Nitrogen Leaching of Two Forest Ecosystems in a Karst Watershed

Abstract

Karst watersheds are a major source of drinking water in the European Alps. These watersheds exhibit quick response times and low residence times, which might make karst aquifers more vulnerable to elevated nitrogen (N) deposition than nonkarst watersheds. We summarize 13 years of monitoring NO 3 − , NH 4 + , and total N in two forest ecosystems, a Norway spruce (Picea abies (L.) Karst.) forest on Cambisols/Stagnosols (IP I) and a mixed beech (Fagus sylvatica L.) spruce forest on Leptosols (IP II). N fluxes are calculated by multiplying concentrations, measured in biweekly intervals, with hydrological fluxes predicted from a hydrological model. The total N deposition in the throughfall amounts to 26.8 and 21.1 kg/ha/year in IP I and IP II, respectively, which is high compared to depositions found in other European forest ecosystems. While the shallow Leptosols at IP II accumulated on average 9.2 kg/ha/year of N between 1999 and 2006, the N budgets of the Cambisols/Stagnosols at IP I were equaled over the study period but show high inter-annual variation. Between 1999 and 2006, on average, 9 kg/ha/year of DON and 20 kg/ha/year of DIN were output with seepage water of IP I but only 4.5 kg/ha/year of DON and 7.7 kg/ha/year of DIN at IP II. Despite high DIN leaching, neither IP I nor IP II showed further signs of N saturation in their organic layer C/N ratios, N mineralization, or leaf N content. The N budget over all years was dominated by a few extreme output events. Nitrate leaching rates at both forest ecosystems correlated the most with years of above average snow accumulation (but only for IP I this correlation is statistically significant). Both snow melt and total annual precipitation were most important drivers of DON leaching. IP I and IP II showed comparable temporal patterns of both concentrations and flux rates but exhibited differences in magnitudes: DON, NO 3 − , and NH 4 + inputs peak in spring, NH 4 + showed an additional peak in autumn; the bulk of the annual NO 3 − and DON output occurred in spring; DON, NO 3 − , and NH 4 + output rates during winter months were low. The high DIN leaching at IP I was related to snow cover effects on N mineralization and soil hydrology. From the year 2004 onwards, disproportional NO 3 − leaching occurred at both plots. This was possibly caused by the exceptionally dry year 2003 and a small-scale bark beetle infestation (at IP I), in addition to snow cover effects. This study shows that both forest ecosystems Water Air Soil Pollut (2011) 218:633-649

Model-aided quantification of dissolved carbon and nitrogen release after windthrow disturbance in an Austrian karst system

“…The high values of the epikarst variability constant and the groundwater constant indicate a low development of preferential flow paths in the rock, which is typical for dolomite aquifers (Ford and Williams, 2007). A low degree of karstification was already known for our study site (Jost et al, 2010) and the calibrated recharge areas fall well within the ranges found in previous modelling studies (Hartmann et al, 2012a(Hartmann et al, , 2013c.…”

“…Though nitrate pollution of drinking water is usually attributed to fertilization of crops and grassland, an excess input of atmospheric nitrogen (N) from industry, traffic and agriculture into forests has caused reasonable nitrate losses from forest areas Erisman and Vries, 2000;Gundersen et al, 2006;. The Northern Limestone Alps area is exposed to particularly high nitrogen deposition (Rogora et al, 2006) and nitrate leaching occurs at increased rates (Jost et al, 2010). In addition to this, forest disturbances such as windthrow and insect outbreaks disrupt the N cycle and cause pronounced nitrate losses from the soils, at least in N-saturated systems that received elevated N deposition due to elevated NOx in the atmosphere (Bernal et al, 2012;Griffin et al, 2011;Huber, 2005).…”

“…While many studies identify N and DOC as source of contamination in karst systems (Einsiedl et al, 2005;Jost et al, 2010;Katz et al, 2001Katz et al, , 2004Tissier et al, 2013) or provide static vulnerability maps (Andreo et al, 2008;Doerfliger et al, 1999), only very few studies use models to quantify the temporal behaviour of a contamination through the systems (Butscher and Huggenberger, 2008). Some studies use N and DOC to better understand karst processes (Charlier et al, 2012;Mahler and Garner, 2009;Pinault et al, 2001) or for advanced karst model calibration (Hartmann et al, 2013b(Hartmann et al, , 2014b, but to our knowledge there are no applications of such approaches to quantify the drainage processes of N and DOC, and particularly so after strong impacts on ecosystems (e.g.…”

“…The mean N deposition in bulk precipitation between 1993 and 2006 was 18.7 kg N ha −1 yr −1 , out of which 15.3 kg N (82 %) was inorganic (approximately half as NO Jost et al, 2010). Due to the dominance of dolomite, the catchment is not as heavily karstified as limestone karst systems, but shows typical karst features such as conduits and sink holes (Jost et al, 2010). The site can be split into steep slopes (30-70 • , 550-850 m a.s.l.)…”

Métodos e técnicas de pesquisa em bacias hidrográficas

“…O aumento dos nutrientes (NH 4 + e NOD) após a passagem pelo dossel e consequente aumento no rio pode ser explicado pela dissolução na água da chuva de compostos depositados através da lixiviação das copas das árvores (PARKER, 1983;LEITE et al, 2011;JOST et al, 2011;HOFHANSL et al, 2012).…”