**5. National and regional status estimates**

The results presented here are examples of a few of the ways to present and interpret the results from the NLA. We do not present a comprehensive assessment of lake condition based on NLA results here (see [34]). The first objective of the NLA is to describe the biological integrity of lakes within the conterminous USA. Based on a pelagic zooplankton multimetric index (MMI) of biological integrity, only 53 ± 7% of lakes in the conterminous USA ("National") are considered to be in good condition (**Figure 2**). A greater percentage of the natural lakes are in good condition (61 ± 10%) when compared with man-made lakes (43 ± 8%; **Figure 2**).

#### **Figure 2.**

*Water Quality - Science, Assessments and Policy*

tion and riparian vegetation cover indicators.

physical integrity goals expressed in the CWA.

The approach used to measure and describe various dimensions of littoral and riparian physical habitat is described in [43–46]. These measurements result in indicators of lake habitat complexity, shallow water habitat alteration, riparian vegetation cover, lakeshore disturbance, and lake drawdown exposure in the littoral zone [30, 45, 46]. The shallow water habitat alteration indicator is based on visual estimates of the areal cover of several types of natural cover (e.g., snags, macrophytes, overhanging vegetation) observed in the littoral zone around each lake. The riparian vegetation cover indicator is based on visual estimates of vegetation cover and structure in three layers of riparian vegetation observed around each lake. The lakeshore disturbance indicator is based on visual estimates of the presence and proximity of several types of human disturbance (e.g., agricultural activities, residences, marinas) to the lake margin observed around each lake. The lake habitat complexity indicator is based on the mean value of the shallow water habitat altera-

For each of the physical, chemical, and biological indicators used in the assessment, a set of benchmarks or thresholds was developed against which to evaluate the quality of the lake relative to that indicator. For the NLA, expected values were developed for each indicator within each of the 9 aggregated ecoregions shown in **Figure 1** based on the distribution of measured values (observed scores), or observed/expected values (calculated scores) of the indicator in the set of leastdisturbed reference lakes within that region. Condition thresholds were developed using the 5th and 25th (or 95th and 75th) percentiles of the distribution of the indicator scores in the set of regional reference sites, as described in the NLA 2012 technical report [30], and all sampled sites were assigned to good, fair, or poor condition based on those thresholds. More detailed discussions of the concepts underpinning behind the use of reference sites to model regional or individual lake expected indicator values in least-disturbed reference sites can be found in

The analytical goal of the assessment is to produce estimates of the number of lakes (or percent of lake number) falling into a condition class or stressor level based on the indicator data and the weights from the survey design [49]. Examples of how this was done for lakes and wetlands are presented in [21, 50]. The weight assigned to an individual lake is an estimate of the number of lakes in the target population represented by that lake and is used to develop a cumulative picture of the total target population. Status of the total lake population can be assessed for each of the indicators measured, whether they are biological, chemical, or physical. These population estimates represent the assessment of biological, chemical, and

The final element of the assessment is intended to answer another key NLA question—"What is the relative importance of the different stressors impacting lakes?" This element ranks the potential stressors to biological condition that were measured during the survey. This assessment element is not intended to determine the "cause" of poor conditions at an individual lake but rather to evaluate and then rank the relative improvement in national status that might be gained, biologically, if one were to eliminate the adverse influence of each stressor

through policy changes or management efforts. The quantitative approach

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[25, 45, 47, 48].

**4.3 Population estimates**

**4.4 Ranking of stressors**

*Status of lake biological condition for the 2012 National Lakes Assessment based on a multimetric index (MMI) for the zooplankton assemblage. Results are presented nationally and by lake origin type (natural versus man-made) in the conterminous United States (i.e., lower 48 states). Estimates are presented as percent of lakes in each condition class (good, fair, or poor relative to regional determination of least-disturbed condition) and as the absolute numbers of lakes. Values in parentheses are the estimated number of target lakes in the population. Error bars are 95% confidence intervals.*

Estimates produced for the 9 aggregated ecoregions allow one to consider regional patterns of condition in the context of the national estimates (**Figure 3**). Four regions (the Northern Appalachians, the Upper Midwest, the Southern Plains, and the Western Mountains) have more than 60% of their target population of lakes in good condition based on the zooplankton MMI. Three other regions (the Southern Appalachians, the Northern Plains, and the Xeric West) have a higher percentage of lakes in their target population in poor condition than good condition based on the zooplankton MMI (**Figure 3**).

