Whole-lake algal responses to a century of acidic industrial deposition on the Canadian Shield

A century of cultural acidification is hypothesized to have altered algal community structure in boreal lakes. To date, this hypothesis has remained untested because of both the lack of data predating the onset of industrial pollution and incomplete estimates of whole-lake algal community structure. High-pressure liquid chromatography (HPLC) of sedimentary pigments was used to quantify whole-lake algal responses to acid deposition in six boreal lakes located in Killarney Park, Ontario, Canada. Concomitant significant increases in chlorophyll and carotenoid concentrations, diatom-inferred lake acidity, and metal levels since 1900 suggested that algal abundances in four acidified lakes and one small, circumneutral lake were enhanced by aerial pollution. An alternate explanation is that increased acidity and underwater light availability in the acidified lakes shifted algal abundance towards phytobenthos and deepwater phytoplankton, whose pigment signatures were better preserved in the sediments. Taxonomically diagnostic pigment stratigraphies were consistent with shifts in algal community structure towards filamentous green phytobenthos and deepwater phytoflagellates in the acidified lakes. Our findings suggest that decades of aerial pollution have altered the base of foodwebs in boreal lakes, potentially rendering them less resilient to other environmental stressors.

A paleolimnological assessment of the effects of post-1970 reductions of sulfur deposition in Sweden

Analysis of diatoms in sediment cores from 10 acidic (pH < 6) lakes in southern Sweden shows that eight of the lakes have acidified after 1950, while two lakes have not significantly acidified. However, since the 1970s, sulfur deposition has decreased by 50%, and lake water chemistry monitored since 1983 shows an initial reversal of acidification. However, the diatom data do not indicate that a general recovery in pH has occurred yet. The diatoms show that a small recovery has occurred in only one lake (pH increase from 4.7 to 4.9). The 10 lakes vary in total organic carbon content from 2 to 17 mg·L–1. According to the diatoms, the lakes with high total organic carbon (>9 mg·L–1) have not acidified as much as the lakes with lower total organic carbon (<7 mg·L–1). We ascribe this difference in response to acid deposition to the buffering capacity of organic acids. Knowledge of the role of organic acids when combined with anthropogenic acid deposition is important in predicting responses to decreasing acid deposition and the time scales required for recovery. Paleolimnological methods are shown here to provide valuable information for these purposes as well as to provide a long-term perspective on lake acidity changes needed for the evaluation of recovery.

Lake pH and aluminum concentration: consequences for developmental stability of the water strider Rheumatobates rileyi (Hemiptera: Gerridae)

Lake acidity and metal contamination are environmental stresses that negatively affect many aquatic organisms in lakes in eastern Canada. Developmental stability, as indexed by fluctuating asymmetry (FA), is a putative cost-effective measure of environmental stress. In this study, we measured FA of the water strider Rheumatobates rileyi (L.) in lakes in the Sudbury area in relation to lake acidity (pH) and aluminum concentration. We did this to test the prediction that water striders inhabiting degraded lakes (low pH or high Al concentration) would exhibit decreased developmental stability (increased FA) compared with water striders from circumneutral lakes. As predicted we found that Al concentration (corrected for pH) was positively related to the average FA of samples. Contrary to expectation we found that pH (corrected for Al concentration) was also positively related to FA; thus, for a given Al concentration, more acid lakes had more symmetrical water striders than expected. We discuss the importance of our findings in relation to the use of FA as an index of environmental stress, for both water striders and other organisms.

The diet of insectivorous ducklings and the acidification of small Ontario lakes

We examined the diet of insectivorous ducklings of four species of waterfowl, Common Goldeneye (Bucephala clangula), Ring-necked Duck (Aythya collaris), Hooded Merganser (Lophodytes cucullatus), and American Black Duck (Anas rubripes), collected from small lakes covering a range of acidity in northeastern Ontario. The numbers of Odonata larvae, aquatic Hemiptera, aquatic Coleoptera, and Trichoptera larvae eaten by the ducklings were estimated from combined esophageal and gizzard contents and analysed with respect to differences in lake acidity and fish presence. Ducklings of all species, especially Common Goldeneye and Hooded Merganser, ate significantly more nektonic prey, especially Notonectidae (Hemiptera) and Dytiscidae (Coleoptera), from lakes without fish than from lakes with fish. Ducklings of species other than American Black Duck ate more Anisoptera larvae on acidic lakes. American Black Duck ducklings ate more teneral Odonata on acidic lakes. There was a tendency for more Trichoptera larvae to be eaten on non-acidic lakes than on acidic lakes. All four species adjusted, to some extent, for the absence of acid-sensitive prey in acidified lakes by feeding on prey that are most abundant under acidic, Ashless conditions. Differences in diet among species were related to differences in diving and foraging behaviour, and to hatch date.