Nitrogen In Surface Sediments Research Articles

Spectroscopic Characteristics of Dissolved Organic Nitrogen in Surface Sediments from Lake Chaohu

Spectroscopic Characteristics of Dissolved Organic Nitrogen in Surface Sediments from Lake Chaohu

The sources characteristics of stable isotope organic carbon and nitrogen in suspended particles and surface sediments in Lake Erhai and their water quality implications

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.

Speciation and spatial distribution of nitrogen in surface sediments of in Ming Lake

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&gt;middle&gt;southeast&gt;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.

Using Isotopes to Identify the Sources of Organic Carbon and Nitrogen in Surface Sediment in Shallow Lakes Alongside Poyang Lake

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.

Historical record of nutrients inputs into the Xin’an Reservoir and its potential environmental implication

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.

Time-Space Distribution Characteristics of Nitrogen in Surface Sediment from the Inner Mongolia of the Yellow 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.

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

Total organic carbon (TOC), total nitrogen (TN) and their δ13C and δ15N values were determined for 42 surface sediments from coastal Bohai Bay in order to determine the concentration and identify the source of organic matter. The sampling sites covered both the marine region of coastal Bohai Bay and the major rivers it connects with. More abundant TOC and TN in sediments from rivers than from the marine region reflect the situation that most of the terrestrial organic matter is deposited before it meets the sea. The spatial variation in δ13C and δ15N signatures implies that the input of organic matter from anthropogenic activities has a more significant influence on its distribution than that from natural processes. Taking the area as a whole, surface sediments in the marine region of coastal Bohai Bay are dominated by marine derived organic carbon, which on average accounts for 62±11% of TOC.

Distribution and Fractions of Phosphorus and Nitrogen in Surface Sediments from Dianchi Lake, China

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.

Organic carbon, phosphorus and nitrogen in surface sediments of the marine-coastal region north and south of the Paria Peninsula, Venezuela

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.

Contents and distribution characteristics of soluble organic nitrogen in surface sediments of lakes

选择鄱阳湖、洞庭湖等6个湖泊的15个表层沉积物样品,用1mol/LKCl溶液提取沉积物中的可溶性有机氮(SON),并研究了SON的含量、分布状况及特性.结果表明,所研究的沉积物SON含量变异较大,在17.18-292.31mg/kg之间波动,平均为134.45mg/kg,占可溶性总氮(TSN)的51.86%,沉积物总氮的7.14%.污染程度重的沉积物中SON含量均较污染程度轻的高,且SON含量与TN、TSN含量呈正相关,即与沉积物氮污染程度呈正相关.分布状况则与湖泊污染程度、人类活动干扰强度等紧密相关.所研究表层湖泊沉积物中游离氨基酸(FAA)含量处于4.69-42.04mg/kg间,平均为23.27mg/kg,占SON的18.80%,TN的1.24%.FAA与SON含量呈显著正相关,在沉积物中的平均含量及在SON中的比例均较土壤中高,说明湖泊沉积物SON有较大的易分解组分.SON与沉积物可溶性无机氮、有机质、CEC等显著相关.因此,SON是湖泊沉积物氮的重要组成部分,对湖泊富营养化具有重要的影响,特别是对污染严重的沉积物而言,更应重视其SON在湖泊氮循环及富营养化中的作用.;The contents and distribution characteristics of soluble organic nitrogen (SON) extracted with 1mol/L KCl from thesediments of six typical lakes including Lake Poyang, Lake Dongting in Hunan and Jiangxi Provinces were studied. The resultsindicated that the SON contents varied greatly from 17.18mg/kg to 292.31mg/kg (mean content,134.45mg/kg), comprising 51.86% oftotal soluble nitrogen (TSN) and 7.14% of total nitrogen (TN) in six lakes. The SON contents were significantly correlated with theircontents of TN and TSN, and SON were higher in the heavily polluted sediments than the light polluted ones. Their distributions ofSON were closely related to their lake pollution levels. The contents of free amino acid in the sediments were also studied, and theyvaried from 4.69 to 42.04mg/kg, comprising 18.80% of SON, and 1.24% of TN, and were significantly correlated with their SONcontents. The mean content of FAA was 23.27mg/kg, higher than those in soils in the same region. It indicated that there was morebioavailable SON from lake sediment than those from soil. The contents of SON in the sediments were also correlated with inorganicnitrogen, OM and CEC and so on. As one of the most important nitrogen compositions in lake sediments, SON should be paid moreattention to the nitrogen cycling and entrophication control in lakes.

