JKAU: Mar. Sci., Vol. 19, pp: 149-166 (2007 A.D. /1428 A.H.)

The Fractional Composition of Phosphorus in Edku Lagoon and Adjacent Marine Sediments,

Mona Kh. Khalil National Institute of Oceanography and Fisheries, , Egypt [email protected]

Abstract. Four short sediment cores representing different sub basins of Edku lagoon and two cores from the adjacent marine sediments were studied. The sediments were sequentially analyzed to determine four phosphorus fractions (Pex, POH, PHCl and PR) and non-sequentially treated for total-P (TP) and inorganic P (IP). The results generally showed that the fraction associated with apatite mineral (PHCl) is the dominant. It constitutes 56% and 52% of the TP for lagoonal and ¯ ¯ marine sediments implying that apatite is the main storage of PO4 , while the exchangeable and associated with CaCO3 (Pex) fraction is the least content representing 6% and 4% for the lagoonal and marine sediments, respectively. The lagoon sediments are controlled by three factors namely, organic, biogenic and inorganic phosphorus factors. While the marine sediments are controlled by silt/clay factor, biogenic and inorganic phosphorus factors. Keywords: Edku Lagoon, , Sediments, Phosphorus forms.

Introduction

Phosphorus (P) is, an essential nutrient element limiting the biological productivity (Codispoti, 1989); especially important on geologic time scales because it lacks a volatile form to facilitate transfer between the ocean, atmosphere and terrestrial biosphere (Broecker, 1982). It is a key element in global biogeochemical cycles (Sanudo-Wilhelmy et al., 2001). Phosphorus constitutes about 0.1% of the earth’s crust and exists in all known minerals, mainly in hydroxy-apatite {Ca5 (PO4)3 (OH)} and fluoro-apatite {Ca10(PO4)6 F2}, as orthophosphate. In the aquatic systems, the incorporation of dissolved phosphate in sediments occurs 149 150 Mona Kh. Khalil via several mechanisms including precipitation, adsorption onto the settled particles, absorption or uptake by biota and deposition after death as detrital matter. Precipitation and complexation reactions are important in determining the soluble phosphate concentrations in natural waters. The solubility of P is controlled by Fe (III), Al (III) and Ca (Stumm and Leckie, 1971). The influence of the solid phase, whether it is suspended particles or sediments, is of considerable importance in regulating the dissolved P phase of natural waters systems. The sediments are a major P sink for the overlying waters including the well-mixed surface waters (the epilimnion), transporting P to the deep waters (hypolimnion) and ultimately the sediments especially for shallow sea water and lake systems (Stabel, 1984). In large shallow lakes, internal loading of nutrients from bed sediment is a major source of phosphorus for the ecosystem (Qin et al., 2004). Sediments properties, such as pH and redox potential could have caused significant variation of phosphorus release potential (Gao et al., 2005), beside mineral-water equilibrium, sorption processes, organisms (bioturbation) and bottom sediment characteristics. The eastern Mediterranean Sea is the largest water body, which is at present phosphate limited (Krom et al., 1991). This unusual nutrient limitation may be due to adsorption of phosphate by inorganic particulate matter in the deep-water column and its subsequent removal into the sediment. The two principal sources of inorganic particulate matter are atmospheric dust from Sahara desert and, prior to completion of the Dam, Nile flood mud. The present study is restricted to the northwestern part of the Nile Delta, including Edku Lagoon and the adjacent marine sediments. The southeastern Mediterranean is a densely populated region undergoing substantial environmental modification as a result of increased anthropogenic pressure. Of major importance in this region is the sediment load carried by the River Nile to the northeastern African coast, which has been greatly reduced since close of the High Dam in 1964. At present, only a small volume of silt and clay bypasses the Nile Delta to the sea via River Nile distributaries, lagoon out-lets and canals (Stanley, 1996). Edku lagoon is the third largest coastal water body in the northern 2 Nile Delta, having a total area of about 115 km and depth range of 40 – 150 cm. It is located in the northwestern part of the delta, approximately 20 km to the east of Alexandria and 15 km to the west of the Rossetta branch of the River Nile. The lagoon lies 60 cm above sea level, exchanging water with the Mediterranean Sea through a narrow channel The Fractional Composition of Phosphorus in Edku lagoon … 151 called Boughaz El-Maadyia. The average sediment accumulation rates range to ~ 0.2 cm/yr (Chen et al., 1992). This is about 10 times more than on the Nile cone off Egypt (Stanley and Maldonado, 1977) and about 50 times greater than the rate of deposition on the Egyptian continental shelf (Stanley, 1988). The speciation of total phosphorus in different forms is necessary for the understanding of phosphate exchange mechanisms by sediments, its potential removal from the water column and the availability of phosphorus for primary producers (Antonio et al., 2006). The primary purpose of this paper is to determine the distribution of various chemical forms of phosphorus in shallow eutrophic Edku lagoon and the adjacent marine environment. The results obtained are correlated with the area far from the direct effect of the Land-based sources, in order to assess the bioavailability status in these systems. Materials and Methods Four sediment cores from Edku Lagoon were chosen from the cores collected by (Khalil, 1994) (Fig.1) in a way to represent the different lagoon sub-basins; core 1 from the lagoon-sea communication, core 2 from the western basin, core 3 from the central basin and core 4 from the eastern basin.

