Development of Use-Based Chlorophyll Criteria for Recreational Uses of Reservoirs

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Courtesy of Water Environment Federation (WEF)

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.

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.

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