Ecological Indicators for the Nation (2000) / Chapter Skim
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4 Indicators for National Ecological Assessments
4 Indicators for National Ecological Assessments
Pages 64-115
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From page 64... ...
and unmanaged ecosystems; the indicators of nutrient-use efficiency and overall nutrient balance are specific to agricultural ecosystems. · Information about the extent and status of the land use and cover types that together make up the nation's ecosystems.
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From page 65... ...
However, a land use indicator requires much synthesis of existing information and some new information, and thus will take longer to develop than a land cover indicator. Meanwhile, land cover can serve as a valuable indicator.
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From page 66... ...
, and Production Capacity Lake Trophic Status Stream Oxygen Soil Organic Matter* Nutrient-Use Efficiency and Nutrient Balance Land Use*
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From page 67... ...
Thus the indicators in this category include land cover and land use; nutrient runoff to coastal waters (a measure of loss of an element of the matrix) ; and soil quality as measured by soil organic matter.
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From page 68... ...
The mathematical tools needed to assess land cover patterns and how they change are detailed in Appendix B To assess this component of human impacts on the land, the committee recommends a land cover indicator to track the amount of land in each of an array of land cover types, such as croplands, forestlands, wetlands, and nature reserves.
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From page 69... ...
The condition of the nation's flowing waters is clearly an important element of the land cover indicator. An aggregated measure of flow patterns of the nation's rivers would be useful, but the complexities of river-flow dynamics make such a measure computable and understandable only at the level of river basins.
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From page 70... ...
Therefore, for this reason it will be desirable for the land cover indicator to include a measure of percent freeflowing, or the length of free-flowing parts of streams and rivers divided by their total length. The percentage can be computed for each river basin and then aggregated into a single nationwide value.
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From page 71... ...
, and forest reserves, as well as into categories such as deciduous forest, boreal forest, and Pacific coast rainforest. Such categories can be aggregated into fewer categories as needed, but to identify forests in which the human impact is being reduced, is not changing, or is increasing, the disaggregated input data will be needed.
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From page 72... ...
Temporal and Spatial Variability. The land cover indicator itself does not retain the spatial information in the underlying data.
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From page 73... ...
Because the use of remote sensing to quantify land cover change is an active area of research and application within the scientific community and operational agencies, the statistical properties of land cover should be clarified in the near future. The classification of land cover types in the land cover indicator must be sufficiently comprehensive for all the additional indicators that are derived from it.
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From page 74... ...
The greatest barriers to developing and using the land cover indicator are probably conceptual: developing the detailed techniques for classifying, combining, and interpreting changes in land cover categories by means of which remote-sensing and in situ data are evaluated. Data Quality Control, Archiving, and Access.
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From page 75... ...
The first, total species diversity, is a measure of the ecological capital actually present. The second, native species diversity, compares the number of native species an area of land supports with the number it would support in the absence of human impacts.
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From page 76... ...
The total species diversity indicator would then be the average number of species in all land cover categories. However, this method fails to consider differences in the areas covered by each land cover category.
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From page 77... ...
If a land cover category sampled at two different scales is adjusted in this manner, its species density will be the same. To compute the total species diversity indicator, multiply each D times Pi, the proportion of i in the land cover indicator.
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From page 78... ...
To compute total species diversity, this process is repeated in each category of terrestrial and aquatic land cover, to calculate a separate score for each. Then each score is multiplied by the proportion of the nation devoted to that particular land cover, Mi x Pi (where Pi is the proportion of i in the land cover indicator)
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From page 79... ...
If the referent standard values of Sn are adjusted to that new situation, a steady decline in Sn and a concomitant steady but fallacious rise in total species diversity would result. Recalculating Sn would be an unfortunate example of the hazards of the shifting baseline phenomenon (Pauly 1995~.
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From page 80... ...
The native species diversity indicator covers only natives, because its purpose is to measure human impacts. If humans cause a native species to be replaced by an exotic, native species diversity counts that as an impact; total species diversity does not.
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From page 81... ...
