scholarly journals Biomarker evidence for nitrogen-fixing cyanobacterial blooms in a brackish surface layer in the Nile River plume during sapropel deposition

Geology ◽  
2019 ◽  
Vol 47 (11) ◽  
pp. 1088-1092 ◽  
Author(s):  
Nicole J. Bale ◽  
Rick Hennekam ◽  
Ellen C. Hopmans ◽  
Denise Dorhout ◽  
Gert-Jan Reichart ◽  
...  
Keyword(s):  
Surface Layer ◽  
Nile Delta ◽  
Eastern Mediterranean ◽  
Cyanobacterial Blooms ◽  
Nile River ◽  
Head Group ◽  
Free Living ◽  
Heterocystous Cyanobacteria ◽  
Primary Core ◽  
Sediment Layers

Abstract Sapropels are organic-rich sediment layers deposited in the eastern Mediterranean Sea during precession minima, resulting from an increase in export productivity and/or preservation. Increased freshwater delivery from the African continent resulted in stratification, causing deepwater anoxia, while nutrient input stimulated productivity, presumably at the deep chlorophyll maximum. Previous studies have suggested that during sapropel deposition, nitrogen fixation was widespread in the highly stratified surface waters, and that cyanobacteria symbiotic with diatoms (diatom-diazotroph associations, DDAs) were responsible. Here we analyzed sapropel S5 sediments for heterocyst glycolipids (HGs) from three locations in the eastern Mediterranean. HG biomarkers can differentiate between those heterocystous cyanobacteria that are free living (found predominately in freshwater or brackish environments) and those that are from DDAs (found in marine settings). In our primary core, from a location which would have been influenced by the Nile River outflow, we detected a HG with a pentose (C5) head group specific for DDAs. However, HGs with a hexose (C6) head group, specific to free-living cyanobacteria, were present in substantially (up to 60×) higher concentration. These data suggest that at our study location, free-living cyanobacteria were the dominant diazotrophs, rather than DDAs. The C6 HGs increased substantially at the onset of sapropel S5 deposition, suggesting that substantial seasonal cyanobacterial blooms were associated with a brackish surface layer flowing from the Nile into the eastern Mediterranean. Two additional S5 sapropels were analyzed, one also from the Nile delta region and one from the region between Libya and southwestern Crete. Overall, comparison of the HG distribution in the three S5 sapropels provides evidence that all three locations were initially influenced by surface salinities that were sufficiently low to support free-living heterocystous cyanobacteria. While free-living heterocystous cyanobacteria continued to outnumber DDAs during sapropel deposition at the two Nile-influenced sites, DDAs, indicators of persistent marine salinities, were the dominant diazotrophs in the upper part of the sapropel at the more westerly site. These results indicate that N2 fixation by free-living cyanobacteria offers an important additional mechanism to stimulate productivity in regions with strong river discharge during sapropel deposition.

scholarly journals Hydrology and circulation in the North Aegean (eastern Mediterranean) throughout 1997 and 1998

2002 ◽  
Vol 3 (1) ◽  
pp. 5 ◽  
Author(s):  
V. ZERVAKIS ◽  
D. GEORGOPOULOS
Keyword(s):  
Surface Layer ◽  
Black Sea ◽  
Sea Water ◽  
Saline Water ◽  
Eastern Mediterranean ◽  
Late Summer ◽  
Cyclonic Circulation ◽  
The Black Sea ◽  
The North ◽  
North Aegean

