Lake Simcoe Science
Applying Innovation to
Phosphorus Monitoring
Improving Phosphorus Monitoring in
Streams and Rivers
Phosphorus is an essential nutrient for living things.
In nature it is found in small amounts, where it is
needed for processes such as plant growth. When
a little extra phosphorus is added to an ecosystem
(think of fertilizing a garden), it helps plants grow.
However, too much phosphorus is not good and
causes excessive plant growth, on land and in water.
As described in previous Science newsletters, Lake
Simcoe has a problem of too much phosphorus. This
has led to increases in algae, increases in aquatic
plants, and a corresponding decrease in deep
water oxygen (when the plants die, they take away
oxygen). This, in turn, has negatively impacted cold
water fish such as lake trout and lake whitefish.
Reducing phosphorus is essential to a healthy lake.
Phosphorus Concentrations at
Water Quality Stations
Legend - [TP] (mg/L)
0 - 0.020
0.021 - 0.03
0.031 - 0.10
> 0.100
LSRCA staff manually collects water quality samples from watershed
tributaries. This traditional spot sampling captures data from a
single moment in time when the sample was collected. Our new pilot
project uses probes installed underwater to provide us more data with
continuous sampling.
We know that most of the phosphorus (about
60%) enters the lake from its tributaries (rivers).
We know this through our sampling program and
we are continually seeking ways to improve on
our data collection methods as well as increasing
our understanding of phosphorus behaviour in the
tributaries.
This issue is about the results of a pilot project
we started in 2011 to enhance our phosphorus
data collection and better understand phosphorus
characteristics in Lake Simcoe tributaries.
The Forms of Phosphorus
Figure shows the average total phosphorus concentrations (2007-2011) at
Lake Simcoe water quality stations (Provincial Water Quality Objective
= 0.030 mg/L).
In water, phosphorus has two main forms - dissolved
(soluble) and particulate (attached to or a component
of particulate matter). When added together, you get
a measurement of total phosphorus (TP). The target
concentration of total phosphorus in rivers is 0.03
mg/L to avoid nuisance plant and algae growth.
Volume 11
Dissolved phosphorus is quite literally dissolved in the
water, much like salt. This type of phosphorus is not
attached to a particle and can pass through filters.
It is the form most easily used by plants or algae.
It is therefore considered more “bioavailable” than
particulate phosphorus.
Particulate-bound phosphorus is attached to
suspended particles in the water such as minerals or
algae. This type of phosphorus can be collected on a
filter. Most tributaries of Lake Simcoe have a “cloudy”
or “turbid” appearance because of those suspended
particles, much of which can contain phosphorus.
Spot Samples vs. Continuous Sampling
LSRCA researchers collect tributary water samples –
one sample every two weeks at 31 different locations
- to test for phosphorus and various other factors.
We’ve been doing this for many years and have data
at some sites dating back to the 1970s.
While this spot sampling method is informative and
has provided the basis for our understanding of
phosphorus entering Lake Simcoe, it’s not without
its own issues. For one, it can get quite expensive
because of the manual labour involved in collecting
the samples and the fact that the samples have to be
analysed by an external laboratory.
Another drawback of spot sampling is that each
sample represents a single moment in time - when
that actual water sample was collected. However,
rivers are dynamic and a single sample cannot
account for the changes in phosphorus concentrations
that happen during storms or droughts or as a result
of other biological activity. We could try and offset
this by collecting more samples, but then we’d run
back into the issue of the cost. Ideally, to track all
these changes in concentration, we would like to
automate sample collection and collect them more
often – hourly or even more often. That’s where
turbidity comes in.
Turbidity’s Relationship to Phosphorus
Turbidity is a measure of the amount of material suspended in water. This suspended material can include
soil particles (clay, silt and sand), algae, plankton, microbes and other particulate substances. These
particles enter a tributary through a variety of ways… by eroding stream banks or soils or run-off from
paved surfaces in urban areas. A stream that is normally clear can have high levels of turbidity during rain
storms because that’s when the soil is “scoured” from unprotected fields, unstable stream banks and nonporous surfaces into the stream.
Turbidity is measured by determining the amount of light that is reflected off particles in a water sample.
Because particles in water can contain phosphorus, by measuring turbidity, we can estimate how much
phosphorus is being transported in a tributary.
Baseflow vs. Storm Event Flow at Kettleby Creek
Above left is Kettelby Creek under baseflow conditions; note the clarity of the water. Above right is the same stretch of the creek during a storm event.
The turbidity of the water is due to the higher water levels, water velocity and particulate washed off the catchment into the creek during the event.
2
East Holland River Sample Concentrations
These are graphs of sample concentrations, flow and turbidity, from East Holland River. The left graph has just flow and measured TP concentrations
for the section called Spot Sample vs. Continuous Sampling (graph of sample points and flow). By adding in Turbidity and Modelled TP to the same
graph, it can also be used in the Results section (graph of spot samples with probe).