Native species diversity uses the same power-law relationships that were measured in natural reserves for total species diversity (Sn = cAZ) , but thereafter its construction differs.
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From page 82... ...
Native species diversity decreases if more land is shifted to human use and if human use is intensified without regard to the ecological consequences. Native species diversity increases if management strategies on some lands are changed from those with heavy impacts to those with lighter impacts, if management strategies improve, and if land shifts to a less ecologically damaging use.
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From page 83... ...
Land in the Safe Harbor program should be separated from other similar land into a special land use category in the land cover indicator. It would have an entry in the land cover indicator and special measurements would be made of its contribution to total species diversity and native species diversity.
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From page 84... ...
Because of widespread concern about the impacts of nutrient loadings on coastal waters, and the lack of quantitative information to develop related national policies, the committee recommends the development of national- and regional-scale indicators for N and P runoff from the land to coastal areas. Data are already being collected to produce such statistics.
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From page 85... ...
and to estimate total runoff from the conterminous United States to coastal waters. An even larger effort has estimated N and P fluxes to the North Atlantic Ocean from rivers in 14 regions of North and South America, Europe, and Africa (Howarth et al.
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From page 86... ...
and total phosphorus (TP) runoff in rivers in kg P km-2 yr -I (bottom)
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From page 87... ...
Comparison of trends in runoff with trends in fertilizer use, crop production, and coastal water quality can give further insights into the need for changes in policies, regulations, and management practices. Soil Organic Matter Soils promote the growth of vegetation, including crops; control the flow paths of precipitation as it becomes surface and groundwater; and serve as a filter for potentially harmful substances that would otherwise enter this water and the atmosphere (Larson and Pierce 1991, Parr et al.
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From page 88... ...
Therefore, the committee recommends soil organic matter content as the best currently available indicator of the state of soil quality. SOM is an indicator of ecological condition (soil condition, relationship to erosion)
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From page 89... ...
1997) , probably as the result of erosion, increased soil temperature, and reduced organic matter input.
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From page 90... ...
The fourth indicator, trophic status, characterizes primary production in lakes. The trophic status indicator is derived by combining measures of Secchi-disk transparency, total phosphorus, and chlorophyll a concentrations (Carlson 1977~.
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From page 91... ...
, environments in which primary production is used to synthesize easily digested tissues, than in forested ecosystems, where much NPP is allocated to the production of wood. NPP that is not consumed by animals eventually enters the soil or aquatic sediments as undecomposed organic matter, where it is metabolized by detritivores and returned to the atmosphere as CO2.
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From page 92... ...
If NPP is greater than the sum of nonplant respiration, NEP is positive, and the ecosystem gains carbon. Over the long term in most ecosystems, NEP is zero; otherwise organic matter would disappear (NEP < 0)
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From page 93... ...
To obtain the aggregated national-level annual indicators of production capacity (total chlorophyll) , NPP, and carbon storage, the values computed for each land cover category are summed.
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From page 94... ...
NDVI measurements show that, over the past decade, the length of the growing season (period of high chlorophyll density) has increased in the North Temperate Zone by 10 days (Myneni et al.
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From page 95... ...
The USDA's National Resources Inventory provides a comprehensive assessment of the state and performance of natural and agricultural ecosystems on private lands every five years. Inventory measurements from 800,000 sites and regression models are used to estimate productivity, carbon storage, biomass, land use, vegetation cover, species ranges, and characteristics of soils.
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From page 96... ...
, its mix of mechanism and reliance on data make it ideal for relating chlorophyll density, NPP, and NEP. An Indicator of Aquatic Productivity Trophic Status of Lakes People tend to settle around water and to discharge wastes, treated or not, into lakes, rivers, bays, and estuaries.
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From page 97... ...
Together, these characteristics define a lake's trophic state. Together with basic physical conditions, such as morphology and hydrology, primary production in lakes is determined by inputs of energy and chemicals most importantly nutrients, inorganic ions, and natural organic matter.