The combination of two research projects offered us the opportunity to perform a comprehensive study of the seasonal evolution of the hydrological structure and the circulation of the North Aegean Sea, at the northern extremes of the eastern Mediterranean. The combination of brackish water inflow from the Dardanelles and the sea-bottom relief dictate the significant differences between the North and South Aegean water columns. The relatively warm and highly saline South Aegean waters enter the North Aegean through the dominant cyclonic circulation of the basin. In the North Aegean, three layers of distinct water masses of very different properties are observed: The 20-50 m thick surface layer is occupied mainly by Black Sea Water, modified on its way through the Bosphorus, the Sea of Marmara and the Dardanelles. Below the surface layer there is warm and highly saline water originating in the South Aegean and the Levantine, extending down to 350-400 m depth. Below this layer, the deeper-than-400 m basins of the North Aegean contain locally formed, very dense water with different θ /S characteristics at each subbasin. The circulation is characterised by a series of permanent, semi-permanent and transient mesoscale features, overlaid on the general slow cyclonic circulation of the Aegean. The mesoscale activity, while not necessarily important in enhancing isopycnal mixing in the region, in combination with the very high stratification of the upper layers, however, increases the residence time of the water of the upper layers in the general area of the North Aegean. As a result, water having out-flowed from the Black Sea in the winter, forms a separate distinct layer in the region in spring (lying between “younger” BSW and the Levantine origin water), and is still traceable in the water column in late summer.

scholarly journals Three Decades Monitoring of Shoreline Change Pattern of Damietta Promontory, Nile Delta, Egypt

2020 ◽  
Vol 8 (2) ◽  
pp. 1
Author(s):  
Ayman A. El-Gamal ◽  
Sherif H. Balbaa ◽  
Mohamed A. Rashed ◽  
Ahmed S. Mansour
Keyword(s):  
Grain Size ◽  
Coastal Area ◽  
Nile Delta ◽  
Shoreline Change ◽  
Sediment Flux ◽  
Heavy Minerals ◽  
Nile River ◽  
Physical Parameters ◽  
Change Pattern ◽  
The Impact

The Nile Delta is located on the Egyptian Mediterranean coast extending along nearly 240 km from the east of Alexandria to Port Said. The coastal area of the Nile Delta Promontories has been suffering extensive erosion problem. This was achieved after the construction of many water regulation structures in Nile River as dams and barrages, particularly the Aswan High Dam. It has nearly stopped the sediment flux carried by the Nile River to the Delta. This process has caused the Mediterranean Sea to reshape the Nile Delta coastal area. In order to cease these problems several engineering hard structures have been built. These structures avoided in ceasing the problem in the site of construction but shifted the erosion problem to the adjacent sites. This study aimed to analyze the shoreline change pattern on the term of three decades during the period between 1985 to 2015 at the coastal strip of Damietta Promontory and the impact of these protective structures on the coastal area. This was accomplished by the automated delineation of the successive shorelines covering this period using remote sensing imagery. The shorelines were extracted using the MNDWI index. The extracted shorelines were manipulated through the Digital Shoreline Analysis System (DSAS) software. The shoreline change rates were compared with sediments grain size for the past thirty years, heavy minerals content and radioactivity of recent marine sediment samples collected from different locations of marine profiles over the study area. The study revealed that Damietta Promontory has suffered from erosion during the study period reached its maximum shoreline retreat at the eastern side, nearly – 43 m/y. The total cumulative shoreline regression during the study period at this area was 1311m. The relation between the shoreline change process (erosion or accretion) and the physical parameters of coastal sediment showed that; as erosion increases, the heavy minerals content and radioactivity increases, while the mean grain size decreases and vice versa.

scholarly journals THE NILE LITTORAL CELL AND MAN'S IMPACT ON THE COASTAL ZONE OF THE SOUTHEASTERN MEDITERRANEAN

1984 ◽  
Vol 1 (19) ◽  
pp. 109 ◽  
Author(s):  
Douglas L. Inman ◽  
Scott A. Jenkins
Keyword(s):  
Coastal Waters ◽  
Coastal Erosion ◽  
Large Scale ◽  
River Flow ◽  
Nile Delta ◽  
Mediterranean Coast ◽  
Nile River ◽  
Sediment Source ◽  
Littoral Cell ◽  
The Mediterranean

