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Selection of Phosphorus Loading Model for Nova Scotia- Phase I

Web page of the Soil & Water Conservation Society of Metro Halifax (SWCSMH)

Updated: November 18, 2020              TP/Cha Predictive Models

Note: For an overview of the predictive modelling conducted by us for approx. one thousand (1,000) lakes/ponds in Nova Scotia, see the TP/Cha Predictive Models web page

Acknowledgements

Contents:

(cf., Scott, R., Hart, W., Mandaville, S., and Lowe, J. 2003. Selection of a Phosphorus Loading Model for Nova Scotia, Phase I. For: Nova Scotia Water Quality Objective and Model Development Steering Committee and Nova Scotia Dept. of Environment and Labour. 85p.)


Cautionary notes

Due to a combination of factors inclusive of time constraints and the contract terms-of-reference with the Province, the models developed by Shalom Mandaville have not been fully explored in the said report. As time unfolds, Mandaville makes other revisions and alterations inclusive of where highly coloured lakes are known to exist.

We have also established that the Ontario models (Dillon et al) are not, with exceptions, suitable for TP concentrations over 20 µg/l; for higher trophic ranges, the OECD regressions along with those derived from the OECD research are more applicable. This is probably because the OECD lakes cover a wide trophic range, from ultraoligotrophy to hypereutrophy!

In addition, Mandaville has been incorporating other regressions published in the latest international limnological journals as deemed necessary (lakescienceImg-atsign-bold.gifoutlook.com).

As opportunity presents 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!

With respect to areas served by septic 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 in 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.

points of interestFurther, 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).


Excerpts from the report

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Acknowledgements

Nova Scotia Dept. of Environment & Labour, and the CWRS, Dalhousie University!


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