Control Measures: Aluminum salts injection and wetlands management
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
BACKGROUND
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.
Phosphorus Inactivation
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.
Wetlands Management
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.
Tables
Table 1
Table 2
Table 3
Table 4
REFERENCES
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: *
NCEPI
11029 Kenwood Rd., Bldg 5
Cincinatti, OH 45242
FAX (513) 489-8695
* This document has not been printed yet due to Continuing Resolution
printing restrictions