276
D. Soto and J.G. Stockner
Zuniga, 1991). More productive oligotrophic and mesotrophic lakes have
more complex food webs but shorter pathways that tend to be more
efficient and provide more direct carbon flows to fish (Stockner, 1987)
(Figure 13.2). Microbial food webs in these lakes are more ephemeral
and tend to be less important in material and energy transfers (Weisse &
Stockner, 1994). It is possible that the food web structure of Chilean
lakes, which in contrast to BC lakes includes a littoral/benthic component,
may partially explain why the biomass turnover rates (aP: B) are considerably faster and appear to support a greater abundance and variety of
fishes.
Future Changes
Short Term
With increased disturbance of the catchments comes the possibility of
higher nutrient loads and accelerated lake production (eutrophication) in
both Chilean and BC lakes. Both agricultural development and rainforest
harvesting with reforestation using monocultures of introduced conifers
(exotics) are presently a serious problem for Chilean lakes. The endemic
nonconiferous evergreen rainforests have extensive root systems and low
leaf export that in combination with volcanic soils provide and efficient
nutrient retention system on the catchment (Perez , Armesto, & Ruthsatz,
1991). The continued loss of the native forests, with their buffering effect,
will increase the possibility of soil erosion and nutrient loss, especially
nitrogen, with the likelihood of rapid lake eutrophication. Logging of the
Be coastal rainforests has not had a major effect on the primary productivity of BC lakes or rivers. This is largely because the soil structure is
highly adsorptive of phosphorus and little increase in TP has been seen
following logging of the catchments (Feller, 1977).
The introduction of exotic Pacific coho salmon (Oncorhynchus kisutch)
and Atlantic salmon (Salmo salar) to Chilean lakes could alter food web
structure and affect lake metabolism. Over the past few years escaped
salmon have become common in Chilean lakes and there is concern that
their planktivory as juveniles and piscivory as adults could affect the
abundance of percas, the only endemic piscivore in the lakes (Soto &
Zuniga, 1991). In some BC lakes, where net-pen rearing of Atlantic
salmon fry is being done on an experimental basis, there is now concern
about the possible impacts of the introduction of Atlantic salmon, another
piscivore (exotic), on the fish communities and food-web structure.
Long Term
The lakes of Chile and British Columbia are both likely to be affected by
global climate change. There are three aspects to consider: rising water
temperatures (e.g., epilimnion) , increased UVB , and increased winter
D. Soto and J.G. Stockner
Zuniga, 1991). More productive oligotrophic and mesotrophic lakes have
more complex food webs but shorter pathways that tend to be more
efficient and provide more direct carbon flows to fish (Stockner, 1987)
(Figure 13.2). Microbial food webs in these lakes are more ephemeral
and tend to be less important in material and energy transfers (Weisse &
Stockner, 1994). It is possible that the food web structure of Chilean
lakes, which in contrast to BC lakes includes a littoral/benthic component,
may partially explain why the biomass turnover rates (aP: B) are considerably faster and appear to support a greater abundance and variety of
fishes.
Future Changes
Short Term
With increased disturbance of the catchments comes the possibility of
higher nutrient loads and accelerated lake production (eutrophication) in
both Chilean and BC lakes. Both agricultural development and rainforest
harvesting with reforestation using monocultures of introduced conifers
(exotics) are presently a serious problem for Chilean lakes. The endemic
nonconiferous evergreen rainforests have extensive root systems and low
leaf export that in combination with volcanic soils provide and efficient
nutrient retention system on the catchment (Perez , Armesto, & Ruthsatz,
1991). The continued loss of the native forests, with their buffering effect,
will increase the possibility of soil erosion and nutrient loss, especially
nitrogen, with the likelihood of rapid lake eutrophication. Logging of the
Be coastal rainforests has not had a major effect on the primary productivity of BC lakes or rivers. This is largely because the soil structure is
highly adsorptive of phosphorus and little increase in TP has been seen
following logging of the catchments (Feller, 1977).
The introduction of exotic Pacific coho salmon (Oncorhynchus kisutch)
and Atlantic salmon (Salmo salar) to Chilean lakes could alter food web
structure and affect lake metabolism. Over the past few years escaped
salmon have become common in Chilean lakes and there is concern that
their planktivory as juveniles and piscivory as adults could affect the
abundance of percas, the only endemic piscivore in the lakes (Soto &
Zuniga, 1991). In some BC lakes, where net-pen rearing of Atlantic
salmon fry is being done on an experimental basis, there is now concern
about the possible impacts of the introduction of Atlantic salmon, another
piscivore (exotic), on the fish communities and food-web structure.
Long Term
The lakes of Chile and British Columbia are both likely to be affected by
global climate change. There are three aspects to consider: rising water
temperatures (e.g., epilimnion) , increased UVB , and increased winter