Seasonal and spatial distribution of particulate organic matter (POM) in the Chukchi and Beaufort Seas

As part of the Western Arctic Shelf–Basin Interactions (SBI) project, the production and fate of organic carbon and nitrogen from the Chukchi and Beaufort Sea shelves were investigated during spring (5 May–15 June) and summer (15 July–25 August) cruises in 2002. Seasonal observations of suspended particulate organic carbon (POC) and nitrogen (PON) and large-particle (>53 μm) size class suggest that there was a large accumulation of carbon (C) and nitrogen (N) between spring and summer in the surface mixed layer due to high phytoplankton productivity. Considerable organic matter appeared to be transported from the shelf into the Arctic Ocean basin in an elevated POC and PON layer at the top of the upper halocline. Seasonal changes in the molar carbon:nitrogen (C:N) ratio of the suspended particulate organic matter (POM) pool reflect a change in the quality of the organic material that was present and presumably being exported to the sediment and to Arctic Ocean waters adjacent to the Chukchi and Beaufort Sea shelves. In spring, low particulate C:N ratios (<6; i.e., N rich) were observed in nitrate-replete surface waters. By the summer, localized high particulate C:N ratios (>9; i.e., N-poor) were observed in nitrate-depleted surface waters. Low POC and inorganic nutrient concentrations observed in the surface layer suggest that rates of primary, new and export production are low in the Canada Basin region of the Arctic Ocean.     

The organic carbon in the water,the particulate matter,and the upper layer of the bottom sediments of the west Kara Sea

In three sections in the Kara Sea, the contents of the dissolved and particulate organic carbon (the DOC and POC, respectively), as well as of the organic carbon of the bottom sediments (C_org) were determined. The contents of varied from 6.3 to 2400 μg/l for the DOC and from 0.84 to 12.2 mg of C/l for the POC. The average concentrations for all the samples tested amounted to 200 μg/l for the DOC (n = 78, σ = 368) and 2.7 mg/l for the POC (n = 92, σ = 2.7). The concentrations of Corg in the samples of the upper layer of the bottom sediments of the area treated varied from 0.13 to 2.10% of the dry substance at an average value of 0.9% (n = 21, σ= 0.49%). It is shown that the distribution of the different forms of organic matter (OM) is an indicator of the supply and spreading of the particulate matter in the Kara Sea and that the DOC and POC of the Kara Sea are formed under the impact of the runoff of the Ob and Yenisei river waters. It is found that the distribution of the OM of the bottom sediments in the surveyed area of the Kara Sea is closely related to their grain-size composition and to the structure of the currents in the area studied. The variations in the Corg content in the bottom sediment cores from the zone of riverine and marine water mixing represent the variability of the OM burial.     

Dissolved and particulate organic carbon and nitrogen in the Northwestern Mediterranean

The distribution of dissolved organic carbon (DOC) and nitrogen (DON) and particulate organic carbon (POC) and nitrogen (PON) was studied on a transect perpendicular to the Catalan coast in the NW Mediterranean in June 1995. The transect covered a hydrographically diverse zone, including coastal waters and two frontal structures (the Catalan and the Balear fronts). The cruise was conducted during the stratified period, characterized by inorganic nutrient depletion in the photic zone and a well established deep chlorophyll a maximum. DOC concentrations were measured using a high-temperature catalytic oxidation method, and DON was determined directly, with an update of the Kjeldahl method, after removal of inorganic nitrogen.The ranges of DOC and DON concentrations were 44–95 μM-C and 2.8–6.2 μM-N. The particulate organic matter ranged between 0.9 and 14.9 μM-C and from 0.1 to 1.7 μM-N. The DOC : DON molar ratio averaged 15.5±0.4, and the mean POC : PON ratio was 8.6±0.6. The distribution of dissolved organic matter (DOM) was inverse to that of the salinity. The highest concentrations of DOM were found in coastal waters and in the stations affected by the Catalan front, located at the continental shelf break.It was estimated that recalcitrant DOM constituted 67% of the DOM pool in the upper 50 m. The data suggest that accumulation of DOC due to the decoupling of production and consumption may occur in the NW Mediterranean during stratification and that the organic matter exported from the photic layer is dominated by C-rich material.     

