تغییرات مکانی و زمانی زیستگاه های ساحلی خلیج گرگان تحت تأثیر نوسانات دریای خزر

نوع مقاله : مقاله پژوهشی

نویسنده

استادیار مؤسسه تحقیقات آب، وزارت نیرو

10.22131/sepehr.2020.47885

چکیده

گرمایش زمین و افزایش سطح تراز آب اقیانوس ها تهدید جدی برای محیط زیست تالاب های ساحلی می باشد.  عکس العمل محیط زیستی بزرگترین دریاچه کره زمین در مقابل عوامل اقلیمی طی هفتاد سال اخیر به گونه ای رقم خورده است که کاهش سطح تراز آب دریای خزر موجب خشک شدن سطح وسیعی از تالاب های ساحلی شده است.  هدف اصلی این پژوهش، ارزیابی تغییرات بوم شناختی زیستگاه های ساحلی مهم خلیج گرگان طی سال های 1995 تا 2019 میلادی میباشد.  با آنالیز تصاویر ماهواره ای لندست و پردازش نتایج داده ها در محیط سامانه اطلاعات جغرافیایی نرخ تغییرات خطوط ساحلی، وضعیت عمق بستر، تبدیل پوشش زمین و تغییر زیستگاه های ساحلی خلیج گرگان محاسبه و طبقه بندی گردید و نتایج به دست آمده با شواهد میدانی صحت سنجی شد.  نتایج مطالعات نشان داد که با کاهش  150 سانتی متری سطح تراز آب دریای خزر طی سال های 1995  تا 2019  میلادی، وسعت خلیج گرگان به میزان  176 کیلومتر مربع کاهش یافته است.  نقشه عمق نسبی حاصل از مطالعات شبیه سازی در سنجش از دور نشان می دهد که عمق بستر خلیج در راستای شرق به غرب به شدت کاهش یافته است.  مهم ترین عوارض زمین و زیستگاه های ساحلی خلیج گرگان و درصد فراوانی پوشش آن ها در سال  2019  میلادی شامل خاکریز ساحلی (2 %) مارش شور (7 %)، مارش لب شور (14 %)، تالاب کم عمق (15 %)، پهنههای گلی (7 %)، پوشش گیاهی جنگلی (10 %) و آبگیر خلیج گرگان و تالاب میانکاله  0.45 %) بود.  همچنین مساحت زیستگاه های تالابی، پوشش گیاهی جنگلی و خاکریز ماسه ای با افت سطح تراز آب دریای خزر دچار کاهش شده بود در عوض به وسعت زیستگاه های مارش لب شور، شور، پهنههای گلی و پیت زارها افزوده شده بود.  این موضوع به خوبی جایگزینی بوم سازگان های خشک زی و نیمه آبزی را در قلمرو بوم سازگان آبزی تأیید می کند که نوسانات سطح تراز آب دریای خزر تأثیر مستقیم بر روی تغییرات محیط زیستی تالاب های ساحلی داشته است. 

کلیدواژه‌ها


عنوان مقاله [English]

Spatial and temporal variations of Coastal habitats in Gorgan Bay resulting from fluctuations in the Caspian Sea

نویسنده [English]

  • Homayoun Khoshravan
Assistant professor of water research institute Caspian Sea national research and study center
چکیده [English]

