The regeneration of pore water (PW) nutrients was investigated and the contribution of benthic nutrient fluxes to the overlying bottom water (BW) was examined. Dissolved inorganic nutrients (NO - 2, NO - 3, PO 3- 4 and SIO 4- 4) were measured in PW and BW in El Mex Bay and surround drains during spring 2010. Nutrient concentrations gradiance in PW with overlying seawater were evaluated according to Fick’s Law. Average inorganic nutrient fluxes were estimated using the pore water gradient concentration across the sediment-water interface. Calculated nutrient fluxes had averages of ﹣7.24, ﹣1.36, ﹣7.86 and ﹣1.33 in El Mex Bay. Additionally, the fluxes in the drains were ﹣34.39, ﹣32.28, ﹣53.20 and ﹣117.6 mg·m ﹣2·day ﹣1 for NO - 3, NO - 2, PO 3- 4 and SIO 4- 4, respectively. Mineralogical studies of sediment samples by using IR, X-ray analysis were carried out to identify the chemical structure of sediments. The results revealed that calcite, aragonite and quartz are the dominant minerals. On the other hand, differential thermal analysis (DTA) was used to evaluate and discuss different kinetic parameters such as Ea #, ΔG #, ΔH #, ΔS #, Z and Tm support the view of the extra stability of these sediments.
During the last century, the Egyptian coastal areas along the Mediterranean sea were strongly impacted by the development of anthropogenic activities on their shores and the subsequent inputs of inorganic including nutrients and organic pollutants [
Nutrient fluxes at the sediment-water interface can indeed influence or regulate the nutrient composition of the water column since the sediment can behave as a sink or as a source of inorganic nitrogen, phosphorus and silicate through different biogeochemical processes [
Sediments may originate from a number of sources. The proportions of sediments from different sources at any particular location will depend on a variety of hydrological and geological factors, e.g. circulation patterns, tidal movement, weathering conditions and source rocks. It was pointed out that the two extreme sources of sediments i.e. landward and seaward, together with intermediate sources, such as river mouths slope impose severe limitations on the geochemical interpretation of sedimentary processes [
El-Mex Bay is part of the Alexandria coast on the Mediterranean Sea. It is adjacent to the center of Alexandria that is populated with about six million inhabitants and is considered as one of the main fishing sources in Egypt. It extends for about 15 km between El-agamy head land in the west and the western harbor to the east and from the coast to a depth line of about 15 km. the bay has a mean depth of about 10 m and surface area of about 19.4 km2 (
Bottom water samples were collected using a five liters Nisken’s plastic bottle provided with a thermometer.
Surficial sediments were collected in April 2010 from seven stations, distributed at El-Mex Bay of Alexandria, and four stations in the drains (El-Umum, El-Noubaria, El-Qalah and Mariout Lake) as shown in
Nutrient salts were spectrophotometrically determined using a double beam spectrophotometer (UV VIS- SPEKOL® 1300/1500 single beam), according to the methods described by Strickland and Parsons [
a) Extractions of Interstitial Waters from Sediments
The choice of the techniques used for extraction the interstitial water from sediments is usually governed by the nature of sediments and available facilities as follows; 1―In case of silty sediment fractions, the squeezer technique was used [
b) Nutrient Salts Analysis
a) Preparation of Samples
After extraction of the interstitial waters, sediment samples were subjected to air dryng, by spreading them on clean plastic sheets. All these were made inside a clean cabinet. The quartering was made using the familiar cone and quarter technique. Air dried samples were placed inside an electric oven for overnight at 70˚C. One half of each dry sediment sample was lightly hand ground in an a agate mortar, sieved through a screen of 0.2 mm mesh size and kept in clean and well stopper polyethylene vials to be ready for geochemical analysis. The remainder of each dry sample was used for the mechanical or grain size analysis.
