Agricultural causes of desertification risk in Minqin, China

This study uses statistical modeling techniques to develop a desertification risk index (RI) for Minqin County, Gansu Province, China. Twenty socio-economic factors were selected and compared with the RI results to explore the spatial and temporal variability of desertification risk in the study area and to identify possible local driving forces behind desertification risk. The explanatory factors were different in 1988, 1992 and 1997, possibly reflecting the role of temporal variation as a contributor to desertification. The average number of sheep per-household was found to be an important indicator of change in desertification risk, while changes in ridge crop planting area explained the distribution of the rate of change in desertification risk in 1988-1992. The results suggests that the RI was useful in expanding the understanding of spatial temporal desertification issues in Minqin County, as well as identifying a current set of agricultural activities related to desertification risk. Further, given the limited nature of consistent data and observations for the area, development of the RI also served to establish a baseline for future investigations into desertification change and the risks such change might pose for the region.     

The Applicability of National Critical Loads Data in Assessing Designated Sites

Critical loads have been successfully used within Europe in the development of effects-based policies for pollution abatement, including the Second Sulphur Protocol and the Protocol to abate acidification, eutrophication and ground-level ozone (CLRTAP, 1979). This success has encouraged the UK Environment Agency and Conservation Agencies to use the national critical load maps as a screening tool in assessing the threats from acidification and eutrophication to designated (Natura 2000) sites. The UK maps of critical loads are based on national-scale data sets appropriate for national-scale assessments, and were never intended for use at the site-specific level. Site-based assessments are often targeted at Special Areas of Conservation, a sub-set of the UK Natura 2000 sites. The spatial data available includes the boundaries of the sites but not the location of the designated features. Ancillary data is variable from one site to another; habitat types may be described in detail with cross-reference to classes of the National Vegetation Classification (NVC: Rodwell, 1991 et seq), but information available on soils and geology is generalised and has not been related to the habitats or species being protected. Hence it can be difficult to relate the individual sites to the national maps, even where appropriate to do so. This paper examines the underlying uncertainties in the national critical load maps showing how the maps could give misleading results if used for site-specific assessments. It also includes advice on how to determine when the national data may be appropriate as a policy-tool at the site-level.     

Prediction of fish bioconcentration factors of nonpolar organic pollutants based on molecular connectivity indices.

The relationship between bioconcentration factors and molecular connectivity indices was investigated. A regression model was developed using 80 measured BCFs of nonpolar organic pollutants. The five topological parameters used were 1 chi, 2 chi, 3 chi c, 0 chi v and 2 chi v. Modified jackknife tests were applied to examine the robustness of the model by repeatedly removing a set of or a class of compounds from the database. The model was compared with one using Kow as an independent parameter. The mean absolute errors for the 80 compounds studied were 0.288 and 0.302 log-unit for the two models, respectively.     

Predicting Sample Source Location from Soil Analysis Using Neural Networks

A system combining a national soils database with a neural network was developed for prediction of source location for soil samples. The neural network was trained to predict environmental characteristics, which can be of crucial importance to investigating officers in a police operation or to environmental agencies attempting to locate the source of a pollutant. When coupled with maps of environmental conditions and a generalized opinion pool approach, the system was used to produce weighted maps of source location. The system was capable of reducing search areas of a sample source to less than 0.1% of the total area.     

Responses of Desert Annual Plants to Ozone and Water Stress in an in situ Experiment

Desert winter annual plants: Camissonia claviformis, C. hirtella, Caulanthus cooperi, Chaneactis carphoclinia, C. stevioides, Cryptantha angustifolia, C. pterocarya, Erodium cicutarium, Festuca octoflora, Lupinus concinnus, Oenothera californica, Plantago insularis, Platystemon californica, Salvia columbariae, Thelypodium lasiophyllum, and Thysanocarpus curvipes growing on irrigated and non-irrigated plots were exposed in situ to elevated levels of ozone dispensed from an open air exposure system. Plants were exposed intermittently to a gradient of ozone of concentrations ranging between 44 and 133 ppb (nL L^?1) for 35 h over a total of 216 h. Only three species were injured by ozone at the highest ozone concentrations. Leaf injury to C. claviformis—2 percent total foliar injury (TFI), C. hirtella—1 percent TFI, and Erodium cicutarium—2 percent TFI, developed at the highest ozone concentrations. Leaf injury to these species was similar on the irrigated and nonirrigated plots. Leaf water potential and stomatal conductance significantly decreased in C. claviformis, and C. hirtella due to water stress but not ozone. Similar trend for net photosynthesis was also determined. The highest water potential and stomatal conductance values as well as the largest differences in water potential between irrigated and non-irrigated plants were found in the morning.     

