Seasonal denitrification in flooded and exposed sediments from the Amazon floodplain at Lago Camale�o

Abstract

Denitrification processes were measured by the acetylene-blockage technique under changing flood conditions along the aquatic/terrestrial transition zone on the Amazon floodplain at Lago Camale~o, near Manaus, Brazil. In flooded sediments, denitrification was recorded after the amendment with NO3-(100 txmol liter <) throughout the whole study period from August 1992 to February 1993. It ranged from 192,3 to 640.7 fxmol N m -2 h -1 in the 0-to 5-cm sediment layer. Without substrate amendment, denitrification was detected only during low water in November and December 1992, when it occurred at a rate of up to 12.2 ~xmol N m -2 h -~. Higher rates of denitrification at an average rate of 73.3 Ixmol N m -2 h -~ were measured in sediments from the shallow lake basin that were exposed to air at low water. N20 evolution was never detected in flooded sediments, but in exposed sediments, it was detected at an average rate of 28.3 Ixmol N m -2 h -~ during the low-water period. The results indicate that under natural conditions there is denitrification and hence a loss in nitrogen from the Amazon floodplain to the atmosphere. Rates of denitrification in flooded sediments were one to two orders of magnitude smaller than in temperate regions. However, the nitrogen removal of exposed sediments exceeded that of undisturbed wetland soils of temperate regions, indicating a considerable impact of the flood pulse on the gaseous turnover of nitrogen in the Amazon floodplain.

Sediment and nutrient dynamics following a low-head dam removal at Murphy Creek, California

“…When previously reduced sediments are oxidized, metals can be mobilized (Saeki et al 1993;de Carvalho et al 1998) with certain species (most notably Fe), binding with and immobilizing phosphate (Degroot and Vanwijck 1993;Kleeberg and Heidenreich 2004). Nitrogen in the sediment may be mineralized, nitrified (Sparling and Ross 1988), and leached (Perrin et al 2000), denitrified (Kern et al 1996), or assimilated into riparian vegetation (James et al 2001). Predicting nutrient export and/or retention after dam removal can thus be complex.…”

Nitrogen fixation and denitrification in a floodplain forest near Manaus, Brazil

“…The water and N exchange between the river and its floodplain is crucial for the várzea (Kern and Darwich, 1997). But N 2 fixation and denitrification also may be important processes for the várzea forest, as reported for other ecotopes within the Amazon floodplain (Melack and Fisher, 1988;Doyle and Fisher, 1994;Kern et al, 1996). Furthermore, denitrification was identified as the major pathway for N loss from the várzea at Lago Camaleão (Kern et al, 1998).…”

“…Two incubation methods, with and without added water and N 2 gas as headspace, were used to represent the range of hydrological conditions during the exposed and the submerged periods (Kern, 1995). Nitrous oxide (N 2 O) and ethylene (C 2 H 2 ) were analysed by gas chromatography (Hewlett Packard 5890 Series II), detected by electron capture detector and flame ionization detector, as described by Kern et al (1996). The amount of fixed N was calculated using the theoretical factor of three (C 2 H 2 :N 2 ).…”

Sediment Denitrification in Two Contrasting Tropical Shallow Lagoons

“…Low or absent denitrification rates were previously reported in other tropical lagoon sediments (Biesboer, Esteves et al, 1998) and floodplain lake sediments in the Pantanal (Figueiredo Souza, et al, 2012) and clearwater Amazonian lakes (Kern, et al, 1996;Esteves, 1998;Esteves et al, 2001;Nielsen et al, 2004). Denitrification rates were also absent in periphytic communities associated with Amazonian aquatic macrophytes (Enrich-Prast & Esteves, 1998, Enrich-Prast et al, 1999 and stream tropical sediments (Solomon et al, 2009).…”