F. Domingo

Hydrological and erosion response of a badlands system in semiarid SE Spain

A long term monitoring program is being conducted to study runoff and erosion processes in a semiarid badlands environment (Tabernas Desert, SE Spain). The first six years of data from an instrumented experimental area with nested microcatchments are presented. The overall area is composed of a complex mosaic of soil surfaces with contrast hydrological and erosion behaviour. At microcatchment scale, runoff and erosion are controlled by the types of soil surfaces: small bare microcatchments had the highest runoff coefficients and the highest erosion rates, while those completely covered by vegetation had the lowest. Rainfall intensity significantly affected water and sediment budgets. The effect of antecedent soil moisture could only be observed when soil was near saturation and a few millimetres of additional rainfall were sufficient to produce Horton-type runoff, but it was very difficult to separate this from the effect of surface crusts formed in the first minutes of rainfall. Most of the rainfall events were below the threshold for producing runoff although they were important for sediment preparation through weathering. Small magnitude, low-intensity rainfall events along with protective plant cover over half of the total surface, are the main factors explaining low overall erosion rates at microcatchment scale.

Measurement and modelling of rainfall interception by three semi-arid canopies

The main aims of this study were, firstly, to adapt the rainfall interception model of Rutter et al. (Agric. Meterology, 1971, 9, 367‐384) to individual plants of two semiarid shrubs (Anthyllis cytisoides L. and Retama sphaerocarpa (L.) Boiss.) and a tussock grass (Stipa tenacissima L.) and secondly, to understand how the different canopy structures influence rainfall partitioning by individual plants. The selected species represent contrasting canopy types typical of vegetation of semiarid areas. Free throughfall coefficients were estimated from field measurements of low volume rainfall events and vertical photographs taken beneath the plant canopy. Canopy drainage curves were measured by continuous weighing of wetted plants. Canopy boundary layer conductances were calculated by measuring the evaporation of water from wet canopies. Field measurements of gross rainfall, throughfall and stemflow were taken for each rainfall event for A. cytisoides and R. sphaerocarpa. The Rutter type model of rainfall interception was adapted for individual shrubs and tested with measured rainfall events showing a good agreement between observed and predicted values for R. sphaerocarpa and for A. cytisoides. The interception model was then run to simulate interception loss during actual rainfall events, using atmospheric conditions measured every 5 s. The results from this simulation showed significant differences in interception loss between species, which can be explained by differences in canopy drainage and boundary layer conductance, and are caused primarily by the structural differences in their canopies. R. sphaerocarpa gave lower interception than the other two species, S. tenacissima gave higher interception, while A. cytisoides had an intermediate value. The low interception loss by R. sphaerocarpa can be explained by its low total area index, thus, high free throughfall and high canopy drainage rate per unit projected canopy area. On the other hand, S. tenacissima and A. cytisoides, show a low free throughfall and drainage rate per unit projected canopy area because of their higher aerial biomass density. The ecological implications of these adaptations are discussed. # 1998 Elsevier Science B.V. All rights reserved.

Evaluating the long-term water balance of arid zone stream bed vegetation using evapotranspiration modelling and hillslope runoff measurements

The difference between long-term actual evapotranspiration (AET) and precipitation (P) provides a useful indication of the extent to which a site retains or loses water resources, and therefore of the likely occurrence of specific land degradation processes. Sink areas OAET q PU receive lateral water inputs from other parts of the catchment. In arid and semi-arid environments these areas are frequently found in, or next to, the stream beds of ephemeral rivers and are often characterised by intensive land use or high conservation values. For both types of land use it is important to know if, and how much, AET exceeds P, and where the lateral water inputs come from. Thick sedimentary fills in the stream bed, variable climate conditions and ephemeral flow conditions pose specific difficulties to the evaluation of the water balance of these sites. The objective of this study was to develop an approach to explore the relative importance of lateral water inputs to shrub stands growing in thick sedimentary fills of semi-arid ephemeral rivers. The approach is based on (i) estimating long-term AET2 P balances in the channel sediments and (ii) assessing whether these inflows originate mainly from surrounding hillslopes or from the upstream part of the catchment. A physically based evapotranspiration model for sparse vegetation was used to estimate the long-term AET rates. The relative importance of hillslope runoff and channel flow was evaluated in a semi-quantitative fashion from a combination of surface area estimates and mostly published values of soil hydrological parameters. The approach was developed and tested in a selected stand of Retama sphaerocarpashrubs in a stream bed at the Rambla Honda field site (Tabernas,