Man's intervention with coastal processes takes many forms. However, the most serious large scale, long term coastal erosion results from the interception by dams of rivers supplying sediment to the coast. This loss of sediment may have catastrophic effects along coasts where streams discharge directly into coastal waters. The Nile littoral cell is an impressive example of the effect of dams on coastal erosion. The Nile littoral cell is located in the southeastern Mediterranean Sea and extends 700 km from Alexandria, Egypt in the south to Akko, Israel in the north. The sediment load from the Nile River was deposited along the submerged portion of the delta, where it was sorted and transported to the east by the prevailing waves and by currents of the counterclockwise east Mediterranean gyre that commonly flows at about 50 cm sec over the delta. Prior to 1964, the turbid plume of the flood waters of the Nile River could be traced along the Mediterranean coast for over 700 km to the shores of Lebanon. Fine silt and clay sized material were carried easterly and into deeper water, while sand is carried easterly along the shelf and shore as far as Haifa Bay. Until 1964, the major sediment source of the littoral cell was the Nile River. Construction of the High Aswan Dam, which began filling in 1964, has resulted in a near absence of Nile River flow into the Mediterranean and a corresponding complete loss of the Nile River as a source of nutrients to coastal waters, and as an active sediment source for the delta and the coastline of the Nile littoral cell. As a result, the Nile Delta is now subject to severe erosion in a number of localities.

Sediment transportation systems to the Levant basin and the role of the Nile River since the Pliocene

2020 ◽  
Author(s):  
Yael Sagy ◽  
Oz Dror ◽  
Michael Gardosh ◽  
Moshe Reshef
Keyword(s):  
Sea Level ◽  
Late Pleistocene ◽  
Nile Delta ◽  
Set Covering ◽  
Transport Systems ◽  
Gradual Transition ◽  
Nile River ◽  
Deep Basin ◽  
Early Pliocene ◽  
Levant Basin

<p>The progradation of the Nile River Delta and the thick (~1500m) Sinai-Israel shelf since the Pliocene provide a world class source to sink system feeding a deep (>1.5 km) siliciclastic basin.  The general agreement that the Pliocene-to-Recent succession originates from the Nile Delta dispersing sediments via a system of counterclockwise currents does not reveal how the sediments were transported to the deep basin. Particularly, how sediments originating from the Nile Delta could have bypassed the ~50 km wide Sinai-Israeli shelf. Here, we examine the various sources that contributed to the accumulation of the Pliocene-to-Recent succession in the deep Levant basin, and the temporal and spatial contribution of each source. The analysis of a unique seismic data set covering the shelf, slope and deep basin enable us to track submarine sediment transport systems.</p><p>Following attribute analysis of the seismic volumes we map channel sets, analyze their morphological features and interpret their erosional and depositional patterns. Direction flow maps indicate that sediments sources vary from eastward remnant Arabian drainage network at the onset of the Pliocene, to direct Nilotic origin during the Pliocene. Since the Late Pleistocene reworked sediments, deriving from the Israeli shelf and northern Sinai provide a major source to the deep basin. Furthermore, our results demonstrate an increase in channel’s complexity since the Early Pliocene to Recent suggesting a gradual transition from sporadic submarine flow events, carrying fewer sediments to the deep basin at the Early Pliocene, to more frequent events during the Late Pleistocene-to-Recent characterized by an increase in sediment load. The gradual increase of channel complexity from Pliocene-to-Recent is discordant to the general trend of sea-level fluctuation, suggesting that sea-level has a minor effect on sediment accumulation in the deep basin. We propose that the balance between the northward prograding Nile Cone and the longshore currents building the Sinai-Israeli shelf dictate siliciclastic accumulation in the southeastern Mediterranean basin as well as the paleogeography of its margin.</p>

Salt tectonics in the Eastern Mediterranean: Chronology, kinematics, and driving forces

2020 ◽  
Author(s):  
Elchanan Zucker ◽  
Yechiel Ben Zeev ◽  
Yehouda Enzel ◽  
Zohar Gvirtzman
Keyword(s):  
Driving Force ◽  
Driving Forces ◽  
Nile Delta ◽  
Eastern Mediterranean ◽  
Elevation Gradient ◽  
Fault System ◽  
Deep Basin ◽  
Squeeze Out ◽  
Levant Basin ◽  
Levant Margin

