Third national assessment

5.0 Biological Monitoring Studies Investigating Observed Effects

Biological monitoring studies designed to assess and confirm effects are typically conducted in the “near-field” area, i.e., an area of higher effluent concentration located close to the effluent discharge point. When effects are confirmed and results of previous monitoring studies do not indicate the magnitude and geographic extent (M&E) of confirmed effects, mines are required to conduct biological monitoring in one or more additional sampling locations within the exposure area (MMER, Schedule 5, paragraph 19(1)(d)). The Metal Mining Technical Guidance for Environmental Effects Monitoring (Environment Canada 2012a) recommends that M&E studies be conducted in an area of low effluent concentration, near the downstream boundary of the effluent mixing zone known as the far-field.

Once the M&E of confirmed effects have been determined, mines are required to conduct an investigation of cause (IOC) study that includes field and laboratory studies designed to determine the causes of the effects. Results from completed M&E and IOC studies are summarized in the next two sections and mine-by-mine descriptions of study results are listed in Appendix H.

5.1 Magnitude and Geographic Extent Studies

Magnitude and geographic extent studies have been conducted by 29 mines (27 studies).^{Footnote 12} Thirteen mines assessed M&E during biological monitoring studies to assess effects (i.e., prior to confirmation of effects), and 15 mines conducted M&E studies after effects had been confirmed. One mine assessed the M&E of benthic and fish effects in separate phases (before and after confirmation of effects, respectively). An additional 11 mines with confirmed effects did not sample far-field areas to assess M&E due to confounding factors in the receiving environment or because M&E could be determined from existing information. Far-field areas sampled to assess the M&E of confirmed effects observed in the near-field areas were located between 0.2 and 60 kilometres downstream from mine effluent discharge points (Figure 13a&b).^{Footnote 13}

Of the 29 mines that sampled far-field areas to assess M&E, 86% (25/29) reported at least one effect in the far-field area that was the same as an effect confirmed in the near-field area. Twenty-five mines assessed the M&E of multiple confirmed effects, and 56% (14/25) of these mines reported multiple far-field effects that were the same as the effects confirmed in the near-field area. Far-field effects the same as those confirmed in near-field areas were observed more frequently for fish habitat than for fish. There was no relationship between occurrence of effects in the far-field area and distance from the mine effluent discharge point.

For fish populations specifically, the M&E of confirmed effects was assessed in far-field areas by 14 mines (Figure 13a). Ten of these mines (71%) observed at least one effect in far-field areas that was the same as the effect confirmed in the near-field area, with three of these mines observing multiple effects that were the same as those confirmed in the near-field area. Four mines did not observe the same confirmed near-field effects in the far-field area.

For fish habitat specifically, the M&E of confirmed effects were investigated by 28 mines (Figure 13b). Twenty of these mines (71%) observed at least one fish habitat effect in the far-field area that was the same as the effect confirmed in the near-field area, with 10 of these mines observing multiple effects that were the same as those confirmed in the near-field area. Eight mines did not observe the same confirmed near-field effects in the far-field area.

The number of fish effects confirmed in the near-field area that were assessed for M&E and the number of the same fish effects that were also observed in the far-field area is shown for each fish population indictor in Figure 14. Of the 51 near-field confirmed fish effects, 31% (16/51) were also observed in the far-field area. The fish effects that were observed the most in both near- and far-field areas were increased body condition, decreased growth, and decreased gonad weight (reproduction). Increased survival, decreased liver condition, and increased gonad weight (reproduction) were not observed in far-field areas. Sixty-nine percent (35/51) of the near-field confirmed fish effects were equal to or greater than the critical effect size (CES),^{Footnote 14} whereas 44% (7/16) of the far-field fish effects were equal to or greater than the CES.

Note: Effects are denoted as > when the indicator was larger in the exposure area relative to the reference area and denoted as < when the indicator was smaller in the exposure area relative to the reference area. 

The number of fish habitat effects confirmed in the near-field area that were assessed for magnitude and geographic extent, and the number of same effects that were also observed in the far-field area is shown for each fish habitat indicator in Figure 15. Of the 56 near-field confirmed fish habitat effects, 55% (31/56) were also observed in the far-field area. The fish habitat effect that was observed the most in both near- and far-field areas was an effect on the benthic invertebrate community structure (similarity index), followed by effects of increased density and decreased taxon richness. Twenty percent (1/5) of confirmed decreases in density were also observed in the far-field area and the single confirmed effect of increased richness was also observed in the far-field area. Effects confirmed in the near-field area on evenness were not observed in the far-field area. 

Ninety-three percent (52/56) of fish habitat effects confirmed in near-field areas were equal to or greater than the CES,^{Footnote 15} and 87% (27/31) of far-field effects were equal to or greater than the CES. Of the four near-field confirmed effects lower than the CES, three were also observed in the far-field area, but with a magnitude equal to or greater than the CES.

Note: Effects are denoted as > when the indicator was larger in the exposure area relative to the reference area and denoted as < when the indicator was smaller in the exposure area relative to the reference area.

