Deep water oxygen levels in Sandy Lake (Bedford, NS) fall to precariously low levels 21Mar2023

Sackville River Regional Park as envisaged in a 1979 report. (Click on image for a larger version ).View 1979 Report. View website for the Sandy Lake – Sackville River Regional Park Coalition for the current vision of this park.

The concept of a ‘Sandy Lake-Sackville Regional Park’ harks back to the 1970s,   It would encompass lands surrounding Sandy and Marsh Lakes and the adjacent lands by the Sackville River (see map at right).   In our first  (2006) Regional Plan, reference was made  to  “Jacks Lake Park” as an “Additional Regional Park”  focussed on the east side of the lake.  There was reference to an existing “Sandy Lake Regional Park” – 130 forested acres on the east side of Sandy Lake officially opened in 2004 as the “Sandy Lake Park” –  but  lands to the west of Sandy Lake were given an “Urban Settlement” designation, meaning they were identified as an area for future growth (housing) in HRM, not conservation & recreation. (For more details see “2006 Regional Plan Note” at the bottom of  this post).

The Urban Settlement designation set in motion a requirement for a watershed study under Policy E-17 of the 2006 Regional Plan (see pp 44-52 in AECOM 2014 for details).

The desktop study (except for a few water samples taken in 2013), requested in June 2013, was completed Aug 25, 2014. From AECOM 2014:

The primary, overarching objective of the Sandy Lake Watershed Study, as expressed in Regional Plan Policy E-17,
is to: “…determine the carrying capacity of the watersheds to meet the water quality objectives which shall be adopted following the completion of the studies.”

Carrying capacity is a measure of the watershed’s ability to accommodate inputs from both man-made and naturally occurring pollutants without experiencing a significant decline in water quality and ecological function. In this study, different land development scenarios are evaluated to understand the potential water quality effects resulting from each scenario. The outcome of the study is to provide a number of guidelines and recommendations for the planning, design and implementation of new developments that will help to maintain existing water quality.

“In 2013, a large swath of land including Acadian old growth forest along the west side of Sandy Lake was suddenly clear-cut by a residential developer. (The land was subsequently sold to a different developer.) This action came as a surprise to residents as it was in an area originally designated for the Sandy Lake Regional Park. It became clear that rather than park land, those lands lying close to Sandy Lake could be developed with residences for as many as 16,000 people, and would add 8,000 vehicles to the Hammonds Plains Road.” SOURCE: Sandy Lake Conservation Association

AECOM (2014) used historic water quality info. and a few samples they collected in 2013  to “identify water quality objectives  for parameters that are affected by development” and then applied a Lake Capacity Model “to predict how future development may impact the phosphorus concentrations of the lakes”.

They set the WQOs (Water Quality Objectives) for Total P  at 50% above the “current values”  for Total P (12 ug/L  for Sandy Lake, 10 ug/L for Marsh Lake or 10.5 ug/L if they used their modelled current value). The resultant WQOs were 18 ug/L for Sandy Lake and 15 ug/L for Marsh Lake (or 15.5 ug/L if they used their modelled current value).

The Lake Capacity Model predicted Total P levels of 13-16 ug/L for Sandy Lake and 12 to 15 ug/L for Marsh Lake under 3 scenarios (Planned Development; Planned Development + Removal of Uplands WWTF and Septic Systems near Sandy Lake;  Adding Advanced Stormwater Management), i.e. the predicted levels with development fell within or not far above the WQOs. (In a subsequently modelled scenario 2b (Revised Planned Development extended) the predicted values for Sandy Lake  (18.1 ug/L) and Marsh Lake (16.0) slightly exceeded the WQOs.)

The Lake Capacity Model provides only a first approximation to reality.
Notes AECOM (2014):

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.

A robust water quality monitoring plan as recommended above  was not initiated following the acceptance of the AECOM 2014 Report.

The major variable of interest in relation to phosphorus loading for stratified lakes such as Sandy Lake is the deep water oxygen levels.  There is really no substitute for actually measuring those levels (rather than making a broad inference based on predicted &/or measured Total P levels) to assess actual lake health.

Beginning in 2017, I worked with two volunteers with the Sandy lake Conservation Association, Ed G and Derek S, to obtain three limnological profiles in the deepest area of Sandy Lake during the period of summer stratification in 2017, 2019 and 2022* and two profiles during the spring turnover period (2021, 2022). The variables, measured at 1 m or shorter intervals from top to bottom, were temperature, electrical conductivity (a measure of salt content) and dissolved oxygen.* The Aug 2022 sampling was conducted in collaboration with HRM under its new LakeWatchers Water Quality Monitoring Program.

These were the first  complete limnological profiles obtained  for Sandy Lake, however  top and bottom values for the same variables were obtained in previous studies in 1971 and 1998, giving us a set of 5 top-and-bottom measurements during the period of summer stratification covering a span of 51 years:

Table 1. Historic Shallow and Deep Water Temperature, EC and Oxygen values for Sandy Lake (Bedford) during the summer stratification period. 
1971: from Metropolitan Area Planning Committee 1971-1972: Water Quality Survey for Selected Metropolitan Area Lakes.  Lake sampled on Aug 30, 1971. Deep sample at  59 feet (18 m). Chloride was  8.0 at surface, 12.0 at 59 feet (18 m). EC and chloride were elevated  in the Southern Inlet sample (57.0 µS/cm, 11.0 mg/L). 1998: Nova Scotia Lake Inventory Program Sep 2, 1998. Deep sample at 19 m. Chloride   at surface was 29 mg/L at 19 m, 34 mg/L. 2017: Sampled Oct 3, deep sample at 17.5 m. 2019: Sampled Sep 30, Deep sample at 21 m. 2022 Sampled Aug 22. Two profiles, averaged the values (at 19,5 and 20m)

Although the data are limited, it’s clear that there have been big changes in deep water (bottom) dissolved oxygen and in conductivity (both top and bottom) over the 51 year period.

