Soil processes in the Aeolian Litoral Sheet of Doñana National Park (Huelva, SW Spain): the catena of Colón small-lake ecosystem

Ecol. Noospher., 34(2) 54 ECOLOGY AND NOOSPHEROLOGY ISSN 1726-1112 (Print) ISSN 2310-4309 (Online) Ecol. Noospher., 34(2), 54–60 doi: 10.15421/032309 Soil processes in the Aeolian Litoral Sheet of Doñana National Park (Huelva, SW Spain): the catena of Colón small-lake ecosystem J. M. Recio*, F. Díaz-Olmo**, C. Borja**, R. Cámara**, F. Borja*** *University of Córdoba, Córdoba, Spain **University of Sevilla, Sevilla, Spain ***University of Huelva, Huelva, Spain Article info Received 26.04.2023 Received in revised form 04.05.2023 Accepted 12.05.2023 University of Córdoba, Campus de Rabanales, 14071-Córdoba, Spain. E-mail: bv1rees[email protected] University of Sevilla, Maria de Padilla, 41004-Sevilla, Spain. University of Huelva, Campus del Carmen, 27001-Huelva, Spain. Recio, J. M., Díaz-Olmo, F., Borja, C., Cámara, R., Borja, F. (2023). Soil processes in the Aeolian Litoral Sheet of Doñana National Park (Huelva, SW Spain): the catena of Colón small-lake ecosystem. Ecology and Noospherology, 34(2), 54–60. doi:10.15421/032309 The wetlands on the quartz sands aeolian sheet make up one of the ecosystems most recognized and important of the Doñana National Park and Doñana Biological Reserve (South Spain). More than 650 temporal small-lakes have been surveyed in the abundant sand depressions of the aeolian sheet, the most are a hydro-geomorphological dune-small-lake system. This paper studies the pedological processes around Colón small-lake ecosystem wetland (COL), one of the more interesting temporal small-lakes. The movement of fine particles through sand dunes ("sand washing") and their subsequent accumulation in depth is the process responsible for the formation of a large part of the small and medium small-lakes in the Eolian Litoral Sheet of Doñana. Their bodies of water are supported by these clay layers generated corresponding sometimes to ancient soil horizons formed under previous different ecological conditions. The vegetation, the soil morphology and the evolution of the physical-chemical processes studied in this geosystem small-lake of Colón allow understand this phenomenon of chronologies very recent. Keywords: sand dunes; pedogenesis; small-lakes; Doñana; Spain Introduction On the so-called "wet mantle" of the Abalario-Doñana Aeolian Litoral Sheet of the Doñana National Park (Borja, 2011) there is a large set of small and medium-sized smalllakes that make up ecosystems of high ecological value. Its genesis has always been attributed to the rise of the general aquifer whose piezometric surface would cut the undulating relief that makes up the porous and permeable buildings of the existing dunes. The studies carried out by Borja (2011) revealed, however, that many of these wetlands present a functioning where the formation of their body of water is due to the direct retention of rainwater and the participation of subsurface water that circulates through the interstices of the sands (epigenic type). Others are related to specific discharges from the general aquifer, such is the case of Charco del Toro (hypogenic regime) (Bejarano et al., 2010; Recio et al., 2009), and others such as Navazo del Toro are derived from a mixed situation (mesogenic regime) (Díaz del Olmo et al., 2014). This epigenic regime is possible given the presence at the bottom of the basins of impermeable and neosynthesized smectitic clay layers generated in earlier pedo-paleopalustrine situations with chronologies of 4.255 +/- 438 BP (Díaz del Olmo et al. 2014; Recio et al., 2014), subsequently transformed by the hydromorphy itself and biological activity of the smalllake ecosystem. This situation leads at the same