Central place theory and intercommunity input-output analysis

This paper explores trade hierarchies and interindustry relationships, first in theory, then in the empirical context of a western United States timber economy facing a large reduction in its timber harvest. Principles of central place theory guide construction of a hybrid intercommunity input-output model. A nonsurvey technique for estimating central place trade is developed, and is compared with MRIO methods. The effect of central place dominance on intercommunity multipliers is examined theoretically, as is the nature of feedback linkages in a central place hierarchy. The empirical magnitude of feedback effects is small, and although effects vary in magnitude from community to community, neglect of central place considerations can understate intercommunity sawmill multipliers by as much as 36 percent.     

Treatment of poultry manure wastewater using a rotating biological contactor

A pilot scale, six stage rotating biological contactor was used to evaluate the feasibility of this process for the stabilization of liquid animal manures. Total disc surface area was approx. 16.7 m². Treatment efficiencies were determined at various waste strengths and influent flow rates.With loading rates of 14.7–322 g m⁻² day⁻¹, the average COD reduction was 61%. With loading rates of 4.88-24.4 g m⁻² day⁻¹, the average BOD₅ reduction was 87%. Total nitrogen removal averaged approximately 30% for the entire study. Mixed liquor oxygen uptake rates were generally in excess of 80 mg 1⁻¹ h⁻¹.Clarified effluent was non-odorous and suitable to be reused for manure flushing or spray irrigation. Treatment was not sufficient to permit effluent discharge to surface waters.     

Dissolution of copper, tin, and iron from sintered tungsten-bronze spheres in a simulated avian gizzard, and an assessment of their potential toxicity to birds

The rates of dissolution of copper, tin, and iron from sintered tungsten-bronze spheres (51.1%W, 44.4%Cu, 3.9%Sn, 0.6%Fe, by mass) were measured in an in vitro simulated avian gizzard at pH 2.0, and 42C. Most of the spheres had disintegrated completely to a fine powder by day 14. Dissolution of copper, tin, and iron from the spheres was linear over time; all r>0.974; all P<0.001. The mean rate of release of copper, tin, and iron was 30.4 mg, 2.74 mg, and 0.38 mg per g tungsten-bronze per day, respectively. These rates of metal release were compared to those in published studies to determine whether the simultaneous ingestion of eight spheres of 3.48 mm diameter would pose a toxic risk to birds. The potential absorption rates of iron and tin (0.54 mg Fe/day, and 3.89 mg Sn/day) from eight tungsten-bronze spheres of total mass 1.42 g would not prove toxic, based on empirical studies of tin and iron ingestion in waterfowl. The release of 43.17 mg copper/day from eight tungsten-bronze spheres, while exceeding the daily copper requirements of domesticated birds, is far below the levels of copper known to cause copper toxicosis in birds. We conclude that sintered tungsten-bronze material made into gunshot, fishing weights, or wheel balance weights, would not pose a toxic risk to wild birds when ingested.     

Organochlorine insecticides and PCB'S in sediments of Lake St. Claire (1970 and 1974) and Lake Erie (1971).

Sediments were collected on a grid from Lake St. Clair in 1970 and 1974 and from Lake Erie in 1971 and analysed for organochlorine insecticides and PCBs. Suspended solids were centrifuged from pumped water in the Detroit River in 1974. Residues of DDE, TDE and DDT were highest in sediment from the Western Basin (70.3 ppb) Lake Erie and lowest in sediment from Lake St. Clair (6.6 ppb in 1970 and 2.6 ppb in 1974). The Central and Eastern Basins of Lake Erie contained residues that fell about mid-way between these means. TDE was the predominant component of ΣDDT and was followed by DDE at approximately half this residue. While DDT represented the lowest component in lake sediments, it was the highest component in suspended solids from the Detroit River.HEOD was present in the entire lake system but at only a fraction of the level of ΣDDT. The mean residue in Lake St. Clair was only 0.1 ppb while Lake Erie sediments contained 1–2 ppb. The highest mean residue (3.6 ppb) was in suspended solids in the Detroit River. Other organochlorine insecticides were only occasionally identified.PCB residues in sediment were approximately 3 times higher than the total organochlorine insecticide residue, being highest in the Western Basin (252 ppb) and lowest in Lake St. Clair (19 ppb in 1970 and 10 ppb in 1974). The Detroit River and Central and Eastern Basins of Lake Erie had intermediate residues.Residues in Lake St. Clair indicated a decline in ΣDDT, HEOD, and PCB residues between 1970 and 1974, and this coincided with the restrictions on the materials. A core sample from the Western Basin of Lake Erie indicated that ΣDDT, HEOD and PCB began to accumulate in sediments in 1958, 1953, and 1956, respectively. This appeared to indicate a lag period of 2–5 years after wide-spread use occurred.     

A new mathematical model to evaluate simazine removal in three different immobilized-biomass reactors

A new mathematical model based on the cinetical Langmuir equation is developed to interpret and predict the effectiveness of simazine (SZ) removal in immobilized-biomass reactor (IBR), to consider herbicide-support affinity (Cx), and herbicide-cell affinity (Cy). Three solid supports: sepiolite monolith, granular sepiolite, and alginate were used in pilot-scale reactors that were inoculated with Klebsiella planticola DSZ. The abiotic process was analysed by measuring the SZ sorption capacity of the reactor supports. Sepiolite monolith showed the maximum value for herbicide-support affinity (28.02+/-0.9%). The effectiveness of the biotic process was estimated considering the formation of biomass and SZ biodegradation. Granular sepiolite showed either higher affinity with SZ and viability rate (0.90) throughout the process, and SZ removal rate was 3.39+/-0.06 mg/h. The mathematical model presented in this paper provides useful insights into the interpretation of experimental data as well as prediction for the implementation of biological reactors.     

Congratulations to Valerii Viktorovich Mikheev

Anniversaries and Memorable Dates

Congratulations to Valerii Viktorovich Mikheev Candidate of Technical Sciences, honorable builder of the Russian Federation, and recipient of the prize awarded by the Council of Ministers of the USSR     

Urban policies and gentrification trends in Madrid's inner city

This article was written as part of a wider research project on Madrid's social geography supported by the Spanish Ministry of Education and Science (Project PB88/0181). It was initially presented as a paper at the International Research ConferenceEuropean Cities: Growth and Decline The Hague, The Netherlands, 13–16 April 1992.     

Does oyster size matter for modelling trace metal bioaccumulation?

The aim of this study was assessing whether trace metal bioaccumulation models for oysters need to account for the effect of size-structured demography. To achieve this, we used a Bayesian generalised additive mixed modelling (BGAMM) approach. This nonparametric regression approach allowed us to estimate potentially nonlinear size effects of the oysters as well as random and structured spatial effects. Native oysters were collected from ten locations around the shoreline of Moreton Bay, a subtropical estuary in southeast Queensland, Australia. The soft-tissue of these sampled oysters were weighed (dry weight basis) and then analysed for Al, Cu, Fe, Mg, Mn and Zn. Of the six trace metals analysed, only Mg was found to have a significant (negative) effect of soft-tissue mass. The correlated spatial effects for Cu, Mn and Zn indicated that the source of these trace metals in the oysters was from anthropogenic inputs while the correlated spatial effects for Al and Mg indicated natural inputs. The correlated spatial effect for Fe was characterised by 'hotspot' concentrations in regions of Moreton Bay where algal blooms have previously occurred and consequently oysters might be useful as an indicator of algal blooms in the Bay. Overall, the absence of an observed size effect for five of the six trace metals indicates that bioaccumulation models do not necessarily need to account for size-structured demography therefore enabling simpler models to be used.