TABLE 2
Physical-chemical variables in Araguari River - Maré Channels - Amazonas
River recorded significant differences, mainly during the dry season
(reduced dilution capacity) (Abreu et al., 2020), with emphasis on
variables associated with increased solids contents in lotic aquatic
ecosystems, namely: EC, TDS, Turbidity, SSC and
Transparency (Tables 2 and 3).
However, based on the spatial factor, EC and TDS recorded significant
variation between both seasons in all sites – it was relatively smaller
in ARA1. Turbidity has followed the same variation trend. Such a
variation was smaller at URU2, which recorded high turbidity levels in
both seasons - 328 (NTU) during the dry period and 313 (NTU) during the
rainy season. Similar behavior was recorded for associated parameters
(SSC and Transparency) at URU2 station (Table 3).
TABLE 3
Salinity was higher at URU1 and URU2 – it presented greater seasonal
than spatial variation (Tables 2 and 3). Maximum salt concentration
found in URU2 was 0.05 ppt and 0.04 ppt in URU1, during the dry season.
This behavior was also observed by Cunha and Sternberg (2018) in
Northern Igarapé Tabaco during the dry season in 2015, when maximum salt
concentration reached approximately 0.08 ppt. High TDS and EC values
were correlated to salinity during the dry season.
DO recorded low concentrations during the rainy season (Tables 1, 2 and
3). However, mean DO has remained higher than 5 mgL-1,
based on the limit established by CONAMA Resolution n. 357/2005 (Brazil
2005). Nevertheless, critical points have shown means lower than, or
remarkably close to, this limit (5.0 mgL-1) during the
rainy season. Urucurituba Channel has shown minimum values of
approximately 3.71 mgL-1 at the mouth (URU 2) and 4.66
mgL-1 close to the confluence with Araguari River
(URU1) during the rainy season. Mean DO concentration at Gurijuba River
mouth (GUR) reached 5.0 mgL-1 during the dry season,
whereas Araguari River, just upstream Urucurituba Channel (ARA2),
presented mean DO of 5.1 mgL-1 during the rainy season
(Table 3).
Water pH was slightly acid during the rainy season, if one takes into
consideration that the acceptable range for this parameter is 6.0 ≤ pH ≤
9.0 for class II rivers (Brasil 2005). However, all stations recorded pH
lower than 6.0 during this period - Araguari River (ARA1) and Igarapé
Novo recorded the lowest values – mean pH was 4.9. On the other hand,
water pH during the dry season was approximately 6.0 and temperature was
higher than 29°C (Table 3).
Spatial variation in water quality was also significant (Tables 1 and
3), except for water and air temperature (Tw and
Tair), which tended to show homogeneity in the
investigated geographical area. Similar results were observed by Cunha
and Sternberg (2018) along lakes distributed on the estuarine coast of
Amapá State. Temperature homogeneity was observed in all stations and in
the two seasons. However, it presented significant variations during the
tidal phases (p < 0.05) (Table 1).
Distances between monitoring sites and the Amazon River recorded
significant differences, which suggested influence of water connectivity
and water quality variables, except for water and air temperatures (p
> 0.05) (Table 1).