Attached Algae Research

Research Objectives
Based on initial field sampling in 2002, researchers from both the National Water Research Institute (NWRI) and the University of Waterloo carried out intensive field work in the summer of 2003 to address the following:

• The distribution of Cladophora on the north shore of Western Lake Ontario and determine if point sources of nutrients are associated with high Cladophora production
• The importance of watershed point vs. non-point sources of nutrients for Cladophora growth and if hydrodynamic processes deliver higher nutrient levels to Cladophora in nearshore waters
• The role of ambient nutrient levels in controlling growth

Using the field sampling data, the approach for 2004 focused on:

• Predictability - implementing existing Cladophora growth models, tracking historical changes, and developing rapid assessment tools
• Management - using a validated Cladophora growth model to predict the outcomes of possible management interventions to identify the most cost effective means of reducing Cladophora biomass

Key Research Findings

Role of Phosphorus (P)
In 2002, "hot spots" in both biomass and P were identified. This reinforces the role for P in Cladophora biomass as identified in the 1960s and 1970s. It was difficult to establish clear relationships between high P concentrations and point sources of nutrients.

Point vs. Non–Point Sources
In 2003, three locations were chosen to represent point sources of nutrients: a river, an outfall and an unimpacted (control) site. For each of the locations, 8 sampling sites at distances of 0 to 2 km west of each location along the nearshore and at depths within the water column of 2 and 5m were selected and sampled for water chemistry and plant tissue on a biweekly basis starting in May.

Results indicated that on average the Soluble Reactive Phosphorus (SRP) concentrations (the type of phosphorus in the water that is in the right form for plants and algae to use) was highest at the river and outfall sites. As one moved away from the river or outfall sites, the concentrations of SRP decreased. No noticeable change was noted with distance from the unimpacted (control) site. Total Phosphorus levels showed a similar trend.

Levels of phosphorus found in the plant tissue (tissue P) were found to be higher in the river and outfall sites samples but did not decrease with distance from the sites as SRP did, however, seasonal differences in tissue P were noted. Predictive models indicate that Cladophora seems to be less limited by P early in the growing season. It then experiences some nutrient stress during the summer and then rebounds in late August. These differences may be due to environmental factors influencing P delivery to the plants.

Cladophora growth along the north shore
A large scale west to east survey of the north shore was conducted from late July to early August of 2003 with 15 sites sampled at depths of 2, 5, 8 & 10 m for total phosphorus (TP), tissue P and when applicable an underwater video was recorded.

On average the 2 m sites showed higher levels of TP in the water than the deeper sites. There was an overall increase in TP, and tissue P, as you moved from west to east which may be the result of the greater urbanization and associated surface runoff as you move towards Toronto. 3 noticeable hotspots were found that displayed significantly higher TP concentrations than the other sampled sites. An in-depth look at these sites is underway to determine the specific source of the TP.

Cooperative research with stakeholders in the Halton Region found that stormwater outfalls are a major source of TP to the nearshore zone.

Role of Storm Water Runoff
Non-point sources of nutrients also contribute to measurable concentrations of nutrients in lake waters. However, their relative contribution and role in plant growth remains unclear. Water and plant Phosphorus concentrations were measured following a three-day rainstorm event. Surges in both parameters relative to pre-event levels were detected. This suggests that ephemeral peaks in nutrients, particularly Phosphorus, may sustain Cladophora growth rates even though ambient background levels of nutrients are relatively low.

Nutrients in the Nearshore Waters
The physical stratification of the lake can also play a role in algae growth early in the season. In the spring, water temperature increases most rapidly in shallow areas along the shorelines of the lake. As the season progresses, a band of warm, less dense water forms along the shore, creating a ‘thermal bar’ separating the nearshore zone from the dense cool offshore water. The difference in the densities of the water in these zones prevents them from mixing. As a result, nutrients from point and non-point sources remain trapped in the nearshore area and are readily available to Cladophora early in the season. This "thermal bar" gradually expands towards the centre of the lake until the lake becomes thermally stratified.

In 2002, the evolution of the thermal bar in Lake Ontario was intensively studied. This work, funded by the OWWRC has enhanced earlier research on the function and formation of the thermal bar.