Fig. 1. Area of study and sampling stations. 152 Mona Kh. Khalil

The samples were collected by pressing a long PVC-tube, of 5cm diameter. The collected cores are being short and ranging in length from 40 to 90 cm. In addition two cores ranging in length from about 140 to 150 cm were collected from marine environment by the Russian vessel “R/V Academic Levrantive” in December 1988 by gravity corer of 5 cm diameter. The location of these cores is shown in Table 1.

Table 1. Location and depth of the marine core sediments.

Core No Latitude N Longitude E Water Depth (m)

5 31º 40′ 3″ 30º 25′ 24″ 25

6 31º 40′ 12″ 30º 01′ 18″ 400

The samples were analyzed following Folk (1974) to determine the mean grain size (Mz = ф16 + ф50+ ф84/3) and the proportions of sand, silt and clay content using a standard sieving and pipette techniques. Chemical analysis includes the determination of total organic carbon by dichromate wet oxidation method. The carbonate contents were determined by titration technique (Black, 1965). Total, inorganic and organic phosphorus were determined according to Aspila (1976). The fractionation of phosphorus forms was extracted according to de Lange (1992) as shown in Table (2). The non-apatite inorganic-P (NAIP) are fractioned into: (a) Exchangeable and carbonate-associated phosphate (Pex) and (b) iron- and aluminium-associated phosphate (POH) beside the calcium-associated phosphate (PHCl) as apatite inorganic-P (AIP) and residual phosphate (PR).

Table 2. Sequential extraction procedure of phosphorus forms.

Step Extract using Form of phosphorus extracted Sign

1 Sediment + 2N NH4Cl Loosely bound (exchangeable + {Pex} carbonate-associated) 2 Residue + 0.1N NaOH Fe, Al-associated {POH}

3 Residue + 0.5N HCl Ca-associated, (apatite) {PHCl}

4 Done in a way similar Residual phosphate (mostly non- {PR} Total-P labile Org-P and Inorg-P The Fractional Composition of Phosphorus in Edku lagoon … 153

The accuracy of the total phosphorus was tested against standard reference material of certified VKIQC loam Soil Reference material (QMB 1-6), using four replicate sub samples. The standard deviation was 11.9. The data revealed that a coefficient of variation was 1.44 and the recovery of the TP was 105%. While the standard deviations for the four test fractions of phosphorus were 1.3, 3.2, 3.9 and 3.1for Pex, POH, PHCl and PR, respectively. In addition, the data revealed that a coefficient of variety percentages was 7.5, 2.9, 1.1 and 4.5.

