SESSION 4D WATER QUALITY 2

Transcription

1 SESSION 4D WATER QUALITY 2 139

2 UNDERSTANDING POLLUTANT TOXICITY ON FRESHWATER MUSSELS Nancy Scott, 1 MEM, The Catena Group Dwarf wedgemussel (DWM) is an endangered mussel species found in the eastern United States. Endemic to a variety of Atlantic slope drainages from New Brunswick, Canada to Raleigh, North Carolina, the population has always been found in low numbers and has been on the decline in recent years. Carolina heelsplitter is also endangered and is found in North and South Carolina. Like other freshwater mussel species, these species susceptible to sedimentation, point and non-point discharges, and stream modification (impoundments, channelization, etc.). Recent studies indicated that previous federal water quality criteria for many pollutants commonly found in wastewater discharges and stormwater runoff were likely not protective of freshwater mussels. Criteria are often based on the effects on fish or benthic invertebrates. It has been demonstrated that freshwater mussels are more sensitive than these species. As a result, the EPA recently revised the freshwater ammonia aquatic life ambient water quality criteria for acute and chronic standards to reflect freshwater mussel species sensitivity thresholds. A 2007 study by the USFWS analyzed water quality samples for ammonia, copper, and chlorine from three river systems in NC. These parameters are thought to be some of the most detrimental to freshwater mussel health. This study was based on the 1999 ambient water quality criteria for ammonia, the 2002 National recommended water quality criteria (for chlorine), and several studies on protection of freshwater mussels for copper (Augspurger et al 2003 and March et al 2007). Water samples from streams supporting either Carolina heelsplitter or dwarf wedgemussel were compared with ecological screening values to assess risk. The results of this 2007 study and of a 2012 study with updated methods of determining copper toxicity are compared. A water quality study by Catena in Swift Creek will provide further insight into the recovery of endangered mussels in NC. 1 Environmental Scientist; 410 Millstone Drive Suite B, Hillsborough, NC 27278; ; nscott@thecatenagroup.com 140

3 EXTERNAL NUTRIENT LOADS MUST BE MANAGED WHEN CONTROLLING INTERNAL NUTRIENT LOADS VIA HYPOLIMNETIC OXYGENATION Alexandra B. Gerling, 1 Virginia Tech; Jonathan P. Doubek, 2 M.S., Virginia Tech; Kathleen D. Hamre, 3 Virginia Tech; Zackary W. Munger, 4 M.S., Virginia Tech; Paul A. Gantzer, 5 PE, Ph.D., Gantzer Water Resources Engineering, LLC.; John C. Little, 6 PE, Ph.D., Virginia Tech; Madeline E. Schreiber, 7 Ph.D., Virginia Tech; Cayelan C. Carey, 8 Ph.D., Virginia Tech Hypolimnetic hypoxia poses a substantial threat to water quality because it can trigger the release of reduced metals and nutrients from lake sediments, thereby stimulating algal growth and altering biogeochemical cycling. Consequently, controlling hypolimnetic hypoxia is crucial for sustaining the ecology of freshwater ecosystems. Here, we present the results of a wholeecosystem experiment in Falling Creek Reservoir (Vinton, Bedford County, Virginia) in which we manipulated hypoxia by sequentially injecting water with supersaturated concentrations of oxygen into the hypolimnion of a small, eutrophic drinking water reservoir in summer Throughout the six-month experiment, thermal stratification was maintained during the alternating oxic (~12 mg/l) and hypoxic (<2 mg/l) hypolimnetic conditions. Oxygenation successfully suppressed the release of reduced iron, manganese, and phosphorus from the sediments. Contrary to expectations, we observed higher sediment oxygen demand during oxic than hypoxic periods. Our experiment demonstrated that hypolimnetic oxygenation can successfully reduce internal loads of nutrients and metals. We repeated the sequential oxygenation experiment in summer As a result of much higher inflow into the reservoir in 2014 than 2013, we observed that external loading dynamics dominated nutrient fluxes in 2014, despite oxygenation. Consequently, managing external loads of iron, manganese, and phosphorus must be taken into account when controlling internal nutrient loads via oxygenation. 1 Graduate Student, Department of Biological Sciences; 1027 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; ; alexg13@vt.edu 2 Graduate Student, Department of Biological Sciences; 1027 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; ; jpdoubek@vt.edu 3 Graduate Student, Department of Biological Sciences; 1027 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; ; kdhamre@vt.edu 4 Graduate Student, Department of Geosciences; 4044 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; ; mzacka@vt.edu 5 President; th Pl., NE, Kirkland, WA 98034; ; paul.gantzer@gmail.com 6 Professor, Department of Civil and Environmental Engineering; 1145 Perry St., Blacksburg, VA 24061; ; jcl@vt.edu 7 Professor, Department of Geosciences; 4044 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; ; mschreib@vt.edu 8 Professor, Department of Biological Sciences; 2011 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; ; cayelan@vt.edu 141

