Footnotes for In Conclusion…
1. Some background to my (David Patriquin’s) involvement. I was a faculty member of the Biology Department at Dalhousie University 1973-2008, with specialization in coastal marine biology, plant and microbial ecology; since retirement I have been active in several natural history and trail organizations (more details here). In the late spring of 2017, I was asked by the Sandy Lake Conservation Association if I would do a “flora survey” of Sandy Lake and Environs for along the lines I had conducted on the Williams Lake Backlands in 2013/2014. I agreed and conducted field trips on 22 days over the period June 14 to Nov 1, 2017; a few were mostly on water (paddling), most were on land. It was a volunteer activity, there was no payment and no contract. As a component of that study and because I was familiar with limnological techniques and out of curiosity, on Oct 3, 2017 I conducted limnological observations at 3 points in Sandy Lake with the help of a local volunteer. The results raised some concerns. In the late fall of 2017, I realized that far more observations – and time – were needed to adequately describe “Sandy Lake & Environs” at large. So rather than submit a single final report, I would post observations and related info on a website – Sandy Lake & Environs (Bedford, Nova Scotia) – on an ongoing basis. The website was launched on Dec 20, 2017. I posted a “A DRAFT Report On the State of Sandy Lake, the Historical Trends and its Future Trajectory” on Feb 23, 2021 which integrated all limnological observations to that point, but observations have been continuing and are reported in the section Surface Waters and it subpages.
2. 13 Species At Risk, for documentation, See
Avian & Species at Risk Surveys of the proposed Sandy Lake – Sackville River Regional Park
Report by Natural Wonders Consulting Firm to Sandy Lake Conservation Association, March 2020. 20 pages. “Species at Risk living within the proposed park boundaries include: Barn Swallow, Canada Warbler, Common Nighthawk, Common Snapping Turtle, Eastern Painted Turtle, Eastern Wood-Pewee, Evening Grosbeak, Little Brown Myotis, Monarch, Moose (Mainland Population), Olive-sided Flycatcher, Rusty Blackbird and Wood Turtle. The information on these species is found in this report under Species of Concern and in Table 2. Several important wildlife corridors were identified during the surveys, including two major wildlife corridors. The locations of these two major corridors along with a dozen smaller but important wildlife corridors are marked on Map 2: Wildlife Corridors”
Not in that list, but present in Sandy Lake and downstream waters are American Eel and Atlantic Salmon. The American Eel was assessed as of Special Concern by COSEWIC in April 2006. The status was re-examined by COSEWIC in May 2012 and designated Threatened. It currently has no status under the federal Species at Risk Act. It is listed by ACCDC as S3N (Non-breeding population: Threatened) in Nova Scotia. Some populations of Atlantic Salmon have SAR status federally; Atlantic Salmon is listed by ACCDC for Nova Scotia as SIB and SIN (Both Breeding and Non-breeding populations Critically Imperiled).
3. Details of the 2024 Limnological Observations are presented in these four pages on this website:
(i) versicolor.ca/sandylakebedford/Surface Waters/Sandy Lake/
Limnological Profiles
and
(ii)…Limnological Profiles/
2024 Limnological Profiles – return to historic trend of declining oxygen
and its subpages:
(iii) Addendum 1: Trends in Conductivity/Salt Content
(iv) Addendum 2: On Wetlands
4. The limnological profiles consist of measurements made with a Water Quality Multimeter of temperature, conductivity (a measure of salt content), oxygen and (sometimes) pH at 1 meter or shorter depth intervals at the deepest spot in the lake.
Beginning in April of 2022, we conducted our observations under the umbrella of the newly formed HRM LakeWatchers program, which allowed us to make the observations within more consistent time intervals – prior to that, the equipment was borrowed from community equipment banks and we could not always get it at the desired sampling times.
Sandy Lake is one of 72 Lakes that had been “assessed as either highly vulnerable or moderately vulnerable through a previous study” and were selected initially to be included in the LakeWatchers Program. The Vulnerability Class for Sandy Lake was “Class A – High Vulnerability” and the Priority Concerns concerns were identified as “Eutrophication” and “Bacteria Contamination (Beaches)” – Table 9, p 53 in HRM Water Quality Monitoring Policy and Program Development (AECOM 2020)*. As Sandy lake is a “Class A — High Vulnerability Lake”. 2 sampling events per year are prescribed (Table 12, p 66)
– once in spring during mixed-water column conditions [our samplings have been in April which is at or following spring turnover of the water column]
– once at the end of summer [our sampling have been in the latter part of August which is close to the time of peak summer stratification]
In addition to the limnological profiles at the deepest spot in the lake, the observations at the deepest spot under the LakeWatchers program include a secchi disk measure of water transparency, top and near-bottom water samples analyzed for TP (Total Phosphorous, and chloride (near bottom sample only) . Also, surface water near the outlet is sampled: measurements are made with the Multimeter as described above but there is only one surface water measurement ; and a water sample is taken and analyzed for TP ( the spring sample only) and chloride. Measurements of chlorophyll-a in water samples are sometimes made for some or all samples or none; likewise E.coli counts are sometimes made on some surface water samples.
