Water Quality Analysis of Lakewood Lakes

Transcription

1 Water Quality Analysis of Lakewood Lakes December 2016 Prepared by WEST Consultants, Inc. Bellevue, Washington With support from HDR, Inc., Olympia, Washington

2 TABLE OF CONTENTS EXECUTIVE SUMMARY... V 1 INTRODUCTION METHODS AND MATERIALS Data Data Analyses Database Development RESULTS Transparency Water Temperature Dissolved Oxygen Alkalinity Nutrients Chlorophyll_a Trophic Levels Statistical Analyses Seasonal Trends Year-to-Year Variability Water Quality Processes CONCLUSIONS AND RECOMMENDATIONS American and Gravelly Lakes Lake Louise and Steilacoom Lake Waughop and Carp Lakes Overall Trends in Lakes i P age

3 4.5 Recommendations REFERENCES LIST OF FIGURES Figure 1. Location map showing City of Lakewood, Washington, Lakes Figure 2. Box plots of transparency in the six lakes... 5 Figure 3. Times series of water temperature in American Lake... 6 Figure 4. Profiles of water temperature in American Lake in Figure 5. Box plots of water temperature in the six lakes... 7 Figure 6. Times series of dissolved oxygen in American Lake... 8 Figure 7. Profiles of dissolved oxygen American Lake in Figure 8. Box plots of dissolved oxygen in the six lakes... 9 Figure 9. Times series of alkalinity in American Lake Figure 10. Box plots of alkalinity in the six lakes Figure 11. Times series of total phosphorus in American Lake Figure 12. Box plots of total phosphorus in the six lakes Figure 13. Box plots of ammonia in the six lakes Figure 14. Box plots of nitrites in the six lakes Figure 15. Box plots of nitrates in the six lakes Figure 16. Box plots of chlorophyll_a in the six lakes Figure 17. TSI based on transparency (Secchi depth) Figure 18. TSI based on total phosphorus Figure 19. TSI based on chlorophyll_a ii P age

4 Figure 20. Ammonia and dissolved oxygen in the hypolimnion of American Lake Figure 21. Ammonia and dissolved oxygen in the hypolimnion of Gravelly Lake iii P age

5 LIST OF TABLES Table 1. Lakes Monitored within the City of Lakewood... 3 Table 2. Chemicals Sampled in Lakewood s Lakes... 3 Table 3. Summary of Secchi depths for each lake... 5 Table 4. Comparison of depth and average bottom water temperatures... 7 Table 5. Summary of trophic states iv P age

6 Executive Summary The volunteer lake monitoring program for the City of Lakewood, Washington, started in The program includes monitoring the water quality of six lakes: Gravelly, American, Steilacoom, Louise, Waughop, and Carp. The evaluation included analyses of trends in times, differences among lakes, differences between the upper and lower water column, and relationships among water quality parameters. American and Gravelly Lakes are the deepest of the six lakes studied. They strongly stratify during the summer, resulting in higher temperatures in the upper water column, and temperatures near 10 o C in the lower water column. The upper water column is characterized by dissolved oxygen values near or exceeding 9.5 mg/l. The lower water column often has hypoxic conditions (DO < 2 mg/l) and even approaches anoxic conditions (DO = 0 mg/l) on occasion. However, supersaturated DO values occur near the seasonal thermocline. Water clarity is generally good, with transparencies on the order of 6-7 m. The lower water column has high concentrations of nutrients. The lakes range from oligotrophic to mesotrophic from year to year. Lake Louise and Steilacoom Lake are the intermediate depths of the six lakes studied. They stratify during the summer, resulting in higher temperatures in the upper water column, but the stratification can reach the lake bed and elevate deeper water temperatures. The upper water column is characterized by dissolved oxygen values near or exceeding 9.5 mg/l. However, the lower water column often sees a range of dissolved oxygen from hypoxic conditions and even approaches anoxic conditions on occasion, to higher values between 4-8 mg/l. There is some evidence of somewhat elevated DO values near the seasonal thermocline. Water clarity is generally moderate, with transparencies on the order of m. The lower water column has elevated concentrations of nutrients. Lake Louise ranges from oligotrophic to mesotrophic from year to year, and Steilacoom Lake ranges from mesotrophic to mildly eutrophic. Waughop and Carp Lakes are the shallowest of the six lakes studied. They are generally fairly well mixed during the summer, resulting in little thermal stratification. Dissolved oxygen values range from near or exceeding 9.5 mg/l throughout the water column to occasionally low (2-6 mg/l) at depth. Waughop Lake is the least transparent among the six lakes with transparencies on the order of m. Transparencies in Carp Lake are on the order of 1-3 m, which range from poor clarity to the depth of the shallow lake. There are nutrients available throughout the water column as these lakes tend to be fairly well mixed throughout the year. Waughop Lake is consistently eutrophic, although the record is short. Carp Lake ranges from mesotrophic to mildly eutrophic from year to year, with a tendency towards being eutrophic. The data show that there can be significant variations among lakes as described above. All the lakes show a seasonal influence of summer warming followed by winter cooling and increasing DO levels. Year-to-year, transparences (water clarity) seem to be mildly increasing, total v P age

