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811.
The Mersey Basin Campaign was established in 1985 in the North West of England to address continuing problems of water quality and associated landward dereliction of the River Mersey and its tributaries. The Campaign's premise that water quality should be improved both for its own sake and as a stimulus to regeneration has proved to be well founded and has subsequently been extended to embrace community action to help nurture watercourse improvement and care. The Campaign can now be seen as a model for engaging co-ordinated environmental action through a partnership approach. This paper explores the nature of the Mersey Basin Campaign as an example of the new structures which are being developed in order to help deliver the new environmentalpolicy agenda. It is argued that the Campaign stands as a model for what will become an increasing need to develop focused environmental planning and management at the sub-regional and regional scales.  相似文献   
812.
Chirostoma charari and C. compressum, and they are presumed extinct. Twelve (63%) of the remaining species had declines in distribution. Sixteen (80%) of the 20 localities sampled had lost species. The greatest declines occurred in Lago de Cuitzeo proper and in the lower portion of the Río Grande de Morelia watershed. Species losses from the lake were attributable to drying and hypereutrophication of the lake because of substantial reductions in the amount and quality of tributary inputs, whereas losses from the Río Grande de Morelia watershed were the result of pollution from agricultural, municipal, and industrial sources, especially in the region around the city of Morelia. Three localities in the upper portion of the Río Grande de Morelia watershed—Cointzio reservoir, La Mintzita spring, and Insurgente Morelos stream—contained most of the remaining fish species diversity in the basin and deserve additional protection. Fish faunal changes indicated major declines in the health of aquatic ecosystems in the Morelia–Cuitzeo basin.  相似文献   
813.
Experimental short-term desalination and drainage of salt marsh cores in greenhouse microcosms caused Spartina production to increase after one growing season, reflecting decreased salt stress and sulfide toxicity. However, production thereafter declined, likely due to pyrite oxidation and acidification in drained treatments and sulfide accumulation in waterlogged treatments. A survey of longer-term (decadal) effects of diking on peat composition of Cape Cod, Massachusetts, USA, marshes revealed acidification, Fe(II) mobilization, and decreased organic content in drained sites. Despite the aerobic decomposition of organic matter, abundant nutrients remained as sorbed NH4 and mineral-bound PO4. In diked, seasonally waterlogged sites, porewater alkalinity, sulfide, ammonium and orthophosphate were much lower, and organic solids higher, than in adjacent natural marsh. Seawater was added to cores from diked marshes to study the effects of tidal restoration. Salination of the drained peat increased porewater pH, alkalinity, ammonium, orthophosphate, Fe, and Al; copious ammonium N, and Fe(II) for sulfide precipitation favored Spartina growth. Salination of diked–waterlogged peat increased sulfate reduction and caused 6–8 cm of sediment subsidence. The resulting increase in porewater sulfides and waterlogging decreased vigor of transplanted Spartina alterniflora. Results indicate that seawater restoration should proceed cautiously to avoid nutrient loading of surface waters in drained sites or sulfide toxicity in diked–waterlogged marshes.  相似文献   
814.
815.
ABSTRACT: Erosion and sedimentation data from research watersheds in the Silver Creek Study Area in central Idaho were used to test the prediction of logging road erosion using the R1-R4 sediment yield model, and sediment delivery using the “BOISED” sediment yield prediction model. Three small watersheds were instrumented and monitored such that erosion from newly constructed roads and sediment delivery to the mouths of the watersheds could be measured for four years following road construction. The errors for annual surface erosion predictions for the two standard road tests ranged from +31.2 t/ha/yr (+15 percent) to -30.3 t/ha/yr (-63 percent) with an average of zero t/ha/yr and a standard deviation of the differences of 18.7 t/ha/yr. The annual prediction errors for the three watershed scale tests had a greater range from -40.8 t/ha/yr (-70 percent) to +65.3 t/ha/yr (+38 percent) with a mean of -1.9 t/ha/yr and a standard deviation of the differences of 25.2 t/ha/yr. Sediment yields predicted by BOISED (watershed scale tests) were consistently greater (average of 2.5 times) than measured sediment yields. Hillslope sediment delivery coefficients in BOISED appear to be overly conservative to account for average site conditions and road locations, and thus over-predict sediment delivery. Mass erosion predictions from BOISED appear to predict volume well (465 tonnes actual versus 710 tonnes predicted, or a 35 percent difference) over 15 to 20 years, however mass wasting is more episodic than the model predicts.  相似文献   
816.