Quercus ilex Transpiration as Affected by a Prolonged Drought Period

The effect of an extended drought (from 1992 to 1995) on water relations was assessed on evergreen oak (Quercus ilex L.) in a dehesa ecosystem (Seville, Southern Spain). Diurnal and seasonal transpiration patterns were analysed at leaf (porometry) and whole-tree level (sap flow), focusing on the relationship between tree transpiration rates (Et) and potential evapotranspiration rates (PET). Daily maximum Et varied over the year, becoming higher between May and August, and lower between November and April. Annual Et (169 – 205 mm y−1) accounted for less than 40 % of annual rainfall. The prolonged drought did not affect the water relations of the Q. ilex, mainly due to strong stomatal regulation avoiding the loss of water. Stomatal control was found in all seasons, although it was stronger in summer. This behaviour leads to low water consumption and low Et/PET ratios throughout the year (0.05 to 0.27).

Role of vegetation cover in the biogeochemical balances of a small afforested catchment in southeastern Spain

The budgets of major dissolved nutrients have been determined in a small micaschist catchment (0.34 km2) covered with Mediterranean shrubs and afforested pines at 1560 m altitude in the Filabres range (southeast Spain). The climate is semiarid with 395 mm annual rainfall and 12°C annual mean temperature. During the hydrological year 1988–1989, major element concentrations in open field precipitation, throughfall, stemflow and runoff were recorded as well as the element fluxes of the main solutes. The total rainfall recorded during the sampling year was 650 mm of which 86% was lost through evapotranspiration and 14% through runoff. Mean annual rainfall interception is estimated as 15% and net rainfall reaching the soil is divided between 90% throughfall and 10% stemflow. Two methods were applied to compute bulk precipitation inputs to the ionic balances: (I) bulk open field deposition was estimated from data provided by open field polyethylene collectors (bulk open field precipitation inputs); (II) net throughfall and stemflow were corrected for canopy leaching. The results show that the total deposition calculated using balance (II) is higher than that calculated by (I); the effect of canopy surfaces in scavenging atmospheric dry fallouts and gases is identified in a more efficient way than by simple polyethylene collectors. When comparing both methods of computing balances in several environments, using published data, the authors conclude that the plant canopy effect is larger in sermiarid areas with dusty atmospheres and in industrial regions with higher concentrations of sulphur. These conclusions suggest that the retention of nutrients within the ecosystem may be more widespread than was previously thought. This calls for more research on the assessment of biomass removal and the dynamics of intermediate pools (precipitates). Consequently, it throws doubts on most of the figures available for catchment weathering rates; these were often estimated by difference between bulk open field precipitation inputs measured with polyethylene collectors and runoff outputs.

Variations in daytime net carbon and water exchange in a montane shrubland ecosystem in southeast Spain

Carbon and water fluxes in a semiarid shrubland ecosystem located in the southeast of Spain (province of Almería) were measured continuously over one year using the eddy covariance technique. We examined the influence of environmental variables on daytime (photosynthetically active photons, FP >10 µmol m−2 s−1) ecosystem gas exchange and tested the ability of an empirical eco-physiological model based on FP to estimate carbon fluxes over the whole year. The daytime ecosystem fluxes showed strong seasonality. During two solstitial periods, summer with warm temperatures (>15 °C) and sufficient soil moisture (>10 % vol.) and winter with mild temperatures (>5 °C) and high soil moisture contents (>15 % vol.), the photosynthetic rate was higher than the daytime respiration rate and mean daytime CO2 fluxes were ca. −1.75 and −0.60 µmol m−2 s−1, respectively. Daytime evapotranspiration fluxes averaged ca. 2.20 and 0.24 mmol m−2 s−1, respectively. By contrast, in summer and early autumn with warm daytime temperatures (>10 °C) and dry soil (<10 % vol.), and also in mid-winter with near-freezing daytime temperatures the shrubland behaved as a net carbon source (mean daytime CO2 release of ca. 0.60 and 0.20 µmol m−2 s−1, respectively). Furthermore, the comparison of water and carbon fluxes over a week in June 2004 and June 2005 suggests that the timing—rather than amount—of spring rainfall may be crucial in determining growing season water and carbon exchange. Due to strongly limiting environmental variables other than FP, the model applied here failed to describe daytime carbon exchange only as a function of FP and could not be used over most of the year to fill gaps in the data.

Cave ventilation is influenced by variations in the CO 2 -dependent virtual temperature

This research was funded by the Andalusian regional government project GEOCARBO (P08- RNM-3721) and GLOCHARID, including European Union ERDF funds, with support from Spanish Ministry of Science and Innovation projects CarboredII (CGL2010-22193-C04-02), SOILPROF (CGL2011- 15276-E) and CARBORAD (CGL2011-27493), as well as the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 244122.