<p>In the Late 1970’s, a slope-parallel normal fault system has been recognized offshore Israel. ~25 years later, a system of folds and thrust faults was recognized farther west in the deep Levant Basin. Initially, this combination of updip extension and downdip contraction seemed to fit the classic paradigm known from other salt basins around the world in which sediments overriding salt glide basinward and produce extension upslope and contraction in the deep basin. However, later studies in the Levant Basin showed that the shapes of the updip extension system and the downdip contractional system do not match; the updip normal faults are trending to the NNE, whereas the deep basin folds are trending to the NW and even to the WNW.</p><p>We propose that while extension of the Levant continental slope expresses basinward gliding, the deep basin shortening belongs to the circum-Nile deformation belt (CNDB) that was previously interpreted as an expression of salt squeezing-out from under the Nile Delta.</p><p>However, careful mapping of the salt-overburden thicknesses around the Nile delta and its submarine cone clearly shows that in the majority of the study area salt squeeze-out cannot be the dominant driving force, because the thick delta load (nearshore) does not reach the thick basin salt (distal basin). The dominating driving force in the western side of the Nile Delta towards the Herodotus Basin, as well as along the Levant continental margin, is simply the elevation gradient towards the lowest place leading to downslope gliding of the sediment-salt sequence.</p><p>Only in the easternmost side of the delta, towards the Levant Basin, does the squeeze-out model work. Here, the delta front covers a thick salt layer and differential loading promotes basinward salt flow. Particularly interesting is the southeast corner of the Mediterranean where the CNDB, driven by differential loading (salt squeezing), is pushed against the Levant margin belt, driven by downslope gliding. By improving the chrono-stratigraphy of the Levant Basin we show that during the first 2.5 my after salt deposition only minor deformation occurred. Then, tilting of the Levant margin (inland uplift) initiated downward gliding and rapid extension; and only ~1 my later the CNDB reached the Levant Basin and started suppressing the downward gliding.</p><p>In a wider perspective our analysis shows that the role of salt squeezing by differential loading was previously overestimated in the Eastern Mediterranean and raises the need to carefully map the boundary of the salt basins prior to any interpretation. This conclusion is especially relevant to young basins where deltas and shelves have not propagated far enough into the basin.</p>

Onset and persistence of cyanobacterial blooms in a large impounded tropical river, Australia

2004 ◽  
Vol 55 (1) ◽  
pp. 1 ◽  
Author(s):  
Myriam Bormans ◽  
Phillip W. Ford ◽  
Larelle Fabbro ◽  
Gary Hancock
Keyword(s):  
Surface Layer ◽  
Water Column ◽  
Mixed Layer Depth ◽  
Phosphorus Uptake ◽  
Bottom Layer ◽  
Climatic Conditions ◽  
Cyanobacterial Blooms ◽  
Cylindrospermopsis Raciborskii ◽  
Surface Mixed Layer ◽  
Tropical River

The dynamic interplay between physical, chemical and biological factors in the development and persistence of cyanobacterial blooms in impounded rivers is an important topic. Over a 3-year study period, variable climatic conditions were recorded in the Fitzroy River, Queensland, Australia, which is a typical, impounded lowland tropical river. Post-flood turbidity reduced the available light in the well-mixed water column to levels insufficient for cyanobacterial growth. Only when the water column stratified and the slowly sinking particles dropped from the surface layer did the ratio of surface mixed layer depth to euphotic depth approach 1, allowing cyanobacterial growth. By the time the light climate became favorable, most of the dissolved nutrients had been scavenged from the water column by settling particles or sequestered by fringing macrophytes and other biogeochemical processes. Cyanobacterial blooms dominated by Cylindrospermopsis raciborskii persisted for several months until the next flood flushed the system. The cyanobacterial species dominating that environment were very small and had high specific phosphorus uptake rates. Their nutrient requirement was met by transfer across the oxycline driven by regular high wind mixing events, entraining nutrient-rich bottom waters. Nutrient fluxes from the sediments into the anoxic bottom layer were sufficient to replace the bottom nutrients lost to the surface layer.