Organic carbon and nitrogen in the northern California current system: comparison of offshore, river plume, and coastally upwelled waters

During the first year of the Northeast Pacific GLOBEC program we examined the spatial distributions of dissolved and particulate organic carbon and nitrogen in the surface waters off the Oregon and Washington coasts of North America. Eleven east–west transects were sampled from nearshore waters to 190 km offshore. Hydrographic data and the distribution of inorganic nutrients were used to characterize three distinct water sources: oligotrophic offshore water, the Columbia River plume, and the coastal upwelling region inshore of the California Current. Warm, high salinity offshore water had very low levels of inorganic nutrients, particulate organic carbon (POC) and dissolved organic carbon (DOC). Warm, low salinity water in the Columbia River plume was relatively low in nitrate, but showed a strong negative correlation between salinity and silicate. The river plume water had the highest levels of total organic carbon (TOC) (up to 180 μM) and DOC (up to 150 μM) observed anywhere in the sampling area. Cold, high salinity coastal waters had high nutrient levels, moderate to high levels of POC and particulate organic nitrogen (PON), and low to moderate levels of DOC and dissolved organic nitrogen (DON). Each of these regions has characteristic C:N ratios for particulate and dissolved organic material. The results are compared to concentrations and partitioning of particulate and dissolved organic carbon and nitrogen in other regions of the North Pacific and North Atlantic Oceans.     

Carbon to nitrogen (C:N) stoichiometry of the spring–summer phytoplankton bloom in the North Water Polynya (NOW)

The carbon to nitrogen (C:N) stoichiometry of phytoplankton production varied significantly during the spring–summer bloom in the North Water Polynya (NOW), from April through July 1998. The molar ratio of particulate organic carbon (POC) to nitrogen (PON) production by phytoplankton (ΔPOC:ΔPON) increased from 5.8 during April through early June to 8.9 in late June and July. The molar dissolved inorganic carbon (DIC) to nitrate+nitrite (NO₃) drawdown ratio (ΔDIC: ΔNO₃) increased from 6.7 in April and May, to 11.9 in June (no estimate for July because of ice melting). The discrepancy between ΔPOC:ΔPON and ΔDIC:ΔNO₃ was likely due to dissolved organic carbon (DOC) production. Increased ΔPOC:ΔPON of phytoplankton and surface water ΔDIC:ΔNO₃ throughout the phytoplankton blooms resulted from changes in physical properties of the upper water column, such as reduced thickness of the surface mixed layer that exposed phytoplankton to increased photosynthetically available radiation (PAR), accompanied by NO₃ depletion. This is expected to have significant effects on the cycling of carbon (C) and nitrogen (N) in pelagic ecosystems, as the increased C:N ratio of organic matter decreases its quality as substrate for grazers and microbial communities. Based on ΔPOC:ΔPON, the ratio of POC to chlorophyll a (Chl) production (ΔPOC:ΔChl) and the relationship between Chl yields and NO₃ depletion, we estimate that 71±17% and 46±20% of the depleted NO₃ went to PON production in the euphotic zone over the polynya from April to early June, and late June to July, respectively. The remaining NO₃ was likely channelled to dissolved organic nitrogen (DON) and heterotrophic bacteria, which were not returned to the dissolved inorganic nitrogen (DIN) pool through recycling during the course of the study. Hence, the autotrophic production of organic N and its recycling by the microbial food web were not coupled temporally.     

