HomeMy WebLinkAboutCapital Program Committee Minutes - 12 07 2010_201402121338448968 MASSACHUSETTS ESTUARIES PROJECT
158
reduced from existing conditions based on the load reduction and the observed particulate
organic nitrogen (PON) concentrations within each sub-embayment relative to background
concentrations in Nantucket Sound, as discussed in Section VI.
Table VIII-2. Comparison of sub-embayment watershed septic loads (attenuated) used for
modeling of present and threshold loading scenarios of the Nantucket Harbor
system. These loads do not include direct atmospheric deposition (onto the
sub-embayment surface), benthic flux, runoff, or fertilizer loading terms.
sub-embayment
present
septic load
(kg/day)
threshold “A”
septic load
(kg/day)
Threshold “A”
septic load %
change
threshold “B”
septic load
(kg/day)
Threshold “B”
septic load %
change
Head of the Harbor 0.705 0.141 -80.0% 0.000 -100.0%
Polpis Harbor 0.435 0.087 -80.0% 0.000 -100.0%
Quaise Basin 0.392 0.078 -80.0% 0.000 -100.0%
Town Basin 5.194 0.000 -100.0% 0.000 -100.0%
System Total 6.726 0.306 -95.4% 0.000 -100.0%
Table VIII-3. Comparison of sub-embayment total watershed loads (including septic,
runoff, and fertilizer) used for modeling of present and threshold loading
scenarios of the Nantucket Harbor system. These loads do not include direct
atmospheric deposition (onto the sub-embayment surface) or benthic flux
loading terms.
sub-embayment
present
load
(kg/day)
threshold “A”
load
(kg/day)
threshold “A”
% change
threshold “B”
load
(kg/day)
threshold “B”
% change
Head of the Harbor 1.858 0.792 -57.4% 1.153 -37.9%
Polpis Harbor 3.529 2.175 -38.4% 3.093 -12.3%
Quaise Basin 2.123 1.140 -46.3% 1.732 -18.5%
Town Basin 15.901 10.707 -32.7% 10.707 -32.7%
System Total 23.411 14.814 -36.7% 16.685 -28.7%
Table VIII-4. Threshold “A” sub-embayment loads used for total nitrogen
modeling of the Nantucket Harbor system, with total watershed N
loads, atmospheric N loads, and benthic flux
sub-embayment watershed load
(kg/day)
direct
atmospheric
deposition
(kg/day)
benthic flux
net
(kg/day)
Head of the Harbor 0.792 22.239 -16.795
Polpis Harbor 2.175 2.190 26.450
Quaise Basin 1.140 20.126 43.010
Town Basin 10.707 13.888 -2.892
System Total 14.814 58.443 49.772
MASSACHUSETTS ESTUARIES PROJECT
160
Figure VIII-1. Contour plot of modeled total nitrogen concentrations (mg/L) in the Nantucket Harbor
system, for threshold “A” loading conditions.