Top of page

5.2 Investigation of Cause Studies

Before June 2014, 35 mines had undertaken investigation of cause (IOC) studies.^{Footnote 16} Twenty-six of these mines have completed their IOC studies, 18 in one three-year study period^{Footnote 17} and eight in two consecutive three-year study periods. Nine mines are conducting ongoing IOC studies, each having completed the first of two three-year study periods.

Twenty-six mines conducted IOC studies which included new data collected through investigative field and/or laboratory studies, and nine mines conducted IOC studies based on existing information. Mines that based their IOC studies on existing information were either conducting the first of two three-year study periods (5 mines), or were investigating effects for which existing data were considered sufficient to identify cause (4 mines).

The confirmed effects under investigation included:

• effects on both fish and fish habitat (18 mines)
  • multiple fish and fish habitat effects (14 mines)
  • multiple fish effects and a single fish habitat effect (4 mines)
• effects on fish alone (5 mines)
  • multiple fish effects (2 mines)
  • a single fish effect (3 mines)
• effects on fish habitat alone (12 mines)
  • multiple fish habitat effects (6 mines)
  • a single fish habitat effect (6 mines)

Effects can be described as inhibitory or stimulatory. When the indicator measured is larger in the exposure area than the reference area, the effect is considered stimulatory. An effect is considered inhibitory when the indicator measured is smaller in the exposure area than in the reference area. Of the 35 mines conducting IOC studies, 17 investigated predominantly inhibitory effects, seven investigated predominantly stimulatory effects and 11 investigated a mix of inhibitory and stimulatory effects.

Among the 26 mines with completed IOC studies, 77% (20/26) identified at least one cause that was related to current mine effluent; 14 of these mines identified multiple potential causes including causes related to and unrelated to current mine effluent. Two mines identified effluent substances as a cause, but did not indicate if current mine effluent was the source. Four mines identified causes related to factors other than mine effluent, such as natural differences in habitat between exposure and reference areas, or sources of effluent associated with historic mining activity and urban areas.

Primary and possible contributing causes related to current mine effluent that were identified in IOC study reports include major ions, metals in mine effluent and/or sediment, nitrogen compounds, sedimentation or total suspended solids (TSS), phosphorus, mine effluent in general, and selenium (Figure 16). 

Major ions in mine effluent identified by IOC studies as contributing to the cause of effects included chloride, sulphate, sodium, calcium, and potassium. Major ions were most frequently associated with stimulatory effects, with some studies suggesting they contribute to nutrient enrichment, but major ions were also reported to cause inhibitory effects. Inhibitory effects related to major ions were caused in one case by an increase in lake water total dissolved solids concentration, which reduced lake mixing and caused a depletion of dissolved oxygen at the bottom of the lake. In another case, chloride and salinity toxicity were implicated among other potential causes of inhibitory effects.

Metals identified as causes of effects included copper, nickel, cadmium, and zinc, though some studies did not identify individual metals. Selenium, a non-metal substance, was indicated as a cause along with other metals in one completed study and as a contaminant of concern in one ongoing study. Other metals and non-metal substances observed at elevated concentrations in the receiving environment^{Footnote 18} included aluminum, arsenic, chromium, cobalt, iron, lead, manganese, molybdenum, nickel, strontium, and uranium. 

One of the mines with completed IOC studies identified current mine effluent as the primary source of metals causing effects, and eight mines indicated that the sources of metals could include current mine effluent and/or sediment. Elevated metal concentrations in sediment could be caused by either current mine effluent discharges or historical mine activities (effluent discharges and tailings disposal occurring before MMER implementation or both). Metals were more frequently identified as the cause of inhibitory effects than stimulatory effects.

Nitrogen compounds, primarily ammonia and nitrate, were associated with both stimulatory and inhibitory effects. Several mines indicated that elevated ammonia and nitrate concentrations in mine effluent were related to the use of explosives in mining operations. Stimulatory effects were attributed mainly to nutrient enrichment, whereas some studies suggested that inhibitory effects could be related to nutrient enrichment or toxic effects of nitrogen compounds. Elevated phosphorus concentrations in mine effluent were identified as the primary cause of stimulatory effects by two mines; in both cases, the effects were attributed to nutrient enrichment.

Total suspended solids or sedimentation related to current mine effluent discharge were identified as primary or contributing causes by three mines, all of which had predominantly inhibitory effects. One of these mines indicated that benthic habitats were adversely affected by the deposition of mine-related solids, while the studies conducted by the other two mines suggested that TSS could be contributing to nutrient enrichment, despite the observation of inhibitory effects on fish habitat and fish indicators.

Potential causes identified for further investigation by the nine mines conducting ongoing IOC studies included metals in mine effluent and/or sediment (7), nitrogen compounds in mine effluent (4), non-mine-related factors (2), selenium in mine effluent (2) and major ions in mine effluent (1).^{Footnote 19}

Top of page

Top of page