**6. Change and trend estimates**

Historically, the monitoring community has been focused on tracking trends at individual locations. The historic graphs of CO2 levels at Mauna Loa [54] and decreases in water clarity resulting from increases in primary productivity in Lake Tahoe [55] are excellent examples. Tracking conditions at individual locations can be quite useful and is akin to tracking the weight or obesity status of an individual (i.e., useful for that individual but their use in large-scale policy discussions depends entirely on the circumstance). The Mauna Loa data clearly provide strong evidence for global increases in CO2 given atmospheric circulation. In contrast, the isolated nature of individual lakes such as Lake Tahoe does not lend support for interpreting the Lake Tahoe water clarity data as a signal of a national or a global increase in lake productivity. The changes and trends that the NLA seeks to track are population trends…conceptually similar to asking the human health question

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intended to identify.

**Figure 9.**

*Error bars are 95% confidence intervals.*

**7. Stressor rankings**

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

"Has the number or percent of the population that is obese increased?". For the NLA, that translates to "Has the percent of lakes in poor (or good) condition class changed over time?"…essentially, is there a change in status over time? The current NLA online tools and reports show both status and changes. The best published examples of the intent of the NLA are [56, 57]. In [57], the authors document an increase in total phosphorus across the country that is especially evident in low nutrient lakes and streams. **Figure 9** displays the results discussed in that paper, showing that over the three initial stream surveys conducted as part of the NARS, the percentage of the total length of the stream population that had total phosphorus concentrations less than 10 μg/L decreased from 24.5% to just 1.6% between 2004 and 2014. Lakes were only surveyed twice during this period and showed a similar pattern with 24.9% of lakes with total phosphorus concentrations below 10 μg/L in 2007 decreasing to 6.7% of the lakes in that low nutrient category in 2012 (**Figure 9**). While it may be too early to know if these unidirectional changes and trends will persist, they are excellent examples of the types of population changes and trends that the NLA (and the NARS assessments in general) are

*Changes in total phosphorus (TP) in dilute streams and lakes across the conterminous USA based on the initial surveys of the National Rivers and Streams Assessment and the National Lakes Assessment. Data from [55].* 

While the results presented above are useful for describing status and trends in lake conditions, they do not address the potential associations of different stressors with biological condition. When studying individual lakes, we are used to asking

*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 9.**

*Water Quality - Science, Assessments and Policy*

**6. Change and trend estimates**

Historically, the monitoring community has been focused on tracking trends at individual locations. The historic graphs of CO2 levels at Mauna Loa [54] and decreases in water clarity resulting from increases in primary productivity in Lake Tahoe [55] are excellent examples. Tracking conditions at individual locations can be quite useful and is akin to tracking the weight or obesity status of an individual (i.e., useful for that individual but their use in large-scale policy discussions depends entirely on the circumstance). The Mauna Loa data clearly provide strong evidence for global increases in CO2 given atmospheric circulation. In contrast, the isolated nature of individual lakes such as Lake Tahoe does not lend support for interpreting the Lake Tahoe water clarity data as a signal of a national or a global increase in lake productivity. The changes and trends that the NLA seeks to track are population trends…conceptually similar to asking the human health question

*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* 

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**Figure 8.**

*Mountains.*

*Changes in total phosphorus (TP) in dilute streams and lakes across the conterminous USA based on the initial surveys of the National Rivers and Streams Assessment and the National Lakes Assessment. Data from [55]. Error bars are 95% confidence intervals.*

"Has the number or percent of the population that is obese increased?". For the NLA, that translates to "Has the percent of lakes in poor (or good) condition class changed over time?"…essentially, is there a change in status over time? The current NLA online tools and reports show both status and changes. The best published examples of the intent of the NLA are [56, 57]. In [57], the authors document an increase in total phosphorus across the country that is especially evident in low nutrient lakes and streams. **Figure 9** displays the results discussed in that paper, showing that over the three initial stream surveys conducted as part of the NARS, the percentage of the total length of the stream population that had total phosphorus concentrations less than 10 μg/L decreased from 24.5% to just 1.6% between 2004 and 2014. Lakes were only surveyed twice during this period and showed a similar pattern with 24.9% of lakes with total phosphorus concentrations below 10 μg/L in 2007 decreasing to 6.7% of the lakes in that low nutrient category in 2012 (**Figure 9**). While it may be too early to know if these unidirectional changes and trends will persist, they are excellent examples of the types of population changes and trends that the NLA (and the NARS assessments in general) are intended to identify.

## **7. Stressor rankings**

While the results presented above are useful for describing status and trends in lake conditions, they do not address the potential associations of different stressors with biological condition. When studying individual lakes, we are used to asking

questions about the cause or combination of causes of the problem we have found. This is similar to asking "Why am I over-weight or gaining weight?" In populationlevel or policy-level discussions, it is not about finding a specific cause of problems, but rather finding some way to rank the various causes. In the context of assessing obesity, of all the causes of increasing weight in the U.S., what is their relative importance, and which would result in the largest improvements in the obesity situation if it were tackled? The NLA, and the NARS more broadly, have adapted tools from the human health field (relative risk and attributable risk) to address this question [51, 52].

Three pieces of information are needed to rank stressors according to importance and pervasiveness. The first is relative extent—a measure of how widespread a particular stressor or potential cause of problems is. How many lakes, for example, have high (or poor) levels of total phosphorus? This is shown in the left panel of **Figure 10**. From the figure, one can see that 40% of the lakes have total phosphorus at levels high enough to be considered poor. Similar information is presented for the other stressors nationally and separately for natural and man-made lakes.

