Particulate organic carbon in the estuarine turbidity maxima of the Gironde, Loire and Seine estuaries: origin and lability

Abstract

A study of the particulate organic carbon (POC) in the estuarine turbidity maxima (ETMs) of the three major French macrotidal estuaries shows that the average contents are 1.5, 3.3 and 3.1% (expressed in % of dry suspended sediment) in the Gironde, Loire and Seine Estuaries, respectively. There is no seasonal variation of POC contents in the Gironde Estuary, whereas, they often increase in the Loire and the Seine Estuaries in spring and summer. The lability of the estuarine particulate organic matter was estimated by two analyses: 1/labile organic matter was measured as the organic carbon loss during incubation tests over one month; 2/ the hydrolysable organic fraction was determined after 6N HCl digestion. The organic fractions of the ETMs are mainly refractory. Any increase in the amount of POC as compared to the background levels (cited above) is always correlated to an increase of organic matter lability. The yearly average fluvial contributions by various particulate organic pools (soil and litter organic matter; organic matter of phytoplanktonic and human origin) that enter the three estuaries were quantified. In the Garonne River, soil and litter are the major (90%) POC sources. In the Loire system, due to the eutrophication of the river water, phytoplankton contributes up to 50% of the total POC load. In the Seine river, soil and litter contribute 70% of the total POC input; POC of human origin is also significant (10%), due to the impact of the City of Paris (10 million inhabitants). The lability of the different types of organic matter ranks as follows: phytoplankton~litter > humanorigin organic matter > > soil. By combining the POC budgets and the lability of each type of organic fraction, it was possible to explain why the POC of the three ETMs is different and characterizes its refractory vs. labile nature.

Export, biodegradation, and disinfection byproduct formation of dissolved and particulate organic carbon in a forested headwater stream during extreme rainfall events

“…While current debates on erosion-enhanced sinks of atmospheric CO 2 have focused on reduced decomposition of eroded C under depositional settings (Van Oost et al, 2007;Lal and Pimentel, 2008), recent findings of high biodegradation potentials of POC in large temperate and tropical rivers (Etcheber et al, 2007;del Giorgio and Pace, 2008;Ward et al, 2013) raise an important question as to whether eroded C degrades faster after entering streams and rivers than in source soils. Our measurements of BDOC and optical properties of SS-DOM in the headwater stream suggest that rapid conversion of labile OM between the DOC and POC pools starts to occur even in upstream source areas of mountainous river systems in monsoon Asia, which have been suggested to transport organic C without significant chemical transformations (Galy et al, 2007;Goldsmith et al, 2008).…”

“…Although the bulk of riverine POC at low flow has been considered aged and metabolically not reactive, it has been suggested recently that not only labile components but also recalcitrant compounds such as lignin and other phenolic compounds can be consumed rapidly by microorganisms in large tropical rivers such as the Amazon (Ward et al, 2013). Studies of POC origin and lability in some European estuaries have shown that the bulk of POC in estuaries might be refractory, whereas seasonal changes in the input of organic matter of autochthonous or anthropogenic origin can significantly increase the lability and biodegradability of POC even to a higher degree than observed for DOC (Etcheber et al, 2007;Garnier et al, 2008). It remains unexplored whether POC in headwater streams has comparable lability relative to DOC.…”

Monitoring water quality in estuarine environments: lessons from the MAGEST monitoring program in the Gironde fluvial-estuarine system

“…The Gironde Estuary was estimated to contribute 60% of the input of fine sediments to the continental shelf of the Bay of Biscay (Castaing and Allen, 1981). Although this system drains one of the less urbanized/industrialized watersheds in Europe (Abril et al, 2002;Etcheber et al, 2007), it is polluted by heavy metals, preventing oyster and mussel production within the estuary (Latouche, 1988). This chronic metal pollution is due to former mining and smelting activities during the late 19th century in the upper reaches of a tributary (Schäfer et al, 2006;Saari et al, 2007).…”

Carbon Stocks of Coastal Wetland Ecosystems on Hainan Island, China

“…The vegetation C stocks of delta ecosystems on Hainan Island were three-fold lower than that of the Pearl River Delta [38]. We investigated the fact that the soil of deltas on Hainan Island was sandy, whereas those elsewhere are predominantly loam and clay soils [39], suggesting that the soil texture had a significant influence on vegetation carbon storage. The study of carbon pool in an area of north Nile Delta, Egypt also proved that sand was the most negative factor correlating to C pools [40].…”