Spatial and temporal variation in sedimentary phosphorus species in Lake Champlain (Vermont, New York, Québec)

Abstract We tested the hypothesis that the analysis of operationally defined sedimentary phosphorus species gives a finer resolution of historical land-use changes in lake watersheds than does total phosphorus alone. We measured loosely sorbed/interstitial, reductant soluble, aluminum-bound, apatite, organic and total phosphorus in eleven cores taken from heterogeneous regions of Lake Champlain using sequential extraction. During the pre-settlement period (before 1770 C.E.) concentrations of all P species were low, stable, and dominated by apatite P. With the exception of apatite P, sediment concentrations of all P species increased from pre-settlement times to the present. When accumulation rates were examined, the three P species least susceptible to post-depositional migration (apatite, aluminum-bound, and organic P) were unaffected by deforestation and the development of small, family-scale farms in the 19th century. Increases in accumulation rates were only detected in the early 20th century coincident with afforestation of the watershed as marginal farms were abandoned. By mid-20th century, the accumulation rate of apatite P decreased in all but the lake regions most affected by the industrialization of agriculture and urban development. Aluminum-bound and organic P rates continued to increase in all regions.