Control of chl a levels and phytoplankton production are complex phenomena
involving the interactions of physical, chemical, and biological processes (Jumars,
1993). Chlorophyll levels are generally controlled by nutrient and light availability,
ratios of limiting resources, water column residence times and structural stability, water
temperatures, and grazing pressure. Estuaries and other coastal embayments often have
greater chlorophyll concentrations than adjacent offshore areas. However, offshore
upwelling and plume activity can generate elevated pigment levels and increase spatial
heterogeneity.
Estuarine zones commonly have complex spatial patterns of
biogeochemical constituents related to wind and tidal driven circulation patterns,
longitudinal mixing gradients and point source inputs, and anthropogenic disturbances
(Jassby et al., 1997). These spatial variability patterns are a major challenge in the
design of estuarine sampling strategies.
In Georgia river transects extending from nontidal river reaches to offshore, we
found a consistent pattern of increased chlorophyll within the estuarine mixing zone
compared to upriver and offshore stations (Figure 4; also see Schalles et al., 1998a;
Alberts et al., 2004). In these Georgia habitats, the mid and lower salinity reaches of the
estuaries often have upper single to double digit chlorophyll levels and offshore shelf
areas are typically low to mid single digit levels. The lower reaches of these estuaries
also have elevated total and inorganic seston levels (Alberts et al., 2004). Upstream
nutrient inputs, increased water residence times, nutrient sequestration and recycling in
tidal wetlands and benthos, complex circulation patterns, ebb tide export of littoral zone
phytoplankton and epibenthic algae, and wind-driven sediment resuspension all
contribute to greater productivity and biomass in many estuaries.
Figure 4. Chlorophyll a (not corrected for phaeophytin) versus salinity patterns for three Georgia
estuaries and adjacent offshore areas (dashed, slanted line demarcates offshore stations). Data
from two transects are shown for the St. Marys River.
33
Optical Remote Sensing Techniques
involving the interactions of physical, chemical, and biological processes (Jumars,
1993). Chlorophyll levels are generally controlled by nutrient and light availability,
ratios of limiting resources, water column residence times and structural stability, water
temperatures, and grazing pressure. Estuaries and other coastal embayments often have
greater chlorophyll concentrations than adjacent offshore areas. However, offshore
upwelling and plume activity can generate elevated pigment levels and increase spatial
heterogeneity.
Estuarine zones commonly have complex spatial patterns of
biogeochemical constituents related to wind and tidal driven circulation patterns,
longitudinal mixing gradients and point source inputs, and anthropogenic disturbances
(Jassby et al., 1997). These spatial variability patterns are a major challenge in the
design of estuarine sampling strategies.
In Georgia river transects extending from nontidal river reaches to offshore, we
found a consistent pattern of increased chlorophyll within the estuarine mixing zone
compared to upriver and offshore stations (Figure 4; also see Schalles et al., 1998a;
Alberts et al., 2004). In these Georgia habitats, the mid and lower salinity reaches of the
estuaries often have upper single to double digit chlorophyll levels and offshore shelf
areas are typically low to mid single digit levels. The lower reaches of these estuaries
also have elevated total and inorganic seston levels (Alberts et al., 2004). Upstream
nutrient inputs, increased water residence times, nutrient sequestration and recycling in
tidal wetlands and benthos, complex circulation patterns, ebb tide export of littoral zone
phytoplankton and epibenthic algae, and wind-driven sediment resuspension all
contribute to greater productivity and biomass in many estuaries.
Figure 4. Chlorophyll a (not corrected for phaeophytin) versus salinity patterns for three Georgia
estuaries and adjacent offshore areas (dashed, slanted line demarcates offshore stations). Data
from two transects are shown for the St. Marys River.
33
Optical Remote Sensing Techniques