7 phosphorus is generally constant, chlorophyll_a concentrations and hypolimnion ammonia are decreasing, and DO, temperature, and alkalinity show no clear annual trends. The data show no significant annual changes in the onset of seasonal stratification (of water temperature and dissolved oxygen) or the occurrence of the fall turn over. The study recommended (1) that the monitoring be expanded to include sampling for ph and total nitrogen, (2) that the monitoring period be extended to include sampling in April and November to enable analysis of year-to-year trends in stratification of temperature and DO, and (3) that the occurrence of low dissolved oxygen in a number of lakes, especially American and Gravelly, be evaluated. Following an analysis of these data, a coordinated groundwater and lake monitoring program could better understand the hydrogeologic and groundwater influences on the lakes. vi P age

8 1 Introduction The volunteer lake monitoring program for the City of Lakewood, Washington, started in The program includes monitoring the water quality of six lakes: Gravelly, American, Steilacoom, Louise, Waughop, and Carp (Figure 1). The City of Lakewood would like the water quality data to be analyzed to evaluate water quality trends, and if possible to determine influences on water quality conditions. Figure 1. Location map showing City of Lakewood, Washington, Lakes. 1 P age

9 The evaluation included analyses of trends in times, differences between lakes, differences between the upper and lower water column, and relationships between water quality parameters. The study was divided into two parts: (1) analysis of existing data, and (2) determination of any causal effects on water quality conditions. 2 P age

10 2 Methods and Materials 2.1 Data Table 1 lists the lakes analyzed, the period of monitoring and the approximate frequency. Table 1. Lakes Monitored within the City of Lakewood Lake Monitoring Monitoring Occurs: Began: American May 2000 May October with one additional monitoring event after turnover Gravelly May 2000 May October with one additional monitoring event after turnover Louise May 2000 May October Steilacoom May 2004 May - October Waughop May 2011 May - October Carp May 2000* May - October *In some years, water levels are too low to allow monitoring, and the data record for Carp is not continuous. The lakes were monitored twice a month (May-October) 2000 through Beginning in May 2005 until present day, the monitoring was monthly, and occurred at the deepest part of each lake. Secchi depths were measured, profiles collected for dissolved oxygen (DO) and water temperature at meter intervals from the water surface to the bottom, the lake levels of American, Gravelly, Louise, and Waughop Lakes were recorded, and grab samples collected for lab analysis for the chemicals in Table 2. Table 2. Chemicals Sampled in Lakewood s Lakes Analysis Sampling Stratum Sampling Frequency Sampling period Total phosphorus epilimnion Every monitoring event Total phosphorus Hypolimnion May, Aug, Oct Chlorophyll a Epilimnion Every monitoring event Chlorophyll a Mid-depth May, Aug, Oct Nitrate nitrogen Epilimnion May, Aug, Oct Nitrate nitrogen Hypolimnion May, Aug, Oct Nitrite nitrogen Epilimnion May, Aug, Oct Nitrite nitrogen Hypolimnion May, Aug, Oct Ammonia Epilimnion May, Aug, Oct nitrogen Ammonia Hypolimnion May, Aug, Oct nitrogen Alkalinity Epilimnion May, Aug, Oct P age

