Eutrophication and water quality in Lake Winnipeg

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 waters carry with them chemicals and nutrients dissolved in rocks and soils, which are transferred into the lake once the flowing waters come into contact with the lake waters (Shaw et al., 2004). 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).

i) Riparian Zones

Riparian zones are the lands adjacent or next to water reservoirs. They are recognized as crucial in the conservation of water sources because water quality is determined in part, by what people do on the land. The Manitoba Habitat Heritage Corporation recognizes the importance of riparian zones as buffer areas to protect the quality of water in Lake Winnipeg. The corporation works together with individual farmers to restore the health of riparian zones, educating farmers on strategies of how to rehabilitate their farmlands including carrying out effective irrigation, regenerating cover crops and so on. The aim of this strategy is to correct and eliminate negative human activities and farming practices in the areas surrounding the lake. If individual farmers at the grassroots can understand and play their own conservation efforts in the restoration of Lake Winnipeg, then the effects of negative human activities on the quality of water in Lake Winnipeg would have a lesser effect.

ii) Secondary and Tertiary Wastewater Treatment Options

Wastewater treatment is the process of making grey water from domestic households and the industrial sector suitable for reuse and release into natural aquatic systems (Malley, Ulrich & Watts, 2009). Conventionally, waste water treatment takes place in three stages -- the primary, secondary and tertiary stages. At the primary stage, solids are screened from the waste water and land-filled (Malley et al., 2009). The secondary treatment stage involves using bacteria to degrade the organic/biological content of sewage, which could cause oxygen depletion. Effluent resulting from the secondary level of treatment is significantly low in BOD and could be used in a number of ways including in the making of commercial fertilizer products (Malley et al., 2009). However, this effluent is usually significantly high in phosphorus, potassium, nitrogen and other nutrients present in the original wastewater (Malley et al., 2009). If applied on agricultural land, and washed away by irrigation water into a water reservoir, such effluent could cause eutrophication. Most municipal waste water treatment plans, however, release the same for use this way.

As part of its efforts to restore Lake Winnipeg, the city made it mandatory for wastewater treatment plans in the city to include tertiary treatment in its processes -- an advanced level of treatment where the effluent from the secondary stage is subjected to chemicals that remove nutrients and toxic compounds, particularly phosphorus before being released into the environment. The combination of secondary and tertiary treatment options ensures that effluent reaching the receiving waters contains acceptable levels of nutrients, particularly phosphorus (Malley et al., 2009).

iii) Alternative farming techniques

Commercially manufactured fertilizers contain varying amounts of potassium, nitrogen and phosphorus, which if leached into the soil could cause eutrophication in water sources. This strategy is focused on educating farmers on the use of alternative techniques of increasing their farmlands' productivity. These alternative farming techniques include crop rotation, where the crops planted on a particular piece of land are varied every season so that soils maintain their richness and are not easily blown away by heavy winds; use of organic fertilizers such as manure and so on.

iv) Urban wetland retention ponds

Retention ponds are designed to hold specific amounts of water; they are designed with an outlet leading to another location to which excess water flows when the level exceeds the required capacity (Moshiri, 1993). Such ponds help to regulate the velocity of storm water, and to consequently reduce its ability to wash away large quantities of soil into the lake (Moshiri, 2993).

v) Lake Level Alterations

As mentioned elsewhere in this text, Lake Winnipeg's small volume in relation to the size of the watershed makes it highly vulnerable to eutrophication. Sedimentation reduces the volume of a lake. One way, therefore, to increase the volume of the lake is by removing the sediments settled on the floor of the lake. This could be done through dredging -- it increases the capacity of the lake and makes it less prone to eutrophication.

Question 7: Why are cyanobacteria a key issue in Lake Winnipeg water quality management? What problems are associated with the growth of cyanobacteria?

The Lake Winnipeg watershed offers popular grounds for tourism and recreation -- it is estimated, for instance, that tourism expenditures around the lake generate approximately $100 million in revenues every year (The Lake Winnipeg Implementation Committee, 2005). Boating and camping are popular activities among tourists and visitors to the beach (The Lake Winnipeg Implementation Committee, 2005). The lake also offers attractive prospects for fishing, generating annual returns of $98 million between 1998 and 2003 alone (The Lake Winnipeg Implementation Committee, 2005). The lake is currently the largest freshwater commercial fishery in the country west of the Great Lakes (The Lake Winnipeg Implementation Committee, 2005). Cyanobacteria, however, threaten the lake's attractiveness as a tourism spot and also as a commercial fishery center. This is particularly because these bacteria pose serious health concerns for humans, livestock, wildlife and pets alike (California Department of Public Health, 2015). The possible health effects that could result from one's exposure to cyanobacteria include rashes, gastrointestinal effects, allergic reactions, tumor growth, neurotoxicity, and liver toxicity (California Department of Public Health, 2015). Such exposure could occur through inhalation, dermal contact, ingestion or when cattle drink water from the lake (California Department of Public Health, 2015).

Apart from this, cyanobacteria are a threat to aquatic life -- their decomposition depletes oxygen levels in water sources, threatening the survival of fish and other aquatic organisms.

Question 8: Describe ten changes you can commit to making that will reduce eutrophication in Lake Winnipeg

Individuals can have an impact on the state of Lake Winnipeg by modifying and being aware of their consumption patterns and daily choices. I commit to making a difference on my own front by:

i) Using non-phosphate detergents when doing laundry -- phosphorus has been shown to be a crucial contributor to eutrophication. Using non-phosphorus detergents could help reduce the amount of phosphorus released into the soil on a daily basis.

ii) Composting organic waste material produced at home -- this helps to return phosphorus present in organic food to the food production system rather than having it washed away directly to the lake

iii) Engage more actively in tree planting exercises to minimize the risk of soil being carried away into the lake

iv) Motor-boating -- avoid excess cruising on jet skis and motor boats on the lake to reduce nitrous oxide emissions

v) Bonfires -- avoiding the lighting of bonfires very close to the lake water to minimize the risk of wood substances being blown into the water and forming sediments

vi) Agriculture -- minimizing the use of commercial fertilizers in farming, and replacing the same with organic manure or alternative farming techniques such as crop rotation and fallow farming

vii) Domestic waste water treatment -- upgrading my domestic waste water systems to the secondary and tertiary levels

viii) Ensuring that nutrients in organic manure are recycled to agricultural land in a manner that is agronomically sound

ix) Continuing to expand personal knowledge of the dynamics of phosphorus on landscapes and in soil

x) Educating those close to me and around me on the importance of water conservation, and the role that they could play in their individual capacity to help restore Lake Winnipeg