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NRBS - HomeTable of Contents |
Northern River Basins Study Final Report
3.0 Major Findings
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Introduction Nutrient Point-Sources Nutrient Trends Effects of Nutrients on Aquatic Organisms Areas of Concern Relevant Documents |
| Related NRBS Question: | |
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| 5. | Are the substances added to the rivers by natural and man-made discharges likely to cause deterioration of the water quality? |
| Figures 3.7.1 | Sources of Nutrients in the Northern River Basins |
Nutrients are the substances that plants need to grow. Major plant nutrients include nitrogen, phosphorus and carbon. In river stretches where phosphorus and nitrogen are limited and other factors (e.g., light, temperature, current speed, etc.) permit growth, the concentrations of nitrogen and phosphorus largely determine the growth and abundance of plants and plant-eating aquatic organisms. The sum of all forms of phosphorus or nitrogen is expressed as total phosphorus (TP) or total nitrogen (TN). Only some of this total amount is available to plants. Bioavailable nutrients are chemical forms that can be used by plants to grow and reproduce, such as phosphate, ammonia, nitrate and nitrite. Nutrients that are not in bioavailable forms cannot stimulate plant growth.
Nitrogen and phosphorus arise from several natural and non-natural sources (Figure 3.7.1). When measuring nutrient loadings, it is useful to distinguish between point and non-point nutrient sources. Point sources are easy to measure and regulate because they are confined to a pipe, ditch, channel, tunnel, conduit or some other discrete method of conveyance. In the northern river basins, the more prominent point sources of nutrients include industrial discharges (e.g., pulp and paper effluent) and municipal sewage. Non-point sources are diffuse and difficult to measure. They include surface runoff from agricultural and forested areas, precipitation, dust, tributaries, groundwater and bottom sediments.
The effect of nutrient addition on aquatic communities (referred to as eutrophication) can be positive, negative or negligible depending upon factors such as the present nutrient status of the river and dilution of the added nutrients. Moderate eutrophication may lead to increased fish size and populations that may benefit anglers. The nutrient-poor headwaters of the Bow River, for example, can only support a limited number of fish. Downstream of Calgary, the Bow River supports a thriving sport fishery due to the influx of nutrient-rich sewage that enriches the food chain. In British Columbia, coastal streams are routinely fertilized to enhance salmon production.
Excessive nutrients can have undesirable effects on the ecosystem. In the absence of other growth-limiting factors, excessive nutrients lead to an overabundance of plant growth. When these plants die, they are decomposed by microorganisms that consume oxygen—the more dead plant matter, the more oxygen is consumed. Highly eutrophic systems can become too low in dissolved oxygen at certain times of year (e.g., during winter ice cover and late summer) to support oxygen-sensitive species of fish and other aquatic organisms. The large amounts of algae in eutrophic waters also impact recreational uses and drinking water quality.
On the other hand, nutrient additions may not enrich plant communities if environmental conditions are already too harsh for additional plant growth. Some stretches of northern rivers are too cold, too turbid or too fast flowing to allow for additional plant growth. In these cases, nutrients are flushed downstream or deposited in the sediments where they can promote changes in nutrient conditions of lakes, reservoirs and deltas.
Nutrients are difficult to regulate for several reasons. First, the relative amount of nutrients arising from uncontrollable natural sources (e.g., natural surface runoff) may be great enough that a reduction in municipal and industrial loadings will have no significant impact on water quality. Second, each river responds to nutrients in a different manner depending on its unique natural characteristics. A regulation that works well for one river reach may not apply to another. Third, the optimal level of nutrients depends upon the desired uses for that particular water body or stretch of river.
At the time this report was prepared, there were no numeric federal nutrient guidelines. A draft guideline is currently under review and will be included in the Canadian Water Quality Guidelines. In Alberta, nutrient guidelines fall under the Alberta Surface Water Quality Objectives which list total phosphorus (TP) at 0.05 "greater or equal to" mg/L phosphorus and total nitrogen (TN) at 1.0 "greater or equal to" mg/L nitrogen in surface waters. Alberta pulp and paper mills must perform nutrient monitoring as part of their licensing requirements but have no nutrient limits. Sewage treatment plants in the Study area have neither a monitoring requirement nor a limit for nutrients. However, upgrades or expansion of any sewage treatment plant with projected wastewater flows greater than 20,000 m3/day must include a plan to reduce total phosphorus concentrations in the effluent to below 1.0 mg/L phosphorus.
