13. The Temperate Rainforest Lakes of Chile and Canada
277
precipitation. We expect that higher rainfall and elevated surface and
groundwater temperatures will influence both lake systems. .They will
experience more rapid winter flushing, a longer period of stratification
(growing season), and a higher seasonal epilimnetic temperature, factors
that would tend to lower annual rates of primary production. Such conditions would also affect food-web structure, especially in BC lakes where a
warmer epilimnion and sustained thermal barrier will restrict access of
juvenile sockeye to their zooplankton forage. This could reduce freshwater
production of juvenile sockeye and increase the abundance of more
thermal tolerate species, e.g., rainbow and cutthroat trout. It has been
proposed that global warming will reduce annual primary production in
some large interior BC lakes because of lower nutrient inputs during the
longer, drier and warmer growing season that is expected (Henderson,
Stockner, & Levy, 1992).
In both regions, increasing air temperatures will have the most immediate and major impact on lakes receiving glacial input. More rapid ice
melt will alter hydrologic, thermal, optical, and chemical properties of the
glacial rivers that will increase turbidity and lower temperatures of glacial
lakes in both regions.
Increased UVB will likely affect lake phytoplankton community structure and production most severely in Chilean lakes where compensation
depths are 3 times higher than in BC lake s. However the magnitude of
the impact on both species composition and primary production is still
unclear and awaits further research in fresh water systems. Extrapolation
of results from UVB work on Antarctic marine phytoplankton would
suggest a small reduction «15%) in daily production and some shifts in
species composition from larger microphytoplankton (diatoms, dinoflagellates) toward smaller cyanobacterial or chlorophyte dominance (Smith,
1989). There is also evidence to suggest that zooplankton may be affected
by UVB by restricting access to there epilimnetic forage base in oligotrophic lakes (Williamson, Zagarese, Schulze, Hargreaves, & Seva, 1994).
Acid rain and atmospheric nutrient deposition has already affected
lakes of North America to a greater extent than in South America due to
greater industrial development. But neither Chilean nor BC lakes have
been seriously affected by these perturbations and should not be affected
in future under the influence of global warming due to their geographic
location along the Pacific Ocean. It appears that Chilean lakes and their
catchment basins are far more sensitive to both floral and faunal species
losses than BC lakes because of their low potential for species replacement
(e.g., geographic isolation).
Acknowledgments. We thank H . Campos and C. Jara for providing
unpublished information and for constructive discussions; F. Jara, E .
MacIsaac, K. Shortreed, and T . Weisse for insightful comments and
review of the manuscript. Earl MacIsaac and Bruce Nidle helped with
277
precipitation. We expect that higher rainfall and elevated surface and
groundwater temperatures will influence both lake systems. .They will
experience more rapid winter flushing, a longer period of stratification
(growing season), and a higher seasonal epilimnetic temperature, factors
that would tend to lower annual rates of primary production. Such conditions would also affect food-web structure, especially in BC lakes where a
warmer epilimnion and sustained thermal barrier will restrict access of
juvenile sockeye to their zooplankton forage. This could reduce freshwater
production of juvenile sockeye and increase the abundance of more
thermal tolerate species, e.g., rainbow and cutthroat trout. It has been
proposed that global warming will reduce annual primary production in
some large interior BC lakes because of lower nutrient inputs during the
longer, drier and warmer growing season that is expected (Henderson,
Stockner, & Levy, 1992).
In both regions, increasing air temperatures will have the most immediate and major impact on lakes receiving glacial input. More rapid ice
melt will alter hydrologic, thermal, optical, and chemical properties of the
glacial rivers that will increase turbidity and lower temperatures of glacial
lakes in both regions.
Increased UVB will likely affect lake phytoplankton community structure and production most severely in Chilean lakes where compensation
depths are 3 times higher than in BC lake s. However the magnitude of
the impact on both species composition and primary production is still
unclear and awaits further research in fresh water systems. Extrapolation
of results from UVB work on Antarctic marine phytoplankton would
suggest a small reduction «15%) in daily production and some shifts in
species composition from larger microphytoplankton (diatoms, dinoflagellates) toward smaller cyanobacterial or chlorophyte dominance (Smith,
1989). There is also evidence to suggest that zooplankton may be affected
by UVB by restricting access to there epilimnetic forage base in oligotrophic lakes (Williamson, Zagarese, Schulze, Hargreaves, & Seva, 1994).
Acid rain and atmospheric nutrient deposition has already affected
lakes of North America to a greater extent than in South America due to
greater industrial development. But neither Chilean nor BC lakes have
been seriously affected by these perturbations and should not be affected
in future under the influence of global warming due to their geographic
location along the Pacific Ocean. It appears that Chilean lakes and their
catchment basins are far more sensitive to both floral and faunal species
losses than BC lakes because of their low potential for species replacement
(e.g., geographic isolation).
Acknowledgments. We thank H . Campos and C. Jara for providing
unpublished information and for constructive discussions; F. Jara, E .
MacIsaac, K. Shortreed, and T . Weisse for insightful comments and
review of the manuscript. Earl MacIsaac and Bruce Nidle helped with