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TitleLakeshore Capacity Assessment Handbook
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Page 1

Lakeshore Capacity Assessment Handbook
Protecting Water Quality in Inland Lakes on
Ontario’s Precambrian Shield


May 2010

i

Page 2

ii

Page 53

42

Table 5. Optimal sampling strategies for the most commonly used trophic status indicators28

Samples per year Number of years

95% confident of being within Indicator Derivation Sample method

10% mean 20% mean 10% mean 20% mean

Time

TP(so)* usually single sample 5m composite 1
I 1I 10 2 during spring turnover prior to thermal stratification

TP(if)*
average of all samples collected
for ice-free period

composites when lake is mixed
volume weighted during
stratification

9-13
(bi-weekly)

4-5
(monthly)

5 1 between ice out and freeze up

TP(epi)*
average of all samples collected
during stratification epilimnetic composite 19 5 7 2 during thermal stratification

Chl a(ss)*
average of all samples collected
during stratification
(e.g. through self help programs)

euphotic zone composites less than for Chl a(if); should use Chl a(if) if spring/fall blooms expected
during thermal stratification

Chl a(if)*
average of all samples collected
for ice-free period euphotic zone composites 10 5 >5 2-5 between ice out and freeze up

Oxygen usually profile data oxygen meter with some Winkler test samples to confirm sample frequency based on final use of data
key period just prior to fall
de-stratification

Secchi individual observations Secchi disc 11-17
(weekly)

3-4
(monthly)

2-5 1 ice-free period



Lakeshore Capacity Assessment Handbook – May 2010

* so = spring overturn; if = ice free; epi = epilimnetic; ss = summer stratified
I usually only enough time for one visit


28 Ontario Ministry of Environment and Energy. 1992. Measuring the trophic status of lakes: sampling protocols. Queen=s Printer for Ontario.

Page 54

Lakeshore Capacity Assessment Handbook – May 2010

The Lake Partner Program is based out of the Ministry’s Dorset Environmental Science Centre.
Annual reports for the program are made available to volunteers, science partners and the
public in hard copy or electronically via the ministry’s website
(http://www.ene.gov.on.ca/en/water/lakepartner/index.php). Inquiries about the Lake Partner
Program can be made by calling 1-800-470-8322 or by emailing [email protected]

The TP samples are analysed by MOE to an average precision of approximately 0.7 µg/L, which
is sensitive enough to detect between-year differences in spring turnover concentrations for
individual lakes. The numbers are also precise enough to test the performance of the Lakeshore
Capacity Model or for use as input to hypolimnetic oxygen models.

Lakes on the Precambrian Shield are sampled once each spring for TP, while water clarity is
measured monthly with a Secchi disc during the ice-free period (May through October). Off-
shield lakes are sampled monthly for both TP and water clarity during the ice-free period.

The program uses volunteers to collect total phosphorus (TP) and water clarity data for lakes
throughout Ontario and cooperates with many science partners (including other MOE
departments and municipalities) to provide accurate TP monitoring for specific lakes of interest.
The program has been quite successful: in 2004, water quality information was collected from
more than 1,000 locations scattered throughout the major cottage areas of the province (Figure
4).

The Ministry of the Environment’s Lake Partner Program works in partnership with the
Federation of Ontario Cottagers’ Associations, the Lake of the Woods District Property Owners
Association and many other organizations to foster lake stewardship by increasing the public’s
awareness of the links between phosphorus and water clarity in Ontario lakes.

6.3 Lake Partner Program



43





http://www.ene.gov.on.ca/en/water/lakepartner/index.php
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]
mailto:[email protected]

Page 105

1

Technical Bulletin No. DESC-25
May 1998

Reprinted June 1999

MINISTRY OF THE ENVIRONMENT
ENVIRONMENTAL SCIENCES AND STANDARDS DIVISION

DORSET ENVIRONMENTAL SCIENCE CENTRE

LONG-TERM MONITORING OF TROPHIC STATUS:
THE VALUE OF TOTAL PHOSPHORUS CONCENTRATION AT

SPRING OVERTURN

There are many reasons to measure the nutrientstatus of a water body. It may be done as
part of an initiative to control nutrient inputs in an
effort to reduce nuisance levels of aquatic plants
or algae. In some cases, measurements are taken
as part of a self-regulation program designed to
monitor inputs to surface waters. In most cases,
however, the nutrient status of a water body is
measured to detect long-term changes in water
quality (the nutrient status) of the water body.