Comparing regional and national estimates addresses the public's questions about whether poor conditions are distributed uniformly across the country or focused regionally. Such information allows for identifying and prioritizing those areas where the greatest need exists to address a specific problem. However, because the quality of least-disturbed sites varies regionally, direct comparisons among aggregated ecoregions need to be interpreted cautiously in terms of the lake population in one region having "better" (or "worse") lake condition than the lake population in another region.

#### **Figure 3.**

*Status of lake biological condition for the 2012 National Lakes Assessment based on a multimetric index (MMI) for the zooplankton assemblage. Results are presented nationally and for 9 aggregated ecoregions of the conterminous United States (i.e., lower 48 states). Estimates are presented as percent of lakes in each condition class (good, fair, or poor relative to regional determination of least-disturbed condition). Values in parentheses are the estimated number of lakes in the target population. Error bars are 95% confidence intervals. Aggregated ecoregion codes: NAP, Northern Appalachians; SAP, Southern Appalachians; UMW, Upper Midwest; CPL, Coastal Plain; TPL, Temperate Plains; NPL, Northern Plains; SPL, Southern Plains; XER, Xeric West; and WMT, Western Mountains.*

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**Figure 4.**

*Jewels across the Landscape: Monitoring and Assessing the Quality of Lakes and Reservoirs…*

Similar assessments can be made for any of the stressor indicators. Lake condition based on two nutrients (total phosphorus and total nitrogen) appears to be similar nationally, with less than 50% of all lakes with nutrient concentrations low enough to be considered in good condition (**Figure 4**). For both nutrients, man-made lakes have a lower percentage of lakes in good condition, and a greater percentage of lakes in poor condition, than natural lakes (**Figure 4**). Despite the fact that regions differ greatly in their proportion of natural versus man-made lakes, the national patterns observed for total phosphorus (TP) and total nitrogen

When we focus on a single nutrient, total phosphorus, 45% of the lakes in the conterminous USA are classified in good condition relative to regional expectations (**Figure 5**). Almost 55% of natural lakes were in good condition based on total phosphorus concentrations, compared with about 30% of man-made lakes (**Figure 4**). Across the 9 ecological regions, the Southern Appalachians, the Northern Plains, and Southern Plains exhibited the smallest percentages of lakes in good condition relative to total phosphorus with 23, 10, and 28% of the lakes classified in good

**Figure 6** shows comparable results at the national scale for the four measures of physical habitat quality in lakes—lake habitat complexity, shallow water habitat alteration, riparian vegetation cover, and lakeshore disturbance. In each case,

*Status of lake condition for the 2012 National Lakes Assessment based on total phosphorus and total nitrogen concentrations. Results are presented nationally and by lake origin type (natural versus man-made). Estimates are presented as the percent of lakes in each condition class (good, fair, poor relative to regional determination of least-disturbed condition) and as the absolute numbers of lakes. Values in parentheses are the estimated* 

*number of target lakes in the population. Error bars are 95% confidence intervals.*

*DOI: http://dx.doi.org/10.5772/intechopen.92286*

condition, respectively (**Figure 5**).

(TN) are remarkably similar for the two types of lakes.

*Jewels across the Landscape: Monitoring and Assessing the Quality of Lakes and Reservoirs… DOI: http://dx.doi.org/10.5772/intechopen.92286*

Similar assessments can be made for any of the stressor indicators. Lake condition based on two nutrients (total phosphorus and total nitrogen) appears to be similar nationally, with less than 50% of all lakes with nutrient concentrations low enough to be considered in good condition (**Figure 4**). For both nutrients, man-made lakes have a lower percentage of lakes in good condition, and a greater percentage of lakes in poor condition, than natural lakes (**Figure 4**). Despite the fact that regions differ greatly in their proportion of natural versus man-made lakes, the national patterns observed for total phosphorus (TP) and total nitrogen (TN) are remarkably similar for the two types of lakes.

When we focus on a single nutrient, total phosphorus, 45% of the lakes in the conterminous USA are classified in good condition relative to regional expectations (**Figure 5**). Almost 55% of natural lakes were in good condition based on total phosphorus concentrations, compared with about 30% of man-made lakes (**Figure 4**). Across the 9 ecological regions, the Southern Appalachians, the Northern Plains, and Southern Plains exhibited the smallest percentages of lakes in good condition relative to total phosphorus with 23, 10, and 28% of the lakes classified in good condition, respectively (**Figure 5**).

**Figure 6** shows comparable results at the national scale for the four measures of physical habitat quality in lakes—lake habitat complexity, shallow water habitat alteration, riparian vegetation cover, and lakeshore disturbance. In each case,

#### **Figure 4.**

*Water Quality - Science, Assessments and Policy*

zooplankton MMI (**Figure 3**).

tion in another region.

