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

Home , Granger Lake, Lake Fork Reservoir

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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.

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.

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

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.

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.

Figure 2 – Chlorophyll Concentrations – Reservoir Main Body and Cove/Headwaters Stations

50 Main Body 40 Cove / Headwater

10 Chlorophyll-a (ug/l)

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 in Each Reservoir (as ug/L)

Reservoir Maximum Minimum Bridgeport 32 2 Canyon 7 2 Cedar Creek 64 10 Georgetown 5 1 Granger 36 1 Lake Fork 44 5 Livingston 115 8 Travis 5 1

Additional quality data for each reservoir are summarized in Table 4. Table 4 presents mean values (including data for both main body and cove/headwaters stations) for nitrogen, phosphorus, DO, and pH. Non-detect values are included in the average at one-half the detection limit.

Table 4 – Reservoir Characteristics: Nutrients, Dissolved Oxygen, pH

Total Total DO Reservoir Nitrogen Phosphorus pH (mg/L) (mg/L) (mg/L) Bridgeport 0.79 0.06 7.4 8.1 Canyon 0.70 0.05 8.6 8.1 Cedar Creek 1.26 0.10 7.8 8.4 Georgetown 0.35 0.11 7.4 8.1 Granger 0.78 0.10 7.0 8.1 Lake Fork 0.95 0.04 7.6 7.7 Livingston 1.34 0.24 9.3 8.4 Travis 0.36 0.01 8.2 8.4

User Surveys

Over the two-year study period approximately 1,800 user survey forms were completed. The eight reservoirs studied have different types of users. Some have a higher percentage of contact recreation users, and some have a higher percentage of fishing users. Table 5 summarizes the predominant uses at each reservoir. Contact recreation users include swimmers and water skiers. The “Other” category includes users engaged in on-shore activities (picnicing, for example) and those who specified “Other”.

Table 5 – User Characteristics of Each Reservoir and Overall

Contact Sampling Fishing Other Reservoir Recreation Boating Crew (%) (%) (%) (%) (%) Bridgeport 15 35 9 26 15 Canyon 19 11 28 19 22 Cedar Creek 8 29 24 23 15 Georgetown 18 11 9 37 25 Granger 8 26 11 35 20 Lake Fork 5 56 6 24 9 Livingston 16 31 12 15 27 Travis 26 6 23 32 13

CONCLUSIONS

After reviewing the data, it was concluded that Granger Lake should not be included in subsequent evaluations because of its special characteristics. Granger Lake has high turbidity due to the presence of a high concentration of inorganic suspended solids. Therefore, the relationship between clarity and chlorophyll concentration and the relationship between user perceptions of impacted uses and chlorophyll concentration are different than those relationships for the other reservoirs studied. Granger Lake exhibited low chlorophyll concentrations, but users reported impacted use. The reported impacts are apparently attributable to the concentrations of inorganic suspended solids present. These results do suggest, however, that there may be reservoirs with high, naturally occurring turbidity where nutrient standards are not required.

The remaining reservoirs were grouped for several evaluations based on clarity. The groupings are presented in Table 6.

Table 6 – Grouping of Reservoirs Based on Clarity

Average Main Body Clarity Class Transparency (m) Reservoirs by Group Low <1.0 Cedar Creek Reservoir Lake Livingston Moderate 1.0 – 2.0 Lake Bridgeport Lake Fork Reservoir High >2.0 Lake Georgetown Canyon Lake Lake Travis

In general, it was found that the existing levels of algal growth are acceptable to the majority of recreational users. Within any single reservoir or any reservoir group, there is not a strong relationship between the degree of perceived impacts on recreational uses and increasing chlorophyll concentrations. This is demonstrated on Figure 3, which was developed as follows:

• For each reservoir group, chlorophyll data were compiled into three subsets, and an average concentration was computed for each subset. The first subset was comprised of the chlorophyll concentrations associated with “a” response (“beautiful, could not be nicer”). The second subset was comprised of the chlorophyll concentrations associated with “b” responses (“very minor aesthetic problems, excellent for swimming, boating enjoyment”). The third subset was comprised of the chlorophyll concentrations associated with “c,” “d,” and “e” responses (these responses ranged from “enjoyment slightly impaired” to “enjoyment nearly impossible”).

Figure 3 –Recreational Suitability Based on Chlorophyll Concentration, Evaluated for Reservoir Clarity Groups

10 Chlorophyll-a (ug/L)

0 Cedar Creek / Fork / Bridgeport Georgetown / Canyon / Livingston Travis

a - beautiful, could not be any nicer b - very minor aesthetic problems, excellent for swimming, boating enjoyment c- swimming and aesthetic enjoyment sligthly impaired or d - desire to swim and level of enjoyment of the lake substantially reduced or e - swimming and aesthetic enjoyment of the lake nearly impossible

As can be observed on Figure 3, the relationship between the degree of perceived use impact and increased chlorophyll concentration is different for the three clarity groups. There is no discernible relationship for the low clarity group, even though the maximum concentration in these reservoirs reached 60 – 100 micrograms per liter (ug/L). The strongest relationship is exhibited in the moderate clarity reservoirs. However, it is notable that a relationship can also be observed in the high clarity reservoir, even though chlorophyll concentrations did not exceed 7 ug/L in any of these reservoirs.

