4. Atmospheric and Geologic Constraints
71
biogeochemical constraint on element supplies to CP forests. Inputs of
Ca 2 + are particularly low to these forests due to limited Ca
2 + in sea-salt
aerosol, and the lack of major geologic sources of Ca
2 + (sections E and
F, Figure 4.3). External element supplies to North American temperate
rainforests, on the other hand, occur as a balance between atmospheric
and geologic sources (Figure 4.3, sections A-D) . Inputs of divalent base
cations (Ca
2 + and Mi+) are dominated by geologic sources, while
monovalent base cations are from atmospheric inputs (Na ") or a balance
of geologic and atmospheric sources (K+) .
Our results provide a view of temperate rainforest ecosystems as relatively poor in many major elements or nutrients. Concentration losses
of major elements were consistently dilute in the watershed streams
considered here (Figure 4.3). The exact patterns of element loss were , to
an important degree, imposed from variations in external atmospheric
inputs of elements (refer to Figures 4.2 and 4.3) . This overall importance
of marine aerosol inputs in defining the biogeochemistry of these forests
results from the consistent influence of marine wind patterns in the
biogeographical regions of both North and South American temperate
rainforests (ca . 40
o-50oN and S; see Lawford, this volume) . Temperate
rainforest ecosystems are therefore naturally closely linked to biogeochemical and meteorological processes that occur within upwind marine
ecosystems (Figure 4.5; Benbow, this volume) .
Forests at CP are unique in that external supplies of major elements
were almost exclusively due to atmospheric sea-salt inputs. This suggests
that CP forest communities have developed over time under evolutionary
and biogeochemical constraints from dilute sea-salt aerosols. The link
between marine processes (including biogeochemical, meteorological,
and climatic processes) and the forest ecosystem (Figure 4.5) is thus
particularly intimate for CP 'forests. In Figure 4.5 we outline major
factors that affect this link between marine processes and coastal ecosystem response. For example, marine emissions of dimethyl sulfide
(DMS) or NH 3 to the atmosphere, from algal productivity and decay
(Andreae & Raemdonck, 1983; Benbow, this volume; Quinn, Charlson,
& Bates, 1988), will enhance atmospheric inputs of sulfur and nitrogen to
coastal watersheds (Figure 4.5). More synoptic influences on coastal
temperate forests can be caused by short- or long-term variations in
weather patterns, including long-term oscillations associated with the EI
Nino-Southern Oscillation (refer to Figure 4.5). Temperate rainforests
at CP show a potentially strong "downwind" biogeochemical, as well as
climatic, link to nearby marine ecosystems.
Because of limited weathering and generally nutrient-poor nature,
temperate rainforest ecosystems may be especially sensitive to biogeochemical changes from human activities. For example, air-pollution inputs
of strong mineral acids are not likely to be strongly buffered by weathering
or base cation exchange reactions.
71
biogeochemical constraint on element supplies to CP forests. Inputs of
Ca 2 + are particularly low to these forests due to limited Ca
2 + in sea-salt
aerosol, and the lack of major geologic sources of Ca
2 + (sections E and
F, Figure 4.3). External element supplies to North American temperate
rainforests, on the other hand, occur as a balance between atmospheric
and geologic sources (Figure 4.3, sections A-D) . Inputs of divalent base
cations (Ca
2 + and Mi+) are dominated by geologic sources, while
monovalent base cations are from atmospheric inputs (Na ") or a balance
of geologic and atmospheric sources (K+) .
Our results provide a view of temperate rainforest ecosystems as relatively poor in many major elements or nutrients. Concentration losses
of major elements were consistently dilute in the watershed streams
considered here (Figure 4.3). The exact patterns of element loss were , to
an important degree, imposed from variations in external atmospheric
inputs of elements (refer to Figures 4.2 and 4.3) . This overall importance
of marine aerosol inputs in defining the biogeochemistry of these forests
results from the consistent influence of marine wind patterns in the
biogeographical regions of both North and South American temperate
rainforests (ca . 40
o-50oN and S; see Lawford, this volume) . Temperate
rainforest ecosystems are therefore naturally closely linked to biogeochemical and meteorological processes that occur within upwind marine
ecosystems (Figure 4.5; Benbow, this volume) .
Forests at CP are unique in that external supplies of major elements
were almost exclusively due to atmospheric sea-salt inputs. This suggests
that CP forest communities have developed over time under evolutionary
and biogeochemical constraints from dilute sea-salt aerosols. The link
between marine processes (including biogeochemical, meteorological,
and climatic processes) and the forest ecosystem (Figure 4.5) is thus
particularly intimate for CP 'forests. In Figure 4.5 we outline major
factors that affect this link between marine processes and coastal ecosystem response. For example, marine emissions of dimethyl sulfide
(DMS) or NH 3 to the atmosphere, from algal productivity and decay
(Andreae & Raemdonck, 1983; Benbow, this volume; Quinn, Charlson,
& Bates, 1988), will enhance atmospheric inputs of sulfur and nitrogen to
coastal watersheds (Figure 4.5). More synoptic influences on coastal
temperate forests can be caused by short- or long-term variations in
weather patterns, including long-term oscillations associated with the EI
Nino-Southern Oscillation (refer to Figure 4.5). Temperate rainforests
at CP show a potentially strong "downwind" biogeochemical, as well as
climatic, link to nearby marine ecosystems.
Because of limited weathering and generally nutrient-poor nature,
temperate rainforest ecosystems may be especially sensitive to biogeochemical changes from human activities. For example, air-pollution inputs
of strong mineral acids are not likely to be strongly buffered by weathering
or base cation exchange reactions.