Information collected by the Northern River Basins Study aims to provide a knowledge base for making decisions regarding the optimal levels of nutrients in the river basins. These decisions require a basic understanding of the sources and effects of nutrients on the aquatic ecosystem. This Section focuses on the Athabasca and Wapiti / Smoky River systems. In comparison to the Peace and Slave Rivers, these two systems have relatively smaller annual flows and higher levels of development along their shores. As a result, the Athabasca and Wapiti / Smoky systems have less capacity to assimilate wastes.
| Figure 3.7.2 | Point Sources of Nutrients to the Athabasca and Wapiti / Smokey River Systems |
| Figure 3.7.3 | Relative Contribution of Nutrient Point Sources to the Athabasca, Wapiti and Smoky Rivers |
Figure 3.7.2 identifies the various municipalities and industries that continuously discharge nutrients into the Athabasca and Wapiti / Smoky Rivers. It also gives average daily loadings of both total phosphorus and total nitrogen.
Within the Athabasca River basin, there are five pulp and paper mills that contribute nutrients to the river or its tributaries. The total phosphorus and total nitrogen loads from all mills total 331 and 1,041 kg/day, respectively. There are also nine municipal sewage treatment plants that continuously discharge nutrients into the river or its tributaries (no discharge data were available for Fort Chipewyan or Barrhead). The pulp mill at Hinton treats both municipal and mill wastes, and releases them as combined effluent.
Generally speaking, pulp and paper mills release more nutrients than do municipalities. In comparison to non-point sources, both pulp mills and sewage treatment plants are higher in bioavailable phosphorus and nitrogen. This means that they have a greater ability to affect the ecosystem than their contribution to total phosphorus and total nitrogen loadings may suggest.
Of the two large oil sands operations in Fort McMurray, only one (Suncor Inc.) continuously discharges utility wastewater. The Suncor effluent has a relatively minor influence on nutrient levels in the Athabasca River. Other activities along the river include four active coal mines, 67 gas plants and 12 gravel-washing enterprises; all of which have little or no discharge to the river. There are also 40 towns and villages which drain their sewage lagoons in spring and / or fall into Athabasca River tributaries. Figure 3.7.3 shows the relative contribution from point sources at several sites on the Athabasca River.
The Wapiti / Smoky River system has fewer nutrient point sources. There is one pulp mill in the river system, located near Grande Prairie that discharges into the Wapiti River. In addition to the pulp mill, there are two municipalities with continuous discharge to the rivers Grande Prairie on the Wapiti River and Grande Cache on the Smoky River. Sewage from Grande Prairie is a relatively large source of both nitrogen and phosphorus to the river system. In addition to these two municipalities, 28 additional communities in the Wapiti / Smoky drainage basin discharge sewage lagoons once or twice yearly to the rivers or their tributaries. Figure 3.7.3 shows the relative contribution from point sources at several sites on the Wapiti / Smoky River system.
Athabasca River System
| Figure 3.7.4 | Annual Nutrient Trends in the Athabasca River (Median Values from 1980-1992) |
Along the Athabasca River, point sources contribute between 6 and 17 per cent of the total annual phosphorous load, the majority of which is attributable to pulp mill effluent. On an annual basis, the Jasper sewage treatment plant accounts for only 8 per cent of the river's total phosphorus load. However, during low flows, Jasper sewage can contribute up to 91 per cent of the total phosphorus load downstream of the town. Likewise, point sources contribute 74 per cent of the total phosphorus load at Hinton and 37 per cent at Old Fort during low flows.
A similar situation exists with regard to total nitrogen. Point sources contribute between 3 and 10 per cent of the annual loadings at various sites in the Athabasca River (Figure 3.7.3). Pulp mills contribute more nitrogen on an annual basis. Municipal loadings are usually less than 1 per cent of the total nitrogen load at any given point along the river, except downstream of Jasper where sewage accounts for an average of 9 per cent of the total nitrogen load on an annual basis. During low-flow periods, Jasper sewage contributes up to 38 per cent of the total nitrogen load.
The effect of point sources on nutrient patterns is evident by looking at concentrations within the river. Increased concentrations of total phosphorus occur downstream of Jasper, Hinton, Whitecourt and Fort McMurray (Figure 3.7.4). This trend is most pronounced during low flow periods in winter, spring (prior to runoff) and fall. The influence of point sources on total nitrogen patterns is not as clear as total phosphorus, but elevated nitrogen concentrations can still be observed downstream of Jasper and Hinton (Figure 3.7.4).
