491
this way, although somewhat diluted, pollutants become bioavailable for a greater
diversity of flora and fauna over the whole extent of the ecocline, and are eventually
transported to adjacent coastal waters, from where they gain access to the continental platform and open ocean (Lima et al. 2014) (Figs. 16.7 and 16.8).
Although dissolved oxygen varies with the intensity of mixing and water renewal,
levels of dissolved oxygen are higher in areas near the estuarine mouth, where photosynthesis is not affected by high turbidity next to the river. Nutrient and organic
matter loads increased by anthropogenic effects can cause eutrophication when
aerobic respiration and the oxidation of the organic matter overpass the recovery
capacity of the estuarine system, even in short seasonal periods of little dynamic
(Costa and Barletta 2016). Thus, oxygen depletion creates temporary or permanent
zones of hypoxia and anoxia, negatively influencing the estuarine community due to
physiological stress and reduced faunal diversity leading fishes to seek for other
habitats or even to fish death (Yakushev 2016). An additional problem to oxygen
depletion in the western South Atlantic is a permanent water temperature around
25 °C, reducing the water capacity to dissolve gases. Whereas estuarine ecocline is
a heterogeneous gradient, zones of hypoxia and anoxia can be retained in particular
habitats of the main channel for a period, and then, levels of dissolved oxygen can
increase again due to the complexity of estuarine dynamics at seasonal scales
(Figs. 16.7 and 16.8).
Salinity suspended particulate matter loads and dissolved oxygen levels are all
strong controllers of metal biogeochemistry and bioavailability in estuaries. In the
Goiana Estuary, for example, fish and bivalve when used as bioindicators of the
influence of the estuarine ecocline in total mercury loads, showed that the metals
availability changes with water quality along the estuary and seasons (Costa et al.
2009; Silva-Cavalcanti et al. 2016). For this estuary, mercury contents decreased in
fish tissues during the late rainy season, when increased rainfall might be responsible for biodilution of this contaminant (Barletta et al. 2012) (Figs. 16.7 and 16.8).
Another marine pollution issue that affects estuarine gradients by following its
spatio-temporal changes is plastic pollution, especially microplastics (>5 mm)
(Thompson et al. 2009; Browne et al. 2010; Costa and Barletta 2015) (Fig. 16.10a–
d). The most obvious source of plastic pollution is the inadequate disposal practices
observed along to river basins and coastal areas (Fig. 16.10a–d). Interactions
between plastics and marine biota include entanglement and ingestion, which might
cause from minor physical damage to the death of animals (Costa and Barletta
2016), both already observed in estuaries and coastal environments of the Western
Atlantic (Dantas et al. 2010; Guebert et al. 2013; Wright et al. 2013; Ferreira et al.
2016; Ramos et al. 2016). The fragmentation of large plastics into smaller fragments lead to the reporting of comparable amounts of microplastics and plankton in
habitats of the Goiana Estuary main channel. The salinity gradient, or ecocline, was
found responsible for the distribution pattern of the microplastic fragments by promoting retention of fragments from the river basin in the upper portion, and fragments of marine or local sources (e.g. fishery) in the lower portion when hydrological
conditions were stable (Lima et al. 2014) (Figs. 16.7 and 16.8). During the dry season, the middle estuary is dominated by turbulence and stratification processes that
16 Estuarine Ecoclines and the Associated Fauna: Ecological Information as the Basis…
this way, although somewhat diluted, pollutants become bioavailable for a greater
diversity of flora and fauna over the whole extent of the ecocline, and are eventually
transported to adjacent coastal waters, from where they gain access to the continental platform and open ocean (Lima et al. 2014) (Figs. 16.7 and 16.8).
Although dissolved oxygen varies with the intensity of mixing and water renewal,
levels of dissolved oxygen are higher in areas near the estuarine mouth, where photosynthesis is not affected by high turbidity next to the river. Nutrient and organic
matter loads increased by anthropogenic effects can cause eutrophication when
aerobic respiration and the oxidation of the organic matter overpass the recovery
capacity of the estuarine system, even in short seasonal periods of little dynamic
(Costa and Barletta 2016). Thus, oxygen depletion creates temporary or permanent
zones of hypoxia and anoxia, negatively influencing the estuarine community due to
physiological stress and reduced faunal diversity leading fishes to seek for other
habitats or even to fish death (Yakushev 2016). An additional problem to oxygen
depletion in the western South Atlantic is a permanent water temperature around
25 °C, reducing the water capacity to dissolve gases. Whereas estuarine ecocline is
a heterogeneous gradient, zones of hypoxia and anoxia can be retained in particular
habitats of the main channel for a period, and then, levels of dissolved oxygen can
increase again due to the complexity of estuarine dynamics at seasonal scales
(Figs. 16.7 and 16.8).
Salinity suspended particulate matter loads and dissolved oxygen levels are all
strong controllers of metal biogeochemistry and bioavailability in estuaries. In the
Goiana Estuary, for example, fish and bivalve when used as bioindicators of the
influence of the estuarine ecocline in total mercury loads, showed that the metals
availability changes with water quality along the estuary and seasons (Costa et al.
2009; Silva-Cavalcanti et al. 2016). For this estuary, mercury contents decreased in
fish tissues during the late rainy season, when increased rainfall might be responsible for biodilution of this contaminant (Barletta et al. 2012) (Figs. 16.7 and 16.8).
Another marine pollution issue that affects estuarine gradients by following its
spatio-temporal changes is plastic pollution, especially microplastics (>5 mm)
(Thompson et al. 2009; Browne et al. 2010; Costa and Barletta 2015) (Fig. 16.10a–
d). The most obvious source of plastic pollution is the inadequate disposal practices
observed along to river basins and coastal areas (Fig. 16.10a–d). Interactions
between plastics and marine biota include entanglement and ingestion, which might
cause from minor physical damage to the death of animals (Costa and Barletta
2016), both already observed in estuaries and coastal environments of the Western
Atlantic (Dantas et al. 2010; Guebert et al. 2013; Wright et al. 2013; Ferreira et al.
2016; Ramos et al. 2016). The fragmentation of large plastics into smaller fragments lead to the reporting of comparable amounts of microplastics and plankton in
habitats of the Goiana Estuary main channel. The salinity gradient, or ecocline, was
found responsible for the distribution pattern of the microplastic fragments by promoting retention of fragments from the river basin in the upper portion, and fragments of marine or local sources (e.g. fishery) in the lower portion when hydrological
conditions were stable (Lima et al. 2014) (Figs. 16.7 and 16.8). During the dry season, the middle estuary is dominated by turbulence and stratification processes that
16 Estuarine Ecoclines and the Associated Fauna: Ecological Information as the Basis…