Blackwater Streams in the Fall

Creeks are running more black than orange since Monday when the rain flushed out the places where leaf litter had been steeping in groundwater seeps.

Streams and storm drains in Monmouth are spring-fed and usually look orange from the iron and the slimy iron bacteria floc that build up in between storms. When groundwater is not exposed to oxygen, iron is dissolved and the water is clear; but as it seeps into surface water and hits the air, iron comes out of solution and turns water rusty. The dissolved state is called ferrous, and the oxidized state is called ferric, or iron hydroxide.

In autumn, the tannins in the fallen leaves react with the iron hydroxide in the groundwater seeps so that surface water darkens for a while. Chemically, the tannic acid in the leaves and the iron hydroxide in the springs form a colloidal solution and "black ferric tannate is precipitated."

This is different than when water turns ink-black during the summer because of chemical changes to dissolved sulfur. When oxygen levels fall to zero in warm water, natural sulfate in the water turns into sulfide, and the water goes septic. The black water smells like rotten eggs from hydrogen sulfide gas and suffocates any aquatic life that can't swim away in time. This often happens during the summer after large algae blooms, or when sea lettuce clogs the mouths of streams along the Bayshore, like Many Mind Creek in Atlantic Highlands and Wagner Creek in Leonardo, or when raw sewage is discharged.

Iron is very common in well water, and if untreated, can also react with the tannins in tea and coffee and form a black residue. On average, iron makes up about five percent of the earth’s crust, and you can see it rusting in all the spring-fed streams and storm drains in Monmouth County colored orange, reddish-brown, or ochre. You can read about it in reports by the N.J. Department of Environmental Protection about groundwater quality in wells that were sampled because of the Private Well Testing Act. Of the 400,000 private wells in New Jersey that were sampled between 2002 and 2004, Monmouth had the highest amounts of iron in well water of all the counties.

RESOURCES

Hem, John David. 1960. Complexes of Ferrous Iron With Tannic Acid. Chemistry of Iron in Natural Water. Geological Survey Water-Supply Paper 1459-D. US Government Printing Office, Washington. http://pubs.usgs.gov/wsp/1459d/report.pdf  http://pubs.er.usgs.gov/publication/wsp1459D

New Jersey Department of Environmental Protection. 2006. NJ Private Well Testing Act Program – September 2002 to October 2004. NJDEP Division of Water Supply/Bureau of Safe Drinking Water and Division of Science, Research and Technology.

Louis, Judy. 2011. The New Jersey Private Well Testing Program: An Evaluation of Domestic Well Water Quality in New Jersey. Presented December 2, 2011, NJ Water Monitoring Summit. Office of Science. http://www.state.nj.us/dep/wms/LouisPWTA.pdf

New Jersey Department of Environmental Protection. July 2008. Private Well Testing Act Program. Well Test Results for September 2002 – April 2007. Division of Water Supply / Bureau of Safe Drinking Water and Division of Science, Research and Technology. New Jersey Department of Environmental Protection. http://www.state.nj.us/dep/pwta/pwta_report_final.pdf