Water Quality and Lake Winnipeg Watershed Management Eutrophication is the process by which nutrients in natural waters increase, causing an overgrowth of algae. Lake Winnipeg is one lake that has been adversely affected by eutrophication. Using Lake Winnipeg as a case study, this text demonstrates the causes of eutrophication, the effects of the same on aquatic life, and ways of minimizing its overall effects.

What are the key differences in the physical, chemical and biological features observed in a comparison of oligoptrophic with eutrophic water bodies? Which condition is more desirable based on the concept of sustainability? Why?

Eutrophication is the process by which nutrients in natural waters increase, causing a subsequent increase in the growth of algae and higher plants. A water body starts from a natural state (the oligoptrophic stage) through a mesotrophic state, and finally reaches the eutrophic state with the further addition of nutrients. In the eutrophic state, the water quality is low and nutrient build-up is evident in both sediments and water. Euphoric water bodies are characterized by among other things, i) low dissolved oxygen concentrations in deeper waters, ii) high nutrient concentration levels, iii) decreasing light penetration, iv) high phosphorus concentrations, and iv) an algae population that is predominantly cyanobacteria. A comparison of the biological, chemical and physical features of eutrophic and oligoptrophic waters is presented in the table below.

Features

Oligoptrophic

Eutrophic

Physical/Chemical Features

Depth

Deep

Shallow

Sediment levels

Low

High

Sediment nutrient concentrations

Low

High

Water column nutrient concentrations

Low

High

Dissolved oxygen levels at the bottom

High

Low

Biological Features

Primary productivity

Low

High

Species diversity

High

Low

Dominant phytoplankton

Diatoms/green algae

Cyanobacteria

Phytoplankton diversity

High

Low

Bloom frequency

Rare

Common

(Source: Shaw, Moore & Garnett, 2004, n.pag)

Oligotrophism is more desirable for sustainability. Here is why: the algae that bloom as a consequence of eutrophication die as they begin to compete among themselves for available nutrients. These dying algal are oxidized by anaerobic bacteria, which deplete oxygen supplies in the water, causing the death of fish and other forms of useful aquatic life (Shaw et al., 2004). Moreover, the increase of anaerobic bacteria in water as a result of eutrophication results in an increase in gases such as methane and hydrogen sulfide, which reduce the quality of water (Shaw et al., 2004).

Question 2: Describe five natural and five human generated point and non-point sources of pollution that lead to eutrophication of water bodies. Of these, which do you believe is the most difficult to regulate?

Eutrophication occurs when pollutant nutrients enter waterways from either diffuse sources or point source discharges (Shaw et al., 2004). This can be as a result of natural occurrences or human activities. One core human source of pollution is industrial effluents -- effluents released by factories into water sources could contain chemicals such as phosphorus, which contaminate the water, promoting the growth of algae. Besides industrial activities, there are also farming/agricultural activities such as irrigation -- irrigation drains carry excess water from farms and plantations, and this water sometimes contains phosphorus, which if released into waterways, could promote algae growth (Shaw et al., 2004). Diaries are another major source of pollution -- the chemicals used in the processing of milk and milk products could contaminate water sources if no effective regulations exist to regulate such release. Feedlots and piggeries are also point sources of pollution -- chemicals used in the fattening of domestic animals could be harmful to water sources if released to the same for prolonged periods. The final source of pollution is sewage treatment plants - waste water treatment plants often carry out the primary and secondary levels of treatment, leaving out the tertiary phase, which is responsible for the elimination of nutrients such as nitrogen and phosphorus. The effluent released from the secondary stage (which contains large amounts of these nutrients) is often used to manufacture commercial fertilizers, which if used on farmlands and washed away into water sources could cause contamination (Malley, Ulrich & Watts, 2009).

A number of natural occurrences could also contribute to the eutrophication process. First, waterways such as lakes are fed by rivers and streams that percolate through organic matter, soils, and rocks (Shaw et al., 2004). These...

