The Gulf of Guayaquil and the Guayas River Estuary, Ecuador
255
results in an outer Gulf productivity of about 200 g C m- 2 year- 1 compared
to 90 g C m- 2 year- 1 in the inner Gulf. Primary productivity in the subestuaries is potentially limited by DIN concentration (N:P ratio <5.8). DIN
limitation appears to be a result of more rapid P than N regeneration from
the organic matter pool (Cardenas 1995). Uncoupling of DIN and SRP in
the nutrient cycles leads to an increase in DON:DOP ratios (around 65) in
the Guayas River estuary. An increase of SRP tends to increase the TP pool
(SRP forms 50% of the TP pool) and reduce TN:TP ratios (about 12). Denitrification and nitrogen deposition has been implicated in low N :P ratios of
sediment-water fluxes that could also affect the availability of DIN to primary producers (Smith et al. 1985).
High TSS concentration and tides (>3m) cause elevated sediment
accumulation rates (4,074-5,151 g m- 2 year- 1 ) in mangrove forests of the
Churute River subestuary. More than 75% of accumulated matter is associated with inorganic sediments. High nutrient concentrations ( C:N ratios
24-30; N:P ratios 7.7 to >40; total phosphorus 0.23-0.71 mg g- 1 ), low salinity ( < 17), and the proximity of the Gulf to the equator result in tall mangrove trees (up to 30m) and biomass between 300 and 400 tons ha- 1
(Twilley et al. 1993). Mangrove litter fall rates vary from 6.47 to
10.64 tons ha- 1 year- 1 , with higher daily rates during the rainy season,
while mean leaf litter standing crop (1.53-9.18g m- 2 ) peaks during the
dry season in September. Leaf litter dynamics in riverine mangroves of
the Guayas River estuary depend on the relative effects of tides and the
activity of the mangrove crab Ucides occidental is. The leaf litter residence
time on the forest floor is less than 1 day when crabs are active (December to July); however, when crabs aestivate (August to November), residence time averages 5.3 days. During the active season, crabs bury leaf
litter in the forest soil at low tide, but at high tide leaf litter is exported to
the estuary, regardless of whether crabs are active or not. Although the
rate of mangrove leaf degradation is related to site, season (rainy> dry),
and initial nitrogen content of senescent leaves, tidal processes are responsible for higher (10-20 times) litter turnover rates than expected
based on leaf degradation alone. A model of leaf litter dynamics
(Fig. 17.5) suggests that geophysical energy (tides, river discharge) controls the fate of mangrove leaf litter, though highest litter turnover rates
are associated with crab activity (Twilley et al. 1986, 1997).
Particulate carbon to chlorophyll-a (PC:Chla) ratios can distinguish
between living (20 to >200) and detrital (>1,000) organic matter in suspended particulate material (SPM; Cifuentes et al. 1988). The lowest
PC:Chla ratio (104) occurs far from terrestrial and intertidal sources in the
Morro Channel, while PC:Chla ratios in the Guayas River near Guayaquil
are 50 times higher. Average PC:Chla (327), 6 13 C (-26.7 to -23.1), and 6 15 N
255
results in an outer Gulf productivity of about 200 g C m- 2 year- 1 compared
to 90 g C m- 2 year- 1 in the inner Gulf. Primary productivity in the subestuaries is potentially limited by DIN concentration (N:P ratio <5.8). DIN
limitation appears to be a result of more rapid P than N regeneration from
the organic matter pool (Cardenas 1995). Uncoupling of DIN and SRP in
the nutrient cycles leads to an increase in DON:DOP ratios (around 65) in
the Guayas River estuary. An increase of SRP tends to increase the TP pool
(SRP forms 50% of the TP pool) and reduce TN:TP ratios (about 12). Denitrification and nitrogen deposition has been implicated in low N :P ratios of
sediment-water fluxes that could also affect the availability of DIN to primary producers (Smith et al. 1985).
High TSS concentration and tides (>3m) cause elevated sediment
accumulation rates (4,074-5,151 g m- 2 year- 1 ) in mangrove forests of the
Churute River subestuary. More than 75% of accumulated matter is associated with inorganic sediments. High nutrient concentrations ( C:N ratios
24-30; N:P ratios 7.7 to >40; total phosphorus 0.23-0.71 mg g- 1 ), low salinity ( < 17), and the proximity of the Gulf to the equator result in tall mangrove trees (up to 30m) and biomass between 300 and 400 tons ha- 1
(Twilley et al. 1993). Mangrove litter fall rates vary from 6.47 to
10.64 tons ha- 1 year- 1 , with higher daily rates during the rainy season,
while mean leaf litter standing crop (1.53-9.18g m- 2 ) peaks during the
dry season in September. Leaf litter dynamics in riverine mangroves of
the Guayas River estuary depend on the relative effects of tides and the
activity of the mangrove crab Ucides occidental is. The leaf litter residence
time on the forest floor is less than 1 day when crabs are active (December to July); however, when crabs aestivate (August to November), residence time averages 5.3 days. During the active season, crabs bury leaf
litter in the forest soil at low tide, but at high tide leaf litter is exported to
the estuary, regardless of whether crabs are active or not. Although the
rate of mangrove leaf degradation is related to site, season (rainy> dry),
and initial nitrogen content of senescent leaves, tidal processes are responsible for higher (10-20 times) litter turnover rates than expected
based on leaf degradation alone. A model of leaf litter dynamics
(Fig. 17.5) suggests that geophysical energy (tides, river discharge) controls the fate of mangrove leaf litter, though highest litter turnover rates
are associated with crab activity (Twilley et al. 1986, 1997).
Particulate carbon to chlorophyll-a (PC:Chla) ratios can distinguish
between living (20 to >200) and detrital (>1,000) organic matter in suspended particulate material (SPM; Cifuentes et al. 1988). The lowest
PC:Chla ratio (104) occurs far from terrestrial and intertidal sources in the
Morro Channel, while PC:Chla ratios in the Guayas River near Guayaquil
are 50 times higher. Average PC:Chla (327), 6 13 C (-26.7 to -23.1), and 6 15 N