Kazem Darvish Bastami a *, Hosein Bagheri a, Mehrshad Taheri a, Ali hamzehpour a, Reza Rahnama a, Mirmahmoud Seyedvalizadeh a
a Iranian National Institute for Oceanography and Atmospheric Science (INIOAS), No. 3, Etemadzadeh St., Fatemi Ave., 1411813389 Tehran, Islamic Republic of Iran
Corresponding author, E-mail address: darvish_60@yahoo.com;
Tel.:+989124450867
Keywords: Bioavailability, Phosphorus, Surface sediment, Caspian Sea Introduction
Phosphorus as a substantial element, plays a crucial role in the regulation of bio-community structure and biogeochemical cycle of other elements in an aqueous environment. In sediments, phosphorus is discovered as Loosely-P, Fe-bound, Authigenic-P, Organic-P and Detrital-P. Hence, identification of phosphorus forms in aqua environment is of great importance (Ruttenberg, 1992).
Various studies have been conducted on different forms of phosphorus in several regions so, but little information is known in the Caspian Sea. Therefore, the present work aimed to identify different forms of phosphorus in the Caspian Sea sediments and their relations with environmental factors.
Material and methods
Surface-sediment sampling was conducted at 12 stations along four transects (3 stations at each transect) using a Van Veen Grab in autumn 2015. For chemical differentiation of phosphorus, sediments were firstly sieved through a mesh-size screen of 63 μm and then 0.5 g freeze dried sediment of each sample in 50 ml extractant were analyzed using Ruttenberg method (Ruttenberg, 1992). In each phase and after extraction, samples were centrifuged at 4000 rpm for 20 minutes and phosphorus content was measured according to the method of molybdenum blue/ascorbic acid (Murphy and Riley, 1962) at 880 nm wavelength using a UV-VIS spectrophotometer.
Results
In this study, the lowest and the highest level of loosely-P was found at stations 1 and 7, respectively, ranging from 35 to 55 ppm (Table 1). The average amount of loosely-P in the studied sites was 46.42±7.10 ppm. Loosely-P proportion to total phosphorus load (%) was least at station 1 (7.02) and most at station 7 (10.09). Also, mean percentage of loosely-P load from all sites was 8.68±1.12 %. No significant difference was observed in loosely-P at various depths (P>0.05) (Table 2).
In the present trial, this form of phosphorus ranged from 50 to 94 ppm with an average value of 73.50±14.59 ppm (Table 1), as its greatest and least proportions were discovered at stations 8 (15.96%) and 6 (10.73%), respectively. Proportionally, iron-bound P at the whole stations averaged 13.68±1.97%. In addition, Iron-bound P content indicated no significant difference at various depths (P>0.05) (Table 2). Authigenic-P was most at station 2 and least at station 4 (Table 1) but the lowest content of this phosphorus as proportion to total phosphorus load (%) was detected at station 8 while the highest content was seen at station 3. Average amount of this ratio was 29.61±3.11 %. The lowest and the highest amount of detrital-P to total phosphorus ratio was 29.78 % and 37.22 %, respectively, with a mean value of 33.18±2.59 %. Organic-P content in the present investigation showed a range of 62-99 ppm, with the lowest amount at station 7 and the highest at station 11
(Table 1). This phosphorus range was 431-594 ppm with an average amount of 535.25±45.05 ppm (Table 1). In the present trial, inorganic-P ranged from 365 to 522 ppm with the lowest at station 2 and the highest at station 11. Inorganic-P was the most abundant form of phosphorus in sediments of the studied area as it comprised 81.90 to 88.53% of total phosphorus. In the current research, the ratio of TOC to OP ranged from 264.23 to 495.6 with the lowest content at station 11 and the highest at station 7. The present investigation revealed bioavailable-P content in a range of 153-240 ppm with the highest and the lowest levels at station 11 and 4, respectively, and average value of 199.41±25 ppm. The largest proportion of bioavailable-P to total phosphorus (%) was detected at station 8 while it was least at station 6. Bioavailable-P proportion throughout the studied sites ranged from 32.57 % to 42.65% with mean level of 37.21±3 %.
Table 1 general characteristics of sediments and content of different forms of phosphorus sampled in the Southern Caspian Sea
Table 2 Comparison of different forms of P concentrations (average ±SD) in different depths
Depth
a 68.25±14.31 144.25±13.60 171.25±22.23 75.25±13.25 428.50±53.90 188±23.81 503.75±54.93 10 47.50±6.19 a 79.25±15.39 160.25±20.61 178.25±11.15 93.00±5.35 b 465.50±24.62 220.25±21.66 558.50±28.20
15 47.00±6.06 a 73.00±16.06 169.75±11.76 183.75±32.40 70.00±4.69 a 473.50±36.41 190±18.85 543.50±38.65
Different letters in each column indicate significant difference in each column (P<0.05) Discussion
Total-P load changes in different marine ecosystems and is affected by sedimentation rate and primary production. Sediment phosphorus content comprises of inorganic and organic phosphorus.
Generally, phosphorus is discharged into marine environments either directly from the atmosphere or via rivers. Atmospheric transport is markedly considered in oceanic areas and off-shore.Total-P load was least at station 4 and greatest at stations 9 and 11. Total-P load obtained in this research was compared with other regions which indicated a higher content rather than some areas but also less than the others. Furthermore, in a previous research by Samadi-Maybodi et al. (2013), the range of total sediment phosphorus was from 124.5 to 328.2 ppm which was less than the one obtained at the present investigation in the studied area.
The application of element ratio in order to determine organic matter origination is regarded as one
1300, the organic matter comes from plants with soft tissue; more than 1300 from wooden tissue;
and in the range of 7-80 reveals that it belongs to bacterial community (Ruttenberg and Goni 1997).
According to TOC/OP ratio, organic matter in sediment of the studied stations proposed a land source.
Acknowledgements
We are grateful to Mr. Neyestani and Mr. Shirzadi for valuable helps regarding the present study.
References
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Mar.Geol. 139, 123–145.
Numerical modeling of long waves in the Caspian Sea A.Yu. Medvedeva
1, E.A. Kulikov
1, I.P. Medvedev
1,21
P.P. Shirshov Institute of Oceanology RAS, Moscow, Russian Federation
2 Fedorov Institute of Applied Geophysics, Moscow, Russian Federation
Keywords: the Caspian Sea, long waves, tsunami, seiche, storm surge, tide, numerical
modelling
Introduction
In the present study results of the numerical modeling of the long waves in the Caspian Sea are presented. The main types of these waves are tides, storm surges, seiches, and tsunami. All mentioned processes are well reproduced by 2D numerical models, which are based on the equations of motion averaged by depth in the longwave approximation. The modeled results were compared with measurements of the sea level of the Caspian Sea.
Materials and methods