* Halifax Regional Municipality Water Quality Monitoring Policy and Program Development, Prepared by: AECOM Canada Ltd., September 2020, 99 pages + Appendices, 505 pages total. Also view Environment & Sustainability Standing Committee June 3, 2021 SUBJECT: Water Quality Monitoring Policy & Program Development (14 pages)
5. Identifying lake water quality trends and effective monitoring strategies in a rapidly urbanizing region
Doucet, C., 2022, [Master of Applied Science, Dalhousie University]. http://hdl.handle.net/10222/82119. The thesis has two Results Chapters. CHAPTER 2 – SYNOPTIC SNAPSHOTS: MONITORING LAKE WATER QUALITY OVER FOUR DECADES IN AN URBANIZING REGION. This chapter is the basis of a significant paper for which Doucet is first author: Synoptic snapshots: monitoring lake water quality over 4 decades in an urbanizing region C. Doucet et al., 2023. In Lake Reservoir Management. “Synoptic water quality surveys—measuring major ions, nutrients, pH, organic matter, and trace elements—have been conducted in ∼50 lakes in the Halifax Regional Municipality (Nova Scotia, Canada) once per decade since 1980. In this study, lake water quality over 40 yr was examined and urban development was evaluated as a possible driver of observed changes.” Sandy lake (Bedford) was one of those 50 lakes.
CHAPTER 3 – TRACKING TROPHIC STATE IN URBAN LAKES IN A CHANGING CLIMATE: ARE EXISTING MONITORING PROTOCOLS STILL EFFECTIVE? This chapter has not yet been published. From the Abstract: Trophic state parameters were tracked over the 2021 open-water season in fifteen lake basins in the Halifax Regional Municipality (HRM), Atlantic Canada, to examine relationships among productivity, nutrient dynamics, thermal stratification, and hypolimnetic anoxia.” Two of those lake basins were in Sandy Lake (Bedford).
6. See A DRAFT Report On the State of Sandy Lake, the Historical Trends and its Future Trajectory (Page on this website). There is also an extended summary.
7. See Quantified Hypoxia and Anoxia in Lakes and Reservoirs
by Gertrud K. Nürnberg in The Scientific WorldJ OURNAL (2004) 4, 42–54. “2mg L–1 measured by a DO probe about 1 m above the sediment usually coincides with anoxic conditions at the sediment surfaces located at that depth.”
8. See 2024 Limnological Profiles – return to historic trend of declining oxygen (Page on this website)
9. See discussion under 2024 Limnological Profiles – return to historic trend of declining oxygen “(ii) There is increased likelihood that intervals of hypoxia (low oxygen) in deep water could result in anoxic conditions (no oxygen) at the sediment surface and associated mobilization of phosphorous, accelerating eutrophication and marked deterioration of water quality…”
10. See, e.g., Anoxia begets anoxia: A positive feedback to the deoxygenation of temperate lakes by A. Lewis et al., 2023 in Global Change Biology,
Fig. 1. Profiles for Temperature, Dissolved Oxygen and Total P at the deep site in Aug 2021 shown in Doucet (2022), reproduced with permission. Identifying lake water quality trends and effective monitoring strategies in a rapidly urbanizing region. Doucet, C., 2022, [Master of Applied Science, Dalhousie University] Profiles for Sandy Lake are shown in Electronic Supplement 3.
11. Casey Doucet’s profiles for Sandy lake in late August 2021 are shown at right. Note in the middle figure the dip in oxygen at about 6 m depth.
12. See 2024 Limnological Profiles – return to historic trend of declining oxygen
13. See Metalimnetic Oxygen Minima (page on this website) for an extract from Wetzel’s Limnology, 3rd ed. (2001), pp159-160.B. Metalimnetic Oxygen Minima; “The converse condition [to a metalimnetic oxygen maximum] a metalimnetic oxygen minimum exhibiting a negative heterograde curve (Fig. 9-5b)*, is much less frequently observed…” Other literature on the MOM (Metalimnetic Oxygen Minima) is also cited on this page. In regard to Nova Scotia: “I have not been able to locate any studies specifically referencing Metalimnetic Oxygen Minima in Nova Scotia which may indicate that to date it has not been a common phenomenon. Regardless, climate warming and increasing urbanization could lead to its more common occurrence. In Brylinski’s 2002 report on the Nova Scotia Lake Hypolimnion Project, Metalimnion Oxygen Minima appear to present in 4 of the 20 lakes surveyed (profiles are given in Appendix III). As mentioned above, of the 4 lake profiles for HRM area lakes presented by Doucet 2022 that were 15 m and greater, distinct dips in the metalimnion oxygen were present in the two (one of them Sandy Lake) that also exhibited very low oxygen and highly elevated total P levels near the bottom.” – from 2023 Limnological Profiles, effects of episodic precipitation, and occurrence of a Metalimnetic Oxygen Minimum in Sandy Lake (Bedford, NS) (page on this website). As well, I discussed the phenomenon with the late Don Gordon and with Shalom Mandeville, both did not know of any formal documentation of MOMs in Nova Scotia.