Estimates produced for the 9 aggregated ecoregions allow one to consider regional patterns of condition in the context of the national estimates (**Figure 3**). Four regions (the Northern Appalachians, the Upper Midwest, the Southern Plains, and the Western Mountains) have more than 60% of their target population of lakes in good condition based on the zooplankton MMI. Three other regions (the Southern Appalachians, the Northern Plains, and the Xeric West) have a higher percentage of lakes in their target population in poor condition than good condition based on the

Comparing regional and national estimates addresses the public's questions about whether poor conditions are distributed uniformly across the country or focused regionally. Such information allows for identifying and prioritizing those areas where the greatest need exists to address a specific problem. However, because the quality of least-disturbed sites varies regionally, direct comparisons among aggregated ecoregions need to be interpreted cautiously in terms of the lake population in one region having "better" (or "worse") lake condition than the lake popula-

*Status of lake biological condition for the 2012 National Lakes Assessment based on a multimetric index (MMI) for the zooplankton assemblage. Results are presented nationally and for 9 aggregated ecoregions of the conterminous United States (i.e., lower 48 states). Estimates are presented as percent of lakes in each condition class (good, fair, or poor relative to regional determination of least-disturbed condition). Values in parentheses are the estimated number of lakes in the target population. Error bars are 95% confidence intervals. Aggregated ecoregion codes: NAP, Northern Appalachians; SAP, Southern Appalachians; UMW, Upper Midwest; CPL, Coastal Plain; TPL, Temperate Plains; NPL, Northern Plains; SPL, Southern Plains; XER, Xeric West; and* 

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**Figure 3.**

*WMT, Western Mountains.*

*Status of lake condition for the 2012 National Lakes Assessment based on total phosphorus and total nitrogen concentrations. Results are presented nationally and by lake origin type (natural versus man-made). Estimates are presented as the percent of lakes in each condition class (good, fair, poor relative to regional determination of least-disturbed condition) and as the absolute numbers of lakes. Values in parentheses are the estimated number of target lakes in the population. Error bars are 95% confidence intervals.*

#### **Figure 5.**

*Status of lake condition for the 2012 National Lakes Assessment based on total phosphorus concentrations. Results are presented nationally and for nine aggregated ecoregions of the conterminous United States (i.e., lower 48). Estimates are presented as percent of lakes in each condition class (good, fair, or poor relative to regional determination of least-disturbed condition). Error bars are 95% confidence intervals. Aggregated ecoregion codes: NAP, Northern Appalachians; SAP, Southern Appalachians; UMW, Upper Midwest; CPL, Coastal Plain; TPL, Temperate Plains; NPL, Northern Plains; SPL, Southern Plains; XER, Xeric West; and WMT, Western Mountains.*

no more than 55% of the lakes in the country are in good condition for the respective physical habitat indicator. Nationally, the percent of lakes in good condition ranged from 28% (lakeshore disturbance) to 55% (riparian vegetation cover). Except for the shallow water habitat indicator, the percentage of natural lakes in good condition was greater than the percentage of man-made lakes in good condition.

Lake trophic state is a general indicator of lake productivity; the National Secchi Dip-In [11] provides an excellent overview that is based primarily on [53]. For the NLA, trophic state was estimated using phytoplankton chlorophyll *a* concentration, and condition was assigned using a single set of benchmarks across all ecoregions. **Figure 7** shows that nationally, about 10% of the lakes are classified as oligotrophic (chlorophyll *a* < 2 μg/L), and about 20% of the lakes are classified as hypereutrophic (chlorophyll *a* > 30 μg/L). The population of natural lakes appears to be less productive (i.e., have a larger percentage of lakes classified oligotrophic and mesotrophic) than the population of man-made lakes, which have a greater percentage of lakes classified as eutrophic and hypereutrophic (**Figure 7**). Across the 9 ecoregions, the largest percentage of oligotrophic lakes (nearly 60%) occurs in the Western Mountains (**Figure 8**). The Southern Plains has >40% of lakes classified as hypereutrophic, while the Temperate Plains has >30% of lakes classified as hypereutrophic (**Figure 8**).