Origin and biochemical cycling of particulate nitrogen in the Mandovi estuary

Mandovi estuary is a tropical estuary strongly influenced by the southwest monsoon. In order to understand, sources and fate of particulate organic nitrogen, suspended particulate matter (SPM) collected from various locations, was analyzed for particulate organic carbon (POC) and particulate organic nitrogen (PON), δ¹³C_POC, total hydrolysable amino acid enantiomers (l- and d- amino acids) concentration and composition. δ¹³C_POC values were depleted (−32 to −25‰) during the monsoon and enriched (−29.6 to −21‰) in the pre-monsoon season implying that OM was derived from terrestrial and marine sources during the former and latter season, respectively. The biological indicators such as C/N ratio, d-amino acids, THAA yields and degradation indices (DI) indicate that the particulate organic matter (POM) was relatively more degraded during the monsoon season. Conversely, during the pre-monsoon, the biological indicators indicated the presence of relatively fresh and labile POM derived from autochthonous sources. Amino acids such as alanine, aspartic acid, leucine, serine, arginine, and threonine in monsoon and glutamic acid, glycine, valine, lysine, and isoleucine in pre-monsoon were relatively abundant. Presence of bacterial biomarker, d-amino acids in the SPM of the estuary during both the seasons signifies important contribution of bacteria to the estuarine detrital ON pool. Based on d-amino acid yields, bacterial OM accounted for 16-34% (23.0 ± 6.7%) of POC and 29-75% (47.9 ± 18.7%) of PON in monsoon, and 30-78% (50.0 ± 15%) of POC and 34-79% (51.2 ± 13.3%) of the PON in pre-monsoon in the estuary. Substantial contribution of bacterial-N to PON indicates nitrogen (N) enrichment on terrestrial POM during the monsoon season. Transport of terrestrial POM enriched with bacterial OM to the coastal waters is expected to influence coastal productivity and ecosystem functioning during the monsoon season.     

Influence of winds and oceanographic conditions on the mucilage aggregation in the Northern Adriatic Sea in 2003–2006

Meteorological and oceanographic conditions in the Northern Adriatic Sea in a year notable for massive mucilage formation (2004) were compared with those in years where this phenomenon did not occur (2003, 2005 and 2006) to suggest possible links. The months preceding the mucilage event in 2004 were considered the ‘incubation period’ and were characterized by a strong freshet in May which increased the water column stability. Winter cooling and scarcity of freshwater inputs from the Po River triggered the dense water formation and intrusion in the northern basin. Weak southeasterly winds and an increase in surface seawater temperatures contributed to maintain and reinforce the water column stability, and at the same time an intense diatom spring bloom created the conditions for accumulation of organic matter. The interplay of climatological forcings and biological processes caused temporal variations of dissolved organic carbon (DOC) and particulate organic carbon (POC) in the basin, with POC playing an important role in the aggregation process, as suggested by its increase relative to DOC before massive mucilage formation. We therefore suggest that high POC/total particulate nitrogen ratios in the suspended particulate organic fraction, a steep increase of POC/Chlorphyll a, and the decreased DOC/POC ratios represent ‘early warning’ signals of the main processes that lead to mucilage events in the Northern Adriatic Sea.     

The influence of organic matter and atmospheric deposition on the particulate trace metal concentration of northwest Atlantic surface seawater

Particulate trace metals (PTM), organic carbon (POC), and organic nitrogen (PON) were measured in a series of surface bucket samples collected between the New England coast of the United States and Bermuda. PTM concentrations were lower or equivalent to the lowest PTM concentrations reported in the literature. Examination of the relative variations in PTM with respect to particulate aluminum and carbon led to the conclusion that organic matter was the probable regulator of PTM abundance in open-ocean surface waters and was important in this respect for continental shelf and slope waters as well.Enrichment factors of trace metals relative to their crustal abundances were found to be similar in the atmosphere sampled in Bermuda and in Sargasso Sea surface water particulate matter. A simplistic vertical flux model was constructed which showed atmospheric input of trace metals to the Sargasso Sea to be of the same approximate magnitude as the rate of removal of PTM from the mixed layer by sinking in association with POC. Essentially all of the particulate Al, Fe, and Mn in the Sargasso Sea mixed layer was attributed to aeolian sources. The fate of other atmospherically derived trace metals in the Sargasso Sea mixed layer was suggested to be a function of their solubility in seawater.     

