La Castanya Research Articles

Quantifying Dry and Wet Deposition Fluxes in Two Regions of Contrasting African Influence: The NE Iberian Peninsula and the Canary Islands

This study considers the role of distance to the African source on the amount of deposition. To this end, dry and wet deposition was measured at a site close to Africa (Santa Cruz de Tenerife in the Canary Islands, SCO) and at a distant site located in NE Spain (La Castanya, Montseny, MSY). Because of the important influence of African influence on the buildup of particles in the atmosphere, we specifically addressed the contribution of North African events (NAF events) compared to other provenances (no-NAF events) in the wet and dry pathways at the two sites. At the site close to Africa, most of the crustal-derived elements were deposited in the dry mode, with NAF events contributing more than no-NAF events. Marine elements, by contrast, were mostly deposited at this site in the wet form with a predominance of no-NAF events. At MSY, wet deposition of SO4–S, NO3–N and NH4–N during NAF events was higher than at the site close to Africa, either in the wet or dry mode. This fact suggests that mineral dust interacts with pollutants, the mineral surface being coated with ammonium, sulphate and nitrate ions as the dust plume encounters polluted air masses in its way from North Africa to the Western Mediterranean. African dust may provide a mechanism of pollution scavenging and our results indicate that this removal is more effective in the wet mode at sites far away from the mineral source.

Comparison of collection methods to determine atmospheric deposition in a rural Mediterranean site (NE Spain)

Wet-only, dry-only, bulk deposition and deposition of sedimentary particles and gases deposited after the last rain (DAR) were collected weekly at La Castanya station in the Montseny mountains (NE Spain, 41°46′N, 2°21′E) from February 2009 to July 2010. These samples were analysed for pH, alkalinity, and the concentrations of major ions (Cl−, NO3 −, SO4 2−, Na+, K+, Ca2+, Mg2+, NH4 +). Significant differences were observed between bulk and wet-only precipitation, with an enrichment of ions associated to coarse particles in bulk deposition. The comparison between wet and dry fluxes revealed that the removal of compounds at Montseny occurred mainly by wet deposition, which accounted for 74 % of total deposition. The dry flux was characterised by the predominance of K+, Ca2+ and Mg2+, which are related to coarse particles. Bulk collection methods at Montseny were considered representative of total atmospheric deposition, since bulk deposition plus DAR accounted for 97 % of total deposition measured with wet and dry-only collection devices. Thus, bulk deposition collectors can be recommended for deposition networks at remote sites (lacking electricity connection) in environments, where coarse particles are a predominant fraction of the aerosol mass.

Source apportionment for African dust outbreaks over the Western Mediterranean using the HYSPLIT model

A source apportionment technique has been applied to determine the geographical distribution of emissions in Northern Africa contributing to dust outbreaks that yield high PM10 levels at Spanish regional background stations. Seven dust episodes have been analyzed in this study. Total suspended particles have been sampled and chemically analyzed for these events at La Castanya background station (Montseny, NE Spain) and differences in the composition of airborne dust have been studied. The dominant role of northern and western source areas (Tunisia, Algeria, Mauritania and the Western Sahara) contrasted with the negligible contribution of major emission source areas such as the Bodelé depression, Libya, Niger, and Sudan. During the simulated events using the dust module of the HYSPLIT model, material from the latter regions is persistently transported across the Atlantic but not towards Western Europe. As a consequence, the composition of the dust turned out to be quite homogeneous since the mixing of dust occurs from various source areas with similar chemical composition. However, differences in Ca/Al ratios have been found in a number of samples that are mainly explained by vertical transport segregation of clay minerals (relatively richer in Al) from coarser dust particles (Ca-carbonate).

