Paleolimnology in an urban environment : the history of environmental change in St. John's, Newfoundland

Christopher, Terry K. (1999) Paleolimnology in an urban environment : the history of environmental change in St. John's, Newfoundland. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (50MB)

Abstract

Lake sediment cores from St. John's and surrounding areas were used to document anthropogenic impacts since European settlement. Environmental indicators preserved in the sediment including, geochemical characteristics, pollen, diatoms, soot and charcoal were analyzed in a chronological sequence to document the physical, chemical and biological impacts over time. -- Two broad-scale eras of direct soil disturbance were identified and related to farming and urban growth. During the farming era, between 1750 and 1950, the natural vegetation cover was removed and lake sedimentation rates increased. The urban era, which began about 1910, resulted in rapid soil erosion and high lake sedimentation rates. During the most intense period of urban development, the mid-1960s, the dry sediment influx rate was 160 times pre-European rates. Storm sewers and pavement played an important role in the urban environment, providing a direct path to the lakes for pollutants. -- Superimposed on these disturbances are atmospheric contributions from coal and automobile emissions. Coal combustion, which began about 1800 and increased to the mid-1950s, emitted soot and toxic metals, as observed in the lake sediment records. Automobile pollution, through leaded gasoline combustion, contributed significant levels of lead. Lake sediment records show the highest inputs and concentrations of lead occurred about 1970. Lead isotopic ratios suggest two or three different gasoline types were used in this area. -- The most notable aquatic impact is a pH increase through the last few decades. Reconstructing water pH in Quidi Vidi Lake from diatom assemblages showed that the earliest farming had little influence on the pH, while an increase of about 1.2 units was observed to the 1980s. The recent high pH has been attributed to increased buffering capacity, believed to be caused by an increase in Mg and Ca contributions from the dissolution of concrete in the watershed. -- The long history of coal combustion and leaded gasoline combustion has probably left the local soils charged with soot and heavy metals. Although the extent of influence is unknown, these soils may be continuous suppliers of contaminants for centuries to come. Any attempt to ameliorate the urban lakes and their watershed soils should consider all consequences, since the lakes appear to be in a 'city-equilibrium'.

Actions (login required)

View Item