Dynamics of mule deer forage in the Sonoran Desert

Forage availability for mule deer (Odocoileus hemionus) in the Sonoran Desert depends on plant biomass, which is influenced by rainfall. We determined how rainfall, temperature and plant characteristics affected biomass of deer forage. We measured forage biomass, rainfall and temperature every 3 months from April 2000 to December 2002. Quarterly rainfall ranged from <1 to 57 mm, and forage biomass in desert washes fluctuated between 6 and 34 g m⁻². There was a positive relationship between forage biomass and rainfall the previous six months (p<0.001), and a negative relationship between biomass and average temperature the previous 3 months (p<0.001). Quarterly forage growth was positively influenced by rainfall (p<0.001) and negatively influenced by forage biomass (p<0.001). The relationships between deer forage and environmental factors established here will be useful in understanding population ecology of mule deer as part of an interactive model of plant–herbivore dynamics in arid environments.     

Growth response of the saltbush Atriplex nummularia L. to inoculation with the arbuscular mycorrhizal fungus Glomus intraradices

Plantlets of Atriplex nummularia were inoculated with the arbuscular mycorrhizal fungi Glomus intraradices in a pot experiment. Plants were grown in a low P soil. Highly significant growth response of a Chenopodiaceae was recorded for the first time. Mycorrhizal colonization of roots was well developed, internal hyphae and vesicles were observed, but not arbuscules. These observations suggest that arbuscules are not necessary to obtain significant growth stimulation from mycorrhizal inoculation. Atriplex nummularia is already used as forage crops, its high mycorrhizal dependency offers possibilities to develop this production and revegetation strategies.     

The 1786 earthquake-triggered landslide dam and subsequent dam-break flood on the Dadu River, southwestern China — Reply

A short reply to discussion by Chanson.     

Environmental Changes at the Desert Margin: An Assessment of Recent Paleolimnological Records in Lake Qarun, Middle Egypt

Lake Qarun has been profoundly affected by a combination of human activities and climatic changes during the past 5000 years. Instrumental records available for the 20th century show that during most of this period both lake water level and salinity increased and that by the late 1980s lake water salinity was approximately that of seawater. Sediment cores (c. 1 m long) were collected from this shallow (Z_max 8.4 m) saline lake in 1998 and the master core (QARU1) was used to examine the potential of paleolimnology for reconstructing the recent environmental history of the site. According to ¹³⁷Cs and ²¹⁰Pb radio-assay, the recent sediment accumulation rate in QARU1 was around 5 mm year⁻¹ during the latter half of the 20th century but radionuclide levels were low. Spheroidal carbonaceous particles (SCPs) were present in the upper c. 30 cm of QARU1 and indicates contamination by low level particulate pollution, probably beginning around 1950. The record of exotic pollen (Casuarina) indicated that sediment at 51–52 cm depth dated to around 1930. Otherwise the pollen spectra indicated a strongly disturbed landscape with high ruderals and increased tree planting particularly since c. 1950. Diatom records were strongly affected by taphonomic processes including reworking and differential preservation but typical marine diatoms increased after the 1920s. Instrumental records show that the lake became more saline at this time. Freshwater taxa were present at approximately similar abundances throughout the core. This distribution probably reflected a combination of processes. Reworking of ancient freshwater diatomites is one likely source for freshwater diatoms in QARU1 but some taxa must also be contributed via the freshwater inflows. Overall, the diatom stratigraphy indicated increasingly salinity since the 1920s but provided no firm evidence of lake eutrophication. Diatom inferred salinity reconstructions were in only partial agreement with instrumental records but inferred for the lower section of the core (pre 20th century to the 1960s) accord with measured water salinity values. Surficial sediments of Lake Qarun contain environmental change records for the 20th century period but high sediment accumulation rate and pollen reflect the high degree of human disturbance in the region. Because of poor preservation and evidence of reworking, the relationships between diatom records and past water quality changes require careful interpretation, especially in the upper section of the core. Nevertheless, early to mid 20th century measurements of increasing lake water salinity are well supported by sediment records, a change that is probably linked to ingress of saline ground water     

Magnetic remanence acquisition in Finnish lake sediments

Summary. Magnetic studies have been carried out on organic sediments from five Finnish lakes to determine the carrier(s) of the stable NRM and to find how the remanence is acquired. Single or pseudo-single domain 'magnetite' is thought to carry the NRM. It was found that drying and cooling sediment samples resulted in a loss of NRM which was attributed to the misalignment of small magnetic particles. Low-field experiments were carried out on sediment samples in different physical states and from the results of these investigations it was concluded that post-depositional processes are important in the acquisition of an NRM. Stabilization of magnetic grains is thought to be due to the growth of gels in the organic sediment rather than to dewatering.