THE IMPORTANCE OF PHOSPHORUS CONTROL IN THE MITIGATION OF BLUE-GREEN ALGAE (CYANOBACTERIA) BLOOMS
By Jessica Lemieux
Cyanobacteria were originally called ’blue-green algae’ because of the pigment that many of them produce which gives them this colour. However, they are in fact bacteria that - like algae (and all plants) - can use the sun as an energy source (i.e. are photosynthetic), and are often found in many types of water systems, including wetlands, rivers and lakes. Under certain environmental conditions, including warm, slow moving and shallow water - in addition to the over-supply of nutrients, such as phosphorus - high growth rates of blue-green algae blooms can occur.
Blue green algae blooms can resemble a layer of slime or scum on the water surface and can range in colour anywhere from a dark green, to yellow, to pink or brownish colour. Some species of cyanobacteria can produce toxins, which impact the health of animals and humans. They often also produce taste and odour, which can affect drinking water and cause off-flavours in fish.
Like plants, cyanobacteria and algae require a balanced supply of essential nutrients to grow - particularly carbon, nitrogen and phosphorus - and in most undisturbed waters, one or more of these nutrients is in short supply, which controls the growth of these organisms. Over the past few centuries, human activity has increased the supply of these nutrients to surface waters, which, in many cases, has resulted in the proliferation of blooms. Management of this issue, however, has often been hindered by a debate as to which nutrient (or other factor) is primarily responsible.
The Experimental Lakes Area (ELA) has provided a very important natural facility to scientists to carry out research aimed to answer these, as well as other important questions, about our waters. ELA was established in 1968 and is located in the Kenora District in northwestern Ontario. The area consists of 46 small, deep, pristine lakes - unaffected by external human influences - and has been used by scientists to answer questions about the way in which lakes behave when perturbed by human or natural impacts. For example, these lakes have been used in experimental studies of the causes and control of the eutrophication of bodies of water.
Eutrophication is the process by which a body of water becomes enriched in nutrients (such as phosphorus and nitrogen), frequently due to runoff from land, which stimulates the growth of cyanobacteria, algae and aquatic plant life. The bacterial degradation of this organic material can often result in the depletion of dissolved oxygen.
In 1974, the famous study by Dr. David William Schindler, Eutrophication and Recovery in Experimental Lakes: Implications for Lake Management, showed that in most inland waters, phosphorus is the primary agent that limits the development of algal/cyanobacteria blooms, not nitrogen or carbon. Schindler used Lake 226 of the Experimental Lakes Area (ELA) to demonstrate this. The lake has a natural division into a north and south basin, with a very narrow channel between the two. Schindler put a curtain down in the middle of the channel, essentially dividing the lake into two - a south and north side. He fertilized the south basins with carbon and nitrogen, and the north basin with carbon, nitrogen and phosphorus. After a few weeks, a photograph and measures were taken. The results were dramatic. They showed massive algal blooms in the north basin (treated with phosphorus) but little change on the south side (which received only carbon and nitrogen).
This study, along with others (for example, by Canadian scientists Richard Vollenweider and Frank Rigler) convinced many managers and policy makers that eutrophication issues could be addressed through phosphorus control, and played a pivotal role in the development of the first Canada-USA Great Lakes Water Quality Agreement (GLWQA) in 1972 to clean up the Great Lakes which were experiencing severe algal blooms. The effort under the GLWQA, acted to reduce phosphorus in detergents and wastewater, and was pivotal in the subsequent recovery of the Lakes.
However, continued population growth and development of our landscape - deforestation, soil erosion, intense agriculture, feedlots, manure and crop and lawn fertilisers, storm sewers, impervious urban surfaces, etc. - along with climate change and runoff, has intensified impacts on our valuable freshwater resources, and reports of blooms are increasing.
Recently, some researchers have questioned whether phosphorous control, alone, can address these blooms or whether nitrogen also needs to be controlled. This suggestion is what spurred Dr. Schindler, now a Professor of Ecology (Emeritus) in the Department of Biological Sciences at the University of Alberta, and his colleagues, to conduct the study, Reducing Phosphorus to Curb Lake Eutrophication is a Success. This study used long-term data from 37 lakes to see if additions or reductions in nitrogen had an effect on algae, in addition to phosphorus control.
It is important to note that, over time, lakes that receive high nutrient inputs can gradually accumulate these in their sediments, and this nutrient bank can be re-released back into the water column, especially when oxygen levels are low. Not surprisingly, this “internal loading” process can stimulate more blooms and delay the response of lakes to management-based reductions to external nutrient control. For effective management, it is also important to distinguish between nutrient limitation that occurs short-term (i.e. hours, days), where algal cells may be temporarily deficient in one or more growth limiting factor including phosphorus (e.g. nitrogen, light, iron etc.), and long-term nutrient limitation (months, years), where the overall risk of algal blooms is controlled by the growth factor that, on average, is in the shortest supply. The results of short-term experiments, which can demonstrate deficiency in any of the above factors, are thus not necessarily applicable to long-term management of this issue. For example, numerous small-scale nutrient enrichment studies have shown nitrogen limitation, but as noted above, these only measure short-term (proximate) nutrient limitation, whereas controlling eutrophication requires reducing inputs of nutrients that provide long-term (ultimate) control.
