Sandy Lake

  PAGE UNDER REVISION Dec 26 – 

SL Fig 1: The three lakes of Sandy Lake & Environs shown on Google Earth. Sandy Lake flows into Marsh Lake and thence into the Sackville River. Jack lake is in a separate watershed. Sandy Lake, but not Marsh Lake and Jack Lake receives waters from storm sewers.
Click on images on this page for larger versions

On this Page: After a brief introduction to the three lakes,   historical information on Sandy Lake is integrated with recent observations (2017-2020 and ongoing, given in other pages on this website) to provide an overview of the history, current state and  future trajectory of Sandy Lake. For simplicity, Tables and Graphs and Charts and Maps are all referred to as “Figures” and are numbered sequentially (Fig SL 1, Fig SL 2…).

Contents
1. THE THREE LAKES
2. SANDY LAKE
2.1 MAJOR STREAMS & BATHYMETRY
2.2 APPROVED AND POTENTIAL FUTURE DEVELOPMENT
& PROPOSED REGIONAL PARK
2.3 AQUATIC LIFE
2.4  TEMPORAL TRENDS IN pH
2.5  ACID SLATE HAZARD
2.6 TEMPORAL TRENDS IN ELECTRICAL CONDUCTIVITY (SALT)
2.7  LIMNOLOGICAL PROFILES
2.8  SPATIAL and SEASONAL  VARIATION IN  pH AND EC
2.9 WATERCOURSE WETLANDS
2.10 BACTERIA AND ALGAE
2.11 FUTURE TRAJECTORY


1. THE THREE LAKES
There are three lakes in the area encompassed by Sandy Lake and Environs/ the proposed Sandy Lake-Sackville River Regional Park:

Sandy Lake, a headwater lake in the Sackville River watershed.

Marsh Lake, downstream from Sandy Lake via Peverill’s Brook; it drains into the Sackville River.

Jack Lake, on a separate watershed,  drains into Papermill Lake (outside of the proposed Sandy Lake Regional Park) and thence to the Bedford Basin.

Some morphometric and water chemistry data for the three lakes from the Jack Lake CHMC/NSDH Report (1986) are given below:

SL Fig 2: Morphometric (above) and chemical (below) stats for the three lakes. From Jack Lake Environmental Evaluation Final Report. Canada Mortgage and Housing Corporation & Nova Scotia Department of Housing, 1986.

So these are quite different lakes. Sandy Lake is  relatively deep,  Marsh Lake shallow, and Jack Lake very small and acidic. Sandy Lake and Jack Lake are deep enough to stratify (according to Brylinski, 2002, such lakes are larger than 1 ha and generally >3 m depth for brown-water lakes and >6 m for clear-water lakes). Jack Lake is a brown water lake, Sandy Lake has very little colour, Marsh Lake, some. Sandy Lake, but not Marsh Lake and Jack Lake receives waters from storm sewers.

2. SANDY LAKE

2.1 MAJOR STREAMS & BATHYMETRY

SL Fig  3:
(a) Watersheds of Sandy Lake & Environs and Major Streams of the Sandy Lake sub-watershed
(b) Ed Glover’s Bathymetric Map of Sandy Lake superimposed on PLV Map.
PLV refers to the Nova Scotia Provincial Landscape Viewer; blue highlighting and directional arrows are inserted on the PLV map. The Ed Glover map is based on depth soundings in 2006.
(Click on image for larger version.)

Above Left: Most of the surface water enters Sandy Lake via streams on the west side of the lake, with the greatest concentration in the southwest, converging on the southwest corner of the lake. The (sub-sub) watersheds for each and all of the major streams flowing into Sandy Lake include settled areas, however currently the lands closest to the lake on the major streams are lightly settled or not not settled. Acid slates occur at the outer reaches of watershed on the western side of Sandy Lake.

Above Right: There are 3 deep spots, with maximum depths of 21 m (northernmost), ~19 m and ~18 m. The lake is normally dimictic, thermally statifying in winter and summer and turning over in the spring and in the fall.  Also view Damon et al., 2002 Map.

2.2 APPROVED AND POTENTIAL FUTURE DEVELOPMENT
& PROPOSED REGIONAL PARK

SL Fig 4: Locations of proposed Sandy Lake-Sackville River Regional Park and impending and proposed major development in the Sandy Lake sub-watershed.  Coloured: Proposed Sandy Lake-Sackville River Regional Park. DND: Dept of National Defense. Mostly mature/old growth forest.  A: Bedford West Development Sub-Area 12 (approved but still largely undeveloped). B: Proposed development (up to 15,000 people)

The coloured lands are those of the proposed Sandy Lake-Sackville River Regional Park (approx 2800 acres/1133 ha in total);  approx. 1000 acres/405 ha  currently belong to HRM. Area= A has been approved for development (Bedford West subarea 12) but is currently largely undeveloped; development has been proposed for Area B. Both Area A and Area B  include significant portions of the streams that converge on the major inlet at the southwest end of Sandy Lake. They also include significant watercourse wetlands.

