Watershed Protection: Clean Lakes Case Study : Phosphorus Inactivation and Wetland Manipulation Improve Kezar Lake, NH
Office of Water (4503F)
Summary:Kezar Lake, located in central New Hampshire (Figure 1), has had a long history of water quality problems. Following a major fish kill and persistent algae blooms beginning in the early 1960s, a Diagnostic/Feasibility Study (Phase I of the Clean Lakes Program) was initiated in 1980 under section 314 of the Clean Water Act. The study established that the lake's problems were from internal loading of phosphorus, and outlined a management strategy to restore the lake. Lake sediments, contaminated by years of effluent discharge from a nearby wastewater treatment facility, were the source of this internal loading.
A Restoration/Protection Project (Phase II of the Clean Lakes Program) commenced in 1984 to implement the recommended management strategy for Kezar Lake. Two main approaches were employed to reduce phosphorus concentrations in the lake. First, aluminum salts were injected into the hypolimnion to inactivate sediment phosphorus. The injections were performed using a modified barge system that was an efficient and cost-effective means of aluminum salts application. Second, upstream riparian wetlands were manipulated by elevating water level and planting new species to encourage phosphorus removal by sedimentation and vegetative uptake.
From 1984 to 1994, comprehensive water quality monitoring programs (including part of the Phase II project, a state-assisted volunteer program, and an EPA Phase III Post-Restoration Monitoring Project) were conducted to assess the effects of the restoration activities. Results from these efforts have generally indicated that water quality has improved following aluminum salts injection, although some parameters did worsen during 1988 and 1993. Furthermore, recreational use of Kezar Lake has increased substantially since restoration.
Contact: Jody Connor, New Hampshire Department of Environmental Services, Water Supply and Pollution Control Division, 6 Hazen Drive, P.O. 95, Concord, NH 03301, phone (603)271-3414
Kezar Lake is a "fairly shallow, north temperate, dimictic, phosphorus-limited lake at 276 m above sea level" that drains approximately 28 square kilometers of land in central New Hampshire (Figures 1 and 2) (Connor and Martin 1989a). Land use in the watershed is comprised of forestland (approximately 70 percent), urban/residential (25 percent), and agriculture (5 percent). The lake's volume is 1,975,500 m and its shoreline measures 3400 m. Mean and maximum depths are 2.7 m and 8.2 m, respectively. Flushing rate for the lake is 44.5 days.
In addition to nonpoint sources of pollution (e.g., runoff and erosion) associated with land use, one point source of particular concern exists in the Kezar Lake watershed. In 1931, the nearby Town of New London opened a sewage treatment facility that began discharging effluent into Lion Brook, the main tributary to Kezar Lake. The New London treatment facility was upgraded in 1969 and decommissioned in 1981.
Water quality problems in Kezar Lake were first documented in 1963, when blooms of algae (Cyanophyceae) were observed. Five years later, following continued blooms and a massive fish kill, lake-shore property values around Kezar Lake dropped significantly. Throughout the 1960s and early 1970s, copper sulfate applications and mechanical destratification were used to attempt to improve water quality. The success of these efforts proved to be short-lived, however, and eventually ineffective in preventing algae blooms. Although New London's waste was rerouted to a new treatment facility in the Town of Sunapee in 1981, algae blooms persisted in Kezar Lake.
ASSESSING AND CHARACTERIZING THE PROBLEM
The Clean Lakes Program, section 314 of the Clean Water Act, provides assistance to states for identifying and restoring lakes that are water-quality-impaired. In 1979, the biennial statewide assessment of lakes in New Hampshire ranked Kezar Lake as having the highest priority for restoration. A Diagnostic/Feasibility Study (Phase I of the Clean Lakes Program) for Kezar Lake was initiated in 1980. The purpose of a Diagnostic/Feasibility Study is to determine the causes and extent of pollution, evaluate potential solutions to water quality problems, and recommend an effective and feasible method for restoring and maintaining water quality in a particular lake.
The Diagnostic/Feasibility Study for Kezar Lake, which was completed in 1983, provided the following information (Connor and Martin 1989a):
Examination of the existing water quality and trophic state of the lake.
Analysis of historical water quality trends.
Determination of hydrologic and phosphorus inputs and outputs (budgets) for Kezar Lake.
Determination of the importance of the lake's sediments in providing phosphorus to support phytoplankton (algae) populations.
Recommendations to improve the water quality in Kezar Lake.
Water quality and quantity data for the study were analyzed from the lake itself, tributaries, groundwater seepage meters and shallow wells, rainfall gauges. Sediments from the lake bottom were also collected and analyzed. Nutrient budgets were developed using mass balance equations.