time to the mixture of the most superficial levels as well as the formation on occasions of an organic-mineral horizon of white color and silty nature where it has been possible to determine new species of diatoms (Blanco et al., 2013; Espejo Alcaide, 2016). In order to show the formation of these deep impermeable clayey layers, the intensity and speed of these processes of translocation of very fine sands, silts and clays (“sand washing”) and the formation of the small-lake water body, the small wetland of the Colón or Fresno small-lake has been chosen as a model (Fig. 1), where the existing vegetation helps to demonstrate these subsurface water flows established in the gradient of the slope (Recio et al. 2014, a and b). Material and methods Three representative soil profiles of the different situations that define the dune-wetland geosystem that make up this Colón small-lake have been studied. Through a detailed altimetric survey with high-precision GPS (Topcon Hiper GD/GPS L1 model), the detailed georeferenced morphotopography of the small-lake basin and its immediate surroundings was obtained, which allowed correlating the different profiles with the different levels identified (Borja, 2011). Similarly Borja (2011) carried out continuous monitoring (every 15 days) of the wetland's water Ecol. Noospher., 34(2) 55 dynamics based on the measurement of its surface and thickness of the water column, of the subsurface water levels as well as the level of the aquifer regional. Figure 1. Colón (Fresno) small-lake in Abalario-Doñana Aeolian Litoral Sheet COL-1 soil profile was opened in the somital zone or crest of the dune that faces the wetland; the COL-2 profile comes to represent the base of the dune slope where the upper basin of the small-lake is positioned, flooded only in years of high rainfall, and in its lower basin occupied annually by its sheet of water the COL-3 soil profile was opened (Fig. 2). The artificial hollow (“zacayón”) open as a trough would complete the morphology of his bucket. and supports an abundant population of ferns (Pteridium aquilina) and rushes (Scirpus holoschoenus) (Fig. 3). In the lower trough, a somewhat more evolved profile of dark and black chroma (10YR 3/1), A1 AC1g C1g horizon sequence and Gleyc Arenosol morphology (COL-3) (FAO, 2015) is developed, which mainly supports grasses (Agrostis The soil profiles have been described and classified according to the standards of FAO (1977) and FAO (2015). The color was determined following the Munsell scale (Munsell, 1990), pH according to Guitián and Carballas (1976) and electrical conductivity (EC) according to USDA (1973) and Duchaufour (1975). Organic matter and organic carbon (C) by Sims and Haby (1971), and the parameters of hygroscopic humidity (H), apparent density (Dap.), real (Dr), porosity (Por) and hydraulic conductivity (H.C.), following the MAPA (1986) methodology. The texture, mineralogy of clays and sands, and magnetic susceptibility (MS) according to the methods described by Soil Survey England and Wales (1982), Brindley and Brown (1980), Montealegre (1976), Parfenoff and Pomerol, (1970) and Dearing (1999) respectively. The study of the vegetation was carried out through the corresponding sampling and collection in the field and its subsequent determination in the laboratory (Blanca et al. 2011). The OSL (Optically Stimulated Luminescence) dating was carried out in the dating and radiochemistry laboratory of the Autonomous University of Madrid (COL-1 and COL-2). Results and discussion In the top zone of the dune (Fig. 2 and 4) a very young soil with few evolution (COL-1) develops with a type A1 C1 horizon profile, about 50 cm thick, olive-brown in color (10YR 7/4 (s), 2.5Y 5/6 (h), and with characteristics of Distric