Direct denitrification in mangrove sediments in Terminos Lagoon, Mexico

Abstract

Rates of direct denitrification were measured using I5N isotope techniques in intact sediment cores from fringe and basin mangroves in Terminos Lagoon, Mexico. Sediments were injected with 15N0, and the distribution of I5N was measured over time in the head space, overlying water, and sediments. Experiments included an investigation of spatial variation in denitrification rates by comparing results from the fringe and basin mangroves in the rainy season (July 1991); a second experiment was to determine the effect of 3 diffel-ent NO.; concentrations (25, 100, 200 pm01 core-' "N-KN03-) on denitrificatlon rates and was performed in the fringe mangrove during the 'Norte' season (January 1992). Highest I5N-N2 fluxes were measured in the fringe mangrove at 9.4 pm01 m-* h-', while denitrification rates in the basin mangrove ranged from 1.9 to 4.5 pm01 m-' h-'. I5N-Nz fluxes in sediment cores from the fringe mangrove were significantly higher (4.5 to 7.7 pm01 m-2 h-') in cores enriched with 200 pm01 core-' 1 S~-~~0 3 -c o m p a r e d to cores enriched with 25 and 100 pm01 core-' I5N-K N 0 3 -( < l pm01 m-2 h''). Most of the applied I5N was recovered as particulate nitrogen in the sediment and a small fraction reduced to NH,' in both experiments. The low denitrification rates observed In the fringe and basin mangroves indicate that the capacity for sediment denitrification is limited by low NO3-availability. Previous nutrient exchange studies concluded that the fringe mangrove was a 'sink' of NO3-since sediment uptake of NO3-was assumed lost through denitrification. Results from this study show ~1 0 % of sediment N O 3 uptake in fringe mangroves may be lost to denitrification; the remainder being immobilized in the sediment.

Ethnobiology, socio-economics and management of mangrove forests: A review

“…Favorable sediment characteristics and high photosynthetic rates of many mangrove systems provide the basis for the biofilter function with high nutrient uptake levels (Rivera-Monroy et al, 1995;Robertson and Phillips, 1995;Alongi et al, 2000). Peri-urban coastal areas of the developing world receive extensive amounts of untreated sewage, and mangroves certainly filter this discharged wastewater, thereby limiting coastal sewage pollution.…”

Benthic nutrient fluxes in euphotic sediments along shallow sub-tropical estuaries, northern New South Wales, Australia

“…However, it is uncertain whether NO 3 -reduction to gaseous N 2 (denitrification) or NH 4 + (dissimilatory NO 3 -reduction to ammonium, DNRA) was the dominant fate for NO 3 -removed from the water column. Both pathways of NO 3 -reduction are known to coexist in sediments (Bonin et al 1998) and compete for NO 3 -as an electron acceptor; however, there are various reports of the relative importance of each process (Nowicki 1994, Rivera-Monroy et al 1995, Omnes et al 1996, Rivera- Monroy & , Rysgaard et al 1996, Barnes & Owens 1998, Bonin et al 1998. As NH 4 + is the product of DNRA, it follows that NO 3 -uptakes should be accompanied by an efflux of NH 4 + at a ratio of 1:1 if this is the dominant process and there are no other processes consuming or producing NH 4 + .…”

“…4C), suggesting that this form of benthic metabolism becomes more important under low oxygen conditions. This shift may be due to a combination of nitrification inhibition caused by O 2 depletion and subsequent nitrate depletion by denitrifiers and the net increase in C:N of OM, both of which may favour DNRA over denitrification (Smith et al 1982, King & Nedwell 1987, Rivera-Monroy et al 1995. This has important implications for the upper and middle Brunswick estuary, which experiences hypoxic conditions in the water column due to the breakdown of algal detritus from large pelagic blooms throughout the year.…”

Biogeochemical cycling and phyto- and bacterioplankton communities in a large and shallow tropical lagoon (Términos Lagoon, Mexico) under 2009–2010 El Niño Modoki drought conditions

“…Denitrification, the dissimilatory reduction of NO 3 to produce N 2 O and N 2 , was considered the main process contributing to NO 3 loss. However, direct measurements of denitrification rates in the fringe and basin mangroves of the Términos Lagoon indicated a low sink of NO 3 (Rivera-Monroy et al, 1995b), contrary to what has been evidenced in other mangrove forests (i.e. Twilley, 2013).…”