The activities in a lake such as Lake Erie are controlled in part by what happens in the watershed. Losses from the land are gained by the lake, for better or for worse–often to the detriment of organisms living in the lake. Nutrients, such as nitrogen and phosphorus that contain compounds from agricultural and residential fertilizers, along with toxic materials such as industrial wastes (e.g., polychlorinated biphenyls, or PCBs) and human hygienic products (e.g., endocrine disrupting estrogen agonists and antagonists) enter lakes largely through riverine inputs, often exacerbated by rainstorms and snowmelt runoff. Also, ecosystem managers need to consider particulate materials, which consist largely of soil particles (i.e., sand, silts, and clays) carried along with flowing water and which may turn into sediment at the bottom of a lake when the flow decreases at the mouth of a river or after entry to a lake.
Although point sources such as pipes from a sewage treatment plant or local industry can be feeders of pollutants to a river, much of point-source pollution is now regulated to prevent large inputs to receiving waters. The major source of pollutants now is from nonpoint sources such as runoff from residential yards and agricultural fields. When runoff occurs from these nonpoint sources, generally it comes as a mix of dissolved and particulate materials. Although most nutrients and many toxic materials are soluble in water, they often are attached to the surface of sediments when they enter a stream or river, complicating the management picture.
Which sediments are worst for holding unwanted materials? Recall from geometry that as the radius of a sphere gets smaller, the ratio of surface area to volume gets larger. So the surfaces of smaller particles (e.g., clays) are proportionately much more coated with nutrient and toxic materials than the larger sand particles. This means that sediments of different sizes can be and need to be managed differently.
Until recently, eroded sediments were treated as a nuisance, filling up harbors at the mouth of rivers and requiring dredging to keep those ports open for commerce. The Cuyahoga River fills its navigation channel with eight to ten feet of sediment each year, requiring the U.S. Army Corps of Engineers to dredge it to maintain shipping access up six miles to the ArcelorMittal steel company. To be exact, the corp dredges 225,000 cubic yards of sediment at great expense to public funds, whether state or federal.
Recent advances in technology have begun to turn bane into bonanza. The Port of Cleveland in partnership with Kurtz Bros., Inc. has been harvesting sand five miles upstream of ArcelorMittal using a sand interceptor that collects sand from the river and deposits it along the riverbank, where it is delivered to trucks and sold for construction, soil conditioning, and stream and beach reconstruction. It is then dried and sorted by size. Because it is collected above most industrial activities, it is sufficiently clean for reuse. It is estimated that with expansion of its capabilities, the sand interceptor may be able to reduce sediment loads to the port by 20%. The interceptor was funded with $1.2 million by the Ohio Healthy Lake Erie Fund. Independent research conducted at the University of Akron and verified by the Ohio EPA found that the material met state and federal standards for cleanliness.
But what about the sediments that are not collected by the sand interceptor? Aren’t those the materials most likely to have hazardous materials adhering to them? Sediments dredged from the mouth of the Cuyahoga River are now placed in a confined disposal facility (CDF) at the eastern end of Burke Lakefront Airport. This is a special experimental CDF that is administered by the Ohio Department of Natural Resources Office of Coastal Management. It is constructed as a series of pools through which sediment slurries pass. The sediment material gradually sinks to the bottom, leaving the water to pass back into the shipping channel in a process called dewatering the sediment. Over time, the sediment consolidates, with the larger, heavier materials settling in the first pond and lighter sediments settling in later pools. Bacterial and fungal activities gradually will decompose the toxic materials (e.g., PCBs and polyaromatic hydrocarbons, or PAHs). In the meantime, small amounts of these dewatered sediments can be combined with other materials and used in soil mixes. The Ohio EPA tests the mixes to ensure that they meet state and federal standards for safety. Once again, these soil mixes are made through the public-private partnership between the state and Kurtz Bros.
Through these innovative measures, sediment no longer need to be considered something to be disposed of; instead, sediment can be considered to be a valuable resource that can be recycled and marketed. It is something to think about and to carefully consider as the next wave of environmental protection: making the environment safe by making it profitable. Time will tell whether this is a valuable direction, especially given the current political aversion to making sweeping environmental regulations.