Sources and transport of dissolved and particulate organic carbon in the Mississippi River estuary and adjacent coastal waters of the northern Gulf of Mexico

Dissolved organic carbon (DOC), stable carbon isotopic (δ¹³C) compositions of DOC and particulate organic carbon (POC), and elemental C/N ratios of POC were measured for samples collected from the lower Mississippi and Atchafalaya rivers and adjacent coastal waters in the northern Gulf of Mexico during the low flow season in June 2000 and high flow season in April 2001. These isotopic and C/N results combined with DOC measurements were used to assess the sources and transport of terrestrial organic matter from the Mississippi and Atchafalaya rivers to the coastal region in the northern Gulf of Mexico. δ¹³C values of both POC (−23.8‰ to −26.8‰) and DOC (−25.0‰ to −29.0‰) carried by the two rivers were more depleted than the values measured for the samples collected in the offshore waters. Strong seasonal variations in δ¹³C distributions were observed for both POC and DOC in the surface waters of the region. Fresh water discharge and horizontal mixing played important roles in the distribution and transport of terrestrial POC and DOC offshore. Our results indicate that both POC and DOC exhibited non-conservative behavior during the mixing especially in the mid-salinity range. Based on a simple two end-member mixing model, the comparison of the measured DOC-δ¹³C with the calculated conservative isotopic mixing curve indicated that there was a significant in situ production of marine-derived DOC in the mid- to high-salinity waters consistent with our in situ chlorophyll-a measurements. Our DOC-δ¹³C data suggest that a removal of terrestrial DOC mainly occurred in the high-salinity (>25) waters during the mixing. Our study indicates that the mid- to high- (10–30) salinity range was the most dynamic zone for organic carbon transport and cycling in the Mississippi River estuary. Variability in isotopic and elemental compositions along with variability in DOC and POC concentrations suggest that autochthonous production, bacterial utilization, and photo-oxidation could all play important roles in regulating and removing terrestrial DOC in the northern Gulf of Mexico and further study of these individual processes is warranted.     

Resuspension-induced partitioning of organic carbon between solid and solution phases from a river–ocean transition

Laboratory experiments were conducted to evaluate the net exchange of organic carbon (OC) between sediments and overlying water during episodes of resuspension. Surface sediment samples collected from six locations within the Hudson River Estuary and the Inner New York Bight were resuspended in their respective bottom waters for periods ranging from 30 s to 2 h. After resuspension, dissolved organic carbon (DOC) concentration generally reached levels greater than that predicted by conservative mixing of pore water and bottom water, indicating net release of OC from the sediment particles. The amount of OC released during the 1-h extractions comprised ≤0.1% of the total sediment pool, but correlated positively (R²=0.65, P<0.052) with the amount of particulate organic carbon (POC) found in the high-density fraction of the sediment matrix. This suggests that the mineral-bound fraction of sedimentary OC was the major source for the excess DOC released into solution, and that across various sedimentary environments, only a small (but fairly constant) fraction of the total sedimentary POC may be poised for rapid transfer to the water column.     

长江干流有机碳的时空输运特征及三峡工程对其影响

2006-04,2008-04,2008-05沿长江干流采集表层水样,并于2006-05~2007-05在下游大通站进行每月2次、为期1 a的连续观测,测定溶解有机碳(DOC)、颗粒有机碳(POC)及总悬浮物(TSM)。结果表明:长江重庆以上江段DOC浓度较低,重庆至河口由于人为污染排放DOC表现出高值;干流POC与TSM显著正先关,POC%(TSM)随TSM含量增大呈负指数关系下降。大通站有机碳浓度及通量均表现出明显的季节性,2006-06~2007-05全年经大通站进入河口的DOC、POC通量分别为1.17×106tC和1.88×106tC,其中洪季(5~10月)输运的有机碳占到总有机碳的70%,组成以颗粒态为主。三峡水库135 m及156 m蓄水后,泥沙在库区的沉降作用显著影响长江POC的输运特征及入海通量;从目前观测结果看,三峡库区DOC浓度并没有表现出明显的升高趋势,可能与水库运行时间尚短有关。     

Seasonal Changes in Quality and Quantity of Food Available for Benthic Suspension-feeders in the Golfo Marconi (North-western Mediterranean)

