60
Bastiaan Knoppers . Bjorn Kjerfve
year, although usually for only short periods of time. In Araruama 1., cyanobacterial
algal mats proliferate where the depth is shallower than 3 m, but the contribution of
these mats is not included in the total chlorophyll a stock estimate. This is an additional problem in applying simple TS ranking to systems with different autotrophic
populations. Some coastal lagoons may, at the same time, support phytoplankton,
benthic micro- and macro algae, macrophytes, and algal mats (Knoppers 1994). Schaffer
(1988) applied different TS indices to 38 coastal lagoons and lakes in RIO Grande do
SuI. His results corroborate that comparative TS ranking of highly diversified coastal
systems requires that the systems first be grouped according to their physical,
geomorphological, and biogeochemical characteristics.
3.15
Human Impact
Many of the coastal lagoons of the microtidal southeastern coast of Brazil are subject
to human impacts similar to Venice, Ebrie, Nichupte, and Peel-Harvey Lagoons (Sfrizo
et al. 1988, Carmouze and Caumette 1985; Reyes and Merino 1991; Hodgkin and Birch
1986). Shore erosion, local rise of relative sea level, uncontrolled land use and drainage basin fertilization, deforestation, and urban-industrial expansion are of particular concern. Patos 1. is the most prominent lagoon affected by all of these factors, but
fortunately, the large size and storage capacity of the lagoon helps to counteract some
of these human impacts. However, this is not true for the small coastal lagoons of the
state of Rio de Janeiro nor Concei<;:ii.o 1., which are heavily impacted by domestic effluent discharge. Cultural eutrophication represents the primary water-quality problem
in these lagoons. The nutrient loads correspond to those of other estuaries and lagoons subject to moderate cultural eutrophication (Nixon and Pilson 1983), and the
lower N: P ratios of the effluent loads may drive some of the lagoons towards more
severe nitrogen limitation. There is no information to support the concept that N-fixation by cyanobacterial may exert a compensatory effect.
Because of the lack of long-term interannual monitoring of trophic state indicators in all of the lagoons, eutrophication trends may be inferred only by indirect methods. Dystrophic crises, fish kills, excessive algal growth, nuisance odours from decaying organic matter, and the presence of pathogenic microorganisms during warm
summer months are the main manifestations of eutrophication observed in some of
the lagoons of RIO de Janeiro and also in Concei<;:ii.o 1. Some of these may also occur
in the upper part of the Patos 1. Estuary close to Porto Alegre and in the enclosed estuarine Saco da Mangueira near RIo Grande (Persich et al. 1996).
All coastal lagoons along the southeastern coast of Brazil are being menaced by
uncontrolled demographic expansion and increased sewage discharge. Estimates of
augmentation of nutrient load due to population growth, from which to infer trends
of eutrophication, have yet to be established. Moreover, such estimates may harbour
problematic caveats (Golterman and Oude 1991). Independent of this, they are very
difficult to calculate because of systematic lack of collection and documentation of
reliable data by local, state, and federal government agencies in Brazil.
Statistical models based on comparative studies that link nutrient loading to standing stock of materials and hydraulic residence time (Vollenweider 1968) also serve to
infer eutrophication trends. However, such models should not be used to extrapolate
Bastiaan Knoppers . Bjorn Kjerfve
year, although usually for only short periods of time. In Araruama 1., cyanobacterial
algal mats proliferate where the depth is shallower than 3 m, but the contribution of
these mats is not included in the total chlorophyll a stock estimate. This is an additional problem in applying simple TS ranking to systems with different autotrophic
populations. Some coastal lagoons may, at the same time, support phytoplankton,
benthic micro- and macro algae, macrophytes, and algal mats (Knoppers 1994). Schaffer
(1988) applied different TS indices to 38 coastal lagoons and lakes in RIO Grande do
SuI. His results corroborate that comparative TS ranking of highly diversified coastal
systems requires that the systems first be grouped according to their physical,
geomorphological, and biogeochemical characteristics.
3.15
Human Impact
Many of the coastal lagoons of the microtidal southeastern coast of Brazil are subject
to human impacts similar to Venice, Ebrie, Nichupte, and Peel-Harvey Lagoons (Sfrizo
et al. 1988, Carmouze and Caumette 1985; Reyes and Merino 1991; Hodgkin and Birch
1986). Shore erosion, local rise of relative sea level, uncontrolled land use and drainage basin fertilization, deforestation, and urban-industrial expansion are of particular concern. Patos 1. is the most prominent lagoon affected by all of these factors, but
fortunately, the large size and storage capacity of the lagoon helps to counteract some
of these human impacts. However, this is not true for the small coastal lagoons of the
state of Rio de Janeiro nor Concei<;:ii.o 1., which are heavily impacted by domestic effluent discharge. Cultural eutrophication represents the primary water-quality problem
in these lagoons. The nutrient loads correspond to those of other estuaries and lagoons subject to moderate cultural eutrophication (Nixon and Pilson 1983), and the
lower N: P ratios of the effluent loads may drive some of the lagoons towards more
severe nitrogen limitation. There is no information to support the concept that N-fixation by cyanobacterial may exert a compensatory effect.
Because of the lack of long-term interannual monitoring of trophic state indicators in all of the lagoons, eutrophication trends may be inferred only by indirect methods. Dystrophic crises, fish kills, excessive algal growth, nuisance odours from decaying organic matter, and the presence of pathogenic microorganisms during warm
summer months are the main manifestations of eutrophication observed in some of
the lagoons of RIO de Janeiro and also in Concei<;:ii.o 1. Some of these may also occur
in the upper part of the Patos 1. Estuary close to Porto Alegre and in the enclosed estuarine Saco da Mangueira near RIo Grande (Persich et al. 1996).
All coastal lagoons along the southeastern coast of Brazil are being menaced by
uncontrolled demographic expansion and increased sewage discharge. Estimates of
augmentation of nutrient load due to population growth, from which to infer trends
of eutrophication, have yet to be established. Moreover, such estimates may harbour
problematic caveats (Golterman and Oude 1991). Independent of this, they are very
difficult to calculate because of systematic lack of collection and documentation of
reliable data by local, state, and federal government agencies in Brazil.
Statistical models based on comparative studies that link nutrient loading to standing stock of materials and hydraulic residence time (Vollenweider 1968) also serve to
infer eutrophication trends. However, such models should not be used to extrapolate