Twenty More Years of Marsh and Estuarine Flux Studies: Revisiting Nixon (1980)

Abstract

In 1980, Scott Nixon reviewed the role of salt marshes in estuarine and coastal productivity. His review was effectively a progress report on the testing of "The Outwelling Hypothesis" (Odum, 1980). Nixon (1980) signaled a crucial turning point in the direction of estuarine flux studies conducted since then. In this review we revisit Nixon (1980), focusing on research and thinking that has been guided by The Outwelling Concept in the last two decades. Since 1980, estuarine flux studies have been conducted at 41 different sites and presented in over 42 publications. More than a third of these were conducted in Europe, Africa, Australia, or Mexico. Our review of these studies highlighted several important advances. The first was evolution of a conceptual approach that decomposes the estuary-coastal ocean landscape into interacting subsystems (i.e., the coastal ocean, estuarine basins, and marsh). Most post-1980 flux studies have addressed interactions between these individual subsystems, often in an hierarchical sense. Over half of these quantified exchanges between marsh-dominated basins and the greater estuary-generally through a single, well-defined tidal channel. From these data, we found that tidal range, subsystem area, and distance to the ocean together explained 87% of the variability in total organic carbon (TOC) exchanges and 92% of the variability in total suspended solids (TSS) fluxes, with exports occurring at lower tidal ranges, areas, and distances. Tidal range explained 40% of the variability in nitrate + nitrite (NN) exchange (with uptake at ranges below about 1.2 m and export at greater tidal ranges) and 39% of available phosphorus (SRP) flux variation (with export at

Salinization during salt-marsh restoration after managed realignment

“…MacLeod et al 1999;Blackwell et al 2004). However, when greater soil depths are considered, a slower response of salinization to the return of tidal influence may be expected because it depends on the rate of vertical seepage of flood water from the marsh surface into the subsoil (Childers et al 2000). continued increase of marine-associated metal ions in the second year after de-embankment.…”

“…Zedler et al 1999;Bockelmann et al 2002;Pétillon et al 2010). The influx of salt into the salt-marsh bed occurs during tidal inundation when soil pore water is refreshed by vertical seepage (Childers et al 2000). This explains the generally negative relationship between elevation and salinity.…”

Salt marsh tidal exchange increases residence time of silica in estuaries

“…and secondary production in estuaries. The several existing reviews of flux studies (Nixon 1980;Childers et al 2002) have been unable to definitively reject or accept the Outwelling Hypothesis, but a general trend for the marsh to import organic matter and export inorganic matter has been noted (Nixon 1980). Our DIN and DIP data support this hypothesis.…”

“…The fate of this ''extra'' water entering the marsh is likely losses through evapotranspiration, ponding on the marsh surface, and infiltration into marsh sediment. Vertical seepage, or infiltration, during the flood tide is a well-recognized means of restoring water to sediments, as pore water drains the marsh during the low tide and needs replenishment (Childers et al 2002;Vieillard et al 2011).…”

Organic matter governs N and P balance in Danube Delta lakes

“…Living biomass in wetlands is an important source of DOM, and senescing detritus mainly contributes to the formation of particles and regenerated nutrients (Wetzel 1979;Childers 2000;Stepanauskas et al 2000). In such systems, organic N and P can constitute the dominant fractions of TN and TP in flowing water.…”