WATER QUALITY OBJECTIVES FOR OKANAGAN LAKE A FIRST UPDATE January 2005 Prepared for the Ministry of Water, Land and Air Protection Penticton and Kamloops BC by Richard N. Nordin Ph.D. Limnos Water Associates 1226 Laurel Road North Saanich BC V8L 5K8 Water Quality Objectives for Okanagan Lake – A First Update Library and Archives Canada Cataloguing in Publication Data Nordin, Richard Nels, 1947- . Water quality objectives for Okanagan Lake [electronic resource] : a first update. Update to the report: Phosphorus in the Okanagan Valley lakes : sources, water quality objectives and control possibilities. 1985 (i.e. 1993) Available on the Internet. Issued also in printed format on demand. Technical report. An overview is issued separately. ISBN 0-7726-5389-5 1. Water quality – British Columbia – Okanagan Lake. 2. Water quality management - British Columbia – Okanagan Lake. 3. Okanagan Lake (B.C.) – Environmental conditions. 4. Aquatic resources – British Columbia – Okanagan Lake. I. British Columbia. Ministry of Water, Land and Air Protection. II. British Columbia. Water Protection Section. III. Title: Phosphorus in the Okanagan Valley lakes : sources, water quality objectives and control possibilities. TD227.B7W37 2005 363.73’946’097115 C2005-960145-0 ii Ministry of Water, Land and Air Protection Water Quality Objectives for Okanagan Lake – A First Update Summary Water quality objectives for Okanagan Lake are proposed to protect the water resource from deterioration. This report is designed to be an update and expansion of a report produced by the Ministry of Environment in 1985. That report proposed water quality objectives for all the main stem lakes in the Okanagan valley for one indicator, the spring phosphorus concentration. This report confines itself to Okanagan Lake but recommends an increased number of water quality objectives that might be used to provide guidance for long-term water quality protection. Okanagan Lake is an extremely important water body for a number of uses. The objectives proposed were designed with consideration of three major uses: recreation and aesthetics, drinking water and aquatic life (fisheries). Inclusion of all these uses is necessary for long-term management and protection of this lake. A review of extensive background information provides the basis for proposed new objectives. A review of water uses including aquatic life provides the background for setting new objectives. Although there have been a variety of changes in different components of the ecosystem, some components, like phytoplankton and zooplankton, have shown remarkable stability with few changes over the period of record. iii Ministry of Water, Land and Air Protection Water Quality Objectives for Okanagan Lake – A First Update A summary of the objectives that are proposed for Okanagan Lake: North Basin Central Basin South Basin Armstrong Arm Secchi disc 6 6 7 5 Transparency (m) (growing season average) Dissolved Oxygen - - - 5 mg/L min in bottom waters Total Phosphorus 8 8 7 10 (μg/L) (maximum at spring overturn) Chlorophyll-a 4.5 4.5 4 5 (μg/L)(maximum seasonal average Total Nitrogen 230 230 230 250 (μg/L) (maximum) N:P ratio >25:1 >25:1 >25:1 >25:1 (spring .weight ratio) Phytoplankton <5% <5% <5% <5% Structure (heterocystous cyanobacteria by numbers) Phytoplankton <0.75 g/m3 <0.75 g/m3 <0.75 g/m3 <0.75 g/m3 growing season average biomass Zooplankton 50 ug/m3 50 ug/m3 50 ug/m3 50 ug/m3 designated species mix minimum biomass Zooplankton 5% 5% 5% 5% Structure (minimum of cladocerar by numbers) Contaminants in fish tissue Below human Below human Below human Below human and Mysis tissue consumption consumption consumption consumption and and wildlife and wildlife and wildlife wildlife protection protection protection protection guidelines guidelines guidelines guidelines iv Ministry of Water, Land and Air Protection Water Quality Objectives for Okanagan Lake – A First Update Table of Contents Summary.................................................................................................................... Table of Contents....................................................................................................... Preface........................................................................................................................ 1.0 INTRODUCTION..................................................................................................... 1 2.0 THE WATERSHED AND LAKE............................................................................ 5 2.1 Morphometry......................................................................................................... 5 2.2 Hydrology............................................................................................................... 7 2.3 Lake Water Balance............................................................................................. 10 2.4 Water Movements ............................................................................................... 11 2.5 Population Trends .............................................................................................. 12 2.6 Economy of the Okanagan Catchment ........................................................... 13 3.0 WATER USE ............................................................................................................ 15 3.1 Human Consumption and Use......................................................................... 15 3.2 Aquatic Life.......................................................................................................... 18 3.2.1 Phytoplankton .............................................................................................. 18 3.2.2 Chlorophyll................................................................................................... 24 3.2.3 Periphyton..................................................................................................... 28 3.2.4 Aquatic Macrophytes .................................................................................. 30 3.2.5 Zooplankton.................................................................................................. 30 3.2.6 Benthos .......................................................................................................... 35 3.2.7 Mysis............................................................................................................... 36 3.2.8 Fish ................................................................................................................. 37 3.2.8.1 Kokanee ......................................................................................................... 39 3.2.8.2 Rainbow Trout.............................................................................................. 45 3.2.9 Comments on the data describing the aquatic resources of Okanagan Lake 46 3.3 Recreational Use.................................................................................................. 48 4.0 INFLUENCES ON WATER QUALITY............................................................... 49 4.1 Point Source Inputs ............................................................................................ 50 4.2 Non-point Source Inputs................................................................................... 55 4.2.1 Agriculture.................................................................................................... 56 4.2.2 Forest Harvesting......................................................................................... 57 4.2.3 Septic Tank Systems .................................................................................... 58 4.2.4 Dustfall and Precipitation........................................................................... 59 4.2.5 Watershed Sources.......................................................................................... 59 4.2.6 Phosphorus Mass Balance .......................................................................... 66 4.2.7 Nitrogen Mass Balance................................................................................ 67 4.3 Hydrology............................................................................................................. 68 v Ministry of Water, Land and Air Protection Water Quality Objectives for Okanagan Lake – A First Update 4.3.1 Effects of inter-annual differences in precipitation and runoff............. 68 4.3.2 Response Time.............................................................................................. 70 4.3.3 Climate Change............................................................................................ 71 5.0 WATER QUALITY ASSESSMENT AND OBJECTIVES................................ 73 5.1 Introduction ......................................................................................................... 73 5.2 Secchi Disk (water clarity) ................................................................................ 75 5.3 Dissolved Oxygen............................................................................................... 79 5.4 Phosphorus........................................................................................................... 80 5.5 Nitrogen ................................................................................................................ 83 5.6 N:P ratios and Aquatic Food Chain Response .............................................. 86 5.7 Chlorophyll a ......................................................................................................