Year of Publication: 1996
Abstract:
The aim of this report was to address the Northern River Basins Study (NRBS) question: “Are the substances added to the rivers by natural and manmade discharges likely to cause deterioration of the water quality?” In this report, the word “substances” was taken to mean nutrients or, more specifically, nitrogen and phosphorus. Other NRBS reports have addressed the impact of effluent loading from the perspective of contaminants. This report synthesizes results from research and monitoring studies undertaken as part of the NRBS to characterize nutrient loading from all point and diffuse sources in the Northern River basins, evaluate the impacts of nutrient loading on river chemistry, assess the response of riverine biota to nutrient loading from pulp mill and municipal effluents in situ, quantify nutrient responses of benthic biota, and investigate interactions between nutrients and contaminants in pulp mill effluent on food webs. These findings are used to assess the state of aquatic ecosystem health, and develop scientific and management recommendations for the Northern River basins.
During fall, winter and spring, elevated nitrogen and phosphorus concentrations were observed on the Athabasca River downstream of Jasper, Hinton, Whitecourt and Fort McMurray and on the Wapiti River downstream of Grande Prairie. In the Athabasca River, 20% of all TP samples and 2% of all TN samples exceeded the Alberta Surface Water Quality Objective of 0.05 mg/L TP as P and 1.0 mg/L TN as N. Most of these exceedances occurred during summer and were likely due to high particulate concentrations. In the Wapiti River, 74% of TP samples and 19% of TN samples collected near the mouth exceeded the Alberta Surface Water Quality Objectives compared with exceedances of only 12% for TP and 0% for TN upstream of Grande Prairie. This suggests that nutrients from the City of Grande Prairie and Weyerhaeuser of Canada Ltd. effluents contribute to non-compliance. Annually, continuously-discharging industrial and municipal sources contribute 4 to 10% of the TN load and 6 to 16% of the TP load in the Athabasca River, with the contribution being higher during winter. Likewise, continuously- discharging industrial and municipal sources contribute 20% of the TN and 22% of the TP load in the Wapiti River annually. For the Peace River mainstem there is no evidence of nutrient impacts and the same is likely, true for the Slave River, although there are only limited nutrient data for this river.
Elevated nutrient concentrations in the Athabasca and Wapiti rivers have increased periphyton biomass and benthic invertebrate densities and, for the Athabasca River downstream of Hinton, increased the length and body weight of spoonhead sculpin (Cottus ricei), a small insectivorous fish species. Enrichment studies conducted with nutrient diffusing substrata in fall 1994 showed that periphyton growth was nutrient saturated for at least 2.5-4 km downstream of Jasper, from downstream of Hinton to upstream of Whitecourt, for at least 3 km and possibly up to 48 km downstream of Fort McMurray, and for at least 2 km downstream of the Grande Prairie bleached kraft pulp mill. Phosphorus concentrations at sites immediately upstream of the outfalls to these nutrient-saturated reaches were usually < 2 g/L SRP in the Athabasca River and 4-6 g/L SRP in the Wapiti River. These concentrations are similar to the 2-5 g/L SRP that was determined to be the concentration above which the growth of individual cells and thin periphyton films in artificial streams are phosphorus saturated. Periphyton growth was nitrogen limited from downstream of the Alberta Newsprint Co. to the confluence of Lesser Slave River and in the Smoky River. The increase in periphyton biomass and benthic invertebrate densities downstream of effluent outfalls and, in the case of the benthic invertebrates, no loss of species suggests that the response to effluents is one of nutrient enrichment not toxicity. Studies conducted in artificial streams further showed that periphyton biomass and growth of several mayflies, stoneflies and caddisflies increased in response to nutrient or 1% effluent addition, with no significant difference between the two treatments. These results further verify that the response to the current level of effluent loading is one of nutrient enrichment. There is no evidence of adverse effects to the ecosystem (e.g., no benthic invertebrate species loss, no problems with dissolved oxygen levels that are directly caused by nutrient addition). While detailed investigations of spawning grounds and early rearing habitat for fish in the Northern Rivers were not undertaken, it does appear not that dissolved oxygen problems caused by nutrient addition are adversely affecting fish populations at present.
The concern with nutrient addition to the Athabasca and Wapiti rivers appears, at present, to be largely one of aesthetics as perceived by increased periphyton growth. Aesthetic criteria for the protection of water bodies are often site specific and developed in consensus with the users of the lake or river. In the absence of any detectable deleterious effects of nutrient loading on the Athabasca and Wapiti rivers, the users must determine whether the increase in periphyton growth downstream of outfalls is acceptable or unacceptable. Given our current state of knowledge, setting effluent permit limits for phosphorus to control periphyton biomass at a specific level is not possible since there is as yet no quantitative relationship between river phosphorus concentrations and periphyton biomass for a given site. For example, periphyton biomass 1 km downstream of Hinton was found to range from 25 to 242 mg chlo/m2 for October 1990, 1992, 1993 and 1994 despite relatively constant TP loads from Weldwood of Canada Ltd. and relatively constant river flows (111, 134, 97 and 118 m3/s for October 1990, 1992, 1993 and 1994, respectively). Yet despite the lack of site-specific quantitative relationships between periphyton biomass and phosphorus concentration, experiments and in situ observations undertaken by the NRBS and other agencies have clearly shown that phosphorus (and, in some locations, nitrogen) are controlling factors for periphyton abundance in the Athabasca, Wapiti and Smoky rivers.
Based on findings from studies reviewed in this synthesis report, the following key recommendations are proposed:
• regular monitoring and reporting of nutrients from sewage treatment plants. This should be a license requirement. In addition, provision is needed for ensuring compliance with sampling and analytical procedures for all licensed dischargers (industrial and municipal) and to ensure training of certified operators to measure (and record) flow rates and discharge volumes and for enforcement of reporting requirements. Standard reporting requirements for water quality parameters should be established and reporting proper data should be a license requirement.
