Hutchinson Environmental Sciences Ltd. Revised Water Quality Model and Lake System Health Program Prepared for: District Municipality of Muskoka Job #: J150074 April 2016 Final Report Hutchinson Environmental Sciences Ltd. J150074 , District Municipality of Muskoka Revised Water Quality Model and Lake System Health Program April 5, 2016 HESL Job #: J150074 Ms. Christy Doyle Director of Watershed Programs District Municipality of Muskoka 70 Pine St. Bracebridge ON P1L 1N3 Dear Ms. Doyle: Re: Revised Water Quality Model and Lake System Health Program – Final Report We are pleased to submit this final report of the Revised Water Quality Model and Lake System Health Program for the District Municipality for Muskoka lakes. This has been a most challenging and scientifically interesting project, and we thank The District of Muskoka for their continued support over the course of the last several years while we worked to develop recommendations to revise the program to reflect the results of review in 2013, and again in 2015 to change the program emphasis. We appreciate that there may still be discussions required to move the technical recommendations presented herein into planning policy and look forward to the opportunity to assist with that. Sincerely, per: Hutchinson Environmental Sciences Ltd. Neil J. Hutchinson, Ph.D. President [email protected] Hutchinson Environmental Sciences Ltd. J150074 , District Municipality of Muskoka Revised Water Quality Model and Lake System Health Program Signatures Dörte Köster, Ph.D. Tammy Karst-Riddoch, Ph.D. Senior Aquatic Scientist Senior Aquatic Scientist Brent Parsons, M.Sc. Aquatic Scientist Hutchinson Environmental Sciences Ltd. J150074 , District Municipality of Muskoka Revised Water Quality Model and Lake System Health Program Acronyms 1 m off the lake bottom 1 mob Background Plus 50% BG+50% Dissolved Organic Carbon DOC Dissolved Oxygen DO District Municipality of Muskoka DMM Dorset Environmental Science Centre DESC Geographic Information System GIS Georgian Bay Forever GBF Hutchinson Environmental Sciences Ltd. HESL Lake of Bays Association LOBA Lake Partner Program LPP Lake System Health LSH Lakeshore Capacity Model LCM Muskoka Lakes Association MLA Muskoka Water Quality Model MWQM Ontario Base Map OBM Principal Components Analysis PCA Provincial Water Quality Objective PWQO Total Phosphorus TP Wastewater Treatment Plant WWTP Natural Heritage Review NHR Hutchinson Environmental Sciences Ltd. J150074 , District Municipality of Muskoka Revised Water Quality Model and Lake System Health Program Executive Summary Background The District Municipality of Muskoka (DMM) uses their Water Quality Model (MWQM), a variant of MOE’s “Lakecap” Model (2010), as one component of the Lake System Health program to guide planning policies for recreational lake development in a large and complex watershed of over 500 lakes and lake segments. The MOECC released their “Lakecap” Model and guidance document in 2010 as their recommended means of Lakeshore Capacity Planning. Prior to 2010, the MOECC encouraged use of this approach, although it had not yet been finaIized as formal Provincial guidance. In 2010, the DMM began a project to review and update the model to address changes in the Provincial approach and scientific background to the model since the last update was completed in 2005. The “Lakecap” approach is based on modelling the current phosphorus concentrations in a lake resulting from natural (or “background) sources and human inputs and then calculating the amount of phosphorus from human inputs (generally shoreline development) that the lake can sustain while remaining below a modelled phosphorus concentration of “Background + 50%” (the “lake capacity”). The MOECC approach requires that the model produce accurate estimates of phosphorus concentration that can be verified through a reliable lake monitoring program, such as that of the DMM. Although the MOECC model was developed and calibrated on a set of small headwater lakes in Muskoka and Haliburton, the MOECC advise that the model should be used in a watershed context – that is, any lake that is being modelled should incorporate hydrologic and phosphorus loading for all upstream lakes in its watershed (p. 29, MOE 2010). The Muskoka application of the model is thus complex, as it includes over 500 lakes and lake segments in the Muskoka, Black and Severn River watersheds. The Muskoka application also includes lakes and watersheds that exceed the calibration range used to develop the MOE model, as it did in the previous versions. The MOECC recognizes this in their guidance document and caution that modelling lakes that fall outside of the calibration range may be one reason that the model does not perform well. Results of 