The second piece of information is an estimate of the relative risk posed to biological condition (e.g., as assessed using the zooplankton MMI) by each stressor (**Figure 10**, center panel). This provides an estimate of the impact of a particular stressor on the zooplankton community when the stressor occurs at high levels (poor stressor condition). At a relative risk of 1, zooplankton are equally likely to be in poor condition if the stressor is at high levels (poor stressor condition) or at low to medium levels (good and fair stressor condition). At a relative risk of 2,

#### **Figure 10.**

*Estimates for ranking stressors relative to their impact on the zooplankton assemblage for the 2012 National Lakes Assessment. Results are presented nationally and by lake origin type. Solid line represents a relative risk of 1, below which a stressor poses no risk to the biological assemblage. Error bars are 95% confidence intervals.*

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of these threats.

biointegrity.

**8. Tracking specific threats and emerging threats**

Among the biggest challenges and frustrations in monitoring is the time lag in addressing specific or new threats. When the acid rain issues arose in the 1980s, among the first questions raised was "How big is the problem?". Sadly, a reluctance to invest the time to assemble the technical experts to design and then implement a survey prompts premature policy decisions in the absence of solid information. While it is not possible to design a survey that anticipates every single problem that will arise, it is possible to design a survey that answers key questions about the health of our lakes and the relative importance of currently known stressors. The NLA does this well, in part because of the flexibility to adapt the survey design to new threats (e.g., see [58]). Additionally, the NLA serves as a platform from which to launch initial investigations into emerging issues to understand the nature of their size and distribution as well as track past and ongoing threats. The NLA continues to track the trophic state of lakes across the country (**Figure 10**). While the specific cause of eutrophication may have shifted from point sources to nonpoint sources it is still important to track this status as a key measure of how we manage our lakes. As other threats emerge, the NLA provides a platform to track their extent in lakes. Currently, harmful algal blooms and the toxins they produce (e.g., microcystin), mercury, and atrazine are among the specific stressors being tracked via NLA. The NLA 2012 website [59] has excellent presentations to explore the breadth

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

the zooplankton community is two times as likely to be in poor condition in the presence of high stressor levels as it is to be in poor condition with low to medium levels of the stressor. Nationally, zooplankton communities are more than 3.5 times as likely to be in poor condition with high levels of total phosphorus than with low

The third piece of information combines the relative extent values and relative risk values to generate an attributable risk (AR) estimate (**Figure 10**, right panel). This answers the question: "How much of an improvement in lake biological condition would be seen if all the total phosphorus values in poor condition were improved to fair or good condition?". In the case of the potential risk of total phosphorus to lake biological condition as represented by the zooplankton community, we would expect a 52% reduction in the number of lakes in the target population in poor biological condition for zooplankton if the total phosphorus concentrations in these lakes were decreased enough to change the stressor condition from poor to either fair or good. The point of calculating the attributable risk is to generate an estimate of the potential benefit in zooplankton communities determined the same way for all stressors. Ranking via AR allows a consistent and relevant approach for providing a relative ranking of the stressors. **Figure 10** suggests that for natural and man-made lakes combined, the greatest potential benefit to the pelagic zooplankton community would result from nutrient control or reducing lakeshore disturbance. In natural lakes, the attributable risks to zooplankton from poor shoreline habitat complexity, riparian vegetation condition, excessive shoreline disturbance, and nutrients (total nitrogen and total phosphorus) are all at high values (between 32 and 43%). These results are consistent with abundant research showing that near-shore habitat alteration and increased nutrient loading are associated, and further suggest that near-shore habitat protection and restoration may be a fruitful strategy for controlling nutrients and improving zooplankton

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

to medium levels of total phosphorus.

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

the zooplankton community is two times as likely to be in poor condition in the presence of high stressor levels as it is to be in poor condition with low to medium levels of the stressor. Nationally, zooplankton communities are more than 3.5 times as likely to be in poor condition with high levels of total phosphorus than with low to medium levels of total phosphorus.

The third piece of information combines the relative extent values and relative risk values to generate an attributable risk (AR) estimate (**Figure 10**, right panel). This answers the question: "How much of an improvement in lake biological condition would be seen if all the total phosphorus values in poor condition were improved to fair or good condition?". In the case of the potential risk of total phosphorus to lake biological condition as represented by the zooplankton community, we would expect a 52% reduction in the number of lakes in the target population in poor biological condition for zooplankton if the total phosphorus concentrations in these lakes were decreased enough to change the stressor condition from poor to either fair or good. The point of calculating the attributable risk is to generate an estimate of the potential benefit in zooplankton communities determined the same way for all stressors. Ranking via AR allows a consistent and relevant approach for providing a relative ranking of the stressors. **Figure 10** suggests that for natural and man-made lakes combined, the greatest potential benefit to the pelagic zooplankton community would result from nutrient control or reducing lakeshore disturbance. In natural lakes, the attributable risks to zooplankton from poor shoreline habitat complexity, riparian vegetation condition, excessive shoreline disturbance, and nutrients (total nitrogen and total phosphorus) are all at high values (between 32 and 43%). These results are consistent with abundant research showing that near-shore habitat alteration and increased nutrient loading are associated, and further suggest that near-shore habitat protection and restoration may be a fruitful strategy for controlling nutrients and improving zooplankton biointegrity.