Occasionally, concentrations of both total phosphorus and total nitrogen have exceeded Alberta Surface Water Quality Objectives. Between 1980 and 1993, guidelines were exceeded in approximately 20 and 2 per cent of total phosphorus and total nitrogen samples, respectively. For the most part, however, these violations were due to particulate nutrients that are washed down the river during summer high flows when the current is strong enough to scour away material from the river bottom and the shoreline. Since only a small fraction of particulate nitrogen or phosphorus is likely bioavailable, it would not be expected to be a significant factor in encouraging plant growth.
Wapiti / Smoky River SystemLess information is available for the Wapiti / Smoky River system, although point sources affect nutrient patterns in this river system. At the mouth of the Wapiti River, municipal and industrial point sources contribute 23 per cent to the annual total phosphorus load, of which roughly half can be attributed to the Grande Prairie pulp mill (Figure 3.7.3). During low flows, point sources can contribute up to 42 per cent of the total phosphorus load to the Wapiti River.
With respect to total nitrogen, point sources account for 20 per cent of the total annual nitrogen load at the mouth of the Wapiti River, with only 5 per cent of the total annual load attributable to municipal sources. During low flows, the combined point sources can account for up to 35 per cent of the total nitrogen load.
The influence of point sources is once again evident in nutrient patterns. Concentrations of both total phosphorus and total nitrogen tend to increase past the sewage and pulp mill outfalls in Grande Prairie and then decline after the Wapiti River joins with the Smoky River. As with the Athabasca River, concentrations of total phosphorus and total nitrogen occasionally exceed Alberta Surface Water Quality Objectives. In the Wapiti / Smoky River system, however, this phenomenon may be attributed to point sources. Only 12 per cent of water samples exceeded total phosphorus objectives upstream of Grande Prairie compared to 74 per cent at the mouth of the Wapiti River. Similarly, none of the samples exceeded total nitrogen objectives upstream compared to 19 per cent downstream of the city.
As the previous sections demonstrate, point sources affect nutrient levels in reaches of the Athabasca and Wapiti / Smoky Rivers. At most sites, pulp mills contribute relatively more nutrients than municipalities. But are the added nutrients stimulating the growth of plants and organisms in the Athabasca and Wapiti / Smoky River systems?
NRBS studies showed that pulp mill effluent in the Athabasca and Wapiti / Smoky River systems, to varying degrees, increase the abundance of plants and the growth of benthic invertebrates and fish located downstream of the mills. Pulp mills also discharge contaminants that may limit growth, but these appear not to be present in high enough concentrations to limit the growth of plants or benthic invertebrate communities.
| Figure 3.7.5 | Nutrient-sensitive Areas in Athabasca, Wapiti and Smoky Rivers |
Due to the large nutrient inputs from both natural and man-made sources, many reaches of the Athabasca and Wapiti / Smoky River systems have excessive levels of nutrients during the fall, when flows (and consequently nutrient dilution) is lowest (Figure 3.7.5). While some of the phosphorus in these rivers originates from sewage treatment plants and pulp mills, natural sources may also be important. For example, the Clearwater River contributes a sizeable amount of nutrients to the Athabasca River downstream of Fort McMurray.
To minimize the impact of future development on the rivers, it is useful to know which reaches will still respond to additional nutrient loadings (i.e., growth is "nutrient-limited"). Most of the nutrient-limited sites are located upstream of pulp mills or sewage treatment plants where natural nutrient levels are low. Phosphorus is the limiting nutrient in most of these areas, while nitrogen limitation is more sporadic.
Figure 3.7.5 illustrates zones within the basins that will still respond to further nutrient additions. It should be noted that this is not a complete list—further research is needed to identify all of these zones. In the meantime, future developments could have impacts on the aquatic ecosystem in these river stretches. It is not yet known how much additional nutrients would be required to saturate these sites, but one experiment at Hinton revealed that only a small amount of phosphorus (5 µg/L) was required to saturate the growth of periphyton films (i.e., algal communities living on rocks or sediments at the bottom of a river or lake). Figure 3.7.5 also illustrates the zones of nutrient saturation. Further nutrient enrichment may have no substantial effect on the growth and abundance of aquatic organisms in these areas, but could have consequences for downstream regions in the delta or lakes.
On a positive note, current nutrient levels do not appear to cause the loss of any fish or other aquatic organisms. As such, the concern with increased plant and algal growth in these areas is presently an aesthetic issue related to the amount of green "slime" on rocks downstream of nutrient point sources. Whether these conditions constitute a need for change is a societal decision that must be based on the desired ecosystem attributes for these river stretches.