The three most common measures of the nutrient
status of a water body are TP (total phosphorus),
chlorophyll a and Secchi depth. In Ontario,
Secchi depth is often controlled by DOC rather
than by chlorophyll and the chlorophyll
measurements themselves are costly and must be
pooled in large numbers to yield meaningful ice-
free means (see Techbull DESC_ 10 ). For these
reasons, TP is the recommended parameter to
monitor long-term changes in trophic status. This
is supported by the fact that TP is almost always
the limiting nutrient for algal growth in Ontario
lakes. In addition, TP surveys are easy and
comparatively inexpensive to conduct.

Once the decision has been made to monitor
long-term changes in TP, decisions must be made
with respect to the type of sampling regime that
will be followed. Since seasonal variation in TP
would rarely be of interest, it is, in most cases,
desirable to obtain some number that describes an
annual average condition such that the individual
annual means can be monitored through time.

There are many different ways to combine TP
samples to derive some measure of an annual
mean. Monthly samples can be pooled to derive
an "ice-free mean" but care must be taken when
combining these numbers to produce "means" that
can be validly compared to the numbers derived
by similar studies elsewhere. For example,
individual surface water samples when taken as 5
metre composites or euphotic zone composites
when pooled will give an ice free epilimnetic or
euphotic zone (annual) mean. This number will
be different from numbers generated by other
programs that volume weight the stratified season
samples taken from all layers of the lake to
accurately produce a "whole-lake" ice free annual
mean. For these reasons it is often safer to collect
TP samples at spring overturn to detect long-term
trends. Certainly, it is better to have a single,
reliable spring-overturn number than it is to
average several samples that have been collected
in a helter skelter fashion at other times of the
year. The DESC database clearly shows that
long-term average TP concentrations derived for
a given lake using spring turnover samples are
very closely corelated to those derived using ice-
free means by volume weighting. (Fig 1).

TPif = 0.96TPso + 0.31
r2 = 0.93

Page 106

2

TP (long-term mean)

0.0
2.0

4.0
6.0
8.0

10.0

12.0
14.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

Based on spring overturn

B
a
s
e
d

o
n

i
c
e
-f

re
e
m

e
a
n

Fig. 1. The relationship between long term mean
TP derived using spring turnover and ice-free mean
data for the lakes in the Dorset database.

Total Phosphorus

0

1

2

3

4

5

6

7

8

1975 1980 1985 1990 1995

Year

(u
g

/L
)

Ice Free Spring Overturn

Fig.2. Annual TP expressed as spring overturn
concentrations and as ice free means ( mean of
monthly volume weighted concentrations) for Blue
Chalk Lake.

Fig.3. The 5m composite sampling method.

Note: Volume weighting is used to collect data for all
parameters for use in mass balance calculations at
the DESC and probably would not be conducted if
the only goal was to monitor changes through time in
whole lake TP concentrations.

Previous calculations based on DESC data have
shown that a reliable long-term mean can be
derived with 2-4 years of spring turnover data.
The ice-free, volume-weighted means will
provide a reliable long-term mean sooner ie,
within 1-3 years but the extra effort and cost is
usually not justified. In fact, for many lakes, the
long-term trend is described as well or better by
spring turnover TP than by ice-free volume
weighted means (Fig 2).

Spring turnover TP concentrations should be
taken as some form of surface water composite
(ie, 5m composite bottle sample) from the deepest
location in the lake(Fig.3.). Ideally the sample
should be taken a week or so after ice out to
allow the lake to completely mix. Samples should
be taken, however, before water temperatures
reach ~10oC. It is not acceptable, to include
values in the database that are collected outside
this window. It should also be noted that a single

spring TP sample will not be adequate to describe
the conditions that occur in complex systems such
as;
• in very large lakes
• where large inflows dominate the nutrient

concentrations in the lake
• in eutrophic lakes where there are large

nutrient fluxes or a high degree of spacial
variation

• in lakes where anthropogenic loads are
high such as in lakes that adjoin urban
centres.

For more information, contact
Bev Clark, DESC, 705-766-2150
email: [email protected]

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