NJ-AWRA - Hopkins Pond

New Jersey Section of American Water Resources Association (NJ-AWRA)

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The New Jersey Section of the American Water Resources Association (NJ-AWRA)
The 2013 Excellence in Water Resources Protection and Planning Awardee
Winner for "Exceptional Water Resources Planning and Management Initiatives"

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 long.

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 reduce nutrients.

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