THE THREE LAKES
Sandy Lake, a headwater lake for the Sackville River.
Marsh Lake, downstream from Sandy Lake via Peverill’s Brook; it drains into the Sackville River. (Sandy Lake Watershed is a sub-watershed of the Sackville River Watershed.)
Jack Lake, on a separate watershed; it drains into Papermill Lake (outside of the proposed Sandy Lake Regional Park) and thence to the Bedford Basin.
Some morphometric water and chemistry data for the three lakes from the Jack Lake CHMC/NSDH Report (1986) are given below:
TEMPORAL TRENDS OF TOTAL P, pH and CONDUCTIVITY IN SANDY LAKE
Based on Total Phosphorus measurements, Sandy Lake has moved from an oligotrophic state towards a mesotrophic state:
pH and conductivity values have also increased since 1980:
The interpretation of pH changes is complicated by the influence of acid rain and the lack of values earlier than 1980. As salmon were in Sandy Lake historically, it seems that pH values favourable for Atlantic salmon (and likely higher than pH 4.91 – the 1980 value above) must have existed in Sandy Lake prior to the era of increasing acid rain. That era occurred from the mid-1950’s through to 1980s when average lake pH dropped 1-1.5 units.2 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.)Urbanization tends to increase stream pH values, also electrical conductivity (EC), a measure of salt content. In Nova Scotia, our liberal use of road salt is blamed for much of the trends of increase in conductivity in Halifax area lakes over the interval 1980-2000 as revealed in synoptic Lake studies. Values in the area of 30-60 uS/cm are typical of pristine lakes in the Halifax region. 6 EC values for Sandy Lake were in that range in 1971 and 1980, not thereafter.
1. 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.
2. 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.
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.Synoptic Water Quality Survey Of Selected Halifax Regional Municipality Lakes On 28-29 March 2000 by P. Clement et al. 2007. Canadian Technical Report of Fisheries and Aquatic Sciences NNNN.
OBSERVATIONS OF LIMNOLOGICAL VARIABLES IN 2017
Three sets of data were obtained:
(i) 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.
(ii) On Aug 10, 2018, I paddled the perimeter of Sandy Lake and measured electrical conductivity (EC), occasionally pH at regular intervals.
These two sets of results are plotted on Google Maps. View EC & pH
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. 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). These waters receive effluent originating from the Uplands Park Wastewater Treatment Facility serving approximately 170 people, which AECOM (2014) identified as a point source of pollutants.
A set of water quality observations on Sandy Lake in 1991* 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 1991 may have reflected peak acidification due to acid rain and/or exposure of acid slates in the northwestern part of the watershed (see AECOM 2014, p 8) and the higher value now observed, reductions in acid rain-causing emissions, and possibly some urban influence of now established development.
*Sandy Lake Development Impact Assessment Final Report by D. Conrad et al. 2002 Biological Engineering Department, Dalhousie University
(iii) 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 oxygen profiles which affect a wide range of life in lakes, 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 indicate oxygen values at depth are lower than values required for cold water fish, but there is not (yet) severe depletion of oxygen. 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.)
The only comparable historical data for Sandy Lake are apparently those reported for the surface and at 59 ft (18 m) on Aug 30, 1971:
So at peak stratification in 1971, the oxygen concentration at the bottom was twice the value in 2017. In 2018 the conductivity on the surface had increased about 4.6 fold and the bottom value was 79 uS/cm greater, compared to a difference of only 2 uS/cm in 1971. As differences in conductivity/salt content between surface and deeper water increase, they increase density stratification of water column and slow down and at some point eliminate seasonal turnover of the water column associated with temperature changes, and thus re-oxygenation of the deeper layers; in turn that can lead to permanently low or no oxygen in the deeper layers.
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.
As noted in the SLCA Response to AECOM study rising temperatures add to the stresses, e.g. by reducing oxygen solubility.
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.
The observations reported here illustrate the paramount importance of routine monitoring of limnological profiles. In addition they illustrate how measurements of 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 now dominated by an emergent aquatic plant, the bayonet rush, which is characteristic of oligotrophic (nutrient-poor) lakes, thus change in that conditions towards species characteristic of mesotrophic/eutrophic conditions could be regarded as significant.*
I think its clear that Sandy Lake could and probably would degrade rapidly with further significant development in the watershed. The morphometrics of Sandy Lake and the degree of development around the lake are similar to those of Williams Lake on the Halifax south mainland. At Williams Lake, there was apparently no seasonal turnover in a recent winter*, and a program of alternatives to road salt on some adjacent streets has been re-introduced.
*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
** View Water quality measurements on Williams Lake and Colpitt Lake (Halifax, N.S.) Dec 7-13, 2015 with reference to possible impacts of road salt by David Patriquin for the Williams Lake Conservation Company (2016)