Algal Availability of Sediment Phosphorus in Drainage Water of the Black Creek Watershed

Abstract

AbstractThe water quality problems resulting from sediment P additions to rivers and lakes can only be assessed if the biological availability of sediment‐borne P is known. A study was conducted to evaluate the availability to algae of sediment P in drainage water samples collected from an agricultural watershed in northeastern Indiana. Sediments suspended in drainage water were separated, resuspended in a nutrient medium, inoculated with Selanastrum capricornutum, and incubated under illumination for 2 weeks. The sediment‐treated media were analyzed for algal numbers and P assimilated by algal cells by sequential extraction with NH4F, NaOH, and HCl initially and after 2 weeks of incubation. Phosphorus assimilated by algal cells was calculated as the decrease in each sediment P fraction observed during the incubation period.The proportions of sediment P available for algal uptake in drainage water samples collected in March and June averaged 20.7% of the total sediment P and 30.1% of the sediment inorganic P(Pi). Of the three sediment Pi fractions investigated, the NH4F‐extractable fraction contributed the largest proportion (42.2%) of the sediment Pi utilized by algae. The NaOH‐ and HCl‐extractable fractions of sediment Pi contributed 36.3% and 21.6%, respectively, of the Pi utilized by algae. A significant proportion (59.8%) of the NH4F‐extractable P present in sediment prior to incubation was utilized by algal cells during the 2‐week incubation period. Of the NaOH‐ and HCl‐extractable Pi present initially, 26.8% and 12.8%, respectively, were utilized by algae during the 2‐week incubation period. Although all of the soluble Pi initially present in the sediment‐medium mixtures was rapidly utilized by algae, sediment P contributed a significantly larger quantity of P than soluble P for algal growth during incubation.