**3. Conceptual approach**

*Water Quality - Science, Assessments and Policy*

The US Clean Water Act (CWA) of 1972 [2] expresses the national desire to restore and maintain the physical, chemical, and biological integrity of USA waters and requires that information on status and trends be reported every 2 years by the states. Different States vary greatly in their monitoring focus and approaches. It has long been recognized that these reports cannot be combined to create a coherent picture of the degree to which lakes in the USA meet the goals of the CWA [3–9]. Looking back at the history of national lake assessments, it is clear that our focus in assessing lake condition has shifted over time as each new threat to lake quality emerged. In the 1960s–1970s, our focus was the "cultural eutrophication" of lakes, that is, the nutrient enrichment of lakes through human activities, via point or nonpoint sources of organic and inorganic nutrients. This enrichment led to everything from "unsightly" algal growth to health problems associated with recreational contact. When extreme, these algal blooms eventually led to low dissolved oxygen levels as the algae died and decayed. The low dissolved oxygen ultimately led to die-off of sensitive fish communities in many lakes. These concerns about eutrophication led to the first ever national lake survey in the USA, the National Eutrophication Survey (NES) [10]. The survey focused on lakes near population centers that were likely subjected to point-source release of nutrients or oxygen demanding compounds. Over 800 lakes suspected of having problems were sampled during this survey using a targeted approach. Ultimately, these concerns led to the funding of the Clean Lakes Program, a Congressionally funded program managed by the fledgling Environmental Protection Agency to provide states and communities with funding to solve specific problems with individual lakes. The concern about eutrophication and desire to engage the public through citizen monitoring continued into the 1990s. In 1994, the National Secchi Dip-In program was implemented. The Dip-In is a volunteer effort in which citizens from various localities send in their Secchi Depth readings (a measure of lake water clarity) for lakes of interest during a particular week during the summer. This event continues under the sponsorship of the North American Lake Management

The 1980s saw increasing concerns about releases of nitrogen and sulfur compounds into the atmosphere and the deposition of these acidic compounds onto lakes and stream watersheds in poorly buffered landscapes. When inquiring into the extent of the problem at the time, William Ruckelshaus, the EPA Administrator at the time, was rumored to have said something along the lines of "What do you mean you don't know how many acid lakes there are?" A definitive answer to this question was not possible at that time for several reasons, including the uncertainty in extrapolating results from site-specific studies to regional or national populations of lakes [12]. These concerns, in Europe and North America, particularly in highly visible regions like the Adirondacks, eventually led to the implementation of the National Acidic Precipitation Assessment Program (NAPAP). Key projects within NAPAP were the National Surface Water Surveys (NSWS), probability-based surveys of lakes (and streams) that set out to document how many acidic lakes and streams there were in the U.S. and how these systems might be changing in response

Following the completion of the initial NAPAP-sponsored surveys, EPA began to ask whether there might be a better, more consistent approach to directly address the CWA objectives for assessing the condition of lakes and other important ecological resources rather than mounting new surveys for each new problem that arose. The Environmental Monitoring and Assessment Program (EMAP) was a research

to the 1990 Clean Air Act Amendments [12–14].

**2. Background**

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Society [11].

Three aspects of the NLA make up the overall conceptual approach – the selection of indicators, the approach (survey design) for selecting sites to sample and making inferences to all lakes, and the strategy (response design) for acquiring data at each site for all indicators [6, 19]. This conceptual approach ensures that the NLA will address the main goal of the CWA as well as address the five big questions most frequently asked by the public:


Past surveys of lakes have pursued individual stressors or anthropogenic problems and measured them, for example, the National Eutrophication Survey focused on nutrients, phosphorus in particular, and the National Surface Water Surveys (NSWS) under NAPAP focused on acidification. The NLA, under NARS, is intended to have a broader perspective by using a variety of indicators to examine the overall health of lakes and ranking the importance of individual anthropogenic stressors.

This perspective drove the NLA to focus on indicators related to the attribute of "biological integrity" referenced in the CWA [2] to describe "condition" of lakes. In addition, indicators of "physical integrity" and "chemical integrity" describe the relative importance of human-mediated disturbances impacting lake condition.

