Spectral Characteristics of Cyanobacteria Soil Crust in Semiarid Environments Arnon Karnieli,* Giora J. Kidron,* Cornelia Glaesser, † and Eyal Ben-Dor ‡ Large areas of sand fields in arid and semiarid regions communities comprising mosses, lichens, liveworts, algae, are covered by cyanobacteria soil crusts. The objective of fungi, cyanobacteria (used to be called blue-green algae), this article is to analyze (systematically throughout the and bacteria (West, 1990). This phenomenon has been VIS, NIR, and the SWIR regions of the spectrum) the reported from the Middle East, the African Sahel and unique spectral features of cyanobacteria crust relative to the Sahara, North and South America, Central Asia, Aus- bare sands and under different moisture conditions. It tralia, and from other locations. was found that: 1) When biogenic soil crusts are wet, Over sand dune environments, cyanobacteria are the their NDVI value can reach 0.30 units due to their pho- most common component of the crust but are often ac- tosynthetic activity; 2) the closer the red edge inflection companied by soil algae, mosses, and lichens. Their point is to the longer wavelengths, the higher the relative structure is similar to that of bacteria, but their photo- abundance and distribution of the microphytic commu- synthetic mechanism resembles that of the green algae. nity; 3) the phycobilin pigments, which are unique to cy- Cyanobacteria have the common chlorophyll a but also anobactria, contribute to higher reflectance in the blue phycobilin pigments. Many are able to fix atmospheric region relative to the sand substrate; 4) a crust index nitrogen which is needed for proteins. All these features based on this uncommon spectral feature can be useful make it possible for them to occupy an ecological niche for detecting and mapping, from remote sensing imagery, in the desert where others cannot live due to extreme different lithologic/morphologic units; 5) although most high temperatures, high pH, and salinity. dune sand areas are generally made of quartz, other no- The cyanobacteria crust constitutes a relatively small table features appear on their spectra. In the study area, portion of the soil profile, only one to a few millimeters, there are absorption features representing minerals (iron but since it occupies the uppermost part of the profile, oxides at 860 nm and clay minerals at 2200 nm) and bio- it plays an important role in the desert ecosystem. The genic crusts (chlorophyll at 670 nm and organic matter cyanobacteria crust, due to the adhesive properties of its at 1720 nm, 2180 nm, and 2309 nm). Elsevier Science filaments, stabilizes the mobile sand dune and prevents Inc., 1999 water and wind soil erosion (Danin, 1991). The composi- tion of cyanobacteria together with relative high content in silt and clay particles change the soil water regime by INTRODUCTION affecting runoff, rain interception, water infiltration and Many arid and semiarid surfaces, whether soils or rocks, percolation, surface evaporation, water-holding capacity, are covered by biogenic crusts of different microphytic and soil moisture content (Lange et al., 1986; Yair, 1990; Zombre et al., 1996; Verrecchia et al., 1995; Kidron and Yair, 1997). It also improves soil fertility due to changes * J. Blaustein Institute for Desert Research, Ben Gurion Univer- sity, Sede-Boker, Israel in the content of different elements such as amino nitro- † Institute of Geography, Martin Luther University, Halle, gen, oxygen, organic carbon, nutrients, and more (Shields Germany et al., 1957). The existence of microphytic communities ‡ Department of Geography, Tel Aviv University, Tel Aviv, Israel in the topsoil provides a starting material for the produc- Address correspondence to A. Karnieli, The Remote Sensing Lab- oratory, Jacob Blaustein Institute for Desert Research, Ben Gurion tion of other soil components (Shields and Drouet, 1962). University of the Negev, Sede Boker Campus 84990 Israel. E-mail: From the remote sensing point of view Karnieli et al. KARNIELI@BGUMAIL.BGU.AC.IL Received 17 April 1998; revised 5 November 1998. (1996) have shown that when the biogenic crust is wet, REMOTE SENS. ENVIRON. 69:67–75 (1999) Elsevier Science Inc., 1999 0034-4257/99/$–see front matter 655 Avenue of the Americas, New York, NY 10010 PII S0034-4257(98)00110-2