2.3 AQUATIC LIFE

Sandy Lake hosts seagoing fish (Atlantic Salmon, American Eel and Gaspereau). Salmon grilse  have been sighted in the last 2 years and salmon were present historically. The Sackville Rivers Association has been working since the late 198os to bring back salmon through habitat restoration and salmon stocking and has installed digger logs on Peverill’s Brook which drains from Sandy Lake through  marsh lake and into the Sackville River. American Eel have also been observed within the past 2 years and historically, and Gaspereau are regularly observed in the shallows in the spring months. Smallmouth Bass invaded the lake some time ago and are the major fish taken by fishers. The fringing wetlands support large populations of frogs, mostly green frogs and bullfrogs, also breeding toads; and Snapping Turtles (endangered).  Sandy Lake has supported two pairs of Common Loons in the past, in recent years, 1 pair. There are also Beavers and River Otters. Beavers regularly build dams on some of the inflowing streams, also on Peverill’s Brook, and maintain lodges on Sandy Lake. The freshwater mussel Pyganodon cataracta occurs in abundance at Sandy Lake.  View About the Lake Fauna and submenus for more info.; also Common Snapping Turtle and Species Lists.

2.3 TEMPORAL TRENDS IN TOTAL P

Based on Total Phosphorus values which have increased over time, AECOM 2014 concluded that Sandy Lake has “transitioned from a generally oligotrophic state to a mesotrophic state.” 

SL Fig 5: Historical Total Phosphorus values for Sandy Lake. This is  a screen capture of Figure 9 from the Halifax Regional Municipality Sandy Lake Watershed Study Final Report (AECOM 2014). Click on image for the report.

Not included on the chart above: Mandell (1994) reported a mean annual Total P value for 1991/92 of 9 ug/L.

2.4  TEMPORAL TRENDS IN pH 

SL Fig 6:  Historical values of Sandy Lake pH. Values are for near surface samples on single days in each of the years shown. View sources

The interpretation of pH changes is complicated by the influence of acid rain and the lack of values earlier than 1955. From the mid-1950’s through to 1980s  average lake pH in NS dropped 1-1.5 units1 due to acid rain. The values for Sandy Lake in 1977 and 1980 are below requirements for salmon (~5.0 and greater for adults, >5,4 for fry 2), while the 1955 value is close to the lower limits for salmon.

As salmon were in The Sackville River system/Sandy Lake historically, it seems that pH values favourable for Atlantic salmon must have existed in Sandy Lake prior to the era of increasing acid rain.  Emission controls were implemented in the 1990s and reductions in stream acidity in northeastern NA began to be observed in the 2000s, although not in much of Nova Scotia on soils developed on slates and granite.3

Increases in pH (less acidity) have been reported recently for the Pockwock and Lake Major water reservoirs.4 As sugar maple, a calcium-demanding species 5, occurs on on the thick drumlins by Sandy Lake, it can be inferred that the forests/drumlins by Sandy Lake (also Marsh Lake) provide some watershed buffering of lake pH. (See AECOM 2014, Fig 5 for distribution of drumlins.)

