Distribution Of Inorganic Nutrients Research Articles

Seasonal Variation and Vertical Distribution of Inorganic Nutrients in a Small Artificial Lake, Lake Bulan, in Mongolia

This is the first seasonal observation study on nutrient dynamics undertaken in a small freshwater lake with eutrophication in Mongolia. The vertical profile and seasonal fluctuation of nutrients are crucial to understanding the biogeochemical cycles in aquatic systems. In this study, field research was carried out at a small and shallow lake, Lake Bulan, in the lower Kharaa River basin. The area has been receiving increased nutrient loads from the water catchment area for the last 20 years. Water samples were collected seasonally from the lake from 2019–2022 and analyzed for nutrients, major cations, trace metals, and dissolved organic carbon. The average concentration of dissolved inorganic nitrogen (DIN) in the surface lake water had a wide seasonal variation from 0.26 ± 0.11 mg N/L in August to 1.44 ± 0.08 mg N/L in January. Seasonal differences were also observed in the vertical profiles. Concentrations were relatively similar at the various water depths in April and September at turnover time. Thermal stratification was observed when the lake was covered in ice, with the maximum concentrations being observed in the bottom layer in the months of January and August. The phosphate concentration showed a similar variation trend. These results indicate that both the summer and winter stratifications are important for regeneration of nutrients in the bottom layer, biochemical cycling, and mitigating impacts of global warming on small and shallow lakes in Mongolia.

Modeling investigation of the nutrients and phytoplankton dynamics in the Moroccan Atlantic coast: A case study of Agadir coast

Although the environmental status of the Moroccan Atlantic coastal waters has been researched in previous studies, there is still a lack of knowledge about its biogeochemical functioning. Especially for the Agadir coast where measurements are quite scarce, realistic ecological models can help identifying the key mechanisms driving fluctuations in such coastal areas. Here we implemented a three-dimensional (3D) coupled hydrodynamic-biogeochemical model in order investigate the time-space distribution of inorganic nutrients (NO₃, PO₄ and SiO₄), and their control on phytoplankton (diatoms, flagellates) biomass on the Agadir coast. Model performance was evaluated against satellite observations and climatology data. The model achieved satisfactory representation of the sea surface temperature, chlorophyll-a, and a reasonable agreement in the seasonal pattern of inorganic nutrients. Based on nutrient concentrations and their stoichiometric ratio; the study points to nitrate as the key factor controlling phytoplankton distribution (largely dominated by flagellates). Nitrate depletion occurs faster than phosphate and silicate, thus driving the area towards nitrogen limitation.

Hydraulic stopper effect as a regulator of inorganic nutrients distribution in Mar Chiquita coastal lagoon (Argentina)

Estuaries are transitional systems that link both land and oceans, with particular dynamics regulated by their own characteristics. The main aim of the present study was the assessment of the effects generated by a strong dry period on the distribution of inorganic nutrients and biological production within Mar Chiquita coastal lagoon, comparing this information with that from periods of precipitation regularly conducted. For this study we selected Mar Chiquita coastal lagoon and analyzed a 20-year data series for concentration and distribution of physical and chemical parameters, in particular salinity, inorganic nutrients (i.e. dissolved inorganic nitrogen, phosphate, silicate) and photosynthetical pigments (i.e. chlorophyll a). We also evaluated the association between these parameters and climate conditions within the region, and found a strong relationship and very quick response to changes. As a result, we report, for the first time in the region, rainfall as a main driver of biogeochemical processes within the estuarine system. The obtained results allowed us to confirm the clear transference processes between land and oceanic systems, and the role of climate as a driver of the corresponding transference processes.

In situ analyses of inorganic nutrient distribution in sweetcorn and maize kernels using synchrotron-based X-ray fluorescence microscopy.

Understanding the spatial distribution of inorganic nutrients within edible parts of plant products helps biofortification efforts to identify and focus on specific uptake pathways and storage mechanisms. Kernels of sweetcorn (Zea mays) variety 'High zeaxanthin 103146' and maize inbred line 'Thai Floury 2' were harvested at two different maturity stages, and the distributions of K, P, S, Ca, Zn, Fe and Mn were examined in situ using synchrotron-based X-ray fluorescence microscopy. The distribution of inorganic nutrients was largely similar between maize and sweetcorn, but differed markedly depending upon the maturity stage after further embryonic development. The micronutrients Zn, Fe and Mn accumulated primarily in the scutellum of the embryo during early kernel development, while trace amounts of these were found in the aleurone layer at the mature stage. Although P accumulated in the scutellum, there was no direct relationship between the concentrations of P and those of the micronutrients, compared with the linear trend between Zn and Fe concentrations. This study highlights the important role of the embryo as a micronutrient reserve for sweetcorn and maize kernels, and the need to understand how biofortification efforts can further increase the inorganic nutrient concentration of the embryo for human consumption.

