Selected Water Quality Processes in Rivers and Streams - Hydro-Environmental Analysis: Freshwater Environments - page 156

in the National Water Quality Inventories, are based on qualitative or narrative standards, rather
than numeric standards. All states are developing numeric nutrient criteria.
Nutrients, such as phosphorus and nitrogen, are required for plant growth and are necessary for
a healthy aquatic ecosystem. However, excess nutrients can result in excessive plant growth that can
clog waterways, reduce oxygen concentrations, and have other negative impacts on aquatic health.
The initial focus of regulation and water treatment was on DO concentrations in rivers and
streams. As indicated earlier, considerable improvements have been achieved. The early focus on
nutrients was primarily due to their impact on oxygen, by oxygen consumption due to nitriication,
and on toxicity, such as due to unionized ammonia. Ammonia and ammonia toxicity standards were
established for freshwater and saltwater as described in the U.S. EPA's ammonia aquatic life criteria
(http://www.epa.gov/ost/standards/ammonia/99update.pdf).
More recently, nutrients as pollutants have become a nationwide regulatory and management
issue. The CWA plan, a presidential initiative released in February 1998, included an initiative to
address the nutrient enrichment problem. In 1998, the U.S. EPA developed a report entitled “National
strategy for the development of regional nutrient criteria,” and in 2000, it released “Nutrient criteria
technical guidance manual: Rivers and streams.” Today, all states are required to develop nutrient
criteria (USEPA 2000).
A number of issues are involved in developing nutrient criteria and in managing nutrient loads
to rivers and streams. One issue is that a large percentage of nutrient loads is from nonpoint sources
that had previously been unregulated. Also, nutrient cycling is a complicated process in rivers and
streams, involving the impacts of advective transport, the degradation of organic materials in the
water column and sediments, and other processes impacting nutrient cycling. Also, it is not really
the nutrients that are the issue, but the effect of excess nutrients. That is, since nutrients are essential
to healthy ecosystems, the question becomes “how much is too much?” Most regulatory agencies
and management organizations continually struggle with this issue.
5.8 TOXIC MATERIALS
The discharge of toxic materials into waters and streams without a clear understanding of the con-
sequences of those discharges has also long been a problem, as discussed earlier in this chapter. In
early U.S. history, streams and rivers were often treated as waste conduits, leading to the contami-
nation of many rivers and streams that still persists today (Figure 5.35).
Many of the organic chemicals that are of major concern today are persistent organic pollutants
(POPs), such as polychlorinated byphenyls (PCBs), dioxins, and dichlorodiphenyltrichloroethane
(DDT), and other materials that have not been legally discharged for decades, in many cases not since
the early 1970s. These materials often occur in very low concentrations in the water column (are
hydrophobic) and are strongly associated with sediments, particularly organic sediments. Even though
their concentrations in the water column are low, those concentrations are of environmental impor-
tance since the materials bioconcentrate and biomagnify. Also, many of the POPs are carcinogenic.
One example is DDT, an example of “one generation's solution is the next generation's problem”
chemicals. DDT was initially heralded as an ideal insecticide. Paul Müller, who developed DDT,
was awarded the Nobel Prize in Physiology or Medicine in 1948 “for his discovery of the high efi-
ciency of DDT as a contact poison against several arthropods.” The use of DDT greatly increased
following World War II, and it was only later that its detrimental effects and extreme persistence in
the environment were realized. Although DDT was banned in the United States in 1972, many areas
in the United States remain contaminated. For example, the entire Mississippi Delta is presently
under ish consumption advisories due to elevated concentrations of DDT in ish and the consequent
human health risks associated with the consumption of contaminated ish.
Today, while many of the past “generation's solutions” are “this generation's problems,” a new
suite of toxic materials are emerging. These include a variety of pharmaceuticals and personal care
products as pollutants (PPCPs). A 2002 report by the Toxic Substances Hydrology Program of the