pH of surface water tends to increase with the urbanization/the degree of development within a watershed e.g. though runoff of lawn fertilizers including lime,   so some or most of the more recent increase in pH is probably associated with more settlement and roads.6, 7
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1. Ginn et al. 2007. Assessing pH changes since pre-industrial times in 51 low-alkalinity lakes in Nova Scotia, Canada Can. J. Fish. Aquat. Sci. 64: 1043–1054.
2. Also,  pH in the range  4.5 to 5  is cited by White et.al  1981 for Sandy Lake in 1980; liming had only a transitory effect (White et.al  1981. On the feasibility of rehabilitating acidified Atlantic salmon habitat in Nova Scotia by the addition of lime. Fisheries Vol 9(1):1-3).  Salmon fry are highly sensitive to ph 5.4 and below, adults to pH <5.0, but it depends on the source of acidity, tolerance being less when the acidity is derived from sulphates in acid rain than from naturally occurring humic acids. Critical pH values for brook trout are cited as pH 4.7 to 5.2. Farmer, G. Effects of low environmental pH on Atlantic salmon in Nova Scotia. 2000. Canadian Stock Assessment Research Document 2000/050. Baldigo and Lawrence 2001. Effects of stream acidification and habitat on fish populations of a North American river. Aquat.Sci.63 (2001) 196–222.
3. Clair, T.A., Dennis, I.F., and Vet, R. 2011. Water chemistry and dissolved organic carbon trends in lakes from Canada’s Atlantic provinces: no recovery from acidification measured after 25 years of lake monitoring. Can. J. Fish. Aquat. Sci. 68(4): 663–674.
4. L.E. Anderson et al., 2017.Lake Recovery Through Reduced Sulfate Deposition: A New Paradigm for Drinking Water Treatment. Environ. Sci. Technol., 2017, 51 (3), pp 1414–1422.
5. Long, R.P. et al. 2009. Sugar maple growth in relation to nutrition and stress in the northeastern United States. Ecol Appl. 2009 19:1454-66.
6. Impervious surface as an indicator of pH and specific conductance in the urbanizing coastal zone of New Jersey, USA. Tenley M.Conway 2007. Journal of Environmental Management 85: 308-316.
7. For Halifax area, see Synoptic water quality survey of selected Halifax-area lakes : 2011 results and comparison with previous surveys Pierre M. Clement and Donald C. Gordon 2011. Can. Manuscr. Rep. Fish. Aquat. Sci. 3170: xi + 98 p.

2.5  ACID SLATE HAZARD

A set of water quality observations on Sandy Lake in 20018 revealed an exceptionally low pH value of 3.38 for the “Northern Inlet”. The same site sampled on Aug 21, 2017 had a pH value of 5.7. The low value in 2001 is likely due to  exposure of acid slates in the northwestern part of the watershed (see AECOM 2014, p 8) as the origin of the brook (Northwestern Brook or Karen’s Brook) lies at the edge of the acid slates (Conrad et al., 2002 p31.    Conrad et al. 2002, p28 commented: “We suspect that much of the flow from the Northern Inlet “short-circuits” the lake by flowing directly across to the northern outlet and leaves the lake, with relatively low impact.”

While flow into Sandy Lake at the Northern Inlet may have relatively little influence on water quality of Sandy Lake at large, flushes of such highly acidic water into Peverill’s Brook could be very hazardous to aquatic life.  A local  example: release of highly acidic water by blasting for development in the upper part of the Woodens River system is suspected to be the cause of a sudden decline in Mayfly populations in 1989, followed by precipitous decline in brook trout and increase in yellow perch. View Where have all the mayflies gone? The problem is akin to well documented impacts of acid mine drainage, and is very expensive to counteract or to remediate.9 Clearly, blasting of acid slates in the Sandy lake watershed needs to be avoided.
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8. Sandy Lake Development Impact Assessment Final Report by D. Conrad et al. 2002 Biological Engineering Department, Dalhousie University
9. Acid mine drainage formation, control and treatment: Approaches and strategies. Jeffrey G.Skousen et al., 2018. The Extractive Industries and Society 6:241-249

2.6 TEMPORAL TRENDS IN ELECTRICAL CONDUCTIVITY (SALT)

Values of electrical conductivity (EC)  in the area of 30-60 uS/cm are typical of pristine lakes in the Halifax region. 7 EC values for Sandy Lake were in that range in 1955  and 1971, and 1980 (not in 1977 however) but samples taken from 1985 onward were well above 100 with an overall upward trend. The low values in 1955 and 1971 are consistent with  the lake being well below the mesotrophic range in those earlier years (AECOM 2014, as cited above).

SL Fig 7: Historical values of Sandy Lake EC (electrical conductivity). Values are for near surface samples on single days in each of the years shown, except for 2020 value which is a an average for values (11) over a whole year. View sources. More values to be added from Appendix C of AECOM 2014 but that will not change the overall trend.

Electrical conductivity (EC) tends to increase with urbanization.6 In Nova Scotia, our liberal use of road salt is blamed for much of the trend of increase in conductivity in EC of Halifax area lakes over the interval 1980-2000 as revealed in synoptic studies7:

SL Fig 8: Historical EC values for selected Halifax-area lakes including Sandy Lake (enlarged in inset).  From Clement, P.M. and D.C. Gordon. 2019, Fig. 5 (Conductivity readings as measured by Environmental Services Laboratory) in Synoptic water quality survey of selected Halifax-area lakes: 2011 results and comparison with previous surveys. Can. Manuscr. Rep. Fish. Aquat. Sci. 3170: xi + 98 p.

SL Fig 9. Depth profiles of temperature, EC and oxygen at the deepest point in Sandy Lake on Sep 30, 2019.