4 HYPOLIMNETIC OXYGENATION ALTERS PLANKTONIC COMMUNITY STRUCTURE Jonathan P. Doubek, 1 M.S., Virginia Tech; Kathleen D. Hamre, 2 Virginia Tech; Alexandra B. Gerling, 3 Virginia Tech; Zackary W. Munger, 4 M.S., Virginia Tech; Paul A. Gantzer, 5 PE, Ph.D., Gantzer Water Resources Engineering, LLC; John C. Little, 6 PE, Ph.D., Virginia Tech; Madeline E. Schreiber, 7 Ph.D., Virginia Tech; Cayelan C. Carey, 8 Ph.D., Virginia Tech Hypolimnetic oxygenation is increasingly implemented to improve water quality in freshwater reservoirs. However, all studies to date examining the efficacy of oxygenation have focused on the effects of altered redox conditions on internal nutrient or metal loads, not biological response variables. Here, we examined the effects of oxygenation on the planktonic community in Falling Creek Reservoir, a drinking water source in Vinton, Virginia (Bedford County). This reservoir has a hypolimnetic oxygenation system that was turned sequentially on and off for six week periods during the summer of We used a Fluoroprobe fluorometer to quantify the biomass of four different phytoplankton groups: cryptophytes, cyanobacteria, diatoms, and green algae. We also collected zooplankton tows to quantify the relative abundance and biomass of different zooplankton genera in the epilimnion versus the hypolimnion throughout the oxygenation experiment. Surprisingly, the hypolimnetic biomass of all four phytoplankton groups increased when the oxygen system was activated. The Fluoroprobe data suggest that oxygenation may actually stimulate phytoplankton, potentially due to the increased hypolimnetic mixing that occurs when the system is activated. We are currently analyzing zooplankton to examine if hypolimnetic oxygenation was also associated with a change in zooplankton group dominance, or a relative change in the distribution of zooplankton in the water column. Overall, this was the first study to quantify the effects of hypolimnetic oxygenation on plankton communities, which may have further implications for the reservoir food web and water quality. 1 Graduate Student, Department of Biological Sciences; 1027 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; ; jpdoubek@vt.edu 2 Graduate Student, Department of Biological Sciences; 1027 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; ; kdhamre@vt.edu 3 Graduate Student, Department of Biological Sciences; 1027 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; ; agerling13@vt.edu 4 Graduate Student, Department of Geosciences; 4044 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; ; mzacka@vt.edu 5 President; th Pl., NE, Kirkland, WA 98034; ; paul.gantzer@gmail.com 6 Professor, Department of Civil and Environmental Engineering; 1145 Perry St., Blacksburg, VA 24061; ; jcl@vt.edu 7 Professor, Department of Geosciences; 4044 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; ; mschreib@vt.edu 8 Professor, Department of Biological Sciences; 2011 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; ; cayelan@vt.edu 142

5 INTEGRATING MICRO-FLOC INJECTION WITH HYBRID OXYGENATION- AERATION: APPLYING A THEORETICAL APPROACH TO COMBAT EXTERNAL NUTRIENT LOADING Paul A. Gantzer, 1 Ph.D., P.E., Gantzer Water Resources Engineering, LLC; Alexandra B. Gerling, 2 Virginia Tech; Cayelan C. Carey, 3 Ph.D., Virginia Tech; Mark Mobley, 4 P.E., Mobley Engineering, Inc.; Jamie Morris, 5 Western Virginia Water Authority Eutrophic water-supply reservoirs often experience degraded water quality as a result of hypolimnetic anoxia and epilimnetic phytoplankton blooms. Anoxia in bottom waters results in the mobilization of nutrients and soluble metals from the sediments to the water column, which in turn can lead to undesirable algal and cyanobacterial growth, thus exacerbating water treatment problems. Both anoxia and surface phytoplankton blooms can be successfully managed in reservoirs, using hypolimnetic oxygenation and epilimnetic diffused-air mixing, respectively. Combining these two strategies provides a comprehensive way to address water quality problems in the waterbody. However, despite the positive results observed from both of these strategies, water-supply reservoirs can still experience negative consequences from external nutrient loading. When runoff inflows to the reservoir are warmer than the reservoir s bottom temperatures yet cooler than surface temperatures, the result is localized nutrient loading to the metalimnion (i.e., interflow). During periods of high interflow nutrient loading, the localized water quality degradation at the metalimnion will result in hypoxia and even anoxia. Hypolimnetic oxygenation, which is designed to preserve thermal stratification, cannot penetrate the thermocline to oxygenate the metalimnion. Likewise, operation of diffused air mixing would mix the anoxic metalimnetic water to the reservoir s surface, which in turn could result in increased turbidity and accelerate undesirable algal growth. Metalimnetic oxygen minima pose severe risks to water quality treatment and often require shutting down the treatment plant completely. To combat this problem, we propose integrating metalimnetic alum addition with hybrid oxygenation-aeration. Alum addition has been shown to be very effective at binding phosphorus in the water column and sediments. Rather than applying a whole-lake dose, adding a small quantity of alum, termed micro-floc, throughout the year can successfully address high external nutrient loads entering the reservoir as interflow. We have recently introduced a novel hybrid water quality management system for reservoirs that integrates both oxygenation and mixing and includes a chemical feed header at the metalimnion. This management strategy is currently being tested in a shallow water-supply reservoir in Virginia, Falling Creek Reservoir (Zmax = 9.3 m). We have demonstrated the successful hypolimnetic oxygenation of Falling Creek Reservoir, with testing of the diffused air mixing slated for The focus of this presentation is to demonstrate the comprehensive management strategy in place at Falling Creek Reservoir from both a theoretical and applied perspective, including how 1 President; th Pl., NE, Kirkland, WA 98034; ; paul.gantzer@gmail.com 2 Graduate Student, Department of Biological Sciences; 2011 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; alexg13@vt.edu 3 Assistant Professor, Department of Biological Sciences; 2011 Derring Hall, 1405 Perry St., Blacksburg, VA 24061; ; 4 President; P.O. Box 600, Norris, TN 37828; ; mark@mobleyengineering.com 5 Water Production Manager; 8192 Angel Lane, Roanoke, VA 24019; ; jamie.morris@westernvawater.org 143

6 the three system components (oxygenation, diffused-air mixing, and micro-floc addition) can be integrated to successfully address complex water quality problems in concert. 144