The survey design plays a critical role in the overall approach within the NARS and the NLA. Frequently, surveys are developed with little attention to the final statements that are intended to be made from the data. The National Eutrophication Survey, for example, was based on a targeted judgment sample of 817 lakes potentially influenced by nutrient inputs from domestic wastewater treatment plants. Without statistically representative site selection, the only conclusions that could be reliably made from the data were about those 817 specific lakes. The Great Secchi Dip-In acquires data from thousands of lakes each year. The results provide

important information about those lakes being monitored, but because the lakes selected for sampling are chosen by those submitting the data, the results are not necessarily representative of the total lake population (e.g., see [20]). The lake surveys conducted as part of the National Surface Water Surveys (NSWS) used a statistical design restricted to acid-sensitive regions (rather than the whole country) that allowed inference to be made from the sampled lakes to the greater population of lakes they represented in those defined areas. Because the focus was on acidification and acid deposition, the selection of lakes was understandably limited to lakes in regions of the country that had poor buffering capacity in the soils. Therefore, these lakes were potentially sensitive to acidification from acids in atmospheric deposition. By contrast, the NLA is the first national survey that focuses on all waterbodies in the conterminous U.S. meeting the definition of a lake (both natural and man-made) and employs a survey design that ensures that inferences can be made to that full "target" population of lakes [21]. More details of the NLA survey design are provided in following sections of this chapter.

The final aspect of the conceptual approach for indicators or measurements is the "response design," that is, when the crews get to specific lakes, where and how do they collect samples or measurements for the various indicators? This will be described in more detail below.

#### **3.1 Indicators**

Indicators used in the NLA are selected to assess status related to trophic state, water quality, the condition of biological assemblages, physical habitat condition, and human use (**Table 1**). The set of selected indicators are intended to be most appropriate for the assessment of lake condition at regional and national scales. Indicators range from direct measurements of specific variables to more complex indices representing biological or physical habitat condition.

#### **3.2 Survey design**

The target population (i.e., the set of lakes about which inferences are to be made) for the NLA includes all natural lakes and ponds, reservoirs, and man-made ponds within the conterminous USA (i.e., the "lower" 48 states) that are greater than 1 hectare (ha) in surface area, are permanent waterbodies, have an estimated maximum depth greater than 1 m, and have more than 1000 m2 of open water on the day of sampling. An early decision was made to sample lakes as a finite resource and provide estimates of "lake number" and "proportion of lake number" rather than as "lake area" (although areal estimates can also be made with the NLA data). The NLA design requires some level of stratification or unequal sampling probability to accommodate regional variation in the abundance of lakes, and the preponderance of small lakes [22, 23]. A simple random sample will be dominated by small lakes (less than 4 ha), and the bulk of lakes sampled will be in the Upper Midwest where lakes are most abundant. Because of the desire to make both national and regional estimates, care is taken to spread the sample across the conterminous USA and across the size range of lakes available. For regional coverage, variable selection probabilities are set to ensure the ability to describe conditions in all 10 EPA Regions [24], 9 aggregated NARS ecoregions (**Figure 1**) [25] and roughly 15 hydrologic basins. Variable selection probabilities are also set to ensure that the NLA samples are spread across the size range of lakes so that small lakes do not dominate the sample. Samples are currently allocated among 5 lake surface area categories: 1–4, 4–10, 10–20, 20–50 ha, and greater than 50 ha. Each site sampled receives a "weight" inversely proportional to its probability of inclusion in the sample. The weights are then used to make the inferences from

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

Collected from the upper portion of the water column at the open-water site. Organisms were usually identified to genus and an multimetric index was developed based on life history characteristics and

A trophic state index was calculated based on measured

Kicknet samples collected from the lake bottom at 10 shoreline locations and combined into a single composite sample for each lake. Organisms were usually identified to genus and a multimetric index was developed based on life history characteristics and

Collected from a vertically integrated sample of the upper water column at the open-water site. Measured concentrations were compared to benchmarks

Collected from a vertically integrated sample of the upper water column at the open-water site. Measured concentrations were compared to benchmarks

In situ measurements were collected from the entire water column at the open-water site. The mean value of measurements from the top 2 m of the profile was

ANC (corrected for DOC) measured from a vertically integrated sample of the upper water column at the open-water site. Measured concentrations were

Observations were recorded from 10 shoreline locations around each lake. Observed indicator values were compared with lake-specific expected values based on natural controlling factors within each region. Condition determinations were based on magnitude of

Observations were recorded from 10 shoreline locations around each lake. Uniform disturbance level

Observations were recorded from 10 shoreline locations around each lake. Information was compared to distribution of drawdown exposure in regional

Collected from a vertically integrated sample of the upper water column at the open-water site. We report on detection; measured concentrations were compared

Collected from a vertically integrated sample of the upper water column at the open-water site. Concentrations were compared to WHO algal toxin

calculated and compared to benchmarks

compared to benchmarks

deviations from expected values

criteria used nationwide

reference sites

Same as for lake habitat complexity

Same as for lake habitat complexity

to an EPA plant-effects benchmark

benchmark for recreation

tolerance to environmental conditions

tolerance to environmental conditions

chlorophyll *a* concentration

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

Zooplankton assemblage: important element of the food web; responds to stressors such as nutrient enrichment and acidification