Characteristics of nitrogen forms in the surface sediments of southwestern Nansha Trough, South China Sea

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.

Sub-recent nitrogen-isotope trends in sediments from Skagerrak (North Sea) and Kattegat: Changes in N-budgets and N-sources?

We determined 15N/ 14N ratios of total nitrogen in surface sediments and dated sediment cores to reconstruct the history of N-loading of the North Sea. The isotopic N composition in modern surface sediments is equivalent to and reflects the isotopic mixture of oceanic nitrate on the one hand ( δ 15N = 5‰) and the imprint of river-borne nitrogen input into the SE North Sea ( δ 15N up to 12‰ in estuaries of the SE North Sea) on the other hand. We compare the results with δ 15N records from pre-industrial sediment intervals in cores from the Skagerrak and Kattegat areas, which both constitute significant depositional centres for N in the North Sea and the Baltic Sea/North Sea transition. As expected, isotopically enriched anthropogenic nitrogen was found in the two records from the Kattegat area, which is close to eutrophication sources on land. Enrichment of δ 15N in cores from the Skagerrak – the largest sediment sink for nitrogen in the entire North Sea – was not significant and values were similar to those found in sediment layers representing pre-industrial conditions. We interpret this isotopic uniformity as an indication that most riverine reactive nitrogen with its characteristic isotopic signature is removed by denitrification in shallow shallow-water sediments before reaching the main sedimentary basin of the North Sea.

Distribution and retention of effluent nitrogen in surface sediments of a coastal bay

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.

Amino acid remineralization and organic matter lability in Chilean coastal sediments

The spatial distribution of proteinaceous amino acids was investigated in Chilean coastal surface sediments. Proteinaceous amino acids, measured as total hydrolyzed amino acids (THAA), were in the range 37–1335 μmol THAA-N gdw−1 and accounted for 6–70% of total nitrogen in surface sediments. Beggiatoa or Thioploca, motile, filamentous bacteria present in sediments with low oxygen bottom waters, may be a source of the non-protein amino acid, β-aminoglutaric acid. Mineralization of sedimentary THAA accounted for about one quarter of the ammonium production measured in these sampling sites. Reactivity of organic matter in these coastal sediments was assessed using a Degradation Index developed by Dauwe and Middelburg (1998; Limnology and Oceanography 43, 782–798) and Dauwe et al. (1999; Limnology and Oceanography 44, 1809–1814). Both production of ammonium and mineralization of amino acids follow a consistent trend with this index. Thus, we can relate the production of ammonium and mineralization of amino acids to the diagenetic state of the sediment.

The Nature of Organic Matter in the Danube River Particles and North-western Black Sea Sediments

Suspended matter and sediments from the Danube River and the adjacent north-western Black Sea were analysed for organic carbon, nitrogen and biogenic carbonate and silica, as well as for different fractions of organic matter such as amino acids and carbohydrates. In addition, the nitrogen isotopic composition of surficial sediments of the NW Black Sea was examined. Particulate organic carbon (POC) contents decrease with total suspended solid (TSS) concentration due to dilution by mineral matter derived from upstream and riverbed erosion. The contribution of labile constituents such as amino acids and carbohydrates to POC remains uniform across the measured TSS contents. This suggests that any possible decrease in labile POC (LPOC) from dilution with refractory organic matter is masked by inputs of fresh organic matter from tributaries downstream. Comparison of TSS, POC and LPOC leaving the Iron Gate I barrier at the head of the Danube delta shows that the bulk of material currently entering the Black Sea is derived from inputs from tributaries and riverbed erosion, downstream of the Iron Gate I. The nature and distribution of organic matter in the surface sediments of the Black Sea are influenced by mixing between Danube-derived material and freshly produced organic matter on the shelf and in the open sea, on the one hand, and by oxic degradation during transport from the shelf to the abyssal Black sea, on the other. Preliminary data on the stable isotopic composition of nitrogen in surface sediments of the Black Sea further suggest that organic matter production on the shelf and the adjacent north-western Black Sea is fuelled by different nitrogen sources.

