Dissolved Oxygen in the Harpeth River August-September 2006
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Dissolved Oxygen in the Harpeth River August-September 2006 Harpeth River During Low Flow Season downstream from Franklin Sewage Treatment Plant February 2007 Contributing Authors: Dorene Bolze Michael Cain John McFadden Harpeth River Watershed Association PO Box 1127 Franklin, TN 37065 www.harpethriver.org [email protected] Work funded, in part, by World Wildlife Fund and Patagonia. Table of Contents Introduction p.3-5 Methods and Materials p.5-6 Table 1: DO Site Numbers, Locations and Volunteers p.6 Results p.7-8 Figure 1: DO Levels in the Harpeth River p.8 Table 2: HRWA DO Summary p.9-11 Discussion p.13-15 Figure 2: Franklin Low-head Dam p.14 Acknowledgements p.15 References p.16-17 Appendix A: Site Maps Overview Map: HRWA, TDEC DO Sampling Sites p.19 Map 1: Eagleville Area p.20 Map 2: Franklin Area p.21 Map 3: North Williamson County p.22 Map 4: Bellevue Area p.23 Map 5: Kingston Springs Area p.24 Appendix B: USGS Flow Data Figure 3: USGS 03432350 p.25 Figure 4: USGS 03432400 p.25 Figure 5: USGS 03433500 p.25 Figure 6: USGS 03434500 p.25 Appendix C: TDEC 2006 Diurnal Graphs Graph 1: Eagleville, Route 41A and Webb Rd. Crossing p.27 Graph 2: Newsom Mill, Bellevue p.28 Graph 3: Narrows of the Harpeth downstream canoe take-out p.29 Harpeth River Discrete Sampling 2006 p.30 Appendix D: HRWA DO Raw Data 2006 p.32-37 Appendix E: TDEC Diurnal Data 2002, 2003 p.39-41 Appendix F: HRWA DO Study 2002 p.43-48 2 Dissolved Oxygen in the Harpeth River August-September 2006 Introduction The Harpeth River Watershed Association (HRWA) is a 501(c)(3) not-for-profit conservation organization whose mission is to protect and restore the Harpeth River Watershed and provide expertise in statewide conservation policy. HRWA possesses a core scientific staff and has a Science and Technical Advisory Group comprised of experts from various state and federal agencies, academic institutions, and private sector firms who provide assistance in field study design and analysis. In addition, HRWA utilizes volunteers, and some are experts in their fields, to conduct many of its activities including research. In addition to core staff, technical advisors, and volunteers, HRWA works with resource and regulatory agencies such as the Tennessee Department of Environment and Conservation (TDEC), the US Geological Survey (USGS), the Tennessee Wildlife Resources Agency (TWRA), US Fish & Wildlife Service (USFWS) and the US Environmental Protection Agency (EPA). Purpose The purpose of this field study with TDEC was to measure dissolved oxygen (DO) concentrations along the Harpeth River mainstem for most of its length during the low flow season in order to fill data gaps and provide further data on current conditions to guide permitting decisions. One current permit issue is a proposal to increase the withdrawal of water from the Harpeth for an expansion of the city of Franklin’s drinking water plant from 2 to 4 million gallons a day (MGD). This withdrawal is only four river miles upstream from the City’s 12 MGD Publicly Owned Treatment Works (POTW) which is then followed by two much smaller sewage treatment plants not far downriver. One of the aspects of the study was to provide further DO data and river flow data to help with other analyses referenced in this report. Other aspects include determining in-stream flow needs that would prevent low dissolved oxygen problems and provide assimilative capacity. The final aspect of the study was to gather more date to ascertain that the flow is adequate for the river to meet its designated uses for fish and aquatic life and recreation. Another intent of this study and report was to begin compiling the various documents and data on DO along the Harpeth River as part of the next steps in analyzing cost effective management solutions to reduce the low dissolved oxygen problem. The Appendices include recent field data from TDEC since 2002 and the report provides references to other important field data and analyses, such as EPA’s DO data from its work to produce the Final Organic Enrichment/Low Dissolved Oxygen Total Maximum Daily Load (TMDL) for the Harpeth River1, and studies done as far back as 1987 by Barry Sulkin2. This study is an extension of prior DO studies HRWA has conducted that are included in this report. All the references in this report are available either on the HRWA web site or upon request. 