Arenosol (FAO, 2015), which serves as support for isolated stems of Pinus pinea, and Pistacea lentiscus (Table 1, Fig. 3 and 4). On the dune slope, at lower levels and forming the upper basin of the wetland, the COL-2 profile develops, with more grayish chroma (10YR 3/2 (h)) and more powerful (about 80 cm of development), and A1 AC1 C1 horizons sequence, which has been classified as Humic Arenosol (FAO, 2015), stonolífera) and coincides with the levels closest to the surface of the aquifer (Table 1; Fig. 2 and 3). Organic matter (OM) reaches maximum levels in this discharge zone that coincides with the upper basin of the smalllake (4 %) and the population of Pteridium aquilinus. It is almost non-existent (0.19 %) in the highest zone where the feet DístricArenosol (COL-1) Húmic Arenosol (COL-2) GleycArenosol (COL-3) (A1) Figure 2. Soils catena in Colón small-lake Ecol. Noospher., 34(2) 56 of Pinus pinea are located, and reaches 1.52 % in the wetland bottom occupied by grasses (Agrostis stolonifera) (Table 1; Fig. 6). Parameters such as pH and salinity (E.C.) (Table 1, Fig. 7) experience a significant change in the dune-wetland gradient. In this way, the COL-1 profile shows an average pH of 6.7, and more acids than 5.7 in the COL-3 profile, despite the confinement of the water in its lower basin. The salinity (E.C.) is also in line with this gradient, being almost non-existent in the dune sands (0.07 mhs/cm as mean value), and 1.20 mhs/cm in the confined-accumulative environment of the small-lake bottom, even reaching maximum values of 1.72 mhs/cm, coinciding with the maximum acidity (5.1). This textural evolution and movement of fine particles down the gradient is reflected in the hydraulic conductivity (H.C.) with values from 148 cm/h (“very fast”) in the proper dune sands that begin the catena, to 6 cm/h (“moderately fast”) in the lower wetland basin (Table 1, Fig. 4) (MAPA, 1986). This comes to represent 96 % in the slowdown of these interstitial water flows, and therefore cause the accumulation of water at the base of it. Despite the fact that the hydraulic conductivity continues to be “very fast” in the area of the dune slope, values of 45 cm/h would be enough to produce a large brake and discharge on the surface (Fig. 5). All the horizons are made up of aeolian sands (Table 3; Fig. 4) and therefore their texture is always sandy, with maximum contents of 99.75 % (Table 3). In the COL-1 profile they are of medium size (0.5–0.25Ø mm) and wind selected (63.52 % average value). On the dune slope this aeolian character disappears, with medium and fine sands predominating, becoming fine and very fine at the base of the catena (COL-3 profile, 27.06 and 43.6 %; Table 3). The proportion of fines (silts and clays) evolves in the same way, from values of 0.5 % in the upper area of the dune, to 17 % at the base of the dune and the lower basin of the wetland (Table 3, Fig. 5, COL-3 profile), with even higher values in the superficial horizons (20.50 % in the A1 horizon). Despite the textural change caused by this movement of particles (“sand washing”), the porosity presents similar values around 41–46 % (Table 2, Fig. 6) as it evolves from designs of large interconnected pores to smaller ones and disorganized related to the finer texture. Perhaps the low thickness of the profiles motivates the existence of insignificant differences between the apparent (Dapr.) and real (Dreal.) density values found throughout the catena (Table 3) (Recio et al., 2014). The mineralogical analysis shows that despite the low clay contents present, the presence of an interstratified layer is detected at 12–14 Ä in the clays of the COL-1 profile, an Table 1 Physical and chemical characterization of soil profiles studied in Colón small-lake (mr – very