A much stronger relationship between increased chlorophyll concentrations and increased perception of use impairment is observed when the data are compiled for all seven of the reservoirs. The results of this evaluation are presented on Figure 4. To prepare Figure 4, the following values were determined for each reservoir:

• The mean summer chlorophyll concentration for the reservoir (data for both the main body and the cove/headwaters station were included).

• The percentage of the responses at that reservoir that categorized the suitability of the reservoir for recreational use as “c,” “d,” and “e.”

As shown in Figure 4, the relationship is very strong in this study. When the mean summer concentration of chlorophyll in a reservoir was between 20 and 25 ug/L, approximately 25% of the respondents perceived the reservoir as being at least slightly impaired for recreational use.

Figure 4 – Recreational Suitability Based on Chlorophyll Concentration, Evaluated for Combined Database

40%

30%

R2 = 0.904

20%

10% Percent CDE Responses

0% 0 10203040 Chlorophyll-a (ug/L)

(Each data point represents a reservoir)

The data were also evaluated by calculating the average concentration of chlorophyll from all of the reservoirs that produced a response of “a,” “b,” “c,” “d, ”and “e,” respectively. The results of this evaluation are presented on Figure 5. Figure 5 also includes a summary of how the users characterized the amount of algae that was present.

Figure 5 – Average Chlorophyll Concentration for Each Category of Use Suitability and Algal Growth

Use Suitability 30 Number of 51 25 Responses 19 353 20 324 783 15 10 5 Chlorophyll-a (ug/L) 0 abcde Response

a - beautifull, could not be nicer b - very minor aesthetic problems c - swimming and aesthetic enjoyment slightly impaired d - desire to swim and level of enjoyment substantially reduced e - swimming and aesthetic enjoyment nearly impossible

Greenness 30

25 36 213 20 Number of 14 Responses 732 15 535 10 5 Chlorophyll-a (ug/L) 0 abcde Response

a - no algae, or crystal clear water b - a little algae visible c - definite algae visible d - very green; some scum present and/or mild odor apparent e - pea soup green with one or more of the following: massive floating scums on lake or washed up on shore, strong foul odor, or fish kill

ALL DATA POOLED

Other observations from the study included the following:

• There was a better correlation between the perceived degree of recreational use impact and increasing chlorophyll concentration than there was between the perceived degree of impact and decreasing transparency. The r2 value for the chlorophyll relationship is 0.81 and the r2 value for the transparency relationship is 0.69. This confirms that chlorophyll is a good choice for a water quality standard parameter to indicate potential for use impacts.

• Reservoirs with very low chlorophyll concentration and high clarity are most popular with contact recreation users. Usage of these reservoirs by fishermen is very low in terms of the total number of fishermen and the percentage of users that are fishermen. Reservoirs with moderate to low clarity due to chlorophyll concentrations are most popular with fishermen. This suggests that different water quality standards may be appropriate based on the predominant type of recreational use at a reservoir.

RECOMMENDATIONS

The following recommendations relate specifically to criteria that support recreational uses. When establishing water quality standards, nutrient criteria for recreational uses will have to be balanced against criteria that are supportive of other uses such as water supply.

• For reservoirs, the parameter used for the water quality standard should be chlorophyll.

• The chlorophyll standard should be applied to the mean summer concentration of chlorophyll in the main body of the reservoir.

• Reservoirs should be categorized as low clarity (<1.0 m), moderate clarity, (1.0 – 2.0 m), or high clarity (>2.0 m), and a somewhat different approach should be taken for each category.

– In low clarity and high clarity reservoirs, the criteria should be site-specific and based on the range of historical concentrations at the reservoir. However, because the users of high clarity reservoirs perceive impacts when there are very small changes in chlorophyll concentrations and the users of low clarity reservoirs find relatively large changes in concentration to be acceptable, it may be appropriate to use more restrictive confidence intervals for the two types of reservoirs when characterizing the historical data.

– For moderate clarity reservoirs, it may be possible to select one criterion value to support recreational uses, perhaps in the range of 20 – 25 ug/L. Chlorophyll data for a larger group of moderate clarity reservoirs should be reviewed to determine if this is an appropriate value.

• Further investigation is needed to determine if there are currently reservoirs in Texas where chlorophyll concentrations are currently so high that they are adversely impacting

existing uses to a significant degree. If so, it is not appropriate to establish a criterion based on the historical quality for these reservoirs.

• The assessment methodology used to characterize water quality in reservoirs should include trend analyses as well as the comparison of existing quality to the water quality standard.

ACKNOWLEDGEMENTS

The author wishes to express appreciation to the Brazos River Authority, Guadalupe-Blanco River Authority, Lower Colorado River Authority, Sabine River Authority, San Antonio River Authority, Tarrant Regional Water District, and Trinity River Authority for their diligent field work in collecting the data used in this study and for their technical insights during the evaluation of the data; to William W. Walker, Jr., for his guidance and expertise during the development of the study and evaluation of the data; and to the Texas Water Conservation Association, National Association of Clean Water Agencies, and Texas Association of Clean Water Agencies for their financial support.

REFERENCES

Heiskary, S.A. and W. W. Walker (1988), “Developing Phosphorus Criteria for Minnesota Lakes.” Lake and Reservoir Management, Volume 4, No. 1, pp. 1 – 10.

Smeltzer, E. and S.A. Heiskary (1990), “Analysis and Applications of Lake User Survey Data.” Lake and Reservoir Management, Volume 6, No. 1, pp. 109 – 118.