Donald K. McNicol

Fish predation, lake acidity and the composition of aquatic insect assemblages

Aquatic insect assemblages were sampled in 2 sets of 18 small lakes in 2 regions of northeastern Ontario. Both sets included lakes with and without fish. In the set near Sudbury, fishless lakes were acidic. Using a standardized sweep net procedure, fishless lakes in both areas were found to have a greater abundance and richness of insects than lakes with fish. Irrespective of pH, fishless lakes supported a similar aquatic insect assemblage which was characterized by an abundance of nekton, especially Notonectidae, Corixidae, Graphoderus liberus (Dytiscidae) and Chaoborus americanus (Chaoboridae). Those taxa were typically absent from lakes with fish, which often had a marked abundance of Gerridae. It is concluded that fish predation is the most immediate factor structuring such aquatic insect assemblages, and is responsible for their change coincident with lake acidification.

Lake acidity, fish predation, and the distribution and abundance of some littoral insects

Densities of Corixidae (Hemiptera), larval Odonata, and large larval Trichoptera were estimated in the littoral zone of small lakes in an acid-stressed area near Sudbury, Ontario. Fish were present in some lakes and absent in others, and fishless lakes occurred across a wide range of pH. Corixidae were significantly more abundant in lakes without fish than in lakes with fish, and their numbers were not related to the pH of fishless lakes. Anisoptera (Odonata) larvae tended to be more numerous in benthic samples from fishless lakes than from lakes with fish, and their exuviae were significantly more abundant around fishless lakes. In most lakes, the assemblage was dominated by three species; Leucorrhinia glacialis, Libellula julia, and Cordulia shurtleffi. In lakes containing white sucker, Catostomus commersoni, Gomphus spp. were most numerous. In the most acid fishless lakes, L. julia was uncommon, and L. glacialis was extremely abundant. In fishless lakes, numbers of Anisoptera larvae and exuviae were negatively correlated with pH, though species richness was positively correlated with pH. Exuviae of Zygoptera (Odonata) were more abundant around fishless lakes, irrespective of pH. Larvae of Limnephilus (Trichoptera) were most abundant in non-acid fishless lakes, and absent at pH<5.2. Abundances of Banksiola (Trichoptera) were negatively correlated with the pH of fishless lakes.

Presence or absence of fish as a cue to macroinvertebrate abundance in boreal wetlands

Waterfowl that eat macroinvertebrates must select among potential nesting or brood-rearing habitats that may vary in food abundance over the season. We compared the reliability of predicting the relative abundance of macroinvertebrates in boreal wetlands using either the number of macroinvertebrates collected at one sampling period, or presence or absence of fish. Wetlands with fish had fewer macroinvertebrates than fishless wetlands in all five sampling periods. Predictions of the relative abundance of invertebrates in a wetland at other sampling periods based on the presence or absence of fish, were equal to or better than predictions based on the actual number of macroinvertebrates collected during one sampling period. These results suggest that fish status of a wetland is a reliable cue to invertebrate abundance in boreal wetlands.

Evaluating macroinvertebrate responses to recovery from acidification in small lakes in Ontario, Canada

The biomonitoring program of Environment Canada examines food chains in small Ontario lakes to interpret ecological responses of waterfowl and their foods to changing acid deposition. Macroinvertebrates and fish were sampled in three acid-sensitive regions: Muskoka (1991; N=20), Algoma (1992; N=20), and Sudbury (1994; N=22). Small lakes (<11 ha; important breeding habitat for waterfowl) were chosen to cover the range of pH in each region, and include those with and without fish. In all regions, macroinvertebrate taxonomic richness (particularly nekton and benthos) was greater in fishless lakes compared to lakes with fish. Among fishless lakes, taxonomic richness (especially benthos) was positively correlated with pH, although regional differences were evident. Previous studies near Sudbury have shown that several benthic groups have distribution and abundance patterns with respect to pH (Trichoptera, Ephemeroptera, Hirudinea, Amphipoda, and Gastropoda). Those patterns continue near Sudbury, and were also strongly apparent in Algoma. In all regions, the number of acid-sensitive taxa per lake is related to pH, and should increase as lakes recover from acidification. However, predicting macroinvertebrate responses to recovery must consider concurrent effects of fish, as they are a dominant factor structuring these communities.

Using volunteers to monitor the effects of acid precipitation on Common Loon (Gavia immer) reproduction in Canada: The Canadian Lakes Loon Survey

The Common Loon (Gavia immer) is a conspicuous and popular aquatic bird that inhabits large lakes (generally >10 ha) on Precambrian Shield across Canada. Because it relies on fish, it is a key bioindicator species linking acid precipitation to higher trophic levels in aquatic food chains. The Canadian Lakes Loon Survey (CLLS), a monitoring program involving volunteers, was initiated in 1981 to collect information on loon reproductive success, such as the number of loons nesting and the number of young they produce which survive to fledging, to help researchers determine whether loons were adversely affected by acid rain or human disturbance. Between 1987 and 1993, 4236 records for loons nesting on 1529 lakes in Ontario (historically the principal region of study) were received from volunteers. We used logistic regression to examine relationships between loon productivity (number of large young produced per pair for 721 lakes), lake area, and pH (from provincial and federal databases). After controlling for lake size, we determined that loons were less likely to nest on acid lakes (pH<5.5), and when they did attempt to breed, their reproductive success was lower, in part due to the reduced survival of two-chick broods, presumably linked to reduced fish biomass. However, we found no conclusive evidence that breeding success exhibited any temporal trends in relation to pH over this time period. Continued monitoring by volunteers of loon reproduction on CLLS lakes will provide a reliable, costeffective method of assessing the long-term health of large, acid-sensitive lakes across Canada.

