Hydrological impacts of biological invasions.
The quantity and distribution of freshwater are fundamental to many ecosystem services, including water supply, flood attenuation, habitat provision, electricity generation, navigation, and recreation. Non-native plants and animals can degrade hydrological functions through their physiology, morphology, behaviour, and interactions with other species, which can be compounded when non-native species are ecosystem engineers or transformers. Using the hydrological cycle and drawing on key global examples, this chapter outlines seven main ways in which non-native species can disrupt hydrological services and how these impacts can be managed. Non-native plants may alter local and regional climates by modifying land-atmosphere transfers of heat and moisture, surface roughness and albedo, and concentrations of aerosol particles. Differences in native and non-native water use can alter catchment runoff (usually reducing water yield), especially when non-native vegetation covers extensive areas (e.g., mesquite and eucalypts). Non-native plant invasion may alter the seasonal availability of water because of differences in the timing and duration of water use (e.g., deciduous natives vs. evergreen invaders). Non-native animals and plants can change ground surface and soil characteristics, altering surface and subsurface flows, infiltration rates, and water residence times (e.g., earthworms and beavers). Species that invade wetlands, lakes, and rivers can trap sediment, narrowing flow channels and reducing flood attenuation (e.g., tamarisk, Sagittaria, mimosa). Some plant growth forms and animal behaviours can cause channel collapse, increase sediment erosion, and alter flow paths (e.g., willows, coypu). Non-native species can modify water passage and flow velocities by altering geomorphology and hydraulics (e.g., Salvinia, zebra mussels). Invasive species management remains difficult because of feasibility and conflicting values of species (e.g., ecology versus economy, upstream versus downstream effects). An ecosystem services framework may help reconcile the differential impacts that non-native species have in time, space, and on the delivery of various services.