Trophic state, a measure of a lake's level of biological productivity and age, was assessed for Kezar Lake during the Diagnostic/Feasibility Study. Three separate classification models, from the State of New Hampshire, EPA, and Dillon-Rigler, all confirmed that Kezar Lake was eutrophic. Phosphorus, the limiting nutrient for biological growth in the lake, existed in high concentrations (> 30 g/l) at a depth of 6 m during nearly the entire first year of study. Such high levels of phosphorus translate into poor water quality because of increased biological productivity. Water quality parameters measured in Kezar Lake during the study included high chlorophyll a concentrations (indicative of algae blooms), low transparency, and low dissolved oxygen levels, especially during summer months.
Another major determination made in the Diagnostic/Feasibility Study was the source of the phosphorus causing the water quality problems in Kezar Lake. The main external source of phosphorus, the New London Sewage Treatment Facility, had been decommissioned in 1981, eliminating 71 percent of the external phosphorus load. Blooms of algae persisted after this date, however, forcing researchers to look elsewhere for the source. Through sediment core analysis, computer modeling, and mass balance, they established that internal loading of phosphorus from lake sediments was the controlling factor in determining the trophic state of the lake (Snow and DiGiano 1976, Connor and Martin 1989b). The models showed that lake phosphorus concentrations were more sensitive to changes in sediment loadings than to morphological or watershed loading changes. Lake sediments, which often contain much higher concentrations of phosphorus than does the lake water, can provide a net flux of phosphorus into the water under anaerobic conditions (Wetzel 1983).
The final part of the Diagnostic/Feasibility Study focused on providing recommendations to restore and maintain water quality in Kezar Lake. The main objective for lake restoration was to prevent phosphorus in the sediment from continuing to enter lake water. The Diagnostic/Feasibility Study recommended that the most feasible method to accomplish this objective was to inject aluminum salts into the hypolimnion to inactivate the sediment phosphorus.
Although the Diagnostic/Feasibility Study determined that most of the phosphorus in Kezar Lake came from the lake sediments, additional management measures were also recommended to deal with external phosphorus inputs from the watershed. The Study proposed manipulating Chadwick Meadows, an upstream riparian wetland area (Figure 2), to remove phosphorus that would enter the lake from Lion Brook. According to the hydrologic budget developed in the study, Lion Brook contributes nearly 90 percent of the annual inflow to Kezar Lake (Figure 3) and is therefore an appropriate focal point for restoration. Specific activities proposed in the wetland included increasing water level in the Meadows and planting additional vegetation, theoretically causing less phosphorus to enter the lake because of sedimentation and vegetative uptake (Connor and Martin 1989a).
IMPLEMENTATION AND MONITORING EFFORTS
Based on recommendations from the 1983 Diagnostic/Feasibility Study, aluminum salts injection and wetlands management projects were implemented to reduce phosphorus concentrations in Kezar Lake. To measure changes in the lake's status due to restoration efforts, a water quality monitoring program was instituted in 1984 and pursued through 1988 (Connor and Martin 1989a). These activities were performed, in part, through a section 314 EPA grant for a Restoration/ Protection Project (Phase II of the Clean Lakes Program). Additional monitoring activities were also performed from 1988 to 1994 through a state-assisted volunteer program and an EPA Phase III Post-Restoration Monitoring Project.
Aluminum salts injection was selected for Kezar Lake partially because of the success this methodology has had in reducing phosphorus concentrations in other thermally stratified lakes (Connor and Martin 1989a). The effectiveness of aluminum salts application rests on the ability of aluminum to form complexes, chelates, and insoluble precipitates with phosphorus, thereby removing it from the water column and depositing it in the sediment in forms unusable by phytoplankton. Depending on pH, phosphorus concentration, aluminum concentration, and the rate at which additional phosphorus is supplied, aluminum salts can provide long-term inactivation of sediment phosphorus (Connor and Martin 1989a). Furthermore, aluminum has been shown to have no toxicity to aquatic life at the pH and dose necessary for lake restoration (Cooke and Kennedy 1981). Although not all forms of phosphorus (e.g., dissolved organic phosphates) are removed by aluminum salts application, this methodology has proven to be an effective strategy for phosphorus inactivation in many water-quality-impaired lakes.
The week prior to aluminum salts application, copper sulfate was applied as an algicide to remove phosphorus tied up in the phytoplankton. Theoretically, this phosphorus could recycle in the lake system for many years (Connor and Martin 1989a). Additionally, bioassays were conducted to assess the impact of both the copper sulfate and aluminum salts applications to benthic macroinvertebrates in Kezar Lake. Results from before and after the applications indicated no apparent detrimental effects to the macroinvertebrate community (Connor and Martin 1989a).
