Effects of Temperature and Site Characteristics on Phosphorus Dynamics in Four Restored Wetlands: Implications for Wetland Hydrologic Management and Restoration

Abstract

Restoring historic lake-fringe wetlands is considered a favorable means of reducing lake phosphorus levels; however, it is unclear how various strategies for managing wetland connectivity influence phosphorus release. We investigated the relationships between temperature and soil characteristics of restored wetlands to identify management strategies that minimize external phosphorus loading to Upper Klamath and Agency Lakes. We flooded soil cores at various temperatures and analyzed them for several forms of phosphorus and other physical properties. We compared measures of microbial activity and physical characteristics of phosphorus fractions within the wetland soils to forms of phosphorus in water relevant to phosphorus-loading in the lakes. Greater release rates of total phosphorus occurred in summer temperature treatments for all study wetlands (average 31.81 to 240.61 mg/m²/d), while release rates of soluble reactive phosphorus (average −15.9 to 62.19 mg/m²/d) varied with temperature and soil characteristics. Wetlands with mineral soils and direct hydrologic connectivity to the lakes released the lowest concentrations of total phosphorus, while soluble reactive phosphorus release varied across management strategies and soil types. These differences can be explained by the dominant phosphorus processes associated with the hydrology and biogeochemistry of the individual sites, and temperature and potential for microbial activity at the timing of inundation. Our results provide evidence that directly connected wetlands may release less phosphorus than indirectly or mechanically connected wetlands, due to early timing of inundation and longer duration of inundation.