Toxic Substances in the Atmospheric Environment Discussion

The Critical Review on Toxic Substances in the Atmospheric Environment was presented by Bernard D. Goldstein at the 76th Annual Meeting of the Air Pollution Control Association in Atlanta, Georgia. Dr. Goldstein summarized his paper, which had been published in the May 1983 issue of JAPCA. Prepared discussions presented at the Critical Review Session are reproduced here. In addition, comments made from the floor and through the mails have been formalized and are published along with closing remarks by Dr. Goldstein. Dr. Paul J. Lioy served as Moderator for the 1983 Critical Review Session.     

Biotic control of stream fluxes: spawning salmon drive nutrient and matter export

Organisms can control movements of nutrients and matter by physically modifying habitat. We examined how an ecosystem engineer, sockeye salmon (Oncorhynchus nerka), influences seasonal fluxes of sediments, nitrogen (N), and phosphorus (P) in streams of southwestern Alaska. The purpose of this study was to investigate whether salmon act as net importers or net exporters of matter and nutrients from streams and how these roles change as a function of salmon population density. We measured discharge and concentrations of suspended sediments and total N and P every 7-14 days for up to four summers in 10 streams spanning a gradient in salmon densities. We statistically allocated whole-season fluxes to salmon activities, such as excretion and bioturbation, and to export by hydrologic discharge. In addition, we used counts of spawning salmon to estimate nutrient and matter imports by salmon to streams. Large seasonal pulses of suspended sediments, P, and N were associated with salmon spawning activities, often increasing export an order of magnitude higher than during pre-salmon levels. Years and streams with more salmon had significantly higher levels of export of sediments and nutrients. In addition, years with higher precipitation had higher background export of P and N. Salmon exported an average of the equivalent of 189%, 60%, and 55% of total matter, P, and N that salmon imported in their bodies. The relative magnitude of export varied; salmon exported more than their bodies imported in 80%, 20%, and 16% across all streams and years for sediments, P, and N, respectively. A bioassay experiment indicated that the P exported by salmon is directly available for use by primary producers in the downstream lake. These results demonstrate that salmon not only move nutrients upstream on large spatial scales via their migration from the ocean and subsequent death, but also redistribute matter and nutrients on finer spatial scales through their spawning activities.     

Experimental evidence for food limitation and sex-specific strategies of American kestrels (<Emphasis Type="Italic">Falco sparverius</Emphasis>) provisioning offspring

For birds with altricial young, the brood-rearing period is one of the most energetically expensive periods in their lives and may be the bottleneck for fitness. Because parents are expected to be prudent in allocating resources between reproduction and self-maintenance, food supply should be an important factor determining reproductive decisions during brood rearing. Parents with abundant food are expected to have enhanced fitness because they are able to reduce their work rates and increase their own survival chances, because their offspring may be of higher quality, or some combination of these. However, few studies have simultaneously documented all of these variables in a single investigation. We performed a food supplementation experiment to test how food supply influenced provisioning decisions by parent American kestrels (Falco sparverius). Female kestrels showed a strong response to extra food and reduced their provisioning rates. As a result, supplemented females had higher return rates than control females, suggesting significant effects of food on female survival. Because females used extra food to increase their fitness, our results suggest that kestrels raising offspring are limited by food. Male kestrels whose nests were supplemented also responded to extra food by reducing provisioning, but to a much lesser extent than their mates. Male parents did not appear to benefit from supplementation, as their return rates were similar to control males. The total amount of food received on a daily basis by nestlings was similar between supplemented and control nests. Supplemented offspring therefore did not fledge in better condition or have higher survival rates than control nestlings; the only significant factor consistently affecting offspring condition and survival was weather.