Suspended particulate matter was collected, from the water layer at 10 cm above the sediments, over a period of 13 months in the Golfo Marconi (Ligurian Sea, NW Mediterranean). Measurements of seston concentration as well as the elemental (particulate organic carbon and nitrogen; POC and PON, respectively) and biochemical composition (lipids, proteins, carbohydrates, DNA) of particulate organic matter were carried out to assess quality and quantity of food potentially available to benthic suspension-feeders. Particulate organic matter showed wide qualitative and quantitative variations during the sampling year. Seston concentrations and POC did not reflect the quantity and quality of the food available to benthic suspension-feeders. The biopolymeric fraction of particulate matter (C-BPF, i.e. the sum of lipid, protein and carbohydrate carbon) was mostly composed of phytoplankton (which accounted for about 60% of C-BPF). The ratio of C-BPF to POC was utilized as a measure of the fraction which had the potential to be more readily available to consumers. Suspended organic matter showed higher values of the C-BPF:POC ratio during spring, and lower values in summer and autumn–winter. Quantitative estimates of the energy content of the suspended particulate matter were obtained from its biochemical composition. Bacterial dynamics were significantly related to changes in phytoplankton biomass. Bacteria accounted for a significant fraction of the biopolymeric carbon pool (annual average about 15%) and of the total particulate DNA (21·5%), thus enhancing the nutritional value of the particulate organic matter. The results achieved in this study indicate that the biochemical composition of the particulate matter provides additional information on the origin, quality and characteristics of the seston more readily available to benthic suspension-feeders.     

南沙渚碧礁生态系有机碳的分布及周日变化特征

1999 年 4 月对我国南沙群岛渚碧礁海水中溶解有机碳的分布及礁坪区颗粒有机碳 (POC) 和溶解有机碳 (DOC) 的周日变化特征进行了观测。结果表明,渚碧礁表层海水 DOC 变化范围为 1.43~3.62 mg/L,平均为 2.16 mg/L,含量分布大致表现为礁坪区>潟湖>礁外。潟湖 DOC 的垂直分布大致表现为表层高于底层,可能与表层浮游植物的光合作用有关。礁坪区 POC 及 DOC 都呈现显著的周日变化特征,POC 呈现夜晚高,白天低的特点,浮游植物的昼夜垂直移动可能是产生该现象的主要原因。DOC 的周日变化则主要受浮游动物昼夜垂直移动及细菌等生物活动的影响。     

Review and suggestions for estimating particulate organic carbon and dissolved organic carbon inventories in the ocean using remote sensing data

Dissolved organic carbon（DOC） and particulate organic carbon（POC） are basic variables for the ocean carbon cycle.Knowledge of the distribution and inventory of these variables is important for a better estimation and understanding of the global carbon cycle.Owing to its considerable advantages in spatial and temporal coverage,remote sensing data provide estimates of DOC and POC inventories,which are able to give a synthetic view for the distribution and transportation of carbon pools.To estimate organic carbon inventories using remote sensing involves integration of the surface concentration and vertical profile models,and the development of these models is critical to the accuracy of estimates.Hence,the distribution and control factors of DOC and POC in the ocean first are briefly summarized,and then studies of DOC and POC inventories and flux estimations are reviewed,most of which are based on field data and few of which consider the vertical distributions of POC or DOC.There is some research on the estimation of POC inventory by remote sensing,mainly in the open ocean,in which three kinds of vertical profile models have been proposed：the uniform,exponential decay,and Gauss models.However,research on remote-sensing estimation of the DOC inventory remains lacking.A synthetic review of approaches used to estimate the organic carbon inventories is offered and the future development of methods is discussed for such estimates using remote sensing data in coastal waters.     

Relations between free copper and salinity, dissolved and particulate organic carbon in the Oosterschelde and Westerschelde, Netherlands

