Hydrologic Regime Controls Soil Phosphorus Fluxes in Restoration and Undisturbed Wetlands

Abstract

Many wetland restoration projects occur on former agricultural soils that have a history of disturbance and fertilization, making them prone to phosphorus (P) release upon flooding. To study the relationship between P release and hydrologic regime, we collected soil cores from three restoration wetlands and three undisturbed wetlands around Upper Klamath Lake in southern Oregon, U.S.A. Soil cores were subjected to one of three hydrologic regimes-flooded, moist, and dry-for 7.5 weeks, and P fluxes were measured upon reflooding. Soils from restoration wetlands released P upon reflooding regardless of the hydrologic regime, with the greatest releases coming from soils that had been flooded or dried. Undisturbed wetland soils released P only after drying. Patterns in P release can be explained by a combination of physical and biological processes, including the release of iron-bound P due to anoxia in the flooded treatment and the mineralization of organic P under aerobic conditions in the dry treatment. Higher rates of soil P release from restoration wetland soils, particularly under flooded conditions, were associated with higher total P concentrations compared with undisturbed wetland soils. We conclude that maintaining moist soil is the means to minimize P release from recently flooded wetland soils. Alternatively, prolonged flooding provides a means of liberating excess labile P from former agricultural soils while minimizing continued organic P mineralization and soil subsidence.

The mobilisation of phosphorus, organic carbon and ammonium in the initial stage of fen rewetting (a case study from NE Germany)

“…• ion-exchange reactions between solid and aqueous phase (Olila et al 1997;Beltman et al 2000;Kalbitz et al 2000;Olde Venterink et al 2002) • cleavage of particulate OM by hydrolytic and fermentation processes Turner et al 2003) • microbial catalysed redox reactions in dependence of the availability of reducible substances (electron acceptors) and OM as electron donors (Lamers et al 2002;Lucassen et al 2004;Aldous et al 2005;Shenker et al 2005) • abiotic redox reactions such as reduction of Fe(III)-hydroxides by hydrosulphides (Lamers et al 2002;Lucassen et al 2004) or by phenolic substances (Deiana et al 1995;Pracht et al 2001) The continuously lowering of the redox potential, coupled with high increases in iron and ammonium concentrations and rapid decreases in sulphate concentrations during the incubation study imply that the best conditions for microbial decomposition processes exist in highly decomposed peat (Figs. 2a,c,d,and 3c).…”

“…Consequently, drained fens have lost some of their functions as nutrient sinks. In addition, due to seasonally induced and repeated drying/rewetting cycles, these fens act as sources of phosphorus, dissolved organic carbon (DOC) and nitrate which leach into adjacent surface waters (Lenz et al 1992;Olde Venterink et al 2002;Aldous et al 2005;Worrall and Burt 2005).…”

Valuing Ecosystem Services and Disservices across Heterogeneous Green Spaces

“…Phosphorus retention via sorption, burial, and uptake by plants contributes to water quality improvement [36,38]. However, restored or created wetlands on former agricultural lands can act as a source of nutrients to the water column as reflooding of drained agricultural areas stimulates P release [39,40]. Phosphorus from fertilizers, commonly used to increase production in agricultural areas, can accumulate in biotic ecosystem compartments due to incorporation of P into organic matter and abiotic compartments due to adsorption of P by soil and sediments [41,42].…”

Sediment and nutrient loads into river Lwiro, in the Lake Kivu basin, Democratic Republic of Congo

“…TSS levels and fluctuation influence aquatic life from phytoplankton to fish, reduce water clarity, light penetration in the water column and is a useful indicator for assessing the effects of land use changes and engineering practices in watercourses (Senus et al, 2004). Nutrients are required to sustain life, but excess nutrient loads can upset the nutrient cycle balance resulting in changes in water quality harmful to organisms (Aldous et al, 2005). Most TN recorded in the sample is possibly from the farmlands and may be in the form of Nitrate washed with the sediment into the river.…”