b) Grain-size and Granulemetric Analysis
The sediment samples were subjected to grain size analysis according to the method described by Folk [
c) Infrared Spectra (IR) Analysis
Sediment samples were analyzed by Infrared Perkin-Elmer R79521, Ratio Recording FT-IR System Spectrophotometer (USA) that was available from central lab unit, National Institute of Oceanography and Fisheries (NIOF), Alexandria, Egypt.
d) X-ray analysis
The data were obtained using (Pentater Link Oxford, Link ISIS) and JEOL JSM-5300 Scanning electron Microscope. Specttra taken in the range of 1 - 8 Kev. The instrument is available in faculty of science Alexandria University.
e) Thermal analysis
Due to the ever-increasing loads of nitrogen and phosphorus from aquaculture, lots of dissolved or granular nitrogen and phosphorus accumulate on the surface of the sediments by flocculation, adsorption and sedimentation, resulting in growing contents of nitrogen and phosphorus in the overlying waters. This indicates that in El Mex Bay, a large amount of nitrogen and phosphorus from the sediments is released into the overlying water [
where J is the flux (μmol・m−2・d−1),
where D0 is the diffusive coefficient at infinite dilution, and the values for NO2-N, NO3-N, PO4-P, SiO4-Si were 18.3, 17.2, 9.25, 7.07 × 10−6 (cm2/sec) at 21˚C [
Krom and Berne [
For
The diffusion flux (Ji) for phosohorus is estimated by Fick’s law according to:
Therefore:
where
Sakamaki et al., [
Measurements of dissolved inorganic nutrients (
When nutrients from outer sources are discharged into water bodies, a great deal of nitrogen and phosphorus accumulates in sediments and their concentrations may be up to 50 to 500 times that in the overlying water [
Nutrient diffusive fluxes calculated in the present study were illustrated in
St.No. | Nitrite | Nitrate | Phosphate | Silicate | ||||
---|---|---|---|---|---|---|---|---|
BW | PW | BW | PW | BW | PW | BW | PW | |
1 | ND | 24.51 | 1.80 | 4.57 | 6.44 | 911.40 | 4.26 | 51.96 |
2 | 0.38 | 49.03 | 1.43 | 292.85 | 2.66 | 75.95 | 5.33 | 31.17 |
3 | 6.15 | 28.02 | 8.25 | 317.79 | 8.54 | 455.70 | 13.06 | 83.13 |
4 | 0.83 | 178.60 | 9.83 | 53.45 | 0.77 | 260.40 | 3.92 | 114.31 |
5 | 0.38 | 52.53 | 3.34 | 44.04 | 5.88 | 282.10 | 3.96 | 62.35 |
6 | 0.38 | 17.51 | 31.17 | 1175.50 | 1.12 | 32.55 | 3.92 | 31.17 |
7 | 0.50 | 98.06 | 12.05 | 663.50 | 0.70 | 943.95 | 3.11 | 218.22 |
Average | 1.43 | 64.04 | 9.70 | 364.53 | 3.73 | 423.15 | 5.37 | 84.62 |
8 | 12.33 | 487.83 | 20.00 | 591.96 | 9.66 | 2598.58 | 77.59 | 4809.25 |
9 | 0.63 | 4024.85 | 5.00 | 2202.88 | 53.90 | 1703.45 | 49.84 | 2107.42 |
10 | 1.38 | 479.07 | 2.86 | 2453.98 | 1.68 | 971.08 | 6.18 | 1405.99 |
11 | ND | 978.11 | 40.00 | 1562.72 | 10.22 | 6151.95 | 111.00 | 19929.08 |
Average | 4.78 | 1492.47 | 16.96 | 1702.89 | 18.87 | 2856.26 | 61.15 | 7062.94 |
8―El-Umum Drain, 9―El-Qalaa Drain 10―El-Noubaria Drain and 11―Mariut Lake.
