270
D. Soto and J.G. Stockner
show varying degrees of agricultural and recreational development and
human settlement.
The catchment basins of BC lakes lie within the large western hemlock
(Tsuga heterophylla) biogeoclimatic zone (Farley, 1979) that experiences
a moist, cool Mediterranean climate with wet winters and dry summers.
Soils can be characterized as shallow, coarse, textured , and highly organic
with pockets of glacial till. These soils tend to be strongly adsorptive of
phosphorus ions but less so with nitrogen (Feller, 1977). The predominant
forest vegetation is western hemlock, Douglas fir (Pseudotsuga menziesii) ,
western red cedar (Thuja plicata), and Sitka spruce (Picea sitchensis).
There is human settlement around only a few lakes (Sproat, Great Central
lakes), but the most significant disturbance has been the removal of much
of the old growth rainforest from most lake basins since the turn of the
century (e.g., Great Central , Nimpkish, Woss, Sproat , Henderson lakes).
Because of the steep, rocky terrain and the nature of the catchment soils,
little land is suitable for agricultural development and the limited accessibility (roads) has prevented significantrecreational or urban development.
Physicochemical
The Chilean lakes are warm-monomictic with stable stratification occurring
from October-April. In some lakes the epilimnion can attain depths
>40 m (Campos et aI., 1988). In winter during periods of deep mixing
water temperatures rarely fall below lOoC. BC lakes are also warmmonomictic with stable stratification from April to mid-October, but the
average depth of the epilimnion seldom is >20m (Stockner & Costella,
1980). During deep mixing periods in winter, water temperatures range
from 4
0
to 6°C.
Average total phosphorus (TP) concentrations are higher in Chilean
lakes than BC lakes-3.8 and 2.4ug ·L -\ respectively. Total nitrogen
(TN) values in Chilean lakes are about threefold lower than in BC lakes
and average nitrate concentrations in both systems are very low, <20
ug-L-1. The major ion composition of Chilean lakes suggests a greater
marine influence than BC lakes with a predominance of sodium, chloride,
and magnesium ions, and a slightly alkaline average pH value (Table
13.1). The waters of BC lakes are soft and of low alkalinity, with an
average total dissolved solids (TDS) value (32.9mg·L-1) that is considerably lower than the average Chilean lake value (63mg-L-1).
Biological
Picoplankton
Picoplankton (size range 0.2 to 2.0um) have not been well studied in
Chilean lakes and values reported here come only from Lake Rifiihue (S.
Wolf, personal communication), one of the most productive of the
D. Soto and J.G. Stockner
show varying degrees of agricultural and recreational development and
human settlement.
The catchment basins of BC lakes lie within the large western hemlock
(Tsuga heterophylla) biogeoclimatic zone (Farley, 1979) that experiences
a moist, cool Mediterranean climate with wet winters and dry summers.
Soils can be characterized as shallow, coarse, textured , and highly organic
with pockets of glacial till. These soils tend to be strongly adsorptive of
phosphorus ions but less so with nitrogen (Feller, 1977). The predominant
forest vegetation is western hemlock, Douglas fir (Pseudotsuga menziesii) ,
western red cedar (Thuja plicata), and Sitka spruce (Picea sitchensis).
There is human settlement around only a few lakes (Sproat, Great Central
lakes), but the most significant disturbance has been the removal of much
of the old growth rainforest from most lake basins since the turn of the
century (e.g., Great Central , Nimpkish, Woss, Sproat , Henderson lakes).
Because of the steep, rocky terrain and the nature of the catchment soils,
little land is suitable for agricultural development and the limited accessibility (roads) has prevented significantrecreational or urban development.
Physicochemical
The Chilean lakes are warm-monomictic with stable stratification occurring
from October-April. In some lakes the epilimnion can attain depths
>40 m (Campos et aI., 1988). In winter during periods of deep mixing
water temperatures rarely fall below lOoC. BC lakes are also warmmonomictic with stable stratification from April to mid-October, but the
average depth of the epilimnion seldom is >20m (Stockner & Costella,
1980). During deep mixing periods in winter, water temperatures range
from 4
0
to 6°C.
Average total phosphorus (TP) concentrations are higher in Chilean
lakes than BC lakes-3.8 and 2.4ug ·L -\ respectively. Total nitrogen
(TN) values in Chilean lakes are about threefold lower than in BC lakes
and average nitrate concentrations in both systems are very low, <20
ug-L-1. The major ion composition of Chilean lakes suggests a greater
marine influence than BC lakes with a predominance of sodium, chloride,
and magnesium ions, and a slightly alkaline average pH value (Table
13.1). The waters of BC lakes are soft and of low alkalinity, with an
average total dissolved solids (TDS) value (32.9mg·L-1) that is considerably lower than the average Chilean lake value (63mg-L-1).
Biological
Picoplankton
Picoplankton (size range 0.2 to 2.0um) have not been well studied in
Chilean lakes and values reported here come only from Lake Rifiihue (S.
Wolf, personal communication), one of the most productive of the