2005 Review The model was last updated in 2005 by Gartner Lee Ltd1. At that time, we recognized that not all aspects of Provincial guidance were defensible by the science, especially those aspects which advised that shoreline development could be managed by enforcing lakeshore capacities as a specific number of lots on a given lake. In order to do this, the model would have to provide accurate and defensible results for setting specific lot development capacities2. We concluded that the model could not set defensible lot development capacities and the DMM implemented the “Lake System Health” program as a result. “Lake 1 The senior author of the 2005 Gartner Lee report was Dr. Neil Hutchinson, and he lead the 2010-2015 revision project at Hutchinson Environmental Sciences Ltd. 2The model is implemented by calculating that a lake can sustain, for example, the phosphorus loading from 128 seasonal residences and maintain phosphorus concentrations below the Provincial standard of “Background+50%”. Thus, the “capacity’ of the lake is 128 lots and the Province advises that any development beyond 128 lots be refused in OP Policy. Our review concluded that modelled phosphorus concentrations often differed from measured values. The Province advises that the modelled phosphorus concentration should be accurate to within 20% of the measured value. The revised model, on average, overestimated phosphorus concentrations by 38%, and underestimated them by 23%. Error exceeded 40% in 81 of the 206 lakes monitored by DMM. This error means that one cannot defend a “capacity” estimate as fine as 128 lots for use in Policy. Hutchinson Environmental Sciences Ltd. J150074 , District Municipality of Muskoka Revised Water Quality Model and Lake System Health Program System Health” included planning policies and lake classifications that were based on lakeshore capacity calculations but also considered a) the ability of the model to predict phosphorus concentrations in lakes and b) lake sensitivity to additional development, when classifying lakes. The 2005 Lake System Health Program was therefore implemented as a modification of the previous DMM approach. Primary modifications included: Only one planning category (“Over Threshold”) was based on modelled phosphorus concentrations and capacity calculations. The remaining planning categories (“Low”, “Moderate” and “High” Sensitivity) used the model to determine lake sensitivity3 to phosphorus loads but did not set lakeshore capacity limits based on modelled phosphorus concentrations. Instead, the resultant policies addressed the means to manage future development by implementing a series of increasingly stringent study requirements through Water Quality Impact Assessments and Best Management Practices to protect water quality in accordance with lake sensitivity. Results of 2013 Review The most recent review began in 2010. HESL revised the 2005 version of the MWQM to incorporate the most recent MOECC guidance (MOE 2010, Paterson et al. 2006). These revisions included: Revised atmospheric loading coefficients for phosphorus, Revised wetland phosphorus export equation for phosphorus, Incorporation of smaller lakes (8ha and greater) in the model, Refined GIS mapping of lake areas, watershed areas and wetland areas by DMM staff, Updated estimates of existing shoreline development (including developed and vacant lots) from DMM records, Removal of the model factors that accounted for attenuation of septic system phosphorus (soil classification and staged attenuation of septic system phosphorus in 100m increments from the lakeshore to 300m) at the request of the MOECC, and Comparison of model output against the most recent 10 year record of total phosphorus measurements made in DMM lakes by the DMM. After extensive testing and analysis of the revised model we once again concluded that the modelled estimates of phosphorus concentrations in lakes were not reliable enough to set and defend specific lakeshore capacities as numbers of cottage or residential lots, as intended by the MOECC. Similar concerns were expressed by MOECC scientists, based on their recent experience, when we presented our findings to them in a meeting with DMM in January of 20134. 3 Lake sensitivity was defined for each lake based on its relative change in phosphorus concentration to a standard load of phosphorus (i.e. ‘responsiveness’) and the potential for phosphorus from shoreline development to reach the lake (i.e., ‘mobility’). 4 Although MOECC continues to recommend their 2010 “Lakecap” process they also recognize some of its weaknesses and are reconsidering their approach to managing shoreline development. In 2014, MOECC awarded HESL a contract to complete a scan of fourteen jurisdictions located in Canada and the