Dinámica del plancton en la primera milla náutica frente a la provincia de El Oro, Ecuador

Plankton dynamics in the first nautical mile of El Oro province, Ecuador. El Oro includes different coastal and estuarine systems and the important Gulf of Guayaquil. These areas provide different ecosystem services, but with the increase of population and of the varied economic activities, the barely known local natural resources may be negatively impacted. Thus this research aimed to study plankton dynamics, productivity and ecological balance for the area during the dry season of 2012. For this, we established 17 stations and studied the monthly variation and spatial distribution of inorganic nutrients, temperature, dissolved oxygen, salinity, photic zone, plankton and fish larvae abundance and composition with standard methods, while spatial and temporal patterns where identified using cluster and multidimentional scaling analyses. Obtained results of biotic and abiotic parameters defined a pattern characteristic of productive estuarine zones as well as the existence of three specific areas associated with the natural and anthropic conditions of the area, such as: a) inner part of the Jambelí Archipelago and in front of Puná island influenced by productive activities and the hydrography of the area; B) an area, formed by the stations located in the outer estuary where the oceanic influence is evident and c) the Jambelí channel, characterized by mixing processes resulting from tides flow. This was supported by the presence of oceanic, neritic and estuarine phytoplankton; copepods with uniform distribution in the study area, and dominance of Engraulidae fish larvae, representative of this type of aquatic ecosystem. Temporally, rainfall records in May exceeded normal values, which would have influenced the high concentrations of nutrients, decrease of salinity and of the photic zone registered during this month. However, the availability of nutrients throughout the study period, allowed to maintain the composition and abundance of phytoplankton, with changes in representative species, recorded periods of greater (June to August) and lower (October to December) zooplankton abundance, could be the result of specific population patterns of present species, and the influence of the tide and the flows of the contributing river basin. A similar behavior was recorded for ichthioplankton, as a result of Anchoa macrolepidota concentrations, species, characteristics of this type of ecosystem. These patterns of spatio-temporal distribution, allowed the development of multiple abiotic and biotic interactions that determine different strategies to maintain the productivity of the area. We recommend new studies during the rainy season in Ecuador. Rev. Biol. Trop. 66(2): 836-847. Epub 2018 June 01.

Patterns of distribution of inorganic nutrients in Red Sea and their implications to primary production

This paper presents data on inorganic nutrients obtained in several transects within Saudi Arabian waters of the Red Sea in 2012–2015. Increase in their concentrations from north to south is not monotonously linear but is punctuated by regions of high concentrations alternating with those of low concentrations, regardless of the type of nutrient (N, P or Si), season and location. Such a type of distribution could be only explained in terms of eddy circulations within the Red Sea basin. The enrichment with nutrients of the boundary currents of the eddies could be explained partly by entrainment of Gulf of Aden Intermediate Water in the eddies and the mixing of the latter with the underlying Red Sea Deep Water, and partly by a higher biological productivity in the peripheries of the eddies. These results have two major implications for our understanding of biogeochemical cycles in the Red Sea. The first is that the eddy-associated injection of nutrients into the euphotic zone could cause higher levels of production over a substantial spread of the Red Sea. The second is that the anticyclonic eddies may function as traps of nutrients and in that event, their peripheries and centers may function as independent mesocosms.

Physical and bacterial controls on inorganic nutrients and dissolved organic carbon during a sea ice growth and decay experiment

