The effects of tree establishment on water and salt dynamics in naturally salt-affected grasslands

Abstract

Plants, by influencing water fluxes across the ecosystem-vadose zone-aquifer continuum, can leave an imprint on salt accumulation and distribution patterns. We explored how the conversion of native grasslands to oak plantations affected the abundance and distribution of salts on soils and groundwater through changes in the water balance in naturally salt-affected landscapes of Hortobagy (Hungary), a region where artificial drainage performed approximately 150 years ago lowered the water table (from -2 to -5 m) decoupling it from the surface ecosystem. Paired soil sampling and detailed soil conductivity transects revealed consistently different salt distribution patterns between grasslands and plantations, with shallow salinity losses and deep salinity gains accompanying tree establishment. Salts accumulated in the upper soil layers during pre-drainage times have remained in drained grasslands but have been flushed away under tree plantations (65 and 83% loss of chloride and sodium, respectively, in the 0 to -0.5 m depth range) as a result of a five- to 25-fold increase in infiltration rates detected under plantations. At greater depth, closer to the current water table level, the salt balance was reversed, with tree plantations gaining 2.5 kg sodium chloride m(-2) down to 6 m depth, resulting from groundwater uptake and salt exclusion by tree roots in the capillary fringe. Diurnal water table fluctuations, detected in a plantation stand but not in the neighbouring grasslands, together with salt mass balances suggest that trees consumed approximately 380 mm groundwater per year, re-establishing the discharge regime and leading to higher salt accumulation rates than those interrupted by regional drainage practices more than a century ago. The strong influences of vegetation changes on water dynamics can have cascading consequences on salt accumulation and distribution, and a broad ecohydrological perspective that explicitly considers vegetation-groundwater links is needed to anticipate and manage them.

Groundwater-dependent ecosystems: recent insights from satellite and field-based studies

“…This approach has been successfully applied in the Okavango Delta in Botswana (Bauer et al, 2004), an upland grassland catchment in central Argentina (Engel et al, 2005), an oak/grassland site on the Great Hungarian Plain of eastern Hungary (Nosetto et al, 2007), the Sopron Hills of western Hungary (Gribovszki et al, 2008), the Gobi desert of northwestern China (Wang et al, 2014), and various sites in the USA (Butler et al, 2007;Lautz et al, 2008;Martinet et al, 2009). The White method tends to over-estimate ET g (Loheide et al, 2005;Martinet et al, 2009).…”

Evaluating plant community response to sea level rise and anthropogenic drying: Can life stage and competitive ability be used as indicators in guiding conservation actions?

“…Florida's coastal communities have been changing from SLR since the end of the last glacial maximum; however, reduction of freshwater flow and increasing rates in SLR have substantially increased the modern rate of change found in the past century 4,7,[15][16][17][18][19][20][21]51 .…”

“…The competitive effect adds a biological component to the potential causes of community change (Nosetto et al, 2007). The effect of salt on plants, communities, and halophyte:glycophyte habitat competition is well established Ungar, 1998;Armas et al, 2010); however, there are conflicting results on the influence plants have on soil salinity.…”

“…Recent, studies assessed the ability of halophytes and other plant types to desalinize soil via phytoremediation (Qadir et al, 2003(Qadir et al, , 2007Van Oosten and Maggio, 2015). Conversely, other studies have shown that conversion of land into different habitat types can lead to higher, more saline water tables and saltier soils than what was there prior to land conversion (Nosetto et al, 2007;Jayawickreme et al, 2011). As SLR impacts coastal communities salinizing the groundwater and soil, it becomes important to understand how halophytes affect soil salinity under saline groundwater conditions (Van Oosten and Maggio, 2015).…”

“…Shifts in coastal plant composition have been documented along the Florida coast since before the early 1950's 4,7,[14][15][16][17][18][19][20][21] . Saltwater-loving communities have been found moving into freshwater wetlands and uplands 17,20,21 . Since the early 1980's, restoration efforts have attempted to counteract the effects of drainage.…”