WEFTEC®.06 DEVELOPMENT OF USE-BASED CHLOROPHYLL CRITERIA FOR RECREATIONAL USES OF RESERVOIRS Peggy W. Glass, Ph.D. Alan Plummer Associates, Inc. 6300 La Calma, Suite 400 Austin, TX 78752 ABSTRACT This investigation was sponsored by the Texas Water Conservation Association (TWCA) with support from the Association of Metropolitan Sewerage Agencies (AMSA) and the Texas Association of Metropolitan Sewerage Agencies (TAMSA). The study was conducted by seven Texas river authorities in association with Dr. William W. Walker, Jr., Ph.D., and Alan Plummer Associates, Inc. (APAI). Its purpose is to provide data to assist in the development of surface water quality standards for nutrients in reservoirs. This investigation focuses on the identification of use-based criteria to support recreational uses. These results can be compared to criteria to support other types of uses of reservoirs (water supply, aquatic life use, fisheries, etc.) to derive appropriate water quality standards for nutrients. The study method was to collect simultaneous data on user perception of whether recreational use was impaired (and, if so, the extent of the impairment) and water quality data. The water quality parameters measured included water clarity, nutrient concentrations, chlorophyll concentrations, dissolved oxygen, and pH. Data were collected twice each month during the summer in eight reservoirs. Two stations were sampled in each reservoir: one station was in the main body of the lake, and one station was in either a cove or a headwaters area. The study was conducted over two summers. The eight reservoirs studied represent a wide range of sizes, ecoregions, nutrient loadings, and natural (inorganic) turbidity levels. Over the two-year period, approximately 310 sampling events were conducted, and over 1,800 survey forms were completed. Approximately 96% of the survey records could be paired with chlorophyll measurements. Chlorophyll was concluded to be the most appropriate parameter for a water quality standard. KEY WORDS Nutrients, Nutrient Criteria, Recreational Uses, Chlorophyll Criteria, Reservoirs. Copyright © 2006 Water Environment Foundation. All Rights Reserved 4038 WEFTEC®.06 INTRODUCTION This study is a collaborative effort to identify the level at which algal growth is objectionable to recreational users of reservoirs in Texas. A representative range of Texas reservoirs was selected for the two-year study. Sampling was conducted during the summers of 2003 and 2004. Participants in the study were as follows: Brazos River Authority (BRA), Guadalupe-Blanco River Authority (GBRA), Lower Colorado River Authority (LCRA), Sabine River Authority (SRA), San Antonio River Authority (SARA), Tarrant Regional Water District (TRWD), and Trinity River Authority (TRA). Consultants assisting in the effort were Dr. William W. Walker, Jr., and Alan Plummer Associates, Inc. (APAI). The study was sponsored by the Texas Water Conservation Association. Support was also provided by the Association of Metropolitan Sewerage Agencies (AMSA) and members of the Texas Association of Metropolitan Sewerage Agencies (TAMSA). Several researchers have conducted similar studies to identify the level at which algal growth is objectionable to recreational users of reservoirs (for example, Heiskary & Walker, 1988; Smeltzer & Heiskary, 1990). These researchers, and this study, used a method that coordinates user surveys and water quality measurements. Previous researchers determined that algal bloom frequency is the most significant nutrient-related condition for recreational users. However, they have also found that bloom frequency can be correlated to a growing season mean chlorophyll-a concentration, which is a more practical parameter for a regulatory criterion. For the purpose of this study, recreational uses include the full-range of contact and non-contact activities and the aesthetic qualities supportive of these uses. DESCRIPTION OF STUDY RESERVOIRS Eight reservoirs were selected for the study. These reservoirs represent a wide range of conditions with respect to size, drainage area, trophic status, primary uses, and ecoregion location. The eight reservoirs are Lake Bridgeport, Canyon Lake, Cedar Creek Reservoir, Lake Fork Reservoir, Lake Georgetown, Granger Lake, Lake Livingston, and Lake Travis. Table 1 provides a summary of the sizes of the reservoirs and the ecoregion in which each reservoir is located. Copyright © 2006 Water Environment Foundation. All Rights Reserved 4039 WEFTEC®.06 Table 1 –Description of Study Reservoirs Surface Area Volume Reservoir Level III Ecoregion (acres) (acre-feet) Canyon Lake Edwards Plateau 8,230 378,781 East Central Texas Cedar Creek Reservoir Plains/Texas Blackland 32,623 637,180 Prairies Texas Blackland Granger Lake 4,009 54,280 Prairies/Edwards Plateau Central Oklahoma/Texas Lake Bridgeport 11,649 366,236 Plains South Central Lake Fork Reservoir Plains/Texas Blackland 27,690 604,927 Prairies Lake Georgetown Edwards Plateau 1,297 37,010 South Central Lake Livingston Plains/Texas Blackland 83,277 1,741,867 Prairies Lake Travis Edwards Plateau 18,622 1,131,650 DESCRIPTION OF RECREATIONAL USER SURVEYS Persons surveyed were asked to identify which of the following responses best described their perception of how suitable the lake water was for recreation and aesthetic enjoyment on the day the survey was conducted. 