Effects of a Clay Cap on Contaminants in Water, Sediments, Plants and Macroinvertebrates of Kearny Marsh

Participants: MERI, Seton Hall University, Fairleigh Dickinson University & AquaBlok Ltd.

Project Summary:
As a result of agricultural, commercial and industrial activities conducted in the absence of environmental regulations and enforcement in the past, sediments contaminated by organic compounds, heavy metals, and other potentially toxic chemicals have accumulated in many of the world’s deepwater and wetland environments. These sediment-borne contaminants can eventually become incorporated into aquatic food webs and adversely affect ecological receptors like benthic organisms and fish, and ultimately pose a risk to human health.
This project investigated a new in situ capping technology that could be used to remediate and/or manage contaminated sediments. AquaBlok (AB) is a patented, composite-aggregate technology comprised of a solid core, an outer layer of clay material, and polymers. When placed in water and over sediment, AB hydrates forming a layer between contaminants in sediment and the overlying water. Other materials – such as organic matter or plant seeds – can be incorporated into the AB as needed. Kearny Marsh in the NJ Meadowlands was chosen as the site for the field study because it has been chronically contaminated by landfills, leaching and run-off.
The study design involved five treatments done in duplicate. The treatments were as follows:
(1) AB alone;
(2) AB with SubmerSeed (seed mixture of aquatic plants);
(3) AB amended with 2% peat moss and SubmerSeed;
(4) uncapped control – sand (CN); and
(5) uncapped control with SubmerSeed (CP: AB amended with aquatic plants).

Each of the 10 plots was approximately 60 by 60 feet. AB was placed in the marsh by a “stone-flinger” between July 25th and August 3rd of 2005. The study site proved too deep for optimal germination of aquatic plants. Biologs platforms measuring approximately 8’ X 20’ were created and sunken to provide a more suitable depth for plant germination.
Pre and post capping monitoring was conducted on the water quality, sediment quality and benthic macroinvertebrates (BMI) for selected heavy metals as well as organics.

Scientific Questions:
1) Do fauna and flora colonize AB?
2) Does AB improve the diversity of the BMI community?
3) What species of aquatic plants can grow in AB?
4) Does AB alter the bioaccumulation of contaminants by both BMI and aquatic plants?
5) Does AB affect water quality in the marsh?
6.) Does AB affect sediment quality?
7) Does amending AB with peat moss improve its utility as a benthic substrate?


1.) Water quality
Water quality parameters included pH, salinity, dissolved oxygen (DO), redox-potential (ORP), temperature, depth and total suspended solids (TSS).

Temperature, TSS, salinity showed no statistical differences among treatments
pH was significantly increased in AB plots during the first 3 months of research due to the cation binding ability of AB; in later samples it declined in CN compared to unamended and amended AB treatments.
DO increased significantly in CN compared to unamended and amended AB treatments
ORP declined in CN compared to unamended and amended AB treatments

Results indicated that AB was making a difference in water quality and was increasing levels of DO in general. This was likely due to lower levels of microorganism activity in the AB substrate compared to sediment.

2.) Chemicals of concern in water

Heavy metal concentrations in water were similar across the site, and there were no treatment related effects for a particular collection date.
However, metal concentrations did appear to change across the site after capping. Most likely due to increased dissolved oxygen and redox levels associated with AquaBlok capped sites. . Capping with AquaBlok significantly reduced water concentrations of PCBs and OCPs. . Total PCBs declined 2-35x and OCPs declined 12-35x.

3.) Chemicals of concern in sediment:

Heavy metal concentrations in sediment did show treatment related effects.
Metal concentrations in AquaBlok treated plots declined significantly after capping. The concentrations of metals in the cap itself were much lower than in the sediments they covered.
Amending the AquaBlok with peat moss did not affect metal concentrations
The concentrations of PCBs and OCPs in AquaBlok substrate was significantly lower than in sediments left uncapped. Total PCB and OCP concentrations were 10x and 8x lower, respectively.

4.) Benthic macroinvertebrates

BMI abundance showed seasonal variation. Abundance of chironomids, Gammarus and other species was always lowest in November and similar in 2006 and 2007
For the chironomids it was clear that abundance was lower in the controls.
Statistical analyses found organism abundance statistically higher in AB amended with 2% peat moss than in control
There was no significant correlation between abundance of benthic macroinvretebrates and total heavy metals in the sediment.
Overall, it appeared that chironomids were able to control their accumulation of heavy metals such that they were not affected by substrate concentrations.
Tissue concentration was consistent with water concentration, which suggests that the BMI were accumulating metals from water as oppose to the benthic substrate.

5.) Marsh vegetation

The number of plant species capable of colonizing AquaBlok was very small. Only a few species of plants: Scirpus validus, Scirpus sp. and Peltandra virginica were able to germinate and grow.
Dramatic decrease in roots and leaves sizes of plants growing on tubs containing AquaBlook. Plants growing on marsh sediment have a more robust root system than plants growing in AquaBlok.
AquaBlok does reduce the amount of contaminates that becomes available to the plant but does not provide the plant with adequate amounts of nutrients necessary for a healthy marsh growth.

Study area location within the Kearny freshwater marsh

Plot arrangement within the study area

Establishing the clay caps


– Timetable
– Data files
– Final Report
Capping of Contaminated Sediments in Kearny Marsh.pdf