I’m a limnologist. I stopped formally studying lakes and rivers a while ago (my last gig as a scientist was with an environmental consulting firm in British Columbia decades ago). But being a scientist is a little like being a mother; once you are one, you are for life.

So, when my good naturalist friend Merridy and I visited Bewdley for lunch at the Lakeview Restaurant on the western shore of Rice Lake in Ontario, I couldn’t help turning our stroll around the lake’s shoreline into an investigation, complete with algal sampling. In our walks along the shore and on the extended wharves, we’d already observed dense stands of submerged weeds such as Ceratophyllum demersum (coontail) and possible milfoil rising to the surface amid floating rope-like remnants of other weeds such as curly-leaf pondweed and some tapegrass.

Entangled and floating among the weeds were clumps of fluffy cotton-candy yellow-green metaphytic algae; some formed bright green circular islands on the lake surface. All were covered in air bubbles, generated through photosynthesis. Based on what I’d seen on the Otonabee River, one of the inlets, I figured I was seeing one or all of the big three filamentous floating mats: Zygnema-Spirogyra-Mougeotia.

Merridy has a compound microscope in her home and I was eager to identify the bright green blobs of filamentous algae carpeting the shore. I asked Merridy if she had a baggy on her and sure enough she did. I then reached out from the wharf and seized a handful of slimy hair-like bright green algae. When we returned to Merridy’s place after a wonderful lunch on the patio in the Lakeview Restaurant, I slapped an algal sample on her microscope: sure enough, it was virtually all Spirogyra. I recognized at least three species of Spirogyra along with a few flagellated Protista, some invertebrates, and the diatom Fragellaria. Not much else.

Algal Communities as Indicators of Water Quality

When I was looking at the algal scum floating on the lake shore, I knew that despite the homogeneous yellow-green mat or consolidated bright-green mat, I wasn’t looking at one species of alga but a community of several. When you look at some pond scum or green-brown slime on a rock, you are seeing a community of several species of algae, along with bacteria, animals, crustaceans, and fungi, mixed with detritus (decaying and dead parts of plants and associated debris). All these together form a mini-ecosystem that reflects its environmental conditions, from current, temperature, and light, to substrates and chemistry. That ecosystem is often dominated by several main species but also supports a complexity of many others; just as a forest may have a largely maple and beech overstory but also harbour other trees and a rich understory of many other living things. A diverse algal community is an essential part of a functioning aquatic ecosystem.

Algae—as primary producers—are a sign of a healthy living lake; they are the foundation of all aquatic life, from the invertebrates that feed on them to the fish, amphibians, reptiles and mammals that feed on them. The key here is balance: if the something in the system goes off balance—say too many nutrients or some nasty chemical is introduced—the algal community will reflect that. An algal bloom is a symptom of water quality issues.  

Different species of algae show different sensitivities to environmental factors such as temperature, pH and chemistry. Some for instance can thrive in water with high organics or low oxygen; others are intolerant. Because of this, algal communities provide useful indicators of water quality. Specific algal species associated with specific tolerances or intolerances are called sentinels or indicator species, and can be used to detect the presence or absence of particular pollutants.

Because healthy lakes support both sensitive and tolerant species, these communities tend to be more balanced and diverse, with many different organisms represented—like an old-growth forest with high biodiversity. A less healthy lake (over-enriched with nutrients or with toxic compounds) will be restricted to just the more tolerant species—like a monoculture tree plantation. Often the tolerant organisms will monopolize a region, just like a large corporation may monopolize a market; and just as with the monopoly market, the consequences are not healthy for the lake. An over-enriched environment may encourage an algal bloom, resulting in reduced light penetration, low oxygen and fish kills. If the algal bloom is dominated by a blue-green alga (Cynanophyta), harmful toxins may be produced. A lake receiving toxic chemicals may have no algae at all—a very dangerous sign, given that algae are the foundation of life in an aquatic environment.

Algal Ecosystem Services & Algal Ecology

Algae are primary producers; they form an essential part of a lake ecosystem by taking the sun’s energy and converting it through photosynthesis into biomass that is available for other creatures to consume. Algae are eaten by micro-invertebrates and small fish, which in turn feed larger fish and birds and people. Algae recycle carbon dioxide and turn it into oxygen, producing up to 80% of the world’s oxygen.

Aside from sunlight and moisture, algae also need nutrients, such as phosphorus and nitrogen, to grow. Phosphorus and nitrogen are called macronutrients; they’re required in fairly large amounts for algae to grow. These two macronutrients are often therefore the limiting nutrient for algal growth. If one is low, even if the other is high, algae will not thrive.

Algal Mats and Blooms in Rice Lake

The high algal growth in Rice Lake is mostly a result of cultural eutrophication (e.g. when the process of natural nitrification over time is sped up through human interference). In previous decades, the main culprit was point-source pollution: sewage treatment plant outfalls that added high amounts of phosphorus from laundry detergents. Contribution was greatly reduced due to improved sewage treatment and a ban on laundry detergent phosphate. But, thanks to increasing dense development, the region suffers from increasing nutrient input from non-point pollution: runoff and erosion from agriculture, lawns and gardens; roadside erosion and lack of natural buffer marshland; and unregulated urban storm water. In addition to nutrients, these sources contribute alarming amounts of heavy metal toxins, and endocrine disrupting chemicals such as PCBs.

Some Ways to Prevent Nutrient Input to a Lake

Owners of shoreline properties should be encouraged to naturalize the shoreline and create what is called a “buffer zone”. Erosion is a significant source of nutrients and can be minimized by naturalizing a shoreline with a buffer zone of natural wetland community. The terrestrial and marsh plants also help trap sediments and dissolved nutrients and may even filter out some pollutants such as heavy metals (by uptaking them). This shore plant buffer zone is also low-maintenance. It stabilizes the shoreline, deters geese, and provides habitat for birds and other wildlife, and can be quite attractive.

Other ways home owners can prevent excessive nutrient runoff into the lake include: maintaining septic tanks, not dumping grass clippings into the water, removing dog and goose poo, abstaining from using fertilizers and endocrine-disrupting herbicides/pesticides; not washing cars on driveways and not dumping anything down the storm drains.