Print PageMontane Neotropical streams harbor unique aquatic biodiversity and play a critical ecological role at the river basin scale, while draining landscapes increasingly being altered by human activities. Montane Neotropical streams often have high concentrations of endemic species and provide spawning areas or habitat for migratory biota. Ecological processes occurring in these streams strongly influence the geomorphology, biogeochemistry, and ecology of downstream areas. The hydrologic connectivity between montane Neotropical streams and downstream areas is increasingly being disrupted by new hydropower dams. While the ecological consequences of these dams have received some study, there is also a need to consider their effects within the context of additional factors that can alter hydrologic connectivity, such as water withdrawals and climate change.
Results/Conclusions
We focus here on three different regions that provide insight into the challenges and opportunities for maintaining hydrologic connectivity in montane Neotropical streams. Puerto Rico has one of the highest human population densities in the world, and dams for hydropower and water supply have disrupted hydrologic connectivity of many of the island’s streams. Dams have resulted in the complete extirpation of all native migratory shrimp and fish species from ~27% of streams draining the island. In the absence of native shrimps (which influence rates of decomposition and other ecosystem processes) there are numerous cascading effects, including higher levels of algal standing crop, decreased rates of leaf decomposition, altered nutrient dynamics, and increased vulnerability to invasive species. Maintaining hydrologic connectivity by providing just a small amount of spillway discharge over dams can allow native shrimps to recolonize areas from which they have been extirpated. In Costa Rica, a wave of hydropower dam construction (and associated water withdrawals) in the past two decades has fragmented streams along the country’s northern Caribbean slope and affected fish distribution. Design of dams and management of downstream flows may help reduce losses in hydrologic connectivity and maintain habitat for a subset of aquatic species. In the tropical Andes, many montane streams are subjected to extensive water withdrawals for agricultural and urban water supply. Additionally, hundreds of new hydropower dams are being considered for the region and climate change is likely to alter future flow patterns in tropical Andean rivers. In some landscapes, protected areas and special conservation designations for streams may offer opportunity to maintain hydrologic connectivity along elevational and longitudinal gradients.
