The sedimentary record of climatic and anthropogenic influence on the Patuxent estuary and Chesapeake Bay ecosystems |
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| Authors: | Email author" target="_blank">Thomas?M?CroninEmail author Cheryl?D?Vann |
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| Institution: | (1) Department of Geosciences, Princeton University, Princeton, New Jersey, USA;(2) Department of Biology and Marine Biology, University of North Carolina at Wilmington, Wilmington, North Carolina, USA;(3) Present address: Center for Environmental Studies, Brown University, Providence, Rhode Island, USA |
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| Abstract: | Ecological and paleoecological studies from the Patuxent River mouth reveal dynamic variations in benthic ostracode assemblages
over the past 600 years due to climatic and anthropogenic factors. Prior to the late 20th century, centennial-scale changes
in species dominance were influenced by climatic and hydrological factors that primarily affected salinity and at times led
to oxygen depletion. Decadal-scale droughts also occurred resulting in higher salinities and migration of ostracode species
from the deep chanel (Loxoconcha sp.,Cytheromorpha newportensis) into shallower water along the flanks of the bay. During the 19th century the abundance ofLeptocythere nikraveshae andPerissocytheridea brachyforma suggest increased turbidity and decreased salinity. Unprecedented changes in benthic ostracodes at the Patuxent mouth and
in the deep channel of the bay occurred after the 1960s whenCythermorpha curta became the dominant species, reflecting seasonal anoxia. The change in benthic assemblages coicided with the appearance of
deformities in foraminifers. A combination of increased nitrate loading due to greater fertilize use and increased fresh-water
flow explains this shift. A review of the geochemical and paleoecological evidence for dissolved oxygen indicates that seasonal
oxygen depletion in the main channel of Chesapeake Bay varies over centennial and decadal timescales. Prior to 1700 AD, a
relatively wet climate and high freshwater runoff led to oxygen depletion but rarely anoxia. Between 1700 and 1700, progressive
eutrophication occurred related to land clearance and increased sedimentation, but this was superimposed on the oscillatory
pattern of oxygen depleton most likely driven by climatological and hydrological factors. It also seems probable that the
four-to five-fold increase in sedimentation due to agricultural and timber activity could have contributed to an increased
natural nutrient load, likely fueling the early periods (1700–1900) of hypoxia prior to widespread fertilizer use. Twentieth-century
anoxia worsened in the late 1930s–1940s and again around 1970, reaching unprecedented levels in the past few decades. Decadal
and interannual variability in oxygen depletion even in the 20th century is still strongly influenced by climatic processes
influencing precipitation and freshwater runoff. |
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