EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Open Access Biogeosciences Discuss., 10, 13277–13316, 2013 Open Access www.biogeosciences-discuss.net/10/13277/2013/ Biogeosciences Biogeosciences BGD doi:10.5194/bgd-10-13277-2013 Discussions © Author(s) 2013. CC Attribution 3.0 License. 10, 13277–13316, 2013 Open Access Open Access This discussion paper is/has been under review for the journal BiogeosciencesClimate (BG). Climate Biogeochemical Please refer to the correspondingof finalthe Past paper in BG if available. of the Past Discussions characterization of the riverine organic Open Access Open Access matter BiogeochemicalEarth System characterization Earth ofSystem the Dynamics Dynamics M. Higueras et al. riverine organic matter transferredDiscussions to the Open Access Geoscientific Geoscientific Open Access NW Mediterranean Sea Title Page Instrumentation Instrumentation Methods and Methods and Abstract Introduction M. Higueras1,2, P. Kerherve´ 1,2, A. Sanchez-Vidal3, A. Calafat3, W. Ludwig1,2, 1,2 Data Systems1,2 3 Data Systems M. Verdoit-Jarraya , S. Heussner , and M. Canals Discussions Conclusions References Open Access Open Access 1 Geoscientific Univ. Perpignan Via Domitia,Geoscientific Centre de Formation et de Recherche sur les Environnements Tables Figures ´ ´ Model Development Mediterraneens, UMR5110,Model Development 66860, Perpignan, France 2CNRS, Centre de Formation et de Recherche sur les Environnements Mediterran´ Discussionseens,´ UMR5110, 66860, Perpignan, France J I Open Access 3 Open Access GRC Geociencies` Marines,Hydrology Departament and d’Estratigrafia, PaleontologiaHydrology i Geoci encies`and J I Marines, Facultat de Geologia,Earth Universitat System de Barcelona, 08028 Barcelona,Earth System Spain Back Close Received: 19 July 2013 – Accepted:Sciences 23 July 2013 – Published: 8 August 2013Sciences Discussions Full Screen / Esc Open Access Correspondence to: M. Higueras ([email protected])Open Access Published by Copernicus Publications on behalf of the European GeosciencesOcean Science Union. Ocean Science Printer-friendly Version Discussions Interactive Discussion Open Access Open Access 13277 Solid Earth Solid Earth Discussions Open Access Open Access The Cryosphere The Cryosphere Discussions Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract BGD A large amount of terrestrial organic matter is annually delivered by rivers to the con- tinental shelf, where this material is either buried or transferred to the deep sea by 10, 13277–13316, 2013 hydrodynamic processes such as storms. The relative amount of terrestrial organic 5 matter in the marine sediments is often determined by analyzing the stable isotopes Biogeochemical 13 15 (δ C and δ N) and the C/N ratio of organic matter because the various particulate characterization of organic matter (POM) sources have distinct isotopic compositions. With the objective the riverine organic to refine and better interpret POM sources in the marine environment, we have monthly matter characterized terrestrial POM delivered by eight rivers discharging to the NW Mediter- 10 ranean Sea: Rhone,ˆ Herault,´ Orb, Aude, Tet,ˆ Fluvia,` Ter and Tordera rivers. These M. Higueras et al. rivers were simultaneously sampled from November 2008 to December 2009 and the concentrations of total suspended matter (TSM), particulate organic carbon (POC) and nitrogen (PN), as well as their stable isotopic ratios (δ13C and δ15N) were determined. Title Page During the survey, three rainstorm events with winds coming from the E–NE and Abstract Introduction 15 the S–SE impacted the NW Mediterranean. Depending on the direction of incoming winds, the fluvial response (amount of water discharge and TSM) was different. Rivers Conclusions References draining the Alps (Rhoneˆ River) and Central Massif (Herault,´ Orb, and Aude rivers) Tables Figures were mostly impacted by rainstorms associated with winds coming from the S–SE, while rivers draining the Pyrenees (Tet,ˆ Fluvia,` and Ter rivers) and the Montseny Mas- J I 20 sif (Tordera River) were impacted by rainstorms associated with winds coming from the E–NE. In addition, the spatial evolution of water discharges shows different hydro- J I logical regime of the Rhoneˆ River, with relatively constant and high water stages and TSM concentrations when compared to coastal rivers, characterized by long periods Back Close of low water stages. TSM concentrations are positively correlated to water discharges Full Screen / Esc 25 (high water flows