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National Lake Assessment - 2012

NLA sites across the nation

National Lake Assessment (NLA): This was EPA's second snapshot of the condition of the nation's lakes was completed this past summer. Oklahoma has 32 of the over 900 included lakes nationwide. The Lakes team wrapped up the field sampling component for the 2012 National Lakes Assessment in mid-September. The next phase of the project is lab analysis which will be conducted in 2013 by various laboratories across the country, followed by the reporting process in 2014. For more information visit EPA’s NLA web page or thier fact sheet.

The first survey of this kind was performed by the OWRB on 35 Oklahoma lakes in 2007 (EPA 2007 Results Fact Sheet) which also included a state funded component.

NARS
EPA has other similar aquatic surveys ongoing and planned through 2015 collectively known as the National Aquatic Resource Surverys (NARS). These probability-based surveys are all conducted in collaboration with the states and tribes to broadly assess our nation's lakes, rivers & streams, coastal waters, wetlands, and fish tissue collections. - learn more...

What is NLA?
The NLA 2012 was a probabilistic statistical assessment of the condition of our nation’s lakes, ponds (2.5 acre min.), and reservoirs that is designed to:

  • Establish a baseline to compare both future surveys for trends assessment and evaluate change since the 2007 NLA;
  • Help build State and Tribal capacity for monitoring and assessment and promote collaboration across jurisdictional boundaries;
  • One of a series of National Aquatic Resource Surveys (NARS) being conducted by EPA, states, tribes, and other partners;
  • Generate statistically-valid reports on the condition of the nation’s water resources and identify key stressors to these systems.
  • Oklahoma drew 32 lakes for this round of probabilistic sampling. The number of sample lakes varies greatly between states (see National Map).

What were the goals of NLA?
Address two key questions about the quality of the nation's lakes, ponds, and reservoirs:

  • What  percent of the nation’s lakes are in good, fair, or poor condition for key indicators of trophic state,  ecological health, and human use (i.e. recreation)?
  • What is the relative importance of key stressors such as nutrients?

What was measured?
Trophic Indicators:

  • Chlorophyll-a
  • Secchi depth
  • Temperature, pH, and dissolved oxygen
  • Water chemistry (i.e. hardness, redox, conductivity)

Ecological Integrity:

  • Macroinvertebrate assemblage (insect species etc. present)
  • Macrophyte assemblage (plant species present)
  • Habitat characterization
  • Phytoplankton assemblage
  • Sediment diatom assemblage
  • Sediment mercury
  • Zooplankton assemblage

Human Use Indicators

  • Algal toxins (microcystins)
  • Triazine pesticide screen

A comparison of the 2007 and 2012 survey measurements:

2012 NLA Survey
2007 NLA Survey

Phytoplankton, Chl-a & Algal Toxin taken at Index Site and littoral station J

Phytoplankton, Chl-a & Algal Toxin taken only at Index Site

Zooplankton nets: 50 & 150 µm
Standard 5 meter tow length

Zooplankton nets: 80 & 243 µm
Tow length dependent on depth

Macrophyte Assemblage Characterization

Not performed in 2007

Dissolved Organic Carbon and Isotope samples at select lakes

Not collected in 2007

Triazine pesticide screen

Not collected in 2007

Nutrients sample (separately acidified)

Not collected in 2007

NO Fecal Indicator Collected

Fecal Indicator = Enterococci

 




using a zooplankton tow net sediment colletion

National Lake Assessment 2007

In 2007, the Oklahoma Water Resources Board participated in the National Lakes Assessment by sampling thirty-five probabilistic sites. Headquarter 106 monies were leveraged with regional funds for eighteen additional sites allowing a state level survey. The bulk of the entire probabilistic survey included Beneficial Use Monitoring Program lakes (30/53). The Environmental Protection Agency provided many beneficial facets for participating in the survey. One of the key areas was building capacity for improving the monitoring program at the state level. Because the majority of lakes that were sampled by the probabilistic survey were BUMP lakes, the demonstration allowed for long-term BUMP monitoring data to be compared to the data from the survey, an inventory of the lakes within the twelve ecoregions of the state, and biological parameters and data to be added to the assessment of the state's waters. Oklahoma is looking to the future with the possibility of using the data for further development of nutrient and biological criteria, re-evaluating the water quality standards for these waters and incorporating new parameters into the established monitoring program.

Oklahoma State Lakes Survey

Concurrently, a similar statewide survey was conducted, the Oklahoma State Lakes Survey. This probability based survey collected samples representing lakes, ponds and reservoirs 10 acres in Oklahoma. The Oklahoma State Lakes Survey (OSLS) represents the first time 100 percent of the state’s lakes have been assessed in any fashion. The Oklahoma Water Resources Board (OWRB) estimates the bodies of water in this category at approximately 3,056 lakes, ponds and reservoirs within the State of Oklahoma, with a cumulative surface area of approximately 671,777 acres. The OSLS was patterned after and executed in conjunction with U.S. Environmental Protection Agency’s (EPA) National Lake Assessment (NLA). The EPA added 18 additional lakes to the 35 Oklahoma lakes already in the national draw. This made for a statistically robust state level probabilistic survey while following NLA methods with few exceptions. Because of the expansion of the probabilistic survey to more than 50 lakes, water quality status could now be inferred within at least a 95 percent confidence (complete report...).

   

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Page last updated: December 16, 2013

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