14. See: Canadian Water Quality Guidelines for the Protection of Aquatic Life DISSOLVEDOXYGEN (Freshwater). Canadian Environmental Quality Guidelines Canadian Council of Ministers of the Environment, 1999. From that document:
“The Canadian water quality guidelines for the lowest acceptable DO concentrations are 6 and 5.5 mg·L-1 for the early and other life stages, respectively, in warm-water ecosystems, and 9.5 and 6.5 mg·L-1 for the early and other life stages, respectively, in cold-water ecosystems. The guidelines were derived from the U.S. Environmental Protection Agency’s “slight production impairment” estimates (USEPA 1986), with an additional safety margin of 0.5 mg·L-1 to estimate threshold DO concentrations.”
15. “The intensive metalimnetic respiration in lakes forming a MOM can be expected to accelerate nutrient cycling close to the photic zone and thus, may further stimulate primary production.” – from Krelling et al., The importance of physical transport and oxygen consumption for thedevelopment of a metalimnetic oxygen minimum in a lake. Limnol. Oceanogr. 62, 2017, 348–363.
16. Spring Total P values in Oligotrophic to low Mesotrophic range: View (i) values of Spring Total P for Sandy Lake 1980 to 2021 in Synoptic snapshots: monitoring lake water quality over 4 decades in an urbanizing region, Supplemental Material by Doucet et al. 2023 in Lake and Reservoir Management; (ii) Values for Total P 1979-2014 in AECOM 2014, Fig 8, page 22 (spring values only) & Fig 9, page 24 (all values) (iii) Total P spring values, 2022 onward: 2022 – 5.3 ug/L; 2023 – 10 ug/L; 2024 6.6 ug/L at the outlet (see Limnological Profiles).
17. See Trophic States of Lakes (page on this website) for a description of features associated with different lake Trophic Levels.
18. From AECOM 2014, page iii, bolding inserted:
The predictions from the phosphorus load model are consistent with observations of urbanization in other watersheds. However, the degree of influence of urbanization on water quality in Sandy Lake can only be approximated using the phosphorus load model because of limitations arising from assumptions and uncertainty in the application of the model. Therefore a robust water quality monitoring plan is proposed for the Sandy Lake watershed to provide a further assessment of current conditions and to evaluate the impacts of development on the water quality.
19. From AECOM 2014, p. 21:
Total phosphorus in Table 3 ranged from 2 ug/L to 43 ug/L between 2006 and 2013 (Figure 8). The median concentration of total phosphorus is 12 ug/L, which places the current water quality of Sandy Lake in the lower end of the mesotrophic range. This indicates the lake water quality is good and has moderate biological productivity.
From AECOM 2014, p. 31:
For the Sandy Lake watershed AECOM recommends the use of Environment Canada’s trophic status classification to set WQOs for total phosphorus. As noted in section 1.2.1, an objective of the 2006 HRM Regional Plan is to “maintain the existing trophic status of our lakes and waterways”. This suggests that both Sandy and Marsh Lakes should be maintained in their current mesotrophic state and so the WQO for total phosphorus should be the upper limit of the mesotrophic range, or 20 ug/L. However, since both lakes are currently at the lower end of the mesotrophic range, considerable water quality degradation could occur before the lakes were at risk of exceeding such a WQO
20. ‘Shallower and Smaller Lakes are more prone to oxygen deficiency than Deeper and Larger lakes’, see for example,
– For a set of Ontario lakes, Malot et al., 1992 observed that “lake morphometry exerts a large influence on profiles and this influence is particularly evident in shallow (<20 m maximum depth) oligotrophic lakes” and that “Predictions of O2 profiles are sensitive to changes in TP concentrations, with all study lakes predicted to have severely O2-depleted hypolimnions by the end of summer at an epilimnetic TP of only 15 ug.L-1.”
– Extracts from the comprehensive review of Nutrients and Algae Water Quality Guidelines by the B.C. Ministry of Environment and Climate Change Strategy:
A small lake which is stratified and has a phosphorus concentration greater than 10 or 15 ug/L generally has some degree of hypolimnetic oxygen depletion which may be a constraint to fish habitat (loss of cool water refuge) or food supply (particularly change in benthos)…
Some lakes may have marginal hypolimnetic oxygen concentrations at concentrations of phosphorus as low as 7 or 8 ug/L (Nordin and McKean 1984).
21. See: Longer duration of seasonal stratification contributes to widespread increases in lake hypoxia and anoxia, by Jane et al. 2023 in Global Change Biology
22. Document C030 – Sandy Lake, date 2021. Posted on HRM website
“Request by Sandy Lake Holdings (Clayton Developments) for a new serviced mixed-use (residential/ commercial) community”
23. Ecological Features Assessment and Unanimous…
26 Removel of P etc by wetlands
28. large unidentified sink for phosphorous in their budgeting for the Lake Capacity Model.
30. Ref to Addendum 2 Wetlands, give link
32. See the NS Gov. document Wetland Compensation: What’s Required and What Are My Options