Energy and water balance response of a vegetated wetland to herbicide treatment of invasive Phragmites australis

Abstract

The energy and water balance of a Phragmites australis dominated wetland in south central Nebraska was analyzed to assess consumptive water use and the potential for "water savings" as a result of vegetation eradication via herbicide treatment. Energy balance measurements were made at the field site for two growing seasons (treated and untreated), including observations of net radiation, heat storage, and sensible heat flux, which was measured using a large-aperture scintillometer. Latent heat flux was calculated as a residual of the energy balance, and comparisons were made between the two growing seasons and with model simulations to examine the relative impacts of vegetation removal and climate variability. Observed ET rates dropped by roughly 32% between the two growing seasons, from a mean of 4.4 ± 0.7 mm day-1 in 2009 (with live vegetation) to 3.0 ± 0.8 mm day-1 in 2010 (with dead P. australis). These results are corroborated by the Agro-IBIS model simulations, and the reduction in ET implies a total "water savings" of 245 mm over the course of the growing season. The significant decreases in ET were accompanied by a more-than-doubling of sensible heat flux, as well as a ~60% increase in heat storage due to decreased LAI. Removal of P. australis was also found to cause measurable changes in the local micrometeorology at the wetland. Consistent with the observed increase in sensible heat flux during 2010, warmer, drier, windier conditions were observed in the dead, P. australis section of the wetland, compared to an undisturbed section of live, native vegetation. Modeling results suggest that the elimination of transpiration in 2010 was partially offset by an increase in surface evaporation, thereby reducing the subsequent water savings by roughly 60%. Thus, the impact of vegetation removal depends on the local climate, depth to groundwater, and management decisions related to regrowth of vegetation.

Tree‐ring stable isotopes show different ecophysiological strategies in native and invasive woody species of a semiarid riparian ecosystem in the Great Plains of the United States

“…This fluctuation affects riparian vegetation, often at the expense of historically native species (Mortenson & Weisberg, 2010;Mykleby et al, 2016;Richardson et al, 2007;Rood et al, 2007), as we have demonstrated. This fluctuation affects riparian vegetation, often at the expense of historically native species (Mortenson & Weisberg, 2010;Mykleby et al, 2016;Richardson et al, 2007;Rood et al, 2007), as we have demonstrated.…”

“…Over the past century, riparian ecosystems across the United States have experienced drier conditions due to climatic fluctuation, streamflow regulation, vegetation cover change, agricultural practices, or a combination thereof (Huddle et al, 2011;Mykleby et al, 2016).…”

“…The Republican River is part of a larger watershed that extends across the states of Colorado, Nebraska, and Kansas. Nebraska has faced legal difficulties in recent decades as declining streamflow in the Republican River inhibits its ability to meet its commitments to Kansas (Mykleby et al, 2016). The basin was hit particularly hard by the severe Dust Bowl droughts during the 1930s, which led to the creation of the Republican River Compact in 1943.…”

“…The basin was hit particularly hard by the severe Dust Bowl droughts during the 1930s, which led to the creation of the Republican River Compact in 1943. The Compact regulates and oversees the apportion of specific percentages of stream water in the Republican River basin among the three states (Mykleby et al, 2016). Nebraska has faced legal difficulties in recent decades as declining streamflow in the Republican River inhibits its ability to meet its commitments to Kansas (Mykleby et al, 2016).…”

“…Improving our understanding of how invasive species interact and respond to changes in the environment, particularly changes in climate and hydrology, can enhance management practices in riparian areas (Margolis, Meko, & Touchan, 2011;Msanne et al, 2017;Mykleby et al, 2016;Rood et al, 2007;Tene et al, 2011). The use of tree-ring methods for ecological purposes, that is, dendroecology, provides the tools to study tree responses to localized biotic and abiotic environment.…”