11 The City of Lakewood provided the data in an excel spreadsheet. As total nitrogen was sampled only in 2004 and then replaced by individual nitrogen forms, the spreadsheet was expanded to include all the data types collected, and accumulated for all years ( ). Finally, after City review, some data were removed due to poor data quality issues. The time series data were plotted and are presented by lake for each constituent in Appendix A. The profile data for each lake for each constituent are presented in Appendix B. 2.2 Data Analyses The data were analyzed to examine water quality trends, and to examine the relationships among parameters. The data were evaluated in a number of ways: 1. They were examined visually to see if there were clear trends in the data, including temporal trends and differences between lakes. This is especially true for profile data as they are difficult to evaluate statistically. 2. Box plots were developed and examined visually to see if there were clear differences between lakes, and between the upper and lower water column. 3. A detailed statistical analysis was performed on the grab data, including transparency, to examine the relationship between water quality and physical parameters, seasonality, annual variability, and differences between lakes. 2.3 Database Development In these analyses, non-detected values were included at one-half of their method detection limits (MDLs). The suspended algae data were not used in the subsequent analyses as they were qualitative observations estimated by volunteers. City staff reviewed the assembled database, and recommended that some values be rejected due to sampling or other data issues. 4 P age

12 3 Results 3.1 Transparency Figure 2 and Table 3 summarize the transparencies (Secchi depths) from measurements in each lake. The individual plots are shown in Appendix A. The results show generally clearer water in the larger, deeper lakes (American, Gravelly, and Louise), moderate transparencies in the medium-size lakes (Steilacoom), and lower transparencies in the shallower lakes (Waughop and Carp) although sometimes the bottom can be seen. The lower transparencies could be caused by wind interacting with the bed in the shallower lakes or increased algal growth. Table 3 also shows the annual trends in transparency. In all lakes, except Carp Lake, the trends are not statistically significant (either marginally increasing or decreasing). Carp Lake shows a statistically significant increase in transparency over time, however, the data set for Carp lake is small. Figure 2. Box plots of transparency in the six lakes Table 3. Summary of Secchi depths for each lake Lake Minimum (m) Average (m) Maximum (m) Annual trend* American Slight increase Gravelly Slight decrease Louise Slight increase Steilacoom (Bottom) Slight increase Waughop Slight decrease Carp (bottom) Increase * Qualitative summary from plots in Appendix A 5 P age

13 3.2 Water Temperature Figure 3 shows an example of a time series of water temperature in American Lake, and Figure 4 shows a typical series of water temperature profiles (in 2004). Figure 5 shows box plots of water temperatures in each of the six lakes, and Appendices A and B show the entire series of plots at all six lakes. The profiles from 2004 show a typical pattern of summer heating, the thickening of the upper thermal layer, and then cooling and turn-over in the fall. Figure 3. Times series of water temperature in American Lake Figure 4. Profiles of water temperature in American Lake in 2004 The plots also show that the deeper temperatures are strongly related to the depth of the lakes (Figure 5 and Table 4). In American and Gravelly Lakes, the seasonal thermocline (the interface between the upper water column heated by the atmosphere and deeper, cooler water) is generally meters below the surface, and does not reach the bottom of these two lakes. However, the other lakes are shallower, and as the upper, warmer water column thickens, it 6 P age

