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 (NH₄⁺), 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 NH₄⁺ 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 NH₄⁺ values were high at the stations showing low DO concentrations, which suggested that due to reducing conditions after NH₄⁺ 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.O₂ year⁻¹. An increase in NH₄⁺ 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 NH₄⁺ year⁻¹. These results demonstrated that the rates of increase in anthropogenic factors were significant (p < 0.05), while the natural factors remained constant.

在27年内（ 1990-2016年；N = 39,008个样本），对巴西东北部的12条热带河流的水质和趋势进行了评估。分析的参数包括温度，电导率，pH，溶解氧（DO），生化需氧量（BOD），氮（NH ₄ ⁺），总磷（P）和粪大肠菌。人口稠密的盆地（> 1000 inhab km ^-2）呈现出较低的DO值（平均3.4 mg l ^-1； DO饱和度为43％），而人口密度低的盆地（<100 inhab km ^-2）呈现出与DO值高度一致的值。环境立法建议（平均5.8 mg l ^-1； DO饱和度为75％）。NH ₄ ⁺P和P化合物的浓度是受城市输入影响的水体的典型特征。所有站的平均p值均高于允许极限（<0.1 mg l ^-1）。在低溶解氧浓度的站点，NH ₄ ⁺值较高，这表明由于NH ₄ ⁺累积后的条件减少，这些水生系统受到青睐。在人口稠密的盆地中，粪便中大肠菌群的平均浓度> 40,000 MPN 100 ml ^-1，表明输入了未经适当处理的家庭/工业废液。在1990年至2016年期间，有45％的台站（N  = 19）的DO降低率介于0.01至0.17 mg l^-1 .O ₂年^-1。在33％的监测站（N  = 14）中观察到NH ₄ ⁺浓度增加，估计的平均增长率从0.013增至1.8 mg l ^-1 NH ₄ ⁺年^-1。这些结果表明，人为因素的增加速度是显着的（p  <0.05），而自然因素则保持不变。