomass should be mainly controlled in the wet season to avoid further deterioration of water quality.

Nitrogen in surface sediments is becoming an ecological risk to the river environment and it is essential to clarify the relationship between the different forms of nitrogen and related microorganisms. A survey was conducted to analyze the distribution characteristics of the nitrogen and related microbial community in the sediments of the Songhua River during normal season and dry season. In the surface sediments of the Songhua River, no total nitrogen (TN) pollution risk was observed according to the U.S. EPA assessment criteria (1000 mg kg−1) for sediment contamination, but TN in several sampling sites (554.9–759.7 mg kg−1) exceeded the alert values (550 mg kg−1) should be concerned according to the guidelines issued by the Ministry of Environment and Energy of Ontario, Canada. The average TN, NH4+–N, NO3−–N and total organic nitrogen (TON) in the surface sediments of the Songhua River during normal season were higher than those in the dry period. TON was the main form of nitrogen in the sediment of Songhua River, NO2−–N content was lowest and no obvious difference was observed between normal and dry seasons. The highest average NH4+–N of both seasons occurred in the Nenjiang River, and the highest average NO3−–N of both seasons were found in the main stream of the Songhua River. The community abundance of AOB genes (1.1 × 107 to 2.5 × 108 copies per g soil in normal season, 7.2 × 105 to 3.3 × 108 copies per g soil in dry season) was higher than that (1.2 × 106 to 9.7 × 107 copies per g soil in normal season, 6.6 × 104 to 3.2 × 107 copies per g soil in dry season) of AOA genes in both normal and dry seasons. The denitrifying nirS genes were predominant in both seasons, and their abundance (1.8 × 106 to 8.0 × 108 copies per g soil) in dry season was higher than that (9.7 × 105 to 4.6 × 108 copies per g soil) in normal season. Moreover, the moisture concentration, pH, dissolved oxygen and different formation of nitrogen were key factors affecting the variation of nitrogen-transformation microorganisms during normal and dry seasons. This research could help to explain the relationship between nitrogen transformation and the related microbial community in the surface sediment, which could provide a scientific basis for water ecological restoration and water environment improvement of Songhua River.

Time-space distribution characteristics of nitrogen in surface sediment from the Inner Mongolia of the Yellow River were investigated using the sequential extraction method. Sedimentary nitrogen were fractionized into four forms: ion exchange nitrogen (IEF-N), nitrogen combined with carbonate (CF-N), nitrogen combined with iron-manganese oxide (IMOF-N), organic nitrogen and combined with sulfides (OSF-N). The rank order according to the mean concentration of N-fraction in surface sediments from the Inner Mongolia of the Yellow River was OSF-N &gt; IMOF-N &gt; IEF-N &gt; CF-N and the N-fraction content in surface sediments of autumn was higher than that of spring. Moreover, the different degrees of positive correlation between different morphological transformation nitrogen forms and the sum of TN, TP, CEC and organic matter of 12 sediment samples.

Seasonal and spatial variations of carbon and nitrogen distribution in the surface sediments of the Gulf of Riga, Baltic Sea

Dianchi Lake is one of the most three seriously eutrophic lakes in China. In the present study, the phosphorus (P) and nitrogen (N) fractions in 37 surface sediments samples collected in the Dianchi Lake were investigated. The total phophorus (TP) in sediments was divided into two parts: inorganic P (IP) and residual P (Res-P). The results showed that the total phosphorus content in surface sediments ranged from 1465.27 to 3650.12 mg/kg, IP was the major component of TP and the Ca bound P was the main fraction of IP. The bio-available phosphorus (BAP) in Dianchi Lake was first estimated in this study. BAP ranged from 215.66 to 678.02 mg/kgand the mean concentration was 382.78±89.77 mg/kgfor all 37 samples. The nitrogen fractions for the whole Dianchi Lake were firstly studied. It was shown that the sediment had been an important N nutrient source of the water, owing to the high content of transferable nitrogen forms in the sediment.