Results and Discussion 1- Grain Size and Sediment Characteristics 1-1Edku lagoon The grain size, total organic carbon, total carbonate and total phosphorus for Edku lagoon sediments were studied by Khalil (1994). The previously mentioned data shown in Table 3 revealed that the mean grain size varies between 4.0 and 8.1Ф. In general, in all the studied sediment cores, variations in sediment grain size characteristics with depth are not substantial reflecting probably a uniform sediment source during the period of deposition. The organic carbon content showed marked and wide variation between 0.73% and 9.79%. The higher value of organic carbon content recorded on the top of core 1 (Table 3) was attributed to the high contents of plant debris. Whereas, the eastern area of the lagoon (core 4) was affected by drainage water loaded with considerable amounts of dissolved and particulate organic matter which lead to the high concentration of organic carbon at the surface layer. The total carbonate (CaCO3) content varies between 2.62% and 22.7%. It is recognized that the biogenic content of lagoon deposits tends to be higher comparing to their principal sediment source (Nile alluvium) (Stanley and Chen, 1991).The total phosphorus content varies between 417 ppm and 1088 ppm. The highest TP content was recorded in the eastern part of the lagoon (Table 3). It was observed that TP content decreases with decreasing in depth for core 3 & 4. Higher TP concentrations near the sediment-water interface may be due to the recently deposited particulate-P that has not undergone significant diagenesis (Kamp-Nielsen 1977, 1978). The results revealed that the IP is the dominant fraction. It is ranging between 397 and 700 ppm (Table 3). 154 Mona Kh. Khalil

Table 3. Results of grain size analysis, total organic carbon (TOC), calcium carbonate (CaCO3), total and inorganic phosphorus (TP & IP) (after Khalil, 1994) for lagoon sediments. Clay TOC CaCO3 core Interval Mean (phi) sand% silt% sediment type TP IP % % % 1 0 - 10 5 43 43 14 sand-silt-clay 4.93 11.31 868 700 10 - 20 5.1 45 46 9 sandy silt 4.01 10.51 658 594 20 - 30 4.5 52 38 10 silty sand 1.68 7.7 609 537 30 - 40 5.4 43 38 19 sand-silt-clay 2.08 6.94 683 610 2 0 - 10 6 26 43 31 sand-silt-clay 2.92 12.5 724 659 10-20 6.5 18 54 28 sand-silt-clay 2.13 9.29 724 684 20 - 30 6.7 21 40 39 sand-silt-clay 2.34 11.16 793 668 30 - 40 6.5 20 40 40 sand-silt-clay 1.85 8.9 793 741 40 - 50 6.4 22 39 35 sand-silt-clay 1.87 7.82 773 733 3 0 - 10 6.2 24 42 34 sand-silt-clay 2.44 21.39 814 684 10-20 7.1 14 41 45 sand-silt-clay 1.41 11.63 748 676 20 - 30 5.9 23 74 3 sandy silt 1.55 18.11 609 569 30 - 40 7.2 0.85 53.8 45.4 clayey silt 0.95 3.72 601 541 40 - 50 8.1 2 25 73 silty clay 2.62 2.73 585 524 50 - 60 8 2 26 72 silty clay 1.82 2.62 417 397 60 - 70 7.6 1 38 61 silty clay 1.87 2.98 593 561 70 - 80 7.7 1.5 40.5 58 silty clay 2.13 3.97 511 459 80 - 90 7.3 7 30 63 silty clay 2.9 7.57 491 459 4 0 - 15 6.9 15 50 35 sand-silt-clay 9.79 22.07 1088 633 15-25 6.5 15 60 25 sand-silt-clay 8.71 21.29 855 554 25 - 35 6.4 26 23 51 sand-silt-clay 1.69 10.61 766 668 35 - 45 5.6 17 76 7 sandy silt 1.43 7.96 725 660 45 - 60 n.d. n.d. n.d. n.d. 0.73 9.02 784 661

n.d. = not detected

1-2 Marine sediments The inner shelf core (core 5) is composed of a homogeneous grey mud with 42% silt and 54% clay (Table 4). The total organic carbon distribution of the sediment of core 5 ranges between 0.39 and 1.29% being more or less consistent. The lower value of organic carbon was more restricted to the upper layer. The CaCO3 content shows more or less consistent value with a mean value of 6.07%. Core no. 6 represents the upper continental slope with no marked variation in mean grain size. It varies between 7.54 Φ and 9.16 Φ with a mean value of 8.4Φ. The Fractional Composition of Phosphorus in Edku lagoon … 155

Table 4. Results of grain size analysis, total organic carbon (TOC) and calcium carbonate (CaCO3) for marine sediments.