We investigated how physical incorporation, brine dynamics and bacterial activity regulate the distribution of inorganic nutrients and dissolved organic carbon (DOC) in artificial sea ice during a 19-day experiment that included periods of both ice growth and decay. The experiment was performed using two series of mesocosms: the first consisted of seawater and the second consisted of seawater enriched with humic-rich river water. We grew ice by freezing the water at an air temperature of −14°C for 14days after which ice decay was induced by increasing the air temperature to −1°C. Using the ice temperatures and bulk ice salinities, we derived the brine volume fractions, brine salinities and Rayleigh numbers. The temporal evolution of these physical parameters indicates that there was two main stages in the brine dynamics: bottom convection during ice growth, and brine stratification during ice decay. The major findings are: (1) the incorporation of dissolved compounds (nitrate, nitrite, ammonium, phosphate, silicate, and DOC) into the sea ice was not conservative (relative to salinity) during ice growth. Brine convection clearly influenced the incorporation of the dissolved compounds, since the non-conservative behavior of the dissolved compounds was particularly pronounced in the absence of brine convection. (2) Bacterial activity further regulated nutrient availability in the ice: ammonium and nitrite accumulated as a result of remineralization processes, although bacterial production was too low to induce major changes in DOC concentrations. (3) Different forms of DOC have different properties and hence incorporation efficiencies. In particular, the terrestrially-derived DOC from the river water was less efficiently incorporated into sea ice than the DOC in the seawater. Therefore the main factors regulating the distribution of the dissolved compounds within sea ice are clearly a complex interaction of brine dynamics, biological activity and in the case of dissolved organic matter, the physico-chemical properties of the dissolved constituents themselves.

Impact of water mass mixing on the biogeochemistry and microbiology of the Northeast Atlantic Deep Water

The extent to which water mass mixing contributes to the biological activity of the dark ocean is essentially unknown. Using a multiparameter water mass analysis, we examined the impact of water mass mixing on the nutrient distribution and microbial activity of the Northeast Atlantic Deep Water (NEADW) along an 8000 km long transect extending from 62°N to 5°S. Mixing of four water types (WT) and basin scale mineralization from the site where the WT where defined to the study area explained up to 95% of the variability in the distribution of inorganic nutrients and apparent oxygen utilization. Mixing-corrected average O2:N:P mineralization ratios of 127(±11):13.0(±0.7):1 in the core of the NEADW suggested preferential utilization of phosphorus compounds while dissolved organic carbon mineralization contributed a maximum of 20% to the oxygen demand of the NEADW. In conjunction with the calculated average mineralization ratios, our results indicate a major contribution of particulate organic matter to the biological activity in the NEADW. The variability in prokaryotic abundance, high nucleic acid containing cells, and prokaryotic heterotrophic production in the NEADW was explained by large scale (64-79%) and local mineralization processes (21-36%), consistent with the idea that deep-water prokaryotic communities are controlled by substrate supply. Overall, our results suggest a major impact of mixing on the distribution of inorganic nutrients and a weaker influence on the dissolved organic matter pool supporting prokaryotic activity in the NEADW.

Distribution of Dissolved Organic Carbon (DOC) in the Southwestern East Sea in Summer

In the summer of 2008 (August 4-14), vertical and horizontal distributions of inorganic nutrients and dissolved organic carbon (DOC) were measured in the southwestern East Sea. Concentrations of DOC were determined for the first time in the southwestern East Sea using the high-temperature combustion oxidation (HTCO) method, and results were compared with those measured by another laboratory. Concentrations of DOC ranged from 58 to 104 <TEX>${\mu}M$</TEX> in the upper 200 m, showing a typical decreasing pattern with depth. Generally, concentrations of DOC were relatively lower, with higher nutrient concentrations, in the upper layer of the coastal upwelling zone. Concentrations of DOC ranged from 54 to 64 <TEX>${\mu}M$</TEX> in the deep Ulleung Basin (200-1500 m), and were higher than those in the Pacific and Atlantic oceans. In association with rapid vertical ventilation of the euphotic, this difference indicates a larger accumulation of semi-labile DOC in the deep East Sea than in the major oceans. A correlation between apparent oxygen utilization (AOU) and DOC in the deep ocean of the East Sea revealed that only a small portion (<10%) of the sinking DOC, relative to the sinking particulate organic carbon (POC), contributes to microbial degradation. Our results present an important data set of DOC in the East Sea, which plays a critical role in carbon cycle modeling and sequestration.

Cross-frontal distribution of inorganic nutrients and chlorophyll-a on the Patagonian Continental Shelf of Argentina during summer and fall

Datos oceanograficos recolectados durante 2001-2003 en la Plataforma Continental Patagonica Argentina fueron analizados para estudiar las principales caracteristicas quimicas en esta gran plataforma. Se presenta la variacion de los nutrientes inorganicos y de la clorofila-a a una distancia de 40 a 60 km de la costa. El nitrato es el nutriente limitante en la region y esta negativamente correlacionado con la clorofila-a. Todas las variables presentan variaciones localizadas en verano, las cuales pueden ser relacionadas con los frentes de marea a traves de la comparacion de nuestros datos con el parametro critico de estabilidad de Simpson (50 J m-3). En otono, la concentracion de nutrientes en la plataforma continental fue mas uniforme y generalmente mayor que en verano debido a la disrupcion de dichos frentes.