2.7  LIMNOLOGICAL PROFILES 
The profiles reveal low oxygen and elevated EC (salts) in the deeper layers (the hypolimnion)

A set of vertical profiles of temperature, oxygen, EC and pH were obtained for 3 sites on Sandy Lake ON Oct 3, 2017, using a Wet-pro Field kit borrowed from the Community Based Environmental Monitoring Network at St. Mary’s University. I had wanted to do these measurements in August to view summer stratification at its peak, but the equipment was not available then. Hence measurements were made on Oct 3 when the water column was likely in the process of “de-stratifying”. View Limnological Profiles for the results.

The oxygen values are of particular note. The phosphorus models in effect attempt to predict lake conditions  but the oxygen profiles give a more direct and description of the state of the lake than total P values. The results from Oct 3, 2017 indicated that  oxygen values the oxygen content of the deeper layers (2.25 mg/L)  were below guidelines for both salmonids and more generally, aquatic life.  (View Limnological Profiles).  This state is consistent with AECOM’s conclusions based on Total Phosphorus measurements that the lake is moving from an oligotrophic (nutrient-poor) into a mesotrophic state.  Mesotrophic lakes are richer in nutrients than nutrient-poor oligotrophic lakes but are not nutrient-rich eutrophic lakes in which oxygen is depleted in deeper layers.)

Another profile, at the deepest point of the lake was obtained by Ed Glover on Sep 30, 2019, and  indicated similarly low oxygen the deepest water, (View Limnological Profiles). The lake was still strongly stratified on that date; the deep water temperature was more than 1 degree above that observed in 2017.

It seems that the profiles obtained in 2017 and 2019 are the only detailed limnological profiles for Sandy Lake. However there are comparable earlier data for water samples taken at the surface, and near the bottom at deeper parts of the lake:

SL Fig 10: Historic Shallow and Deep Water Temperature, EC and Oxygen values
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 at S 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 in  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

So at peak stratification in 1971, the oxygen level at the bottom was twice the values in 2017 and 2019. In 1998 oxygen level (3 mg/L) was already well below that of 1971, but above the values we observed in 2017 and 2019, so the overall trend is downward.

In 2017 the EC (electrical conductivity) of surface water had increased about 4.6 fold over 1971, and the bottom EC was 79 uS/cm greater than at the surface, compared to a difference of only 2 uS/cm in 1971.

The increases in EC are concerning. As differences in conductivity/salt content between surface and deeper water increase,  density stratification of the water column increases  and at some point can impede  seasonal turnover of the water column associated with temperature changes8, and thus re-oxygenation of the deeper layers; in turn that can lead to permanently low or no oxygen in the deeper layers and require physical mixing to be rectified  as at at Oathill lake in Dartmouth.
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8. For example,  view A reduction in spring mixing due to road salt runoff entering Mirror Lake (Lake Placid, NY) by B. Wiltse et al., 2019, Lake and Reservoir Management 36:109–121. Normal spring mixing in Mirror Lake (50 ha, 18 m max depth) failed to occur in 2017 when hypolimnion (deep water) chloride was approx, 70 to 110 mg/L (~316-490 uS/cm) compared to 30 to 50 mg/L (~131-220 uS/cm) at the surface. Surface water values for Sandy Lake are similar to those for Mirror Lake which is of similar size and depth; deep water Sandy values are not there yet but EC of incoming streams are well above those values, especially in winter. The authors conclude: “The incomplete spring mixing resulted in greater spatial and temporal extent of anoxic conditions in the hypolimnion, reducing habitat availability for lake trout. Restoration of lake mixing would occur rapidly upon significant reduction of road salt application to the watershed and improvements in stormwater management.”

There appears to have been a  ‘salt signal’ for Sandy Lake as early as 1971:

SL Fig 11: EC and chloride values for two inlets, middle of the lake shallow and deep and outlet in 1971. From Metropolitan Area Planning Committee 1971-1972: Water Quality Survey for Selected Metropolitan Area Lakes.

The two inlet EC (Conductivity) values were both substantially higher than the lake surface  and outlet values as were the chloride values. Chloride (but not EC) was elevated at depth compared to the surface.

Ogden 1971, cited in Mandell 1994, described Sandy Lake as belonging to his Category 2 : “Oligotrophic lakes showing increase in turbidity after a heavy rain and some influence due to road salting” (Other categories were 1 Highly oligotrophic, 3 Substantial cultural Influence.)

2.8  SPATIAL and SEASONAL  VARIATION IN  pH AND EC

Four sets of data were obtained:

(i) In 2017, I  routinely carried a pocket conductivity meter and frequently a pocket pH meter (the latter borrowed from CBEM at St. Mary’s University), and made measurements of water on surface waters as I encountered them.

