By Jon Shepherd
As a concept in engineering and environmental management, in parallel with solution-proposals, consideration is also given to the consequences of inaction and leaving a challenge unmet with solutions. The “do-nothing” approach to managing algal blooms, therefore, involves taking minimal or no action to actively control or mitigate the effects of algal blooms in natural bodies of water such as lakes and reservoirs. This approach essentially allows nature to take its course, without human intervention.
Decoding Algal Blooms
Algae is a natural and important part of our aquatic ecosystems; as primary producers, using sunlight to photosynthesise, these organisms form the basis of food webs and are therefore essential to life. But in some conditions, a single genus of algae can dominate with exponential out-of-control growth. The mass of cells reduces water clarity, preventing macrophytes, (aquatic plants) on the lake bed from photosynthesising. Their numbers can collapse, reducing habitat, loss of shelter and niches for other organisms within the system. Nutrients in the water, of which nitrate and more so, phosphate are key, are no longer assimilated by plants. This reduces competition for the algae who also need the nutrients. They no longer face a limit to growth and can continue to dominate and bloom, with a positive feedback loop or vicious circle supporting algal growth now established.
With the loss and breakdown of macrophytes, dissolved oxygen levels can crash as bacteria breaks down the organic matter. But the bacteria themselves are aerobic, requiring oxygen to perform their work. As such, incomplete breakdown of organics occurs and sedimentation rates increase with smothering of the lake bed. Nutrients that were previously locked up within the sediment can now be released by the bacteria, with the evolution of ammonium, manganese, and phosphate.
With the macrophyte breakdown requiring oxygen, dissolved oxygen in the water column is consumed and invertebrates and fish either flee the hypoxic conditions, or can die, with the collapse of entire food webs.
Bloom conditions persist uninterrupted for as long as conditions allow. Frequently, the end of a bloom is caused by algae reaching a growth limit. When this limit is met, algae dies and their biomass begins to break down. Again, this causes crashes in dissolved oxygen, and if any toxic genuses were present, their cells rupture with the contents releasing chemicals such as microcystins, 2-Methylisoborneol (MIB) and geosmin, which cause musty, stale taste and odours as well as a health threat to water users, our pets and wildlife. A growing list of medical conditions is attributable to toxic bloom species including respiratory, liver, kidney diseases, paralysis, and neurological conditions.
For water treatment works, WTW, these compounds can be a challenge to remove. The increased organic load of dead biomass, in the presence of the common disinfectant chlorine, used to treat water, allows for the formation of disinfection byproducts, a group of compounds including carcinogenic trihalomethanes, THMs. Frequently, even when a water treatment works is able to meet quality standards for potable water, to do so requires a greater intensity of treatment, using physical and chemical methods and energy, hence algal blooms reduce output of water by large percentages, increasing the cost of treatment and stressing water supply networks.
Rethinking The “Do Nothing” Approach
Whilst algae is natural, in many countries around the globe, algal blooms are becoming more frequent, showing greater intensity and duration, with greater impact to our already stressed ecosystems. Climate change and increased water temperature fuels harmful algal blooms, but the prime increase in the occurrence of blooms is due to anthropogenic causes, with agricultural runoff of fertilisers and point sources from industry and wastewater works, releasing nutrients, of which phosphate is key, into waterbodies.
So what are the key elements that we need to be aware of when considering the do-nothing approach?
- Natural Balance: Proponents of the do-nothing approach argue that ecosystems often have natural mechanisms in place to control algal blooms. Predatory organisms like zooplankton and some fish species may naturally graze on algae, helping to keep their populations in check. Whilst this is true, the rate of change caused by man is outpacing the ability for ecosystems to adapt, and the presence of a bloom in itself is indicative of an ecosystem that is under severe pressure and unable to manage the natural balance
- Limited Intervention: Under this approach, water authorities or landowners may choose to limit their interventions to monitoring water quality and the extent of algal blooms rather than actively treating the water. They may take action only when certain criteria are met, such as when the algal bloom poses a direct threat to public health or water quality. Sometimes, even then, no action is taken.
- Potential Risks: While the do-nothing approach may seem less intrusive, it carries risks. As described previously, algal blooms can produce toxins that are harmful to aquatic life and humans. Allowing these blooms to persist without intervention may have negative consequences for water quality, wildlife, recreational activities, water treatment, and local economies.
- Public Perception: The acceptance of the do-nothing approach often depends on public perception and the tolerance of local communities. When algal blooms become a nuisance or pose health risks, public pressure may lead to a shift in management strategies.
- Long-Term Consequences: Over time, a consistent do-nothing approach can lead to the accumulation of organic matter and nutrients in the water and sediment, worsening algal bloom issues in the future, further stressing the ecosystem, and changing the diversity and richness of macrophytic coverage.
Beyond “Do Nothing”
It’s essential to recognise, therefore, that the do-nothing approach is not universally applicable, and its suitability depends on the circumstances and goals of water management. In many cases, a combination of strategies, including monitoring, nutrient management, and targeted interventions, may be necessary to effectively manage and mitigate the impacts of harmful algal blooms in waterbodies. By managing algal blooms with targeted treatments such as ultrasound, an opportunity is given to the recovery of aquatic vegetation. With this growth, the plants are able to absorb nutrient loads and the ecosystem is better able to manage itself effectively. Chemicals, sediment smothering particles, ‘nutrient absorbers’, and non targeted strategies should never be deployed as these further stress the ecosystem, destroying plants, zooplankton, and invertebrates, as well as preventing natural bacterial processes. Some of these may destroy a bloom in the short term but do not prevent subsequent blooms or allow the ecosystem to recover. Their success therefore relies on constant application of product to maintain a waterbody that has already been killed by the chemicals.
Therefore, the approach chosen to manage algal blooms in aquatic systems should be based on a thorough understanding of local conditions and the potential risks associated with algal blooms as well as treatment options. With data, early preventative actions can be taken to manage algal species before they dominate and their growth becomes troublesome.
At LG Sonic, we manage algal blooms. Our solar-powered, chemical-free ultrasound is proven in over 55 countries to combat harmful blooms without negatively affecting zooplankton, invertebrates, macrophytes, or fish. With water quality instrumentation on board our MPC Buoys, and remote sensing data from satellites, we allow aquatic managers to monitor water quality, nutrients, bloom growth stage, and progression, and make the correct decisions for treatment.
Our low-pressure ultrasound creates a sound barrier that prevents the vertical migration of algae from nutrient-rich deep water to sunlight saturated surface layers. In doing so, their growth is restricted to levels normal to the ecosystem, whilst also allowing sunlight to reach benthic growing vegetation. Blooms do not have the opportunity to dominate, with no biomass and toxin load associated with their growth, nor oxygen depletion, sludge, or release of nutrients with their subsequent death. As algae eventually adapt to the ultrasound barrier, so too does our control thanks to machine-learning based large datasets based on millions of datapoints taken globally for over a decade. We continue to beat the migration of harmful algae, cyanobacteria, and diatoms. With our monitoring, prediction and control platform, and digital twins modeling whole watersheds, the most appropriate ultrasound program is selected to keep ahead of the ever-changing nature of blooms.
Jon Shepherd, Commercial Director at LG Sonic, is a water treatment specialist with 20 years of experience in the water industry. With a strong background in pollution control and environmental management, Jon assists clients in resolving complex water issues, including challenging algae-related problems.