Rivers of the Northern Pacific

The Pacific slope of South America’s Northwest Tropical Andes region encompasses the area from Cape Punta Ardita in Colombia (7°N) to the southern Pacific coast of Ecuador (3°S). The volcanic activity in this part of the Andes is one of the most important features that contributes to a myriad of soils, vegetation, and ecosystems found in this drainage. Rivers of the Northwest Pacific are relatively short (180 to 385km) and cover high elevation ranges, up to 6263ma.s.l. in short distances. The basins have páramo ecosystems in the upper parts, followed by montane, rainforest, and estuarine systems in the lower parts. The San Juan is the largest river by water volume in the whole South American Pacific. The diversity and endemism of fish and invertebrates in these basins are high with several endangered reptiles, amphibians, and bird species. There is limited information available on the biodiversity and ecological status of aquatic plants, algae, and other microorganisms at the basin level. Basins in the North Pacific of Colombia are small and well preserved with more than 50% of the natural vegetation still present due to the complex topography and low access. However, gold mining and mercury pollution are a concern in these basins. Comparatively, most basins in the Pacific of Ecuador are larger and have been impacted by human activities since the 1800s, with agricultural production contributing 60% of the GDP. Naturally, stream water in these basins has low nutrient and major anion concentrations. The low degree of wastewater treatment contributed to the severe degradation of rivers, especially around major cities like Quito and Guayaquil, which are located inside the Esmeraldas and Guayas basins in this versant.