A SEDIMENT CHRONOLOGY OF THE EUTROPHICATION OF CHESAPEAKE BAY

Chesapeake Bay sediments were examined for biogeochemical evidence of eutrophication trends using two mesohaline sediment cores. Measurement s of Pb-210 geochronology and sediment profiles of organic carbon, nit rogen, organic phosphorus, inorganic phosphorus, and biogenic silica ( BSI) were used to develop temporal concentration trends. Recent sedime nts have 2-3 times as much organic carbon and nitrogen as sediments fr om 80 to 100 yr ago, but the increases result from both changes in org anic matter deposition and time-dependent changes in organic matter de composition rates, Despite increases in phosphorus loading, no major c hanges in phosphorus concentration were noted throughout most of the c entury; anthropogenic phosphorus deposition, though not evident in sul fidic mid-bay sediments, must occur in more oxidizing sediment environ ments in both the northern and southern bays. Temporal trends in BSi c oncentrations are much less evident and the lack of substantial increa ses in this century suggest that BSi inputs may be capped by late spri ng-sumner Si limitation.