Extended Abstract:
Introduction
Increased density of Co2 in the atmosphere during the Anthropocene epoch has resulted in pervasive concerns for the global environment. Global warming has resulted in sea level rise and coastal flooding. Forecasting has indicated that a vast area of coastal countries and their economic and social infrastructureswill be damaged due to 200 cm sea level rise by2100. Sea level rise in oceans has caused coastal erosion and flooding. Thus, it is considered as a real threat to coastal environment. The Caspian Sea environment has reacted differently to climate changesduring the last 70 years and vast areas of its coastal lagoons have dried. Therefore, the present study primarily seeks toinvestigate ecological variations of coastal habitats in the Gorgan Bay during the period of 1995 to 2019.
 Materials and methods
Gorgan Bay and Miankaleh Lagoon are considered to be among global biosphere reservesand the most important protected areasalong the southern coasts of the Caspian Sea. The present study has evaluated coastal variations, such as shoreline displacement, changes in the depth of sea bed, land cover and coastal habitats using satellite images and GIS processing. Shorelines of Gorgan Bay are determined usingremote sensing software Envi 5.3, while land cover and coastal habitats are evaluated through GIS processing in Arc – Map 10. 5. The shoreline is determined through the calculationsperformedonthe proportion of green and blue bands in reflected electromagnetic waves and histogram thresholding of near infrared (NIR) spectrum in Envi 5.3. The total area of Gorgan Bay was determinedusingthe Normalized Distance Water Index (NDWI).The most important land covers and coastal habitats are classified using Support Vector Machine (SVM). Finally,variations of coastal habitats are calculated using Change Detection Workflow index and the final maps areproduced in Arc Map 10.5.
 Results and discussion
Results indicate that due to about 150 cm decrease in the Caspian Sea level from 1995 to 2019, the total area ofGorgan Bay has faced about 176 km decrease. Bathymetric maps shows that the depth of Gorgan Bay has decreased dramatically along the East to west side. The depth of the Ashouradeh and Chopoghlei inlets have also decreased and vast areas of these water bodies haveturned into arid islands. The Gorgan Bay is connected to the Caspian Sea through some narrow channels. The most important land covers and coastal habitats of the Gorgan Bay in 2019 include sandy beach (2%), salt marsh (7%), brackish marsh (14%), wetland (15%), mudflat (7%), coastal forest (10%) and coastal lagoons (45%). The total area of coastal lagoons, vegetation covering and sandy beaches have decreased from 1995 to 2019 and the area of the brackish marsh, salt marsh, mud flat and pit wetlands have increased at the same time. The total area of sandy beaches have decreased about 52 Km2 since 1995.Instead,the area covered by salt marshes and brackish marshes have increased by about 87 and 60 Km2 during the same period.62 Km2 of mud flat have been created during the same time,and thus, the area of Miankaleh Lagoon and Gorgan Bay have decreased by about 176 Km2. The environment of Gorgan Bay and Miankaleh Lagoon is directly related to the fluctuations in theCaspian Sea level. Survival of these coastal lagoons depends on permanent water exchange between the Caspian Sea and Gorgan Bay. Rapid fluctuations of the Caspian Sea level and high levelof deposition are considered to be among the most important factorsof coastal habitats destruction and ecosystems displacement. These natural phenomena happened twice during the Anthropocene period (1945- 1978 and 1995-2019).
 Conclusion
Results have confirmed that arid ecosystems have replaced aquatic ecosystems in study area. The main results of the study have confirmed that the fluctuation in the Caspian Sea level has direct impact on coastal habitats of the study area and decreasing sea level could change marginal ecosystems. Due to the decrease in water exchange volume rate between the Caspian Sea and Gorgan Bay during the 1995- 2019 period, a 32 percent decrease has happened in the area ofGorgan Bay and salt marshes have dominated along the Gorgan Bay coastal area. Unfortunately, the continual decrease inthe Caspian Sea level can destroy biodiversity and coastal habitats in the future. Therefore,integrated coastal zone management (ICZM (is influential insaving and preserving of the Gorgan Bay.

کلیدواژه‌ها [English]

