Auditing a flooded quarry prior to marina development

Development of a marina in a flooded brownstone quarry required construction of a canal to the Connecticut river through an isthmus separating the 2 systems. An environmental audit during a 16 month period developed quantitative limnological data required by regulatory agencies. The deep quarry basin, protected by high sandstone walls, became strongly stratified in summer. Development of littoral vegetation in the quarry was prevented by the steep sides of the basin. Unusual characteristics of the manmade quarry basin, compared to most natural lakes in Connecticut, included a mean depth of 14 m, an intense thermocline, and negative heterograde oxygen profiles with metalimnetic minima. Alkalinity, conductivity and nutrient levels differed significantly between the quarry and the river. Mean chlorophyll-a concentrations in the 2 systems were similar, but the distribution of phytoplankton classes were quite different. The environmental audit, by comparing physical, chemical and biological characteristics of the quarry to those of the river, allowed prediction of changes in trophic status when the 2 systems are joined.