14 can eventually reach or almost reach to lake bottoms. Also, a rough estimate of groundwater temperatures is about the average annual air temperature. In the Lakewood area, this would be about o C. This is about equal to the near-bottom water temperatures in American and Gravelly Lakes. Therefore, it is possible, without an analysis of nearby groundwater levels, that groundwater inflows may significantly control temperatures in the hypolimnion of these lakes. It is difficult to infer this interaction for other lakes. Finally, in the shallower lakes (Waughop and Carp), the near-surface temperatures tend to be a little warmer as there is some downward mixing to a lower, cooler water mass. Times series plots indicate little variation from year to year. Figure 5. Box plots of water temperature in the six lakes Table 4. Comparison of depth and average bottom water temperatures Lake Average bottom temperature ( o C) Maximum profile depth (m) American Gravelly Louise Steilacoom Waughop Dissolved Oxygen Figure 6 shows an example of a time series of dissolved oxygen (DO) in American Lake, and Figure 7 shows a typical series of DO profile (in 2004). Appendices A and B show the entire series of plots at all six lakes. The profiles from 2004 show a typical pattern of summer heating, 7 P age

15 which limits the transfer of DO from the atmosphere to the lower layers across the seasonal thermocline. Figure 6. Times series of dissolved oxygen in American Lake Figure 7. Profiles of dissolved oxygen American Lake in 2004 Figure 8 shows box plots of DO in each lake (shallow and deep) and shows that the deeper DO are strongly related to lake depths. In American and Gravelly Lakes, the seasonal thermocline does not reach to the bottom of these lakes and summer DO in the lower water column become very low (hypoxic and approaching anoxic) due to bacterial action in the hypolimnion and because re-aeration is limited by the thermocline. In the other, shallower lakes, the summer thermocline may eventually reach the lake bottoms, and the deeper waters receive some re-aeration, perhaps increased on windy days. Times series plots indicate little variation from year to year. 8 P age

16 DO=9.5 mg/l Figure 8. Box plots of dissolved oxygen in the six lakes The DO profiles also show something else. Looking at Figure 7 as an example, American and Gravelly Lakes also see higher DOs in the vicinity of the seasonal thermocline, with values that exceed saturation. We believe that this is due to mobile algae that are looking for a combination of light for photosynthesis (in the upper water column) and food sources (nutrients in the lower water column). During the day, these algae produce oxygen as a byproduct of photosynthesis, and it accumulates just above the seasonal thermocline. This effect is seen strongly in American and Gravelly Lakes, occasionally in Lake Louise and Steilacoom Lake, but not in Waughop Lake, indicating that it is related to lake depth and therefore seasonal thermal stratification. The data also show that DO in the upper water column generally meets the Washington State surface water quality standards (>9.5 mg/l). DO in the upper water column of Lake Louise and throughout Carp Lake are near, but slight lower than the DO standard. However, DO in lower water column of all lakes (except Carp) lake is well below the standard, and can become hypoxic and even approach anoxic in American and Gravelly Lakes (often below 2 mg/l). 3.4 Alkalinity Figure 9 shows a time series of alkalinity in American Lake, and Figure 10 shows a box plot summarizing the range of alkalinities in all lakes. The times series show that alkalinities vary over a small range in each lake, and show little variation with season or year-to-year. However, the box plots show that there are variations between the lakes, generally with deeper lakes having higher values and shallow lakes having smaller values. 9 P age

17 Alkalinity is a measure of the buffering capacity of water to neutralize acids. It is related to ph, however ph was not measured in these lakes. The larger the value, the greater its ability to neutralize acids from inputs such as acid rain. The data show that American, Gravelly and Steilacoom have more buffering capacity, Lake Louise and Waughop Lake have moderate buffering capacity, and Carp Lake very little. All lakes have alkalinities in the range 0-60 mg/l CaCO 3, which is considered to be soft. Figure 9. Times series of alkalinity in American Lake Figure 10. Box plots of alkalinity in the six lakes 10 P age

