Setting load limits for nutrients and suspended solids based upon seagrass depth-limit targets |
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Authors: | Joel S Steward Whitney C Green |
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Institution: | 1.Division of Environmental Sciences,St. Johns River Water Management District,Palatka |
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Abstract: | Total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS) loadings log (kg ha−1 yr−1)] were regressed against seagrass depth limits (percent of depth-limit targets) to back-predict the load limits or allocations
(kg ha−1 yr−1 or kg yr−1) necessary to meet targeted seagrass depth limits in the Indian River and Banana River (IRBR) lagoons, Florida. Because the
load allocations can be applied as total maximum daily loads (TMDL) for the IRBR (U.S. Environmental Protection Agency mandate),
the method and results are developed and presented toward that end. The regression analyses indicate that the range of surface-discharge
load limits (nonpoint + point source), per watershed area, required to achieve the desired depth limits for seagrass in the
IRBR are approximately 2.4–3.2 kg ha−1 yr−1 TN, 0.41–0.64 kg ha−1 yr−1 TP, and 48–64 kg ha−1 yr−1 TSS. This simple regression method may have application to other shallow estuarine lagoons or bays where seagrass growth
is limited by light and water transparency, water transparency is strongly affected by watershed pollutant loadings, water
residence times are sufficiently long to allow seagrass coverage to respond to and covary with total load inputs, and multiyear
monitoring has yielded sufficient variability in both pollutant loadings and seagrass coverages to develop a statistically
meaningful relationship. |
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