EVIDENCE FOR THE SUCCESS OF PHOSPHORUS CONTROL
Evidence that reducing inputs of phosphorus is effective in reducing eutrophication comes from four approaches, all long-term studies at ecosystem scales: 1. Long-term case histories, 2. Multi-year whole lake experiments, 3. Experiments to directly remove phosphorus from the water column, and 4. Chemical additions to inhibit return of phosphorus from the sediments to the water column.
EVIDENCE THAT REDUCING INPUT OF NITROGEN DOES NOT REDUCE EUTROPHICATION
There are a number of eutrophic lakes where inputs of nitrogen as well as phosphorus were decreased. In one study, [scientists] Edmondson, Lehman and Welch deduced that phosphorus was the controlling element, because after nutrient inputs were reduced, algal biomass decreased in proportion to phosphorus decline, while nitrogen accumulated as nitrate. Similar observations were made in ELA lakes, which had been receiving experimental additions of fertilizer over a course of years, after this nutrient loading was terminated. Increases in nitrate concentrations have also been observed during declines in phosphorus and phytoplankton in the Great Lakes. None of the above cases provides evidence that dual nutrient control (i.e. both Phosphorus and Nitrogen) reduced eutrophication more effectively or rapidly than controlling phosphorus alone. Welch concluded from his study of the recovery of Moses Lake, Washington: “Targeting both N[itrogen] and P[hosphorus] may not only be much costlier than necessary, but may even promote blooms of N[itrogen]-fixing cyanobacteria, especially in cases of high internal P[hosphorus] loading.”
Ultimately, Schindler and colleagues concluded that in the 37 cases, phosphorous control, alone, worked. There was no evidence that control over nitrogen did anything to reduce the problem.
“Wastes from a growing human population and increasing agricultural production are likely to increase P[hosphorus] inputs and eutrophication in coming decades. Decisions about mitigating eutrophication will be made in the context of multiple environmental threats due to changing climate, land use and other factors. These decisions should use the best scientific information relevant to the scale of the problems. There is no evidence that eutrophication can be managed by controlling N[itrogen] inputs. In contrast, multiple lines of evidence at the whole-lake scale of management show that P[hosphorus] control works to mitigate eutrophication.”
Dr. Susan B. Watson, a Research Scientist from Environment and Climate Change Canada, focusing on algal blooms and nutrients, noted that this is not a new observation.
Watson explained, “The relationship between algal growth and phosphorus was published back in the 1960s and earlier, and Schindler and colleagues have done some very important work. He was one of the first scientists to actually demonstrate the relationship of phosphorus in water bodies in his worldwide famous experiment with the experimental lakes - which put Canadian science on the map. The debate over the effect of nitrogen is really a question of scale. Without a sufficient supply of phosphorus, you won’t build cells. Phosphorus is easier to control than nitrogen, which unlike ’P,’ is abundant in the atmosphere. This has been the focus of control for some time in some of the provinces, like Ontario, where provincial guidelines for water quality include phosphorus.”
“Where there is an excess supply of phosphorus, another factor becomes limiting and some scientists are studying lakes that are very high in phosphorus to understand the degree to which other factors control both the size of blooms and the species that dominate these events. Some cyanobacteria can use atmospheric nitrogen (N₂). This provides them with a competitive advantage over other more benign species, because this form of nitrogen cannot be used by most organisms, and these cyanobacteria can access this huge supply of nitrogen from the air and dissolved in the water. Hence where there is a high supply of ’P,’ but a low supply of more bioavailable forms of nitrogen such as nitrate and ammonia, these cyanobacteria can proliferate and outcompete other species.”
Schindler has recently discussed the need for increased provincial regulations in Alberta and improve controls on how much agricultural and cottage development goes on near freshwater lakes.
This season, Alberta Health Services has issued 30 advisories regarding blue-green algae blooms in the province, making Alberta the province with the most reported blue-green algae advisories in the country. Overall, the number of these advisories issued for Alberta this year has increased from the 2015 season.
A representative from Alberta Health Services said, “During the 2015 season, 28 blue-green algae advisories were issued. This is extremely minimal variation, and not at all unexpected. A number of factors - including water temperature, weather conditions and the amount of nutrients available - can influence the growth of blue-green algae, which is why some variation in growth is expected to be seen year to year.”
“Alberta Health Services monitors a number of public recreational beaches through AHS’ Routine Recreational Water Quality Monitoring Program. While the number of public recreational beaches monitored varies from year to year, on average, between 30 and 40 bodies of water with public beaches have been included in the monitoring program each summer season over the past several years. The beaches included in the monitoring program are selected based on a number of factors, with beach popularity a notable influence on inclusion in the Program, as more individuals could be at risk at popular beaches than at one that is rarely used for recreational purposes. As well, history of blue-green algal/bacteriological contamination, and related environmental conditions are also factors on inclusion in the Program.”
