180
U. Seeliger
processes in the estuary and coastal waters. Years of El Nino-Southern
Oscillation (ENSO) cause extreme precipitation in the watershed. The elevated runoff extends the freshwater plume up to 50 km over the continental shelf and a concomitant increase of chlorophyll-a concentrations in
coastal water masses is directly related to eutrophication by high fluvial
nutrient input. The enhanced production processes are likely to modify the
ecological dynamics of the entire coastal region. Furthermore, elevated
runoff together with NE winds causes high current velocities in the inlet.
Under these conditions, the recruitment of many ecologically and commercially important species into the estuary is impeded, resulting in a significant negative relationship between high spring runoff and low secondary production in summer/fall (Castello and Moller 1978). In contrast,
during La Nina drought years, southerly winds may force seawater more
than 200 km upstream into the Patos Lagoon. The protracted salinization
(Costa et al. 1988) of brackish and freshwater areas tends to interfere with
critical life-cycle stages of limnic, estuary-resident, and estuary-dependent
species and may lead to salinity-dependent mortalities. The disruptive
effects of extreme episodic events on ecological processes in both the
estuary and coastal nearshore waters can only be assessed by long-term
ecological studies.
12.6 Impact and Management
The ecological and socio-economic importance of the Patos Lagoon
estuary excels among the coastal regions in the southwestern Atlantic and,
despite early accounts of man's interference (von Ihering 1885), the estuary
appears to have satisfied ecological and human needs without management for more than a century. However, during recent decades ever
increasing demands of society have gradually altered natural runoff processes, changed the quality of water, reduced vital habitats, and exhausted
the seemingly limitless natural resources. Additionally, rising sea levels
and the advance of ozone-poor Antarctic air over southern Brazil (Santee
et al. 1995) may affect ecological processes and pose a future hazard to the
Patos Lagoon estuary ecosystem (Seeliger and Costa 1997).
Over the last 20 years, the growing demand for water for domestic and
industrial use and for irrigated rice cultivation has significantly modified
average annual (109 km 3 ) freshwater flow through the inlet. Especially
during drought years with naturally reduced (75 km 3 ) runoff, the diversion
(> 13 %) of freshwater resources for human use may negatively affect the
balance of salinity and nutrients in the estuary and the export of organic
U. Seeliger
processes in the estuary and coastal waters. Years of El Nino-Southern
Oscillation (ENSO) cause extreme precipitation in the watershed. The elevated runoff extends the freshwater plume up to 50 km over the continental shelf and a concomitant increase of chlorophyll-a concentrations in
coastal water masses is directly related to eutrophication by high fluvial
nutrient input. The enhanced production processes are likely to modify the
ecological dynamics of the entire coastal region. Furthermore, elevated
runoff together with NE winds causes high current velocities in the inlet.
Under these conditions, the recruitment of many ecologically and commercially important species into the estuary is impeded, resulting in a significant negative relationship between high spring runoff and low secondary production in summer/fall (Castello and Moller 1978). In contrast,
during La Nina drought years, southerly winds may force seawater more
than 200 km upstream into the Patos Lagoon. The protracted salinization
(Costa et al. 1988) of brackish and freshwater areas tends to interfere with
critical life-cycle stages of limnic, estuary-resident, and estuary-dependent
species and may lead to salinity-dependent mortalities. The disruptive
effects of extreme episodic events on ecological processes in both the
estuary and coastal nearshore waters can only be assessed by long-term
ecological studies.
12.6 Impact and Management
The ecological and socio-economic importance of the Patos Lagoon
estuary excels among the coastal regions in the southwestern Atlantic and,
despite early accounts of man's interference (von Ihering 1885), the estuary
appears to have satisfied ecological and human needs without management for more than a century. However, during recent decades ever
increasing demands of society have gradually altered natural runoff processes, changed the quality of water, reduced vital habitats, and exhausted
the seemingly limitless natural resources. Additionally, rising sea levels
and the advance of ozone-poor Antarctic air over southern Brazil (Santee
et al. 1995) may affect ecological processes and pose a future hazard to the
Patos Lagoon estuary ecosystem (Seeliger and Costa 1997).
Over the last 20 years, the growing demand for water for domestic and
industrial use and for irrigated rice cultivation has significantly modified
average annual (109 km 3 ) freshwater flow through the inlet. Especially
during drought years with naturally reduced (75 km 3 ) runoff, the diversion
(> 13 %) of freshwater resources for human use may negatively affect the
balance of salinity and nutrients in the estuary and the export of organic