[en] The Black Sea northwestern shelf (NWS) is a shallow eutrophic area in which the seasonal stratification of the water column isolates the bottom waters from the atmosphere. This prevents ventilation from counterbalancing the large consumption of oxygen due to respiration in the bottom waters and in the sediments, and sets the stage for the development of seasonal hypoxia.
A three-dimensional (3-D) coupled physical–biogeochemical model is used to investigate the dynamics of bottom hypoxia in the Black Sea NWS, first at seasonal and then at interannual scales (1981–2009), and to differentiate its driving factors (climatic versus eutrophication).
Model skills are evaluated by a quantitative comparison of the model results to 14 123 in situ oxygen measurements available in the NOAA World Ocean and the Black Sea Commission databases, using different error metrics. This validation exercise shows that the model is able to represent the seasonal and interannual variability of the oxygen concentration and of the occurrence of hypoxia, as well as the spatial distribution of oxygen-depleted waters.
During the period 1981–2009, each year exhibits seasonal bottom hypoxia at the end of summer. This phenomenon essentially covers the northern part of the NWS – which receives large inputs of nutrients from the Danube, Dniester and Dnieper rivers – and extends, during the years of severe hypoxia, towards the Romanian bay of Constanta.
An index H which merges the aspects of the spatial and temporal extension of the hypoxic event is proposed to quantify, for each year, the intensity of hypoxia as an environmental stressor.
In order to explain the interannual variability of H and to disentangle its drivers, we analyze the long time series of model results by means of a stepwise multiple linear regression. This statistical model gives a general relationship that links the intensity of hypoxia to eutrophication and climate-related variables.
A total of 82% of the interannual variability of H is explained by the combination of four predictors: the annual riverine nitrate load (N), the sea surface temperature in the month preceding stratification (Ts), the amount of semi-labile organic matter accumulated in the sediments (C) and the sea surface temperature during late summer (Tf). Partial regression indicates that the climatic impact on hypoxia is almost as important as that of eutrophication.
Accumulation of organic matter in the sediments introduces an important inertia in the recovery process after eutrophication, with a typical timescale of 9.3 yr.
Seasonal fluctuations and the heterogeneous spatial distribution complicate the monitoring of bottom hypoxia, leading to contradictory conclusions when the interpretation is done from different sets of data. In particular, it appears that the recovery reported in the literature after 1995 was overestimated due to the use of observations concentrated in areas and months not typically affected by hypoxia. This stresses the urgent need for a dedicated monitoring effort in the Black Sea NWS focused on the areas and months concerned by recurrent hypoxic events.
Disciplines :
Earth sciences & physical geography
Author, co-author :
Capet, Arthur ; Université de Liège - ULiège > Département de Biologie, Ecologie et Evolution > Océanologie
Beckers, Jean-Marie ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > GeoHydrodynamics and Environment Research (GHER)
Grégoire, Marilaure ; Université de Liège - ULiège > Département de Biologie, Ecologie et Evolution > Océanologie
Language :
English
Title :
Drivers, mechanisms and long-term variability of seasonal hypoxia on the Black Sea northwestern shelf – is there any recovery after eutrophication?
Publication date :
2013
Journal title :
Biogeosciences
ISSN :
1726-4170
eISSN :
1726-4189
Publisher :
European Geosciences Union, Katlenburg-Lindau, Germany
Allen, J. I., Somerfield, P., and Gilbert, F.: Quantifying uncertainty in high-resolution coupled hydrodynamic-ecosystem models, J. Marine Syst., 64, 3-14, doi:10.1016/j.jmarsys.2006.02.010, 2007.
Beckers, J.-M.: Application of the GHER 3D general circulation model to the Western Mediterranean, J. Marine Syst., 1, 315-332, doi:10.1016/0924- 7963(91)90001-B, 1991.
Beckers, J.-M., Grégoire, M., Nihoul, J. C., Stanev, E., Staneva, J., and Lancelot, C.: Modelling the Danube-influenced Northwestern Continental Shelf of the Black Sea. I: Hydrodynamical Processes Simulated by 3-D and Box Models, Estuar. Coast. Shelf S., 54, 453-472, doi:10.1006/ecss.2000.0658, 2002.
