NDLI: Historical trends in Chesapeake Bay dissolved oxygen based on benthic foraminifera from sediment cores

Content Provider	Springer Nature Link
Author	Karlsen, Alexander W. Cronin, Thomas M. Ishman, Scott E. Willard, Debra A. Kerhin, Randy Holmes, Charles W. Marot, Marci
Copyright Year	2000
Abstract	Environmentally sensitive benthic foraminifera (protists) from Chesapeake Bay were used as bioindicators to estimate the timing and degree of changes in dissolved oxygen (DO) over the past five centuries. Living foraminifers from 19 surface samples and fossil assemblages from 11 sediment cores dated by$^{210}$Pb,$^{137}$Cs,$^{14}$C, and pollen stratigraphy were analyzed from the tidal portions of the Patuxent, Potomac, and Choptank Rivers and the main channel of the Chesapeake Bay.Ammonia parkinsoniana, a facultative anaerobe tolerant of periodic anoxic conditions, comprises an average of 74% of modern Chesapeake foraminiferal assemblages (DO-0.47 and 1.72 ml l$^{−1}$) compared to 0% to 15% of assemblages collected in the 1960s. Paleoecological analyses show thatA. parkinsoniana was absent prior to the late 17th century, increased to 10–25% relative frequency between approximately 1670–1720 and 1810–1900, and became the dominant (60–90%) benthic formaniferal species in channel environments beginning in the early 1970s. Since the 1970s, deformed tests ofA. parkinsoniana occur in all cores (10–20% ofAmmonia), suggesting unprecedented stressful benthic conditions. These cores indicate that prior to the late 17th century, there was limited oxygen depletion. During the past 200 years, decadal scale variability in oxygen depletion has occurred, as dysoxic (DO=0.1–1.0 ml l$^{−1}$), perhaps short-term anoxic (DO<0.1 ml l$^{−1}$) conditions developed. The most extensive (spatially and temporally) anoxic conditions were reached during the 1970s. Over decadal timescales, DO variability seems to be linked closely to climatological factors influencing river discharge; the unprecedented anoxia since the early 1970s is attributed mainly to high freshwater flow and to an increase in nutrient concentrations from the watershed.
Starting Page	488
Ending Page	508
Page Count	21
File Format	PDF
ISSN	01608347
Journal	Estuaries
Volume Number	23
Issue Number	4
Language	English
Publisher	Springer-Verlag
Publisher Date	2000-01-01
Publisher Place	New York
Access Restriction	Subscribed
Subject Keyword	Environment Ecology Geosciences Freshwater & Marine Ecology Environmental Management Nature Conservation
Content Type	Text
Resource Type	Article
Subject	Environmental Chemistry Aquatic Science Environmental Science

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