core Interval Mean (phi) sand% silt% clay% sediment type TOC% CaCO3% 5 0 - 5 6.81 10 60 30 sand-silt-clay 0.39 6.82 5-10 8.37 6 44 50 silty clay 0.57 7.57 10-15 8.57 5 43 52 silty clay 0.84 7.03 15 - 20 8.47 5 41 54 silty clay 1.1 7.14 20 - 25 8.25 5 47 48 silty clay 0.76 7.03 25 - 30 8.2 6 46 48 silty clay 0.93 6.06 30 - 35 7.96 8 47 45 clayey silt 0.87 6.82 35 - 40 8.1 4 50 46 clayey silt 0.75 6.6 40 - 45 9.27 1 35 64 silty clay 0.59 6.27 45 - 50 9.73 1 38 61 silty clay 0.97 5.73 50 - 55 8.68 4 41 55 silty clay 1.08 5.84 55 - 60 7.94 3 54 43 clayey silt 0.76 5.84 60 - 65 9.1 0 40 60 silty clay 1.23 5.95 65 - 70 9.44 0 41 59 silty clay 0.93 5.19 70 - 75 8.68 2 40 58 silty clay 1.05 5.73 75 - 80 8.79 2 41 57 silty clay 1 5.95 80 - 85 8.69 3 42 55 silty clay 1.04 5.95 85 - 90 8.68 4 41 55 silty clay 1.02 5.84 90 - 95 8.91 1 37 62 silty clay 0.89 5.73 95 - 100 8.98 4 38 58 silty clay 0.87 5.52 100 - 105 8.87 5 37 58 silty clay 0.97 5.52 105 - 110 8.69 3 42 55 silty clay 0.96 5.95 110 - 115 8.8 4 35 61 silty clay 0.95 6.06 115 - 120 9.26 3 33 64 silty clay 1.29 5.73 120 - 125 8.2 6 46 48 silty clay 0.93 4.87 125 - 130 8.4 11 37 52 sand-silt-clay 1.02 5.69 130 - 135 8.3 10 35 55 sand-silt-clay 1.05 6.15 135 - 140 8.2 11 36 53 sand-silt-clay 1.17 5.47 6 0 - 5 8.23 0 50 50 silty clay 1.26 26.57 5-10 8.27 0 40 60 silty clay 0.94 12.24 10-15 8.34 1 47 52 silty clay 1.19 17.88 15 - 20 8.23 0 50 50 silty clay 1.15 17.54 20 - 25 8.25 1 47 52 silty clay 1.01 17.43 25 - 30 8.27 0 40 60 silty clay 0.94 16.87 30 - 35 8.91 3 32 65 silty clay 1.24 7.84 35 - 40 9.16 1 36 63 silty clay 1.1 12.58 40 - 45 9.03 1 42 57 silty clay 1.38 11.79 45 - 50 8.48 2 45 53 silty clay 1.12 8.4 50 - 55 8.6 1 40 59 silty clay 1.21 20.93 156 Mona Kh. Khalil

Table 4. Continued.

Core No. Interval Mean (phi) sand% silt% clay% sediment type TOC% CaCO3% 55 - 60 8.78 2 40 58 silty clay 1.03 14.5 60 - 65 7.9 1 58 41 clayey silt 1.02 13.82 65 - 70 7.48 0 59 41 clayey silt 1 10.32 70 - 75 7.9 1 58 41 clayey silt 1.08 15.85 75 - 80 8.73 0 39 61 silty clay 1.27 11.9 80 - 85 8.61 2 38 60 silty clay 1.08 10.04 85 - 90 8.91 3 32 65 silty clay 1.12 15.78 90 - 95 8.9 1 34 65 silty clay 1.02 22.51 95 - 100 8.94 1 36 63 silty clay 1.1 12.55 100 - 105 7.73 1 60 39 clayey silt 0.88 9.77 105 - 110 7.54 0 61 39 clayey silt 0.92 10.58 110 - 115 8.61 1 40 59 silty clay 1.14 10.4 115 - 120 8.61 0 46 54 silty clay 0.87 9.32 120 - 125 8.2 1 50 49 clayey silt 0.82 8.96 125 - 130 8.07 1 55 44 clayey silt 1.15 10.4 130 - 135 8.2 1 50 49 clayey silt 1 8.6 135 - 140 8.47 2 47 51 silty clay 1.1 12.28 140 - 145 8.34 2 48 50 silty clay 0.81 12.73 145 - 150 8.2 0 54 46 clayey silt 0.76 6.54