Boesch, D., Brinsfield, R., and Magnien, R.: Chesapeake Bay eutrophication: Scientific understanding, ecosystem restoration, and challenges for agriculture, J. Environ. Qual., 30, 303-320, 2001.
Capet, A., Barth, A., Beckers, J.-M., and Grégoire, M.: Interannual variability of Black Sea's hydrodynamics and connection to atmospheric patterns, Deep-Sea Res. Pt. II, 77-80, 128-142, doi:10.1016/j.dsr2. 2012.04.010, 2012.
Cardoso, A., Cochrane, S., Doemer, H., Ferreira, J., Galgani, F., Hagebro, C., Hanke, G., Hoepffner, N., Keizer, P., Law, R., Olenin, S., Piet, G., Rice, J., Rogers, S., Swartenbroux, F., Tasker, M., and Van de Bund, W.: Scientific Support to the European Commission on the Marine Strategy Framework Directive, vol. 24336, Publications Office of the European Union, Luxembourg, 2010.
Cauwet, G., Déliat, G., Krastev, A., Shtereva, G., Becquevort, S., Lancelot, C., Momzikoff, A., Saliot, A., Cociasu, A., and Popa, L.: Seasonal DOC accumulation in the Black Sea: a regional explanation for a general mechanism, Mar. Chem., 79, 193-205, 2002.
Chen, C., Gong, G., and Shiah, F.: Hypoxia in the East China Sea: One of the largest coastal low-oxygen areas in the world, Mar. Environ. Res., 64, 399-408, 2007.
Conley, D. J., Carstensen, J., Ærtebjerg, G., Christensen, P. B., Dalsgaard, T., Hansen, J. L. S., and Josefson, A. B.: Long- Term Changes and Impacts of Hypoxia in Danish Coastal Waters, Ecol. Appl., 17, S165-S184, http://www.jstor.org/stable/ 40061824, 2007.
Conley, D. J., Carstensen, J., Vaquer-Sunyer, R., and Duarte, C. M.: Ecosystem thresholds with hypoxia, Hydrobiologia, 629, 21-29, doi:10.1007/s10750-009-9764-2, 2009.
Delhez, E.: Reconnaissance of the general circulation of the North- Western European Continental Shelf by means of a threedimensional turbulent closure model, Earth Sci. Rev., 41, 3-29, doi:10.1016/0012-8252(96)00012-8, 1996.
Diaz, R. J.: Overview of hypoxia around the world, J. Environ. Qual., 30, 275-281, 2001.
Diaz, R. J. and Rosenberg, R.: Spreading Dead Zones and Consequences for Marine Ecosystems, Science, 321, 926-929, doi:10.1126/science.1156401, 2008.
Ekau, W., Auel, H., Pörtner, H.-O., and Gilbert, D.: Impacts of hypoxia on the structure and processes in pelagic communities (zooplankton, macro-invertebrates and fish), Biogeosciences, 7, 1669-1699, doi:10.5194/bg-7-1669-2010, 2010.
Friedl, G., Dinkel, C., and Wehrli, B.: Benthic fluxes of nutrients in the northwestern Black Sea, Mar. Chem., 62, 77-88, 1998.
Friedrich, J., Dinkel, C., Friedl, G., Pimenov, N., Wijsman, J., Gomoiu, M.-T., Cociasu, A., Popa, L., andWehrli, B.: Benthic nutrient cycling and diagenetic pathways in the north-western Black Sea, Estuar. Coast. Shelf S., 54, 369-383, 2002.
Grégoire, M., Beckers, J.-M., Nihoul, J. C., and Stanev, E.: Reconnaissance of the main Black Sea's ecohydrodynamics by means of a 3D interdisciplinary model, J. Marine Syst., 16, 85-105, doi:10.1016/S0924-7963(97) 00101-2, 1998.
Grégoire, M., Soetaert, K., Nezlin, N., and Kostianoy, A. G.: Modeling the nitrogen cycling and plankton productivity in the Black Sea using a three-dimensional interdisciplinary model, J. Geophys. Res.-Oceans, 109, C05007, doi:10.1029/2001JC001014, 2004.
Grégoire, M., Raick, C., and Soetaert, K.: Numerical modeling of the central Black Sea ecosystem functioning during the eutrophication phase, Progr. Oceanogr., 76, 286-333, doi:10.1016/j.pocean.2008.01.002, 2008.
