NATURAL and CULTURAL FEATURES of MONMOUTH COUNTY

lie between the Piedmont cobble to the northwest and the coarse Kirkwood-Cohansey sands of
the Outer Coastal Plain.
MCHD’s Rapid Bioassessment work has uniquely identified a multitude of stream sites in
glauconitic soils that are dominated by pollutant-tolerant benthic organisms that are associated
with erosion and siltation. During streambank erosion, clay and silt sized particles remain
colloidally suspended in the water column, prolonging turbidity. These fines blanket the
streambed and smother the least hardy macroinvertebrates that live in the sediment. Additionally,
streams in glauconitic soils downcut as they erode and eventually lose their ability to overflow
into adjacent wetlands. In contrast, streams flowing in the coarse sands of the Kirkwood-
Cohansey outcrop can maintain wetland availability during 2-year, bankfull storms (3.4 inches in
24 hours). They are more stable than downcut streams since they can store stormwater in the
wetlands and release it over longer periods of time. That is why the majority of Non-Impaired
streams with pollutant intolerant macroinvertebrates are found in the sandy mid to southern part
of the County. Sandy streams like the Metedeconck even retain their excellent, Non-Impaired
quality near developed areas like Route 9 in Howell, but the few Non-Impaired streams in the
glauconitic outcrops are always found in undeveloped areas.
The eroded clay and silt fines that blanket streambeds and lakes also adsorb pollutants and
nutrients more efficiently than sand, and provide habitat for the regrowth of bacteria and other
microbes during the warmest months of the summer. This bacterial-laden muck will resuspend in
the water column during rainfall, and has been linked to ocean beach closures near lake outfalls.
As freshwater colloids enter estuaries, the increase in salinity causes these pollutant-laden fines
to acquire an ionic charge and clump together into aggregates, which sink and accumulate in the
estuarine sediment. It has been estimated that up to 80% of freshwater pollutants accumulate in
estuaries; furthermore, “probably less than 5% of the sediment reaching the coastal zone in the
Atlantic seaboard of the U.S. is transferred to the continental shelf or to the deep sea” (DePetris,
1996).
A general rule regarding streambank erosion is that the southern (north-facing) and eastern
(west-facing) streambanks erode faster than the opposite banks because of the higher rates of
freezing and thawing during the winter. Occasionally erosion is significantly increased during
the winter when a frozen slurry of streambank is sloughed off after the temperature rises and it
rains (Smith, 2000). Erosion from road runoff first escalated in the County with the development
that followed the opening of the Garden State Parkway in 1954. For example, Lake Matawan
was originally created in 1923 by damming Gravelly Creek. The lake extended to Church Street
in Matawan, where an extensive wooden railroad tressel was built over the lake at nearby Water
St. But because of the siltation that began in the 1960’s, the Lake ends near Little St. in
Matawan, and the still-existing tressel at Water St. now crosses over wooded wetlands instead of
a lake (Kisk, 2006; Starace, 2006).
GLAUCONITE
Glauconite (marl, greensand, rotten stone, poison marl, hardpan) is a green to black silicate of
iron, potassium, and phosphorous that formed from the droppings of sediment-dwelling
invertebrates in the shallow regions beyond the breakers of Cretaceous and Tertiary seas
(Tedrow, 1986); specifically, in a low oxygen, reduced iron environments in a specific facies
array associated with silica-consuming diatom blooms in upwelling zones close to the coast
(Earthscape, 2007). A modern, anthropomorphic example of glauconite formation: glauconite