In a previous investigation, relatively simple relations were found to estimate free Cu, and hence a good approximation of bio-available Cu, at two sites in estuarine waters of the Dutch Oosterschelde and Westerschelde. In the present study, these relations are validated for the remainder of the two sea arms. In the Westerschelde the relation between the concentration of a dissolved organic ligand (K=10¹³), DOC (dissolved organic carbon) and salinity is valid in a range of salinities at least from 10 up to 25 to 30. This ligand group is primarily riverine and partly estuarine. It is, as far as we know, the strongest ligand for Cu, and its concentration dominantly affects the free Cu ion concentrations, which are around 50 fM. At high salinities, dilution and mineralisation diminish the riverine member of the ligand group too much and the relation with salinity and DOC is no longer valid. In the Oosterschelde the relations between POC (particulate organic carbon) and particulate Cu and between POC and the ratio of particulate and dissolved Cu are valid for the western, central and eastern compartments. Since equilibrium was assumed to exist between dissolved and particulate Cu, free Cu can be calculated from POC and particulate Cu concentrations. Due to the large adsorption capacity of POC, the Oosterschelde is with respect to Cu a very well-buffered system with [Cu²⁺] of 20 fM.     

Distribution and transport of organic matter along a filament-eddy system in the Canaries – NW Africa coastal transition zone region

The distribution and transport of chlorophyll a (Chla), particulate (POC) and dissolved (DOC) organic carbon, and the respiratory ETS activity of the microplankton community were studied along a filament-eddy system located in the transition zone between the NW Africa upwelling and Canary Islands waters. Two independent filaments (F1 and F2) stemming from the coastal jet, between Cape Juby and Cape Bojador, merged about 100 km offshore, turning southward and onshore forced by the circulation of a recurrent oceanic cyclonic eddy. In general, the coastal upwelling waters presented higher Chla, but lower POC, DOC and ETS activity than filament waters. However, differences in organic carbon distribution and respiratory activity were observed among stations from the two filaments. The bio-chemical fields were strongly influenced by a complex sub-mesoscale hydrography resulting from the interaction of cyclonic and anticyclonic island eddies with the filaments. The combined F1 + F2 filament system transported 97.1 kg s⁻¹ of excess (non-refractory) total organic carbon (e-TOC), a value comparable to other published estimates from upwelling filaments in the NE Atlantic. About 90% of e-TOC was exported as DOC, since eddy re-circulation precluded the offshore transport of POC. Assuming that the calculated transport of e-TOC is representative of the annual average, the yearly offshore transport (3.1 x 10⁹ kg C) would represent about 25% of the upwelling primary production of the region of study.     

2016年夏季黄、渤海颗粒有机碳的分布特征及影响因素

本文根据2016年6-7月黄、渤海航次获得的调查数据,分析了黄、渤海海域颗粒有机碳（POC）的浓度变化、空间分布特征并结合盐度、叶绿素a、POC/PON、POC/Chl a平面分布特征和相关性分析,探讨了黄、渤海海域POC的来源和影响因素。结果表明:2016年夏季渤海海域POC平均浓度（500.2±226.5）μg/L,北黄海POC平均浓度（358.2±101.5）μg/L,南黄海POC平均浓度（321.0±158.1）μg/L,渤海海域POC浓度高于黄海,整个海域POC浓度表层高于底层。POC的平面分布特征为近岸高,外海低。调查海域表层POC/PON均值为8.89,POC/Chl a均值为182.52;中层POC/PON均值为8.87,POC/Chl a均值为179.56;底层POC/PON均值为9.41,POC/Chl a均值为178.80。黄海海域浒苔衰败对POC/PON与POC/Chl a影响较大。相关性分析结果表明渤海海域盐度、总悬浮物和叶绿素a与POC存在显著的相关性,是影响POC分布的主要控制因素。南黄海除表层POC浓度与盐度、总悬浮物和叶绿素a浓度有很好的相关性外,中层和底层POC浓度与盐度、总悬浮物和叶绿素a浓度不存在显著的相关性。渤海海域POC主要受陆源和浮游植物共同影响,浮游植物是POC的主要贡献者,而黄海海域POC受长江冲淡水、黄海暖流、苏北沿岸流、生物活动和底层沉积物等多种因素影响,其中苏北近岸和青岛外海,有机碎屑为POC的主要贡献者。     