Temporal variations of surface phytoplankton, nutrients and chlorophyll a in the Dardanelles (Turkish Straits System): a coastal station sample in weekly time intervals

In this study, weekly distributions of inorganic nutrients and phytoplankton cell volumes were investigated in relation to the hydrology of the Dardanelles. The data were collected between March 2001 and March 2002. NO^{-}_{2}+NO^{-}_{3}, PO_{4}^{-3}, and SiO_4 concentrations ranged between 0.050-6.887 µM, 0.051-1.152 µM, and 0.64-10.74 µM, respectively. During the study, the highest nutrient values were measured between late fall and mid-winter. Inorganic N:P and Si:P ratios in the surface water were lower due to high PO_{4}^{-3} concentrations. The chlorophyll a concentrations ranged from 0.03 to 8.67 µg L^{-1}. Phytoplankton cell density and cell volume ranged from 1.54E + 05 to 6.46E + 07 cell L^{-1} (mean 7.65E + 06; SD 1.44E + 07 cell L^{-1}) and from 2.51E + 09 to 8.66E + 10 µm^{-3} L^{-1} (mean 1.98E + 10; SD 1.86E + 10 µm^{-3} L^{-1}) between less productive and high productive periods. During the study period, 8-10 species controlled the phytoplankton community structure in the coastal zone of the Dardanelles. Others did not contribute to the phytoplankton population and they only can be considered as accessory species, which do not cause significant fluctuations in the phytoplankton production. Relationships between chlorophyll a, cell density, and cell volume of phytoplankton revealed that chlorophyll a is rather controlled by the cell density than by the cell volume. Furthermore, the physicochemical variables, such as nutrients and chlorophyll a and phytoplankton cell density and cell volume, are affected by the counter flows in the Dardanelles. Phytoplankton population was more limited by nitrogen than by phosphate due to extra phosphate inputs coming from various sources, such as domestic waste waters as well as the vertical mixing between upper and lower layers.

Nutrient biogeochemistry in an upwelling-influenced estuary of the Pacific northwest (Tillamook Bay, Oregon, USA)

Tillamook Bay, Oregon, is a drowned river estuary that receives freshwater input from 5 rivers and exchanges ocean water through a single channel. Similar to other western United States estuaries, the bay exhibits a strong seasonal change in river discharge in which there is a pronounced winter maximum and summer minimum in precipitation and runoff. The behavior of major inorganic nutrients (phosphorus, nitrogen, and silica) within the watershed is examined over seasonal cycles and under a range of river discharge conditions for October 1997–December 1999. Monthly and seasonal sampling stations include transects extending from the mouth of each river to the mouth of the estuary as well as 6–10 sites upstream along each of the 5 major rivers. Few studies have examined nutrient cycling in Pacific Northwest estuaries. This study evaluates the distributions of inorganic nutrients to understand the net processes occurring within this estuary. Based upon this approach, we hypothesize that nutrient behavior in the Tillamook Bay estuary can be explained by two dominant factors: freshwater flushing time and biological uptake and regeneration. Superimposed on these two processes is seasonal variability in nutrient concentrations of coastal waters via upwelling. Freshwater flushing time determines the amount of time for the uptake of nutrients by phytoplankton, for exchange with suspended particles, and for interaction with the sediments. Seasonal coastal upwelling controls the timing and extent of oceanic delivery of nutrients to the estuary. We suggest that benthic regeneration of nutrients is also an important process within the estuary occurring seasonally according to the flushing characteristics of the estuary. Silicic acid, nitrate, and NH4 + supply to the bay appears to be dominated by riverine input. PO4 −3 supply is dominated by river input during periods of high river flow (winter months) with oceanic input via upwelling and tidal exchange important during other times (spring, summer, and fall months). Departures from conservative mixing indicate that internal estuarine sources of dissolved inorganic phosphorus and nitrogen are also significant over an annual cycle.