As the sediments of the inner shelf (core 5), here the TOC contents are also similarly consistent in most of the core levels. The values fall in the range between 0.81 and 1.38% (Table 4). The rate of sedimentation is one of the important factors, which controls the TOC levels in sediments. The carbonate content determined in core 6 varies between 6.54 and 26.6% with marked increase in the surficial layer. Such coarse calcareous surficial sediment reflects effective bottom erosion by currents when sea level was stabilized by 5000 – 4000 years B.P. This was illustrated by Stanley (1988) and Stanley et al. (1998). The bottom erosion affected many areas of the Nile Delta shelf even at its outer parts. The carbonate content shows gradual increase off shore direction, this was also shown by Khalil (2003). Summerhays et al. (1978) hint at the lower terraces and outer shelf slopes. The TP content of the marine sediments varies between 583 and 891 ppm. The low concentration recorded at the lower intervals of core is due to relatively rich sand fraction (Table 4). Also, as shown in lagoonal sediments the IP represented the dominant form. The Fractional Composition of Phosphorus in Edku lagoon … 157

2- The Forms of Phosphorus Association The percentages of recoveries of phosphorus by the sum of all extracted phosphorus phases, for Edku lagoon and marine sediments are 83.2% ±9.5 % and 82 % ± 8.7% of total phosphorus respectively. While Penn et al. (1995), Khalil (2003) and El-Rayis et al. (2005) showing values equal to 76.3%, 85.4% and 85% respectively. Many investigators have sought to identify which of the operationally defined fractions might correspond to the labile sediment P pool. Chang and Jackson (1957) and Hieltjes and Lijklema (1980) termed the fraction extracted with NH4Cl as labile inorganic phosphorus. Others (Williams et al. 1980; De pionto et al. 1981; and Klapwijk et al. 1982) have found good agreement between the fraction extracted with NaOH and the sediment P available to support algal growth as determined in bioassays. Boström (1984) suggested that both fractions (NH4Cl and NaOH extracts) contribute to the labile phosphorus pool. Also, Jin and Tu (1990) show that Pex, Al-P and Fe-P are easily desorbed from the sediments and released to the overlying water as the bio-available forms of phosphorus in sediments. 2-1- Lagoonal Sediments

Table 5, shows that the apatite phosphorus (PHCl) is the dominant form accounting for 56% of the TP, followed by the residual phosphorus (PR) 26%, Fe and Al associated (POH) 12% and the exchangeable phosphorus (Pex) 6%.

Exchangeable and Carbonate-Associated Phosphate (Pex) The concentration of this form is ranged from 15 to 69 ppm accounting for 3-8% of the TP. The pattern of distribution of Pex along the vertical sections is quite similar to that of OC and CaCO3. They show slightly decreasing with the increased depth. The higher values of Pex are restricted to the eastern basin which was affected by the drainage water. Pettersson (1986) emphasized that such sediment type is characterized by having the highest values of loosely sorbed P. Bostrom (1984) showed by experiments that these sediments may release P under both aerobic and anaerobic conditions at pH 8-10. Also these sediments are suitable grounds for bacteria, which are important sink and source of PO4 (Gächter et al., 1988 and Laczko, 1988). 158 Mona Kh. Khalil

Bacterial activity with physico-chemical reactions determines the concentration of P in the sediment porewater (Yamada and Kayama, 1987). This concentration also relies on P-exchange through the sediment-water interface (Hakanson and Jansson, 1983).

Table 5. Concentration (ug/g) of different P forms and percentages of each fraction to total (TP or Psum) Beside Psum/TP% along the studied lagoon core sediments.

