Excreta disposal in Dar-es-Salaam

The sociocultural and socioeconomic situation of sanitation in Dar-es-Salaam (Dsm), Tanzania, was studied with explicit emphasis on pit-latrines. Without considering the sociocultural conditions, the so-called best solution might not be the right one. Therefore, in order to achieve the intended goal, a literature review, a questionnaire survey, and personal visits to the chosen study areas were done. In total, 207 household questionnaires were filled in 16 areas of the city. Interviewers did house-to-house visits and questionnaires were filled out on the spot. Results indicated that the city population is about 3.8 million at present, with over 80% of the dwellers using pit-latrines; some 3% use septic tanks with soakage pits, about 6% are connected to the sewerage system, and 1% have no excreta disposal facility. Difficulties faced include dismal budget allocations, fragmentation of sanitation activities among subsectors, lack of or poor sanitation record keeping, unsatisfactory machinery for septic tank and pit-latrine emptying, lack of a clear policy on pit-latrine handling and, in competition for resources, low priority is accorded to an excreta disposal system among the people. City residents will continue to use the pit-latrines for a long time to come. Reusing the fecal sludge is not known by most city dwellers and is influenced by sociocultural habits. To prevent groundwater pollution and to recover useful products in human excreta and urine, ecological sanitation toilets and anaerobic digesters offer a good option.     

Sustainable rural development in Sokoto State, Nigeria

In Nigeria, as in most countries, institutional barriers to successful rural development exist and need to be addressed. In Sokoto State, a variable and unpredictable Sahelian climate in combination with conditions of high population growth, low levels of income, and environmental degradation, create and intensify institutional challenges. This study examines the sustainability of government initiatives regarding the provision of agricultural inputs, assistance and extension services to farmers, and the extent to which agency efforts are coordinated and integrated, particularly regarding water management. In some cases, rural development agencies demonstrated the capability to meet the needs of the people. Some farmers were satisfied with government assistance and in some areas the tube well programme was quite successful. Yet in Sokoto State many institutional barriers to sustainable rural development exist and need to be addressed. In general, implementation strategies and management procedures appeared narrowly focused and placed little emphasis on coordination and integration among rural development agencies. The result was often inappropriate overlap or oversights in activities .     

Regulated flushing in a gravel-bed river for channel habitat maintenance: A Trinity River fisheries case study

The operation of Trinity and Lewiston Dams on the Trinity River in northern California in the United States, combined with severe watershed erosion, has jeopardized the existence of prime salmonid fisheries. Extreme streamflow depletion and stream sedimentation below Lewiston have resulted in heavy accumulation of coarse sediment on riffle gravel and filling of streambed pools, causing the destruction of spawning, nursery, and overwintering habitat for prized chinook salmon (Salmo gairdnerii) and steelhead trout (Oncorhynchus tschawytscha). Proposals to restore and maintain the degraded habitat include controlled one-time remedial peak flows or annual maintenance peak flows designed to flush the spawning gravel and scour the banks, deltas, and pools. The criteria for effective channel restoration or maintenance by streambed flushing and scouring are examined here, as well as the mechanics involved.The liabilities of releasing mammoth scouring-flushing flows approximating the magnitude that preceded reservoir construction make this option unviable. The resulting damage to fish habitat established under the postproject streamflow regime, as well as damage to human settlements in the floodplain, would be unacceptable, as would the opportunity costs to hydroelectric and irrigation water users. The technical feasibility of annual maintenance flushing flows depends upon associated mechanical and structural measures, particularly instream maintenance dredging of deep pools and construction of a sediment control dam on a tributary where watershed erosion is extreme. The cost effectiveness of a sediment dam with a limited useful economic life, combined with perpetual maintenance dredging, is questionable.     

The role of stochasticity and priority effects in floodplain restoration.

This paper is a test of two widely held assumptions in the practice of riparian restoration: (1) if physical processes are restored, plant communities will naturally reassemble themselves, and (2) restored communities will resemble reference sites. Seasonal flooding was restored to two interconnected floodplains in the Central Valley of California (USA), and plant community establishment was studied for six years at 300 permanent vegetation plots. If these two assumptions are valid, then the two floodplains should end up with similar plant assemblages, and they should both have followed a similar trajectory. Then, once the relevant physical processes are restored, (1) plots with similar environmental conditions should have increasingly similar species compositions, (2) plant communities should become more stable and cohesive, (3) both species distributions and plant communities should respond to changes in environmental conditions, (4) plot diversity should decrease, and (5) perennial species should replace annuals. The plots were classified into communities using TWINSPAN, and these communities differed significantly with respect to the main environmental gradient (inundation). Bray-Curtis similarities were calculated for each pair of plots. Patterns in similarity were used to test the strength of communities and the relative importance of proximity and inundation. On the northern floodplain, there was a trend of increasing similarity for plots with similar environmental conditions over the course of the study; plant communities became more stable and clearly responded to changes in environmental conditions. Plot diversity decreased, and the proportion of perennial species increased. On the southern floodplain, however, plots with similar environmental conditions became less similar, while plots that were close together became more similar; plant communities did not become more stable though they did shift in response to changes in environmental conditions. Taken together, this evidence suggests that assembly of communities is more stochastic than deterministic.     