18 3.5 Nutrients Figure 11 shows an example of a time series of total phosphorus in American Lake. Appendices A and B show the entire series of plots at all six lakes. Figure 12 to Figure 15 show the range of values in each lake for all the nutrients (phosphorus and nitrogen) measured in the six lakes. Total nitrogen was not included because it was sampled only in 2004, and all samples were below detections limits. From 2005 to 2015, ammonia, nitrites and nitrates were sampled. Inorganic nitrogen was not sampled. Figure 11. Times series of total phosphorus in American Lake Dashed lines shows MDL Figure 12. Box plots of total phosphorus in the six lakes 11 P age

19 Dashed lines show MDLs (1 mg/l between , 0.1 then 0.05 mg/l from 2008) Figure 13. Box plots of ammonia in the six lakes Dashed lines shows MDL Figure 14. Box plots of nitrites in the six lakes 12 P age

20 Dashed lines shows MDL Figure 15. Box plots of nitrates in the six lakes The data show little variability in all nutrients from year to year. Total phosphorus tends to be higher during the summer and fall, and significantly higher in the hypolimnions of the larger lakes (American and Gravelly). Epilimnion concentrations are much lower, and more similar between lakes. Ammonia concentrations are also higher in the hypolimnion of Gravelly Lake and to a lesser extend in American Lake. Epilimnion values are much lower. Nitrites were usually below the method detection limits (MDLs) with only a few outlier values recorded in Gravelly Lake. Nitrates were observed throughout the water column in Steilacoom Lake, but were generally near or below MDLs in the other lakes. It is not clear why nitrate levels are higher in Steilacoom Lake. 3.6 Chlorophyll_a Chlorophyll_a is the primary photosynthetic pigment in all photosynthetic organisms requiring oxygen and is found in all freshwater phytoplankton species. Although there are several different forms of chlorophyll present in plants, chlorophyll_a is the dominant form and is generally considered an indicator of algal biomass in freshwater ecosystems (Wetzel 1975). Figure 16 show box plots of chlorophyll_a in the six lakes. Concentrations are generally below 20 μg/l in all lakes except Steilacoom and Waughop Lakes where concentrations are below 40 μg/l 95 percent of the time, with occasionally higher concentrations in all lakes. 13 P age

21 Dashed lines shows MDL Figure 16. Box plots of chlorophyll_a in the six lakes 3.7 Trophic Levels The biological productivity, or trophic state, can be classified into three general categories: oligotrophic (low productivity), mesotrophic (moderate productivity), and eutrophic (high productivity). Lakes with low nutrient concentrations and low rates of algal productivity are classified as oligotrophic. Lakes with high nutrient concentrations and high rates of algal productivity are classified as eutrophic. Mesotrophic lakes have nutrient concentrations and algal productivity between eutrophic and oligotrophic lakes. The water quality parameters most often used to assess the trophic state of a lake are total phosphorus, chlorophyll_a, and transparency (Secchi depth). These three variables have been used by Carlson (1977) to develop a trophic state classification system. A useful way to group lakes by trophic classification is with the trophic state index (TSI) which is based on linear regression relationships developed for total phosphorus, chlorophyll_a, and transparency in lakes (Carlson 1977). Trophic state indices were computed using equations developed by Carlson (1977) and Carlson and Simpson (1996) with summer (June-September) average values from the epilimnion in each lake. Using total phosphorus (TP) in µg/l, the TSI(TP) is calculated as: TSI(TP) = 14.42ln(TP) (1) Using chlorophyll_a (chl_a) in μg/l, the TSI(chl_a) is calculated as: TSI(chl_a) = 9.81ln(chl_a) (2) 14 P age