St.No. | Nitrite | Nitrate | Phosphate | Silicate | ||||
---|---|---|---|---|---|---|---|---|
D0 = 18.3 × 10−6 | D0 = 17.2 × 10−6 | D0 = 9.25 × 10−6 | D0 = 7.07 × 10−6 | |||||
dc | J | dc | J | dc | J | dc | J | |
1 | 24.51 | −0.53 | 2.77 | −0.06 | 904.96 | −16.97 | 47.7 | −0.80 |
2 | 48.65 | −1.06 | 291.42 | −5.94 | 73.29 | −1.37 | 25.84 | −0.43 |
3 | 21.87 | −0.47 | 309.54 | −6.31 | 447.16 | −8.38 | 70.07 | −1.18 |
4 | 177.77 | −3.86 | 43.62 | −0.89 | 259.63 | −4.87 | 110.39 | −1.85 |
5 | 52.15 | −1.13 | 40.7 | −0.83 | 276.22 | −5.18 | 58.39 | −0.98 |
6 | 17.13 | −0.37 | 1144.33 | −23.34 | 31.43 | −0.59 | 27.25 | −0.46 |
7 | 97.56 | −2.12 | 651.45 | −13.29 | 943.25 | −17.69 | 215.11 | −3.61 |
Average | 62.61 | −1.36 | 354.83 | −7.24 | 419.42 | −7.86 | 79.25 | −1.33 |
8 | 475.5 | −10.32 | 571.96 | −11.67 | 2588.92 | −48.54 | 4731.66 | −79.49 |
9 | 4024.22 | −87.33 | 2197.88 | −44.84 | 1649.55 | −30.93 | 2057.58 | −34.57 |
10 | 477.69 | −10.37 | 2451.12 | −50.00 | 969.4 | −18.18 | 1399.81 | −23.52 |
11 | 978.11 | −21.22 | 1522.72 | −31.06 | 6141.73 | −115.16 | 19818.1 | −332.94 |
Average | 1487.69 | −32.28 | 1685.93 | −34.39 | 2837.39 | −53.20 | 7001.79 | −117.63 |
8―El-Umum Drain, 9―El-Qalaa Drain 10―El-Noubaria Drain and 11―Marriut Lake. D0; is the diffusive coefficient at infinite dilution at 21˚C cited from Zhang et al. [
During Spring, when the surface cools, a point is reached at which the temperature of the surface and bottom are equal. The disappearance of thermal stratification cause the entire body of water to behave as a hydrological unit, and the resultant mixing is known as overturn. During the overturn, the chemical and physical characteristics of any body of water becomes much more uniform, and a number of chemical, physical, and biological changes may result. Biological activity may increase from the mixing of nutrients. Higher and negative flux values (upword flow from sediment to over laying water) of all nutrients could be attributed to higher sediment organic matter content and high biological activity. Delange [
Mean grain size and the median diameter may reflect the general characteristics of granule metric composition of sediment. While the values of skewness and kurtosis reflects the uniformity of distribution of sediment composition. The distribution of sediment composition depends on the equilibrium between gravity of sediments and water forces. In the present study, the results of the grain size analysis of the grab sediments of the study area, (
El-Mex sediments contained appreciable amounts of tubeworm skeletons of some calcareous organisms, bivalve shell fragments (placipoda, plyciopoda and gastropod) and gravel. The texture of sediments was mainly sandy, with some muddy sediments in stations 1, 2 and 5 (
IR curves are normally used in mineralogy for qualitative analysis and identification of different minerals, even complex mixtures. It is based on positions and shapes of absorption bands [
A weak band within the range of 2300 - 2400 cm−1 is characteristic for absorption of carbonate minerals (calcite and magnesium calcite) according to Smolander et al., [
Station No. | Clay | Silt | Sand | Sediment type | Sorting | Sortig |
---|---|---|---|---|---|---|
% | (Folk, 1974) | Coefficient (phi) | Type | |||
1 | 9.12 | 90.88 | 0.00 | Silt | 1.12 | Poorly sorted |
2 | 0.42 | 40.55 | 59.03 | Silty Sand | 1.01 | Poorly sorted |
3 | 0.00 | 0.00 | 100.00 | Sand | 1.10 | Poorly sorted |
4 | 0.00 | 0.00 | 100.00 | Sand | 1.20 | Poorly sorted |
5 | 2.06 | 91.20 | 6.75 | Silt | 0.75 | Moderately sorted |
6 | 0.00 | 0.00 | 100.00 | Sand | 0.98 | Moderately sorted |
7 | 0.00 | 0.00 | 100.00 | Sand | 0.36 | Well sorted |
8 | 37.72 | 54.90 | 7.39 | Silt Clay | 2.03 | Very poorly sorted |
9 | 15.74 | 44.97 | 39.30 | Silty Sand | 2.53 | Very poorly sorted |
10 | 18.36 | 77.06 | 4.57 | Silt | 1.45 | Poorly sorted |
11 | 23.79 | 73.85 | 2.36 | Silty Sand | 1.76 | Poorly sorted |
8―El-Umum Drain, 9―El-Qalaa Drain, 10―El-Noubaria Drain, and 11―Mariut Lake.