Watson said that, while Alberta seems to have high numbers of blue-green algae contaminated lakes, these events are more natural to the area that most regions of Canada. Alberta and other areas of the prairies are on a very fertile landscape. As an old seabed, it is naturally high in nutrients and blooms are not new to the area, but are intensified where there is increased nutrient loading from agriculture and other sources. It is more useful to compare lakes across geographical regions rather than provincial boundaries, and to consider the different drainage basin characteristics of each body of water.
“Some lakes are naturally eutrophic, like many prairie lakes. On the other hand, the Great Lakes were not eutrophic until human development of the watershed occurred. Lake Superior has a relatively undeveloped drainage basin and a large volume and capacity to process the material that is delivered to the lake from the watershed; on the other hand Lake Erie - which develops severe blooms - is smaller, shallower and warmer and is one of the most intensely developed of the Great Lakes.”
“Climate change is playing an increasing role, by extending the ice-free growing season, warning the water, changing the mixing patterns and flushing rates and resulting in intense soil-laden runoff events. Furthermore, due to the size of these watersheds it is much harder to identify the source of nutrients when there are multiple contributing factors. Most notably, there has been gradual changes in how nutrients are delivered to lakes, making them difficult to control. In many waterbodies such as the Great Lakes, there has been a switch from a predominance of ’point source’ nutrient inputs from pipes (e.g. wastewater) to diffuse inputs, from shoreline runoff, fields, agriculture and so on. Watersheds are made up of many areas, each contributing to the nutrient inputs to our surface waters making it difficult to identify these sources and understand their relative impacts. In the past, where most inputs were from point sources, it wasn’t so difficult to address these, once the problem had been recognized. Diffuse inputs require more detective work before an effective management plan can be developed.”
“Alberta and other prairie lakes may be more vulnerable to phosphorus inputs and more likely to proliferate blooms than other water bodies in different areas, due to their naturally rich basin. However in any region, the development of the watersheds into agriculturally intense areas and proliferation of cottages with multiple septic systems and fertilized lawns - as well as the clearing of trees and natural vegetation, the draining of wetlands - hasn’t helped.”
Watson continues, “It is also really important to point out that, as individuals, we all contribute to this problem. For example, we contribute to the impact that agriculture has on the bodies of water through the choices that we make in the grocery store. By buying cheap, mass-produced food we’re supporting large-scale agricultural organizations that often may not have that same stewardship approach to the land that a family-run, long-term operation does. Small family-owned farms need to pass land from one generation to the next and thus have a vested interest in maintaining the health of the soil through appropriate tilling practices, crop rotation, fertilizer applications and so on. Large farming industries don’t have that vested interest in the soil; soil horizons are becoming depleted of their organic material, and irrigation is wicking up the salt from the underlying seabed in some of the prairie areas - and the soil is becoming more saline. This can be addressed with best-management practices and from the public’s perspective, by the purchases made in the grocery store.”
The National Oceanic and Atmospheric Administration (NOAA), releases Harmful Algal Blooms (HABs) forecasts, to estimate and predict the severity of blooms for a particular region in the upcoming season.
The Harmful Algal Bloom forecasts alert coastal managers to blooms before they cause serious damage. Short-term - meaning once or twice weekly - forecasts identify which blooms are potentially harmful, how big they are, where they are as well as where they’re likely headed. Longer-term, seasonal forecasts predict the severity of HABs for the bloom season in a particular region.
The National Centers for Coastal Ocean Science (NCCOS) scientists and their partners have completed technical preparations for the first deployment of an Environmental Sample Processor (ESP) in the Great Lakes. The ESP is an autonomous, underwater robot that can detect harmful algal bloom cells and toxins in water samples that it collects and analyzes. The ESP is already in use on the U.S. East and West Coasts.
According to NCCOS, “The month-long deployment of the instrument - planned for this fall near the Toledo, Ohio, water intake - will generate near - real time measurements of microcystins, a class of freshwater cyanobacterial toxins that threaten drinking and recreational water supplies. The toxin sensor was developed by NCCOS in collaboration with NOAA’s Great Lakes Environmental Research Laboratory (GLERL) and the University of Michigan’s Cooperative Institute for Limnology and Ecosystems Research.”
BLUE-GREEN ALGAE: They adapt, multiply and can be deadly
BLUE-GREEN ALGAE: How they thrive in our overfed, invaded and warming lakes
Toledo after the slime - The crisis, the causes, the roadblocks to a fix
400,000 TOLD NOT TO DRINK OR BOIL TOLEDO WATER, OH - Today Dailies 8/2/14
Experts comment on Toledo - 8/3/14
Blue-Green Advisory Map - Canada