Long-term water quality conditions and trends in 12 tropical coastal rivers in Northeast Brazil

• Published in: Environmental monitoring and assessment Vol. 193; no. 5; p. 308
• Main Authors: Noriega, Carlos, Medeiros, Carmen, Araujo, Moacyr, Silva, Andrea Xavier, Costa, Mauricio, Pereira, Newton Antas, de Lima, Eduardo Elvino Sales, da Silva, Deive S. Teixeira, de Campos Pereira, Sonali, Rollnic, Marcelo
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01-05-2021; Springer Nature B.V
• Subjects: Anthropogenic factors; Aquatic environment; Atmospheric Protection/Air Quality Control/Air Pollution; Basins; Biochemical oxygen demand; Brazil; Coliforms; Dissolved oxygen; Earth and Environmental Science; Ecology; Ecotoxicology; Environment; Environmental law; Environmental legislation; Environmental Management; Environmental Monitoring; Environmental science; Faecal coliforms; Fecal coliforms; Household wastes; Industrial wastes; Legislation; Liquid wastes; Monitoring/Environmental Analysis; Nitrogen; Nitrogen - analysis; Oxygen; Phosphorus; Phosphorus - analysis; Population density; Rivers; Saturation; Stations; Total oxygen demand; Trends; Tropical climate; Water Pollutants, Chemical - analysis; Water Quality; Brazil; Temporal series; Tropical rivers; Nutrients; Anthropogenic sources; Natural sources; Water quality
• ISSN: 0167-6369; 1573-2959
• DOI: 10.1007/s10661-021-09074-2

The water quality and trends in 12 tropical rivers in northeastern Brazil over a 27-year period (1990–2016;
N
 = 39,008 samples) were evaluated. The analyzed parameters included temperature, conductivity, pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), nitrogen (NH
4
+
), total phosphorus (P), and fecal coliforms. Densely populated basins (> 1000 inhab km
−2
) presented lower DO values (average 3.4 mg l
−1
; 43% DO saturation), while those with low demographic density (< 100 inhab km
−2
) presented values that aligned well with the recommendations of environmental legislation (average 5.8 mg l
−1
; 75% DO saturation). The NH
4
+
and P compound concentrations were typical of water bodies affected by urban inputs. The average
p
values were above the allowable limit (< 0.1 mg l
−1
) at all stations. The NH
4
+
values were high at the stations showing low DO concentrations, which suggested that due to reducing conditions after NH
4
+
accumulation was favored in those aquatic systems. In densely populated basins, the average fecal coliform concentrations were > 40,000 MPN 100 ml
−1
, indicating the input of improperly treated domestic/industrial liquid wastes. For the period from 1990 to 2016, 45% of the stations (
N
 = 19) showed a rate of DO reduction that ranged from 0.01 to 0.17 mg l
−1
.O
2
year
−1
. An increase in NH
4
+
concentrations was observed in 33% of the stations (
N
 = 14), with an estimated average increase rate from 0.013 to 1.8 mg l
−1
NH
4
+
year
−1
. These results demonstrated that the rates of increase in anthropogenic factors were significant (
p
 < 0.05), while the natural factors remained constant.