Core 1/5 2/5 3/5 4/5 5/TP Interval TP IP OP P (1) P (2) P l (3) P (4) P (5) No. ex oH HC R sum % % % % % 1 0 - 10 868 700 168 43 71 293 186 593 7 12 49 31 68 10 - 20 658 594 64 33 45 337 156 571 6 8 59 27 87 20 - 30 609 537 72 28 51 302 101 482 6 11 63 21 79 30 - 40 683 610 73 29 53 306 151 539 5 10 57 28 79 mean 705 610 94 33 55 310 148 546 6 10 57 27 78 2 0 - 10 724 659 65 35 63 321 163 582 6 11 55 28 80 10-20 724 684 40 35 63 317 177 591 6 11 54 30 82 20 - 30 793 668 125 41 87 340 188 656 6 13 52 29 83 30 - 40 793 741 52 34 78 345 205 662 5 12 52 31 84 40 - 50 773 733 40 37 73 360 172 644 6 11 56 27 83 mean 761 697 64 36 73 337 181 627 6 12 54 29 82 3 0 - 10 814 684 130 35 78 319 178 609 6 13 52 29 75 10-20 748 676 72 35 73 339 157 605 6 12 56 26 81 20 - 30 609 569 40 40 49 332 153 575 7 9 58 27 94 30 - 40 601 541 60 29 90 291 123 533 5 17 55 23 89 40 - 50 585 524 61 40 98 318 85 541 7 18 59 16 92 50 - 60 417 397 20 15 88 252 78 433 3 20 58 18 104 60 - 70 593 561 32 20 151 229 119 519 4 29 44 23 88 70 - 80 511 459 52 33 90 273 95 490 7 18 56 19 96 80 - 90 491 459 32 18 51 309 90 469 4 11 66 19 95 mean 597 541 55 29 85 296 120 530 5 16 56 22 90 4 0 - 15 1088 633 455 61 68 404 234 767 8 9 53 30 71 15-25 855 554 301 106 41 391 210 748 14 5 52 28 87 25 - 35 766 668 98 26 57 320 119 522 5 11 61 23 68 35 - 45 725 660 65 36 96 372 162 667 5 14 56 24 92 45 - 60 784 661 123 36 62 329 101 529 7 12 62 19 67 mean 844 635 208 53 65 363 165 647 8 10 57 25 77

Iron and Aluminium-Associated Phosphate (POH) Generally, low concentrations are found in core 1 i.e. the lagoon-sea connection area (Table 5), in contrast the high levels recorded in the deeper layer of core 3 (central basin). However, the concentrations of The Fractional Composition of Phosphorus in Edku lagoon … 159

POH reflect the influence of sediment texture, whereas, higher clay % enhances the level of POH. Moreover the increase of CaCO3 reduces the POH levels. Variabilities in POH concentration levels among stations and inter station can thus be attributed to the amounts of fine clay minerals including kaolinite, (El-Sabrouti and Sokkary, 1982) which have the ability to form complexes with phosphate. This may be related also to the competition between phosphate and other elements including humic substances for available complexing sites (Reuter and Perdue, 1977).

Calcium-Associated Phosphate/ Apatite (PHCl) The apatite-P comprises the major portion of TP in Edku lagoon. It forms 56% on the average, with a range of concentration lies between = 229 and 404 ppm, therefore, it is the main storage of the PO 4 in Edku Lagoon. de Lange (1992), Khalil (2003) and El-Rayis et al. (2005) found that, the apatite-P content makes the majority of all the extracted P forms in Madera Abyssal Plain, Manzala lagoon and its neighboring marginal Mediterranean Sea and Abu-Kir Bay sediments, respectively. The high content of apatite-P value (320 – 404 ppm) was found in the eastern part of the lagoon (core 4) indicating the importance of continuous discharge from the drains. de Lange (1992) pointed out that apatite-P is stable under both oxidizing and reducing conditions and can not be released again from the sediment to the overlying water.

Residual Phosphate (PR) The residual phosphate content represents the second most dominant phase after apatite-P; it represents 26% of the TP content. The highest contents of PR are found at the surface of core 4 whose sediments were TP-rich.

2-2- Marine Sediments

Exchangeable and Carbonate-Associated Phosphate (Pex) The Pex form occurs as minor fraction comprising 4% on the average. Its concentration varies between 11 and 42 ppm (Table 6). In general, no significant differences were found between the Pex levels in the two studied environments. 160 Mona Kh. Khalil

Table 6. Concentration (ug/g) of different P forms and percentage of each fraction to total (TP or Psum) Beside Psum/TP % along the studied marine core sediments.