cm−1 could be attributed to the asymmetrical C-H stretching of methyl (-CH2) groups being characteristic of aliphatic hydrocarbon [
Figures 3-5 and Tables 4-6 showed that the sediments comprise two main minerals: silicate and carbonate that appear in some sediments profile as Mg-calcite as a result of Mg substitution [
Differential thermal analysis is a thermoanalytic technique. In DTA, the material under study and an inert reference are made to undergo identical thermal cycles, while recording any temperature difference between sample and reference [
DTA figures gave steps due to dehydration, rearrangement and decarbonation.
Label | Mg | Si | P | S | Cl | Ca | Mn | Co | Cu | Pb |
---|---|---|---|---|---|---|---|---|---|---|
% Total | 0.5 | 4.2 | 0.3 | 1.7 | 0.3 | 91 | 1.4 | 0.2 | 0.5 | 0.1 |
Label | Na | Mg | Al | Si | S | Cl | K | Ca | Ti | Cr | Mn | Fe | Zn |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
% Total | 0.3 | 1.7 | 12.4 | 46.9 | 0.6 | 0.7 | 3.1 | 18.1 | 1.5 | 0.4 | 13.4 | 0.9 | 0.1 |
Label | Na | Mg | Al | Si | S | Cl | K | Ca | Ti | Cr | Mn | Fe | Co | Cu | Hg |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
% Total | 0.2 | 1.4 | 8.1 | 70.7 | 1.9 | 0.9 | 1.6 | 6.3 | 0.5 | 0.2 | 6.7 | 0.7 | 0.2 | 0.4 | 0.3 |
Sample | Peak | −ΔS# | −ΔH# | ∆G# | ||||
---|---|---|---|---|---|---|---|---|
Temp (˚C) | n | α | Tm (K) | Z | ||||
(kj・K−1・mol−1) | (kJ/mol) | (kJ/mol−1) | ||||||
El-Mex | 768.97 | 0.46 | 0.76 | 1041.97 | 0.98 | 0.26 | 256.69 | 9.19 |
El-Qalaa | 122.97 | 1.45 | 0.56 | 395.97 | 2.86 | 0.24 | 85.58 | 8.56 |
Mariut lake | 127.36 | 1.45 | 0.56 | 400.36 | 2.82 | 0.24 | 86.70 | 8.57 |
The inorganic nutrient concentrations in the BW column of El Mex Bay and its surround drains indicate that this area suffers from acute eutrophication, resulting from a great amount of anthropogenic nutrients entering the sea through numerous land-based sources. Continuous burial and decomposition of organic matter in the topmost layer of the sediment is the main reason for the high nutrient concentrations in the PW compared to those in the OBW. The variations in concentrations between sites can be mainly attributed to variations in supply and input of reactive organic matter. Nutrient diffusive fluxes calculated in the present study during spring, 2010 from sediments had averages of −7.24, −1.36, −7.86 and −1.33, however in the drains were −34.39, −32.28, −53.20 and −117.6 mg・m−2・day−1 for