Assessing Potential Removal of Low-Head Dams in Urban Settings: An Example from the Ottawa River,NW Ohio

This is a study of the scientific component of an effort to restore an urban river by removing a low-head dam. The Secor Dam is owned by a local government entity near Toledo, Ohio. The proposed removal of the last structure impeding flow on the Ottawa River has broad appeal, but the owner is concerned about liability issues, particularly potential changes to the flood regime, the presence of contaminated sediments behind the dam, and possible downstream transport of reservoir sediments. Assessing sediment contamination involved sediment sampling and analysis of trace metals and organic contaminants. Forecasting sediment transport involved field methods to determine the volume and textural properties of reservoir and upstream sediment and calculations to determine the fate of reservoir sediments. Forecasting changes in the flood regime involved HEC-RAS hydrological models to determine before and after dam removal flood scenarios using LiDAR data imported into an ArcGIS database. The resulting assessment found potential sediment contamination to be minor, and modeling showed that the removal of the dam would have minimal impacts on sediment transport and flood hazards. Based on the assessment, the removal of the dam has been approved by its owners.     

Long-term changes in the Georges Bank food web: trends in stable isotopic compositions of fish scales

Fish scales from seven species of demersal fish in an archival collection were analyzed for stable isotopic compositions of carbon and nitrogen to study long-term changes in trophic structure of the Georges Bank food web. Nitrogen isotopic compositions are often used to infer trophic level. In the case of haddock, Melanogrammus aeglefinus (Linnaeus), there was a trend towards feeding at 2/3 of one trophic level (2.45% in ¹⁵N) lower in 1987 than in 1929. Values of °¹³C, frequently employed to identify sources of organic carbon to consumers, declined by 1.5 from 1929 to 1960, and then increased again toward the present, suggesting changes in the food web at the level of the primary producers. Superimposed on long-term isotopic trends were short-term variations (1 to 10 yr).To identify potential causes for these isotopic trends, canonical correlation analysis was performed between isotopic data and a suite of environmental and population factors including sea surface temperature, the Greenland Regional Pressure Anomaly (GRPA), the North Atlantic Oscillation (NAO), and the following haddock stock parameters; stock size, fishing mortality, recruitment, and weight-at-age-2 (a measure of growth rate). Isotopic variation was significantly correlated with a combination of environmental and population variables: GRPA, NAO, weight-at-age-2, stock size, and fishing mortality. On the basis of published gut content analyses, the seven fish species were predicted to vary in trophic level (TL) from American plaice, Hippoglossoides platessoides (Fabricius), (TL 2.9) to summer flounder, Paralichthys dentatus (Linnaeus), (TL 4.5), whereas measured °¹⁵N values suggested smaller differences in the trophic levels of these species (less than one TL). Four species showed good agreement between gut-predicted and measured ¹⁵N values, while three species did not. Inclusion of information on ontogenetic dietary shifts in our predictions improved the agreement in some cases but not in other. Differences between stable isotope analysis and gut content analysis in terms of what they measure, i.e., integrated assimilated diet vs short-term ingested diet, respectively, may account for some of the differences in results. Based on our analyses and previous studies, feeding habits of these fish may undergo considerable year-to-year and geographic variation, some of which may have been missed in gut content analyses. To the extent that these fish are representative members of the food web, trophic variation in these fish may indicate more general changes in the food web.     

Acoustic orientation via sequential comparison in an ultrasonic moth

Orientation of female lesser wax moths (Achroia grisella) to male calling song was tested on a locomotion-compensator device that withheld all inter-aural acoustic differences from the insect. Under these circumstances, females remained longer in the vicinity of the sound source if they experienced a variable sound level that increased when approaching the source rather than a level that remained constant at all times. Analyses of orientation paths revealed that greater retention near the source was achieved by enhanced turning when the perceived sound level remained unchanged or decreased but retaining the previous heading when the level increased. These findings suggest that acoustic orientation can be supplemented by mechanisms based on sequential, as opposed to instantaneous, comparison of auditory input. Such mechanisms may be valuable when binaural hearing is impaired or asymmetric or in environments where acoustic differences at the two ears are unreliable indications of direction to the sound source.     

Mineral landscapes: The next ten years?

A review of changes in approach to the restoration of mineral sites in Britain since the introduction of planning control in 1947, together with likely trends for the next decade.The period has seen great technological advances in the capacity of machinery, increased demand, and more rapid rates of extraction. The resulting re-organisation of the industry through mergers and take-overs has led to concentration into fewer and larger units of production, with the parallel closure of many smaller works and quarries. It is to assess the significance of such changes in their effect upon both restoration and after-use that this study has been prepared.     