Anthropogenic nitrogen (N) often causes coastal eutrophication, yet little is known about the fate and retention of effluent N in coastal waters and, hence, about the system’s ability to assimilate excess N loads. We used the spatial distribution of stable N isotope ratios and algal pigments in sedimentary organic matter from a Baltic bay receiving tertiary‐treated effluent to evaluate the extent of effects and the role of nearshore marine environments as sinks of anthropogenic N. Surface sediments (0–2 cm and 2–4 cm) exhibited a pronounced spatial gradient of δ15N, with the most elevated values (~8‰) near the outfall; values decreased linearly to values of ;4‰ outside the bay. Sedimentary pigment concentrations were consistent with water‐column data and showed that phytoplankton biomass was elevated in the inner reaches of the bay. In particular, diatoms were heavily labeled (δ15N ~ 10‰), reached maximum abundance near the effluent outfall, and were likely the main mechanism delivering effluent N to the sediments. Sediments within the bay removed ~5–11% of wastewater N inputs, with 50% of the sequestered effluent N buried in the basin nearest to the outfall. Magnitudes of N removal by sediments (23–26 x 104 kg N yr−1) were less than those estimated for denitrification (30–60 x 104 kg N yr−1), but they were substantially greater than biological uptake by macroalgae (~2 x 104 kg N yr−1). Taken together, these patterns demonstrate the idea that coastal sediments can be effective sinks of wastewater N, even after 30 yr of effluent input.

The estuarine wetland of Luoshijiang River, which flows into Erhai Lake in Yunnan province, was regarded as the typical research object. Sediment samples in the estuarine wetland of Luoshijiang River were collected by the cylindrical sediment sampler and the samples were from surface layer (0-10cm), middle layer (10-30 cm), and bottom layer (30-60 cm). The vertical distribution of total nitrogen, total phosphorus, and total organic material in dry and rainy season was analyzed and contamination risk assessment of sediment was accomplished. The results showed that: ① In dry season, average concentrations of total nitrogen in sediment on surface, middle and bottom layer at estuarine wetland of Luoshijiang River were respectively 1.734, 1.453 and 1.255 g·kg-1, the average concentrations of total phosphorus were respectively 1.085, 1.034 and 0.992 g·kg-1, the average concentrations of organic material were respectively 59.051, 47.730 and 42.133 g·kg-1. In rainy season, average concentrations of total nitrogen in sediment on surface, middle and bottom layer at estuarine wetland of Luoshijiang River were respectively 1.147, 0.948 and 0.895 g·kg-1, the average concentrations of total phosphorus were respectively 0.599, 0.523 and 0.519 g·kg-1, the average concentrations of organic material were respectively 53.098, 46.897 and 43.395 g·kg-1. ② Single factor pollution index, organic nitrogen and organic index assessment were used to evaluate the contamination level of sediment, the assessment results showed that: In dry season, the contamination level of nitrogen and phosphorus in sediment was on severe level, organic material contamination was on medium level. In rainy season, the contamination levels of ON and OI were medium, and that of PI was mild. Generally, the contamination levels of nitrogen, phosphorus and organic material in sediment tendency were as follows: dry season>rainy season, and the pollution index of each layer followed the sequence of surface layer > middle layer > bottom layer, and the most extraordinary contamination of them on surface layer was uncovered whatever the season was. ③ Pollution origin of estuarine wetland of Luoshijiang River in dry and wet season had great differences, it was mainly the exogenous source in dry season, but it was the internal source in wet season; The potential risk of release of nutrient salt of sediment in dry season was higher than the wet, and the risk in the surface layer was the highest.

The Xin'an Reservoir is an important water supply source and water conservation area for the Qiantang River. However, after the occurrence of the two algae blooms in 1998 and 1999, the safety of water quality has been put into question. In order to study the historical deposition of nutrients, sediment cores were collected in different regions from the Xin'an Reservoir. The stable isotopes δ13C and δ15N, nutrients, total organic carbon (TOC), and inorganic carbon (IC) in the sediment cores were determined. Radiometric methods (210Pb and 137Cs) were used to obtain sediment chronologies. Spatially, it was found that the average total nitrogen (TN) content in the upper 5cm of sediments increased from 0.21% in the riverine zone, to 0.33%, and then to 0.57% in the lacustrine zone. The average TP content in the upper 5cm increased from 0.67gkg-1 in the riverine zone, to 1.03gkg-1 in the estuary region, and then to 1.65gkg-1 in the lacustrine zone. In addition, TOC levels showed a distinct increase from 1.42% in the bottom to 5.97% in the surface of the lacustrine zone. These results demonstrated that although primary productivity and the input of nutrients constantly increased in recent years, algae blooms rarely occurred in the Xin'an Reservoir, due to "depth effect" and an aquatic environment protection-oriented fishery policy. However, high TOC flux and high bio-available phosphorus and nitrogen in surface sediment demonstrated that the reservoir is still confronted with the potential risk of algae blooms.

