John M. Gunn

Effects of emission reductions from the Sudbury smelters on the recovery of acid- and metal-damaged lakes

Aquatic ecosystems in a 17,000 km2 area around Sudbury, Ontario, Canada, have been affected by the atmospheric deposition of pollutants from nearly a century of operations at the Sudbury area metal smelters. Effects were most severe in the lakes closest to the smelters which historically received very high deposition of both acid and metal particulates. After smelter emissions were greatly reduced in the 1970‘s, evidence began to emerge of improvements in lake water quality, and some recovery of biological communities, and the emphasis of Sudbury area monitoring programs changed from the assessment of damage to the tracking of recovery patterns. Further reductions in smelter emissions during the1990‘s have been accompanied by continuing improvements in aquatic habitat quality, but the evaluation of lake responses to emission controls is complicated by the interaction of lake acidity and metal concentrations with other factors. Weather-related variations in storage and release of sulphur from lake catchments appear to greatly influence chemical recovery. Despite the general water quality improvements observed to date, some lakes are still highly acidic and elevated levels of copper and nickel persist in the water and sediments of many lakes. Severely damaged biological communities have been slow to recover, probably reflecting a combination of continuing habitat quality limitations and restricted opportunities for dispersal.

Evidence of biological recovery in acid-stressed lakes near Sudbury, Canada

Reductions in the emissions of SO2 and trace metals from the Sudbury smelters have resulted in substantial improvements in water quality in many surrounding lakes. Significant biological changes have accompanied the chemical improvements. Evidence of relatively rapid recovery was found for benthic filamentous algae, phytoplankton, zooplankton, mobile species of benthic invertebrates, and some fish populations. Organisms with low dispersal ability (e.g. Hyalella azteca) have not yet recolonized these lakes. The partial recovery observed to date shows movement toward re-establishment of biological communities typical of natural Precambrian Shield lakes in this area. These findings offer strong support for further efforts to reduce industrial emissions of pollutants to the atmosphere.

Use of Water Clarity to Monitor the Effects of Climate Change and other Stressors on Oligotrophic Lakes

We present evidence from studies oflakes in Killarney Park, Ontario, Canada that waterclarity is a key variable for monitoring theeffects of climate change, high UV exposure andacidification. In small oligotrophic lakes, thesestressors affect water clarity primarily byaltering the concentration of DOC in lake water. Clear lakes (<2 mg L-1 DOC) proved to be highlysensitive indicators of stressors, exhibiting largethermal and optical responses to small changes inDOC. Extremely clear (<0.5 mg L-1 DOC) acidic lakesshowed the effects of climate change and solarbleaching in recent decades. These lakes becamemuch clearer even though they were slowlyrecovering from acidification.

Acid rain - perspectives on lake recovery

During the 1970‘s and 1980‘s, the acidification of surface waters by atmospherically deposited sulphur became a major international concern. Large sulphur emission control programs were implemented in Europe and North America with the expectation that many affected aquatic ecosystems would recover. Because of a variety of factors, these positive expectations have been slow to be realized. Only limited evidence of the chemical recovery of acid lakes has emerged from areas other than the Sudbury, Canada region, where sulphur emission reductions were particularly large. Lake response models indicate that when current sulphur emission control strategies in Europe and North America are fully implemented, many lakes will still be acid-damaged even though substantial overall improvements in lake chemistry are expected. An increasing body of evidence indicates that substantial biological recovery, among many groups of organisms,can be expected when chemical conditions improve in lakes. Not all species, however, are capable of unassisted recovery and some lakes can pose biological or physical barriers to colonizers. Thus, stocking may be an important element in management strategies for the restoration of some recovering lakes. Communities in recovered lakes may not achieve pre disturbance conditions, but establishment of typical communities appears to be a reasonable recovery target.

Spawning Behavior of Lake Trout: Effects on Colonization Ability

Available information on spawning behavior of lake trout (Salvelinus namaycush) is reviewed to assess factors that affect colonization by this species. Selection of coarse clean substrate appears to be of primary importance for successful reproduction. Spawning sites are expected to occur in areas of high currents or wave energy with low paniculate accumulation rates. In most lakes, such sites are usually shallow areas along windswept shores. A variety of behavioral stimuli and cues (e.g., chemosensory cues, memory of site, kin recognition) also have the potential of influencing spawning site selection and may ultimately contribute to sympatric stock separation. Overall, the species appears to be rather adaptable and able to colonize new environments that satisfy basic habitat requirements. Behavioral abnormalities do not appear to be responsible for difficulties in reestablishing reproducing populations of lake trout in the lower Great Lakes.