A second natural source of pollution is the convention process -- the process by which surface water in lakes or reservoirs mixes with phosphorus-enriched water from deeper layers as a result of temperature changes. The third source is the collapse of stream banks as a result of earthquakes, water saturation or tectonic failure -- when a stream or river bank collapses, it adds fine sediments into the water source. Repeated collapses could cause downstream sediments, which reduce the velocity of flow and affect the river's ability to carry away pollutants. As a result, these pollutants accumulate, promoting algae growth. The fourth source of pollution in this regard is the natural release of nutrients by bottom sediments into the water system. Finally, there is the atmospheric fall-out process -- the process by which airborne particles ejected into the atmosphere as a result of volcanic eruptions, explosions, tornadoes and so on settle back to the ground. If these particles settle inside water reservoirs, they accumulate to form sediments, which contribute to the eutrophication process in the same way as collapsed stream banks.
Of the two groups of sources, natural sources are the most difficult to regulate. The simple reason is that these events occur naturally, and no one can accurately predict when they are likely to occur.

Question 3: Describe the relationship between eutrophication and biological diversity based on the key features of:

i) Water chemistry involving the N/P ratio, biochemical oxygen demand and dissolved oxygen

Nitrogen and phosphorus occur naturally in aquatic systems - when the N/P ratio is favorable, algae grow at a favorable rate. The eutrophication process, however, causes an increase in the levels of nitrogen and phosphorus available in water sources; as a result, the N/P ratio is tampered with and algae multiply at a faster rate than the ecosystem can handle. These algae oxygenate the water as nutrients are assimilated. However, the oxygen produced during the assimilation process is consumed as the macrophytes die and algae senesce. The large numbers of dying algae are oxidized by anaerobic bacteria as they decompose in a process referred to as the biochemical oxygen demand (BOD) (Shaw et al., 2004). The oxidization process consumes large amounts of dissolved oxygen, depleting oxygen levels in the water and making biological life less likely to thrive. As such, the biological diversity levels in eutrophic water sources remain significantly low (Shaw et al., 2004).

ii) Species richness, evenness and dominance

The eutrophication process disrupts the N/P balance, increasing the levels of nitrogen and phosphorus, but not silica (Shaw et al., 2004). Silica is responsible for richness in aquatic species; since the same exists in low levels in eutrophic sources, the species therein are significantly low in richness. Moreover, the low silica levels and high N-P levels cause dominance by cyanobacteria, and not chrysophytes or diatoms as is the case in oligoptrophic systems (Shaw et al., 2004). The species in eutrophic waters are unevenly distributed, with most occurring in the surface waters, where oxygen levels are higher (Shaw et al., 2004).

iii) Food web responses in producers, consumers and decomposers

In the early phases, the eutrophication process causes an increase in the abundance of primary producers in the ecosystem as a result of the increasing nitrogen and phosphorus levels. Moreover, there is an increase in the number of consumers such as fish owing to the increase in food resources. The abundant food resources increase the reproductive ability of consumers, causing them to increase in number. At this point, the high oxygen levels in the ecosystem inhibit the growth of anaerobic bacteria (decomposers), causing them to occur in significantly low numbers. As the eutrophication process progresses, however, the primary producers overgrow and begin to compete among themselves for available nutrients and carbon dioxide. As the level of competition increases, they begin to die in large numbers, causing a decrease in the levels of oxygen in the ecosystem. The consumers also begin to compete for the low levels of oxygen available and they eventually decrease in number. The low oxygen levels, however, favor the growth of anaerobic bacteria, which then increase in number. Thus the decomposers display bottom-top responses as a result of the eutrophication process whereas the consumers and primary producers display top-bottom responses.

Part Two

Question 4: Describe in detail the key features of the Lake Winnipeg watershed that make this lake particularly vulnerable to eutrophication

Two fundamental features of Lake Winnipeg's watershed make the lake particularly vulnerable to eutrophication. First, the Lake Winnipeg watershed is around forty times the lake's surface area (Zubrycki et al., 2015). This, according to the International Institute for Sustainable Development, represents the largest drainage-surface area ratio in the world and makes the lake highly vulnerable to accumulating large amounts of nutrients and pollutants (Zubrycki et al., 2015). The second feature that makes Lake Winnipeg particularly vulnerable to eutrophication is its volume relative to the size of its watershed (the volume-basin…