Hagy III, J. D. and Murrell, M. C.: Susceptibility of a northern Gulf of Mexico estuary to hypoxia: An analysis using box models, Estuar. Coast. Shelf S., 74, 239-253, doi:10.1016/j.ecss.2007.04.013, 2007.
Ho, D., Law, C., Smith, M., Schlosser, P., Harvey, M., and Hill, P.: Measurements of air-sea gas exchange at high wind speeds in the Southern Ocean: Implications for global parameterizations, Geophys. Res. Lett., 33, 16611, doi:10.1029/2006GL026817, 2006.
Kanakidou, M., Duce, R. A., Prospero, J. M., Baker, A. R., Benitez- Nelson, C., Dentener, F. J., Hunter, K. A., Liss, P. S., Mahowald, N., Okin, G. S., Sarin, M., Tsigaridis, K., Uematsu, M., Zamora, L. M., and Zhu, T.: Atmospheric fluxes of organic N and P to the global ocean, Global Biogeochem. Cy., 26, GB3026, doi:10.1029/2011GB004277, 2012.
Kara, A. B., Helber., R. W., Boyer, T. P., and Elsner, J. B.: Mixed layer depth in the Aegean, Marmara, Black and Azov Seas: Part 1: General Features, J. Mar. Syst., 78, S169-S180, 2009.
Kemp, W. M., Testa, J. M., Conley, D. J., Gilbert, D., and Hagy, J. D.: Temporal responses of coastal hypoxia to nutrient loading and physical controls, Biogeosciences, 6, 2985-3008, doi:10.5194/bg-6-2985-2009, 2009.
Kostylev, E. F., Tkachenko, F. P., and Tretiak, I. P.: Establishment of Zernov's Phyllophora field marine reserve : Protection and restoration of a unique ecosystem, Ocean Coast. Manage., 53, 203-208, doi:10.1016/j.ocecoaman. 2010.04.010, 2010.
Langmead, O., McQuatters-Gollop, A., Mee, L., Friedrich, J., Gilbert, A. J., Gomoiu, M.-T., Jackson, E. L., Knudsen, S., Minicheva, G., and Todorova, V.: Recovery or decline of the northwestern Black Sea: A societal choice revealed by socio-ecological modelling, Ecol. Model., 220, 2927-2939, doi:10.1016/j.ecolmodel.2008.09.011, 2009.
Legendre, P. and Legendre, L.: Numerical Ecology, in: Developments in Environmental Modelling, vol. 20, Elsevier, doi:10.1016/S0167-8892(98)80062-6, 1998.
Levin, L. A., Ekau,W., Gooday, A. J., Jorissen, F., Middelburg, J. J., Naqvi, S.W. A., Neira, C., Rabalais, N. N., and Zhang, J.: Effects of natural and human-induced hypoxia on coastal benthos, Biogeosciences, 6, 2063-2098, doi:10.5194/bg-6-2063-2009, 2009.
Ludwig, W., Dumont, E., Meybeck, M., and Heussner, S.: River discharges of water and nutrients to the Mediterranean and Black Sea: Major drivers for ecosystem changes during past and future decades?, Progr. Oceanogr., 80, 199-217, doi:10.1016/j.pocean.2009.02.001, 2009.
Mee, L.: Reviving dead zones, Sci. Am., 295, 78-85, 2006.
Mee, L., Friedrich, J., and Gomoiu, M.-T.: Restoring the Black Sea in times of uncertainty, Oceanography, 18, 32-43, 2005.
Naqvi, S.W. A., Bange, H.W., Farías, L., Monteiro, P. M. S., Scranton, M. I., and Zhang, J.: Marine hypoxia/anoxia as a source of CH4 and N2O, Biogeosciences, 7, 2159-2190, doi:10.5194/bg- 7-2159-2010, 2010.
Peña, M. A., Katsev, S., Oguz, T., and Gilbert, D.: Modeling dissolved oxygen dynamics and hypoxia, Biogeosciences, 7, 933- 957, doi:10.5194/bg-7-933-2010, 2010.
Rabalais, N. N., Díaz, R. J., Levin, L. A., Turner, R. E., Gilbert, D., and Zhang, J.: Dynamics and distribution of natural and humancaused hypoxia, Biogeosciences, 7, 585-619, doi:10.5194/bg-7- 585-2010, 2010.
