National Lakes Assessment
by Jeremy Wease, MU Environmental Sciences Senior
The National Lakes assessment (NLA) is a general study conducted every five years by the EPA. The survey examines the current biological, chemical, physical, and recreational lake conditions across the US. This information will provide information about lake degradation on a national scale. The study is also designed to help identify which stressors are most associated with the degradation of biological conditions of lakes. Our lab at the University of Missouri previously participated in the study in 2007, 2012, and 2017.
Lakes are selected randomly using a survey designed to statistically represent the population of lakes in each ecological region (the geographic area in which climate, ecological features, and plant and animal communities are similar). The NLA sampling is comprised of natural lakes, ponds, and reservoirs across the lower 48 states. Starting with the NLA 2012, to be included in the survey a water body had to be a natural or man-made freshwater lake, pond, or reservoir, greater than 2.47 acres (1 hectare), at least 3.3 feet (1 meter) deep, and with a minimum quarter acre (0.1 hectare) of open water. The Great Lakes and the Great Salt Lake were not included in the survey, nor were commercial treatment and/or disposal ponds, brackish lakes, or ephemeral lakes.
Map showing sampling locations and ecoregions for the 2017 National Lakes Assessment effort.
The first step in the NLA survey is to visit the index site, located in the middle of the lake. Here we identify the photic zone of the lake by conducting a Secchi measurement. The photic zone is the top layer of water that receives sunlight. Sunlight is necessary for phytoplankton (algae and cyanobacteria, or bluegreen algae) to photosynthesize. Phytoplankton are important because they make up the base of the food web in lakes. Next, we use a YSI portable water quality sensor to measure dissolved oxygen, pH, and temperature at half meter increments from the surface to the bottom. Dissolved oxygen is essential for the survival of fish and aquatic invertebrates. After that we collect samples for analysis of chlorophyll , water chemistry, phytoplankton species composition, algal toxins, and atrazine.
Lily Ramsay collects a zooplankton sample for the National Lakes Assessment.
With the water sampling at the index site complete, we next sample the zooplankton. The composition of the zooplankton community can indicate the presence of nutrient pollution in the lake. The zooplankton community varies with water quality as some species are more tolerant of poor water quality than others.
After sampling the index site we visit ten physical habitat stations, equidistant around the lake perimeter. Genetic material from various species should be found in the water. For example, a bass releases DNA into its surrounding environment from skin cells and feces. To measure the genetic material, we collect a littoral eDNA sample from the surface of the water. At each station we use a small bottle to suck up surface scums, films and dead bugs present, then combine the water in a 1L bottle. At each station we also collect a benthic macroinvertebrate sample. This sample is collected by dragging a fine-meshed net across the bottom of the lake for one meter. As with zooplankton, the benthic macroinvertebrate community is another indicator of lake health. Benthic macroinvertebrates live on the bottom of the lake. Many types feed on decaying material while others are predators that eat other macroinvertebrates. They are also a good source of food for the fish living in the water. At the final station we collect an enterococci sample. Enterococci are a group of gut bacteria and analysis of this sample will quantify fecal contamination at this station.
The author collects an eDNA sample near the shoreline of a Missouri lake.
After collecting the samples at each station, we record multiple observations about the composition of the land and water near the shoreline. These observations will be checked against the data to help understand which physical characteristics are associated with good and bad water quality.
New to this year’s NLA sampling is fish tissue analysis. The fish tissue samples will be analyzed to determine which chemicals and toxins are found within the lake. This is important because throughout their life a fish’s tissue can slowly accumulate certain toxins. The fish we target are fish that people would typically consume, therefore any toxins found in the fish could be transferred to humans.
Results from the previous NLA effort are available by following the link below. Our lab at the University of Missouri was responsible for collecting Missouri's lake samples.
The author displays a largemouth bass collected for tissue analysis