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Hydrological consequences of declining land use and elevated CO 2 in alpine grassland
Author(s) -
Inauen Nicole,
Körner Christian,
Hiltbrunner Erika
Publication year - 2013
Publication title -
journal of ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.452
H-Index - 181
eISSN - 1365-2745
pISSN - 0022-0477
DOI - 10.1111/1365-2745.12029
Subject(s) - grassland , environmental science , evapotranspiration , growing season , agronomy , biomass (ecology) , transpiration , grazing , water content , lysimeter , leaf area index , precipitation , water balance , soil water , hydrology (agriculture) , ecology , soil science , biology , geography , botany , photosynthesis , geology , geotechnical engineering , meteorology
Summary Large areas of alpine pastures and meadows currently face declining land use or abandonment, which leads to tall‐grass transition ecosystems with higher leaf area index ( LAI ), potentially increased evapotranspiration ( ET ) and thus, reduced water yield. Elevated atmospheric CO 2 , on the other hand, is known to reduce stomata opening and hence, leaf‐level transpiration, which may translate into higher soil moisture and enhanced total runoff. Here, we quantify these opposing effects of global change on the water balance of alpine grassland in a field experiment in the S wiss A lps (2440 m a.s.l.). Rates of ET and deep seepage (percolation water) of four alpine grassland types (dominated by A grostis, N ardus, C arex or forbs) were measured using intact monoliths in 51 weighing lysimeters. A part of the monoliths was clipped to simulate sheep grazing during three seasons (2008–2010). Another set was exposed to elevated CO 2 (580 ppm) using free‐air CO 2 enrichment ( FACE ) during the 2009 growing season. Simulated grazing reduced bright day ET by on average −12% across all years, with the most pronounced effects in the high‐stature swards. Correspondingly, the higher biomass and LAI in unclipped grassland lowered the seasonal sum of deep seepage by −13% in a drier summer (2009) and by −5% in a rather wet summer (2010) compared to clipped swards. CO 2 enrichment reduced ET in all grassland types by −3 to −7%, increased δ 18 O in foliage and enhanced soil moisture, but not deep seepage. Hence, future CO 2 slightly counteracts the land use effects at canopy level, however, not in terms of water yield. Synthesis . Our results indicate that both grazing and elevated CO 2 are mitigating the effects of dry spells on alpine vegetation. The net effect of the continuous decline in the land use and of elevated CO 2 is negative for catchment water yield and thus, for potential hydroelectric power production. Although these economic ‘costs’ are rather moderate per hectare of alpine grassland, sums are substantial when scaled to the vast areas potentially affected in the Alps. These calculated ‘costs’ attribute economic value to the eco‐hydrological benefits of land care at these high elevations.