Pilot jar and tank studies were also performed before aluminum salts application to determine the best ratio and dosage of aluminum sulfate and sodium aluminate for phosphorus inactivation. Based on results from these studies, a 10-hectare portion of Kezar Lake was treated using 30 mg Al/m at a 2:1 aluminum sulfate-to-sodium aluminate ratio. Since no adverse impacts on aquatic biota were observed following this application, an additional 48-hectare area of Kezar Lake was treated at a higher concentration (40 mg Al/m at the same ratio) to improve flocculation.
A special method for applying aluminum salts on Kezar Lake was developed to improve both efficiency and cost (Connor and Smith 1986). Prior to the Kezar Lake project, aluminum salts were applied using large barges that were slow and imprecise. A weed harvester was modified to simultaneously apply two aluminum salts and carry a large payload. These alterations provided a less cumbersome, more maneuverable means by which to deliver aluminum salts accurately and quickly.
Table 1 summarizes cost-effectiveness information associated with seven phosphorus inactivation projects. Note the varying degrees of effectiveness based on the application system used. Additional improvements (i.e., "new barge system" in Table 1) have further increased the efficiency and cost-effectiveness of aluminum salts application since the development of the modified barge for Kezar Lake (Connor and Smith 1986).
As part of the Phase II Project for Kezar Lake, intensive monitoring was conducted for 4 years to determine the effectiveness of the aluminum salts applications. Water quality parameters included in the monitoring program were dissolved oxygen, pH, alkalinity, total dissolved aluminum, total phosphorus, chlorophyll a, transparency, phytoplankton, and zooplankton. A qualitative summary of the response of each of these parameters from 1984 to 1988 is given in Table 2. Initial success was realized following treatment, but
within 4 years many parameters returned to near pretreatment levels, although this change may be due to meteorologic variability. Most parameters did show stabilization (i.e., less extreme variability), however, at the end of the 4-year monitoring period (Connor and Martin 1989b). Furthermore, and most significantly, these levels were suitable for recreation, and average attendance at Wadleigh State Park, which abuts the lake, increased by almost 2000 people per summer in 1984 and 1986.
Additional monitoring from a state-assisted volunteer program and an EPA Phase III Post-Restoration Monitoring Project was performed from 1988 to 1994 to supplement the Phase II monitoring and provide a longer time frame by which to evaluate water quality changes in the lake. Results from these monitoring studies indicate that water quality had, in fact, generally improved since restoration and that the poor quality measured during the last year of the Phase II project in 1988 (as well as in 1993) was not indicative of overall water quality trends. A quantitative example of the concentrations of chlorophyll a from 1980 to 1994, shown in Figure 4, represents the improving water quality trend following restoration.
The second management action taken to restore Kezar Lake's water quality was manipulation of the 20-hectare Chadwick Meadows (a seasonally flooded riparian area) along Lion Brook. Research has shown that wetlands attenuate phosphorus with distinct seasonal variation (Connor and Martin 1989a). Although wetlands might not attenuate or might even be a source of phosphorus in the fall and spring during periods of high flow, several studies have shown phosphorus removal in wetlands to be greater than 80 percent during the summer growing season, when algae growth is most common. Macrophytic nutrient uptake and sedimentation of suspended particulates are the primary mechanisms responsible for phosphorus removal in wetlands.
To encourage sedimentation of phosphorus-laden particles, the water level at Chadwick Meadows was elevated in the fall of 1983 by installing flashboards below the confluence of Lion Brook and Clark Brook Pond (Connor and Martin 1986). The macrophyte community in the wetland, composed primarily of blue-joint grass (Calamagrostis canadensis), was also supplemented with plantings of wild rice (Zinzania aquatica) in 1985 and 1986, to aid in phosphorus attenuation. It was anticipated that these manipulations to Chadwick Meadows would decrease phosphorus concentrations in Lion Brook, ultimately benefiting Kezar Lake (Connor and Martin 1989a).
A monitoring program was established from 1984 to 1988 to calculate changes in the phosphorus budget and measure the effects of the wetlands management activities. Phosphorus concentrations and flow measurements were taken monthly at the three tributaries and at the outlet of Chadwick Meadows (Connor and Martin 1989a). Results from the monitoring are shown in Figure 5. Although there were a few months when the wetland acted a sink, the overall effectiveness of Chadwick Meadows in removing phosphorus from Lion Brook was poor (Connor and Martin 1989a). The restoration activities did, however, prove valuable in increasing sedimentation and wildlife habitat. Furthermore, costs associated with the wetland manipulation were negligible, totaling $250.00 for the purchase of wild rice.