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From page 98... ...
is the most commonly used measure of trophic state. Oligotrophic lakes generally have TP concentrations of less than 10 ,ug/L, and eutrophic lakes TP concentrations greater than 20 to 30 ,ug/L (the criterion separating trophic state classes varies somewhat by geographic region)
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From page 99... ...
The three indicators have been transformed into simple indices that express one concept of trophic state quantitatively (Carlson 1977~. Some states use these indices to classify their lakes according to trophic state; for example, Minnesota uses the following Trophic State Index (TSI)
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From page 100... ...
Deviations from the expected relationships among chlorophyll a, total phosphorus, and Secchidepth transparency signal regional variations in water color, factors other than primary production that limit transparency, or limitation of production by some nutrient other than phosphorus. TSI can be aggregated nationally by computing a frequency distribution of trophic states across lakes.
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From page 101... ...
The distribution of trophic states needs to be reported and interpreted in two ways: as overall number of lakes in various trophic states, and as numbers of lakes that have changed and the direction of that change. The distribution of trophic states of lakes is a useful national indicator, but the distribution of trophic states can also be compiled regionally or locally relatively simply.
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From page 102... ...
An Indicator of Trophic Status of Streams Stream Oxygen Indicators of the status of streams could be based on models of flowing-water ecosystems, such as the River Continuum Concept (RCC) , which is a broad, integrative framework for conceptualizing streamriparian systems (see Chapter 2~.
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From page 103... ...
Spatial and Temporal Variability. Because stream oxygen can change rapidly in surface waters, care must be taken to obtain data that can be interpreted and compared with data from other sites.
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From page 104... ...
Improved technology should allow more sophisticated and varied use of stream oxygen as an indicator. For example, natural patterns of primary production and respiration can produce day-night differences in stream oxygen.
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From page 105... ...
The importance of animal protein in human diets, which is consumer-driven, is an important factor in agriculture's impacts on the biosphere. Nations, such as the United States, with extensive concentrated animal production facilities generate large amounts of excess nutrients because nutrient use in animal production is much less efficient than in producing crops (van der Ploeg et al.
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From page 106... ...
Losses of agricultural chemicals account for a major share of nonpoint-source N and P pollution of ground and surface waters (NRC 1993~. Because pointsource control of N and P inputs to surface and groundwaters has been easier to achieve, nonpoint sources account for an increasing share of the total inputs (Sharpley and Meyer 1994~.
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From page 107... ...
This large import of nutrients is driving countrywide nutrient enrichment as the manure is applied to Dutch agricultural land and excess nutrients make their way into ground and surface waters (Van der Molen et al.
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From page 108... ...
If animal products become less important in people's diets, overall agricultural nutrient losses will decrease (van der Ploeg et al.
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From page 109... ...
Na = N content of crops produced for human consumption + N content of animal products produced (mass N ye) Chemical N fertilizer applied to cropland + N fixed by legumes (mass N ye)
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From page 110... ...
in West Germany resulted from increasing rates of applications of chemical fertilizers, the rise of livestock production (a much less efficient user of nutrients than crop production) , and an attendant 10-fold increase in imported N in feed (van der Ploeg et al.
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From page 112... ...
112 oo V)
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From page 113... ...
Population cycles are well studied, but how population cycles affect temporal patterns of species diversity, carbon storage and flow, and nutrient runoff is unknown. Experimental and theoretical investigations into the relationship between current population cycles and related ecosystem processes will provide the mechanistic understanding needed to improve predictions and interpret the causes of indicator behavior.
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From page 114... ...
Unfortunately, although a number of keystone species have been identified, no predictive theory of keystone species yet exists. Tolerant Species and Assessing the Regional Importance of Local Sites Evaluating places using only indicators that focus on each site separately would not lead to decisions that would sustain the greatest amount of species diversity.
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From page 115... ...
INDICATORS FOR NATIONAL ECOLOGICAL ASSESSMENTS 115 can be used to suggest ways to evaluate the contribution of a site, Ri, to regional diversity. To achieve this, for example, separate Si into two components.
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