Shape and efficiency of wood ant foraging networks

We measured the shape of the foraging trail networks of 11 colonies of the wood ant Formica aquilonia (Formica rufa group). We characterized these networks in terms of their degree of branching and the angles between branches, as well as in terms of their efficiency. The measured networks were compared with idealized model networks built to optimize one of two components of efficiency, total length (i.e., total amount of trail) and route factor (i.e., average distance between nest and foraging site). The analysis shows that the networks built by the ants obtain a compromise between the two modes of efficiency. These results are largely independent of the size of the network or colony size. The ants’ efficiency is comparable to that of networks built by humans but achieved without the benefit of centralized control.     

Influence of groundwater recharge and well characteristics on dissolved arsenic concentrations in southeastern Michigan groundwater

Arsenic concentrations exceeding 10 μg/l, the United States maximum contaminant level and the World Health Organization guideline value, are frequently reported in groundwater from bedrock and unconsolidated aquifers of southeastern Michigan. Although arsenic-bearing minerals (including arsenian pyrite and oxide/hydroxide phases) have been identified in Marshall Sandstone bedrock of the Mississippian aquifer system and in tills of the unconsolidated aquifer system, mechanisms responsible for arsenic mobilization and subsequent transport in groundwater are equivocal. Recent evidence has begun to suggest that groundwater recharge and characteristics of well construction may affect arsenic mobilization and transport. Therefore, we investigated the relationship between dissolved arsenic concentrations, reported groundwater recharge rates, well construction characteristics, and geology in unconsolidated and bedrock aquifers. Results of multiple linear regression analyses indicate that arsenic contamination is more prevalent in bedrock wells that are cased in proximity to the bedrock-unconsolidated interface; no other factors were associated with arsenic contamination in water drawn from bedrock or unconsolidated aquifers. Conditions appropriate for arsenic mobilization may be found along the bedrock-unconsolidated interface, including changes in reduction/oxidation potential and enhanced biogeochemical activity because of differences between geologic strata. These results are valuable for understanding arsenic mobilization and guiding well construction practices in southeastern Michigan, and may also provide insights for other regions faced with groundwater arsenic contamination.     

A Constant Erosion Rate Model for Fine Sediment in the York River,Virginia

Results of field experiments using the Virginia Institute of Marine Science' Sea Carousel and tripod system reveal a highly dynamic sediment activity at the Clay Bank site in the York River. At the water-sediment interface, the critical bed shear stress for sediment erosion varied between 0.026 Pa and 0.1 Pa. For the well consolidated sediment below the interface, the critical bed shear stress increased significantly, to more than 0.6 Pa. The seasonal variation of erosion rate for the surficial sediment is significant. For the well consolidated sediment below the surficial sediment, however, the seasonal variation diminished and erosion rate approached a constant. Experimental results from the Carousel deployments imply that the erosion process for quasi-steady tidal flows is always near equilibrium. For this reason, a constant rate erosion model is proposed for the time during tidal acceleration phases. For other times, the erosion rate would be zero. The measured suspended sediment concentration at 10 cm above bed from the VIMS tripod system also Supports this model.     

EPA’s Perspective on Risks from Residential Radon Exposure

Indoor radon has been judged to be the most serious environmental carcinogen which the EPA must address for the general public. The optimal strategy for dealing with this problem depends on the magnitude of the risk, how the risk is distributed within the population, as well as the effectiveness and costs of mitigation measures. Based on current exposure and risk estimates, radon exposure in single-family houses may be a causal factor in roughly 20,000 lung cancer fatalities per year. Most of these projected fatalities are attributable to exposures in houses with average or moderately elevated radon levels (below 10 pCi/L). Hence to appreciably reduce radon-induced lung cancers, remediation efforts must include houses not highly elevated in radon. From either an individual risk or a cost-benefit standpoint, reduction of a few pCi/L per home appears to be justified. The optimal strategy for dealing with the indoor radon problem depends on the magnitude of the risk per unit exposure, the distribution of exposures in houses, and the effectiveness and costs of mitigation. EPA’s current views with respect to these factors and the associated uncertainties are discussed.     