Analysis of Decadal Time Series in Wet N Concentrations at Five Rural Sites in NE Spain

Nitrogen emissions have grown in Spain during the last 15 years. As precipitation scavenges gases and aerosols from the atmosphere, an effect on rainwater concentrations can be expected. However, time-series studies on wet N concentrations in the Iberian Peninsula are very scarce. This paper aims to fill this gap by analysing weekly rainfall N concentrations at a set of rural sites in Catalonia (NE Spain) from 1995/1996 to 2007 and a forest site monitored from 1983 to 2007. The sites encompass a range of rural environments and climate conditions, from the inland pre-Pyrenees (Sort) to the Mediterranean coast (Begur) and from north (Sort and Begur) to central (Palautordera and La Castanya) and south Catalonia (La Senia). We found a 1-year cycle for concentrations of NH 4 + and NO 3 − whereby higher values were reached at the end of spring–early summer, except at the easternmost coastal site of Begur. Weekly NH 4 + concentrations decreased with time at all sites (except at La Senia) whilst NO 3 − concentrations increased at all sites during the same period. Rainfall SO 4 2− concentrations decreased with time at all sites. The opposite trends in NO 3 − and SO 4 2− concentrations determined a shift in the relative acid contribution of those anions during the 12–13-year period. To interpret the increasing trend, mean annual NO 3 − concentrations were regressed against NO2 Spanish emissions and to some indicators of local anthropogenic activity. The increase at Sort and Palautordera showed good correlation with local anthropogenic indicators. Wet inorganic N deposition ranged between 4.2 and 6.7 kg ha−1 year−1. When including estimates of dry deposition, total annual deposition rose up to 10–20 kg ha−1 year−1, values that have been found to initiate adverse effects on Mediterranean-type forest ecosystems.

Precipitation chemistry at a rural Mediterranean site: Between anthropogenic pollution and natural emissions

The chemistry of weekly rainwater collected at a rural site (La Castanya, Montseny Mountains, northeast Spain), exposed both to anthropogenic pollutants and natural African dust, was analyzed for the period 1983–2000. On the basis of back trajectories and synoptic charts we distinguished four source regions: (1) African, (2) European, (3) Oceanic, and (4) Local. The chemical characteristics of each provenance were interpreted in relation to the emission processes at each source region. The temporal trends between 1983 and 2000 in the volume weighted mean (VWM) concentrations showed an upward trend for alkalinity in European, Local, and Oceanic provenances, while they showed a slight (nonsignificant) downward trend for African rains. All provenances exhibited a significant decline in excSO4−2, which was most pronounced for European rains (b = −5.7 μeqL−1 yr−1). Because NO3− remained about constant (except for European rains), NO3− acquired a more important role in the acid anion contribution. A reduction of the acid deposition for European, Local, and Oceanic rains was observed, as well as an increase in the global deposition of alkalinity. The role of African rains appeared as a determinant in the accumulated alkalinity during the period. A quantification of the transport of pollutant species (SO4−2, NO3−, and NH4+) from eight contributing European subregions was obtained on the basis of the residence time of the trajectories in each subregion. It suggested that not only subregions closer to the receptor point, such as the Iberian Peninsula, France, and the United Kingdom, were important contributors to the deposition of SO4−2, NO3−, and NH4+ but also distant sites such as Scandinavia contributed considerably.

Nitrogen circulation in a Mediterranean holm oak forest, La Castanya, Montseny, northeastern Spain

Abstract. The importance of storm frequency as well as the groundwater and hyporheic inputs on nitrate (NO3-N) and ammonium (NH4-N) levels in stream water were studied in a small perennial Mediterranean catchment, Riera Major, in northeast Spain. NO3-N concentrations ranged from 0.15 to 1.9 mg l-1. Discharge explained 47% of the annual NO3-N concentration variance, but this percentage increased to 97% when single floods were analysed. The rate of change in nitrate concentration with respect to flow, ΔNO3-N/ΔQ, ranged widely from 0 to 20 μg NO3-N s l-2. The ΔNO3-N/ΔQ values fitted to a non linear model with respect to the storm flow magnitude (ΔQ) (r2=0.48, d.f.=22, P<0.01). High values of ΔNO3-N/ΔQ occurred at intermediate ΔQ values, whereas low ΔNO3-N/ΔQ values occurred during severe storms (ΔQ > 400 l s-1). N3-N concentrations exhibit anticlockwise hysteresis patterns with changing flow and the patterns observed for autumnal and winter storms indicated that groundwater was the main N3-N source for stream and hyporheic water. At baseflow, NO3-N concentration in groundwater was higher (t=4.75, d.f.=29, P>0.001) and co-varied with concentrations in the stream (r=0.91, d.f.=28, P<0.001). In contrast, NO3-N concentration in hyporheic water was identical to that in stream water. The role of the hyporheic zone as source or sink for ammonium was studied hyporheic was studied comparing its concentrations in stream and hyporheic zone before and after a major storm occurred in October 1994 that removed particulate organic matter stored in sediments. Results showed high ammonium concentrations (75±28 s.d. μg NH4-N l-1) before the storm flow in the hyporheic zone. After the storm, the ammonium concentration in the hyporheic dropped by 80% (13.6±8 μg N4-N l-1) and approached to the level found in stream water (11±8 μg NH4-N l-1) indicating that indisturbed hyporheic sediments act as a source for ammonium. After the storm, the ammonium concentrations in the stream, hyporheic and groundwater zones were very similar suggesting that stream ammonium concentrations are sustained mainly by input from groundwater. The present study provides evidence that storm flow magnitude is an important source of variability of nitrate concentration and fluxes in Mediterranean streams subjected to an irregular precipitation regime with prolonged dry periods. Keywords: nitrate, discharge regime, hyporheic zone, groundwater, Mediterranean, stream, Riera Major

