Establishing a tracer-based sediment budget to preserve wetlands in Mediterranean mountain agroecosystems (NE Spain)

Abstract

Mountain wetlands in Mediterranean regions are particularly threatened in agricultural environments due to anthropogenic activity. An integrated study of source-to-sink sediment fluxes was carried out in an agricultural catchment that holds a small permanent lake included in the European NATURA 2000 Network. More than 1000 yrs of human intervention and the variety of land uses pose a substantial challenge when attempting to estimate sediment fluxes which is the first requirement to protect fragile wetlands. To date, there have been few similar studies and those that have been carried out have not addressed such complex terrain. Geostatistical interpolation and GIS tools were used to derive the soil spatial redistribution from point (137)Cs inventories, and to establish the sediment budget in a catchment located in the Southern Pyrenees. The soil redistribution was intense and soil erosion predominated over soil deposition. On the areas that maintained natural vegetation the median soil erosion and deposition rates were moderate, ranging from 2.6 to 6 Mg ha yr(-1) and 1.5 to 2.1 Mg ha yr(-1), respectively. However, in cultivated fields both erosion and deposition were significantly higher (ca. 20 Mg ha yr(-1)), and the maximum rates were always associated with tillage practices. Farming activities in the last part of the 20th century intensified soil erosion, as evidenced by the 1963 (137)Cs peaks in the lake cores and estimates from the sediment budget indicated a net deposition of 671 Mg yr(-1). Results confirm a siltation risk for the lake and provide a foundation for designing management plans to preserve this threatened wetland. This comprehensive approach provides information useful for understanding processes that influence the patterns and rates of soil transfer and deposition within fragile Mediterranean mountain wetlands subjected to climate and anthropogenic stresses.

Estimating soil redistribution patterns with 137Cs measurements in a Mediterranean mountain catchment affected by land abandonment

“…The results of the sediment budget for the study catchment evidence that higher soil redistribution rates are concentrated in the relatively small central agricultural area and do not occur over most of the catchment. The specific sediment yield in our catchment is comparable with values of 7.56 Mg ha − 1 yr −1 obtained in nearby small endorheic catchment (Navas et al, ). A similar specific sediment yield of 4.7 Mg ha − 1 yr −1 was computed in the Barasona reservoir catchment (Palazón & Navas, ).…”

“…For example, agricultural lands occupy the lowest altitudes and have lower percentages of stoniness, SOM, and 137 Cs activity. This pattern is generally reported in different environments where zones with higher percentages of vegetation cover are related to high 137 Cs activities (Fukuyama, Onda, Takenaka, & Walling, ; Navas, Gaspar, López‐Vicente, & Machín, ; Schoorl, Boix Fayos, de Meijer, van der Graaf, & Veldkamp, ) and lower soil redistribution rates (Navas et al, ). In addition to the accumulation of fine particles at the bottom of hillslopes where most cultivated fields are located, tillage practices contribute to the breakdown of soil aggregates.…”

“…In general, scrub areas were abandoned more recently than natural forest areas, although poorer soil conditions at the time of abandonment cannot be totally excluded. Both 137 Cs and SOM were the lowest under cropland, which could both be related to the higher erosion rates that lead to the preferential export of fine particles enriched in 137 Cs and organic matter (Navas et al, ). Our spatial analysis indicated a similar distribution of 137 Cs and SOM suggesting both are influenced by similar redistribution processes.…”

“…To date, there are only few studies using 137 Cs to quantify soil redistribution rates at catchment scale (Mabit & Bernard, ; Navas, López‐Vicente, Gaspar, & Machín, ; Porto, Walling, Ferro, & di Stefano, ). Furthermore, fewer studies investigated the impact of recent land use changes on soil erosion (Evrard et al, ; Gaspar & Navas, ; Gharibreza et al, ; Navas, López‐Vicente, Gaspar, Palazón, & Quijano, ). Accordingly, we quantify soil redistribution rates using fallout 137 Cs measurements and Geographic Information Systems to investigate changes in spatial variability of soil redistribution patterns resulting from land use change associated with vegetation cover in the recent decades.…”

Validating the Use of 137Cs Measurements to Derive the Slope Component of the Sediment Budget of a Small Rangeland Catchment in Southern Italy

“…However, while valuable as a concept and synthesizing tool, establishing a sediment budget can prove a difficult task owing to the wide range of processes involved and their temporal and spatial variability. Most successful attempts to establish a sediment budget have involved the integration of several different techniques/methodologies that together provide the required information on sediment mobilization, redistribution, transport and storage within a catchment (Loughran et al ., ; Walling et al ., , ; Keesstra et al ., ; Porto et al ., , ; Gellis & Walling, ; Navas et al ., , , Minella et al ., ). The use of fallout radionuclides, particularly caesium‐137 ( 137 Cs), as a sediment tracer has been shown by many of those studies to provide an effective and valuable means to document the mobilization and redistribution of soil and sediment on the slopes of a catchment (Mekuria et al ., ; Li et al ., ).…”