Effects of Regional Reductions in Sulphur Deposition on the Chemical and Biological Recovery of Lakes within Killarney Park, Ontario, Canada

The lakes in KillarneyProvincial Park, located 40–60 km southwest ofSudbury, Ontario, were some of the first lakesin North America to be acidified by atmosphericpollutants. Acidification affected thousandsof fish and invertebrate populations in dozensof lakes. Since the 1970s, water quality hasimproved in response to atmospheric pollutionreductions and some lakes have alreadyrecovered to approximately their pre-industrialpH levels, as inferred from diatom microfossilsin lake sediments. Since the 1970s, fishspecies richness has not changed substantially,but zooplankton species richness has increasedin acidified lakes. The critical sulphur load,the amount of SO2-derived acid depositionthat can occur while still maintaining suitable water quality, was estimated to beexceeded in 38% of the park area in 1997. Depending on which of four possible NorthAmerican emission control scenarios (CLR =currently legislated reduction; CLR + 25%; CLR+ 50%; CLR + 75%) is achieved by 2010, theprojected critical loads will be exceeded inabout 0-30% of the park area in the future. There are many factors that can affectbiological recovery rates of damaged lakes, butit is expected that biological recovery willlag considerably behind observed chemicalrecovery rates.

Survival and Growth of Stocked Lake Trout in Relation to Body Size, Stocking Season, Lake Acidity, and Biomass of Competitors

Abstract Juvenile, hatchery-reared lake trout Salvelinus namaycush, 25–36 months old, were stocked (about 24 fish/hectare) in six small oligotrophic lakes to test the effects of fish size, stocking season, and lake water acidity on survival and growth of introduced fish. The test lakes had few, if any, native lake trout. Little or no survival of stocked lake trout occurred in lakes with pH 5.0 or less. High survival and growth occurred in intermediately acidic (pH 5.6–6.1) and circumneutral (pH 6.9–7.3) lakes. Survival of stocked lake trout increased with size at the time of stocking. Size differences of the three size-classes introduced in each lake were maintained throughout the 2-year study. Competition with other resident fish species appeared to influence stocking success strongly. There was an inverse relationship between the biomass of stocked lake trout subsequently recaptured and biomass of all hypolimnefic species present in the lake. Intraspecific competition with previously stocked lake trout ...

Mortality of Walleye Eggs and Rainbow Trout Yolk-Sac Larvae in Low-pH Waters of the LaCloche Mountain Area, Ontario

Abstract Freshly fertilized eggs of walleye Stizostedion vitreum were incubated in the outlet waters of George Lake (pH 5.4) and sections of a nearby stream (pH 6.0, 6.6). Ten-day bioassays with yolk-sac larvae of rainbow trout Salmo gairdneri were run concurrently at the walleye sites and at additional sites with low pH (4.6) and with humic water (pH 5.5). Walleye egg mortality was low (25.5–33.5%) at pH 6.0. High mortality (90.5%) occurred between fertilization and the eyed-egg stage at the pH 5.4 site. Mortality of rainbow trout yolk-sac larvae approached 100% within 5 days at both pH 4.6 and 5.4. In contrast, total mortality was less than 3% at pH 6.0 and also in low-pH humic water (pH 5.5). The high mortality of walleye eggs in the acidic outlet waters of George Lake suggests that the acidification of this lake was responsible for the extinction of its walleye stock. The striking differences in mortality of rainbow trout yolk-sac larvae between sites of similar pH (5.4–5.5) indicated that H+-toxicity...

Northern Lakes Recovery Study (NLRS) — Biomonitoring at the Ecosystem Level

NLRS is a joint Canadian/Norwegian study of the pace and extent of recovery of lake ecosystems from acidification. Twenty-one oligotrophic lakes within Killarney Park, Ontario were selected as the principal Canadian sites for this study. NLRS objectives for Killarney included: testing of new biomonitoring techniques, assessment of multiple stressor effects on recovery, and development of biological endpoints for critical load modelling. Sampling included: phytobenthos, phytoplankton, pelagic zooplankton, littoral zooplankton, sublittoral chironomids, and fish, as well as sediment cores for paleolimnological assessment of pre-industrial biotic communities. Strong statistical models were developed relating biotic composition to water quality variables. Prediction of future recovery will require additional understanding of the effects of differential colonization rates, climate variability, and the impact of unique events such as the arrival of an exotic species. Recovery proved to be best measured against modern reference data from circumneutral lakes rather than against historic data from acidified systems.

The Behavioral Response of Lake Trout to a Loss of Traditional Spawning Sites

We experimentally tested the behavioral response of native lake trout (Salvelinus namaycush) to the loss of spawning habitat in a 67 ha lake. In the first year, two of the historically utilized spawning sites (15 % of the historic spawning habitat) were covered to prevent spawning fish from using the sites. Lake trout responded by selecting 12 new sites around the lake. In the second year, when an additional 35 % of the historic spawning habitat was removed, the density of eggs deposited at the remaining traditional site increased and 8 more new sites were selected. These manipulations produced no detectable change in the timing of spawning and fish appeared to rapidly abandon efforts to use the former sites. This study demonstrates that lake trout will actively seek out alternate spawning sites when traditional habitat is lost. Initial indications are that useable spawning habitat is not limited in Whitepine Lake, but the long-term effects of the selection of alternative sites are not yet known.