Nitrates can be both bad and good. First the good. For most agricultural production, the addition of nutrients is a required part of the process of growing plants. This applies to both crop growing and raising animals, as they must consume vegetation (hay, grains, etc.). For crops, the soil is a medium to grow the plant, but there also must be nutrients present to allow growth. Nitrogen in the form of nitrates is one of the key nutrients, along with phosphorous and potassium. Soil naturally contains organic matter including nitrogen compounds, which are converted by bacteria to nitrates. Even farmers in the past knew that adding nutrients resulted in increased yields and applying mussel mud as a soil amendment was a traditional winter activity. Because the nutrients were bound up in the shells, the fields could be fertilized less frequently than takes place now.
The problem is when nitrates become over abundant in the water, whether it is ground water, streams or estuaries. Nitrates are highly water soluble and if there are more nitrates available than can be used by the plants, the nitrates leach into the ground water. If drinking water has nitrate levels above 10 mg/L it can present health risks. Nitrates can interfere with the ability of red blood cells to carry oxygen and can result in Blue Baby Syndrome. The requirement for nitrates also applies to aquatic plants. The plants absorb nitrates from the water and because nitrates are often the limiting factors in the biomass produced, they can be critical to the health of aquatic ecosystems.
When nitrates enter the groundwater and then flow into streams, there becomes an abundance of nutrients. This can result in increased plant growth in ponds, but is especially a problem in estuaries. The plants, especially algae or fast growing plants like sea lettuce, proliferate quickly. When estuaries are a “Lime Rickey” green colour, this is the result of an abundance of algae. During the day these plants produce oxygen, but at night they consume oxygen, the resulting great shifts in oxygen make it difficult for aquatic wildlife to survive.
The sudden proliferation of plant material near the surface also blocks sunlight from reaching other plants further down in the water column. Because these plants can’t get sunlight, they die and in decomposing, use up oxygen. The lack of oxygen (anoxia or anaerobic conditions), results in the water turning white, and then all of the animal life that can’t quickly move out of the area dies from lack of oxygen, and a smell is produced. This is the situation found above Corran Ban Bridge.
The mussel and other shellfish growing industries generate significant income to the Tracadie Bay area and we would not want to see this industry negatively impacted as has happened in other estuaries.
The solution is to get better water circulation, which is why dredging took place at the Corran Ban Bridge, and to decrease the amount of nitrates entering the groundwater. We are working with farmers to minimize their nutrient use, but are also urging residential land owners to minimize the application of fertilizers to lawns. Non-functioning septic systems which allow material to flow directly into water courses or the estuary can also be a contributing factor.
Over the past year we have been working on a local nutrient management program. We have inventoried most of the fields in the watershed to determine crops being grown. With this information it will be possible to determine the approximate nitrate loading from agriculture.
To better analyze the concentration of nitrate in the water, we have monitored about 25 springs on a weekly or biweekly basis. A goal was to determine how much seasonal variability occurred in the water flowing from the springs. Initially attempts were made to do the analysis ourselves or by staff at Bedeque Bay Environmental Management Association but with the equipment available, the results were not accurate enough to give figures that would show seasonal or more frequent changes. Additional funding was secured to allow for analysis by the provincial lab which allowed for results which were about 10 times more accurate.
A major focus was to work with 10 farmers in the watershed on a more detailed review of farming practices. For potato farmers, the amount of nutrients being applied was collected. This included both organic potato growing as well as conventional growing. There were at least 8 different potato varieties being grown in our watershed. For the dairy farmers and one beef cattle farmer, the amount of nutrients being applied from synthetic fertilizers and manure was determined. For an apple farmer, the amount of nutrients being applied was collected. It should be noted that all of the information collected for individual farms is confidential and only data from types of farming will be released.
As part of the water collection, devices were installed to record flow from springs, and the main stem of the river, when the flow was low enough to allow the devices to operate. It is significant that near the wellfields, the flow in the main river was less than that of tributaries which flowed into the river further downstream. The reduction in spring flow, and in major tributaries a total elimination of spring flow, causes a lack of water, hence the streams dries up, but as well, in places with reduced water flow the temperatures are much higher. In order to monitor river temperatures, both to help analyze problems and to compare to past and future conditions, automatic temperature recorders were installed at five locations in the river. In the Brackley Branch there was no temperature recorded as the stream totally dried up.
Discussions were held with both the provincial government, which approves water extraction levels, and the City of Charlottetown to discuss opportunities to reduce the level of extraction from Winter River.
We have a printable document on this topic: Nitrate in the Environment