Geochemistry of organic carbon and nitrogen in surface sediments of coastal Bohai Bay inferred from their ratios and stable isotopic signatures

Water exchange in shallow lakes alongside Poyang Lake is weak because of sluggish water flow, and thus these lakes are susceptible to the effects of human activities and nutrient oversupply. Therefore, it is meaningful to study the sources of organic matter in these lakes, which is supposed to provide theoretical basis for the control of eutrophication of the lakes. The sources of organic matter in surface sediment in shallow lakes (Bang, Sha, Dahuchi, and Zhu lakes) alongside Poyang Lake and urban lakes (Qingshan and Xiang lakes) in Nanchang City were investigated by measuring the δ15N and δ13C values, total organic carbon and total organic nitrogen contents, and C/N ratios of sedimented organic matter (SOM). The δ15N, δ13C, and C/N ratios indicated that SOM in Sha and Dahuchi lakes mostly originated in phytoplankton, SOM in Bang and Zhu lakes was supplied by phytoplankton and soil organic matter, SOM in Qingshan Lake was strongly affected by sewage organic matter, and SOM in Xiang Lake mainly came from aquatic macrophytes. The results demonstrate that stable isotopes in SOM in lakes can be used to discriminate between different sources of organic material.

The area of the southwestern Nansha Trough is one of the most productive areas of the southern South China Sea. It is a typical semi-deep sea area of transition from shoal to abyssal zone. To understand distributions and roles of nitrogen forms involved in biogeochemical cycling in this area, contents of nitrogen in four extractable forms: nitrogen in ion exchangeable form (IEF-N), nitrogen in weak acid extractable form (WAEF-N), nitrogen in strong alkali extractable form (SAEF-N) and nitrogen in strong oxidation extractable form (SOEF-N), as well as in total nitrogen content (TN) in surface sediments were determined from samples collected from the cruise in April–May 1999. The study area was divided into three regions (A, B and C) in terms of clay sediment ( 60%, respectively. Generally, region C was the richest in the nitrogen of all forms and region A the poorest, indicating that the finer the grain size is, the richer the contents of various nitrogen are. The burial efficiency of total nitrogen in surface sediments was 28.79%, indicating that more than 70% of nitrogen had been released and participated in biogeochemical recycling through sediment-water interface.

Amino acid remineralization and organic matter lability in Chilean coastal sediments

The organic carbon, phosphorus and nitrogen content of silt and clay fractions of surface sediments from the marine-coastal region north and south of the Paria Peninsula (PP) were quantified. Organic carbon concentrations (Corg) were determined by dry combustion after decarbonation with 10% hydrochloric acid, and total phosphorus (TP) and total nitrogen (TN). This information was then used to produce maps of the iso-concentrations of the distribution of these elements in the sub-marine continental shelf north of the PP and in the Gulf of Paria (GP). In the silt fraction, the Corg concentration, TP and TN showed average values of 1.53, 0.04 and 0.03%, respectively. The highest Corg, PT and NT values were recorded from silts from the PP with a gradual increase towards the west and the lowest figures were found in the GP. In the clay fraction, Corg, TN and TP had mean values of 1.64, 0.13 and 0.04%, respectively, and showed a spatial distribution very similar to the silt fraction, indicating the influence of ocean currents and coastal upwelling patterns. The C/N ratio had an average of 23.67 and showed that the Corg present in the PP sediments is of marine origin, resulting from primary productivity, especially towards the west. This zone has been identified as the most productive in this region due to coastal upwelling and the influence of the Orinoco and Amazon rivers (Gomez 1996; Monente 1997). In contrast, a greater variability in the parameters measured was found in the GP sediments, probably due to the mixing of marine and continental Corg, confirming the influence of the Orinoco and Amazon waters brought by the Guyana Current.

Geochemical Fractions and Release Risk of Nitrogen in Surface Sediments from a Tropical Eutrophic Embayment