Presenter/Author Information

P. Wang
L. C. Linker

Keywords

n-p tradeoff, surface analysis, estuarine model, nutrient limitation, dissolved oxygen

Start Date

1-7-2006 12:00 AM

Description

Low summer dissolved oxygen (DO) in the Chesapeake Bay is primarily due to excessive nitrogen (N) and phosphorus (P) inputs. These nutrients cause algal blooms in the spring and summer with subsequent algal decay leading to summer oxygen depletion. In the Chesapeake Bay, N and P are generally higher than their half saturation constants for algal growth. Controlling both N and P loads are necessary due to spatial and temporal shift in nutrient limitation. Based on a set of water quality model runs, we used a surface analysis technique to establish a function of DO versus N and P loads, which plots as a 3-D surface. For a specific criterion for DO, a continuous curve of DO versus N and P loads that meet the DO criterion can be isolated. Each of the paired N and P loads on this tradeoff curve results in an equivalent level of DO, but usually at different costs. This paper explores cost-effective alternatives in nutrient reduction to achieve DO water quality standards in the Deep Water designated use of Segment CB4, which is the last and most difficult region for achievement of DO standards in the Chesapeake, by analyzing DO surface plots and N-P tradeoff curves. The effects of nutrient limitation on algae growth, water clarity, and DO concentrations in two different N and P load scenarios are examined to understand the responses of water quality to N and P trades.

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Jul 1st, 12:00 AM

Use of Surface Analysis on Water Quality Model Outputs to Assess Tradeoff of Nitrogen and Phosphorus Controls

Low summer dissolved oxygen (DO) in the Chesapeake Bay is primarily due to excessive nitrogen (N) and phosphorus (P) inputs. These nutrients cause algal blooms in the spring and summer with subsequent algal decay leading to summer oxygen depletion. In the Chesapeake Bay, N and P are generally higher than their half saturation constants for algal growth. Controlling both N and P loads are necessary due to spatial and temporal shift in nutrient limitation. Based on a set of water quality model runs, we used a surface analysis technique to establish a function of DO versus N and P loads, which plots as a 3-D surface. For a specific criterion for DO, a continuous curve of DO versus N and P loads that meet the DO criterion can be isolated. Each of the paired N and P loads on this tradeoff curve results in an equivalent level of DO, but usually at different costs. This paper explores cost-effective alternatives in nutrient reduction to achieve DO water quality standards in the Deep Water designated use of Segment CB4, which is the last and most difficult region for achievement of DO standards in the Chesapeake, by analyzing DO surface plots and N-P tradeoff curves. The effects of nutrient limitation on algae growth, water clarity, and DO concentrations in two different N and P load scenarios are examined to understand the responses of water quality to N and P trades.