ABSTRACT
Desert oases are fragile agrarian areas, very vulnerable to sand encroachment by wind. Ensuring their conservation highly depends on our capacity to identify sand encroachment patterns, e.g. the origin of sand and its spatial distribution in the irrigated plots. Here we show how to tackle this issue using the case study of Erg Chebbi (Morocco), where two oases (Hassilabiad and Merzouga) are surrounded by dunes, Hamada and alluvial sediments from the Wadi Ziz. We combine field interviews with the study of wind dynamics, sediment sampling, Particle Size Distribution (PSD) tests and End-Member Modelling Analysis (EMMA). We observe that the most relevant contributor to sand encroachment is the Wadi Ziz (30%), followed by the Hamada (28%), an undetermined source of dust (25%), and the Erg dunes (16%). These genetically different sediments cluster unevenly in the oases, indicating the existence of areas with contrasting degrees of exposure to sedimentary sources. The results allow to define on solid grounds which sand source areas should be stabilized first in order to obtain the greatest reduction in sand encroachment. Our approach also provides policy-makers with better tools to identify which spots are specially vulnerable to accumulate a specific sediment, thus allowing for a more nuanced management of sand in oasis environments.
ABSTRACT
Historical and traditional flood-irrigated (FI) schemes are progressively being upgraded by means of drip irrigation (DI) to tackle current water and demographic challenges. This modernization process is likely to foster several changes of environmental relevance at the system level. In this paper we assess the effects derived from DI uptake on soil health and structure in ancient FI systems through the case study of Ricote, SE Spain, first established in the 10-13th centuries CE. We approach the topic by means of physico-chemical analyses (pH, electrical conductivity, available P, carbon analyses, bulk density, soil water content and particle size distribution), Electrical Resistivity Measurements (ERT) and robust statistics. We reach a power of 1-ß = 77 aiming at detecting a large effect size (f ≥ 0.4). Results indicate that, compared to FI, DI soils present significantly higher water content, a higher proportion of coarse particles relative to fines due to clay translocation, and less dispersion in salt contents. The soils away from the emitters, which were formerly FI and comparatively account for larger extensions, appear significantly depleted in organic matter, available P and N. These results are not affected by departures from statistical model assumptions and suggest that DI uptake in formerly FI systems might have relevant implications in terms of soil degradation and emission of greenhouse gases. A proper assessment of the edaphological trade-offs derived from this modernization process is mandatory in order to tackle undesired environmental consequences.
Subject(s)
Agricultural Irrigation , Environmental Monitoring , Soil Pollutants , Agriculture , Soil , Spain , WaterABSTRACT
The ages of a fruticose lichen of Usnea aurantiacoatra (Jacq.) Bory, from Fildes Peninsula, King George Island, Southwest Antarctic, were determined by radiocarbon (14C), and it is 1993-1996 at bottom and 2006-2007 at top of the lichen branch. The growth rates of U. aurantiacoatra calculated are 4.3 to 5.5 mm year(-1) based on its length and ages. The comparisons show that the growth rates of U. aurantiacoatra are higher than those of U. antarctica (0.4 to 1.1 mm year(-1)). The growth rates of fruticose lichens are always higher, usually >2 mm year(-1), than those of crustose ones, usually <1 mm year(-1), in polar areas. A warming trend on Fildes Peninsula is recorded in the period from 1969 to 2010 obviously: the mean annual temperature rose from -2.75 to -1.9°C and the average temperature of summer months from 0.95 to 1.4°C, as well as the average temperature of winter months from -6.75 to -5.5°C. The alteration of lichen growth rates in polar areas may respond to the climatic and environmental changes, and the lichens may act as bio-monitor of natural condition.
