1 CREAF, Campus Universitat Autònoma de Barcelona, E08193 (Cerdanyola del Vallès), Catalonia, Spain
Keywords: terrestrial ecology, forest ecosystem functioning, long-term trends, streamwater chemistry, atmospheric deposition, Mediterranean catchment, holm oak, Quercus ilex , Montseny, La Castanya
Introduction and antecedents
Hydrological and biogeochemical studies in the Montseny holm oak (Quercus ilex ) forests started in 1978 with funding from a Hispano-American project that allowed the onset of terrestrial ecology studies in Spain. Later funding was provided by a suite of projects from the Spanish Government and the European Commission. This research followed the small catchment approach developed at Hubbard Brook (Bormann et al. 1979) and, sustained over several decades, has been instrumental in showing the responsiveness of forested ecosystems to atmospheric deposition changes (Avila and Rodà 2012; Bernal et al. 2013; Avila et al. 2020) and the uniqueness of stream N response to deposition in Mediterranean forests as compared to temperate forests (Templer et al. 2022). The effects of forest management on (1) stream chemistry has been modelled (Neal et al. 1995) and that of climate change on stream chemistry (Avila et al. 1996) and on the habitat suitability for an endangered amphibian species as well (Ledesma et al. 2019). Mineral dust, originated in North Africa (Avila et al. 2007) has been shown to be an important contributor of nutrients and alkalinity to these forest ecosystems (Avila et al. 1997, 1998). Further research and new hypothesis testing may take advance of the collected data series in these long-term study sites. This is the motivation for the publication of the quality-checked original stream and atmospheric deposition chemistry files of well curated small catchments at Montseny whose links accompany this paper.
Site description
Two catchments, named TM9 and TM0, were instrumented in La Castanya valley (Montseny mountains; 41,774853 °N / 2,351109 °E) in the early 1980s within a broad-scope study on forest ecosystem functioning (Rodà et al. 1999). A gauging station was built at each site, consisting of a stilling pond and a V-notch weir. At TM0 the V-notch had a 120° angle, while the smaller TM9 weir had a 60° opening.
La Castanya valley is 40 km to the NNE of Barcelona and 27 km from the Mediterranean coast. Climate is subhumid mesomediterranean: annual precipitation is around 900 mm with a typical summer drought, but interannual variability is very high. The bedrock is a metamorphic phyllite, with quartz, chlorite, albite and muscovite as major minerals. Two catchments were instrumented in Torrent de la Mina stream, a major stream draining La Castanya valley: TM0, the main catchment and TM9, a small tributary (Fig. 1, Table 1). Relief is steep and there are some rock outcrops in the upper slopes of TM0 and in the TM0 stream channel. TM9 is located in the lower slopes of TM0 and is totally covered by holm oak. In TM0, two distinct physiographic units can be distinguished: holm-oak and beech forests on very steep slopes and heathlands and grasslands in the upland plateau (Fig. 1). Soils in the slopes of TM0 are colluvial, stony, well drained, and spatially heterogeneous due to the rugged topography. Typically, they are shallow with a 0-5-cm organic layer and depths varying between 0.25 to 1.5 m (Hereter, 1990, Hereter and Sánchez 1999). They are classified as Entisols (Lithic Xerorthents) or Inceptisols (Typic, Lithic or Dystric Xerochrepts; Soil Survey Staff 1992).
Table 1. Site characteristics