渤海春季浮游细菌分布与生态环境因子的关系

研究了 1 999年 4～ 5月渤海水体浮游细菌分布与生态环境因子的关系。结果显示 ,渤海春季表层水体浮游细菌含量与水温和溶解性有机碳呈正相关 ,相关系数分别为 0 .6 0 1 (P<0 .0 1 )和0 .4 0 6 (P<0 .0 5 ) ,并与溶解氧含量呈负相关 ,相关系数为 0 .5 1 9(P<0 .0 1 ) ;底层水体浮游细菌含量与水温、溶解性有机碳 (dissolved organic carbon,DOC)、颗粒性有机碳 (particulate organic carbon,POC)和叶绿素 a含量呈正相关 ,相关系数分别为 0 .82 0 (P<0 .0 1 ) ,0 .6 6 1 (P<0 .0 1 ) ,0 .5 31 (P<0 .0 1 )和 0 .4 42 (P<0 .0 5 ) ,并与溶解氧含量呈负相关 ,相关系数为 0 .6 5 0 (P<0 .0 1 )。表明水温和DOC、POC含量是渤海水域浮游细菌含量的主要限制因子 ,而水体中的溶解氧 (dissolved oxygen,DO)含量与浮游细菌的含量有关     

Distribution and Seasonal Variability of Organic Matter in a Small Eutrophicated Salt Lake

Distribution and seasonal variability of dissolved organic carbon (DOC) and surface active substances (SAS) were studied along the depth profile (15 m) in a small eutrophicated and periodically anoxic sea lake (Rogoznica Lake, Eastern Adriatic coast) in 1996 and 1997. The range of DOC concentrations was characteristic for productive coastal marine ecosystems (60% of samples in the range of 1–2 mg l⁻¹and 40% between 2 and 3 mg l⁻¹). Distribution of SAS concentrations was uniform and shifted toward higher concentrations in comparison to other coastal areas in the Adriatic Sea. Eutrophication in the lake is generated by nutrient recycling under anaerobic conditions. Systematically higher concentrations of chlorophyll a, DOC and SAS were determined at the chemocline in the bottom layer (10–12 m) than in the upper water layer (0·5–2 m). Seasonal variability of organic matter was discussed regarding distributions of microphytoplankton (cells >20 μm) and photosynthetic pigments as well as oxygen and salinity changes along the depth profile. The dissolved oxygen saturation reaching up to 300% in the water layer between 8 m and 10 m depths in May and June 1996, was correlated with enhanced concentrations of phytoplankton biomass (reflected as chl a and b, fucoxanthin, peridinin, zeaxanthin) and increased concentrations of DOC and SAS.     

Distribution of marine lipid classes in salty Rogoznica Lake (Croatia)

Lipid classes in a small, eutrophicated salty lake (Rogoznica Lake, middle Adriatic), which is often subject to appeareance of anoxic conditions, were analyzed at the end of winter (March) and in summer (July) 2008. The results are supported with DOC, POC, phytoplankton, temperature, salinity and oxygen data. During both March and July massive, diatom blooms were recorded with maximum values at 5 m depth. Total lipids were found at high concentrations that were similar for the samplings in two months. Total particulate lipids dominated the pool, and showed large variations from 46.37 to 369.88 μg/l, with the highest concentration observed in the bottom anoxic layer in March. The variations for dissolved lipids were smaller and ranged from 44.82 to 124.35 μg/l. Opposite to lipids, DOC values increased 1.5 times between the two samplings, from the value of average 0.95 mg C/l in March to the average value of 1.44 mg/l in July. Conformingly with diatom blooms, POC was found in July at high concentrations (0.28–1.50 mg C/l), contributing to total organic carbon up to 46%. The distribution of organic carbon and lipids showed the tendency of accumulation toward deeper layers. The characterization of individual lipid classes revealed the dominance of phospholipids, indicating that the lipids in the lake mainly originated from the photosynthetically active phytoplankton community, which is sustained by high production of oxygen (oxygen saturation up to 200%). Low contribution of neutral lipids in the particulate fraction points to high availability of nutrients for present phytoplankton community. Lipid breakdown indices were found at significantly higher concentrations in March compared to July. Sea surface microlayer, the hydrophobic boundary, appeared to be generally lipid depleted in comparison to the sub-surface water. Qualitative analysis of sulfolipids revealed the potential of the lake for the occurrence of chemical interaction of sulfur with present organic matter.