Why the limiting nutrient differs between temperate coastal seas and freshwater lakes: A matter of salt

Abstract

Comparison of bottom-water chemistry in the marine-limnic habitat gradient shows greater phosphorus availability in marine waters, primarily because of enhanced iron sequestration by sulfide. In the oxidative hydrolysis of iron and the concomitant precipitation of phosphate, a minimum of two iron atoms are needed to precipitate one phosphate molecule (Fe : P ϭ 2). However, dissolved Fe : P Ͻ 2 predominates in anoxic marine waters, therefore leaving some phosphate in solution after oxygenation because of a shortage of dissolved iron for phosphate coprecipitation by iron oxyhydroxide. In contrast, anoxic bottom waters in most freshwater lakes show Fe : P Ͼ 2, allowing almost complete phosphate removal on oxygenation. This difference is a consequence of the high sulfate content of sea salt, and a main reason why nitrogen normally limits net primary production in temperate coastal waters, in contrast to the predominant phosphorus limitation of near-neutral lakes.

Sulfide induces phosphate release from polyphosphate in cultures of a marine Beggiatoa strain

“…In spite of the plausibility of this model, Einsele and later authors (Boströ m et al, 1988;Hupfer and Lewandowski, 2008) realized that it does not always sufficiently explain the observed phosphate fluxes in lake sediments. In marine environments, reactive iron concentrations are lower, as are iron-associated phosphate concentrations (Blomqvist et al, 2004). Nevertheless, high sulfide concentrations in anoxic marine bottom water often co-occur with increased phosphate concentrations, which is interpreted as a concurrent release of sulfide and phosphate by the bacterial degradation of organic matter (Shen et al, 2002).…”

Nitrogen as the limiting nutrient for eutrophication in coastal marine ecosystems: Evolving views over three decades

“…Iron sulfides are less adsorptive of phosphate than are other iron minerals (Krom and Berner 1980). Although estuarine sediments in general are less likely to adsorb and immobilize P than are lake sediments (Caraco et al 1990;Blomqvist et al 2004), the importance of this process is variable among estuaries (Sundby et al 1992;Howarth et al 1995). At one extreme, little or no P is adsorbed by the sediments of Narragansett Bay, and virtually all of the phosphate produced during decomposition in the sediments is released back to the water column (Nixon et al 1980).…”

Degradation of organic phosphorus compounds in anoxic Baltic Sea sediments: A 31P nuclear magnetic resonance study

“…Once phosphate has been mobilized from, e.g., organic compounds in the anoxic sediment, sorption to iron, a major inorganic P retention process, is absent. Formation of iron sulfide complexes inhibits iron from sorbing phosphate in marine sediments, resulting in a more pronounced P release from marine sediments compared with freshwater ones (Blomqvist et al 2004). …”

“…Eutrophication is a major environmental problem in the Baltic Sea (e.g., Rö nnberg and Bonsdorff 2004), but there is a lack of consensus whether nitrogen (N) (Blomqvist et al 2004) or phosphorus (P) (Hecky 1998) is limiting overall primary production in the Baltic proper. Contrary to N, P has no gaseous phase, meaning that the supply of P for primary production is dependent on external sources as well as internal recycling.…”