Natural gas formation in the western Nile delta (Eastern Mediterranean): Thermogenic versus microbial

2007 ◽  
Vol 38 (4) ◽  
pp. 523-539 ◽  
Author(s):  
Claudius Vandré ◽  
Bernhard Cramer ◽  
Peter Gerling ◽  
Jutta Winsemann
Keyword(s):  
Natural Gas ◽  
Nile Delta ◽  
Eastern Mediterranean ◽  
Gas Formation

scholarly journals Lars Hällbom; Nitrogenase regulation and ultrastructure of heterocystous cyanobacteria; free living and in lichen symbiosis.

Rangifer ◽  
1982 ◽  
Vol 2 (1) ◽  
pp. 52
Author(s):  
Sven Skjenneberg
Keyword(s):  
Font Size ◽  
Free Living ◽  
Heterocystous Cyanobacteria ◽  
Nitrogenase Regulation ◽  
Lichen Symbiosis

<span style="font-family: Arial Unicode MS,Arial Unicode MS; font-size: xx-small;"><span style="font-family: Arial Unicode MS,Arial Unicode MS; font-size: xx-small;"><p align="justify">Doktoravhandling forsvart i Botanisk auditorium, Uppsala Universitet 19. mai 1982. (Inst. for fysiologisk botanik, Uppsala Universitet).</p></span></span>

scholarly journals Optimization-Based Proposed Solution for Water Shortage Problems: A Case Study in the Ismailia Canal, East Nile Delta, Egypt

Water ◽  
2021 ◽  
Vol 13 (18) ◽  
pp. 2481
Author(s):  
Elsayed M. Ramadan ◽  
Heba F. Abdelwahab ◽  
Zuzana Vranayova ◽  
Martina Zelenakova ◽  
Abdelazim M. Negm
Keyword(s):  
Water Scarcity ◽  
Water Reuse ◽  
Nile Delta ◽  
High Water ◽  
Water Shortage ◽  
Nile River ◽  
System Control ◽  
Water Demands ◽  
Demand Node ◽  
East Nile Delta

Water conflicts in transboundary watersheds are significantly exacerbated by insufficient freshwater sources and high water demands. Due to its increasing population and various development projects, as well as current and potential water shortages, Egypt is one of the most populated and impacted countries in Africa and the Middle East in terms of water scarcity. With good future planning, modeling will help to solve water scarcity problems in the Ismailia canal, which is one of the most significant branches of the Nile River. Many previous studies of the Nile river basin depended on quality modeling and hydro-economic models which had policy or system control constraints. To overcome this deficit position and number, the East Nile Delta area was investigated using LINDO (linear interactive, and discrete optimizer) software; a mathematical model with physical constraints (mass balances); and ArcGIS software for canals and water demands from the agriculture sector, which is expected to face a water shortage. Using the total capital (Ismailia canal, groundwater, and water reuse) and total demand for water from different industries, the software measures the shortage area and redistributes the water according to demand node preferences (irrigation, domestic, and industrial water demands). At the irrigation network’s end, a water deficit of 789.81 MCM/year was estimated at Al-Salhiya, Ismailia, El Qantara West, Fayed, and Port Said. The model was then run through three scenarios: (1) the Ismailia Canal Lining’s effect, (2) surface water’s impact, and (3) groundwater’s impact. Water scarcity was proportional to lining four sections at a length of 61.0 km, which is considered to be optimal—based on the simulation which predicts that the Ismailia canal head flow will rise by 15%, according to scenarios—and the most effective way to reduce water scarcity in the face of climate change and limited resources as a result of the increasing population and built-in industrial projects in Egypt.

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