Values of electrical conductivity, pH and temperature for surface waters on various dates in 2017.
Lake EC
Above: Values of electrical conductivity, pH and temperature for surface waters on various dates in 2017.
Click on image for larger version
Higher EC values were observed for streams on the west side of the lake than on the east side of the lake. In general, the pH values for streams were lower than values for Sandy Lake (see also figure above) except for Bob’s Brook (also known as Johnson’s Brook; it enters the lake at the southwest corner of the lake) and Peverill’s Brook flowing to Marsh Lake.REWRITE. pH values for Sandy Lake were in the range 6.6 to 7.2, while EC values were mostly in the range 170 to 180. Streams on the east side of Sandy Lake had EC values in the range 30-51 uS/cm, pH 4.9 to 5.8. EC values for 2 streams on the west side were 78 and 98 uS/cm (pH 4.8, 5.4) likely reflecting some input of solutes from developments in the Gatehouse run/Lucasville Road area within the watershed.

(ii) On Aug 10, 2017, I paddled the perimeter of Sandy Lake and measured electrical conductivity (EC), occasionally pH at regular intervals.

Lake EC
Above: Values of electrical conductivity (yellow numerals; units are uS/cm), pH (red) and temperature (red) of surface water at different locations on Sandy Lake on Aug 10, 2017.
Click on image for larger version

pH values for Sandy Lake were in the range 6.6 to 7.2, while EC values were mostly in the range 170 to 180. Elevated EC values (203, 271/291, and 420/398 uS/cm) occurred in 3 bays  where streams draining settled areas at the south of the lake (view Stream Map).

The highest stream EC and pH values were for the major inlet at the southwest corner of the lake (EC 346, 348 uS/cm pH 7.4) where Johnson’s Brook (sometimes known as Bob’s Brook) enter the lake; values were also elevated in two other bays at the south of the lake where streams enter the lake (CORRECT THIS!!//SHOW FIGURES.)))

(iii) To further investigate the origins of the high EC water coming into Sandy Lake via the SW Inlet,  On Nov 8, 2018 I sampled 3 streams associated with Johnson’s Brook and water entering the lake via the culverts at the SW corner of the lake (just down from the road to the dairy).

Above: EC and pH values for streams associated with Johnson’s (Bob’s) Brook on Nov 8, 2018. #1  Upper Johnson’s Brook. #2 Brook receiving drainage from Uplands Park wastewater treatment area, also from streams south of Hammonds Plains Road. #3 and # 4: Brook draining construction/trucking yard and community just to the SE of the Dairy Road. These 3 system converge in the area of sites 5& 6 and then water flows downstream to enter Sandy Lake through two large culverts at site #7. Nos 8 and 9 were taken at Sandy Lake Beach Park for reference. There were strong flows in the brooks at sites 1 and 2. A steady but weaker flow was observed at site 3-4 (it crosses the road from 3 to 4 through a culvert and that water was very cloudy and had a lot of suspended material.

There was very high water flow at this time, but a clear salt signal was evident in two of the streams converging at “Murphy’s Pit”. One was the stream that receives drainage from  Uplands Park wastewater treatment area (EC 125 uS/cm). Another was the stream draining the construction/trucking yard and community just to the SE of the Dairy Road (EC 410). Water at the latter site was very cloudy and full of particulate material. This stream does not seem to have been identified as a significant source of pollutants in the AECOM 2014 study and should be further investigated.  Samples were taken again at this site on Dec 13, and through the winter by a volunteer (B. Sarty). These continued to show a salt signal. View details under Ec-pH and submenus for that page.

(iv) Following those observations, local resident Bruce Sarty volunteered to take monthly samples for measurement of EC from the streams sampled above, and in Sandy  Lake beginning on Jan 19, 2019.  That sampling continues. In both 2019 and 2020, EC values of the incoming streams peaked in March, and consistently stream #4 (see figure above) had the highest EC. For stream #2 the peak values were 638 and 516 uS/cm in March or 2019 and 2020 respectively and for stream #4  1442 and 1744 uS/cm. Contrarily, the values for water coming out of the culvert at the inlet (site 7) peaked in October in 2019 (440 uS/cm) and in July (680 uS/cm) in 2020.  We would need measurements of flow to make more sense of these values, also water in the area of the big culvert at site 7 gets frozen over at times complicating sampling and interpretation. Regardless,  collectively the data illustrate that very high EC water is entering Sandy Lake at certain times. Continuous sampling of water EC on the Little Sackville River in 2015 illustrated peak values in March-April, and  large day to day fluctuations.