  • Caspian Sea
  • Gorgan Bay
  • environment
  • GIS and Remote sensing
  • Fluctuation
  • Habitats
1.خوشروان، ه.، وفایی، ب. (1395). نوسانات سطح تراز آب دریای خزر  (گذشته، حال، آینده)،هجدهمین کنفرانس بین المللی صنایع دریایی، جزیره کیش.
2.سازمان بنادر و دریانوردی (1393). گزارش مطالعه هیدرودینامیک خلیج گرگان، مهندسین مشاور شرکت طرح پویا پارس،  240 صفحه.
3.   Aarón M. Santana-Corderoa, María L. Monteiro-Quintanab, Luis Hernández-Calvento Reconstruction of the land uses that led to the termination of an arid coastal dune system: The case of the Guanarteme dune system(Canary Islands, Spain), 1834–2012, Land Use Policy 55 (2016) 73–85
4.   Afshin, A 2004, Iranian Rivers report, Ministry of energy, Jamab company, internal report, Vol. 2, 251 Pages (In Persian).
5.   Alesheikh, A., A., Ghorbanali, A., Nouri, N., 2007, Coastline change detection using remote sensing, Int. J. environment. Sci. Tech. 4 (1) 61-66
6.   Amini, A., 2012, Holocene sedimentation rate in Gorgan Bay and adjacent coasts in southeast of Caspian Sea, Journal of basic and applied scientific research, 2(1)289-297
7.   Barbier, E.B., Hacker, S.D., Kennedy, C., Koch, E.W., Stier, A.C. & Silliman, B.R. (2011). The value of estuarine and coastal ecosystem services, Ecological Monographs, 81(2), 169-193.
8.   Cahoon, D. (2007). Factors affecting coastal wetland loss and restoration.Synthesis of U.S. Geological Survey science for the Chesapeake Bay ecosystem and implications for environmental management. S. W. Phillips, editor. Department of the Interior, US Geological Survey, Laurel, MD, USA, 50–53.
9.   Church, J.A., Clark, P.U., Cazenave, A., Gregory, J.M., Jevrejeva, S., Levermann, A., Merrifield, M.A., Milne, G.A., Nerem, R.S., Nunn, P.D., Payne, A.J., Pfeffer, W.T., Stammer D. and Unnikrishnan, A.S. (2013). Sea Level Change Supple­mentary Material. In: Climate Change 2013, The Physical Science Basis, Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Available from www.climat­echange2013.org and www.ipcc.ch.
10. Costanza, R., d’Arge, R., de Groot, R., Farber, S., Grasso, M., Hannon, B., Limburg, K., Naeem, Sh., V. O’Neill, R., Paruelo, J., G. Raskin, R., Sutton, P. and van den Belt, M. (1997). The value of the world’s ecosystem services and natural capital. Nature, 387, 253–260.
11. Dame, R.F. and Gardner, L.R. (1993). Nutrient processing and the development of tidal creek ecosystems. Marine Chemistry, 43, 175–183.
12. Davidson, N.C., Fluet- Chouinard, E. & Finlayson, C.M. (2018). Global extent and distribution of wetlands: trends and issues. Marine and Freshwater Research, doi.org/10.1071/MF17019.
13. Feng, S., Hu, Q., Huang, W., HoiHo, Ch., Li, R. and Tange, Zh. (2014). Projected climate regime shift under future global warming from multi- model and multi scenario CMIP5 simulation, Global and planetary change, Vol. 112, 41- 52.
14. Hoogendoorn, R. M., Boels., J. F., Kroonenberg, S. B., Simmons, M. D., Aliyeva, E., Babazadeh, A. D. &Huseynov, D. (2005), Development of the Kura delta, Azerbaijan; a record of Holocene Caspian Sea-level changes, Marine Geology, 222–223, 359–380.
15. Kakroodi, A. A., S. B. Kroonenberg, R. M. Hoogendoorn, H. MohammdKhani, M. Yamani, M. R. Ghassemi& H. A. K. Lahijani, 2012b, Rapid Holocene sea level changes along the Iranian Caspian coast. Quaternary International, 263: 93-103
16. Kaplan, D., Munoz-Carpena, R., Wan, Y., Hedgepeth, M., Zheng, F., Roberts, R. and Rossmanith. R. (2010). Linking river, floodplain, and vadose zone hydrology to improve restoration of a coastal river affected by saltwater intrusion. Journal of Environmental Quality, 39, 1570–1584.
17. Kaplin, P.A. &Selivanov, A.O. (1995). Recent coastal evolution of the Caspian Sea as a natural model for coastal response to the possible acceleration of global sea-level rise. Marine Geology, 124, 161-175.
18. Kazama, P., S. and Sawamoto, M. 2006. Effects of climate and land use changes on groundwater resources in coastal aquifers. Journal of Environmental Management 80: 25–35.
