Groundwater transpiration of a salt steppic oak forest in the extreme dryness of 2022

Abstract

Groundwater use of a lowland forest is especially important from the point of view forest ecosystem survival as drought periods become more severe, and the groundwater is going deeper in the Great Hungarian Plain. Diurnal methods using high frequency water table data are more and more popular nowadays to quantify groundwater consumption of groundwater dependent ecosystems. Riparian forest ecosystems were typical natural vegetation form alongside Great Hungarian Plain Rivers. These ecosystems were supplied by the river inundation of the river. Nowadays these forests are very rare and generally groundwater dependent. A representative of the rest of this ecosystem is a salt steppic oak forest in Ohat, on the edge of Hortobágy. Maps from the 18. century proof, that this area was continuously covered by forests before the great levee-building and water-regulation of Hungary, which drained the significant part of the Hungarian Great Plain.The hydrological year of 2021-2022 is particularly interesting in terms of water uptake analysis because of its extreme dryness and heat.Two groundwater wells settled in this research area and were instrumented by pressure transducers. The groundwater time series shows strong diurnal water table fluctuations, which we used for the calculation of oak forest groundwater transpiration. We found significant relationshipForest groundwater transpiration was significant at the first part of the growing season despite the relatively deep water table. When the water table sank to a depth of 4.7-4.8 m transpiration from the groundwater reduced very significantly. The relationship between water table depth and groundwater transpiration is significantly different when comparing the years 2021 and 2022. Results showed that drought caused lowering of the water table poses a threat to the groundwater dependent forest ecosystem.This article was made in frame of the project TKP2021-NKTA-43 which has been implemented with the support provided by the Ministry of Innovation and Technology of Hungary (successor: Ministry of Culture and Innovation of Hungary) from the National Research, Development and Innovation Fund, financed under the TKP2021-NKTA funding scheme.