Disclaimer & Copyright Notices;
Optimized for the MS Edge
Soil & Water Conservation Society of
Metro Halifax (SWCSMH)
Modified: May 08, 2017
© S.M. Mandaville
Post-Grad Dip., Professional Lake Manage. (limneschebucto.ns.ca)
The citation for this documentation is:
Mandaville, S.M. TP/Cha
Predictive Models. Nova Scotia, Canada. Electronic media.
- Peruse our overview correspondence to regulatory authorities:-
- Deep station total phosphorus (TP)- comparison with our hindcast models; October 18, 2013 (14 p.)
- Phosphorus:- Details on LCC (Lake
Carrying Capacity)/Threshold values of lakes, and comparison with
artificially high values chosen by the HRM; March 14, 2014 (21 p.)
See also Selection of Phosphorus
for Nova Scotia- Phase I.
Predictive TP modelling
was based primarily on the following: extensive decadal research
spearheaded by several international peers in limnology under the
chairmanship of Richard A. Vollenweider PhD, formerly of the Canada
Centre for Inland Waters, Environment Canada, which culminated with the
consensus OECD (1982)- Organisation
for Economic Co-Operation and Development Report; on the Vollenweider(1976) TP
Predictive Model; and the published research of Peter J. Dillon FRSC et
al., formerly of the Dorset Research Centre, Ontario Ministry of
been incorporating other regressions published in the latest
international limnological journals as deemed necessary. This process will take several years for model
revisions as well as calibrations.
direct aerial deposition) concentrations were computed utilizing
published export coefficients in generally undisturbed similar natural
soils in Nova Scotia (cf., Hart et al, 1978; Mandaville, 2000; Scott et
Scott et al, 2003);
the post-development concentrations were obtained utilizing published
export coefficients (end-of-pipe mean year averages) of typical
residential and commercial/institutional developments (cf.,
Scott et al, 2003;
Vokey, 1998; and typical pollutants in
itself, we are continuing our intensive field sampling, generally at
storm sewer outfalls (inclusive of open channels), in order to expand
the data base for post-development scenarios and revise the predictive
models, if needed.
to areas served by
systems, our revised models did not incorporate the same assumptions as
in Hart et al (1978)
and Scott et al (2003) where the authors assumed
50% septic-derived phosphorus retention within 300m
of lakes in the Halifax/Wolfville soils. In
the Scott et al (2003)
report where Mandaville was a co-author, there was an inadvertent
omission made by not noting this down (and Mandaville regrets that).
Our export coefficients in such areas include all potential sources of
phosphorus inputs incorporated into the 50% export assumption; it
actually varied from 50% in some watersheds based on local info.
as I upgrade the models as needed, I am applying a much higher soil
retention of phosphorus in areas served with contour beds in comparison
with areas served with area beds. This was as a result of intense
discussions over the years with the engineering developer of contour
beds, David Pask MEng PEng.
As a worst case scenario, 0% retention may be assumed for the long term as per the Province of Ontario's guidelines, "Protecting Water Quality in Inland Lakes on Ontario’s Precambrian Shield" (2010).
characterisation of lakes impairment of various uses
and Kerekes, 1982)
|General level of production ........
|Green and/or blue-green algae fractions
|Hypolimnetic oxygen content .....
|Impairment of multi-purpose use of lake
graphical models utilized
Predictive graphical models are constructed with the EasyPlot software utilizing the data in our MS Excel spreadsheet models, the latter being `dynamic'. The world renown and internationally used base
models are the Organization for
Economic Co-Operation and Development (OECD)'s Management Model, and
the Vollenweider (1976) Model. These graphs
visually depict the modelled theoretical as well as any relevant
`recent' field values, hence, serve as superb bases.
This model synthesizes the standard OECD
equations for the relationships between average inflow phosphorus
concentration (Pj), expected average lake concentration Pλ,
and expected average chlorophyll concentration (Cha) as a function of
the average water residence time T(w). The model also gives approximate
indications of the expected trophic category.
As these categories are
management oriented, they are slightly more stringently defined (i.e.,
approximately at the class midpoints) than are the categories used for
diagnostic purposes. This provides a certain safety margin for the
design of the loading objectives. Since the model requires the
hydraulic residence time as one of the axes, it is not possible to plot
most lakes due to insufficient bathymetric data.
Although this model pre-dates the above OECD
(1982) Model, in most
cases it is more appropriate since one of the axes-variables, qs (areal
water load) is available for all lakes. In order to incorporate the
probabilistic scenario, the management categories from the OECD (1982)
model have been incorporated into this model.
When possible and relevant, lakes with sufficient bathymetric data were
plotted on both of the above models.
-plus- aerial deposition (B+A):
The theoretical background loading -plus-
direct aerial deposition have
been noted as "Th B+A", and in clearwater lakes it is expected that
these were the natural background values including direct aerial
Recent development scenario:
Onsites- those existing within 300 m
of all watercourses inclusive of
upstream areas (Dillon and
Rigler, 1975; Dillon et
al., 1986; and Dillon et
Urban/Serviced- existing developed areas in the watersheds with
sanitary sewerage exported out of the watershed.
Sewage Treatment Plant (STP) contributions taken into account.
Future development scenario:
- Onsite disposal systems:
- F-P (Future Probable)= lands within 300m of all lakes developed
with onsite systems @ 2.5 lots/ha density.
- F-U (Future Ultimate)= F-P scenario + lands within 300m of all
streams developed with onsite systems @ 2.5 lots/ha.
- Future Sewage Treatment Plant (STP) contributions taken into
- Urban/Serviced (watersheds developed as residential- sanitary
sewerage exported out of the watershed):
- F-P (Future Probable)= Urban/serviced area export coeff. @ 0.52
kg/ha.yr (Waller, 1977;
- F-U (Future Ultimate)= Urban/serviced area export coeff. @ 1.1
kg/ha.yr (Waller and
Notes of caution:
- Contribution from humans to sanitary sewage systems- Our original
models assumed 0.8 kg/capita/yr TP based on the Ontario models from the
1970's to the 1990's. Ontario reported lower values of 0.66
kg/capita/yr in 2006 due primarily to decreases in the phosphorus
content of detergents. We have now updated most predictive models in Excel. Though, we
have not revised the graphical models, but the pre-cultural values
would not change.
- Regarding pets (dogs and cats), we
calculated the contribution based on the relative body weights in
comparison with an average human being. Most of this would be
contributed via stormwater inputs.
- For contributions from waterfowl, peruse our submission to the Halifax
Watershed Advisory Board in year-2000.
- The predictive
modelling does not take into account potential large inputs of
phosphorus from failing pumping stations, bypasses
from treatment plants, cross-connections between sanitary and storm
sewers, and other unforeseen sources. But if a value is known, it can
easily be added in the `miscellaneous' column of the control
We salute the Chebucto
Community Net (CCN) of Halifax, Nova Scotia, Canada for
hosting our web site, and we applaud its volunteers for their devotion
in making `CCN' the best community net in the world!