Assessing decadal changes in rainwater alkalinity at a rural Mediterranean site in the Montseny Mountains (NE Spain)

Annual volume-weighted mean (VWM) concentrations in rainwater collected at La Castanya (LC, Montseny Mountains, NE Spain) were analysed from 1983 to 2000 to study the temporal trends in precipitation chemistry, and the causes behind the changes. A significant positive correlation was found between annual rainwater SO 4 2− concentrations at LC and Spanish SO 2 emissions ( r=0.73, P=0.0008) both decreasing remarkably during this period. Rainwater alkalinity increased during the period, shifting from negative values at the beginning (VWM in the 5 initial years=−2.7 μeq l −1) to alkaline values in recent years (VWM in the 5 final years=18.0 μeq l −1). Stepwise regression analysis indicated that 88% of the variation of alkalinity could be accounted for by the variability of non-marine Ca 2+ and non-marine SO 4 2−, with a more prominent dependence on Ca 2+. Rains of African provenance were highly enriched in alkalinity and Ca 2+, but no significant increases in their occurrence were found for the study period. Because of the reported higher dust updraft in northern Africa during years of high North Atlantic Oscillation (NAO) index, we also explored the relationship between rainwater variables associated with an African provenance and NAO. Annual precipitation was inversely related to NAO ( r=−0.61, P=0.007). The annual wet deposition of African dust-related elements showed no correlation with NAO, probably because wet deposition of these elements depends on two factors (precipitation and dust updraft) which have opposite behaviour with respect to NAO. We hypothesise that dry deposition of African dust during dry spells (not sampled in this study) might be higher during high NAO-index years.

Determinación de los componentes del balance de radiación en un área experimental del Macizo del Montseny

In the present day research on physical geography, mass and energy budgets are of capital importance. The energy budget in an experimental area requires the previous estimate of the corresponding radiation budget. In this paper, the obtaining of the components of the radioactive budget is explained for La Castanya (Montseny) experimental site. Measurements were carried out in October 1989 with the field instrumentation provided by the French co-author and under his supervision. Data from the 22nd October is analyzed in detail as an example of model characteristics.

Estructura y funcionalismo de un encinar montano en el Montseny. III: contenido de sodio, potasio, calcio y magnesio en las aguas de lluvia

Volume and dissolved nutrient content (Na,K,Ca, and Mg) of incident precipitation and throughfall are under study in a montane-Mediterranean evergreen-oak (Quercus ilex L.) forest at La Castanya (Montseny, Barcelona). Amount of precipitation is measured with 4 (within) and 2 (outside the forest) polyethylene gauges with 19 cm funnels. Precipitation chemistry is monitored through 8 (within) and 2 (outside the forest) acid-washed, continuously-open polyethylene rain collectors with the funnels covered by a hood made of 2 mm plastic mesh to exclude insects and coarse debris. Rain collectors are changed by clean ones on a biweekly basis and the precipitation samples deep frozen until chemical analyses. This paper reports preliminary results from the first year of study : 24 June 1978 to 30 June 1979. As judged through the records of a nearby weather station, this year proved to be a normal one as for total rainfall, although an abnormal one as for monthly distribution of precipitations. Total incident precipitation and throughfall amounted to 969 and 617 mm, respectively. Concentrations of the four analysed cations were highly variable along the year (figs. 1-2), being generally higher in spring-summer than in autumn-winter rains both within and out side the forest. Volume-weighted mean concentrations are given in table 1, and nutrient fluxes in table 2. On the average, incident precipitation at La Castanya is relatively high in Ca (1.5 mg 1 ), medium in Na (0.7), and low in K (0.2) and Mg (0.2). Throughfall is enriched in all four elements with respect to incident precipitation: K 21 times, Mg 3 times, Ca 2.5 times, and Na 2 times.

