Nonpoint Source Pollution:
Part 5

This is the fifth and final article in a series about Nonpoint Source Pollution (NPSP). In the last four issues of The Water Line we introduced the concept of NPSP, discussed urban sources, rural sources, and the impacts that we, as individuals, have. Up to this point we have focused on pollution that comes off of the landscape. With this last article we turn our eyes towards the sky as well as the water.

By Air
Hopefully everyone reading this is familiar with the term watershed. If not, a lake's watershed is the area of land that drains into the lake (either by flowing over land or through the soil). A new term for all of us to learn is AIRSHED. The EPA defines an airshed as the geographical area that emits 75% of the air pollution reaching a given waterbody. Airsheds are calculated through mathematical models and are therefore grounded more in theory than an actual physical delineation. The concept is further complicated by the fact that not all air pollution behaves the same. A lake's airshed for Pollutant A may be twice the size as the airshed for Pollutant B.

How does air pollution get into the lake? The answer - ATMOSPHERIC DEPOSITION! Airborne pollutants can fall as a wet deposition (with rain or snow) or as dry deposition (as dust or a gas). This deposition can occur directly onto the water surface or onto the watershed, where the pollutant is carried into the lake with runoff.
Air pollutants that are the greatest threat to our lakes and streams fall into five categories; nitrogen, mercury, other metals, pesticides, and combustion emissions (pollutants from incinerators). While there are natural sources for many of these pollutants, human activities account for most of the air pollution in these categories. The Lakes of Missouri Volunteer Program measures the amount of nitrogen in lake water and has addressed terrestrial inputs in the past. Now let's take a brief look at nitrogen pollution from the air.

Atmospheric deposition can be a significant source of nitrogen into a waterbody. Studies estimate that 21% of the nitrogen pollution entering Chesapeake Bay comes from the air. Although the air we breathe is 78% nitrogen (N2), it is ammonia (NH3) and nitrogen oxides (NO#) that are considered pollution. A major source of atmospheric nitrogen pollution is the burning of fossil fuels. Nitrogenous air pollution can make a waterbody more productive, causing algal blooms and decreased water clarity (the same problems that are associated with terrestrial nitrogen pollution). Airborne nitrogen can also, under the right conditions, fall as acid rain in the form of nitric acid (sulfur is the other major contributor to acid rain). Acid rain can impact a waterbody by leading to changes in pH. Shifts in a lake or stream's pH can harm aquatic biota.

By Water
Threats to water quality don't just come from the land and air. They also come directly from those of us who are out on the lake! Millions of people regularly enjoy recreational boating. All of these boats can and do have impacts on water quality. NPSP associated with recreational boating includes chemicals from cleaning compounds, petroleum products, sewage, and shoreline disturbances.

Boat cleaning products can contain chlorine, ammonia, and phosphates. Chlorine and ammonia can be harmful to some aquatic life forms, while phosphates, as well as ammonia, can lead to increased algal production. Petroleum products find their way into sediments where they can persist and accumulate, causing harm to bottom dwelling creatures. Sewage...its sewage, do I really need to go into why this isn’t desirable in our lakes? Shoreline disturbances (such as wakes created by boating) can negatively impact plant growth in shallow areas and cause erosion along the shore. This leads to more soil material and nutrients in the water as well as a loss of aquatic habitat.

While the impacts from one single boat may seem negligible, the combined impact of hundreds or thousands of boats can be significant. Use of non-toxic cleaning products, careful refueling, proper engine maintenance, proper disposal of sewage, and lake-friendly boating practices (i.e. limited wake in shallow or near shore areas) can go a long way to reduce boater impacts.

We are all part of the solution
Hopefully this series on Non-Point Source Pollution has made you more aware of the many threats that face our lakes and streams. We have come a long way since the passing of the Clean Water Act. Gone are the days of burning rivers and a biologically dead Lake Erie. Regulation of Point Source Pollution has made a great impact, but we are only half-way there. Nonpoint Source Pollution, which is difficult to regulate, is the next focus. If we are to make future gains we must educate ourselves, our children, and our neighbors. Everyone must take an active role and the efforts must start on the community level.

Evaluate your impacts, educate those around you (lead by example!), and become active. Our goal is to leave our lakes, rivers and streams fishable and swimable for the next generation.

Dan Obrecht


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