CHAPTER 6 . The Argentina Estuaries: A Review
III
ebb tide, sediments move along the bottom as bed load and the bank obstructs the
back flow.
Mar Chiquita Lagoon is inhabitated by a dense population of two intertidal grapsid
crab species. Cyrtograpsus angulatus and Chasmagnathus granulata. Besides frequently
occurring larvae of the two dominating crab species, those of three other brachyurans
(Plathyxantus crenulatus, Uca uruguayensis,Pinnixa patagonica) and of one anomuran
(Pachychelis haigae) are also found occasionally. Caridean shrimp larvae also are found
in the lagoon (Anger et al. 1994).
6.3.2
Quequen Grande Estuary
Quequen Grande River (Fig. 6.1) is one of the most important rivers of the SE Buenos
Aires province (37°2iS-38°29'W). The river basin is located in a highly developed farming zone of Argentina and it has an area of 9 370 km 2 • The river is 173 km in length. In
the mouth of the estuary is found a vital harbour, Puerto Quequen and an important
resort area, Necochea. The harbour is a very active commercial and industrial site,
where many of the main products of Argentina are exported. In the last ten years the
industrial and economical activities of the harbour have greatly increased and presently the estuary area in one of the most important economical zones of the province.
In the last 15 km the river has developed a meandering channel with cliffy banks
cut on Pleistocene semiconsolidated sediment with high carbonate content. The width
of the cross section is variable, between 150 and 200 m, reaching 400 m in the harbour area. Mean river discharge has varied along the years form 20 m3 S-1 (1918) to
5.25 m3 S-1 (1992), being the mean value 11.3 m3 S-1 (Sala 1975). Due to the harbour activities, the last 2 km of the estuary are kept with 12 m in depth by continuous dredging. However, further upstream the thalweg has a depth of 2-4 m.
Sediment in the estuary are composed of sand, clayey sand and silty clay. Sediment
mean size decrease headward and it is function of the high energy conditions prevailing near the mouth of the estuary (wave activity, strong currents and tidal action)
(Wright 1968). The bottom sediments within the estuary reflect the influence of the
Pleistocene sediments of the adjacent area. However, at the head of the harbour and
due to its particular dynamics, sediments are very fine and the conditions are highly
reductive.
Salinity and currents are the major environmental factors which considerably vary
in the estuary. Due to the tides, the salinity undergoes a daily variation of up to 23 psu
at the harbour site of the estuary. Salinities greater than 30 psu are found in the first
2-3 km from the mouth of the estuary, meanwhile 1 psu are found at 15 km from the
sea. However, maximum salinity intrusion varies from 15 km in high tide to 10 km at
low tide. Mean temperatures varied between 7° C and 25° C along the year.
Vertical salinity profiles within the harbour area clearly show a strong halo cline at
about 1-2 m depth that is present along the tidal cycle. The upper layer is mostly freshwater with increased salinity towards the mouth due probably to upward salt transport
by entrainment. The lower layer is vertically homogeneous reaching up to 33-35 psu.
Current velocity profiles taken at different stations for at least one tidal cycle both
within the harbour and at the river show that the tidal influence is uncoupled between
III
ebb tide, sediments move along the bottom as bed load and the bank obstructs the
back flow.
Mar Chiquita Lagoon is inhabitated by a dense population of two intertidal grapsid
crab species. Cyrtograpsus angulatus and Chasmagnathus granulata. Besides frequently
occurring larvae of the two dominating crab species, those of three other brachyurans
(Plathyxantus crenulatus, Uca uruguayensis,Pinnixa patagonica) and of one anomuran
(Pachychelis haigae) are also found occasionally. Caridean shrimp larvae also are found
in the lagoon (Anger et al. 1994).
6.3.2
Quequen Grande Estuary
Quequen Grande River (Fig. 6.1) is one of the most important rivers of the SE Buenos
Aires province (37°2iS-38°29'W). The river basin is located in a highly developed farming zone of Argentina and it has an area of 9 370 km 2 • The river is 173 km in length. In
the mouth of the estuary is found a vital harbour, Puerto Quequen and an important
resort area, Necochea. The harbour is a very active commercial and industrial site,
where many of the main products of Argentina are exported. In the last ten years the
industrial and economical activities of the harbour have greatly increased and presently the estuary area in one of the most important economical zones of the province.
In the last 15 km the river has developed a meandering channel with cliffy banks
cut on Pleistocene semiconsolidated sediment with high carbonate content. The width
of the cross section is variable, between 150 and 200 m, reaching 400 m in the harbour area. Mean river discharge has varied along the years form 20 m3 S-1 (1918) to
5.25 m3 S-1 (1992), being the mean value 11.3 m3 S-1 (Sala 1975). Due to the harbour activities, the last 2 km of the estuary are kept with 12 m in depth by continuous dredging. However, further upstream the thalweg has a depth of 2-4 m.
Sediment in the estuary are composed of sand, clayey sand and silty clay. Sediment
mean size decrease headward and it is function of the high energy conditions prevailing near the mouth of the estuary (wave activity, strong currents and tidal action)
(Wright 1968). The bottom sediments within the estuary reflect the influence of the
Pleistocene sediments of the adjacent area. However, at the head of the harbour and
due to its particular dynamics, sediments are very fine and the conditions are highly
reductive.
Salinity and currents are the major environmental factors which considerably vary
in the estuary. Due to the tides, the salinity undergoes a daily variation of up to 23 psu
at the harbour site of the estuary. Salinities greater than 30 psu are found in the first
2-3 km from the mouth of the estuary, meanwhile 1 psu are found at 15 km from the
sea. However, maximum salinity intrusion varies from 15 km in high tide to 10 km at
low tide. Mean temperatures varied between 7° C and 25° C along the year.
Vertical salinity profiles within the harbour area clearly show a strong halo cline at
about 1-2 m depth that is present along the tidal cycle. The upper layer is mostly freshwater with increased salinity towards the mouth due probably to upward salt transport
by entrainment. The lower layer is vertically homogeneous reaching up to 33-35 psu.
Current velocity profiles taken at different stations for at least one tidal cycle both
within the harbour and at the river show that the tidal influence is uncoupled between