19. Khoshravan and Jabbari, 2015, Reconstructing the past fluctuations of Urmia Lake, International Journal of Marine Science, Vol.5, No.31 1-6 (doi: 10.5376/ijms.2015.05.0031)
20. Khoshravan, H. and Vafai, B., 2016, Caspian Sea level fluctuations (past, recent and future), the 18th international marine industries conference, Kish Island, Persian Gulf, Iran (In Persian).
21. Khoshravan, H. Naqinejad, A. 2018. International conference of Environmental consequence of Caspian rapid sea level changing in GorganBay,understanding the problems of inland waters: case study for the Caspian basin (UPCB) 12-14 May 2018 Baku, Azerbaijan,pp: 314- 317
22. Khoshravan,H, Naqinezhad, A , Alinejad-Tabrizi, T, Yanina,T. 2019, Gorgan Bay environmental consequences due to the Caspian Sea rapid water level change, Caspian J. Environ. Sci. Vol. 17 No. 3 pp. 213~226, DOI: 10.22124 / CJES.2019.3664
23. Kostianoy, A. G. &Kosarev, A. N. (2014). The Caspian Sea Environment, 278, 18- 48, Geographic Department, Lomonosov Moscow State University, Vorobievy Gory, 119992 Moscow, Russia.
24. Kroonenberg, SB, Badyukova, EN, Storms, JEA, Ignatov, EI&Kasimov, NS 2000, a full sea level cycle in 65 years: barrier dynamics along Caspian shores, Sedimentary Geology, 134, pp. 257-274.
25. Lahijani, H, HaeriArdakani, O, Sharifi, A, NaderiBeni, A 2010, Sedimentological and geochemical characteristics of Gorgan Bay sediments, the journal of oceanography, No. 1, pp. 45- 55 (In Persian).
26. Moore, L.J., (2000). Shoreline mapping techniques. J. Coast. Res., 16 (1), 111-124.
27. NaderiBeni, A. (2013). Caspian Sea-level changes during the last millennium: historical and geological evidence from the south Caspian Sea, Clim. Past, 9, 1645–1665.
28. Nazarali, M, JandaghiAlaee, M &Pattiaratchi, Ch 2014, Estimation of atmospheric pressure anomaly using Acoustic Doppler Current Profiler (ADCP). 11th International Conference on Coasts, Ports and Marine Structures, Tehran, Iran, 103-107 (In Persian).
29. Nicholls, R. J., Hoozemans, F. M. and Marchand, M. (1999). Increasing flood risk and wetland losses due to global sea-level rise: regional and global analyses. Global Environmental Change, 9, 69–87.
30. Port and maritime organization (PMO), 2014, Hydrodynamic study on Gorgan Bay, 240 pages (In Persian).
31. Ramsar Convention Secretariat.(2018). Global wetland outlook state of the world wetlands and their services to people. Gland, Switzerland: Ramsar Convention Secretariat
32. Rojas, C., Pino, J., Basnou, C., Vivanco, M., 2013, Assessing land-use and -cover changes in relation to geographic factors and urban planning in the metropolitan area of Concepción (Chile). Implications for biodiversity conservation,  Applied Geography 39 93-103
33. Saeidi, Sh, Naghinejad, AR &Kazemi-Gorji, Z 2014, Investigation of vegetation changes and diversity of habitats of coastal of Miankaleh biosphere using ecological transects. Journal of Natural Environment (Iranian Journal of Natural Re sources), 68: 67-82
34. Saunders, M., Leon, J., Phinn, S. R., Callaghan, D., O’Brien, K. R., Roelfsema, C. M., Lovelock, C. E., Lyons, M. and Mumby, P. J. (2013). Coastal retreat and improved water quality mitigate losses of seagrass from sea level rise, Global Change Biology, 19, 2569–2583.
35. Sharbati, S &Ghanghermeh, A 2015, the forecasting of Impacts of the Caspian Sea level decreasing on Gorgan Bay, the Journal of science and technology of environment, No. 4, pp. 33-45 (In Persian).
36. Short, F.T., Polidoro, B., Livingstone, S.R., Carpenter, K.E., Bandeira, S., …,Waycott, M. &Zieman, J.C. (2011). Extinction risk assessment of the world’s seagrass species. Biological Conservation, 144(7), 1961-1971.
37. Slangen ABA, Katsman CA, Van deWal R, Vermeersen L, Riva R. 2012. Towards regional projections of twenty-first century sea-level change based on IPCC SRES scenarios. Climate Dynamics 38:1191–1209 DOI 10.1007/s00382-011-1057-6.
38.          Winarso, G., Budhiman, S., (2001). The potential application of remote sensing data for coastal study, Proc. 22nd.Asian Conference on Remote Sensing, Singapore. Available on: http://www.crisp.nus.edu.sg/~acrs2001.