Nutrient Issues in Lake Ontario. Lisa Trevisan Ontario Ministry of the Environment and Climate Change

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1 Nutrient Issues in Lake Ontario Lisa Trevisan Ontario Ministry of the Environment and Climate Change March 26, 2015

2 Outline Lake Ontario facts and figures Nutrient stressors in Lake Ontario Cyanobacteria Nuisance attached algae o Cladophora o Nitellopsis obtusa Conclusion 2

3 Depth (m) Lake Ontario Facts and Figures 14th largest lake in the world average depth is second only to Lake Superior 56% of Ontarians live in the watershed length of shoreline 1,146 km drainage basin: 64,030 km 2 Surface areas (to 30 m depth): 4253 km 2 (23%) Volume (to 30 m depth): 64.5 km 3 (4%) mean depth: 86 m surface areas: 18,960 km 2 volume: 1,640 km 3 replacement time: 6 years 3

4 Nutrient Stressors in Lake Ontario Growing urban centres on the north shore of the lake High population density Urban storm water pollution Numerous sewage treatment plants Agricultural activity Nearshore phosphorus concentrations post storm event Lab measured Total Phosphorus (TP) highly enriched in surface waters TP levels over track estimated from linear regression with turbidity and interpolated by kriging 4 Note: TP estimates are under estimates >120 FTU due turbidity sensor out of range

5 Cyanobacteria Blooms in Eutrophic Embayments of Lake Ontario Hamilton Harbour and the Bay of Quinte Long standing problem of anthropogenic eutrophication, along with a long history of environmental actions (and study) to abate nutrient pollution Large embayments with restricted circulation with oligotrophic Lake Ontario Phosphorus levels have declined from the past yet conditions remain eutrophic An upsurge in seasonal cyanobacteria blooms since 2009 Microcystis spp. a present-day feature of mixed species blooms, seemingly more so than in the recent past; cyanotoxins (microcystins) routinely detected Suspicion that colonization of invasive dreissenid mussels in the 1990's is in some way contributing to frequency/character of recent blooms Bay of Quinte Lake Ontario 5 Bay of Quinte Hamilton Harbour Hamilton Harbour Landsat Image September 8, 2001 Lake Ontario

6 Nuisance Attached Algae The green alga Cladophora has extensively colonized nearshore lakebeds, impacting beaches and shoreline Cladophora aesthetically degrades waterfront and can lead to microbial pollution It remains a paradox as to why there is so much algae given the moderate and falling overall phosphorus levels in the nearshore since phosphorus is viewed as the macro-nutrient limiting Cladophora growth in the Great Lakes Recent complaints regarding algal mats in Presqu ile Bay have led to finding the macro-algae Nitellopsis obtusa (starry stonewort) Nitellopsis contributes to dense mats of vegetation along the nearshore areas 6

7 Western Basin and Cladophora In Lake Ontario, Cladophora co-exists with dreissenid (largely quagga) mussels The question is whether nutrient sources drive the overabundance of Cladophora Lake Ontario s basin chemistry, shoreline loading and lakebed flux are nutrient drivers Periodic runoff and ongoing discharges from outfalls potentially enriches shallow nearshore 2003 Cladophora cover at 5 m depth Wilson et al. (2006) J. Great Lakes Res. 32: April 19, 2012 Cobourg (10.1 m)

8 Lake Ontario Study Areas: Local, Regional and Within-Lake Contrasts Study Purpose: would controlling local to regional nutrient inputs to the nearshore decrease the presence of Cladophora? Study Process: TP 9.8 DP 4.4 SRP 1.3 TP 7.8 DP 4.0 SRP 1.0 TP 6.7 DP 3.9 SRP 0.9 benthic surveys and near-bed nutrient sampling TP 5.4 DP 3.0 SRP 0.6 Measure levels of bio-available phosphorus among sites and areas Measure abundance of Cladophora and Dreissenia among sites and areas Surveys conducted in 2012 and 2013 P values (ug/l) are means (surface samples) for sites at 3-20 m depths June and July 2013

9 Study Results Is Cladophora Biomass Correlated with Near-bed Phosphorus? Cladophora and DP Cladophora and SRP Blue - Cobourg Green Oshawa Red - Ajax Symbols indicate depth ranges note: m depth with little Cladophora Onshore - Offshore Gradients DP Dissolved Phosphorus TP TP TP SRP Soluble Reactive Phosphorus TP Total Phosphorus 9

10 Cladophora Biomass Plotted Against Dreissenia Abundance August 2012 Sites < 7 m depth Dreissenia biomass Sites < 7 m Sites >7 to 11 m depth Dreissenia density 10

11 Why is Cladophora Abundant in Seemingly Low Nutrient Areas? Two phosphorus sources contribute to Cladophora growth: 1) from the open lake, and, 2) land runoff and point discharges creating nearshore mixing areas enriched in phosphorus Uncertainty as to the relative importance of these phosphorus sources for the growth of Cladophora has constrained any attempt to manage phosphorus to decrease Cladophora Phosphorus flux from the dreissenid covered lakebed appears to benefit Cladophora in a low phosphorus water column which supports nuisance levels of algae growth Urban development near the study areas appears to result in relatively higher near-bed levels of SRP and DP However, factors other than P-availability affect the increase of Cladophora; higher bioavailable P while representing potential for increased growth may not be realized due to other factors; notably light regime and substrate. 11

12 Depth (m)!. Presqu'ile Bay Ba y of Q ui n te!. Secchi Depth (m)!.!. Presqu ile Bay Concern with perceived deteriorating water quality and increase in aquatic vegetation Index Station!. Presqu'ile Bay It is unclear whether weeds in the bay are related to excess nutrient issues ± Kilometres Lake Ontario Continued mesotrophic conditions (TP, chlorophyll) and in range where algal blooms are possible However, TP has been decreasing over time PWQO to avoid nuisance algae in lakes Clarity has increased over time (Secchi depth) Depth Secchi

13 Nitellopsis obtusa (Starry Stonewort) Invasive species first identified in St. Lawrence river in 1978, St. Clair River in 1981 We don t know how long it s been in Lake Ontario Macroscopic green algae that resembles Chara spp. - may have been misidentified as Chara until recently Was positively identified in Presqu ile Bay, September 2013 A combination of other invasive species and factors other than nutrients may be contributing to perceived issues in Presqu ile Bay 13

14 Conclusion The Great Lakes ecosystem is stressed and changing; ongoing urban development around Lake Ontario is likely to exacerbate the nutrient issue over time Establishing targets will be challenging without good scientific understanding of the systems to make predictions Average water column TP is no longer a good predictor of nearshore benthic algae problems We are hard pressed to understand how to solve nutrient related problems: how do we deal with invasive mussels relative to focus on discharge of nutrients? how do we handle necessary infrastructure expansions (eg. STPs)? how do we support the agricultural community while limiting non-point source runoff? how do we deal with issues of perception vs. reality? Going forward, we need to: better quantify the significant effect of mussel-algae phosphorus recycling quantify and predict the biological response of reduced external loads (assume a significant lag due to internal sources) undertake source modelling and quantification of the effectiveness of best management practices identify source watersheds where targeted actions would lead to measurable/achievable reductions 14

15 Acknowledgements Todd Howell, Great Lakes Ecologist, MOECC Nadine Benoit, Surface Water Specialist, Water Investigations, MOECC Mary Thorburn, Special Projects Coordinator, MOECC Stefanie Gray, Management Support Coordinator, MOECC A special thanks to all the other MOECC scientists and field staff who helped with gathering data 15