Hopkins Pond - A Multifaceted Approach to Improve Water Quality and Habitat
By Mike Haberland, Rutgers Cooperative Extension & Craig McGee, Camden County Soil Conservation District
In eutrophic lakes and ponds,
conditions of warm, calm water, with elevated nutrients, can cause
photosynthetic blue-green algae (cyanobacteria) to increase dramatically. These “blooms” may be visible as floating
scum that resembles blue, green or even red paint on the surface of the
water. Blue-green algae can spoil water
quality producing pungent odors or a thick scum, affecting recreational use,
reducing oxygen levels, as well as impacting other plants and animals in the
water. When these cyanobacteria respire
they use oxygen that can alter the balance of the ecosystem to the point of
causing fish kills. Decomposition of the
bloom also consumes oxygen in the pond.
In addition, some species produce toxins that can cause illness in humans,
pets or livestock.The 5 acre Hopkins Pond located in
Haddonfield, New Jersey, part of the Camden County Parks System, experiences
intense blue-green algae blooms due to thermal stratification and
eutrophication caused by excessive nutrients.
These nutrients enter the pond as runoff from nonpoint sources such as
fertilized lawns, recreation fields, soil erosion, allochthonous material, or
re-suspension from bottom sediments. The
high phosphorous and nitrogen levels lead to blue-green algae blooms during
warmer, sunny weather with little wind and low water flow. In the Spring of 2013, Hopkins Pond
was fitted with a Hydro Logic “Airlift” diffused air aeration system designed
to maximize the water lift rate and transfer rate of dissolved oxygen by the
release of bubbles ranging in size from 500 to 100 micron in diameter along the
pond bottom. The rise of bubbles to the
lake surface draws bottom water along with them creating an artificial
circulation. This circulation mixes water that otherwise would thermally
stratify, and increases the dissolved oxygen content throughout the water
column. Oxygenating deeper waters near
the pond bottom may result in a decrease in the release of phosphorous from the
sediment. The circulation also keeps
blue-green algae moving through the water column and doesn’t allow it to reach
nuisance conditions. In addition to the aeration system, at
the start of summer, we designed and are installing artificial floating
wetlands for nutrient removal.
Artificial floating wetlands (AFWs) offer a unique way to reduce the
amount of nitrogen and phosphorous in a water body using natural microbial
action and obligate aquatic vegetation.
Planted with the same species of macrophytes that might be grown in a
land based constructed wetland, we extend the range of the vegetation out into
deeper waters of a lake or pond. Using
an artificial substrate, AFWs are anchored offshore in water depths that exceed
the normal habitat requirements for the plant material and yet are able to
continue to provide the same water treatment ecosystem services of their land
based counterparts. Microbiological
activity plays a major role in nutrient removal in wetland systems and the
large surface area of the woven floating wetland material provides a tremendous
amount of substrate for the growth of bacteria.
The drawback to using AFWs is that the expense of the commercially
available products makes it unlikely that they would be purchased without the
funding of grant, municipal or corporate dollars. To this end, we’ve designed a lower cost
Do-it-Yourself wetland using layers of commercial outdoor pond biological
filter media, marine foam floatation and native obligate wetland plants.
Through the first summer
of installation the pond water column is mixing well, with DO levels only
0.5ppm difference from surface to bottom;
zooplankton have had an explosive population growth which will benefit
the fishery; and Hopkins Pond did not experienced a bloom until the end of
August, unlike the next pond downstream which experienced blooms all summer
Fig. 1 Hopkins Pond with aeration diffusers operating.
Fig. 2 Planting native plants into artificial floating
wetland filter material.
Fig. 3 Artificial floating wetland anchored in pond to