Algal Availability of Sediment Phosphorus in Drainage Water of the Black Creek Watershed1
- R. A. Dorich,
- D. W. Nelson and
- L. E. Sommers2
The 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). 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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