13. The Temperate Rainforest Lakes of Chile and Canada
273
Lake System Comparisons
There are many similarities between Chilean and BC lakes. The lakes and
their catchments are of similar glacial origin and age, and they lie within
temperate rainforest biogeoclimatic zones. They are strongly influenced
by a cool, moist, maritime climate, and both experience high annual
precipitation during winter months . BC lakes are considerably cooler
than Chilean lakes, but both have similar ranges between their winter
minimum and summer maximum temperatures (12°C) and both have 7 to
8 month growing seasons (periods of stratification). Chilean lakes are
clearer, with a higher dissolved ion content , but a lower dissolved organic
content, than BC lakes. This suggests major differences in catchment soil
characteristics and nutrient (ion) retention capacities (Feller, 1977). Apart
from sharing some similar phytoplankton genera , all endemic zooplankton
and fishes in Chilean lakes belong to genera and/or families from other
southern hemisphere continents (e.g., Australia, New Zealand) (Campos,
1977; Pezzani, 1977). The pelagic food webs of both lake systems are
configured by size selective planktivores that reduce the average size of
macrozooplankton to between 0.6 to 1.5 mm (Soto & Zuniga, 1991 ;
O'Neill & Hyatt, 1987). Although both systems have low ambient nutrient
levels, Chilean lakes have higher TP levels and lower N levels than BC
lakes. One of the more important differences between systems is that
Chilean lakes have higher rates (>2X) of annual and daily primary
production with lower phytoplankton biomass (CHL) levels. Using annual
production (aP) and average CHL (B) values yields an aP/B ratio that is
almost 5-fold higher biomass turnover rate in Chilean lakes. Both warmer
winter minimum and summer maximum lake temperatures would partially
explain the faster turnover of organic carbon and higher metabolic rates
seen in Chilean lakes.
Resilience
Most temperate lakes show a significant CHL response to large increases
in nutrient income (TP, TN) , due largely to increases in the abundance of
large microphytoplankton, such as diatoms, dinoflagellates, and colonial
cyanobacteria (Dillon & Rigler, 1974; Smith, 1982; Vollenweider, 1968).
This has been the case in BC lakes, where significant CHL peaks occurred
when some lakes were fertilized with Nand P to increase salmon production (Stockner, 1981, 1987; Hardy, Shortreed, & Stockner , 1986).
However in some Chilean lakes (e.g., Lake Llanquihue), increasing TP
inputs over the past decade have not appreciably increased average CHL
content (D. Soto , unpublished data) (Figure 13.3). What are some of the
factors that may account for this apparent resilience by Chilean lakes to
increasing TP income?
1. Nitrogen limitation . The Chilean lakes are more consistently Nlimited and apparently respond only to N inputs rather than P (Soto et
273
Lake System Comparisons
There are many similarities between Chilean and BC lakes. The lakes and
their catchments are of similar glacial origin and age, and they lie within
temperate rainforest biogeoclimatic zones. They are strongly influenced
by a cool, moist, maritime climate, and both experience high annual
precipitation during winter months . BC lakes are considerably cooler
than Chilean lakes, but both have similar ranges between their winter
minimum and summer maximum temperatures (12°C) and both have 7 to
8 month growing seasons (periods of stratification). Chilean lakes are
clearer, with a higher dissolved ion content , but a lower dissolved organic
content, than BC lakes. This suggests major differences in catchment soil
characteristics and nutrient (ion) retention capacities (Feller, 1977). Apart
from sharing some similar phytoplankton genera , all endemic zooplankton
and fishes in Chilean lakes belong to genera and/or families from other
southern hemisphere continents (e.g., Australia, New Zealand) (Campos,
1977; Pezzani, 1977). The pelagic food webs of both lake systems are
configured by size selective planktivores that reduce the average size of
macrozooplankton to between 0.6 to 1.5 mm (Soto & Zuniga, 1991 ;
O'Neill & Hyatt, 1987). Although both systems have low ambient nutrient
levels, Chilean lakes have higher TP levels and lower N levels than BC
lakes. One of the more important differences between systems is that
Chilean lakes have higher rates (>2X) of annual and daily primary
production with lower phytoplankton biomass (CHL) levels. Using annual
production (aP) and average CHL (B) values yields an aP/B ratio that is
almost 5-fold higher biomass turnover rate in Chilean lakes. Both warmer
winter minimum and summer maximum lake temperatures would partially
explain the faster turnover of organic carbon and higher metabolic rates
seen in Chilean lakes.
Resilience
Most temperate lakes show a significant CHL response to large increases
in nutrient income (TP, TN) , due largely to increases in the abundance of
large microphytoplankton, such as diatoms, dinoflagellates, and colonial
cyanobacteria (Dillon & Rigler, 1974; Smith, 1982; Vollenweider, 1968).
This has been the case in BC lakes, where significant CHL peaks occurred
when some lakes were fertilized with Nand P to increase salmon production (Stockner, 1981, 1987; Hardy, Shortreed, & Stockner , 1986).
However in some Chilean lakes (e.g., Lake Llanquihue), increasing TP
inputs over the past decade have not appreciably increased average CHL
content (D. Soto , unpublished data) (Figure 13.3). What are some of the
factors that may account for this apparent resilience by Chilean lakes to
increasing TP income?
1. Nitrogen limitation . The Chilean lakes are more consistently Nlimited and apparently respond only to N inputs rather than P (Soto et