Estructura y funcionalismo de un encinar montano en el Montseny. II: biomasa arbórea

Above-ground tree biomass data are reported as first results of a study on the structure and dynamics of the tree stratum in the evergreen-oak wood at La Castanya (Montseny, Barcelona). 15 evergreen-oaks (Quercus ilex L.ssp ilex) were fallen from a spot near the experimental plot. An alometric table for the evergreen-oak is given, together with estimates of the total above-ground tree biomass for the experimental plot, partitioned in wood 0>5 cm, wood 0 < 5 cm, bark, and leaves by leave-age. Results are compared with those from evergreen-oak woods obtained by other workers.

Estructura y funcionalismo de un encinar montano en el Montseny. IV: producción de hojarasca

Litterfall and its concomitant mass and nutrient (Na, K, Ca and Mg) fluxes to the forest floor are studied in a montane-Mediterranean evergreen-oak (Quercos ilex L.) wood at La Castanya (Montseny, Barcelona). Litterfall is colected biweekly in 16 (only 8 during the first 6 months) conical, 0.25 m litterfall traps randomly distributed over a 0.22 ha experimental plot. Results from the first year of study (May 1978 - May 1979) are reported in this paper. Litterfall a mounted to 4.5 t ha-1 yr-1, not including in this figure the branches longer than 40 cm or thicker than 5mm. Leaves represented 3.08 t ha-1 yr-1 (68.11% of litterfall), twigs 1.05 t ha-1 yr-1 (23.22%), and fruits and inflorescences 0.14 t ha-1 yr-l (3.21%). Leaf fall exhibited a distinct seasonal maximum in late spring-early summer, but total litterfall peaked later when an autumn hailstorm and a November windstorm struck the forest. Nutrient contents of freshly-fallen evergreen-oak litter were within the range of published values for this species. Nutrient fluxes in litterfall were (kg ha-1 yr-1): Na 0.76, K 18.28, Ca 41.64 and Mg 5.43. Throughfall data from Roda et al. (1980) allowed to compute the following nutrient fluxes in litterfall plus throughfall (kg ha-1 yr-1): Na 9.1, K 38.0, Ca 64.7 and Mg 9.3.

Estructura y funcionalismo de un encinar montano en el Montseny. I: planteamiento del estudio y descripción del área experimental

This paper is a preliminar one on objectives of a new project in terrestrial ecology and on the characteristics of selected study area. The project is being drived by Ecology departments of Universitat de Barcelona and Universitat Autonoma de Barcelona, and is embodied in a larger one on nutrient cycles in forest ecosystems. The parameters measured and their relationships are exposed and future developments briefly discussed. The La Castanya valley is included in the Montseny nature park, a Biosphere Reserve, in a Mediterranean mountain stage with relatively humid climate but with great interanual fluctuation. The bedrock is nearly all constituted by paleozoic shales and valley-side slopes are pronounced (30%) . There is a soil catena from litosols to rankers and brown acid soils that can be lixiviated in some places. Vegetation is a green oak mountain forest (Quercetum ilicis mediterraneo-montanum) in nearly all the valley. There are, however, some grasslands and a beech forest near the summits and also a little Taxus baccata trees clump. The green oak forest is a young one, in a regeneration stage, after a very intensive explotation period (wood for fuel and coal making) interrupted some years ago, and an early farming period. In the experimental plot direct insolation is lowered by topographic position and the soil is colluvial, deep but with loose rocks at surface. Herb and shrub layer are poor, being the young Quercus ilex also dominants. The experimental plot surface is 0,22 ha, including 450 trees (more than 5 cm dbh) between 7 and 12 m high. The branch system has a lowe layer level, with a few horizontal branches, and a higher one with near vertical branches. The major axis is not clearly defined, as it divides in two or three over 2,5-4 m.