Monitoring of eutrophication and nutrient limitation in the Izmir Bay (Turkey) before and after Wastewater Treatment Plant

The distribution of inorganic nutrients and phytoplankton chlorophyll- a was investigated and N/P ratios were determined in Izmir Bay during 1996–2001. The average concentrations showed ranges of 0.01–0.19 and 0.01–10 μM for phosphate-phosphorus; 0.11–1.8 and 0.13–27 μM for (nitrate+nitrite)-nitrogen, 0.30–4.1 and 0.50–39 μM for silicate and 0.02–4.3 and 0.10–26 μg l −1 for chlorophyll- a in the outer and middle-inner bays, respectively. The results are compared with the values obtained from the relatively unpolluted waters of the Aegean Sea. The N/P ratio is significantly lower than the assimilatory optimal (N/P=15:1) in conformity with Redfield's ratio N/P=16:1. Nitrogen is the limiting element in the Izmir Bay. Phosphate, which originates from detergents, is an important source for eutrophication in the bay, especially in the inner bay. In early 2000, a Wastewater Treatment Plant (WTP) began to treat domestic and industrial wastes. This plant treats the wastes about 60% capacity between 2000 and 2001. The sampling periods cover before and after treatment plant. Although the capacity of wastewater plant is sufficient for removal of nitrogen from the wastes, it is inadequate for removal of phosphate. This is also in accordance with the decreasing N/P ratios observed during 2000–2001 (after WTP) in the middle-inner bays.

Distributions of inorganic nutrients in the bohai sea of china

To study the contents and distribution of inorganic nutrients in the Bohai Sea of China, two cruise surveys were undertaken in August (summer) 2000 and January (winter) 2001, respectively. A total of 595 water samples were collected from 91 stations and five nutrients, i.e., nitrate, nitrite, ammonia, phosphate and silicate, were analyzed for each sample. The results show that the average concentration of dissolved inorganic nitrogen (DIN) in the Bohai Sea in winter (6.529 μmol L−1) is significantly higher than that in summer (3.717 μmol L−1). The phosphorus concentration in winter (0.660 μmol L−1) is also significantly higher than that in summer (0.329 μmol L−1). Mean silicate concentration in winter (7.858 μmol L−1) is, however, not significantly different from that in summer (7.200 μmol L−1). Nutrients also vary considerably in different areas in Bohai Sea. DIN concentration in the Laizhou Bay (4.444 μmol L−1), for example, is significantly higher than those in the Bohai Bay (2.270 μmol L−1) and Bohai Strait (2.431 μmol L−1), which is caused by the discharge of large amounts of nitrogen into Laizhou Bay via Yellow River. The nutrients show different vertical distribution patterns. In summer, nutrients in bottom layer are generally richer than those in surface and middle layers. In winter, however, nutrients are not significantly different in different layers. Compared with historic data, DIN contents have increased continually since the early 1980 s. Based on atomic ratios of different nutrients, nitrogen is still the limiting factor for algal growth in the Bohai Sea.

