350
B. Kjerfve et a!.
Paranagua, Brazil (see Chap. 10 by Lana et al.), are gulf-like, large drowned
river valley estuaries on the west and east coast of the continent, respectively. Rio de la Plata is a gigantic coastal plain estuary bordered by Buenos
Aires and Montevideo (see Chap. 13 by Mianzan et al.). The Maracaibo
system in Venezuela is characterized by anoxic conditions in a large area of
the hypolimnion (see Chap. 3 by Rodriguez). Bafa de Guanabara in Rio de
Janeiro, Brazil, is eutrophic and polluted as a result of largely untreated
drainage from a population of 8 million in the catchment (see Chap. 8 by
Kjerfve et al.).
Freshwater runoff and sediment loads into the coastal areas have a profound effect on the character of coastal ecosystems. However, human
activities within the river basins not only alter water and sediment supplies
but also the inputs of nutrients and pollutants, which impact the quality of
these environments. Most Latin American coastal marine systems have
been impacted by the damming of rivers, closing of tidal inlets, or diversion of freshwater and deforestation within the watershed, which has
changed the seasonal cycle and the amount of freshwater runoff and
increased sediment loading of rivers due to soil erosion. Subsequent changes of salinity levels and cycles and high siltation have adversely affected
shallow nearshore habitats and coastal wetlands, which play an important
role as nursery areas. The damming of the Colorado River has produced a
hypersaline environment in the inner Gulf of California (see Chap. 22 by
Alvarez-Borrego). Humans have profoundly altered the Cienaga Grande
coastal lagoon during the past four decades with a general degradation of
the ecosystem, primarily by eliminating coastal inlets when constructing a
coastal highway (see Chap. 2 by Polania et al.). The diversion of freshwater
and sediment into the Cananeia estuary has significantly modified most
aspects of the estuarine environment (see Chap. 9 by Tundisi and Matsumura-Tundisi). The levels of nutrient flux from terrestrial ecosystems to
the aquatic environment are a function of drainage and land use. Although
the overall productivity of coastal and inland seas is normally increased by
nutrient runoff, excess nutrients may negatively influence fisheries of
semi-enclosed water bodies (see Chap. 4 by Conde and Chap. 2 by Polania
et al.). Apart from the serious impact of many land-bound human activities on marine systems, oil and gas extraction in nearshore waters and
semi-enclosed seas will also have to be reconciled with sustainable
development of marine resources (see Chap. 3 by Rodriguez).
Furthermore, high density aquaculture in coastal water bodies with
reduced water exchange can provoke excessive nutrient loading and local
eutrophication with negative feedback on the aquaculture activities themselves. The extensive conversion of mangrove forests to shrimp pond culture may reduce natural shrimp populations which use mangrove systems
B. Kjerfve et a!.
Paranagua, Brazil (see Chap. 10 by Lana et al.), are gulf-like, large drowned
river valley estuaries on the west and east coast of the continent, respectively. Rio de la Plata is a gigantic coastal plain estuary bordered by Buenos
Aires and Montevideo (see Chap. 13 by Mianzan et al.). The Maracaibo
system in Venezuela is characterized by anoxic conditions in a large area of
the hypolimnion (see Chap. 3 by Rodriguez). Bafa de Guanabara in Rio de
Janeiro, Brazil, is eutrophic and polluted as a result of largely untreated
drainage from a population of 8 million in the catchment (see Chap. 8 by
Kjerfve et al.).
Freshwater runoff and sediment loads into the coastal areas have a profound effect on the character of coastal ecosystems. However, human
activities within the river basins not only alter water and sediment supplies
but also the inputs of nutrients and pollutants, which impact the quality of
these environments. Most Latin American coastal marine systems have
been impacted by the damming of rivers, closing of tidal inlets, or diversion of freshwater and deforestation within the watershed, which has
changed the seasonal cycle and the amount of freshwater runoff and
increased sediment loading of rivers due to soil erosion. Subsequent changes of salinity levels and cycles and high siltation have adversely affected
shallow nearshore habitats and coastal wetlands, which play an important
role as nursery areas. The damming of the Colorado River has produced a
hypersaline environment in the inner Gulf of California (see Chap. 22 by
Alvarez-Borrego). Humans have profoundly altered the Cienaga Grande
coastal lagoon during the past four decades with a general degradation of
the ecosystem, primarily by eliminating coastal inlets when constructing a
coastal highway (see Chap. 2 by Polania et al.). The diversion of freshwater
and sediment into the Cananeia estuary has significantly modified most
aspects of the estuarine environment (see Chap. 9 by Tundisi and Matsumura-Tundisi). The levels of nutrient flux from terrestrial ecosystems to
the aquatic environment are a function of drainage and land use. Although
the overall productivity of coastal and inland seas is normally increased by
nutrient runoff, excess nutrients may negatively influence fisheries of
semi-enclosed water bodies (see Chap. 4 by Conde and Chap. 2 by Polania
et al.). Apart from the serious impact of many land-bound human activities on marine systems, oil and gas extraction in nearshore waters and
semi-enclosed seas will also have to be reconciled with sustainable
development of marine resources (see Chap. 3 by Rodriguez).
Furthermore, high density aquaculture in coastal water bodies with
reduced water exchange can provoke excessive nutrient loading and local
eutrophication with negative feedback on the aquaculture activities themselves. The extensive conversion of mangrove forests to shrimp pond culture may reduce natural shrimp populations which use mangrove systems