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WHAT'S THE FUSS ABOUT PHOSPHORUS?
In cities and suburbs, the incremental runoff of the nutrient phosphorus (P) from sources like
lawn fertilizer—whether organic or conventional—is a serious concern because it feeds
algae and weeds in waterways. About half of Lake Champlain's phosphorus problem is from
developed lands and one acre of urban/suburban land contributes about four times more
phosphorus to the Lake than one acre of farm land!
Developed land has many impervious surfaces, such
as paved roads, sidewalks and roofs. When it rains,
these impervious surfaces rush pollutants into storm
drains that lead directly to
waterways.
Research suggests that
just one pound of
phosphorus can feed 300-500 pounds of algae in a water body.
While most algae blooms are generally harmless to humans,
decomposing algae and weeds take up oxygen in the water that
is vital to fish and other animals. Furthermore, algae and weeds
discourage swimmers, anglers, and boaters—and even lower
property values. Phosphorus also feeds toxic blooms of bluegreen algae (actually a bacteria called cyanobacteria) that are
occasionally found in the parts of Lake Champlain. In recent summers, cyanobacteria
blooms have caused beach closings and health alerts in parts of northern Lake Champlain.
Please don't feed the algae—switch to phosphorus-free fertilizer!
WHAT'S THE FUSS ABOUT PHOSPHORUS?
Introduction
As in all living systems, the balance of nutrients within the Lake Champlain ecosystem is
critically important in maintaining the condition of the Lake. If the concentrations of nutrients are
significantly altered, the ecosystem will become unbalanced and noticeable changes in Lake
condition will result. Like most lakes in the northeast, the concentration of phosphorus in Lake
Champlain is a key factor in determining the quality of the ecosystem as humans have come to
know and enjoy it.
Phosphorus is typically known as the limiting nutrient in a lake ecosystem, meaning that algal
growth is limited by the amount of phosphorus that is available. Algae require other nutrients as
well, but phosphorus is commonly the one nutrient that is most needed. When phosphorus is
available in excessive amounts, more algal growth than usual may result, including unsightly
algae blooms. These changes in plant growth, in turn, can affect many other aspects of the
Lake ecosystem, including the amount of oxygen in the water, the types of fish we catch, the
smell, the appearance, and potability of the water itself.
Residents and visitors to the Basin can take many actions to reduce the phosphorus load
carried by streams to Lake Champlain. The Lake Champlain Basin Program (LCBP), together
with its governmental partners, has identified a number of specific actions that are most needed
to protect the lake. These actions are provided in the tables at the end of this chapter,
accompanied by the intended schedule for their implementation.
Sources of Phosphorus
Phosphorus is most commonly found attached to soil particles and may be released into the
water column when soils are disturbed. Phosphorus typically arrives in Lake Champlain bound
to sediments carried down rivers and streams or as dissolved phosphorus that has been
released from the sediments into the water column. For purposes of this plan, phosphorus
pollution is grouped into two general categories. The most obvious category is point source
pollution, in which pollutants can be directly attributed to a tangible source in a particular place
– a wastewater treatment plant, for example. Point source pollution accounts for about 5 percent
of the total load reaching Lake Champlain. The second category, while less obvious, is currently
the more important problem in the Lake Champlain watershed, about 95 percent of the total
phosphorus load (Smeltzer et al. 2009), and is called nonpoint source pollution. Nonpoint
source pollution is associated with discharges of stormwater and snowmelt and is produced
across a broader geographical region. Examples include soil erosion and runoff from agricultural
fields; stormwater washing off roads, lawns, and parking lots; and unstable streams and stream
bank erosion from modified water flows. Because the exact origin of nonpoint source
phosphorus cannot easily be identified, it is much harder to control. Management actions to
address nonpoint source phosphorus pollution are addressed in this chapter.
Recent research in the Lake Champlain Basin shows that, acre for acre, developed land
contributes up to four times more nonpoint source phosphorus than average agricultural lands
and seven times more than forests (Troy et al. 2007). However, far more acres of Basin land are
in agriculture and forests than in urban settlements; it is now clear that substantial reductions in
nonpoint phosphorus runoff are required in both agricultural and developed lands in order to
meet our targets for a clean Lake Champlain. Developed lands contributed about 46 percent of
the phosphorus runoff Basin-wide in 2001, and agricultural lands contributed about 38 percent.
These proportions, however, vary greatly among the various sub-watersheds. For example, in
2001 developed land was the largest contributor to phosphorus in Burlington Bay, Vermont
(about 99 percent) and Cumberland Bay, New York (about 57 percent). But agricultural land
contributes the majority of phosphorus load to the Missisquoi Bay, Vermont and Québec (about
64 percent) (Troy et al. 2007).