ALGAL AVAILABILITY OF PHOSPHORUS IN SEDIMENTS DERIVED FROM CROPLAND
Abstract
Although the mechanisms of phosphorus (P) movement from cropland to surface waters have been extensively investigated, studies relating to the availability of suspended sediment P to algae and to development of rapid methods for assessing sediment P availability are limited. More than 90% of P in runoff from cropland is sediment-bound. Therefore, the availability to algae of sediment P must be known if the effects of P additions on water quality are to be assessed or modeled. A series of studies were conducted to evaluate the availability to algae of P in suspended stream sediments during short-(2 days) and longer-term (2 weeks) sediment:algal incubations, to develop a rapid chemical extraction procedure which is best suited for estimating algal available P, and to determine if P availability varies as a function of sediment aggregate or primary particle size. Eighty-five % of the sediment P available to algae in 2 weeks was assimilated within 2 days. In 2 day and 2 week sediment:algal incubations, 21 and 26% of the total sediment P, respectively, and 42 and 50% of the sediment inorganic P(P(,i)), respectively, was assimilated by algae. Essentially all of the 2 day and 2 week available P(,i) originated in the sediment P(,i) fraction extractable with 0.1 N NaOH. About 56 and 71% of the NaOH-extractable P(,i) was assimilated in 2 days and 2 weeks, respectively. Inorganic P supply to algae from sediments likely occurs by P(,i) release from the labile sediment P(,i) pool (i.e., the NaOH-extractable fraction) to the water phase as algae deplete solution P(,i) levels. Of 4 chemical extraction schemes tested, a single 17 hour NaOH (0.1 N) extraction removed amounts of P(,i) best correlated with 2 day and 2 week available P concentrations (r = 0.89 and 0.95, respectively, n = 28). The algal availability of suspended sediment P in size-fractionated aggregates was not related to aggregate size over the range of < 2, 2-20, 20-53, 53-212, and > 212 (mu)m. On the other hand, available P levels in size fractionated soil separates eroded during a simulated rainstorm consistently increased with decreasing particle size over the range of < 0.2, 0.2-2, 2-53, and > 53 (mu)m.
Degree
Ph.D.
Subject Area
Agronomy
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.