Other Contributing Factors
Other factors that may be contributing to the recent increase of biomass are the invasion of zebra mussels and climate change. The hypothesis for the role of mussels is that they increase P in the near shore waters through their filtering action. Moreover, they increase water clarity by removing suspended particles and may allow Cladophora to grow in deeper water.

Climate change may be leading to more severe summer rainstorms, with resulting impacts on non-point sources of P. Alternatively, if there are warmer springs Cladophora growth would increase.

Under Water Videography, Biosonics and Artificial Substrates
Experiments using under water videography, biosonics and artificial substrates constructed of ceramic tiles and floats were conducted to determine the extent of offshore algal growth. The biosonics experiment revealed extensive growth of Cladophora in shallow water (25-50 cm) and copius growth at 5m. Although mussels were mostly found at 10m and 15m, Cladophora growth was still evident.

Artificial substrates were installed off Coronation Park east of Bronte. Water depth over tiles was the same at all stations. This experiment revealed more Cladophora growth on inshore tiles than offshore tiles. In addition, Phosphorus content of algae tended to be higher at stations situated nearest to the shore.

Growth Models
Numerical models have been developed to predict Cladophora growth and biomass accumulation in Lake Erie. Once they have been calibrated and verified with historical data from Lake Ontario, the models can be applied to recent data to predict current Cladophora growth rates. Among the most important model inputs are solar irradiance, water turbidity, water temperature and TP concentrations in the water column.

Tracking Historical Changes
Estimated annual and seasonal TP loadings to the nearshore are based on historical sewage treatment plant effluent discharges, storm sewer contributions, river data and nearshore modeling of dilution rates. Historical reconstructions of loadings are necessary to assess if TP loadings to the Lake are changing over the long-term and if these changes are driving increased Cladophora growth. This project is using data from municipal and provincial agencies as well as modeling to determine the extent to which each of the sources of P contributes to nuisance growth of Cladophora.

Using Rapid Assessment Tools To Predict Growth
Preliminary experiments were undertaken in 2004 to develop a rapid assessment tool that can predict differences in potential growth rates of Cladophora. These experiments assessed how changes in light and temperature affect the response of Cladophora to TP and tested if these responses can be rapidly measured in the field.

Management
Of the key variables influencing Cladophora growth - light, temperature and TP concentrations - TP concentration is the only factor that can be locally managed. Analysis of concentrations measured 2002 and 2003 suggests that while Cladophora growing at some sites would likely respond to small reductions in TP concentration, Cladophora in many areas will require more dramatic reductions before changes in growth rates and, therefore, biomass accumulation are noticeable.

Currently, it is unclear what species of Cladophora predominates or if there are multiple species present in the western basin of Lake Ontario. Sample differences have been seen in the branching pattern of Cladophora plants taken from Oakville (Dingle Park) and from Pickering (OPG Pickering plant). This has clear management implications as different species are likely to differ in their environmental requirements, includig P needs. Researchers at the University of Waterloo continue to address this issue in the laboratory.

Research conducted in 2003 showed that sites near point sources of nutirents have higher water column TP concentrations and higher plant tissue P concentrations than unimpacted sites. Analyses of samples taken at 16 sites at various distances from the mouth of Cooksville Creek in 2004 indicate that storm events can significantly increase local concentrations of TP and, thus, storm water discharges have to be considered in developing management strategies.

2005-2006 Research Plan

The factors influencing Cladophora growth are complex. Increased emphasis on modelling, with extensive ground proofing, should help to understand these factors in the future.

• Isolation and cultivation of Cladophora samples from Lake Ontario to determine if variations in phosphorus, light and temperature requirements exist between isolates
• Analysis of historical data to better understand wastewater treatment plant discharges, river and storm water loadings to determine their contribution to making P available for Cladophora growth
• Biological/hydrodynamic modeling of TP concentrations and Cladophora growth in nearshore waters
• Compilation and interpretation of 2002-2005 field data
• Completion of a final report encompassing the 2002-2006 research efforts and final recommendations for possible management action
  

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