1) Beautiful, could not be any nicer 2) Very minor aesthetic problems; excellent for swimming, boating enjoyment 3) Swimming and aesthetic enjoyment slightly impaired 4) Desire to swim and level of enjoyment of the lake substantially reduced 5) Swimming and aesthetic enjoyment of the lake nearly impossible Additional questions were included in the survey to determine the users’ perception of how much algae was in the water, the nature of the recreational use (swimming, fishing, picnicing, etc.) and whether factors other than algae (muddiness, boat traffic, etc.) were causing the impairment of recreational use. Also, data were obtained regarding whether the survey respondent was a frequent or infrequent visitor. During each sampling event, at each sampling location, two Copyright © 2006 Water Environment Foundation. All Rights Reserved 4040 WEFTEC®.06 survey forms were completed by the technical staff collecting the water quality samples; and, when possible, five survey forms were completed by recreational users of the lake. DESCRIPTION OF SAMPLING PROGRAM Sampling events were conducted twice each month during the summers of 2003 and 2004. Two stations were sampled/surveyed in each reservoir. One station was always in the main body of the reservoir. The other station was always in a cove or headwaters area. Whenever possible, sampling events were conducted a minimum of two weeks apart. An effort was made to avoid conducting sampling events during, or immediately after, significant rainfall events. (During data evaluation, a few of the measurements were determined to have been influenced by rainfall; these results were not included in subsequent evaluations.) Table 2 identifies the water quality parameters that were measured. All chlorophyll analyses were performed by the LCRA Environmental Laboratory Services to provide data consistency. Table 2 – Water Quality Parameters Measured Field Measurements Laboratory Measurements Conductivity Algae Dissolved Oxygen (DO) Chlorophyll-a pH Pheophytin Secchi Disc Depth Nitrogen Temperature Nitrate Nitrite Total Kjeldahl Nitrogen Phosphorus Total Phosphorus Solids Total Suspended Solids (TSS) Volatile Suspended Solids (VSS) Turbidity RESULTS Following are summaries of the study results. Quality characteristics of the reservoirs are summarized, and the results of the user surveys are presented. Copyright © 2006 Water Environment Foundation. All Rights Reserved 4041 WEFTEC®.06 Reservoir Water Quality Figure 1 presents a summary of the transparency characteristics of each reservoir, as indicated by Secchi disc measurements. The values presented are the mean summer transparency measurements in the main body of each reservoir. Figure 1 – Average Summer Transparency – Reservoir Main Body Stations 3.5 3 2.5 2 1.5 1 0.5 Transparency (meters) 0 t er n k to or or on vis F a rang ngs e etown Tr i g Cany G iv ridgep L B Lak Cedar Creek Geor The reservoirs are grouped on the figure based on transparency. Lake Granger has the lowest transparency. Lake Granger is different than the other reservoirs in the study in that the low transparency is the result of high TSS in the water column, which is predominantly inorganic. In the other reservoirs, increases in TSS are typically associated with increased VSS (as previously noted, samples where TSS may have been influenced by rainfall runoff have been eliminated from these evaluations). Figure 2 presents a summary of chlorophyll concentrations in each reservoir. The reservoirs are again grouped based on transparency, as shown on Figure 1. The values presented are the mean summer concentrations in the main body and the cove or headwaters of each reservoir. Table 3 summarizes the range of chlorophyll measurements in each reservoir. Both main body and cove/headwaters data are included in Table 3. Copyright © 2006 Water Environment Foundation. All Rights Reserved 4042 WEFTEC®.06 Figure 2 – Chlorophyll Concentrations – Reservoir Main Body and Cove/Headwaters Stations 50 Main Body 40 Cove / Headwater 30 20 10 Chlorophyll-a (ug/l) 0 t is or ton p nger gs ra Creek e Fork Trav r k Canyon G ridge Livin B La Ceda Georgetown Table 3 – Range of Chlorophyll Concentrations