This study examined spatial variations in the concentration,grain size and heavy mineral assemblages on Cedar Beach（Lake Erie,Canada）.Magnetic studies of heavy mineral-enriched,dark-reddish sands present on the beac...This study examined spatial variations in the concentration,grain size and heavy mineral assemblages on Cedar Beach（Lake Erie,Canada）.Magnetic studies of heavy mineral-enriched,dark-reddish sands present on the beach showed that magnetite（～150μm） is the dominant magnetic mineral.Surficial magnetic susceptibility values defined three zones：a lakeward region close to the water line（Zone 1）,the upper swash zone（Zone 2） and the region landwards of the upper swash zone （Zone 3）.Zone 2 showed the highest bulk and mass susceptibility（κ,χ） and the highest mass percentage of smaller grain-size（250μm） fractions in the bulk sand sample.Susceptibility（i.e.κandχ） values decreased and grain size coarsened from Zone 2 lakewards（into Zone 1） and landwards （into Zone 3）,and correlated with the distribution of the heavy mineral assemblage,most probably reflecting preferential separation of large,less dense particles by waves and currents both along and across the beach.The eroded western section of Cedar Beach showed much higher concentrations of heavy minerals including magnetite,and finer sand grain sizes than the accreting eastern section, suggesting that magnetic techniques could be used as a rapid,cost-effective way of examining erosion along sensitive coastline areas.展开更多
The Eastern Great Lakes region covers 51,000 square km of land, and is home to 15 million people. This region is rich in natural resources, industry and agriculture, and forms the heartland of both Canada and the Unit...The Eastern Great Lakes region covers 51,000 square km of land, and is home to 15 million people. This region is rich in natural resources, industry and agriculture, and forms the heartland of both Canada and the United States. The development of this region has a history that is closely tied to waterways, and the development of canals that promoted growth and prosperity. The St. Lawrence Seaway connects Western and Eastern Great Lakes to the St Lawrence River and the Gulf of Saint Lawrence. The New York State Canal and the St. Lawrence Seaway were linked by the Oswego canal and provided a shorter route for cargo via barges to New York City. The New York State (NYS) Barge Canal and the St. Lawrence Seaway provided pathways for the settlement of the Eastern Great Lakes. Lake Erie drains into Lake Ontario via the Niagara River but the river was not navigable due to the obstacles of Niagara Falls and the Niagara Escarpment. Until the 1820s ships could not travel into Lake Erie. It was not possible to engineer a bypass of Niagara Falls with a series of locks due to the 100 m high Niagara escarpment. This escarpment obstacle to Niagara River navigation was overcome in 1829 with the completion of the first of four Welland Canals with locks 40 kilometers west of the Niagara River through the glacial till and alluvium that overlays the Niagara Escarpment. This permitted ocean going ships to enter Lake Erie and to continue on to Lake Michigan, Lake Huron and Lake Superior. The Eastern Great Lake shorelines, river banks and canals are actively eroding as a consequence of high surface water levels and flooding. The settlement of millions of people into the Eastern Great Lakes via the NYS Barge Canal and St. Lawrence Seaway migration pathways have created environmental and natural resource risks and challenges. These challenges and risks include deterioration of the Fourth Welland Canal and the need to replace it with the Fifth Welland Canal, industrial and urban wastewater disposal, shoreline, river bank and canal erosion a展开更多
Toxic cyanobacterial blooms are becoming a global problem. Previous research of cyanobacterial bloom development has examined how high nutrient concentrations promote cyanobacteria dominance, and how positive buoyancy...Toxic cyanobacterial blooms are becoming a global problem. Previous research of cyanobacterial bloom development has examined how high nutrient concentrations promote cyanobacteria dominance, and how positive buoyancy provides an ecological advantage over sinking phytoplankton. Tributaries responsible for loading nutrients into lakes often simultaneously contribute high concentrations of suspended sediments. High concentrations of suspended sediments may also influence blooms by affecting the ambient light climate, reducing photodamage, and increasing the efficiency of photosynthesis. We examined the effects of sediments and vertical mixing in potentially reducing photodamage to Microcystis by measuring photosynthetic parameters and pigment content of Microcystis in western Lake Erie during the 2008 bloom and in laboratory experiments. Photosynthetic efficiency increased with increasing sediment concentration in the lake and laboratory experiment. Content of photo-protective carotenoid pigments per dry weight decreased with increasing sediment concentrations, while the light-harvesting pigments, chl a and phycocyanin, increased with sediments. These results indicate that suspended sediments reduce photoinhibition for Microcystis. Further, photosynthetic damage was higher when Microcystis was concentrated on the surface compared to a mixed water column. Measurements of Microcystis abundance and light were also recorded, in addition to photosynthetic measurements. Greatest Microcystis abundances in Lake Erie were recorded during light-limiting conditions, which offer Microcystis both physiological and ecological benefits by reducing photoinhibition and increasing Microcystis’ advantage in light competition via buoyancy. Efforts to reduce cyanobacterial blooms may include reducing suspended sediments loads in combination with reducing nutrient loading.展开更多
Environmental magnetic research on beaches and shoreline processes is limited.Therefore,we carried out environmental magnetic studies on the heavy mineral-enriched,dark-reddish sands on Cedar Beach of western Lake Eri...Environmental magnetic research on beaches and shoreline processes is limited.Therefore,we carried out environmental magnetic studies on the heavy mineral-enriched,dark-reddish sands on Cedar Beach of western Lake Erie(41.68°N,82.40°W).Magnetite has been identified as the dominant magnetic mineral of these sands.This study reveals a spatial variation in concentration of magnetite particles,distribution of展开更多