3 Dissolved Oxygen Dissolved oxygen is critical to the health of aquatic systems with a generally accepted minimum of 4 mg/L for maintaining aquatic life. Although, sustained levels below 5 mg/L impair biological function result in decreased productivity3. Oxygen levels are subject to variation based on time of day, time of year, flow, atmospheric conditions and anthropogenic influence. Plants, such as algae, produce oxygen as a byproduct of photosynthesis, increasing oxygen content of surface waters during daylight hours, though reducing oxygen in the surface waters during nighttime hours due to algal respiration. In addition, input of DO in rivers occurs through the water surface/air interaction primarily in areas of turbulence, such as riffles. In the state of Tennessee, the water quality standard for dissolved oxygen to support fish and aquatic life is 5 mg/l at all times with specific exceptions set at higher concentrations for trout streams (Chapter 1200-4-3-.03(3)(a)). Sources of DO degradation include plant and animal respiration as well as bacterial processes of degradation of organic material from natural inputs such as leaf litter and from anthropogenic sources such as sewage treatment plant effluents (biochemical oxygen demand - BOD). Oxygen depletion also occurs as a result of a wide variety of substance degradation, including sediments (sediment oxygen demand- SOD)4 and agricultural and industrial chemicals (chemical oxygen demand- COD)5. Water volume or flow positively correlates with DO concentration. Higher flows typically carry higher amounts of dissolved oxygen, while water’s ability to hold oxygen is inversely related to temperature. Water at 00 C can hold approximately 14 mg/L of DO at 100% saturation where water at 350 C can only hold approximately 7 mg/L6. The total amount of DO (concentration x volume) is a primary factor in a stream’s capacity to assimilate waste products as measured by BOD. In simple terms, to maintain DO levels in the river at or above the state standard of 5 mg/L, for every pound of oxygen demanding material (BOD) added to the river, one pound of extra oxygen has to already be in the river or the algae or natural aeration factors have to add this one pound of additional oxygen. Low flow and increased temperature conditions in the summer months represent the limiting conditions relative to DO and thus a river’s assimilative capacity. Additionally, during the critical summer low flows, natural reaeration is at a minimum which compounds the problem of oxygen replenishment. Biological Condition As part of the city of Franklin’s effort to study if the Harpeth can support an increase in its withdrawal of water for a larger drinking water plant, several field studies were conducted. One involved a fish and macroinvertebrate study by Pennington and Associates (PAI)7. The PAI survey was carried out in March of 2006 and demonstrates that the river at each station is slightly impaired based on comparisons of BMI data to the 71h ecoregional reference stream data. Metrics calculated for the analysis included but were not limited to percent Oligochaetes and Chironomids, percent EPT and the North Carolina Biotic Index (NCBI). The NCBI ranges from 0 (pollution intolerant) to 10 (pollution tolerant). NCBI values ranged from 4.79 (stations 3 and 4) to 5.63 (Station 6) with an average of 5.12. The average NCBI of 5.12 is indicative of an intermediately pollution tolerant BMI community. Oligochaetes and Chironomids ranged from 27.71% (Station 5) to 61.97% (Station 1) and averaged 47.21%. Oligochaetes and Chironomids are primarily pollution tolerant and thus high numbers for this metric indicate a stressed system. Lastly, EPT ranged from 4.18% to 19.91% with an average of 10.07%. EPT species are primarily pollution sensitive and thus low percentages in this metric indicate a stressed 4 system. The BMI sample, represented by the BMI index scores and in particular, the above referenced metrics indicates the system is under significant stress. Other benthic macroinvertebrate data have also been collected on the main Harpeth as well. For example, the city of Franklin does an annual benthic survey as part of its NPDES permit for its sewage treatment plant. This report on the DO 2006 field survey is not meant to be an exhaustive review and analysis of all the data available. The PAI study also conducted a fish survey and found 33 species of fish across all the stations sampled in the river’s section through downtown Franklin between the low head dam and the Franklin STP discharge. The fish communities are considered to reflect “Fair” ecological conditions for four sites and “Poor to Fair” for the remaining two sites when compared to reference stream data provided by the Tennessee Valley Authority for the Nashville Basin Ecoregion based on Index of Biotic Integrity (IBI) data. At one site downstream from the Franklin Road bridge, the small scale darter (Etheostoma microlepidum) was found. This species is considered by TDEC to be a species “Deemed in Need of Management” or a species of “Special Concern.” This species range is now limited to the Harpeth and Red Rivers, according to Dr.