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Review the indicators
at a glance
- How fragmented are natural lands into smaller, more isolated
patches? How are developed lands intermingled within the natural
landscape? This indicator requires further development. There
is widespread recognition that these patterns are important ecologically
and that they can affect people’s quality of life, but there
is less agreement among scientists on the most appropriate indicators
to use in measuring such patterns and the most appropriate geographic
scales on which to apply them. This report includes several indicators
of fragmentation and landscape pattern—for forests,
farmlands , grasslands/shrublands,
and urban/suburban areas (land
use change and patches)—but
these indicators focus on different aspects of fragmentation and
pattern from system to system. This indicator requires further
development.
Chemical and Physical Conditions
Out of the many important indicators of chemical and physical condition,
we have identified two as national indicators. Nitrogen is a vital
plant nutrient, but if present in excess it can cause ecological
problems, especially in coastal waters. One indicator tracks the
amount of nitrogen that leaves the land and is delivered to coastal
waters. The second is a multipart indicator that tracks such contaminants
as pesticides, PCBs, and heavy metals in streams, sediment, groundwater,
and fish.
- How much nitrogen leaves watersheds across the country,
and how much is delivered to coastal waters? Delivery
of nitrogen from rivers and streams to coastal waters can
cause excess algae growth, which reduces recreational and
aesthetic values and can contribute to low-oxygen conditions.
Watersheds in the upper Midwest and Northeast contribute the
most nitrogen per square mile to rivers and streams. The amount
of nitrate carried by two of the four largest rivers in the United
States increased over the past few decades, with the amount
carried by the Mississippi River—which
drains more than 40% of the area of the lower 48 states—
approximately doubling since the 1950s
- How often are chemical contaminants found in ecosystems,
and how often do they exceed standards and guidelines for
the protection of human health and aquatic life? This
indicator describes the numbers of contaminants that can be
detected and the frequency with which concentrations exceed
applicable standards or guidelines. The indicator covers stream
water, streambed and coastal sediments, freshwater and saltwater
fish, and groundwater. Numbers of contaminants found, and
the frequency with which they exceed applicable standards
or guidelines, vary by ecosystem. For example, all streams
tested averaged one or more contaminants at detectable levels
throughout the year, as did 94% of freshwater fish samples
and about 90% of groundwater wells tested. About three-quarters
of stream samples and half of stream sediments tested had
one or more compounds that exceeded guidelines for the protection
of aquatic life, and about 42% of estuary sediments exceeded
levels that indicate possible negative effects on aquatic
life. About 15% of stream sites and one-quarter of groundwater
wells had concentrations of contaminants that exceeded standards
or guidelines for the protection of human health. No trend
data are available for this indicator.
Biological Components
Three indicators describe biological conditions. The first tracks
how many plant and animal species are at risk of extinction, because
plants and animals are important as components of ecosystems and
because people value them for many reasons. A second indicator,
not yet developed, will measure how much of U.S. lands and waters
are altered, to varying extents, from natural conditions. A third
indicator tracks trends in annual plant growth, the energy that
drives and sustains ecosystems.
- How many native plant and animal species are at different
levels of risk of extinction? About 19% of native animal species
and 15% of native plants species in the U.S. are ranked as “imperiled”
or “critically imperiled”; such species are typically
found in 20 or fewer places, may have experienced steep or very
steep declines, or display other risk factors. In addition, about
4% of animals and 1% of plants are, or are believed to be, extinct.
When species ranked as “vulnerable” are included, about
one-third of all plant and animal species are “at risk.”
The degree of risk for any particular plant or animal species
varies considerably, from those species at relatively low risk,
to those that are in imminent danger of extinction. Hawaii has
a much higher percentage of at-risk plants and animals than any
other region, followed by the Pacific Coast. The Midwest and Northeast/Mid-Atlantic
have the lowest percentages. Interpreting these figures is complicated,
however, because the rankings are influenced by differences in
the number of naturally rare species among regions and species
groups, as well as by different types and levels of human activities
that can cause species declines.
- What fraction of U.S. lands and waters are highly managed
or highly altered, and what levels of disturbance are found on
natural/semi-natural lands? How highly managed or altered
an area is affects the type of species the area can support, and
this directly influences the goods and services available from
the area. This indicator requires further development. It is possible
to identify areas that are physically altered (that is, they have
a high percentage of asphalt, concrete, etc.) or highly managed
(that is, they are farms, forest plantations, golf courses, etc.).
However, it is not now possible to distinguish among the different
levels of disturbance in natural/semi-natural lands.
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