생물검정실험에 의한 섬진강 하구역 식물플랑크톤 성장의 제한영양염 평가

1999년 3월부터 2001년 10월까지 섬진강 하구역에서 영양염의 DIN/DIP 비와 생물검정실험을 이용하여 식물플랑크톤 성장을 제한하는 영양염을 파악<TEX>$\cdot$</TEX>비교하였다. 조사기간 동안 용존무기질소와 인산 인의 비는 평균 14.7<TEX>$\~$</TEX>681.1의 범위로, 조사시작 지점인 난초도 주변 해역을 제외한 25 psu 이하 염분역과 엽록소 a의 농도가 매우 높았던 구간에서는 계절에 관계없이 N/P 비가 16 이상으로 매우 높아 식물플랑크톤의 성장을 조절하는 제한 영양염은 인산 인인 것으로 판단된다. 반면, 약 25 psu 이상의 염분역인 난초도 주변 해역은 광양만으로부터 공급되는 인산 인의 영향으로 인해 DIN/DIP 비는 16 이하로 낮아, 용존무기질소가 식물플랑크톤의 성장을 제한하는 것으로 판단된다. 섬진강 하구역에서의 DIN/DIP 비의 변화양상은 인산 인의 공급양상, 즉 육상으로부터 의 낮은 공급 및 광양만으로 부터의 높은 공급 그리고 시<TEX>$\cdot$</TEX>공간적인 식물플랑크톤의 성장에 의해 주로 영향을 받는 것으로 판단된다. Skeletonema costatum 및 nalassiosira rotula와 현장 식물플랑크톤을 이용한 생물검정실험 결과는 인산 인이 첨가된 배지에서 성장이 상대적으로 높게 나타나, 섬진강 하구역에서 식물플랑크톤을 조절하는 제한영양염은 인산 인인 것으로 검증되었다. S. costatum은 타종에 비해 염분 적응이 빠르고, 인산 인에 대해 반응이 크게 나타나, 섬진강 하구역에서 가을철에 우점율 <TEX>$90\%$</TEX> 이상의 costatum bloom이 발생되는 주요 원인이었을 것으로 추측된다 현장식물플랑크톤을 이용한 생물검정실험에서는 배양시작 초기에 미량금속 첨가계에서 비교적 빠른 성장을 보였으며, 20일 이후에 는 인산 인 첨가계에서 월등한 성장을 보였다. 이는 주변 해수의 영양염 분석과 식물플랑크톤 현존량만으로는 판단하기 어려운, 영양염 이외의 미량금속 그리고 비타민 등의 성장제한 요인에 대한 정보를 얻을 수 있다는 것을 시사해 준다. limiting nutrients for phytoplankton were determined by dissored inorganic nitrogen/phosphorous (DIN/DIP) in situ and algal bioassay experiment in the Seomjin River estuary during a study period from March 1999 to October 2001. DIN/DIP ranged from 14.7 to 681.1 during the study period. DIN/DIP was over 16 at the upper and middle estuarine region where salinity was lower than 25 psu and chlorophyll a concentration was high, probably indicating P-limitation in this region while the ratio was less than 16 at the high saline (> 25 psu) region, reflecting the supply of DIP from Gwangyang Bay and thereby indicating N-limitation at the lower estuarine region. These results suggested that the spatial distribution of DIN/DIP in the study region was controlled by the high supply of phosphate from Gwangyang Bay, the low input from Seomjin River and the active uptake by phytoplankton within the estuarine system. The bioassay experiments using Skeletonema costatum, Thalaasiosira rotula and in situ phytoplankton assemblage displayed relatively higher growth of phytoplankton in the P-added culture media, indicating P-limitation. This result was well consistent with the spatial distribution of inorganic nutrients. S. costatum showed a rapid adaptation to the low salinity compared to other phytoplankton species. This phenomenon seemed to account for the strong (> <TEX>$90\%$</TEX> in total cell number) S. costatum bloom in autumn in this estuary. Moreover, although phytoplankton growth rate was higher in the P-added culture media at the end of culture experiment of in situ phytoplankton, the fast growth in the trace metal-added media at the beginning of the experiment suggested a possibility of limitation by other micro-nutrients such as trace metal and vitamin etc.

Biogeochemical Transformations of Inorganic Nutrients in the Mixing Zone between the Danube River and the North-western Black Sea

Biogeochemical transformations of inorganic nutrients were studied in the mixing zone between the Danube and the north-western Black Sea in July 1995 and in the winter–spring transition period of 1997. Inorganic nutrients, phytoplankton carbon-biomass and biogenic silica were analysed at 10 different locations across the entire salinity gradient in combination with parallel measurements of phytoplankton carbon and inorganic nutrient uptake rates, making use of different tracers ( 14C, 15N, 32Si and 32P). The quantitative and qualitative nutrient signature of the Danube outflow into the Black Sea varied seasonally, depending on upwards processes of consumption, remineralization, transformation and elimination. Danube DSi (dissolved silicon) and DIN concentrations decreased from winter to summer, although PO 4 remained constant for the whole season. The winter distribution of inorganic nutrients along the salinity gradient was conservative, and phytoplankton biomasses and activities were very low due to strong light limitation. However, significant phytoplankton carbon and inorganic nutrient uptake rates were measured in early spring and during summer at salinities depending on the hydrodynamics of the Danube and Black Sea mixing. Between a salinity of 0 and 10 (using the Practical Salinity Scale), phytoplankton (diatom) growth and mortality processes have been evidenced, which at first strongly lower the inputs of inorganic nutrients to the coastal zone, but also affect the balance among which nutrients are spread over the shelf. These modifications have important consequences for phytoplankton dynamics and species dominance at salinities above 10; diatom growth being apparently P-limited during spring and N-limited during summer. Surprisingly, no DSi limitation of diatom growth has been shown during this study, and a background DSi level of 2–3 μM was measured in the entire shelf area. Causes for such an observation appear to be (1) an efficient biotic and abiotic removal of PO 4 during mixing, (2) an important denitrification in the upper estuary and (3) an important recycling of Si, both in the water column and at the sediment–water interface. The negative long-term effect of the quantitative and qualitative (deficiency in DSi) changes of the Danube inputs on the functioning of the Black Sea pelagic and benthic food-webs have been clearly reported in the literature and cannot be questioned by the present data set. Rather, this study simply highlights the complexity of the mechanisms by which propagation of the Danube eutrophication beyond the river plume possibly occurs.

