Ginger Jahn, Hawaii Pacific

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Abstract:

The potential influence of large-scale climatic processes on freshwater flow into Chesapeake and Delaware Bays was assessed using indices of the North Atlantic Oscillation (NAO): the NAO index and the North Atlantic Center of Action (NACOA) indices. This influence has far-reaching implications for the ecology of the bays because freshwater flow controls physical and biological processes that affect a suite of organisms, including blue crabs. Significant correlations were found between the NAO and NACOA indices and freshwater flow in multiple river systems (Susquehanna River, Delaware River, Potomac River, James River, and the Chesapeake basin) during selected months (March - May, July - October). Five variable regression models had adjusted R² values that ranged from 0.10 to 0.61 with highest predictive ability for total Chesapeake flow in April. NACOA variables with lags of 18-22 and 33-35 months were significant terms in several regression models of flow in May and July-September, indicating that freshwater flow may be influenced by coupled ocean-atmospheric processes that occurred ~2.8 and ~1.5 years prior to these months. Results support the use of parameters that describe the intensity and location of the Icelandic Low and Azores High pressure systems (i.e., the NACOA indices) in addition to, or instead of, the NAO index (which is the difference between the normalized pressures of the two systems). The predictive ability of the regression equations was tested by comparing observed versus modeled values from 1992 to the present. R² values of observed versus modeled ranged from nearly zero to 0.74 and suggest that in some months and river systems these large-scale climate indices could be used to reasonably predict freshwater flow.