Reschke, S., Ittekkot, V., and Panin, N.: The nature of organic matter in the Danube River particles and north-western Black Sea sediments, Estuar. Coast. Shelf S., 54, 563-574, 2002.
Slomp, C. P. and Van Cappellen, P.: The global marine phosphorus cycle: sensitivity to oceanic circulation, Biogeosciences, 4, 155-171, doi:10.5194/bg-4-155-2007, 2007.
Soetaert, K., Middelburg, J. J., Herman, P. M., and Buis, K.: On the coupling of benthic and pelagic biogeochemical models, Earth Sci. Rev., 51, 173-201, doi:10.1016/S0012-8252(00)00004-0, 2000.
Stanev, E. V. and Beckers, J.-M.: Numerical simulations of seasonal and interannual variability of the Black Sea thermohaline circulation, J. Mar. Syst., 22, 241-267, 1999.
Stanev, E. and Kandilarov, R.: Sediment dynamics in the Black Sea: numerical modelling and remote sensing observations, Ocean Dynam., 62, 533-553, doi:10.1007/s10236-012-0520-1, 2012.
Steckbauer, A., Duarte, C. M., Carstensen, J., Vaquer-Sunyer, R., and Conley, D. J.: Ecosystem impacts of hypoxia: thresholds of hypoxia and pathways to recovery, Environ. Res. Lett., 6, 025003, doi:10.1088/1748-9326/6/2/025003, 2011.
Stow, C., Jolliff, J., McGillicuddy, D., Doney, S., Allen, J. I., Friedrichs, M., Rose, K., and Wallhead, P.: Skill assessment for coupled biological/physical models of marine systems, J. Mar. Syst., 76, 4-15, 2009.
Turner, R. E., Rabalais, N. N., and Justic, D.: Gulf of Mexico hypoxia: Alternate states and a legacy, Environ. Sci. Technol., 42, 2323-2327, 2008.
Turner, R., Rabalais, N., and Justić, D.: Predicting summer hypoxia in the northern Gulf of Mexico: Redux, Mar. Pollut. Bull., 64, 319-324, doi:10.1016/j.marpolbul.2011.11.008, 2012.
UkrSCES: State of the Black Sea Environment, National report of Ukraine, 1996-2000, Astroprint, Odessa, 2002.
Vaquer-Sunyer, R. and Duarte, C. M.: Thresholds of hypoxia for marine biodiversity, P. Natl. Acad. Sci., 105, 15452-15457, 2008.
Walling, D. and Fang, D.: Recent trends in the suspended sediment loads of the world's rivers, Global Planet. Change, 39, 111-126, doi:10.1016/S0921- 8181(03)00020-1, 2003.
Wijsman, J. W., Herman, P. M., and Gomoiu, M.-T.: Spatial distribution in sediment characteristics and benthic activity on the northwestern Black Sea shelf, Mar. Ecol.-Prog. Ser., 181, 25-39, 1999.
Zaitsev, Y.: Impact of eutrophication on the Black Sea fauna, Tech. Rep. 64, General Fisheries Council for the Mediterranean, FAO, Rome, 1993.
Zaitsev, Y.: Marine biological diversity in the Black Sea : A study of change and decline, in: Black Sea environmental series, vol. 3, United Nation Publications, New York, 1997.
Zernov, C.: The Fauna of Phyllophora (Algae, Rhodophyceae) of Phyllophora field in North-Western part of Black Sea, Zool. muzeum Annual.-Academy of Science of the USSR, 3-4, 1909.
Zhang, J., Gilbert, D., Gooday, A. J., Levin, L., Naqvi, S. W. A., Middelburg, J. J., Scranton, M., Ekau, W., Peña, A., Dewitte, B., Oguz, T., Monteiro, P. M. S., Urban, E., Rabalais, N. N., Ittekkot, V., Kemp, W. M., Ulloa, O., Elmgren, R., Escobar-Briones, E., and Van der Plas, A. K.: Natural and human-induced hypoxia and consequences for coastal areas: synthesis and future development, Biogeosciences, 7, 1443-1467, doi:10.5194/bg-7-1443- 2010, 2010.