Contributed by Troy Glover
The idea of a source to sea of the Vaal River in South Africa came from our expedition leader Franz Fuls after witnessing the gradual deterioration of its water quality over past years. There are really two central concerns with respect to water quality on the Vaal; Eutrophication and heavy metals. Using Lake Erie in Canada as a case study, this post will discuss the former and a subsequent post the latter.
Eutrophication is most simply defined as an excessive richness of nutrients in any water body. More specifically, it is characterized by rapid plant growth as a result of an overabundance of one or more of the limiting resources required for photosynthesis; sunlight, carbon dioxide (CO2), and nutrients. More commonly, an unnatural loading of nutrients such as nitrates and phosphates from fertilizers and sewage runoff result in a massive imbalance of available nutrients. With both sunlight and carbon dioxide (CO2) in relative abundance, this results in explosive plant growth.
Eutrophication is most simply defined as an excessive richness of nutrients
So what’s the big deal? Firstly, nitrates and phosphates aren’t the only resources plants require for growth. Their growth pulls a significant quantity of other nutrients, minerals, and dissolved gases from the water which later exhausts the ecosystem of available resources. Once exhausted, the massive quantity of resulting plant growth dies and begins decomposing. In the process of decomposition, an immense quantity of oxygen is used leading to anoxia, described as a severe deficiency in oxygen. Without available oxygen, most aquatic species are unable to survive. The overall result can be called a dead zone, devoid of all signs of life.
As the backbone of any watershed, rivers are the prime carriers of eutrophic ingredients. Fed by tributary streams, rivers collect any source of water in a given catchment area. These catchments include farmland, sewage treatment ponds, etc. This water then begins its often long journey, following the lowest point of land until it eventually leads to a delta where it meets the sea. It is in these coastal waters that the effects of eutrophication are truly realized. This is where the highest levels of nutrient loading occur and where we most frequently see a dead zone.
Of course, eutrophic water bodies leading to dead zones have significant economic costs. Anoxia greatly affects the fisheries which many depend on as a food source. This is especially true along coastlines where rivers meet the sea. Along the way, however, reservoirs formed by dams can also become eutrophic and can lead to collapse. This is because of their warm slow-moving water and large catchment area. Reservoirs also tend to attract human settlement since water is in relative abundance. Anywhere there are people there is sewage effluent, further driving eutrophication.
There is perhaps no greater an example of how extreme eutrophication can become than Lake Erie
There is perhaps no greater an example of how extreme eutrophication can become than Lake Erie in the Canadian province of Ontario. Lake Erie is the 11th largest lake in the world by surface area and one of the Laurentian Great Lakes which collectively form the largest quantity of available freshwater in the world. 95% Of its water comes from the Detroit River after having flowed through the “Upper Lakes” (Superior, Michigan, and Huron). As a relatively shallow lake compared to the Upper Lakes, it is the warmest and most biologically productive. In other words, it is most susceptible to eutrophication.
Algae growth was so thick, one could not launch a boat from shore
Its susceptibility was proven in the 1950’s before eutrophication really became a widely known concept when large algal blooms began to form. By the 1960’s the 11th largest lake in the world was considered “dead”. Explosive algal growth led to the exhaustion of all available nutrients, competing with native aquatic species for oxygen. Algae growth was so thick, one could not launch a boat from shore without it becoming entangled in its propeller. You could even see the green algal mats from space.
So where did the nutrients come from for this to be possible? Lake Erie and the Detroit River which feeds it is surrounded by agriculturally fertile land, urban sprawl, industries, and resulting sewage treatment facilities. The largest culprit was phosphorus in a variety of forms from all of the above sources. At the time, it was found in nearly all fertilizers, detergents, and sewage. In 1972, Canada and the United States signed the Great Lakes Water Quality Agreement (GLWQA) in response to public concern and a recommendation made by the International Joint Commission for immediate action.
Successful international cooperation and strong public advocacy have led to a better understanding and concern for the effects of human activity on water quality.
Fortunately in this case, action led to results. Phosphorus in detergents was banned, use of nitrates and phosphates in fertilizers controlled, and sewage treatment improved. Within ten years, native aquatic species returned and eutrophication slowed. While intense urban sprawl and the use of chemical fertilizers continued, Lake Erie was no longer considered a dead zone and nutrient loads were kept below the maximum allowed in the GLWQA. Successful international cooperation and strong public advocacy led to a better understanding and concern for the effects of human activity on water quality.
“That we do not learn very much from the lessons of history is the most important of all the lessons of history.” –Aldous Huxley
This was all true until recently when it seems those monitoring Lake Erie nutrient loading forgot their lesson from history. In 2010, a number of Lake Erie tributaries showed record high phosphorus levels compared to all previous years studied. The number one source of phosphorus currently? By far, fertilizer use on farmland. The spring of 2010 brought heavy rainfall, washing an unusually high quantity of phosphorus into the lake. The use of phosphorus-based fertilizers has continued to show more negative effects than positive. They encourage the exhaustion of other limiting minerals and nutrients required for plant growth, requiring ever increasing amounts of artificial fertilizers. This process leads to eutrophication of our watersheds, and ultimately, to dead zones in our aquatic ecosystems.
While the Vaal River may be thousands of kilometers away from Lake Erie, they share a lot in common; mainly the basic principles of aquatic ecology. If an excess in nutrients is added to a system with little else to limit its growth, it will grow. Once it has exhausted those resources, it will crash. This crash will come with great consequences. Over one million South Africans directly depend on the Vaal River for their food and water. It is integral to South Africa’s sovereignty and water security. If eutrophication is let out of hand, one million people’s lives will change, likely with great affects to their quality of life.