Sandy Lake Beach at 11:13 am on Aug 6, 2019. “an unpleasant, suspended, reddish, soapy material” appeared quite suddenly and the beach was closed.

Of particular concern is the progressive decline in bottom oxygen values over the 5 sampling dates, going from 5.o mg/L in 1979 to 1.18 mg/L in 2022. This has two major repercussions:

(i) Deterioration of the cool deep water refuge for salmonids  in summer.   5.o mg/L oxygen is at best on the border line for brook trout and salmon (Doudoroff & Shumway, 1970, CCME 1999). (Salmon have been returning to the Sackville River Watershed including Sandy Lake through the efforts of  the Sackville Rivers Association). Other species are also affected: “DO is considered an important measure of water quality as it is a direct indicator of an aquatic resource’s ability to support aquatic life…While each organism has its own DO tolerance range, generally, DO levels below 3 milligrams per liter (mg/L) are of concern and waters with levels below 1 mg/L are considered hypoxic and usually devoid of life.”- US EPA

(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* e.g., due to blooms of BGA  (Blue-Green Algae, or Cyanobacteria).  Numberg (2004) states that  “2 mg 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.”* See the introductory paragraphs in Tammeorg et al., 2020 for an explanation.

The continuous decline in deep water oxygen over time with levels below 2 mg/L reached in 2022* should be alarming. If this trend continues, the lake could go fully eutrophic and ‘skunky’ in the not-very-distant future.
*See  the limnological profiles: in 2022, oxygen levels at 16 m and deeper were all below 2 mg/L.

More observations e.g., as advised by Numberg (2004) would be required to determine the full extent of the “oxygen problem” in Sandy Lake. However, given that:

– already approved development in the watershed is ongoing (Bedford West Area 12),
– no special efforts have been implemented to reduce current phosphorus loading,
– elevated deep water P levels were noted by AECOM 2014 for two of three samplings in 2008, 2010 and 2011 and were suspected to be associated with low oxygen levels,
– increasing salt levels (mainly from de-icing road salt) coupled with salt stratification could at some point impede normal spring turnover, increasing oxygen deprivation (view Sandy Lake: Road Salts),
– an intense algal bloom occurred in 2019, and a BGA warning for the lake was issued in 2022,
– climate warming is leading to increased harmful algae blooms globally (see e.g., Paerl et al., 2019, Ho and Michalak, 2019)

there is little reason to believe that a major new development, as modelled by AECOM 2014, could be compatible with maintaining – or re-establishing – desirable water quality of Sandy Lake.

Clearly, if we value Sandy Lake  and Marsh Lake downstream for their many ecological and recreational benefits, we need to take steps now to reduce organic, salt and phosphorus loading from developed areas of the watershed.

We should also retain as much as can of the remaining undeveloped  lands in the Sandy lake Watershed in  their current natural or near-natural state as envisaged in the 1970s, and promoted more recently by the Sandy Lake-Sackville River Regional Park Coalition. 

2006 Regional Plan Note
The Final Draft of the 2006 Regional Plan is no longer available in full online. I did retain an electronic copy of the Regional Municipal Planning Strategy (downloaded at the time as a file lablleled “RMPS_FinalDraftApril06.pdf” Sandy Lake and Jacks Lake are cited as follows:

In CHAPTER 2 ENVIRONMENT,  Section 2.1.3 Regional Parks (pages 24 & 25)

…The 1975 Halifax Dartmouth Regional Development Plan, repealed in 1998, contained policies and Regional Park designations supporting a Regional Parks and Trail System. The objectives were to preserve seven natural landscapes of outstanding value and to establish interconnected trail system between them. Over the years, the Province and former municipalities acquired lands to create the present Regional Park system. However, the full scope of the plan was not completed. This, coupled with future population growth contemplated at higher densities for urban and suburban areas, requires additional areas to be preserved for future Regional Park development.

HRM intends to create additional Regional Parks at various locations throughout HRM including the Western Common, Blue Mountain – Birch Cove Lakes, Feely Lake, Jacks Lake, Second Lake, and Porters Lake. The existing and additional Regional Parks are identified in Table 2-3…

The Jacks Lake lands are under the ownership of HRM except for approximately 20 hectares (exact boundaries to be determined) in the ownership of the Province of Nova Scotia. HRM intends to carry out a study to determine the appropriate geographic boundaries of the  Jacks Lake Park. Remainder lands, including the lands owned by the Province, should be re-designated for development as appropriate as determined through the secondary planning process for the Sandy Lake Urban Settlement area.

In CHAPTER 3: SETTLEMENT AND HOUSING Section 3.1 Urban Settlement Designation (p. 38)


Evidently, “Sandy Lake Regional Park” cited in the 2006 Regional Plan refers to the “130 forested acres with frontage on Sandy Lake” included in the “Sandy lake Park” opened in 2004:

Evidently the “Jacks Lakes Park” identified in the 2006 Regional Plan refers to the ~1000 acres around Jack Lake that CHMC gave to the Province in 1986 and that was turned over to HRM in 1996 – see TIME LINE of SANDY LAKE – SACKVILLE RIVER (Marsh/Jack Lakes) Regional Park (on Sandy Lake Conservation Association website).

This entry was posted in Sandy Lake, Water Quality, watershed. Bookmark the permalink.