fast; r – fast; md – moderately fast; m – moderately) Profile Horiz/Prof. (cm) Colour pH E.C. O.M. H.C. Wet. (s) (h) (H2O) (mhs/cm) (%) (cm/h) (%) COL-1 Dístric Arenosol AC1 (0–10) 10YR 7/4 2,5Y 5/6 7.10 0.08 0.19 189 (mr) 0.03 C1 (10–25) 10YR 7/4 2,5Y 5/6 6.60 0.06 0.19 117 (mr) 0.04 C2 (25–50) 10YR 7/4 2,5Y 5/6 6.40 0.07 0.19 140 (mr) 0.04 (mean) 6.70 0.07 0.19 148 0.03 COL-2 Húmic Arenosol A1 (0–20) 10YR 6/2 10YR 3/2 5.30 0.74 4.06 72 (mr) 0.79 AC1 (25–50) 10YR 6/2 10YR 3/2 6.00 0.23 1.73 45 (mr) 0.44 C1 (50–80) 10YR 7/1 10YR 4/2 6,30 0.12 0.43 20 ( r) 0.11 (mean) 5.86 0.36 2.07 45 0.44 COL-3 Gleyc Arenosol A1 (0–20) 10YR 6/3 10YR 3/3 6.40 0.63 1.52 7 (md) 0.70 AC1g (20–30) 10YR 4/1 10YR 2/1 5.60 1.72 1.24 4 ( m) 0.50 C1g (30–55) 10YR 6/1 10YR 3/1 5.10 1.26 0.52 8 (md) 0.11 (mean) 5.70 1.20 1.09 6 0.43 Table 2 Physical and mineralogical properties of soil profiles (c – common; f – frequent; o – occasional; r – rare) Profil Horiz/Prof. (cm) Dapr. Dreal Por. Ilmenite. M. S. (g/cm3) (g/cm3) (%) (%) (χ10-9) COL-1 Dístric Arenosol AC1 (0–10) 1.62 2.70 40 14.11 (c) 128 C1 (10–25) 1.63 2.81 42 10.05 (f) 116 C2 (25–50) 1.61 2.79 42 15.89 (c) 120 (mean) 1.62 2.76 41 13.50 121 COL-2 Húmic Arenosol A1 (0–20) 1.26 2.43 48 8.50 (f) 104 AC1 (25–50) 1.32 2.63 50 1.43 (o) 68 C1 (50–80) 1.54 2.63 41 2.80 (o) 44 (mean) 1.37 2.56 46 4.24 72 COL-3 Gleyc Arenosol A1 (0–20) 1.34 2.56 48 2.99 (o) 60 AC1g (20–30) 1.39 2.56 46 0.83 (r) 52 C1g (30–55) 1.57 2.77 43 0.51 (r) 36 (mean) 1.43 2.63 45 1.44 49 Ecol. Noospher., 34(2) 57 -- “hollow” low basin high basin (Pinewood) (ferns) (rushes) (grasses) “zacayón” -- dune front ---- -- -- -- -- -- -- -- -- COL-3 COL-1 COL-2 (N) Pinus pinea (Pteridium aquilina) (Juncus scholoenus) (Agrostis stolonífera) (Scirpus lacustris) Pistacea lentiscus Figure 3. Scheme of the surrounding vegetation Table 3 Distribution particule size Profil Horiz/Prof. (cm) Sand fraccions Silt+Clay 2–1 1–0,5 0,5–0,25 0,25– 0,125 0,125– 0,063 Total mm (%) (%) (%) COL-1 Dístric Arenosol AC1 (0–10) 0.00 0.20 58.38 38.54 2.86 99.00 1.00 C1 (10–25) 0.00 1.98 68.45 37.03 2.09 99.75 0.25 C2 (25–50) 0.00 0.81 63.73 33.29 2.14 99.75 0.25 (mean) 0.00 0.99 63.52 36.28 2.36 99.50 0.50 COL-2 Humic Arenosol A1 (0–20) 0.16 4.75 45.80 38.78 10.40 88.55 11.45 AC1 (25–50) 0.47 8.33 32.97 40.72 17.49 87.30 12.70 C1 (50–80) 0.89 11.71 34.46 35.19 17.73 90.95 9.05 (mean) 0.50 8.26 37.79 38.23 15.20 88.94 11.06 COL-3 Gleyc Arenosol A1 (0–20) 0.75 6.66 25.91 42.32 24.33 79.50 20.50 AC1g (20–30) 0.62 6.26 25.87 42.85 24.37 80.20 19.80 C1g (30–55) 1.08 7.22 29.40 44.31 17.97 89.20 10.80 (mean) 0.81 6.71 27.06 43.16 22.22 82.97 17.03 Ecol. Noospher., 34(2) 58 incipient vermiculitation process that evolves under the protection of acidity and the organic matter present, and which reaches a maximum on the surface of the COL-2 profile. The illite and kaolinite clays inherited from the aeolized parent substrate are the predominant ones, and the absence of neosynthesized smectites in the confined small-lake bottom itself (COL-3 profile, Table 4) would be indicative of the recent nature with which all these dynamic processes occur (Díaz del Olmo et al., 2014; Recio et al., 2014). 5 COL-1 (dune) COL-3 (low basin botton) “hollow” COL-2 (high basin botton) ---- -- ---- -- -- -- ---- -- ---- -- Eolic sands -- Sands and fines hydric-eolics. -- -- -- -- ---- -- Colón small-lake (maximun flood level) (minimun flood level) -80 cm -40 -0 -0 -40 -80 cm -- -- -- -- -- -- -- -- ---- -- -- -- -- C2 AC1 C1 A1 AC1 C1 A1 -80 cm -0 -40 AC1g C1g (light brown olive) (light brown olive) (light brown olive) (very dark greyish brown) (very dark greyish brown) (dark greyish brown) (dark brown) (black) (very dark grey) (groundwater) COL-1 COL-2 COL-3 6 m 0 m 60 m Figure 4. Depth, sequence