22 And using transparency (Secchi disk [SD] depths in meters), the TSI(SD) is calculated as: TSI(SD) = ln(SD) (3) The Carlson TSIs classify a lake as oligotrophic with a TSI value less than 40, as mesotrophic with a TSI value between 40 and 50, and as eutrophic with a TSI value greater than 50. Figure 17 to Figure 19 show the three trophic state indices (TSI) for each of the six lakes. TSI based on Secchi depth are not included in Waughop and Carp Lakes because these lakes are very shallow and other processes can influence the values. Generally, the larger lakes (American, Gravelly and Louise) are mesotrophic (and often oligotrophic), Steilacoom is borderline eutrophic, and Waughop and Carp Lakes are eutrophic. However, none of the lakes become extremely eutrophic. Figure 17. TSI based on transparency (Secchi depth) 15 P age

23 Figure 18. TSI based on total phosphorus Figure 19. TSI based on chlorophyll_a 16 P age

24 Table 5. Summary of trophic states Lake Range of TSIs Trophic State American Oligotrophic-mesotrophic Gravelly Oligotrophic-mesotrophic Louise Oligotrophic-mesotrophic Steilacoom Mesotrophic-eutrophic Waughop Eutrophic Carp Eutrophic 3.8 Statistical Analyses A variety of statistical analyses were performed to determine the following: Seasonal trends Annual variations and trends The relationship between water quality parameters The variability between lakes The analyses included ANOVA, which evaluates the dependency of a single parameter on other parameters; T-tests, which test the significance of identified relationships; correlation coefficients, which calculate the strength of correlations; and principal component analyses, which analyzing multiple correlated variables to identify the linear combinations of the variables that provide the strongest overall correlation effects. These analyses and results are presented in Appendix C and Appendix D Seasonal Trends The analyses showed that: All lakes, except Carp Lake, can show (from the time series plots in Appendix A) very low DO in the hypolimnion in the summer and fall. American, Gravelly and Louise can also exhibit low DO values in the spring. Most ammonia measurements in the epilimnion are below or near method detection limits (MDLs). In the hypolimnion of the larger lakes, higher values can be seen, and tends to peak during the Fall. Nitrates have a noticeable spike during the spring for all lakes except Louise and Waughop, and is statistically significant for Steilacoom Lake. The results show significant effects of the position of the metalimnion. In American and Gravelly Lakes (the deeper lakes), the depth of the thermocline (used to define the position of the metalimnion) increases from spring through fall from about 8 m to 13 m. In Lake Louise and Steilacoom Lake (the intermediate depth lakes), the thermocline is shallower, between 4-8 m, and begins to become shallower in the fall as seasonal cooling is felt more quickly. In Waughop Lake, the thermocline is weak and very 17 P age

25 shallow, 2-3 m, and varies little with season, suggesting that it can easily mix on windy or stormy days. There is no clear change in the time that the seasonal stratification begins or when turn over occurs in the fall. The effect of overall lake depth is also apparent in the water temperature versus season (Appendix C, Figure 5), in which the average temperature for all lakes increases from Spring to Summer (as expected) but strong seasonal stratification is only apparent in American, Gravelly, and Steilacoom Lakes. Lake Louise and Waughop Lake do stratify, but it is generally weaker. Total phosphorus levels in the hypolimnion of American and Gravelly Lakes show considerable variability during the summer and fall up to 750 μg/l, compared to the other lakes, which generally do not exceed 100 μg/l Year-to-Year Variability Hypothesis testing was performed on the water quality data, using regression analysis and Spearman correlations (see Appendix C), to determine if year-to-year observations show significant trends. For the correlation analyses, the individual data types are plotted against month, and best fit lines calculated. The slopes of these best-fit lines are then statistically analyzed (using a t-test) to determine if they are significant predictors of the observations. The Spearman analysis is similar, except that the data are first ranked. This type of testing is useful, because while a simple regression line might appear to display a visually significant dependence (for example, trend lines can be fit to total phosphorus in the hypolimnion of each lake), statistical analyses find that these trends are not significant because there is much scatter in the data (also indicated by their low R-squared values). The analyses found that: Alkalinity remains relatively uniform in most lakes, but are significantly decreasing in American and Waughop Lakes. Overall chlorophyll_a decreases in American Lake, Gravelly Lake, Lake Louise and Carp Lake are statistically significant. DO levels are statistically uniform in all lakes, and show no year-to-year variations. Total phosphorus levels are statistically uniform in the hypolimnion and epilimnion of all lakes, except for a weakly significant decrease in the epilimnion of Gravelly Lake. Ammonia levels are significantly decreasing in the hypolimnion of American, Gravelly, Louise and Steilacoom Lake. Levels are also weakly increasing (marginal significance) in the epilimnion of American Lake, but significantly decreasing in the epilimnion of Louise and Steilacoom Lakes. Transparency is slightly trending (marginal significance showing either increasing or decreasing) in American Lake, Gravelly Lake, Steilacoom Lake, Lake Louise, and Waughop Lake, and increasing in Carp Lake (although the data set for carp Lake is small). The depth of thermal stratification is remaining constant in all lakes. 18 P age