Temporal dynamics of soil water balance components in a karst range in southeastern Spain: estimation of potential recharge

Abstract This paper analyses the temporal dynamics of soil water balance components in a representative recharge area of the Sierra de Gádor (Almeria, southeastern Spain) in two hydrological years. Two approaches are used to estimate daily potential recharge (PR): Approach 1 based on deriving PR from the water balance as the difference between measurements of rainfall (P) and actual evapotranspiration (E) obtained by eddy covariance; and Approach 2 with PR obtained from the dynamic pattern of the soil moisture (θ) recorded at two depths in the sites thin soil (average 0.35 m thickess). For the hydrological year 2003/04, which was slightly drier than the 30-year average, E accounted for 64% of rainfall and occurred mainly in late spring and early summer. The PR estimated by Approach 1 was 181 ± 18 mm year-1 (36% of rainfall), suggesting an effective groundwater recharge in the study area. In the unusually dry hydrological year 2004/05, E was about 215 mm year-1, close to the annual rainfall input, and allowing very little (8 ± 12 mm year-1) PR according to Approach 1. Estimation of PR based on Approach 2 resulted in PR rates lower than those found by Approach 1, because Approach 2 does not take into account the recharge that occurs through preferential flow pathways (cracks, joints and fissures) which were not monitored with the θ probes. Moreover, using Approach 2, the PR estimates differed widely depending on the time scale considered: with daily mean θ data, PR estimation was lower, especially in late spring, while θ data at 30 min resolution yielded a more reliable prediction of the fraction of total PR resulting from the downward movement of soil water by gravity. Citation Cantón, Y., Villagarcía, L., Moro, M. J., Serrano-Ortíz, P., Were, A., Alcalá, F. J., Kowalski, A. S., Solé-Benet, A., Lázaro, R. & Domingo, F. (2010) Temporal dynamics of soil water balance components in a karst range in southeastern Spain: estimation of potential recharge. Hydrol. Sci. J. 55(5), 737–753.

Water Relations Only Partly Explain the Distributions of Three Perennial Plant Species in a Semi-arid Environment

The water relations and stomatal conductances of three perennial plant species, Stipa tenacissima L., Anthyllis cytisoides L., and Retama sphaerocarpa (L.) Boiss., dominant on the upper slopes, mid-slopes and floor of a valley, respectively, in semi-arid south-east Spain, were investigated to test the hypothesis that differences in plant-soil water relations could account for the different distributions of each species in the catena. Diurnal measurements of water potential (Ψw), relative water content (RWC) and stomatal conductance (gs) of leaves were made over one year. Leaf temperature, air humidity, wind-speed and incident quantum flux density were measured concurrently. Soil water content was determined gravimetrically at 0 – 5 cm and 15 – 20 cm depths. Measurements of Ψw, RWC and gs were analysed according to meteorological conditions, based on the maxima for daily air temperature and atmospheric saturation water vapour deficit and on soil moisture content. The hypothesis that plant-soil water relations can explain the distribution of the three species along the catena from valley side to valley floor was rejected for Anthyllis and Stipa but confirmed for Retama.

Seasonal water-use efficiency and chlorophyll fluorescence response in alpha grass (Stipa tenacissima L.) is affected by tussock size

AbstactTwelve randomly chosen Stipa tenacissima L. individuals were grouped into three tussock size classes, small (ST), medium (MT), and large (LT) with 5.6±0.8, 34.1±4.2, and 631.9±85.8 g of dry green foliar matter, respectively, in three plots with different S. tenacissima cover. Instantaneous (WUEi) and long-term (WUEl) water-use efficiencies were measured in two seasons of contrasting volumetric soil water content (early winter 21.0±0.8 % and summer 5.8±0.3 %). Maximum photochemical efficiency of photosystem 2 and stomatal conductance in summer assessed the extent of water and irradiance stress in tussocks of different size. WUEi was lower in MT and ST “water spender” strategies than in LT during the high water-availability season. In summer net photosynthetic rate and WUEi were higher and photoinhibition was lower in LT than in MT and ST. Significant spatial variability was found in WUEi. Water uptake was competitive in stands with denser alpha grass and more water availability in summer, reducing their WUEi. However, WUEl showed a rising tendency when water became scarce. Thus it is important to explicitly account for plant size in ecophysiological studies, which must be combined with demographic information when estimating functional processes at stand level in sequential scaling procedures.