Rivers and floodplains on the Andean-Amazon interface have been much less studied but are clearly distinct in their hydrological regimes and thus the ecological roles that floodplain inundation plays in these ecosystems. Flooding occurs seasonally in multiple discrete events that control the water regime of floodplains, fish migration, plant phenology, and human activities associated with these processes. Yet at the outset of this research we lacked even a fundamental description of the hydrological features of these river systems, which are lined with vast floodplains. The Napo River is a major Amazon tributary that drains ~105 km2 and flows through the Andean foreland, a sparsely inhabited rainforest region of exceptional biodiversity. The Napo River corridor includes a diversity of floodplain and lacustrine ecosystems, many of which are hydrologically connected to the main stem of the river. Large-scale hydrological modifications have been proposed in the basin, including the Napo barge waterway along the lowland reaches of the river in Ecuador and Peru, the Mazán hydroelectric project near its confluence with the Amazon, and the Coca Codo Sinclair hydroelectric project in the Andean portion of the basin. These works would modify the geomorphology and hydrology of the river channels, and impacts may extend far inland where extensive floodplains exist, as well as far upriver and downstream, with unknown environmental consequences. A comprehensive assessment of the hydrology and ecology of these environments is required to predict and minimize impacts of these kinds of development projects. Thus, with this in mind I set off to improve our understanding of the ecohydrological relationships between the Napo River and its floodplains. To address this goal during nine field campaigns conducted from 2007 to 2013 I used a combination of field observations and water sampling, deployment of sensor networks (including unattended sensors and water collectors), and ground truthing of remotely sensed imagery. Study sites were reached by boat along ~800 km of river reaches in Ecuador and Peru. Floodplains and wetlands were explored on foot with guides from the local communities and a research assistant, during low water when they were accessible. More than 1000 water samples were collected for major solute analysis to determine the water sources (i.e., river overflow vs local rainfall or runoff) of inundation. Observations of the spatial distribution of inundation and associated vegetation were made to aid in interpretation of field and remote sensing data, and flood regimes (hydroperiod, depth of flooding) of more than 100 sites along the river were determined. Among the outcomes of this project are: 1) the development of a method to assess inundation in different environmental settings using the diel amplitude of temperature, 2) the identification of the main sources of flood waters in the floodplains using major solutes, and 3) the determination of the hydrological regimes of the Napo River floodplains using the approaches listed above. Results obtained through this work improved our understanding of the ecohydrology and diversity of tropical floodplains and wetlands, and serve as a basis for future studies on how hydrology determines the structure and composition of tropical floodplain communities and ecosystem processes, and provide information crucial for the assessment of potential negative impacts on these environments caused by proposed river development projects. This study will help natural resource managers and other decision makers set priorities for conservation and develop guidelines and strategies for the wise use of environments in the region.
Read