(v) On Aug 20, 2020, I sampled several points on the watercourse south of Hammonds Plains Road in Bedford West sub-area 12 which receives drainage from Atlantic Acres Industrial Park and Harmony Park area; most of sub-area 12, while designated for development has not yet been developed. Some high values (>500 uS/cm) were observed, but there was not much water movement at that time. There were some significant rainfalls towards the end of September, recharging most streams. On Oct 2, 202o with the assistance of Bruce Sarty, I conducted a more comprehensive sampling of Johnson’s Brook and all of its tributaries, also Karen’s Brook, Sandy Lake at 2 places, and two streams draining non-developed, forested land on the east side of Sandy Lake:

Map is from the Provincial Landscape Viewer (PLV). Streams converging at the southeast corner of the lake are highlighted (dark blue). Numbers in purple are the Electrical Conductivity values (uS/cm) on Oct 2, 2020. SW= swamp as identified on the PLV. NIA=”No Information Available” as cited on the PLV. Point d is a few meters from the outfall at the Uplands Park Waste Water Treatment Facility

The two streams sampled on the east side of Sandy Lake had EC values of 45 and 55 uS/cm; these drain intact, forested landscape. The highest values are for streams coming from south of HPR (Hammonds Plains Road) (298 uS/cm), and from the southwest/Upland Park water water treatment facility  (282 uS/cm); those converge and the value increases after if crosses by more settled landscape to 324 uS/cm; and the stream draining the swamp just east of the dairy road again had the highest value of all,  769 uS/cm.   Bob’s Brook has a value of 104 uS/cm, and Karen’s Brook 166 uS/cm, those draining areas that are settled at their extremities. The mix where it entered the lake was 231 uS/cm, and the lake itself  191 uS/cm.

Based on the EC values of the lake water, water from intact landscape on the east side of the lake, and values for the major inlet at the southwest corner of the lake, it is estimated  that over 2/3 and as much as 78% of the water going into Sandy Lake enters via that inlet and/or from areas now partially settled.

2.9 WATERCOURSE WETLANDS
Wetlands associated with watercourses can have a big influence on water quality and flows of water downstream, e.g., by removing nutrients and sediment, they improve water quality; by storing water and releasing it slowly, they reduce peak flows and downstream flooding (view Leibowitz et al., 2018  and Golden et al., 2019 for  reviews). They are also very important as habitat – in NS, “53.8 per cent of species protected under the provincial law are dependent on wetlands for survival” (NS L&F Document May 31, 2019).

These features are well recognized as issues to be addressed when open (wild, undeveloped) lands are developed, and so there are legal requirements to protect  watercourses and any associated wetlands.

According to The AECOM 2014 Report “Approximately 85 ha of the watershed are wetlands, which make up about 3.5 % of the watershed area”, commenting   “This is a small proportion relative to the size of the watershed and suggests the watershed is well drained.” However their identification of wetlands (AECOM Fig 3) that could impact Sandy Lake does not include
(i) significant wetlands around the 4 major inlets to Sandy Lake
(ii) NIA (no-information available) patches on watercourses, most of which are likely wetlands (these areas are included under Type I Constraints- Watercourses, Wetlands and Riparian Buffers (AECOM Fig 7).

Of particular note are wetlands labelled in the map below as NIA 1 (approx 3.5 ha) and NIA2 (approx 3 ha) which lie on the watercourse leading from the Upland Park Waste Water Treatment Facility to Sandy Lake, as those could well remove significant amounts of phosphorus. NIA 1 also holds a lot of water and is identified in AECOM 2014, Fig 6 as an area of high groundwater recharge.
For more about the NIA 1 and NIA2 wetlands, view
W and SW of S. Lake 2Oct2020 & the PART II Photo Album referenced on that page;
Wetlands SW of Sandy Lake.

Wetland Inventory for area southwest of Sandy Lake. The base map is from a screenshot of the wetland layer in the PLV (Provincial Landscape Viewer). Streams (“WAM Predicted Flows”) feeding Sandy Lake are highlighted. The names “HP South Brook” and “Western Brook” are my identifiers for these streams. Johnson’s Brook is also known as “Bob’s Brook”.   Coloured polygons are wetlands with vegetation as indicated by the key at top right. The areas in hectares are given at bottom right;  those values are revealed when you click on the polygon in the PLV. NIA1,2 and 3 are  “No Information Available” polygons; no values are given for the areas of the NIA polygons, the values  above are my approximate estimates. Smaller NIAs are not shown  – see Streams and Wetlands Fig SW3

The largest wetland close to Sandy Lake that is identified in the AECOM 2014 Report, S5 in the map above, is highly degraded and could be a significant source of pollutants entering Sandy Lake. That condition was not recognzied in the AECOM 2014 Report. For more about it, view Swamp 5 (degraded).