26 3.8.3 Water Quality Processes Total phosphorus was found to decrease (statistically significant) with increasing dissolved oxygen in the hypolimnion of American Lake, Gravelly Lake and Lake Louise, but to marginally increase in Steilacoom Lake. This was confirmed using a range of statistical tests. There are no significant changes in the epilimnion of each lake. Chlorophyll_a concentrations can directly influence transparency through algal growth in the upper photic zone. Chlorophyll_a was first correlated with all parameters to evaluate those parameters that control its concentrations, and showed that transparency is mostly influenced by chlorophyll_a, water temperature and DO, and to a lesser degree by the availability of nutrients. This does not mean that nutrients are not important, rather that sufficient nutrients are present and increasing chlorophyll_a concentrations are then influenced by transparency, temperature and DO. A second analysis considering only Secchi depth as a function of Chlorophyll_a, showed that chlorophyll_a measurements correlate significantly to shallower Secchi depths. Low DO in the hypolimnion of American and Gravelly Lakes could create the conditions for elevated ammonia to occur. Figure 20 and Figure 21 plot ammonia and DO in the hypolimnion of American and Gravelly Lakes respectively. The ammonia only spikes when DO is at or near 0 mg/l. This suggests that elevated ammonia in the hypolimnion is correlated with low DO, and is probably the result of bacterial decomposition of organic matter and the lack of atmospheric reaeration. Figure 20. Ammonia and dissolved oxygen in the hypolimnion of American Lake 19 P age

27 Figure 21. Ammonia and dissolved oxygen in the hypolimnion of Gravelly Lake 20 P age

28 4 Conclusions and Recommendations The goal of the Lakewood water quality analysis was to characterize the water quality of American, Gravelly, Louise, Steilacoom, Waughop and Carp Lakes. The report presents the data, compares values to State of Washington water quality standards, and analyzes trends and correlations in and between various water quality parameters. From these analyses, we draw the following conclusions. 4.1 American and Gravelly Lakes American and Gravelly Lakes are the deepest of the six lakes studied. They strongly stratify during the summer, resulting in higher temperatures in the upper water column, and temperatures near 10 o C in the lower water column. The upper water column is characterized by dissolved oxygen values near or exceeding 9.5 mg/l. The lower water column often has hypoxic conditions (DO < 2 mg/l) and even approaches anoxic conditions on occasion. However, supersaturated DO values occur near the seasonal thermocline, suggesting the presence of motile algae that prefer the upper photic zone and nutrients found in the lower layer. Water clarity is generally good, with transparencies on the order of 6-7 meters. However, the lower water column has high concentrations of nutrients, with low DO concentrations causing the release of phosphorus from the bed. The lakes range from oligotrophic to mesotrophic from year to year. 4.2 Lake Louise and Steilacoom Lake Lake Louise and Steilacoom Lake are the intermediate depths of the six lakes studied. They stratify during the summer, resulting in higher temperatures in the upper water column, but the stratification can reach the lake bed and elevate deeper water temperatures there too. The upper water column is characterized by dissolved oxygen values near or exceeding 9.5 mg/l. However, the lower water column often sees a range of dissolved oxygen from hypoxic conditions (DO < 2 mg/l) and even approaches anoxic conditions on occasion, to higher values between 4-8 mg/l. There is some evidence of somewhat elevated DO values near the seasonal thermocline, suggesting the presence of some motile algae that prefer the upper photic zone and nutrients found in the lower layer. Water clarity is generally moderate, with transparencies on the order of meters. The lower water column has elevated concentrations of nutrients, with the occasional low DO concentrations perhaps causing some release of phosphorus from the bed. The statistical tests are indeterminate with respect to the drivers of productivity in the lower water column. Lake Louise ranges from oligotrophic to mesotrophic from year to year, and Steilacoom Lake ranges from mesotrophic to mildly eutrophic. 21 P age

