MEASURING THE IMPACT OF INVASIVE JAPANESE KNOTWEED ON STREAM DISCHARGE IN NEW JERSEY

The global supply of freshwater is quickly becoming a limited resource. This is due to increased human demand, decreased supply, and global climate change. Invasive plants are adept at taking advantage of changes in the environment and pose a risk to our freshwater supplies. Unfortunately, most studies of the impacts of invasive plants on water supply have focused on arid and, within the United States, southerly regions; perhaps because of a perception that water is in ample supply in mesic and northern United States regions. However, there is increasing evidence that even in these areas water is becoming limited and certainly there is evidence of major invasive plant encroachment. One such invader is Japanese knotweed, which has been identified as a problem plant in New York and New Jersey, USA. In order to better understand the impact of invasive plant growth on local water supply in this area, we conducted two pilot studies. In the first one, we monitored stream discharge over a four-month period during which we measured total water loss from a stand of knotweed for the first stage of the project. During the second stage the plants were removed to assess the direct impact on stream flow. In the second study, we grew knotweed plants in a greenhouse and studied water transport properties and leaf physiology. In combination, our studies show that Japanese knotweed has the capacity to extract large amounts of water over a small area and that it has the physiological capacity to acclimate to decreasing soil moisture content such that it always can extract water from the soil. In combination, these properties of the plant suggest that it could have a significant impact on local freshwater supplies.