 

2.10 BACTERIA AND ALGAE
Sandy Lake has a reputation as a ‘clean lake’, e.g.,

Drinking Water Quality
The primary sources of drinking water for local residents and cottagers are groundwater from drilled and dug wells and the water of Sandy Lake. Until a couple of sewer breaks that occurredon the sewer main near Giles Drive in 2000 and 2001, residents had no problems with water quality (for drinking or swimming); in fact, they were proud of the high quality of their water. The municipality issued boil water and no swimming advisories following the sewage leaks. – Sandy Lake Community Profile, Dalhousie School of Planning, 2002

However, all tests (2007-onward, view CF Fig 4) have shown coliform bacteria to be present, and so the water is considered non-potable by NS and Canadian standards.

While test results compiled in AECOM 2014 show all tests to be well within the standards for recreational  waters (2007-onward, view CF Fig 4) and there has been only one beach closure due to bacteria in recent years(in 2013),  an in-depth study by Macdonald 2016 revealed some high values in the post open beach season. These were associated with high turbidity/storms. According to AECOM 2014 “The [The Uplands Park Wastewater Treatment Facility] facility may overflow and bypass the treatment cycle during storms or malfunctions” so that is a possible explanation. (view Coliform Notes).

A very unpleasant algal bloom appeared on Sandy Lake of Aug 7, 2019 – I happened to be there, in the water at the time, and documented and  reported it. It had largely dissipated within 2 days and the Risk Advisory was lifted . It’s still not completely clear what caused it, HRM reporting that “the specimens identified in the lab were principally diatoms (a form of algae), with trace amounts of one species of cyanobacteria that does not produce any toxins.” Also view Cyanobacteria Notes

2.11 FUTURE TRAJECTORY

AECOM 2014 Predictions

From 11. Summary and Conclusions (Bolding inserted)

The Sandy Lake watershed is designated as an Urban Settlement area and currently hosts urban development along main thoroughfares (Hammonds Plains Road, Lucasville Road), in industrial areas and in suburban style communities. Portions of the watershed are serviced with municipal water and wastewater services and portions of the watershed utilize on-site water wells and septic systems.

A development constraints map of the watershed identifies areas that are not suitable for development (wetlands, watercourses and riparian zones) and areas that may require environmental mitigation to be included in development plans if the areas are developed.

Possible future development scenarios are identified in the watershed and land use maps depicting existing conditions and three future development scenarios were prepared. The land use maps were used as inputs to a phosphorus load model (Lake Capacity Model) to predict how future development may impact the phosphorus concentrations of the lakes.

Phosphorus is identified as a key water quality parameter to assess the trophic status of the lake. Historic water quality samples and water samples collected during the course of this study were used to identify water quality objectives for parameters that are influenced by development. The water quality in Sandy Lake and Marsh Lake is currently being affected by urban development in the water as displayed by the increasing phosphorus concentration in Sandy Lake. Both Sandy Lake (12 µg/L) and Marsh Lake (10 µg/L) have median phosphorus concentrations that place them in the lower end of the mesotrophic range. Water quality objectives and early warning values are set at 18 µg/L and 15 µg/L for Sandy Lake and 15 µg/L and 13 µg/L for Marsh Lake respectively.

Cumulative impacts of development on phosphorus concentrations are predicted to increase to 16 µg/L for Sandy Lake and 15 µg/L for Marsh Lake when mitigation measures to decrease phosphorus loading are not implemented. These levels are above the early warning values, but below the water quality objectives. Removing point sources of phosphorus such as the Uplands WWTF and septic systems near Sandy Lake by connecting them to municipal wastewater services decreases the predicted phosphorus concentrations to 15 µg/L and 14 µg/L for Sandy Lake and Marsh Lake respectively. Additional phosphorus mitigation measures using advanced stormwater management that reduces phosphorus runoff by 50% is predicted to decrease the phosphorus concentration of Sandy Lake to 13 µg/L and of Marsh Lake to 12 µg/L.

From Executive Summary

The results of the modeling scenarios provide a numerical narrative of how water quality is predicted to be impacted by development. Full development without mitigation measures to control nutrient loading into the lakes will likely result in steady increases in phosphorus concentrations that will approach the water quality objectives. Removal of nutrient sources such as septic systems, wastewater treatment facilities and stormwater runoff from new development areas will reduce the impact of urbanization in the watershed.

