Mississippi Lake Study April, 2019
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Mississippi Lake Study April, 2019 Preliminary Results ISSUE Area residents are concerned about vegetation and algae in the lake that affect swimming and boating activities. While a balance between ecological and recreational needs is desired, some of the algae blooms have been confirmed as the harmful “blue-green algae” a form of toxin- producing bacteria known as Cyanobacteria. When large blooms occur, Cyanobacteria can pose a risk to drinking water quality. BACKGROUND In 2016, the Mississippi Lakes Association (MLA) approached MVCA to provide technical support in studying this issue—a key action identified in their Mississippi Lake Plan. With a $22,500 grant from Mitacs, a study was initiated through a partnership between MVCA, the MLA, and Queen’s University. Mississippi Valley Conservation Authority (MVCA) is looking at changes in algae conditions as a possible indicator of overall lake and watershed health. Work continues, and this report provides preliminary results. Algae is a natural part MISSISSIPPI LAKE of a healthy ecosystem. …is a long shallow lake formed by the widening of the Mississippi River, commonly Too much algae can divided into First Lake, Second Lake, Third Lake and Big Lake. Run-off from 2,685 threaten aquatic km2 of forested Canadian Shield and rural communities enters the lake at its west species and indicate end. In addition to the upper watershed, four main tributaries discharge to poor watershed health. Mississippi Lake: McIntyre Creek, McGibbons Creek, Code Creek, and McCreary’s Creek. Approximately 180 km2 of land drains directly to the lake from over 3,000 properties. 1 STUDY DESIGN PROJECT OBJECTIVES Nutrients such as phosphorous (P) and nitrogen (N) can contribute to vegetation, algae, and bacteria growth. The objective of this study was to improve our understanding of: • sources and movement of nutrients within Mississippi Lake • interactions between physical (flow, temperature), chemical (nutrients) and biological processes (algae growth) • daily, seasonal and annual variations and trends, and • potential implications for other lakes in the watershed. MODEL A 3D ecological model was developed by Nader Nakhaei, Queen’s University Ph.D. and MVCA employee using water samples and flow data collected in 2017 and 2018 by fellow MVCA staff and the MLA at 15 sites in Mississippi Lake and its tributaries. Samples were analyzed for nutrients and Chlorophyll_a, a green pigment found in plants, which is used as an “indicator” of algae growth. (MVCA monitoring equipment cannot distinguish amongst strains of algae or test for Cyanobacteria.) This information combined with weather data obtained from Environment and Climate Change Canada was input to the model to allow for analysis and calibration of the relationship between these physical, chemical and biological variables. SCENARIOS The model was used to artifically “turn-off” sources of nutrients to the lake to determine what impact, if any, were seen on Chlorophyll_a levels and locations in the lake. These theoretical results were run to determine the relative importance of different sources of nutrients. Three scenarios were modelled in addition to base case conditions: • Elimiate all nutrient inputs from the upper watershed (Mississippi River), • Eliminate nutrient inputs from McIntyre Creek, the largest of the tributaries to the lake, and • Eliminate nutrient inputs from internal loading (released from in-lake sediments and plant material). This study will improve our understanding of nutrients and algae in the watershed. 2 Flow vs. Nutrients As a percentage of total sources Mississippi Lake, 2017 and 2018 DRAFT RESULTS 100 94 82 NUTRIENT SOURCES 11.5 Preliminary modelling results indicate that the Mississippi River 10 (upstream drainage area) contributes approximately 94% of the flow and 82% of the nutrients entering the lake. The balance 3.4 2.9 of flow and nutrients come from downstream of the Mississippi 2.3 River inlet. This includes flow from the four main tributaries, 1.3 1.1 1 local streams, ditches and drains, and overland run-off that 1 flows directly into the lake. McIntyre Creek contributes approximately two-thirds of local nutrient inputs. 0.5 TEMPERATURE IMPACTS 0.1 Preliminary modelling results inidicate that peaks in algae Flow Inputs Nutrient Inputs growth are associated with sharp increases in air temperature. The model successfully predicted blooms in surface Chl_a in mid-September and early October, which coincided with confirmed algae blooms in the lake. SPATIAL IMPACTS As shown above, the two largest sources of flow and nutrients to the lake are the Mississippi River and McIntyre Creek. “Shutting off” these sources was used to gauge their impact on Chl_a growth. Preliminary results indicate that eliminating (zero) nutrient inputs from the Mississippi River could reduce average surface Chl_a levels in the lake by as much as 38%. And, eliminating nutrient inputs from McIntyre Creek could reduce average surface Chl_a by roughly 9%. There was no measurable impact from eliminating in-lake plant and sediment sources of nutrients. This map shows how impacts vary spatially across the lake. For example, it appears that eliminating nutrient inputs from Mississippi River can reduce Chl_a growth by as much as 25% in Third Lake but as little as 5% in First Lake. Similarly, eliminating inputs from McIntyre Creek could reduce growth by 14% in Big Lake but have limited to no impact downstream. These preliminary findings raise several questions that we plan to explore further in 2019. 3 NEXT STEPS FURTHER MODELLING The next step is to use the model to examine the impact of more realistic decreases in nutrient sources to Mississippi Lake. This will include decreasing river and tributary nutrient inputs by 10% to 20%, a more practical goal for watershed and municipal planning. The model will also be used to conduct more in-depth assessments of the localized impacts of nutrient inputs and look at changes in predictions over longer time frames. Steve Miller, MLA Volunteer helping with the tribuitary sampling. ENHANCED ALGAE MONITORING More information is needed to improve our understanding of what is happening on the landscape in terms of where, when and the type of algae that is occurring. MVCA will be working with the MLA, Queens University, and the province, to implement an enhanced Algae Monitoring Program in 2019, with more sample locations and frequency. MVCA has developed an on-line reporting tool to make it easy for watershed residents to report algae blooms. Visit: http://mvc.on.ca/algae REPORTING BLUE-GREEN ALGAE CONTACT the Ministry of the Environment, Conservation and Parks (MECP) if you suspect a blue-green algae outbreak: MOECP Spills Action Centre: 1-855-889-5775. DRINKING WATER concerns should be addressed to your local Health Unit. “Blue-green algae” isn’t Mississippi Valley Conservation Authority 10970 Highway 7 algae. Carleton Place, Ontario K7C 3P1 It is a bacteria that releases (613) 253-0006 toxins when it dies. [email protected] www.mvc.on.ca 4 .