The nearshore is an area where land, streams, marshes and the lake all meet — and an area where humans interact with and affect the natural environment. Conservation strategies are essential to maintaining both the ecology and the natural beauty of the nearshore.
What Is The Nearshore?
There is no operational definition of what the nearshore is, it can and has been defined in a variety of ways. Some people define it based on a depth or a distance from the shore, while others define it as the area from the shoreline extending offshore to a depth where warm surface waters reach the bottom of the lake in early fall.
For this study, we define the nearshore as the area beginning at the shoreline (or lake edge) to a depth of approximately 30 metres. This zone includes the higher energy coastal margin areas adjacent to the shoreline, and the nearshore open-water areas of lower energy. It also includes the depth where Cladophora algae grow.
In general, the bottom sediments of the nearshore environment are coarser-grained (e.g., sands) than those found deeper in the lake, and they are moved around by wave driven processes. In the nearshore open-water areas, dominating processes are more similar to characteristics observed in the open lake, however, during storms the nearshore open-waters will experience higher wave energies than normal and can redistribute or “rework” the finer-grained sediments.
In 2011, the sampling design for this study was changed and transects were extended to 5 km. At a distance of 5 km, although not “offshore”, the open-water area is of lower energy and, according to the Ontario Ministry of the Environment and Climate Change, this distance is representative of “background” conditions (e.g., Howell et al., 2012ab). The area extending beyond 25 m, approximately 5 km from the shore, is defined as “background” lake conditions.
Why Is The Nearshore Environment Important?
The nearshore is an important area for a variety of reasons. It is a meeting area between the land, streams, marshes, and the lake. Nearshore areas are spatially diverse, with high biotic diversity creating habitats for a wide variety of aquatic species and where biological activity within the lake is greatest. This junction between land and water is an area where land and people also meet the water, and an area where humans interact with and affect the natural environment. Conservation and restoration strategies are therefore required to maintain the nearshore for both ecological and aesthetic purposes.
Water quality along the 15 km of shoreline which extends through Pickering and Ajax is particularly notable since the beach areas are valued by the public, making aesthetics, odour, and availability for recreation important. The nearshore area close to Carruthers Creek contains the community drinking water intake, while the nearshore area close to Pickering houses the cooling water intake for the Pickering Nuclear Generating Station. The area is also influenced by urban and rural nonpoint sources of nutrients and sediment, as well as by the outfall of the Duffin Pollution Control Plant. Since the nearshore regions are affected by a number of activities caused by humans, in addition to the inputs from rivers, creeks, and streams flowing through the watersheds, it is crucial that we understand how the environment works.
How Do We Assess The Status/”Health” Of The Nearshore?
The conditions and “health” of the nearshore are difficult to summarize as it is a dynamic and heterogeneous environment, which means it’s constantly changing. Often when we think of a healthy lake, we think of “pristine” conditions. However, no lake that has human effects will be “pristine”. It is more useful to think about an aquatic environment in terms of whether it is stable and sustainable. Finding a balance between our influences, and what the lake can handle becomes important. Emerging issues including algal blooms, invasive species, and shoreline development all affect the nearshore and should be considered when thinking about the status of the nearshore. Beach closures could also be used an indicator of ecosystem health.
What Nutrients Are Important To The Ecology Of The Nearshore?
In the same way that flowers or vegetables in our gardens require nutrients in fertilizer to grow abundantly, algae and other plants in the lake require nutrients to grow. We need algae and plants to grow, as they are important members of the lake food web, providing such things as food for other organisms, oxygen, and habitat for fish.
Too many of these aquatic plants, however, can cause aesthetic and odour issues along the shoreline. Some of these algae can also release toxins. When these overgrowths of aquatic plants die and decompose, oxygen levels in the water can be reduced.
In most lakes, including Lake Ontario, phosphorus is the nutrient that is in the shortest supply for aquatic plants. This means that if we add more phosphorus, aquatic plants will be able to grow more abundantly. If there is too much phosphorus, we could see excessive growth of aquatic plants. This process of over-fertilization is known as eutrophication.
