Water use potential and salt tolerance of riparian species in saline-sodic environments
Sessoms, Holly Nicol
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Salinization of soil and water resources exists on a global scale, largely due to irrigated agriculture in semi-arid climates. Coal bed methane (CBM) development, resulting in the co-production of saline-sodic discharge water, is a potential new source of salinzation in the Powder River Basin of Montana and Wyoming. Constructed wetlands may serve to reduce CBM product water volumes while applying saline-sodic product water to a beneficial use. The objective of this study was to assess the potential of constructed wetlands as a new management tool for CBM product water management. To accomplish this, riparian species native to Montana and Wyoming and classified as halophytes were selected as experimental treatments. Species chosen were subjected to saline-sodic conditions designed to mimic CBM product water for a 24-week period and harvested once every 8 weeks. Water use rates, water chemistry, biomass production, forage value, and salinity tolerance of each species were monitored throughout the experimental period. Due to turbulent airflow and high diffusion rates of water vapor from the plant canopy, plant water use rates of mature plants exceeded reference evaporation rates over a range of salinities for most species. For high water use species, ratios between plant water use rates and reference evaporation exceeded 3.00 at lower salinities. High ratios between plant water use and reference evaporation indicate that reference evaporation buckets were not subjected to the same evaporative conditions as the plant canopy, and may not represent potential evapotranspiration. Biomass production of traditional wetland species declined following defoliation and under increasing salinity. Grass species increased biomass production following defoliation and under elevated salinity in the third growth period. Crude protein (CP) also decreased with progressive harvests for wetland species, but increased in the third period for grass species. Based on percent acid detergent fiber and CP, forage value of most species is equal to or greater than average grass hay forage value. Results suggest that wetlands constructed of species analyzed will thrive in salinesodic conditions, and will outperform or perform similarly to evaporation ponds for CBM product water disposal while providing a forage resource and beneficial use.