Trophic state (chlorophyll *a*): responsive to nutrient enrichment and can be associated with

Benthic macroinvertebrate assemblage: responsive to a variety of stressors and can integrate exposure to current and recent past

Total phosphorus: important nutrient affecting trophic state and algal community structure

Total nitrogen: important nutrient affecting trophic state and algal community structure

Dissolved oxygen: low levels can result from nutrient enrichment and lead to loss of biota

Acidification (acid neutralizing capacity—ANC): indicates potential exposure to episodic or chronic acidification, which can affect structure and composition of algal, zooplankton, and fish

Lake habitat complexity: indicates effects of human activities on the complexity of cover features in the riparian, shoreline, and littoral zones. Supports diversity of biotic assemblages such as fish, benthic invertebrates, and birds

Shallow water habitat: indicates effects of human activities on or near lakeshores on the complexity of littoral cover features that support biota

Riparian vegetation: reflects ability to buffer lake from influence of upland land use activities

Lake drawdown exposure: reflects potential loss of littoral habitat and loss of connectivity between littoral and riparian zones due to hydrologic alteration and/or drought

Atrazine: provides an indication of exposure to

Chlorophyll *a*: indirect measure of algal biomass, trophic state, and the potential for presence of

Lakeshore disturbance: indicates types and potential severity of human activities in shoreline

risk of harmful algal blooms

levels

assemblages

and littoral habitats

herbicides

algal toxins

**Indicator and rationale Sample location**

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


*Water Quality - Science, Assessments and Policy*

design are provided in following sections of this chapter.

indices representing biological or physical habitat condition.

maximum depth greater than 1 m, and have more than 1000 m2

described in more detail below.

**3.1 Indicators**

**3.2 Survey design**

important information about those lakes being monitored, but because the lakes selected for sampling are chosen by those submitting the data, the results are not necessarily representative of the total lake population (e.g., see [20]). The lake surveys conducted as part of the National Surface Water Surveys (NSWS) used a statistical design restricted to acid-sensitive regions (rather than the whole country) that allowed inference to be made from the sampled lakes to the greater population of lakes they represented in those defined areas. Because the focus was on acidification and acid deposition, the selection of lakes was understandably limited to lakes in regions of the country that had poor buffering capacity in the soils. Therefore, these lakes were potentially sensitive to acidification from acids in atmospheric deposition. By contrast, the NLA is the first national survey that focuses on all waterbodies in the conterminous U.S. meeting the definition of a lake (both natural and man-made) and employs a survey design that ensures that inferences can be made to that full "target" population of lakes [21]. More details of the NLA survey

The final aspect of the conceptual approach for indicators or measurements is the "response design," that is, when the crews get to specific lakes, where and how do they collect samples or measurements for the various indicators? This will be

Indicators used in the NLA are selected to assess status related to trophic state, water quality, the condition of biological assemblages, physical habitat condition, and human use (**Table 1**). The set of selected indicators are intended to be most appropriate for the assessment of lake condition at regional and national scales. Indicators range from direct measurements of specific variables to more complex

The target population (i.e., the set of lakes about which inferences are to be made) for the NLA includes all natural lakes and ponds, reservoirs, and man-made ponds within the conterminous USA (i.e., the "lower" 48 states) that are greater than 1 hectare (ha) in surface area, are permanent waterbodies, have an estimated

day of sampling. An early decision was made to sample lakes as a finite resource and provide estimates of "lake number" and "proportion of lake number" rather than as "lake area" (although areal estimates can also be made with the NLA data). The NLA design requires some level of stratification or unequal sampling probability to accommodate regional variation in the abundance of lakes, and the preponderance of small lakes [22, 23]. A simple random sample will be dominated by small lakes (less than 4 ha), and the bulk of lakes sampled will be in the Upper Midwest where lakes are most abundant. Because of the desire to make both national and regional estimates, care is taken to spread the sample across the conterminous USA and across the size range of lakes available. For regional coverage, variable selection probabilities are set to ensure the ability to describe conditions in all 10 EPA Regions [24], 9 aggregated NARS ecoregions (**Figure 1**) [25] and roughly 15 hydrologic basins. Variable selection probabilities are also set to ensure that the NLA samples are spread across the size range of lakes so that small lakes do not dominate the sample. Samples are currently allocated among 5 lake surface area categories: 1–4, 4–10, 10–20, 20–50 ha, and greater than 50 ha. Each site sampled receives a "weight" inversely proportional to its probability of inclusion in the sample. The weights are then used to make the inferences from

