A Killer Lake

These are the teaching notes for a case study in which students are presented with data on a particular lake that they must synthesize in order to determine the cause of an event that occurred in 1986 in Cameroon, Africa. The case centers on Cameroon's Lake Nyos, a volcanic lake which released a large quantity of carbon dioxide gas, killing over 1700 people, livestock, and wildlife in the area. The case can be used in a limnology or an aquatic biology course and was intended to introduce and reinforce the concepts of thermal stratification and use students' curiosity about this event to get them to think about how layers of water develop. The case could also be extended to cover or review other concepts such as lake formation (in this case, volcanism as a lake-forming process) or gas solution (in this case, carbon dioxide solution). The case could also be used throughout a limnology course because it deals with many aspects of the subject: lake origins, thermal stratification, gases, water movements, and applied limnology (remediation of problems). Instructors can introduce the case early in a course and refer back to it when each new topic comes up. The case also allows students to synthesize different types of limnological data to solve a serious problem. Educational levels: High school, Undergraduate lower division

Immigration and Distribution of Wages in Austria

Using detailed micro data on earnings and employment, I analyze the effects of immigration on the wage distribution of native male workers in Austria. I find that immigration has heterogeneous effects on wages, differing by type of work as well as the wage level. While there are small , but insignificant, negative effects for blue collar workers at the lower end of the wage distribution there are positive effects on wages at higher percentiles. For white collar workers positive effects occur at most percentiles. The estimated effects of immigration are relatively small in size and not significant for most workers. Overall it seems that most of potentially adverse effects of immigration on natives' wages are offset by complementarities stemming from immigration of workers with different skill levels.Immigration, Labor market, Wage distribution

Immigration and Distribution of Wages in Austria

Using detailed micro data on earnings and employment, I analyze the effects of immigration on the wage distribution of native male workers in Austria. I find that immigration has heterogeneous effects on wages, differing by type of work as well as the wage level. While there are small , but insignificant, negative effects for blue collar workers at the lower end of the wage distribution there are positive effects on wages at higher percentiles. For white collar workers positive effects occur at most percentiles. The estimated effects of immigration are relatively small in size and not significant for most workers. Overall it seems that most of potentially adverse effects of immigration on natives' wages are offset by complementarities stemming from immigration of workers with different skill levels.Immigration, Labor market, Wage distribution

Economically Viable Strategy for Prevention of Invasive Species Introduction: Case Study of Otsego Lake, New York

The literature is full of examples detailing ecological impacts of invasive species and predictions of which and where species will invade next. Many fewer examples of effective prevention strategies are known. Prevention of aquatic invasive species (AIS) to inland lakes should be easily established because most AIS are initially introduced into watersheds by recreational boating activities, especially in North America. The Watershed Management Plan for Otsego Lake, a central New York glacial lake, provides for prevention of AIS via a stringent boat inspection and washing program (BIP). All boats entering Otsego Lake at the public launch are visually inspected and those deemed likely to harbor AIS are required to power wash before launching. However, other sites are available to launch boats. BIP expenses average $30,000 per year, much of which has been covered by collecting a launch fee. After implementation of the BIP, only one boat was refused access, and less than 1% required washing before allowed access, however, zebra mussels (Dreissena polymorpha) and water chestnut (Trapa natans) have since been found in the lake. The BIP continues to be supported because other AIS may have been prevented or may be prevented in the future

Great Expectations: Past Wages and Unemployment Durations

Decomposing wages into worker and firm wage components, we find that firm-fixed components (firm rents) are sizeable parts of workers' wages. If workers can only imperfectly observe the extent of firm rents in their wages, they might be mislead about the overall wage distribution. Such misperceptions may lead to unjustified high reservation wages, resulting in overly long unemployment durations. We examine the infuence of previous wages on unemployment durations for workers after exogenous lay-offs and, using Austrian administrative data, we find that younger workers are, in fact, unemployed longer if they profited from high firm rents in the past. We interpret our findings as evidence for overconfidence generated by imperfectly observed productivity.Unemployment, Job Search, Overconfidence

Great Expectations: Past Wages and Unemployment Durations

Decomposing wages into worker and firm wage components, we find that firm-fixed components (firm rents) are sizeable parts of workers' wages. If workers can only imperfectly observe the extent of firm rents in their wages, they might be mislead about the overall wage distribution. Such misperceptions may lead to unjustified high reservation wages, resulting in overly long unemployment durations. We examine the infuence of previous wages on unemployment durations for workers after exogenous lay-offs and, using Austrian administrative data, we find that younger workers are, in fact, unemployed longer if they profited from high firm rents in the past. We interpret our findings as evidence for overconfidence generated by imperfectly observed productivity.Unemployment, Job Search, Overconfidence

Hydrodynamic Forces Affect Larval Zebra Mussel (Dreissena polymorpha) Mortality in a Laboratory Setting

Mortality of zebra mussel, Dreissena polymorpha, larvae was quantified in a laboratory experiment that was designed to assess the role played by both intensity and duration of the exposure to hydrodynamic forces. Larvae were collected in a plankton net and distributed in 100-ml aliquots to 125-ml Erlenmeyer flasks. The flasks were spun on an orbital shaker at different speeds, 100 rpm and 400 rpm, to change the intensity of the hydrodynamic forces experienced by larvae inside the flasks. Actual shear forces were not quantified. A parallel set of control flasks were not spun. Flasks were spun for 1, 24 and 48 hours. Mortality was highest in the 400 rpm, 48-h trial. Both intensity and duration were highly significant variables in the ANOVA model (p\u3c0.001). However, the interaction term was also highly significant (p\u3c0.001). Larval mortality was significantly higher in the treatments than in the non-spun flasks in only the 400 rpm, 24-h and 400 rpm, 48-h trials. Thus, longer duration of exposure to high intensity hydrodynamic forces increases larval mortality. These results help explain natural recruitment patterns of zebra mussels in natural streams and may be of interest to management and conservation efforts