Dynamics of nitrogen and phosphorus retention during wetland ecosystem succession

Abstract

We compared the mechanisms of nitrogen (N) and phosphorus (P) removal in four young (<15 years old) constructed estuarine marshes with paired mature natural marshes to determine how nutrient retention changes during wetland ecosystem succession. In constructed wetlands, N retention begins as soon as emergent vegetation becomes established and soil organic matter starts to accumulate, which is usually within the first I-3 years. Accumulation of organic carbon in the soil sets the stage for denitrification which, after 5-10 years, removes approximately the same amount of N as accumulating organic matter, 5-10 g/m2/yr each, under conditions of low N loadings, Under high N loadings, the amount of N stored in accumulating organic matter doubles while N removal from denitrification may increase by an order of magnitude or more. Both organic N accumulation and denitrification provide for long-term reliable N removal regardless of N loading rates. Phosphorus removal, on the other hand, is greatest during the first I-3 years of succession when sediment deposition and sorption/ precipitation of P are greatest. During this time, constructed marshes may retain from 3 g P/m2/yr under low P loadings to as much as 30 g P/m2/yr under high loadings. However, as sedimentation decreases and sorption sites become saturated, P retention decreases to levels supported by organic P accumulation (1-2 g P/m2/yr) and sorption/precipitation with incoming aqueous and particulate Fe, AI and Ca. Phosphorus cycling in wetlands differs from forest and other terrestrial ecosystems in that conservation of P is greatest during the early years of succession, not during the middle or late stages. Conservation of P by wetlands is largely regulated by geochemical processes (sorption, precipitation) which operate independently of succession. In contrast, the conservation of N is controlled by biological processes (organic matter accumulation, denitrification) that change as succession proceeds.

Carbon Sequestration and Sedimentation in Mangrove Swamps Influenced by Hydrogeomorphic Conditions and Urbanization in Southwest Florida

“…However, in H + -dominated, acidic soils, other cations are preferentially bound [59]. In oceanic settings cation exchange sites may be sufficiently impregnated with cations commonly found in saltwater (Ca 2+ , K + , Mg 2+ , Na + ), thus excluding 137 Cs from adhering to the clay particles, making the calculation of accretion rates utilizing 137 Cs unreliable.…”

Effects of Small Ponds on Stream Water Chemistry

“…In contrast to the optimal conditions for N removal via denitrication in the summer, P retention is favored by oxygenated water and sediments with an abundance of clay particles and oxides of Fe, Mn and Ca. Treatment wetlands and other constructed nutrient retention systems built to remove P often are most effective in the first several years after construction when these conditions are present (Craft 1997, Gal et al 2003. Consistent with our results, older lakes or ponds with P-saturated, organic sediments instead may exhibit net export of P, particularly in summer when high temperatures and low dissolved oxygen at the sediment surface facilitate the release of iron-bound P (Kozerski et al 1999, Sønder-gaard et al 2002.…”

Fiddler crab control of cordgrass primary production in sandy sediments

“…data for New England marshes). This trend and our results are likely driven by the inability of sandy soils to accumulate nutrient reservoirs because nitrogen leaches rapidly through large-grained, inorganic substrates (Osgood & Zieman 1993, Thompson et al 1995, Craft 1996. Consequently, the persistent deposition of nitrogen by crabs throughout the growing season is likely critical to the production of cordgrass in sandy systems.…”