of open water on the

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#### **Table 1.**

*Indicators and sampling locations for the national lakes assessment.*

#### **Figure 1.**

*Distribution of lakes sampled for the 2012 National Lakes Assessment. Circles represent sites selected as part of the probability-based survey design. Squares represent lakes hand selected as additional candidate "leastdisturbed" reference sites for use in assigning lake condition categories. Aggregated ecoregions are based on Omernik level 3 ecoregions.*

sites sampled to the entire target population of approximately 112,000 lakes targeted by the survey within the conterminous USA. The spatial distribution of sampled lakes in the 2012 survey is shown in **Figure 1**. For more details on survey designs as applied to aquatic resources, see [21, 26–30].

#### **3.3 Response design**

The way in which an individual lake is sampled for the various indicators is considered the "response design" [19]. In some cases, as with water samples, this is rather simple. For other indicators, such as physical habitat indicators, the response

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design is more complex. The NLA consists of two response designs at each lake. A standard single station located at approximately the deepest point in the lake (or midpoint of a reservoir) is used to collect (1) a depth profile of temperature, dissolved oxygen, pH, and conductivity; (2) surface water samples for chemical analyses and phytoplankton; (3) vertical plankton net tows to collect zooplankton; and (4) a sediment core sample. These samples result in data on zooplankton, chlorophyll *a*, acid neutralizing capacity (ANC), conductivity, total nitrogen, total phosphorus, anions/cations, dissolved oxygen, water transparency, temperature, pH, cyanobacteria, atrazine, sediment mercury (total and methyl), and microcystin. Riparian and littoral zone observations are collected at 10 equally spaced locations around the lake perimeter. Benthic macroinvertebrate samples are also collected at these littoral sites around the lake. Details of the collection process can

be found in [29] and a similar document tied to each lake survey (**Table 1**).

The methods for the NLA are described in great detail in its supporting documentation (e.g., see [30–34]). A brief summary of critical elements of the approach

The NLA has developed field protocols intended to be applied consistently at all lakes and reservoirs sampled. This is in contrast to the approach implemented in the European Union to accomplish the objectives of the Water Framework Directive, which employs various methods to arrive at analogous assignments of water body condition (e.g., see [35]). The NLA protocols are also designed to be implemented by field crews who are not all experienced limnologists or aquatic biologists. Many (80–90) field crews (comprised of state and contractor crew employees) are required to sample the selected lakes during a summer sampling window (index period) from June through September. It is important to note that inferences made from the data are estimates of condition found during that index period and do not apply, necessarily, to other parts of the year. In essence, these are "snapshots" of conditions in the lake population during the summer growing season. Standardized

field and laboratory protocols are used to collect and process the samples.

of known and adequate quality to be used in the assessment (e.g., see [33]).

Standardized field forms, either paper or electronic, are used by the crews to record measurements and observations. The samples that are collected are sent to processing laboratories for analyses. The field and laboratory data are sent to a central repository for inclusion into the data sets (see [30] for details). A comprehensive quality assurance program is developed and implemented for all field, laboratory, data analysis, and data management activities in the NLA to ensure that results are

For the benthic macroinvertebrate and zooplankton samples, a comprehensive analysis and evaluation process was used to construct a multimetric index (MMI) of biological integrity for that assemblage. The process was based on general approaches described in [36, 37]. Metrics were developed using autecology information, taxonomic composition, taxonomic diversity, functional feeding groups, habitat preferences and tolerance to disturbance. The rationale and descriptions for

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

**4.1 Data acquisition (field and laboratory)**

**4.2 Indicator development and evaluation**

each of these indicators can be found in [30, 38–42].

**4. Methods**

follows.

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

design is more complex. The NLA consists of two response designs at each lake. A standard single station located at approximately the deepest point in the lake (or midpoint of a reservoir) is used to collect (1) a depth profile of temperature, dissolved oxygen, pH, and conductivity; (2) surface water samples for chemical analyses and phytoplankton; (3) vertical plankton net tows to collect zooplankton; and (4) a sediment core sample. These samples result in data on zooplankton, chlorophyll *a*, acid neutralizing capacity (ANC), conductivity, total nitrogen, total phosphorus, anions/cations, dissolved oxygen, water transparency, temperature, pH, cyanobacteria, atrazine, sediment mercury (total and methyl), and microcystin. Riparian and littoral zone observations are collected at 10 equally spaced locations around the lake perimeter. Benthic macroinvertebrate samples are also collected at these littoral sites around the lake. Details of the collection process can be found in [29] and a similar document tied to each lake survey (**Table 1**).