**101**

**Figure 7.**

**Figure 6.**

*Jewels across the Landscape: Monitoring and Assessing the Quality of Lakes and Reservoirs…*

*Status of lake condition based on four indicators of physical habitat measured in the 2012 National Lakes Assessment: lakeshore habitat complexity, shallow water habitat alteration, riparian vegetation cover, and lakeshore disturbance. Results are presented nationally and by lake origin type (natural versus man-made). Estimates are presented as percent of lakes in each condition class (good, fair, poor relative to regional determination of least-disturbed condition) and absolute numbers of lakes. Values in parentheses are the* 

*Status of lake trophic state for the 2012 National Lakes Assessment. Trophic classes are based on chlorophyll a concentration. Results are presented nationally and by lake origin type. Estimates are presented as the percent of lakes and as the absolute number of lakes in each trophic category. Values in parentheses are the estimated* 

*number of lakes in the target population. Error bars are 95% confidence intervals.*

*estimated number of lakes in the target population. Error bars are 95% confidence intervals.*

*DOI: http://dx.doi.org/10.5772/intechopen.92286*

*Jewels across the Landscape: Monitoring and Assessing the Quality of Lakes and Reservoirs… DOI: http://dx.doi.org/10.5772/intechopen.92286*

#### **Figure 6.**

*Water Quality - Science, Assessments and Policy*

no more than 55% of the lakes in the country are in good condition for the respective physical habitat indicator. Nationally, the percent of lakes in good condition ranged from 28% (lakeshore disturbance) to 55% (riparian vegetation cover). Except for the shallow water habitat indicator, the percentage of natural lakes in good condition was greater than the percentage of man-made lakes in good

*Status of lake condition for the 2012 National Lakes Assessment based on total phosphorus concentrations. Results are presented nationally and for nine aggregated ecoregions of the conterminous United States (i.e., lower 48). Estimates are presented as percent of lakes in each condition class (good, fair, or poor relative to regional determination of least-disturbed condition). Error bars are 95% confidence intervals. Aggregated ecoregion codes: NAP, Northern Appalachians; SAP, Southern Appalachians; UMW, Upper Midwest; CPL, Coastal Plain; TPL, Temperate Plains; NPL, Northern Plains; SPL, Southern Plains; XER, Xeric West; and* 

Lake trophic state is a general indicator of lake productivity; the National Secchi

Dip-In [11] provides an excellent overview that is based primarily on [53]. For the NLA, trophic state was estimated using phytoplankton chlorophyll *a* concentration, and condition was assigned using a single set of benchmarks across all ecoregions. **Figure 7** shows that nationally, about 10% of the lakes are classified as oligotrophic (chlorophyll *a* < 2 μg/L), and about 20% of the lakes are classified as hypereutrophic (chlorophyll *a* > 30 μg/L). The population of natural lakes appears to be less productive (i.e., have a larger percentage of lakes classified oligotrophic and mesotrophic) than the population of man-made lakes, which have a greater percentage of lakes classified as eutrophic and hypereutrophic (**Figure 7**). Across the 9 ecoregions, the largest percentage of oligotrophic lakes (nearly 60%) occurs in the Western Mountains (**Figure 8**). The Southern Plains has >40% of lakes classified as hypereutrophic, while the Temperate Plains has >30% of lakes classified as

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hypereutrophic (**Figure 8**).

condition.

*WMT, Western Mountains.*

**Figure 5.**

*Status of lake condition based on four indicators of physical habitat measured in the 2012 National Lakes Assessment: lakeshore habitat complexity, shallow water habitat alteration, riparian vegetation cover, and lakeshore disturbance. Results are presented nationally and by lake origin type (natural versus man-made). Estimates are presented as percent of lakes in each condition class (good, fair, poor relative to regional determination of least-disturbed condition) and absolute numbers of lakes. Values in parentheses are the estimated number of lakes in the target population. Error bars are 95% confidence intervals.*

#### **Figure 7.**

*Status of lake trophic state for the 2012 National Lakes Assessment. Trophic classes are based on chlorophyll a concentration. Results are presented nationally and by lake origin type. Estimates are presented as the percent of lakes and as the absolute number of lakes in each trophic category. Values in parentheses are the estimated number of lakes in the target population. Error bars are 95% confidence intervals.*

#### **Figure 8.**

*Status of lake trophic state for the 2012 National Lakes Assessment. Trophic classes are based on chlorophyll a concentration. Results are presented nationally and for nine aggregate ecoregions. Estimates are presented as the percent of lakes in each trophic category. Values in parentheses are the estimated number of lakes in the target population. Error bars are 95% confidence intervals. Aggregated ecoregion codes: NAP, Northern Appalachians; SAP, Southern Appalachians; UMW, Upper Midwest; CPL, Coastal Plain; TPL, Temperate Plains; NPL, Northern Plains; SPL, Southern Plains; XER, Xeric West; and WMT, Western Mountains.*
