Nitrogen removal in marine environments: recent findings and future research challenges

• Respiratory reduction of nitrate (denitrification) is recognized as the most important process converting biologically available (fixed) nitrogen to N-2. In current N cycle models, a major proportion of global marine denitrification (50-70%) is assumed to take place on the sea floor, particularly in organic rich continental margin sediments. Recent observations indicate that present conceptual views of denitrification and pathways of nitrate reduction and N, formation are incomplete. Alternative N cycle pathways, particularly in sediments. include anaerobic ammonium oxidation to nitrite, nitrate and N-2 by Mn-oxides, and anaerobic ammonium oxidation coupled to nitrite reduction and subsequent N, mobilization. The discovery of new links and feedback mechanisms between the redox cycles of, e.g., C, N, S, Mn and Fe casts doubt on the present general understanding of the global N cycle. Recent models of the oceanic N budget indicate that total inputs are significantly smaller than estimated fixed N removal. The occurrence of alternative N reaction pathways further exacerbates the apparent imbalance as they introduce additional routes of N removal. In this contribution, we give a brief historical background of the conceptual understanding of N cycling in marine ecosystems, emphasizing pathways of aerobic and anaerobic N mineralization in marine sediments, and the implications of recently recognized metabolic pathways for N removal in marine environments. (c) 2004 Elsevier B.V. All rights reserved.

Ämnesord

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

nitrogen

removal

marine

ANAEROBIC AMMONIUM OXIDATION

EARTHS EARLY ATMOSPHERE

ORGANIC-MATTER

MINERALIZATION

PROTEROZOIC OCEAN CHEMISTRY

EARLY DIAGENETIC

PROCESSES

NITRATE-REDUCING BACTERIA

OXIC-ANOXIC INTERFACE

BIOGEOCHEMICAL CYCLES

ESTUARINE SEDIMENT

FERROUS IRON

FERROUS IRON

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)