Determination of time-dependent partition coefficients for several pesticides using diffusion theory

Diffusion-retarded partitioning of pesticides with aggregated soils results in a time-dependent partition coefficient (Kd') which is different at equilibrium from the partition coefficient derived from conventional 24-h batch studies (Kd) measured on dispersed soil. An experiment was undertaken to determine the importance of Kd' for the prediction of pesticide concentrations in solutions bathing artificial soil aggregates and to determine whether diffusion theory could accurately predict the concentrations. Two clay soils were mixed with polyacrylamide to create artificial aggregates of 0.8, 1.4 and 1.7 cm diameter when dry. After saturation, the aggregates were immersed in solutions containing isoproturon or a mixture of isoproturon, chlorotoluron and triasulfuron. The decline with time of the pesticide concentrations in the bathing solution was monitored and the results were compared with predictions from a diffusion-based model. The effective diffusion coefficients of the compounds were obtained by either fitting the non-linear diffusion model to the data (D(ef)) or by independent calculations based on the properties of the compounds and of the aggregates (D(ec)). The diffusion model was able to predict the temporal variation in pesticide concentrations in the bathing solution reasonably well whether D(ef) or D(ec) values were used. However, equilibrium concentrations in solution were sometimes overestimated due to increased sorption with time at the particle scale. Overall, the ratio between D(ef) and D(ec) ranged from 0.23 to 0.95 which was a reasonable variation when compared to the range of aggregate sizes used in the experiments and of the Kd values of the compounds.     

Prenatal diagnosis of a craniopharyngioma using ultrasonography and magnetic resonance imaging

We report an infant with a craniopharyngioma which was detected in utero. Maternal uterine ultrasonography, done at 27 weeks because of polyhydramnios, revealed a 4 cm midline mass near the base of the fetal skull. At 31 weeks, magnetic resonance imaging of the maternal abdomen confirmed the presence of a mass in the region of the third ventricle and revealed hydrocephalus. Two days post-partum a computed tomography (CT)-guided needle biopsy of the mass was performed and recovered tissue which was histologically consistent with a craniopharyngioma. The infant' s postnatal period was complicated by seizures, which were treated with phenobarbital, and by progressive hydrocephalus, necessitating placement of a ventriculo-peritoneal shunt. He also received therapy for central hypothyroidism and diabetes insipidus. The infant' s parents refused permission for attempted resection of the tumour and he died at 8 weeks of age. This represents the second reported case of an antenatally detected craniopharyngioma. Four other cases of different intracranial tumours have been detected in utero using ultrasound, with no reported survivors past 3 days of age. There is a uniformly poor prognosis of such infants, but earlier diagnosis and intervention may change this result.     

Invasive prey impacts the abundance and distribution of native predators

While an extensive literature exists on the negative effects of invasive species, little is known about their facilitative effects on native species, particularly the role of invasives as trophic subsidies to native predators. The invasive gypsy moth (Lymantria dispar) undergoes periodic outbreaks during which it represents a super-abundant food source for predators capable of consuming it, particularly native cuckoos (Coccyzus erythropthalmus and C. americanus). We examined how gypsy moth outbreaks affect the abundance and distribution of cuckoos using the North American Breeding Bird Survey and 29 years of U.S. Forest Service gypsy moth defoliation records. Abundances of both Black-billed and Yellow-billed Cuckoos were significantly above average during outbreaks, but populations were average or below average in preceding and subsequent years, suggesting that cuckoos are immigrating to defoliations during outbreak years. Spatial analyses showed that cuckoo abundances approximately 40-150 km outside of defoliation areas were significantly below average, and these under-occupied breeding areas extended in all four compass directions around outbreaks. This result supports the idea that cuckoos locate gypsy moth outbreaks during a post-migratory nomadic phase. By shifting the annual distribution of cuckoos, gypsy moths may be shifting the trophic impact of cuckoos across large distances, which could affect native insect herbivores and plants.     

Modeling inverted biomass pyramids and refuges in ecosystems

Although the existence of robust inverted biomass pyramids (IBPs) seems paradoxical, they are well known to exist in planktonic communities, and have recently been discovered in pristine coral reefs and in a reef off the North Carolina coast. Understanding the underlying mechanisms which produce inverted biomass pyramids provides new ecological insights. Some ecologists hypothesize that “the high growth rate of prey and low death rate of predators” causes IBPs. However, we show this is not always the case (see Sections 3.1 and 4). We devise predator–prey models to describe three mechanisms that can lead to IBPs: (1) well-mixed populations with large prey turn-over rate, (2) well-mixed populations with prey immigration, and (3) non-mixed populations where the prey can hide in refuges. The three models are motivated by the three ecosystems where IBPs have been observed. We also devise three refuge mediated models, with explicit refuge size, which incorporate different prey responses in the refuge, and we discuss how these lead to IBPs.     

Contingent valuation of ecotourism development in country parks in the urban shadow

To optimise the use and management of Hong Kong's country parks, ecotourism has recently been promoted by the government and echoed by the leisure sector. Visitors' valuation of ecotourism development hitherto remains scant and could add a new dimension to the knowledge and management base. This study estimated the potential value of ecotourism development using the contingent valuation method (CVM). A total of 613 visitors in three country parks were interviewed. The results showed that the bid amounts and the motives to experience and learn more about nature were significant predictors of willingness-to-pay (WTP). The mean and median WTP were, respectively, HK$101.1 and HK$85.0 annually, varying slightly between parks. The differences were associated with the special ecological and accessibility characteristics of individual parks. The results could justify financial support from the government for ecotourism development and associated nature conservation endeavours and promote the incorporation of natural resource valuation in formulation of public policies in Hong Kong and other developing regions.