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

The variations in concentrations of carbon and nitrogen in surface sediments of the Gulf of Riga were investigated between December 1993 and January 1995. The sediment samples were taken nine times during this period at two sampling sites. One sampling site, G5, exhibited high abundance of burrowing amphipods, whereas at the second site, T3, the number of macrozoobenthic organisms was comparatively small. Similar vertical profiles of mean sediment dry-weight concentrations of total carbon (TC) and total nitrogen (TN) were obtained at both sites G5 and T3. However, during autumn–winter considerable differences of TC and TN concentrations in surface sediments (0–2 cm) between sites were observed. This was probably the effect of differences in the bioturbation level. During summer, when decline in numbers of amphipods were recorded, the vertical profiles of TC and TN at site G5 were similar to those at site T3. Significant differences between months were detected for TN at site T3 reflecting sedimentation of spring and autumn blooms in April and late October–early November, respectively. This was supported also by lower atomic C/N ratios in surface sediments during corresponding sampling events.

Modern Coastal Swamp Sediments of Southwestern Florida, and Their Usefulness in Recognizing Ancient Coastal Swamp Deposits: ABSTRACT

Calcareous, quartzose and organic-rich (peaty) sediments accumulating in two modern mangrove estuarine swamps, the Ten Thousand Islands and the Whitewater Bay areas of southwestern Florida, were studied to derive criteria that would aid in recognizing similar ancient coastal swamp deposits. Both areas are at the seaward margin of the Everglades and are associated with an imposing coastal mangrove forest. The sediments forming in these two coastal swamps are modern analogues of ancient limestone, quartzite, and coal beds, and the coastal mangrove forest is the modern counterpart of ancient coal forests of cratonic and miogeosynclinal areas. Evaluation of results yields three principal criteria which may be useful in distinguishing ancient coastal swamp deposits. 1. Organic matter and carbon/nitrogen ratio: The content of organic matter and the ratio of organic carbon to nitrogen in surface sediments (upper 0.25-0.50 foot) along the southwestern Florida coast increases toward land on the open marine shelf and attain their highest values (organic matter ranging from 6 to more than 50 per cent and C/N ratio ranging from 17 to 37 per cent) within the coastal swamps. The increase in organic matter and C/N ratio in a shoreward direction is due to a progressive increase in the amount of organic matter contributed to surface sediments by terrestrial plants (mangrove trees) compared with that supplied by plankton and benthos. Fossil coastal swamp deposits, therefore, may be recognized by their exceptionally high organic matter content and C/N ratio with respect to laterally adjacent sediments. 2. Faunal assemblages: The areal distribution of molluscan faunal assemblages in the vicinity of the coastal swamps of southwestern Florida suggests that biofacies of ancient coastal swamp deposits would trend parallel with the coastline and delineate a direction of decreasing average water salinity toward the land area supplying run-off waters to the coastal swamps. 3. Grain size of carbonate and detrital minerals: Calcareous particles and detrital quartz along the southwestern Florida coast decrease in grain size from the open marine shelf toward and into the estuarine mangrove swamps. Hence, with support by criteria 1 ind 2, fossil coastal swamp sediments may be differentiated by their tendency to be noticeably finer-grained than adjacent sediments. End_of_Article - Last_Page 278------------