Water fluxes and coupled nitrogen export in a managed prealpine grassland: identifying the effects of climate change and agricultural management

It is generally accepted that climate change likely alters the ratio of water balance components in mid-latitude environments. Higher temperatures and an elevated water vapour deficit may increase evapotranspiration rates and reduce groundwater recharge rates. At the same time, agricultural management may interfere these effects, e.g. through reduced plant transpiration rates due to a high cutting frequency.

The study analyses climate change and agricultural management effects on the water fluxes and coupled nitrogen export in a prealpine grassland. It makes use of the grassland lysimeters, which are part of the TERENO preAlpine observatory in southern Bavaria (Germany). In a “space-for-time” approach, soil cores with an area of 1 m² and a depth of 1.5 m have been excavated and translocated to lower elevations. Furthermore, soil cores from the same area (that have not been translocated to lower elevations) act as control plots in the lysimeter network. The elevation gradient between the highest (864 m a.s.l.) and lowest (695 m a.s.l.) lysimeter station accounts for a temperature increase of approx. 2°C, while precipitation decreases from approx. 1350 mm a^-1 to approx. 960 mm a^-1. Following local agricultural practice, intensive as well as extensive grassland management is applied at the lysimeters: intensive management refers to a higher frequency of cutting (up to five times per year) and manure application (approx.. 250 kg N ha^-1 a^-1) than extensive management (two cuts and approx. 80 kg N ha^-1 a^-1).

The study compares the effects of temperature and precipitation changes (i.e. elevated temperature and decrease in precipitation) and different agricultural management on water balance components (evapotranspiration, groundwater recharge, Ammonia and Nitrate fluxes) measured at the lysimeters. Preliminary result show that the ratio of evapotranspiration to precipitation increases in the climate change treatment. Water-bound nitrogen fluxes are comparably low on all sites, indicating that nitrogen uptake by plant plants is dominating over nitrogen leaching.