Dynamic Interactions Between Groundwater Level and Discharge by Phreatophytes

Many traditional models that predict plant-groundwater use based on groundwater level variations, such as the White method, make various simplifying assumptions. For example, these models often neglect the role of plant hydraulic redistribution, a process that can contribute up to 80% of transpiration. Thus, this work aims to avoid such assumptions and subsequently explore the dynamic interactions between groundwater levels and phreatophytic vegetation, including plant nocturnal transpiration, hydraulic redistribution, and response to atmospheric conditions, in shallow-groundwater ecosystems using Loblolly pine ( Pinus taeda) ) as a model species. The model scenarios are formulated using a stomatal-optimization model coupled to the soil-plant- atmosphere continuum. Flow through soil and groundwater are described using the Richards equation and a linear reservoir approximation, respectively, with groundwater in contact with an external water body of fixed elevation. Results show that nocturnal transpiration, mediated by plant residual conductance, and hydraulic redistribution, are able to reduce groundwater levels at night and alter the groundwater recharge rate. Projected atmospheric conditions of increased carbon dioxide and elevated temperature have opposing effects on groundwater levels, which tend to roughly cancel each other under a projected scenario of 500 ppm carbon dioxide and 1.5( degrees)C warming. Such detailed modeling can be used to provide further insights into coupled interactions between vegetation, climate and groundwater levels in phreatophyte-dominated ecosystems.