NRBS Synthesis Reports
Chambers, P.A. 1996. Nutrient Enrichment in the Peace, Athabasca and Slave Rivers: Assessment of Present Conditions and Future Trends. Northern River Basins Study Synthesis Report No. 4.
NRBS Technical ReportsCulp, J.M. and C.L. Podemski. 1996. Impacts of Contaminants and Nutrients in Bleached Kraft Mill Effluent on Benthic Insect and Periphyton Communities: Assessments Using Artificial Streams, Athabasca River, 1993 and 1994. Northern River Basins Study Technical Report No. 92.
Culp, J.M., Podemski, C.L. and C. Casey. 1996. Design and Application of a Transportable Experimental Stream System for Assessing Effluent Impacts on Riverine Biota. Northern River Basins Study Technical Report No. 128.
Chambers, P.A. and A.R. Dale. 1996. Contribution of Industrial, Municipal, Agricultural and Groundwater Sources to Water Quality in the Athabasca and Wapiti - Smoky Rivers. Northern River Basins Study Technical Report No. 110.
Dale, A.R. and P.A. Chambers. 1996. Growth Rate and Biomass Responses of Periphytic Algae to Phosphorus Enrichment in Experimental Flumes, Athabasca River, April and May 1994. Northern River Basins Study Technical Report No. 67.
Dale, A.R. and P.A. Chambers. 1996.Growth Rate and Biomass Responses of Periphytic Algae to Phosphorus Enrichment in Experimental Flumes Located on the Upper Athabasca River, Seasonal Variation, 1993 and 1994. Northern River Basins Study Technical Report No. 68.
Dunnigan, M. 1993. Aquatic Macroinvertebrate Identifications on Ekman Dredge Samples, Upper Athabasca River, April and May, 1992. Northern River Basins Study Technical Report No. 19.
Gibbons, W., Munkittrick, K. and W. Taylor. 1995. Suitability of Small Fish Species for Monitoring the Effects of Pulp Mill Effluent on Fish Populations, Athabasca River. Northern River Basins Study Technical Report No. 100.
Headley, J., Chambers, P.A., Culp, J. and K. Peru. 1995. Evaluation of Small Volume Techniques for Broad Spectrum Analysis of Biofilm Materials and Bleached Kraft Mill Effluents. Northern River Basins Study Technical Report No. 60.
Perrin, C.J., Chambers, P.A. and M.L. Bothwell. 1995. Growth Rate and Biomass Responses of Periphytic Algae to Nutrient Enrichment of Stable and Unstable Substrata, Athabasca River. Northern River Basins Study Technical Report No. 46.
R.L. & L. Environmental Services Ltd. 1993. Aquatic Macroinvertebrate Identifications, Upper Athabasca River, Spring 1992. Northern River Basins Study Technical Report No. 5.
Saunders, R.D. and E. Dratnal. 1994. Aquatic Macroinvertebrate Identifications on Under- Ice Samples, Athabasca River, February and March, 1993. Northern River Basins Study Technical Report No. 38.
Scrimgeour, G.J. and P.A. Chambers. 1996. Identification of Spatial and Temporal Patterns in Nutrient Limitation with Herbivory Effects, Wapiti, Smoky and Athabasca Rivers. Northern River Basins Study Technical Report No. 96.
Scrimgeour, G.J., Chambers, P.A., Culp, J.M. and C. Podemski. 1995. Identification of Spatial and Temporal Patterns in Nutrient Limitation, Athabasca River, October to December, 1993. Northern River Basins Study Technical Report No. 49.
Scrimgeour, G.J., Chambers, P.A., Culp, J.M., Cash, K.J. and M. Ouellette. 1995. Long-term Trends in Ecosystem Health: Quantitative Analysis of River Benthic Invertebrate Communities, Peace and Athabasca Rivers. Northern River Basins Study Technical Report No. 56.
Sentar Consultants Ltd. 1994. An Annotated Bibliography of Nutrient Loading on the Peace, Athabasca and Slave Rivers. Northern River Basins Study Technical Report No. 27.
Sentar Consultants Ltd. 1994. Regulatory Requirements for Nutrient Effluent Discharges. Northern River Basins Study Technical Report No. 39.
Sentar Consultants Ltd. 1994. Nutrient Loading on the Peace, Athabasca and Slave Rivers. Northern River Basins Study Technical Report No. 28.
Other Relevant DocumentsAlberta Environment. 1977. Alberta Surface Water Quality Objectives. Water Quality Branch, Standards and Approvals Division.
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