The word eutrophication is often used when looking at aquatic systems. According to Art (1993), eutrophication is “the process by which a body of water acquires a high concentration of nutrients, especially phosphates and nitrates. These typically promote excessive growth of algae. As the algae die and decompose, high levels of organic matter and the decomposing organisms deplete the water of available oxygen, causing the death of other organisms, such as fish. Eutrophication is a natural, slow-aging process for a water body, but human activity greatly speeds up the process.”
Eutrophication can include excessive growth of larger plants (called macrophytes), that can grow in dense stands in the nearshore and eventually wash up on the shoreline, causing aesthetic and odour problems. Along with a combination of other conditions (such as light, temperature, lake bottom substrate, mussel biomass, etc), too many nutrients can contribute to the growth of these aquatic plants.
Excess phosphorus can also cause overgrowth of microscopic plants, resulting in a condition called an algal bloom, in which the lake water can become noticeably green, with floating forms of these microorganisms sometimes forming clumps on the water surface. If these organisms are dense, they can block the sunlight from reaching the lower levels of the lake causing the algae to die. When these organisms die, their decomposition (breakdown) removes oxygen from the water, which can be very harmful or fatal for certain aquatic species including fish and invertebrates. The decomposition and wash up of this material can cause aesthetic and odour issues along the shoreline.
The photo of the shoreline was taken by a researcher at the Ontario Ministry of the Environment and Climate Change currently studying the growth of Cladophora (algae) in the Great Lakes, including the Ajax and Pickering waterfront. Other researchers interested in Cladophora growth are located at Michigan Technological University, the University of Waterloo and Environment Canada.
Another important plant nutrient is nitrogen. In some cases, the proportion of nitrogen and phosphorus can affect the types of aquatic plants that we find in the lake. If these nutrients are out of balance, they can result in the growth of undesirable or, in some cases, toxic forms of algae. However, the solution to algal blooms is not to get rid of all of the phosphorus and nitrogen in the nearshore.
If there is too little phosphorus, then the lake’s aquatic food web can starve. We need a certain level of nutrients for a healthy aquatic ecosystem, and to ensure that the fish have continual food sources. Since nitrogen and phosphorus are key indicators of water quality in shallow coastal areas, scientists in Canada and the United States are researching what a healthy balance of these nutrients is in order to set guidelines for both countries to follow.
Plants and algae cannot use all forms of nitrogen and phosphorus. Only dissolved nutrients are directly available for algal growth. Some of the common ones are listed below:
Phosphorus:
Scientists commonly measure two forms of phosphorus: Total Phosphorus and Soluble Reactive Phosphorus.
Total Phosphorus (TP)
- Contains all forms of phosphorus in the water – both dissolved and particulate form.
- Is easy to measure in aquatic systems.
- Includes some forms of phosphorus that aquatic plants cannot use easily, so in some cases, might not be a good indicator of the potential for the overgrowth of aquatic plants.
Soluble Reactive Phosphorus (SRP)
- A dissolved form of phosphorus that is readily available for use by aquatic plants, so is sometimes a better indicator for the potential for the overgrowth of aquatic plants.
- Is more difficult to accurately measure than total phosphorus.
- Is a small component of total phosphorus.
Nitrogen:
There are three forms of dissolved nitrogen commonly measured as water quality indicators: ammonia, nitrate, and nitrite. The most common form in the nearshore waters of of Lake Ontario in Ajax and Pickering is nitrate.
Nitrate (NO3)
- Is an important form of nitrogen in freshwater.
- Is naturally present in soil and water, but human activities have increased the amount of nitrate in rivers and lakes.
- Is dissolved in water.
- Can be used by aquatic plants and algae to support their growth.
- Nitrate levels below 0.5 mg/L seem to have no effect on warm water fish.
- The drinking water limit for nitrate is 10 mg/L.
Bacteria:
E.coli
Although not a nutrient, in Ajax and Pickering area, E. coli is an important indicator of water quality
- It is a type of bacteria that is an indicator of recent fecal contamination.
- Fecal contamination could be from human sources, wildlife, or pet and animal waste.
- Beaches are closed as a precaution when their levels are high.