Core P l P 5/TP Interval TP IP OP P (1) P (2) HC P (4) sum 1/5% 2/5% 3/5% 4/5% No. ex oH (3) R (5) % 5 0 - 5 729 608 121 11 32 341 231 615 2 5 55 38 84 5-10 735 675 60 42 87 364 222 716 6 12 51 31 97 10-15 842 600 242 14 45 340 265 665 2 7 51 40 79 15 - 20 759 711 48 14 91 246 268 619 2 15 40 43 82 20 - 25 741 629 112 14 64 294 237 610 2 10 48 39 82 25 - 30 822 650 172 14 90 289 270 663 2 14 44 41 81 30 - 35 767 617 150 14 65 327 204 610 2 11 54 33 80 35 - 40 713 607 106 35 75 356 224 690 5 11 52 32 97 40 - 45 765 647 118 14 58 300 229 601 2 10 50 38 79 45 - 50 835 622 213 15 83 299 242 641 2 13 47 38 77 50 - 55 821 689 132 15 94 279 285 674 2 14 41 42 82 55 - 60 796 600 196 18 66 290 260 635 3 10 46 41 80 60 - 65 729 610 119 13 95 269 277 654 2 14 41 42 90 65 - 70 761 671 90 14 80 283 283 660 2 12 43 43 87 70 - 75 812 657 155 16 90 291 264 662 2 14 44 40 81 75 - 80 768 649 119 23 60 300 309 693 3 9 43 45 90 80 - 85 761 671 90 23 93 326 225 667 3 14 49 34 88 85 - 90 812 627 185 16 81 319 225 641 2 13 50 35 79 90 - 95 860 597 263 18 76 321 240 655 3 12 49 37 76 95 - 100 808 679 129 14 68 323 203 608 2 11 53 33 75 100 - 105 702 637 65 18 67 320 263 669 3 10 48 39 95 105 - 110 747 646 101 16 52 316 288 673 2 8 47 43 90 110 - 115 849 635 214 20 80 305 271 676 3 12 45 40 80 115 - 120 720 619 101 20 90 309 286 705 3 13 44 41 98 120 - 125 583 558 25 17 80 266 215 578 3 14 46 37 99 125 - 130 665 530 135 23 55 304 194 576 4 10 53 34 87 130 - 135 676 550 126 20 56 312 211 599 3 9 52 35 89 135 - 140 679 644 35 22 57 326 214 619 3 9 53 35 91 mean 759 630 129 18 73 308 247 645 3 11 48 38 85 6 0 – 5 680 502 178 26 20 255 249 550 5 4 46 45 81 5-10 748 642 106 22 29 257 249 556 4 5 46 45 74 10-15 721 624 97 25 18 253 257 553 4 3 46 47 77 15 - 20 780 617 163 27 24 251 288 590 5 4 43 49 76 20 - 25 863 646 217 11 34 287 181 512 2 7 56 35 59 25 - 30 818 614 204 18 36 332 162 549 3 7 61 30 67 30 - 35 801 706 95 12 79 334 207 633 2 12 53 33 79 35 - 40 891 722 169 18 57 360 180 615 3 9 59 29 69 The Fractional Composition of Phosphorus in Edku lagoon … 161

Table 6. Continued. Core P l P 5/TP Interval TP IP OP P (1) P (2) HC P (4) sum 1/5% 2/5% 3/5% 4/5% No. ex oH (3) R (5) % 40 - 45 890 735 155 23 48 370 171 612 4 8 60 28 69 45 - 50 850 731 119 21 66 361 182 630 3 11 57 29 74 50 - 55 784 620 164 27 22 338 206 594 5 4 57 35 76 55 - 60 754 662 92 26 33 346 151 556 5 6 62 27 74 60 - 65 744 671 73 27 33 354 165 579 5 6 61 28 78 65 - 70 768 675 93 26 42 347 141 556 5 8 62 25 72 70 - 75 746 648 98 16 27 361 124 528 3 5 68 23 71 75 - 80 732 675 57 19 44 342 183 589 3 8 58 31 80 80 - 85 794 672 122 23 52 345 171 591 4 9 58 29 74 85 - 90 718 652 66 23 27 302 164 516 4 5 58 32 72 90 - 95 683 550 133 22 21 346 141 529 4 4 65 27 77 95 - 100 744 645 99 21 39 338 191 590 4 7 57 32 79 100 - 105 775 647 128 27 46 350 161 584 5 8 60 28 75 105 - 110 700 646 54 28 30 333 160 550 5 5 60 29 79 110 - 115 758 672 86 31 36 335 199 600 5 6 56 33 79 115 - 120 694 680 14 28 48 340 173 590 5 8 58 29 85 120 - 125 717 563 154 32 46 360 239 677 5 7 53 35 94 125 - 130 739 562 177 32 46 349 241 667 5 7 52 36 90 130 - 135 730 560 170 32 51 365 245 692 5 7 53 35 95 135 - 140 697 542 155 30 39 353 239 660 5 6 53 36 95 140 - 145 733 571 162 37 34 353 237 661 6 5 53 36 90 145 - 150 748 578 170 29 60 371 240 700 4 9 53 34 94 Mean 760 634 126 25 40 333 197 594 4 7 56 33 79

Iron and Aluminium-Associated Phosphate (POH) This chemical fraction represents the second minor content with average about 11% in the near shore and 7% for the offshore.

