Input of Nutritionally Rich Organic Matter from the Mississippi River to the Louisiana Coastal Zone

Abstract

Isotopes have often been used to discern riverine subsidies to coastal food chains, but there are few direct measurements of nutritional quality of riverine particulates. We tested for nutritionally enriched organic matter in the Mississippi River suspended sediment and evidence for its delivery to Louisiana coastal sediments by measuring enzymatically hydrolysable amino acids (EHAA). Riverine suspended sediments contained EHAA concentrations of up to 5 mg g −1 , higher than reported in any coastal sediment. Pigment concentrations indicated that EHAA in some river samples were dominated by phytoplankton, but many samples contained significant non-algal EHAA. Coastal sediments showed EHAA concentrations lower than riverine sediments but still higher than most reported shelf values. Incubation of riverine sediment showed losses of 28-34% of their EHAA over 6 days, similar to differences found between riverine and coastal sediments. EHAA concentrations decreased more rapidly than total nitrogen, indicating the relative lability of this pool of material in the studied region. These EHAA-enriched materials provide fuel for various coastal biota whose composition likely depends on factors such as disturbance regimes.

Trophic state of benthic deep-sea ecosystems from two different continental margins off Iberia

“…Also, slope sediments of the Portuguese margin were characterized by significantly higher enzymatically hydrolyzed organic matter concentrations when compared to slope sediments of the Catalan margin. The comparison with available literature information indicates that the sediments investigated in this study are characterized by enzymatically hydrolyzed protein and carbohydrate concentrations similar to those determined in shallow benthic systems Mayer et al, 2008 and citations therein for a comparison with results based on different approaches/protocols), but up to 2-3 fold higher than those determined in abyssal sediments of the NE Atlantic Ocean Danovaro et al, 2001a). The lower amount of enzymatically digestible organic matter pools in abyssal sediments of the NE Atlantic Ocean is consistent with the lower organic carbon inputs reaching the seafloor (ca.…”

“…Such an approach, despite its intrinsic limitations, has been extensively used across a wide range of benthic ecosystems to provide quantitative information on food availability for heterotrophic consumers (Mayer et al, , 2008Dauwe et al, 1999a;Dell'Anno et al, 2000;Danovaro et al, 2001a;Pusceddu et al, 2003;Grémare et al, 2005;Bourgeois et al, 2011).…”

“…In this study we found a significant relationship between enzymatically hydrolyzed protein concentrations and phytopigment contents in the sediments of the Portuguese margin (n = 8, r = 0.723, p < 0.05), though this was not the case for the Catalan margin. High concentrations of nonalgal bioavailable organic N compounds (in terms of enzymatically hydrolysable aminoacids) have been documented in benthic systems influenced by major river outflows (Mayer et al, 2008;Bourgeois et al, 2011), including sediments previously collected in the Gulf of Lion (Grémare et al, 2005;Bourgeois et al, 2011). Previous findings, based on temporal investigations carried out by mooring trap arrays deployed at ca.…”

“…biomimetic approach, sensu Mayer et al, 1995), has been proposed for mimicking organic matter degradation steps in deposit feeding (George, 1964;Mayer et al, 1995;Dauwe et al, 1999a). The enzymatically hydrolyzed organic matter pools represent a reliable estimate of the food availability for heterotrophic consumers, thus providing insights on benthic trophodynamics (Dauwe et al, 1999b;Dell'Anno et al 2000;Pusceddu et al, 2003;Grémare et al, 2005;Mayer et al, 2008;Bourgeois et al, 2011).…”

Biogeochemistry of fatty acids in a river-dominated Mediterranean ecosystem (Rhône River prodelta, Gulf of Lions, France): Origins and diagenesis

“…While it is true that terrestrial OM is generally more resistant to degradation than recently synthesized marine OM (Aller, 1998), river biogenic inputs derive from a wide variety of allochthonous sources, each of which differ in their specific reactivities. For example, soil-derived OM, which accounts for most fluvial inputs, is relatively refractory (Burdige, 2007), but non negligible amounts of labile POC (such as freshwater phytoplankton) are also transported by large rivers to deltaic settings, and the relative proportions of these different sources vary with discharge conditions and the season (Mayer et al, 2008;Harmelin-Vivien et al, 2010).…”