A Comparative Analysis of 4 Shallow Urban Impoundments

Abstract

Shallow urban impoundments are known for low water transparency, and generally low water quality. This thesis investigates the effects of land use, management regime, and carp density on the water quality in 4 shallow urban impoundments on the Laurel Creek system in Waterloo, Canada. The focus of this study is to look at how these factors affect suspended solids, total phosphorus, and phytoplankton assemblages within the impoundments. The land upstream of the impoundments is lightly to heavily urbanized. The impoundments differ in how they are managed as well, with the most upstream impoundment being completely drawn-down every year with drastic effects downstream.

Clair and Silver Lakes received significantly higher total inorganic solids (TIS) concentrations compared to Laurel Creek Reservoir and Columbia Lake during the study period; however there were no significant differences between the impoundment inlets for total organic solids (TOS) or total phosphorus (TP) concentrations during the same period.

Three of the four impoundments were found to export significantly higher concentrations of TIS; these were Columbia, Clair and Silver Lakes. Additionally, Clair and Silver Lakes exported significantly higher TIS concentrations than both Columbia Lake and Laurel Creek Reservoir. Laurel Creek Reservoir discharged very low TIS concentrations throughout the study period. The same pattern as TIS concentrations was seen for the TOS concentrations leaving the impoundments, with Columbia, Clair, and Silver Lakes having significantly higher outlet TOS concentrations when compared to Laurel Creek Reservoir; additionally Clair and Silver Lakes discharged significantly higher TOS concentrations when compared to Columbia Lake. There were no significant differences among TP concentrations leaving the impoundments during the study period. In general, Laurel Creek Reservoir and Silver Lake discharged the highest phytoplankton densities; while Columbia and Clair Lakes discharged lower densities; however, there was no significant difference in these discharge densities between the different impoundments.