Nitrogen fixation in freshwater, estuarine, and marine ecosystems. 1. Rates and importance

作者：Robert Warren Howarth, Roxanne M. Marino, Judith L. Lane, Jonathan J. Cole · 发表于：Limnology and Oceanography · 年份：1988 · DOI：10.4319/lo.1988.33.4_part_2.0669 · 被引用次数：552 · 研究领域：Marine and coastal ecosystems、Aquatic Ecosystems and Phytoplankton Dynamics、Marine Biology and Ecology Research

Nitrogen fixation is mediated by a variety of autotrophic and heterotrophic bacteria. Cyanobacteria appear responsible for most planktonic fixation in aquatic ecosystems, and rates of fixation are high only when these organisms make up a major percentage of the planktonic biomass. Planktonic nitrogen fixation tends to be low in oligotrophic and mesotrophic lakes ≪ 0.1 g N m−2 yr−1) but is often high in eutrophic lakes (0.2–9.2 g N m−2 yr−1). We found no data on planktonic nitrogen fixation in estuaries or coastal seas except for the Baltic Sea and for the Peel‐Harvey estuary in Western Australia. Fixation rates are quite high in the Peel‐Harvey estuary; rates are low offshore in Baltic waters but can be high near shore. As in lakes, fixation in these systems is associated with major blooms of planktonic, heterocystic cyanobacteria. However, nitrogen‐fixing cyanobacteria are much more abundant in the Baltic Sea and in the Peel‐Harvey estuary than in other estuaries or coastal waters. In most estuaries and coastal waters, species of nitrogen‐fixing cyanobacteria are absent or make up a very small percentage of the phytoplankton biomass (< 1%), suggesting insignificant amounts of nitrogen fixation. Annual average rates of nitrogen fixation reported for blooms of Trichodesmium and for Rhizosolenia mats in oceanic waters are also low. Unlike nitrogen fixation by planktonic organisms, there appear to be no major differences between freshwater and marine ecosystems with regard to fi...