29 4.3 Waughop and Carp Lakes Waughop and Carp Lakes are the shallowest of the six lakes studied. They are generally fairly well mixed during the summer, resulting in little thermal stratification. Dissolved oxygen values range from near or exceeding 9.5 mg/l throughout the water column to occasionally low (2-6 mg/l) at depth. Water clarity is generally poor in Waughop Lake with transparencies on the order of meters. Transparencies in Carp Lake are on the order of 1-3 meters, which range from poor clarity to the depth of the shallow lake. There are nutrients available throughout the water column as these lakes tend to be fairly well mixed. Waughop Lake is consistently eutrophic, although the record is short. Carp Lake ranges from mesotrophic to mildly eutrophic from year to year, with a tendency towards being eutrophic. 4.4 Overall Trends in Lakes The data show that there can be significant variations between lakes, especially with depth as described above. All the lakes show a seasonal influence of summer warming followed by winter cooling and increasing DO levels. Overall, transparences (water clarity) seem to be mildly increasing, total phosphorus is generally constant, chlorophyll_a concentrations and hypolimnion ammonia are decreasing, and DO, temperature, and alkalinity show no clear trends. The data show no significant changes in the onset of seasonal stratification (of water temperature and dissolved oxygen) or the occurrence of the fall turn over. However, the monitoring schedule may be too short to (May October instead of April November) capture trends in stratification. 4.5 Recommendations After reviewed the available data and conducting a series of water quality and statistical analyses, we recommend the following: That the monitoring be expanded to include sampling for ph and total nitrogen. ph is a measure of the acidify of water. Its normal range is , and values outside this range can suggest the presence of pollution sources including acid rain or the release of carbon dioxide. Total nitrogen, along with total phosphorus can be used to determine the limiting nutrient for algal growth. Phosphorus is usually limiting in freshwater lakes. That the monitoring period be extended to include sampling in April and November to enable analysis of year-to-year trends in stratification of temperature and DO. That the occurrence of low dissolved oxygen in a number of lakes, especially American and Gravelly, be evaluated. We recommend that the City obtain any water quality data in nearby groundwater, and see if it is consistent with temperatures, general water quality concentrations, and low dissolved oxygen in the hypolimnion. Data collection should be preceded by a literature review of groundwater movement and lake 22 P age

30 interaction, examining factors such as the elevation range of the groundwater table; groundwater movement in the area (especially towards the lakes); and the existence of confining soil strata that cause groundwater upwelling into the lake. Following an analysis of these data, a coordinated groundwater and lake monitoring program could better understand the hydrogeologic and groundwater influences on the lakes. 23 P age

31 5 References Carlson, R.E. March A Trophic State Index for Lakes. Limnology and Oceanography. Vol. 22 (2). 9pp. Carlson, R. E. and J. Simpson A Coordinator s Guide to Volunteer Lake Monitoring Wetzel, R. G., Limnology. W.B. Saunders Company, Philadelphia, PA. 24 P age