Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Doctorat → États-Unis → 2010 → Fog contributions to pedogenesis and hydrology in Pinus muricata ecosystems on Santa Cruz Island, California

University of California, Davis (2010)

Fog contributions to pedogenesis and hydrology in Pinus muricata ecosystems on Santa Cruz Island, California

Baker, Juliet Barbara

Titre : Fog contributions to pedogenesis and hydrology in Pinus muricata ecosystems on Santa Cruz Island, California

Auteur : Baker, Juliet Barbara

Université de soutenance : University of California, Davis

Grade : Doctor of Philosophy (PhD) 2010

Résumé partiel
Fog has been shown to be an important water source for coastal vegetation, but the extent to which fog influences soil processes and hydrology has not been well studied. Precipitation inputs from fog and rain, along with soil moisture and throughfall under Bishop pine (Pinus muricata) canopy, were measured at two site pairs on Santa Cruz Island, California. Each pair consisted of a forested site which received fog drip and had an isomesic soil temperature regime and a grass site which did not receive fog drip and had a thermic soil temperature regime, on two parent materials, chlorite schist (WS) and rhyolitic tuff/breccia (SB). Fog drip measured as throughfall provided an average of 10 mm (SB) to 20 mm (WS) additional water per month to the pine sites during the summer when no rainfall is available. Soil moisture sensors at 5 cm incremental depths to about 20 cm recorded infiltration of water from fog events, confirming that fog drip can infiltrate to the rooting zone. Modeled water balances for each site indicate that actual evapotranspiration (AE) nears zero in July at the grass sites, but soil moisture continues to be utilized throughout the summer at the pine sites. Organic matter decomposition rates are influenced by climatic factors, organic matter composition, and soil microbial communities. Both temperature and moisture can be limiting factors in organic matter decomposition, but the role of fog in determining decomposition rates has not been well studied. In a litterbag decomposition experiment performed over 3 years, decomposition rates of both pine and grass litter were highest at the pine sites, suggesting that moisture is a limiting factor in this environment. The additional moisture received as fog drip at the pine sites may accelerate decomposition processes regardless of temperature. Decomposition rates of both litter types decreased with time at the pine sites, while rates for both litters remained relatively constant at the grass sites over the duration of the experiment. Pine forest soils were Typic Haplustalfs (WS) and Ultic Paleustalfs (SB), and grassland soils were Typic Haplustalfs (WS) and Ultic Argixerolls (SB). Soils formed under pine canopy tended to be deeper, have greater total clay, lower pH and base saturation than soils formed under grass or shrub vegetation. Higher Feo/Fed ratios from selective dissolution indicate that iron oxides in the pine soils may be less crystalline than in the grass soils, corresponding to decreased drying of the pine soils due to summer fog drip. On a total profile basis, total pedogenic iron (Fed) and Feo/Fed ratios also indicate that the pine soils are more weathered than the grass soils, and that the schist soils may be more weathered that the rhyolitic tuff/breccia soils. The apparent ratio of kaolinite to smectite, based on XRD peak intensity, is highest in the upper horizons and decreases with depth. A similar pattern is found in the WS grass soils. The SB pine soils are dominated by quartz and feldspar in the silt and sand fractions, and kaolinite in the fine clay fraction, with smectite found in the lower horizons of the pedon. The SB grass soils are dominated by smectite in the fine clay fraction, with minor amounts of kaolinite.

Mots clés : Fog, Pedogenesis, Santa Cruz Island, California, Pinus muricata

Présentation et l version intégrale (PQDT Open)

Page publiée le 17 décembre 2010, mise à jour le 11 décembre 2019