Better Monitoring through Technology
While we need a laboratory to analyse how much
phosphorus is in a water sample, another method
of calculating phosphorus is to study its relationship
to turbidity. We can do this through the use of
permanent optical probes installed in the river that
can take frequent samples.
In a pilot project initiated in 2011, LSRCA installed
four turbidity probes at test locations throughout
the watershed to evaluate the effectiveness of using
turbidity to measure phosphorus.
Using the spot sampling method, LSRCA typically
collected 26 samples per year at each sampling
station. But using the continuous monitoring turbidity
probes (which collect data every 15 minutes), we
were able to collect 35,040 measurements per
year at each station. These samples are being used
to fill in the gaps inherent in the spot sampling
method and will help us improve phosphorus load
calculations, understand phosphorus dynamics,
phosphorus contributions from various land use
types, or evaluate best management practices.
What We've Learned
We selected four test locations to compare results
under different circumstances and with different land
uses around them – different land uses influence
turbidity and phosphorus concentrations, but can
also influence the strength of the relationship
between the two.
What is a Concentration vs. a
Load?
A water quality sample result is
expressed as a concentration, that is a
mass (milligram) in a given volume of
water (litre) typically as mg/L.
A load in a river is a mass of material
transported by that river over a given
time, such as 44 tonnes per year.
To calculate a load (phosphorus) we
need to know the concentration (mg of
P /L) and flow rate of the river (volume
of water (L) over time (sec)). Then
Load equals concentration times flow.
The sites we chose included the East Holland River,
the Beaver River, North Schomberg and Hawkestone
Creek. The East Holland River is a large tributary
with a lot of urban area, specifically Aurora and
Newmarket. The Beaver River runs through a largely
agricultural area. North Schomberg is a small
subwatershed that is heavily influenced by a large
highway. And Hawkestone Creek is the most natural
catchment with some of the best water quality in the
watershed.
3
the 0.03mg/L guideline was exceeded. From this we
saw two exceedences of the guideline. However, the
probes showed us there were actually 19 exceedances
with concentrations elevated above the guideline for a
total of 16 days.
Challenges
There are some rivers where turbidity probes won’t
work. For example, in the West Holland River, we
know that there is a higher proportion of dissolved
phosphorus in the water, which makes for a poor
turbidity-phosphorus relationship.
Other challenges include probes getting damaged,
access to probes during winter or probes freezing.
Ironically, one of the greatest challenges stems from
one of its benefits – the volume of samples that
a probe can collect. Having all this data requires
resources to analyse it.
Inset: LSRCA turbidity probe removed for routine cleaning and
maintenance. Right: the probe in action, installed underwater in
Hawkestone Creek. Tthe probe has a silicone wiper to keep optical
sensor window clear of algae build-up.
The results told us that the best relationship between
turbidity and phosphorus was at our East Holland
River site. This is very useful to know since the East
Holland River is one of the largest contributors of
phosphorus to Lake Simcoe. A better understanding
of phosphorus dynamics at this location allows us to
make more accurate phosphorus load calculations
and have a better understanding of what transports
phosphorus in the river (storms, seasonal changes).
At the Beaver River site, we found a different
pattern. While turbidity and phosphorus
concentrations rise in relation to the water levels
during a storm, the turbidity and thus phosphorus
concentrations decrease faster than the water levels
as they subside. From this, we know that to improve
phosphorus load calculations for this tributary, we
need samples collected before, during, and after
a storm event in order to capture the phosphorus
fluctuations.
Probes will not replace conventional sampling outright
(we will still need the sample data to calibrate and
correct probe readings) but probes can be used to
augment conventional sampling and fill in gaps that
would otherwise be missed.
Innovation at LSRCA
The Turbidity Probe Project is just one example of how
LSRCA is constantly finding, evaluating and applying
new, innovative technologies and techniques that can
help us to better understand, protect and restore Lake
Simcoe and its watershed.
/lakesimcoeconservation
Subscribe
YouTube/TheLSRCA
Follow us on
Twitter @lsrca
Another advantage is that the turbidity probes are
essentially always sampling – 24 hours a day, 7
days a week. Spot sampling at Hawkestone Creek
only gave us 26 opportunities in the year to see if
120 Bayview Parkway,
Newmarket, ON L3Y 3W3
905-895-1281 1-800-465-0437
www.LSRCA.on.ca [email protected]
Established in 1951, the Lake Simcoe Region Conservation Authority provides leadership in the
restoration and protection of the environmental health and quality of Lake Simcoe and the surrounding
watershed with our community, municipal and other government partners. To learn more visit www.
LSRCA.on.ca. Alternative formats of this publication are available upon request.
4
© 2015 Lake Simcoe Region Conservation Authority