The conclusions of the Restoration/Protection Project in the Phase II Final Report (Connor and Martin 1989a) offered four main hypotheses for the water quality response observed. First, the authors indicated the possibility that the aluminum bonding sites provided by the 1984 treatment eventually were all occupied, preventing long-term phosphorus inactivation. Second, the heavier aluminum salts, which initially created a physical barrier between the sediment and water interface, may have migrated vertically downward through the sediment. This migration exposed some of the sediment that may contribute additional internal phosphorous loading. Third, additional phosphorus entered the lake from the tributaries, perhaps as a result of biological assimilation of phosphorus in Lion Brook that occurred during effluent discharge from the New London wastewater treatment facility. Fourth, historical anoxic conditions that occur in the hypolimnion during summer months in Kezar Lake increase the rate at which sediment phosphorus is released into the hypolimnion.
A final hypothesis generated from more recent monitoring data (collected from 1988 to 1994) suggests that the water quality in Kezar Lake may be influenced by the amount of annual precipitation (J. Connor, pers. comm., May 1995). As Figure 4 indicates, chlorophyll a levels following restoration (after 1984) fell below those measured before restoration efforts, except during 1988 and 1993. During both of these years, annual precipitation considerably exceeded normal amounts, as did runoff. It is thought that nonpoint source loads from the Kezar Lake watershed may contribute enough additional phosphorus during periods of high precipitation to noticeably decrease the water quality in Kezar Lake. It appears now that the quality of Kezar Lake is regulated by climatic conditions. High summer precipitation produces high productivity while drought years, like 1995, produce record transparency and low productivity.
LONG-TERM MONITORING STUDIES
As previously discussed, a state-assisted Volunteer Lake Assessment Program was established to continue water quality data collection for Kezar Lake and to provide a means of public education following completion of the Phase II Project in 1988. An ongoing 5-year EPA Phase III Post-Restoration Monitoring Study is also assessing specific longer-term effects of aluminum salts application in Kezar Lake. Research in the Phase III Study includes:
An assessment of potential leaching of sediment aluminum into overlying water.
A comparison of aluminum levels in horned pout (Ictalurus nebulosus) and yellow perch (Perca flavescens) between Kezar Lake and several control lakes.
A comparison of macroinvertebrate diversity and density between Kezar Lake and several control lakes.
A comprehensive description of this research and the results will be published in the near future in the Phase III Final Report.
Connor, J.N. and M.R. Martin. 1986. Wetlands management and first year response of a lake to hypolimnetic aluminum salts injection. New Hampshire Department of Environmental Services, Water Supply and Pollution Control Commission, Staff Report Number 144. 76 pp.
Connor, J.N. and M.R. Martin. 1989a. An assessment of wetlands management and sediment phosphorus inactivation, Kezar Lake, New Hampshire. New Hampshire Department of Environmental Services, Water Supply and Pollution Control Division, Staff Report Number 161. 109 pp.
Connor, J.N. and M.R. Martin. 1989b. An assessment of sediment phosphorus inactivation, Kezar Lake, New Hampshire. Water Resources Bulletin 25(4):845-853.
Connor, J.N. and G.N. Smith. 1986. An efficient method of applying aluminum salts for sediment phosphorus inactivation in lakes. Water Resources Bulletin 22(4):661-664.
Cooke, G.D. and R.H. Kennedy. 1981. Precipitation and inactivation of phosphorus as a lake restoration technique. U.S. EPA Ecological Research Series. EPA- 600/3-81-012. U.S. Environmental Protection Agency, Washington, DC.
Snow, P.D. and F.A. DiGiano. 1976. Mathematical Modeling of Phosphorus Exchange Between Sediments and Overlying Water in Shallow Eutrophic Lakes. Report ENVE.54-76-3 to the Massachusetts Division of Water Resources, Department of Environmental Quality. 244pp.
Wetzel, R.G. 1983. Limnology. 2nd Edition. Harcourt Brace Jovanich, Orlando, FL. 767 pp.
This case study was prepared by Tetra Tech, Inc., Fairfax, VA, in conjunction with EPA's Office of Wetlands, Oceans, and Watershed Branch. To obtain copies, contact your EPA Regional Clean Lakes Coordinator or request a copy from: *
* This document has not been printed yet due to Continuing Resolution printing restrictions