Risk-taking by incubating Common Goldeneyes and Hooded Mergansers

We studied nest defense by Common Goldeneyes (Bucephala clangula) and Hooded Mergansers (Lophodytes cucullatus) nesting near Sudbury, Canada between 1989-1995. As incubation proceeded, female Common Goldeneyes took greater risks by allowing the observer to approach the nest more closely before flushing, landing closer to the nest after flushing, vocalizing more commonly when flushed, and giving more broken wing or distraction displays. Hooded Merganser females exhibited relatively strong defense at all stages, including giving distraction displays much earlier in incubation. An index of all four behaviors increased for each species as incubation proceeded. Nest defense by these cavity-nesting ducks differed from patterns known for ground-nesting waterfowl, perhaps due to effects of nest location, predation type and intensity, and nest parasitism. Future nest defense studies should consider the overall suite of behaviors that comprise parental strategies for defending their nests and/or offspring.

Peatland water chemistry in Central Ontario in relation to acid deposition

Thirty-one peatlands from two areas of central Ontario were sampled to assess the influence of acid deposition on peatland water chemistry. Factor analysis differentiated peatland water chemistry along three major axes of chemical variation, interpreted as axes of organic concentration, mineral concentration, and deposition influence. Water from the surface mats had a higher organic concentration than water from open pools. Mineral influence in peatland waters was reflected by higher concentrations of Ca, Mg, Na, and silica in fen pools compared to bog pools. The influence of high acid deposition in the Wanapitei study area was indicated by high concentrations of sulphate, Ni, Mn, and Cu, and lower pH compared to an area that has received less acidic deposition (Ranger). Regression analyses indicated that H+ variation in bogs could be largely explained by organic C concentration, but that sulphate concentration was also positively associated with acidity, while Ca was negatively associated with acidity.

Recent Temporal Patterns in the Chemistry of Small, Acid-sensitive Lakes in Central Ontario, Canada

We monitored the chemistry of 603 small water bodies in three acid-sensitive regions of central Ontario, Canada (Algoma n=235, Muskoka n=216, Sudbury n=152) between 1988–1996 to determine whether they have responded to recent SO2 emission reductions, and whether any chemical changes were related to lake characteristics. During the study, 27–56% of lakes declined in SO 4 2− concentrations, 41–57% declined in base cation concentrations, but only 26–28% increased in pH or ANC (acidity status). Increases in pH were greatest in lakes with low ANC, but had weak relationships to lake color or volume. No consistent trends were observed for DOC, NO 3 − -N or TP concentrations. Clearly, the long-term biological recovery of these sensitive aquatic ecosystems will depend on interactions among several environmental stressors, including acidification.

Cyprinid assemblages, and the physical and chemical characteristics of small northern Ontario lakes

SynopsisThe cyprinid species, and physical and chemical characteristics were recorded from 58 small lakes in the Algoma district of northern Ontario. A group of typical stream-dwelling lithophilous species, which included common shiner, Notropis cornutus, creek chub, Semotilus atromaculatus, and blacknose dace, Rhinichthys atratulus, tended to occupy lakes of larger than average drainage areas. Phoxinus spp., pearl dace, Semotilus margarita, and fathead minnow, Pimephales promelas, occurred commonly in lakes with small drainage areas, and the average drainage area of lakes they occupied was near or below the overall average. Lakes without stream cyprinids were discriminated from lakes with them on a combination of chemical variables, including pH, alkalinity and calcium, which indicated that they were more susceptible to anthropogenic acidification.

Trends in small lake water chemistry near Sudbury, Canada, 1983–1991

While many studies have documented improvements in chemical conditions of large lakes near Sudbury, Canada in response to reduced smelter emissions, few have examined changes in water chemistry of small lakes. We studied trends in water chemistry of 97 small (<10 ha), shallow (<15 m) lakes northeast of Sudbury that are important habitat for breeding waterfowl. Currently, many small lakes near Sudbury are acidified, with little acid-neutralizing capacity and with relatively high concentrations of Al, Mn, and Ni. We also present evidence of short-term improvements in pH and SO4 levels, but demonstrate that, over a nine year period, there has been no consistent, long-term trend of chemical recovery. Chemical conditions in these lakes varied considerably between 1983 and 1991, and responded quickly to changes in precipitation levels. However, the present condition of most lakes suggests that further reductions in emissions will be required to improve these habitats for breeding waterfowl.