A toxic axenic strain of Alexandrium fundyense is shown to be capable of removing dissolved free amino acids (DFAAs) until concentrations are similar (low nM) to those found in natural waters. Uptake is greatest during exponential growth, rather than during C and/or N-stress as is usual in diatoms and other flagellates. A wide range of amino acids can be taken up, their concentration being decreased within a few hours to the levels observed prior to DFAA addition. The maximum rate of DFAA-N uptake, during early exponential phase, was 0.8 pmol-N cell−1 h−1, equivalent to ≃20% of the total N requirement. More typically, the contribution of DFAA-N was only ≃5%. However, these uptake rates are not sustainable. It is apparent that this organism cannot use amino-N to support significant growth, even though it can take up DFAAs. This, and the fact that the composition of the internal amino acid pool differed from that externally, is further evidence that the N-physiology of this genus is abnormal (differences to other dinoflagellates include an abnormally high concentration of glutamine and arginine, an effective absence of amine X, and release of nitrite during the␣concurrent assimilation of nitrate and ammonium in␣darkness). There is no evidence that the use of DFAAs enhance toxin content, except when cells are supplied with very high (unnatural) concentrations of arginine. Received: 8 May 1989 / Accepted: 14 September 1998  相似文献   
817.
Patterns of sex ratio variation and maternal investment reported in the literature are often inconsistent. This could be due to intra- and inter-specific variation in social systems, but may also be a result of the a posteriori nature of much of this type of analysis or the testing of models which are inappropriate. Two recent papers reported directly opposed results concerning variation in offspring sex ratios in relation to maternal condition in roe deer, interpreting the results as support for the Trivers and Willard model and for the local resource competition hypothesis, respectively. In this paper, we present data on offspring sex ratios and early juvenile body weight from two long-term studies of this species to test predictions arising from these two models concerning sex biases in litter composition and maternal care. First, we observed no consistent pattern of sex differences in an index of weaning weight or body weight at 1 month old in either population, indicating a lack of sex bias in maternal care. However, in one population, higher maternal body weight was associated with higher juvenile body weight of daughters, but not of sons. Secondly, we found a negative, but not statistically significant, relationship between maternal body weight and litter sex ratio such that heavier females tended to produce more daughters and lighter females to produce more sons. These results indicate that roe females which have additional investment potential available do not invest it in sons, as predicted by the Trivers and Willard model. Our results may provide some support that roe deer are subject to local resource competition acting at the level of the individual mother; however, the fact that particular trends in sex ratio data can be explained in functional terms provides no indication that they are actually adaptive. Received: 9 December 1997 / Accepted after revision: 11 November 1998  相似文献   
818.
819.
This study among a sample of 207 general practitioners (GPs) uses a five‐year longitudinal design to test a process model of burnout. On the basis of social exchange and equity theory, it is hypothesized and found that demanding patient contacts produce a lack of reciprocity in the GP–patient relationship, which, in turn, depletes GPs' emotional resources and initiates the burnout syndrome. More specifically, structural equation analyses confirmed that—both at T1 and T2—lack of reciprocity mediates the impact of patient demands on emotional exhaustion. Emotional exhaustion, in turn, evokes negative attitudes toward patients (depersonalization), and toward oneself in relation to the job (reduced personal accomplishment). Moreover, this process model of burnout was confirmed at T2, even after controlling for T1‐scores on each of the model components. Finally, T1 depersonalization predicted the intensity and frequency of T2 patient demands, after controlling for T1 patient demands. This major finding suggests that GPs who attempt to gain emotional distance from their patients as a way of coping with their exhaustion, evoke demanding and threatening patient behaviors themselves. The theoretical and practical implications of these findings are discussed. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   
820.
This research examined linkages between mentor leadership behaviors (laissez‐faire, transactional contingent reward, and transformational), protégé perception of mentoring functions received (career development and psychosocial support) and job‐related stress of 204 mentor–protégé dyads. Results of Partial Least Squares analysis revealed that mentor transformational behavior was more positively related to mentoring functions received than transactional contingent reward behavior, while mentor laissez‐faire behavior was negatively related to mentoring functions received. Both mentor transformational behavior and mentoring functions received were negatively related to protégé job‐related stress. The relationship between mentor transformational behavior and protégé job‐related stress was moderated by the level of mentoring functions received. Results are discussed as they relate to researchers and practitioners who are becoming interested in finding ways to develop organizational members and allay job‐related stress. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   
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