resuspended riverbed sediments) but show an inverse relationship with POC and PN relative contents (mostly due to dilution and by low availability of Printer-friendly Version light in river waters during flood events). TSM in most of the coastal rivers have in av- erage 2.5–3 times higher POC and PN mean contents than the Rhoneˆ River (8.5 % Interactive Discussion 13278 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | and 1.5 %, respectively for coastal rivers against 3.6 % and 0.5 %, respectively for the Rhoneˆ River). This discrepancy may be caused by the long drought periods in small BGD coastal Mediterranean watersheds that enhance the eutrophication in studied coastal 10, 13277–13316, 2013 rivers. The δ13C ratios of organic matter reflect also this discrepancy between high 13 5 and low water stages with values ranging from −33.2 ‰ to −24.5 ‰. The enriched C values (−26.3 ± 0.4 ‰ for the Rhoneˆ River and −26.9 ± 1.2 ‰ for coastal rivers), mea- Biogeochemical sured during high water stages, express mostly a mixture of terrestrial source (plant characterization of remains and soils) whereas depleted 13C values (∼ −30 ‰) associated with low water the riverine organic stages exhibit a source with predominant freshwater algae. The high δ15N mean values matter 10 (> 8 ‰) found in Tet,ˆ Ter and Tordera rivers underline the importance of denitrification processes as a consequence of the eutrophication and anthropogenic impact. M. Higueras et al. 1 Introduction Title Page Approximately 87 % of Earth’s land surface is connected to the ocean by rivers (Lud- Abstract Introduction wig and Probst, 1998) which represent the primary pathway for water and particulate Conclusions References 15 matter (mostly lithogenic particles and terrestrial organic matter) to the marine envi- ronment, contributing with 35 000 km3 of freshwater (Milliman, 2001) and 18 GTyr−1 of Tables Figures suspended sediment (Milliman and Syvitski, 1992; Ludwig and Probst, 1998; Syvitski, 2003). These inputs are highly variable over time, shifting from low river discharges J I and low sediment inputs to the occurrence of flood events with high sediment supplies J I 20 (Wheatcroft and Borgeld, 2000). Numerous studies have documented the delivery of sediments to the ocean Back Close from large rivers such as the Amazon (e.g., Nittrouer and DeMaster, 1996), Yellow (Huanghe) (Liu et al., 2002, 2004), Ganges-Brahmaputra (Goodbred and Kuehl, 2000; Full Screen / Esc Kuehl et al., 1997), and Yangtze (Changjiang) (Chen et al., 2001; Liu et al., 2007). 25 However, Milliman and Syvitski (1992) emphasized the importance of smaller rivers Printer-friendly Version (< 5000 km2) and speculated that they may account for as much as half of the present- Interactive Discussion day sediment flux to the oceans. 13279 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | River inputs play a major role in the semi-enclosed Mediterranean Sea, because changes in their inputs are therefore potential drivers for long-term changes in the BGD marine ecosystems (Ludwig et al., 2009). Recent studies have shown that freshwater 10, 13277–13316, 2013 discharges by Mediterranean rivers decreased significantly from about 20 % between 5 1960 and 2000 (Ludwig et al., 2009). This reduction is probably the result of several stress factors including climate change and dam construction (Ludwig et al., 2003). Biogeochemical First, the increase of temperature during the 20th century, in particular since the late characterization of 1970’s (Gulf of Lion: 0.5 ◦Cdecade−1 for 1979–2004; Lespinas et al., 2010) and the the riverine organic decrease of precipitation during certain periods of the year in the upstream water- matter 10 sheds may cause a significant water discharge reduction (Lopez-Moreno´ et al., 2008; Lespinas et al., 2010). Second, rivers are highly affected by the artificial river damming M. Higueras et al. often related to water extractions for irrigation (Ludwig et al., 2003) which alter the nat- ural functioning of Mediterranean rivers. The Nile River is a clear evidence of this, with Title Page a decrease from 40–45 to 15 km3 of freshwater discharge to the Mediterranean Sea 15 after building the Aswan High Dam in 1964 (Schroeder et al., 2012). Abstract Introduction At present, the Rhoneˆ River represents the major source of freshwater and terres- trial particulate matter to the Mediterranean Sea (Margat, 1992; Pettine et al., 1998; Conclusions References Semper´ e´ et al., 2000). Furthermore, the Mediterranean