horizons and chroma of the profiles studied Table 4 Semiquantitative analysis of clay fraction (V – vermiculite; Sm – smectites; K – kaolinite; I – illite) Profil Horiz (cm) (V) (%) (Sm) (%) (I) (%) (K) (%) COL-1 Dystric Arenosol AC1 (interstratified) (12A) C1 0 0 69 31 C2 (interstratified) (12 A) COL-2 Humic Arenosol A1 13 0 46 41 AC1 5 0 67 28 C1 0 0 86 14 COL-3 Gleyc Arenosol A1 0 0 75 25 AC1g 0 0 74 26 C1g 0 0 93 7 Pinus wood (Pinus pinea) Ferns (Pteridium aquilina) Reedbeds (Scirpus lacustris; Juncus sholinus) Grasses (Agrostis stolonífera) COL-2 COL-3 COL-1 low basin “hollow” high basin (dune slope) medium sands: 63,52% (C.H.: 148 cm/h) mediumn and fine sands37.79% y finas: 38.23% (C.H.: 45 cm/h) fine sands: 43.16% very fine sands 22.22% (C.H.: 6 cm/h) Subsurface flow (unloading area) -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- Eolic sands -- Sands and hydro-eolic fines Colón small-lake 6 m 0 m 60 m Figure 5. Vegetation, sand distribution, mean values of hydraulic conductivity and pedological and superficial flow regime Ecol. Noospher., 34(2) 59 As representative of the mass of alterable ferromagnesian minerals present (Recio et al., 2009 and 2011), the Fig. 7 shows the ilminite contents in the different horizons (Table 2). "Very common" in the dune (COL-1, mean value of 13.5 %) becomes almost "occasional" and even "rare" at the bottom of the trough (COL-3, 1.44 % as mean value), a consequence of the alteration processes and at the same time responsible for the iron oxy-hydroxide stains that appear in the C1g horizon. In relation to all this would be the values of magnetic susceptibility (M.S.) (128–36χ10-9), indicative of the greater alteration that occurs as we descend in the soil category studied (121, 72 and 49χ10-9 respectively) (Table 2). COL-1 (dune) COL-3 (low basin) “hollow” COL-2 (high basin) Fines: 0.50% O.M.: 0.19% Fines: 11.06% O.M.: 4.06% Fines: 17.03% O.M.: 1.52% Subsurface flow, “sand wash”/ fines trawl -- -- -- -- ---- -- Eolic sands -- Sands and fine hydric-eolic Heritage (10, 7 A) -- -- ---- -- -- -- Colón small-lake 6 m 0 m 60 m Figure 6. “Sand washing” and clay formation, porosity gradient (Por.), fines (silt and clay) and organic matter (OM) contained in the studied catena COL-1 (dune) COL-3 (low basin) “hollow” COL-2 (high basin) Subsurface flow, “sand wash”/ fines trawl -- -- -- -- -- -- -- -- -- -- -- Eolic sands -- Sands and hydro-eolic fines ---- -- -- -- -- -- (Ilmenite: 13 %) (Ilmenite: 4 %) (Ilmenite: 1 %) Colón small-lake 6 m 0 m 60 m Figure 7. pH variation, electrical conductivity (E.C.) and presence of ilmenite COL 1.( Cr.1) Cronology 116 18 BP COL 2.( Cr.1) Cronology: 410 48 BP Figure 8. OSL cronology: sand dune (COL-1) and profile COL-2 Ecol. Noospher., 34(2) 60 The chronology obtained by OSL corresponding to the C1 horizons of the COL-1 (+50 cm) and COL-2 (+80 cm) profiles helps to evaluate the speed with which these processes occur and also to get closer to the chronology and formation of the current wetland. Based on this, the dune that faces the wetland would present a chronology of 116yBP, and the more chromic and darker horizons of the upper basin (COL-2) show an age of around 410yBP (Fig. 8). Conclusion The Colón small-lake ecosystem shows a very marked seasonal character, a high mineralization of the organic matter of its bottom and an acid nature and absence of salts in its waters. The distribution of the fern-based vegetation in the discharge zone, grasses and rushes in the levels closest to its lower basin, and pines and mastics in the highest zone, coincides with the subsurface water flows established in the catena studied, responsible at the same time for the existing pedological evolution. 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