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A Brief History of Time…in Severn Sound

• Severn Sound was Area of Concern – Eutrophication was major factor

• Remedial Action Plan implemented – Emphasis on phosphorus load reductions

• Delisting achieved in 2003 – Under condition that monitoring continue to

prevent regressing

• Severn Sound Environmental Association continues to monitor water quality in open waters and tributaries – New challenges: impacts of climate change,

invasive species, continued landscape changes

2 of 23 www.severnsound.ca

Severn Sound

Watershed

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Toronto ~2 hrs

/PV

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Key Map

Sampling Program

• Biweekly sampling during ice free period (May-Oct)

• Temperature, conductivity, dissolved oxygen and pH profiles - 1m depth intervals (now higher res.)

• Secchi depth - measure of water clarity

• Integrated water samples analyzed for trophic status indicators: nutrients (TP, TNO3, TNH3, TKN), chlorophyll a and algal community (biovolume)

• Also analyzed for metals, ions, basic chemistry

• Zooplankton collected for community analysis (density, biomass, length)


Trends in Trophic Status - TP RAP targets

- Significant trend based on Mann-Kendall trend test (p<0.05)

t= -0.70 t= -0.72

t= -0.60 t= -0.71

t= -0.77

t= -0.65

t= -0.61

t= -0.54


Seasonality - TP

7 of 23 Biweek Dates: 9 Apr22-May5 11 May20-Jun2 13 Jun17-Jun30

15 Jul15-Jul28 17 Aug12-Aug25 19 Sep9-Sep22 21 Oct7-Oct20

Trends in Trophic Status – TNH3


t= -0.30

t=0.39

t=0.46


Trends in Trophic Status – TNO3


t=0.49 t=0.46 t=0.43 t=0.39

t=0.42 t= -0.49 t=0.32 t= -0.31

t= -0.39

t= -0.44 t= -0.50


Seasonality – TNO3

10 of 23 Biweek Dates: 9 Apr22-May5 11 May20-Jun2 13 Jun17-Jun30

15 Jul15-Jul28 17 Aug12-Aug25 19 Sep9-Sep22 21 Oct7-Oct20

Trends in Trophic Status - TKN


t= -0.57 t= -0.67 t= -0.56 t= -0.33

t= -0.44

t= -0.31

t= -0.32


Trends in Trophic Status – Chl a RAP targets


t= -0.43 t= -0.58 t= -0.52 t= -0.44

t= -0.41 t= -0.50

t= -0.46 t= -0.27 t= -0.67


Trends in Trophic Status – Tot Ann Biovol


t= -0.64 t= -0.56 t= -0.46 t= -0.56

t= -0.53

t= -0.48 t= -0.46 t= 0.40

t= -0.54

t= 0.35

t= 0.61 t= 0.42, p=0.06 t= 0.58


Trends in Trophic Status – Algae Community

Microcystis Dolichospermum

• Significant reductions in overall biovolume

• Genus-specific shifts – e.g. Microcystis vs

Dolichospermum

• Decreases in most eutrophic indicator taxa – e.g. Ceratium, Stephanodiscus,

Tabellaria, Aulacoseira, Cryptomonas


Trends in Trophic Status - SDV RAP targets


t=0.37 t=0.40 t=0.34

t=0.47 t=0.21 t= -0.35

t= -0.39

t=0.27

t= -0.72 t= -0.72

t=0.20, p=0.06


Driving Factors – Trends & Station

Differences

• Invasive species (dreissenid mussels – regime shift in 1994/5)

• Phosphorus load reductions (WWTPs, other P control strategies)

• Seasonality (effect on within-year variability)

• Changes in lab methods (esp. TP, chl a)

• Station depth and location (prox. to Severn R.), urban influence


Life “Post-Dreissenids” • Clarity is most obvious marker of filter feeding

effect from dreissenids

– Step trend analysis pinpointed 1994/1995 as time period for regime shift

• Analyzing “Post” trends (1994/5-2017):

– TP no change almost everywhere; ↓ at P1

– NO3 ↓ almost everywhere but conc. higher than “Pre”; no change at P1-3, PS, NB

– TKN no change almost everywhere; ↓ at P1-3

– Chla ↓ almost everywhere; no change at M5, PM1, HH sites (data limitation)

– Biovolume no change in west, ↑ in east, HH sites

– Clarity ↓ almost everywhere; no change at P1-3, M5, BS, PS, NB


Phosphorus Load Reductions • Many strategies implemented

during RAP years

• P control activities now fall under

different programs (DWSP, muni.)


Total STP loading to Penetanguishene

Bay vs Biovolume at Pen Bay Stations

Changes in Lab Methods

• 1969-2005, samples sent to MOECC Rexdale – +/− 6.8 μg/L (0–20 μg/L range)

– +/− 10.2 μg/L (21–40 μg/L range)

• In mid-2000 on, samples sent to MOECC Dorset

• Provide low level analysis, duplicates – +/−0.7 μg/L

• Overlap – 2000-2005; lots of scatter around 1:1 line

• Confidence intervals around annual mean decreased since samples sent to DESC – some of year to year change was due to analytical variability

t = 0.51

p << 0.001


Influence of Depth on Trophic

Status

Deep 14-20 m Moderate 5-13 m Shallow 0-4.5 m


Station Location – West to East

Urban influence

GBay Severn R GBay Severn R

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Summary • Trophic indicators show an improvement in overall conditions

since ’73 – Parts of Severn Sound were eutrophic, now meso- to

oligotrophic

• Important driving factors include dreissenids, P loads, change in lab methods, depth, location, urban influence

• Trends since dreissenids show we’re in a period of higher nitrate (although declining), generally decreasing water clarity despite decreasing algae

• Mostly meeting RAP targets post-dreissenids except in some years for: – SDV at HH, NB, PM1, PM2, SB, BS (plants)

– CHLA at NB, SB

– TP at SB, P1, PM1, BS

• Future focus needed on – Refining monitoring program for efficiency/new areas

– Investigating conditions in shallow nearshore (0-2 m)


Acknowledgements • Funding support from our member municipalities

• COA funding (federal/provincial partnership)

• MOECC (lab analysis, use of historical data, technical

advice)

• Fabulous staff (past and present) at SSEA

[email protected]

@SSEA_SSRAP

www.severnsound.ca 23 of 23

mailto:[email protected]

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