Human exposure to methylmercury from crayfish (Procambarus clarkii) in China

Methylmercury (MeHg) accumulation in aquatic food raises global concerns about human exposure to MeHg. Crayfish is the world’s third largest farmed crustacean species and a favorite aquatic food in many countries. However, human health hazard due to MeHg exposure via crayfish consumption is unclear, partly because appropriate survey data are lacking. We report on mercury concentrations and speciation in edible tail muscle of crayfish collected from restaurants in 23 Chinese cities. On average, MeHg constituted 99.1 % of mercury in tail muscle, and MeHg concentrations were comparable with those reported for fish in China. Variation in MeHg concentrations was not attributable to broad geographic region (i.e., provinces) or tail length. For different populations, potential health risk (characterized by hazard quotient or HQ) of MeHg exposure through crayfish consumption depended largely on crayfish consumption rates. In particular, a health hazard (HQ > 1) was found for high-rate consumers (i.e., 95 %ile or higher) in some cities in the middle and lower reaches of the Yangtze River (MLYR), during the peak consumption season. Our results suggest that more attention should be paid to dietary MeHg intake via crayfish consumption in China, particularly for communities with high consumption in MLYR.

     

Mortality and growth of juvenile hard clams Mercenaria mercenaria during brown tide

Blooms of the picoplankton-sized alga Aureococcus anophagefferens Hargraves et Sieburth, also known as "brown tide," frequently recur in Great South Bay, New York, USA. A field study compared mortality and growth rates of juvenile hard clams, Mercenaria mercenaria (L.), raised at a site that experienced a bloom of A. anophagefferens (>1᎒⁶ cells ml^-1) to clams grown in a nonbloom site from May to September 2000 at two sites on the north and south shores of Long Island. High (67%) cumulative clam mortality was observed for clams raised at the brown tide site (south shore) during the bloom (June-July), and individuals exhibited no measurable growth during that period. After the bloom subsided (mid-July), clams that survived the brown tide suffered low (<5%) cumulative mortality over the remaining sampling period (July-September). These survivors exhibited rapid growth for 4 weeks shortly after the bloom's decline. Subsequently, their growth slowed to rates comparable with those observed at the nonbloom site (north shore). By contrast, a low (<5%) cumulative mortality was observed for M. mercenaria raised at the site with no brown tide, and positive growth occurred throughout the study. These data suggest that some juvenile clams not only survive brown tide but also recover following the bloom.     

Natural concentrations and reference values for trace elements in soils of a tropical volcanic archipelago

Fernando de Noronha is a small volcanic archipelago in the Southern Atlantic, some 350 km NE of the city of Natal in NE Brazil. These remote volcanic islands represent a largely pristine environment, distant from sources of anthropogenic contamination. This study was carried out to determine the natural concentrations of Ag, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sb, V and Zn in the A and B horizons of soils of Fernando de Noronha. The aims of the study were twofold: determine whether there is a relationship between the bedrock geology and soils and to establish quality reference values for soils from Fernando de Noronha. Soil samples were subjected to acid digestion by the USEPA method 3051A, and metals were determined by inductively coupled plasma emission spectrophotometry. The results showed that the trace element distribution largely reflects the geochemistry of the underlying volcanic rocks of the Remedios and Quixaba Formations. The results demonstrate that the concentrations of Ba, Cr, Zn, Ni and Cu from the soils of the volcanic Fernando de Noronha archipelago are higher than those found in soils from continental Brazil. However, concentrations of Ni, Cu and Co are lower in soils of the archipelago as compared to other volcanic islands throughout the world. The elevated trace element concentrations of the volcanic parent material of Fernando de Noronha soils seem to be the main factor governing the relatively high natural concentrations of trace elements.     

The socioeconomic significance of nature-based recreation in Canada

In recognition of the many values that people ascribe to nature, federal, provincial, and territorial agencies worked inpartnership to complete the 'Survey on the Importance of Natureto Canadians' (SINC) in 1981, 1987, 1991, and 1996. Between 1981 and 1996, more than 80% of Canadians 15 years of age and older engaged in one or more nature-related activities. This paper describes the evolution of this cooperative monitoring program, defines a classification system as a context for the values examined by the SINC, highlights trends of some nature-related recreational activities measured by the survey, and comments onthe importance of this information to Canadians.     

Early impacts of alcoholic beverage warning labels: national study findings relevant to drinking and driving behavior

After November, 1989 Federal law required a standard health warning label on all alcoholic beverage containers sold for consumption in the U.S. Results are reported from a cross-sectional national household telephone interview survey of adults, occurring approximately 6 months after implementation of the warning labels (N=2000). Implications for health warnings with respect to information processing theory, the Health Belief Model, and other theories relevant to precaution adoption are briefly reviewed and two derivative hypotheses are tested using log-linear analysis. Relationships between various personal characteristics and (a) seeing the label and (b) recalling the driving impairment message are examined for consistency with theoretical expectations. We also examine associations between message recall, drinking style, and two precautionary behaviors undertaken to avoid drinking and driving. Adjusting for apparent false positives, approximately a quarter of the sample have noticed the label 6 months after its introduction; 16% recalled the specific driving impairment message. As hypothesized, exposure to the warning was predicted primarily by consumption pattern but also was associated with a personal salience factor, that is, ever having drunk alcohol so as to be at risk when driving. About a quarter of the heavy drinkers (5 drinks or more per occasion sometime and drinking at least weekly) who ever drank and drove saw the specific warning. Of two self-regulation strategies — limiting driving after drinking and limiting drinking when about to drive — the latter was the more prevalent. Both strategies were reported more by those who were heavy drinkers, those recalling the driving impairment message, and those perceiving driving after drinking to be very dangerous, than by other individuals.