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.

Critique of the AECOM Predictions

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REVISING dec 26 –

There is evidence that in its current state (at 12 ug/L phosphorus), Sandy Lake is already seriously degraded, and that phosphorus levels need to be reduced from current levels, not allowed to stay the same (or to increase as proposed in the AECOM 2014  Report). In 1979, phosphorus was  7 ug/L or less, well under the upper limit (10 ug/L P) for oligotrophy (the ‘clean’ state of a lake); the transition to mesotrophic status occurred circa 2001 (re AECOM Fig 9), and has been accompanied by declines in deep water oxygen. FROM THE AECOM REPORT (2014) (bolding inserted):


“Table 5 compares the phosphorus concentrations of shallow (epilimnion) to deep (hypolimnion) samples from three sampling events. Total phosphorus concentrations in the shallow surface (epilimnion) samples are less than in the deep (hypolimnion) samples in two of the three examples. Although the data are limited, this suggests that the deeper portions of Sandy Lake may be fully or partially oxygen- deprived during certain times of the year, a situation that may arise when decomposing organic matter consumes available oxygen at depth. This in turn promotes the release of phosphorus from lake sediments, which is recorded in the water samples.

The current state of Sandy Lake and the worsening trend should be a matter of concern. While waters entering the major inlet are likely the major source of pollutants, I note also the apparent “salt signal” in streams draining land in the area of Gatehouse and Lucasville Roads; and that a large volume of clearcut debris entered the northwest side of the lake.

Climate Change

As noted in the SLCA Response to AECOM study, rising temperatures add to the stresses, particularly  by reducing oxygen solubility.  There is paleolimnological evidence based on cores taken in 2005/6 that Sandy Lake has already been affected by climate warming:

Sandy Lake was one of the “19 otherwise relatively pristine lakes had increases in planktonic taxa consistent with observations linked to changes in lake seasonality and limnological changes most closely linked to climate warming in Nova Scotia and other regions. – Establishing realistic management objectives for urban lakes using paleolimnological techniques: an example from Halifax Region (Nova Scotia, Canada)
Brian K. Ginn et al., 2015.
Lake and Reservoir Management, 31:2, 92-108 .

Further Water Quality Monitoring

AECOM has identified a number of measures to be taken to protect Sandy Lake even with further development in the watershed; stronger measures and less development were suggested by SLCA (see Recommendations in SLCA Response to AECOM study).

These recent observations suggest that the lake is currently in a precarious state.

In regard to Water Quality Monitoring, AECOM 2014 advised:

The Water Quality Monitoring Functional Plan identifies Sandy Lake as a Tier I waterbody or “High Vulnerability” to be sampled with a sampling program consisting of monthly collections during the ice free season (April – December) and at least one sample during the winter season…Temperature and dissolved oxygen profiles are recommended to be collected during each sampling event at 1 m intervals with profiling intervals increased to up to 3 m below the 20 m level. Water samples should be collected from 0.5 m below the lake surface, at mid-depth, and 1 m above the lake bottom.

Both discrete and volume-weighted samples from Sandy Lake are recommended to be analyzed. Total phosphorus and chlorophyll a testing must be performed on all discrete water samples. E. coli need only be measured for the 0.5 metre (top) water sample. Volume-weighted samples made up of top, middle and bottom water samples are to be tested for the remaining grouped analytical parameters specified in Table 14.

The water quality monitoring program for Tier 1 lakes (Stantec 2009) is recommended as a suitably robust water quality monitoring plan for Sandy Lake that will allow for the identification of seasonal and long term patterns in water quality and to evaluate how water quality may be impacted by development in the Sandy Lake watershed.

bayonet rushThe observations reported here illustrate the paramount importance of routine monitoring of limnological profiles. To date, the recommendations of AECOM(2014) in regard to water quality monitoring have not been prsued.

Our observations also  illustrate how measurements of electrical conductivity of incoming waters through different seasons would be appropriate for monitoring. The equipment for such measurements is cheap and robust and such measurements could be conducted by a citizens group.

Also, I suggest keeping a watchful eye on the lakeside wetlands. In the more open areas of the lake, those wetlands are currently dominated by bayonet rush,  an emergent aquatic plant characteristic of oligotrophic (nutrient-poor) lakes, thus change species composition towards species characteristic of mesotrophic/eutrophic conditions could be regarded as significant.*

I think it’s clear that Sandy Lake would degrade rapidly with significant further  development in the watershed.
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*I have to report the detailed observations on aquatic plant species in Sandy Lake. Species more characteristic of higher nutrient levels occur closer to the major inlets.
-dp Jan 2, 2017