Calcium-Associated Phosphate/ Apatite (PHCl) The apatite-P contents represent the majority of all the extracted P forms. It constitutes 52% of the Psum therefore; it is the main storage of the PO4 in the sediments. There is no clear variation in the apatite-P contents with depth, while the ubiquitous concentration of about 300 ppm characterizes the two cores.

Residual Phosphate (PR) This chemical form represents the second most dominant P-phase after apatite-P (Table 6). Its average content is about 38% in core 5 and 33% in core 6 of TP content of the sediments. 162 Mona Kh. Khalil

From the above discussion it is evident that the apatite-P is the dominant form in both lagoon and marine sediments. This apatite-P is referred to as non available form. While the available forms of phosphorus represented 18% and 11% for lagoon and marine sediments, respectively. 3- Factor Analysis Three factors explain 79% of the total variance for the lagoon sediments (Table 7a). It is namely, organic factor, biogenic and inorganic phosphorus factors. The biogenic factors shows from the marked +ve loading of organic carbon, organic-P, moderate loading of residual phosphate forms may indicate that part of organic-P is derived from land, apart from insitue organic-P production and another part from transported sewage and industrial wastes. The latter is suggested on the basis of the marked loading of exchangeable P form. For marine sediments four factors explain 69% of total variance namely, silt / clay factor, biogenic, inorganic phosphorus factors (Table 7b). Silt / clay factor is shown of marked – ve loading of silt fraction and + ve loading of clay fraction. Generally, it is shown that biogenic factor seems to play greater role in the lagoon and marine sediments. Organic phosphorus production in the lagoon plays an obvious role in the lagoon sediments as compared to marine sediments. It is also clear that silt / clay ratio seems to play significant role in marine sediments.

Table 7 (a). Factor analysis of the observed variables in lagoon sediments (loading >0.4 or < 0.4)5. Variables Factor 1 Factor 2 Factor 3 Factor 4 Depth -0.7 Mean -0.92 Sand 0.92 Silt Clay -0.78 -0.53 TOC% 0.94

CaCO3 0.71 TP 0.61 0.74 IP 0.94 OP 0.92

Pex 0.84

POH -0.77

PHCl 0.64

PR 0.54 0.73 The Fractional Composition of Phosphorus in Edku lagoon … 163

Table 7 (b). Factor analysis of the observed variables in marine sediments (loading >0.4 or < 0.4).

Variables Factor 1 Factor 2 Factor 3 Factor 4 Depth 0.41 0.57 Mean 0.91 Sand 0.5 Silt -0.88 Clay 0.96 TOC% 0.59

CaCO3 -0.92 TP -0.57 IP -0.91 OP

Pex 0.7

POH 0.84

PHCl 0.87

PR 0.58

Conclusion The total phosphorus content varies between 417 ppm and 1088 ppm in the lagoon sediment. The highest TP content was restricted in the eastern part of the lagoon. While the TP content in the marine sediments have values ranging between 583 and 891 ppm. It was found that inorganic phosphorus (IP) represents the dominant form encountered in this study. The average concentrations of the different P forms determined equals, 36 ppm (Pex), 71 ppm (POH), 367 ppm (PHCl) and 154 ppm (PR). These are corresponding to 6, 12, 56 and 26% of the total-P. The results proved that the apatite-P is the dominant form in both lagoon and marine sediments. This form is referred as non available forms that cannot be remobilized again to the overlying water. While the available forms of phosphorus represent 18% and 11% for lagoon and marine sediment respectively. The biogenic factor seems to play big role in lagoon and marine sediments. Organic phosphorus production in the lagoon sediments plays an obvious role as compared to marine sediments. In addition to, silt/clay ratio seems constitutes significant role in marine sediments.

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