Temporal and Spatial Patterns of Porewater Phosphorus in Shallow Sediments, and its Potential Transport into Narrow Lake, Alberta

Abstract

During 1985 and 1986, summer and spatial patterns of porewater soluble reactive phosphorus (SRP) from sediments ≤ 15-m depth were examined at Narrow Lake, a deep, mesoeutrophic Albertan lake. At three sites (different in depth and macrophyte colonization), trends in porewater SRP concentrations ([SRP]) in the top 5 cm of the sediment from May to August varied, possibly due to root uptake of SRP by macrophytes. At a depth of 5 m, mean (in the top 5 cm of the sediment) and variance of porewater [SRP] at one site (<0.15 m2) were the same as over the entire lake. Excluding data from macrophyte sites, porewater [SRP] were positively related to depth of the water column (P < 0.0001). Molecular diffusion of SRP from sediments with and without macrophytes located in the trophogenic zone was calculated. During summer, molecular diffusion from shallow sediments to the trophogenic zone was 0.05 mg∙m−2 d−1, or 29% of atmospheric deposition of phosphorus (P) (the major external source of P to the lake). A sampling strategy is discussed to enable the calculation of whole-lake P transport from shallow sediments to the trophogenic zone in lakes with similar morphometry and trophic status to Narrow Lake.