Historical Trends in Chesapeake Bay Dissolved Oxygen Based on Benthic Foraminifera from Sediment Cores

• Published in: Estuaries 2000-08, Vol.23 (4), p.488-508
• Main Authors: Karlsen, Alexander W., Cronin, Thomas M., Ishman, Scott E., Willard, Debra A., Kerhin, Randy, Holmes, Charles W., Marot, Marci
• Format: Article
• Language: English
• Subjects: Ammonia; Ammonia parkinsoniana; Animal and plant ecology; Animal, plant and microbial ecology; Anoxia; Anoxic conditions; Biogeochemistry; Biological and medical sciences; Brackish; Cores; Dissolved oxygen; Earth sciences; Earth, ocean, space; Estuaries; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Indicator species; Invertebrate paleontology; Marine; Nutrient concentrations; Nutrient flow; Nutrients; Oxygen; Oxygen depletion; Paleoclimatology; Paleoecology; Paleontology; Pollen; River discharge; River flow; Rivers; Salinity; Sea water ecosystems; Sediments; Species; Stratigraphy; Synecology; Tributaries; USA, Chesapeake Bay
• ISSN: 0160-8347; 1559-2723; 1559-2758; 1559-2731
• DOI: 10.2307/1353141

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 that A. 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 foraminiferal species in channel environments beginning in the early 1970s. Since the 1970s, deformed tests of A. parkinsoniana occur in all cores (10-20% of Ammonia), 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 (${\rm DO}