Evaluation of groundwater quality in and around Peenya industrial area of Bangalore, South India using GIS techniques

Groundwater resource forms a significant component of the urban water supply. Declining groundwater levels in Bangalore Urban District is generally due to continuous overexploitation during the last two decades or more. There is a tremendous increase in demand in the city for good quality groundwater resource. The present study monitors the groundwater quality using geographic information system (GIS) techniques for a part of Bangalore metropolis. Thematic maps for the study area are prepared by visual interpretation of SOI toposheets on 1:50,000 scale using MapInfo software. Physicochemical analysis data of the groundwater samples collected at predetermined locations form the attribute database for the study, based on which spatial distribution maps of major water quality parameters are prepared using MapInfo GIS software. Water quality index was then calculated by considering the following water quality parameters--pH, total dissolved solids, total hardness, calcium hardness, magnesium hardness, alkalinity, chloride, nitrate and sulphate to find the suitability of water for drinking purpose. The water quality index for these samples ranged from 49 to 502. The high value of water quality index reveals that most of the study area is highly contaminated due to excessive concentration of one or more water quality parameters and that the groundwater needs pretreatment before consumption.     

An overview on the properties of eco-friendly concrete paving blocks incorporating selected waste materials as aggregate

Environmental Science and Pollution Research - Paving block is a widely used pavement material due to its long service life, fast and easy production and easily replaced for maintenance purpose....     

Costs of trail construction and maintenance in the leaf-cutting ant Atta columbica

Leaf-cutting ants of the genus Atta use trunk trails during foraging which may persist for months or years. The time and energy costs of trail construction and maintenance were estimated for colonies of Atta columbica on Barro Colorado Island, Panama, to determine if these costs are likely to constrain new trail construction and promote persistence of existing trails. Large workers 2.2-2.9 mm in headwidth participated in trail-clearing significantly more frequently than typical leaf-carriers, indicating that they may form a distinctive task group within the foraging force. Small litter items were carried off trails, while large ones were cut up before removal, greatly increasing the costs of removing large litter items. The average time cost of removing a kilogram of litter was estimated at 3,359 ant-hours, and energy costs at 4.6 kJ. Colonies maintained trail systems 267 m in length and 16.5 m² in area, and built an estimated 2.7 km of trail with an area of 134 m² during a year. Based on litter standing crop and estimates of litterfall rates, total costs to colonies averaged 11,000 ant-days of work and the energy equivalent of 8,000 leaf burdens. These costs are small relative to the number of available workers and rates of mass harvest, suggesting that costs do not significantly constrain trail construction. Instead, trails may persist because they provide access to high-quality resources or because only a few trails are required to fully exploit the foraging territory.     

Effects of disc and arm loss on regeneration byMicrophiopholis gracillima (Echinodermata: Ophiuroidea) in nutrient-free seawater

Clibanarius longitarsus (De Haan), a hermit crab, feeds by means of both micro- and macrofeeding. Microfeeding is of two types: filter feeding and deposit feeding. In macrofeeding, the animal depends mainly on green algae, barnacles and some worms, etc. In filter feeding, the hermit crab uses its paired antennules for trapping microorganisms drawn into the water current created by the second and third maxillipeds; the antennae do not play any role in filter feeding. In deposit feeding, the hermit crab uses its chelae as well as pereiopods for toughing and obtaining detritus food material. In macrofeeding, the organism employs sharp chelae to collect small pieces of muscle from barnacles and then transfer them to the inner mouth parts. In algal feeding, the chelae as well as maxillipeds help in collecting and moving food material towards the mouth. In this investigation functional organisation ofC. longitarsus mouth parts was studied in detail with reference to the various feeding mechanisms, in specimens collected from the intertidal region of Bheemunipatnam, Andra Pradesh, India, in 1988 and 1989.