No abstract

We studied fluxes of methylmercury (MeHg) through a Precambrian Shield lake using a mass balance approach. The primary goal of the study was to determine the importance of various sources of MeHg to the water column of the lake. The relative importance of all sources was: in-lake production ϾϾϾ inflow from a brown-water lake with riparian wetlands ϾϾϾ wet deposition Ͼ inflow from an upstream oligotrophic lake Ͼ direct inflow from uplands surrounding the lake. MeHg accumulated in the hypolimnion of Lake 240 when oxygen was present. Watercolumn sinks for MeHg included photodegradation of MeHg, which was about 3.5 times greater than the loss of MeHg through outflow. At present, there are few studies available on mass balance fluxes of MeHg in lakes, and this is the first study that includes losses of MeHg by photodegradation. The inclusion of photodegradation in this study results in a clear demonstration that in-lake production of MeHg is very important. In drainage lakes, the relative importance of in-lake production versus inflow of MeHg from wetlands will vary according to the extent of wetlands in the drainage basin, as well as the volume of precipitation, which produces runoff and transports MeHg from wetlands to downstream lakes.

Three parameters must be known to use the thin boundary-layer model (or other bulk transfer models) for CO, flux between water and air: the concentration of dissolved CO*, CO,,,,,, the concentration of CO, in the air immediately above the water, COZ(atm), and the wind velocity, which is used to determine the appropriate transfer coefficient. These parameters change hourly and from day to day in a nonlinear fashion, so the frequency of measurements is an important factor in determining the accuracy of flux estimates for any period. To achieve a high frequency measurement, we developed a self-contained, solar-powered, in situ sampling system that continuously measures and records CO,,,,,, COZ(atm), and windspeed. Unique to this technique is an underwater in situ equilibration chamber (ISEC). The ISEC was tested in a shallow wetland pond in which changes in both CO,,,,, and COZ(ntm) were large. The data obtained showed that large errors may result from extrapolating flux calculations made from short-term data (e.g. daily) to longer time periods.The most commonly used method for estimating gas flux across the air-water interface is the thin boundarylayer (TBL) model, which requires measurements of windspeed and of the concentrations of the gas in air and water. Gas concentration data are usually acquired by periodic sampling, and the frequency of sampling is usually limited by accessibility to the site and the time available for analyses.When measurements are made for the purpose of calculating CO2 flux in lakes where diel changes in water and air arc small, limitations on sampling frequency may not be serious. However, there are two common situations in which very frequent measurements in both air and water may be necessary: eutrophic lakes and shallow ponds-both of which have strong diel changes due to high rates of photosynthesis and respiration. Even where diel changes are not so strong (as in oligotrophic lakes), other considerations, such as large changes in windspeed, may make sampling frequency important.Because CO2 flux is proportional to the dzjkwzce bcAcknowledgments

Between 1962 and 1969, 10 tonnes of mercury were discharged from a chlor-alkali plant in Dryden, Ontario, to the English–Wabigoon River. Present-day fish mercury concentrations are amongst the highest recorded in Canada. In 2017, the Grassy Narrows Science Team found no evidence of ongoing discharges from the plant site to the river water, even though large quantities of mercury remain at the site. Instead, our data suggest that ongoing erosion of high mercury particles by the river, as it meanders through contaminated floodplains, is responsible for present-day transport of mercury to Clay Lake and to Ball Lake, located 154 km downstream. In Clay Lake, surface sediment total mercury concentrations and inflow water concentrations are still about 15 times above background (86 km downstream), and in Ball Lake mercury concentrations in sediments appeared to be still increasing. The remobilization of legacy inorganic mercury from riverbank erosion between Dryden and Clay Lake stimulates methyl mercury production there, in Clay Lake, and in Ball Lake. The large quantities of methyl mercury produced between Dryden and Clay Lake are mostly dissolved in water and are swept downstream, elevating concentrations in water and biota throughout the system. Several options for remediating the ongoing contamination are discussed.

Teacher preparation programs are in danger of seriously under-preparing

The Self-Concept and Motivation Inventory: What Face Would You Wear? Preschool/Kindergarten Form has the potential to be of use in measuring the academic self-concept of preschoolers. This study sought to determine if the theoretical, three-factor structure of the SCAMIN could be recovered in a state-wide sample of kindergarten students. In 1986, 5742 kindergarteners from Tennessee schools participating in the Reduced Pupil/Teacher Ratio Project were given the Preschool/Kindergarten form of the SCAMIN. The sample was drawn from 42 school districts in all geographic regions of Tennessee and represented a mix of inner-city, urban, rural, and suburban schools. The intercorrelation matrix of the 24 SCAMIN items was analyzed by the principal components method and extracted factors were rotated to a varimax solution. An initial analysis suggested the presence of an atheoretical factor, and two items which appeared to be unrelated to any obtained factor. Subsequent refactoring of the SCAMIN resulted in the successful recovery of the expected three factor structure. Cronbach's alpha, for the scales Academic Self-Concept; Achievement Investment; and Achievement Needs were .666, .599, and .598, respectively. The results of this factor analysis of the Early Preschool/Kindergarten Form of the SCAMIN suggest both strengths and weaknesses in the factorial composition of the 24 SCAMIN items. Users of the SCAMIN are cautioned against a naive application of this instrument's scales.

Six classes received problem-centered mathematics instruction for 2 years in second and third grade. This instruction was generally reflective of a socioconstructivist theory of knowing and compatible with recommendations for reform in mathematics education. A class-by-instruction factorial design was used to compare students in problem-centered classes for 2 years with students in problem-centered classrooms for 1 year, and with students in textbook classes for 2 years on a standardized achievement test. In addition, classes using problem-centered instruction for 2 years were compared with students in problem-centered classes for 1 year on an instrument designed to assess students' conceptual development in arithmetic and an instrument developed to examine personal goals and beliefs about reasons for success in mathematics. The results of the analyses indicate that significant differences exist in arithmetic learning for students in problem-centered classes for 2 years on the standardized achievement test and the arithmetic test. The results indicate that after 2 years of instruction in reform-based classes, students score significantly higher on standardized measures of computational proficiency as well as conceptual understanding. Additionally, these students hold stronger beliefs about the importance of finding their own or different ways to solve problems.

Longitudinal analyses of the mathematical achievement and beliefs of 3 groups of elementary pupils are presented. The groups consist of those students who had received 2 years of problem-centered mathematics instruction, those who had received 1 year, and those who had received textbook instruction. Comparisons are made for the groups using a standardized norm-referenced achievement test from first through fourth grade. Next, student comparisons are made using instruments developed to measure conceptual understanding of arithmetic and beliefs and motivation for learning mathematics. The results of the analyses indicate that after 2 years in problem-centered classes, students have significantly higher achievement on standardized achievement measures, better conceptual understanding, and more task-oriented beliefs for learning mathematics than do those in textbook instruction. In addition, these differences remain after problem-centered students return to classes using textbook instruction. Comparisons of pupils in problem-centered classes for only 1 year reveal that after returning to textbook instruction, these students' mathematical achievement and beliefs are more similar to the textbook group. Also included are exploratory analyses of the pedagogical beliefs held by teachers before and after teaching in problem-centered classes, and those held by teachers in textbook classes. The results of the student and teacher analyses are interpreted in light of research on children's construction of nonstandard algorithms and the nature of classroom environments.