Temporal development of the distribution of inorganic nutrients and the oxygen situation in the Pomeranian Bight During the flood event (summary)

Temporal development of the distribution of inorganic nutrients and the oxygen situation in the Pomeranian Bight During the flood event (summary)

Regional relationships between biological and hydrographical properties in the Weddell Gyre in late austral winter 1989

The surface layer properties of the Weddell Gyre were measured during a cruise of the R/V “Polarstern” in September and October 1989 on a transect between the tip of the Antarctic Peninsula (northwestern Weddell Sea) and Cape Norvegia (southeastern Weddell Sea). Sea ice cover, hydrography, and the distribution of inorganic nutrients and dissolved oxygen represented late winter conditions: a quasi-homogeneous Winter Water layer with near-freezing temperatures, high salinities and high levels of nitrate, and undersaturated with dissolved oxygen. The area investigated could be divided into three regions based on the physical, chemical and biological patterns: the western and eastern flanks and the gyre interior. In all areas, autotrophic biomass in sea ice was high in comparison with the underlying water column. Within the sea ice mainly diatoms and dinoflagellates were present, but the dominant autotrophic organisms in the water column were nanoflagellates. Ammonium values were relatively high in the Winter Water layer in the central region, indicating heterotrophic activity. Mesozooplankton was dominated by copepods, which can in turn be divided into two groups: overwintering, inactive Calanus acutus were found in the Warm Deep Water, whereas actively feeding Calanus propinquus were most abundant in the upper 120 m of the water column under the sea ice in the central region. These spatial differences may influence development of the respective summer pelagic communities.

Relationship between substrate concentration and oxidation of ammonium and methane in a stratified water column

Distributions and oxidation rates of methane and ammonium were investigated during two cruises in Saanich Inlet, British Columbia in late summer. Distributions of inorganic nutrients were related to oxygen distribution, exhibiting large gradients associated with the oxic-anoxic interface. The depth distributions of oxidation rates were also defined by the oxic-anoxic interface: ammonium oxidation occurred at variable rates (up to 120 nM day −1) between the photic zone and the oxic-anoxic interface. Methane oxidation occurred throughout the oxic layer and increased near the interface. The possibility of interactions such as inhibition and competition between the two substrates, methane and ammonium, were investigated in kinetic experiments. Ammonium oxidation rate was independent of both ammonium and methane concentrations. Methane oxidation rates were linearly related to methane concentration, both in manipulation experiments, and in relation to ambient methane concentrations. There was no evidence of interaction between methane and ammonium as alternative substrates for methanotrophic and ammonium oxidizing populations, which were both present in the environment. In September, we observed a bolus-type mixing event, which introduced oxygenated deep water into the inlet beneath a wedge of anoxic, methane-rich water. This kind of event is probably important in determining the rate of methane loss, due to increased microbial oxidation at the boundaries of the anoxic wedge.

Interpretation of the seasonal variations of nutrients in a mediterranean lagoon: �tang de Thau

A network of 63 stations was used on four occasions (June 1986, October 1986, February 1987, and May 1987) to study the spatio-temporal distribution of inorganic nutrients in Thau Lagoon (‘l'etang de Thau’), which covers 7500 hectares on the French Mediterranean coast. Three environmental factors, revealed by multiple regression models, govern the distributions observed. Allochthonous inputs from the watershed enrich the environment with nitrogen and phosphorus compounds in the winter and autumn. Internal sources are essentially localized in the shellfish breeding zone of the lagoon. In the summer, shellfish excretions and the rapid remineralization of organic deposits produce ammonium ions. Uptake by phytoplankton has a much larger impact on the seasonal variation of inorganic nitrogen than on that of phosphorus; the latter is present in excess in the lagoon waters. Thus, nitrogen appears to be the primary limiting nutrient for the development of the chorophyllous biomass.