A Study of Water Quality in Lake Raleigh

This study was completed to obtain a record of seasonal conditions in Lake Raleigh. The detailed bathymetry map which was constructed as part of this research demonstrates that Lake Raleigh has sustained appreciable sediment loading. In the past 20 years the mean depth has decreased by nearly 2 m, and the former west basin has become a wetland with maximum depth 0.75 m. Throughout the year, the lake is fairly turbid from suspended sediments, with lowest water clarity following periods of precipitation. Although it is shallow, the lake thermally stratifies during summer early autumn, with dissolved oxygen concentrations less than 1 mg/L in the hypolimnion from July September. The lake is softwater and maintained neutral to slightly alkaline pH throughout most of the year, except for mildly acidic conditions during a spring period of high precipitation and overland runoff. Heavy metal concentrations were low during all seasons. Storm sewer drainage enters the lake during moderate precipitation events, however, resulting in high fecal coliform counts well in excess of State standards. Flagellates and small coccoid blue-green algae were codominant in the late summer phytoplankton community, including many mixotrophic taxa. Nutrient concentrations indicate that the lake is mesotrophic and likely would support higher algal production under increasing nutrient enrichment, particularly under reduced sediment loading and improved water clarity. TABLE OF CONTENTS Page ACKNOWEDGMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii ... ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v LISTOFTABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii ... SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vlii RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Origin and History of Lake Raleigh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Drainage Basin and Hydraulic Residence Time . . . . . . . . . . . . . . . . . . . . . . . . 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PURPOSEANDOBJECTIVES 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PROCEDURES 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LakeMorphomet ry 4 Physical, Chemical and Biological Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RESULTS AND DISCUSSION 8 Morphometry of Lake Raleigh ..................................... 8 Physical Conditions . Temperature. Light. Specific Conductance and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SuspendedSolids 9 Chemical Conditions . Dissolved Oxygen. pH. Heavy Metals. and Nutrients .... 14 Phytoplankton Biomass and Community Composition .................... 33 A Monitored Storm Sewer Overflow Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Overall Interpretations ........................................... 45 ...................................................... REFERENCES 47 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GLOSSARY 51 . APPENDIX 1 TEMPERATURE AND DISSOLVED OXYGEN DATA ....... 56 APPENDIX 2 . DATA FOR PHOTOSYNTHETICALLY ACTIVE RADIATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60