基金supported by funding from the 111 Project B07011 of Ministry of Education of China,the China Scholarship Council(CSC) to SWZ (NCIS No.2007103928)an NSERC grant to MTC. D.Chevalier is thanked for her help in sampling. Laboratory assistance was provided bv K.Kawasaki and S.Joshi
文摘This study examined spatial variations in the concentration,grain size and heavy mineral assemblages on Cedar Beach（Lake Erie,Canada）.Magnetic studies of heavy mineral-enriched,dark-reddish sands present on the beach showed that magnetite（～150μm） is the dominant magnetic mineral.Surficial magnetic susceptibility values defined three zones：a lakeward region close to the water line（Zone 1）,the upper swash zone（Zone 2） and the region landwards of the upper swash zone （Zone 3）.Zone 2 showed the highest bulk and mass susceptibility（κ,χ） and the highest mass percentage of smaller grain-size（250μm） fractions in the bulk sand sample.Susceptibility（i.e.κandχ） values decreased and grain size coarsened from Zone 2 lakewards（into Zone 1） and landwards （into Zone 3）,and correlated with the distribution of the heavy mineral assemblage,most probably reflecting preferential separation of large,less dense particles by waves and currents both along and across the beach.The eroded western section of Cedar Beach showed much higher concentrations of heavy minerals including magnetite,and finer sand grain sizes than the accreting eastern section, suggesting that magnetic techniques could be used as a rapid,cost-effective way of examining erosion along sensitive coastline areas.
文摘The Eastern Great Lakes region covers 51,000 square km of land, and is home to 15 million people. This region is rich in natural resources, industry and agriculture, and forms the heartland of both Canada and the United States. The development of this region has a history that is closely tied to waterways, and the development of canals that promoted growth and prosperity. The St. Lawrence Seaway connects Western and Eastern Great Lakes to the St Lawrence River and the Gulf of Saint Lawrence. The New York State Canal and the St. Lawrence Seaway were linked by the Oswego canal and provided a shorter route for cargo via barges to New York City. The New York State (NYS) Barge Canal and the St. Lawrence Seaway provided pathways for the settlement of the Eastern Great Lakes. Lake Erie drains into Lake Ontario via the Niagara River but the river was not navigable due to the obstacles of Niagara Falls and the Niagara Escarpment. Until the 1820s ships could not travel into Lake Erie. It was not possible to engineer a bypass of Niagara Falls with a series of locks due to the 100 m high Niagara escarpment. This escarpment obstacle to Niagara River navigation was overcome in 1829 with the completion of the first of four Welland Canals with locks 40 kilometers west of the Niagara River through the glacial till and alluvium that overlays the Niagara Escarpment. This permitted ocean going ships to enter Lake Erie and to continue on to Lake Michigan, Lake Huron and Lake Superior. The Eastern Great Lake shorelines, river banks and canals are actively eroding as a consequence of high surface water levels and flooding. The settlement of millions of people into the Eastern Great Lakes via the NYS Barge Canal and St. Lawrence Seaway migration pathways have created environmental and natural resource risks and challenges. These challenges and risks include deterioration of the Fourth Welland Canal and the need to replace it with the Fifth Welland Canal, industrial and urban wastewater disposal, shoreline, river bank and canal erosion a
文摘Toxic cyanobacterial blooms are becoming a global problem. Previous research of cyanobacterial bloom development has examined how high nutrient concentrations promote cyanobacteria dominance, and how positive buoyancy provides an ecological advantage over sinking phytoplankton. Tributaries responsible for loading nutrients into lakes often simultaneously contribute high concentrations of suspended sediments. High concentrations of suspended sediments may also influence blooms by affecting the ambient light climate, reducing photodamage, and increasing the efficiency of photosynthesis. We examined the effects of sediments and vertical mixing in potentially reducing photodamage to Microcystis by measuring photosynthetic parameters and pigment content of Microcystis in western Lake Erie during the 2008 bloom and in laboratory experiments. Photosynthetic efficiency increased with increasing sediment concentration in the lake and laboratory experiment. Content of photo-protective carotenoid pigments per dry weight decreased with increasing sediment concentrations, while the light-harvesting pigments, chl a and phycocyanin, increased with sediments. These results indicate that suspended sediments reduce photoinhibition for Microcystis. Further, photosynthetic damage was higher when Microcystis was concentrated on the surface compared to a mixed water column. Measurements of Microcystis abundance and light were also recorded, in addition to photosynthetic measurements. Greatest Microcystis abundances in Lake Erie were recorded during light-limiting conditions, which offer Microcystis both physiological and ecological benefits by reducing photoinhibition and increasing Microcystis’ advantage in light competition via buoyancy. Efforts to reduce cyanobacterial blooms may include reducing suspended sediments loads in combination with reducing nutrient loading.
文摘Environmental magnetic research on beaches and shoreline processes is limited.Therefore,we carried out environmental magnetic studies on the heavy mineral-enriched,dark-reddish sands on Cedar Beach of western Lake Erie(41.68°N,82.40°W).Magnetite has been identified as the dominant magnetic mineral of these sands.This study reveals a spatial variation in concentration of magnetite particles,distribution of
