Effects of two categorically differing emergent wetland plants on evapotranspiration

Abstract

Although wetlands are an important component of many landscapes, emergent plants have had variable impacts on wetland hydrology. In the present study, similar to what others have done with emergent plants, we investigated the impacts of black willow (Salix nigra Marshall) and Pennsylvania smartweed (Persicaria pensylvanica L.) on water loss from standing water relative to water loss with no emergent plants from 2018 to 2020. Pans were established with soil and standing water for three replications of five treatments: open water control, low population density black willow, high density black willow, low density smartweed, and high density smartweed. Each week during the growing season water levels, water temperature, leaf area index, and height were recorded. Pans were then refilled to the standard level. The assumption was that open water was just evaporation and the increase in water loss in the presence of plants was due to transpiration. Thus, we could partition water loss between evaporation and transpiration by calculating the difference between pans without plants and pans with plants. This difference is the transpiration by the plants. Water temperature was measured to check on any possible shading effect. Open water evaporation was lower than black willow and smartweed evapotranspiration. Mean increases in water use relative to the control were 37% for smartweed and 66% for black willow. These differences were even more dramatic when calculated for only the last 2 years. Smartweed increased water use by 40% and black willow by 92%. Because pans with plants had lower maximum daily water temperatures than those of the control in the summer, the increased water loss with plants was largely due to transpiration. Smartweed transpired more than willows. The willow root system and leaf area greatly increased after the first year, resulting in more water loss and lower summer water temperature. Low and high density treatments did not differ significantly Abbreviations: BWH, black willow planted at high density; BWL, black willow planted at low density; ET, evapotranspiration; ETo, maximum potential ET; FIPAR, fraction of intercepted photosynthetically active radiation; k, light extinction coefficient; Kc, crop coefficient; LAI, leaf area index; PAR, photosynthetically active radiation; PET, potential evapotranspiration; SWH, smartweed planted at high density; SWL, smartweed planted at low density.

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“…Some studies report (Roulet N.T and Woo M.K.,1986) this equality for a low arctic site, and a review of swamps/bogs (Linacre E.T.,1976) transpiration concluded rough equality with lakes is probably the most reasonable assumption. Studies by Jiménez-Rodríguez et al, 2019;Bois et al, 2021 andKiniry, 2023) have indicated that when comparing with open water evaporation, the plant type is important as some promote higher evapotranspiration than open water evaporation and some are equivalent.…”