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Lake Monitoring

Monitoring Other Lake Conditions

Monitoring Sedimentation

Sedimentation problems occur when erosion is taking place in the watershed. Surface runoff washes sand and silt into the lake where it settles to the bottom and creates shallow areas that interfere with lake use and enjoyment. In addition, sediments often carry significant amounts of nutrients that can fertilize rooted aquatic plants and algae.

Citizens can characterize the build-up of sediments by measuring water depth and the depth of unconsolidated (soft bottom) sediments in key areas (mouths of tributary streams or near an eroding shoreline). In this manner, a historical record of sedimentat ion can be developed.

To measure sediment, set up a transect line and sample at specified intervals along it. A basic procedure involves the use of two dowels (probes) about one inch in diameter and long enough to stick above the surface at the deepest point of measurement. Se curely attached to the bottom of one probe is a nine-inch plate (a pie pan works well). Both probes are calibrated in meters and tenths of meters.

Working along a transect line:

  • locate the sample site along a transect;
  • measure and record the depth of the water from the surface to the



    top of the sediments using the probe with the plate on the end;

  • push the other probe into the sediments until first refusal (it becomes hard to push) and measure and record the depth. The difference between the two depths is the thickness of the unconsolidated sediments.



    The number of transects and the location of sites along those transects will be decided by the planning committee. By participating in a sediment recording program, the personnel will gain appreciation that erosion and sedimentation is an important lake management problem. 

    Monitoring Suspended Sediment

    Some of the silt and organic matter that enters a lake does not settle to the lake bottom. Instead it remains suspended in the water. These sus -pended solids decrease water transparency and can affect the suitability of the lake habitat for some species. In addition, solids often carry in signifi cant amounts of nutrients that fertilize rooted aquatic plants and algae.

    Total solids is a term used to describe all the matter suspended or dissolved in water. Total suspended solids is that portion of the total solids that are retained on filter paper after a sample of water is passed through.

    Citizens can monitor the suspended sediment condition by mea suring two parameters:

  • water transparency using a Secchi disk; and
  • total suspended solids.



    The Secchi disk is a instrument that measures water clarity. The reader is referred to Chapter 3 of this manual for a thorough explanation of its use in lake monitoring.

    The concentration of total suspended solids in a water sample is analyzed in a laboratory. Procedures involve the use of a filtering appara tus, a special drying oven that can maintain a constant temperature between 103° and 105° F and a sensiti ve analytical balance capable of weighing material to 0.1 milligrams.

    In most cases, you will take a grab sample just below the surface in an area designated by the planning committee. The sample must be kept cold and shipped to the laboratory as soon as possible after collection to minimize microbiological decomposi tion of solids.

    This monitoring is particularly useful for analyzing trends in sus pended material after storm events. For this reason, the planning commit tee may wish to instruct personnel to sample on a two-week schedule for baseline purposes and then to conduct addi tional sampling after storms. 

    Monitoring Acidification

    A citizen monitoring program that focuses on lake acidification usually examines:
  • pH, a measure of lake acidity status; and
  • alkalinity, a measure of the acid neutralizing capacity of a sub stance.



    The pH is measured on a scale of 0 to 14. The lower the pH, the higher the concentration of hydrogen ions and the more acidic the solution. Acid rain typically has a pH of 4.0 to 4.5. In contrast, most lakes have a natural pH of about 6.0 to 9.0. < P> Alkalinity, or acid-neutralizing capacity, refers to the ability of a solution to resist changes in pH by neutralizing acid input. In most lakes, buffering is accomplished through a complex interaction of bicarbonates, carbonates, and hydroxides in the water. The higher the alkalinity, the greater the ability of the water to neutralize acids.

    Lakes with low alkalinity are not well buffered. These lakes are often adversely affected by acid inputs. After a short time, their pH levels will drop to a point that eliminates acid-intolerant forms of aquatic life. Fish are particularly affected by low pH waters.

    The planning committee can designate pH and alkalinity sampling to occur at the lake's center or at special areas of interest. The depth where samples are taken can vary with program objectives, but one meter is usually sufficient for a general characterization of a lake.

    Sampling should occur from spring overturn until the end of the summer season. Both pH and alkalinity are affected by biological activity; there fore, the planning committee may direct personnel to sample every two weeks. The time of the day that the sam ple is taken should be noted on the sampling form. The pH normally rises during active photosynthetic periods.

    The pH of a lake sample can be easily determined by using a portable, battery-powered pH meter. In general, pH meters are accurate and easy to use. However, they do need to be calibrated at regular intervals accord ing to the manufacturer's instructions. Training on both meter use and calibration is important. A pH meter can also be used in the analysis of alkalinity.

    As an alternative to a pH meter, you can use a pH test kit. To conduct the test, personnel add an indicator dye to a measured amount of water sample. The dye produces a color based upon the pH. Personnel can then compare the color with a standard color of a known pH.

    The pH test kits come in several varieties. Some can test for a wide pH range, others are designed to test narrow ranges. It is best to know the approximate pH of the lake to be sampled and choose the kit best suited to the planning committee's purpose. T he program manager should plan to conduct regular quality control checks because when the dyes age, they sometimes give erroneous results.

    The objectives of the monitoring program, economic considerations, and the data quality requirements of the users will guide the decision on whether to use a colorimetric test kit or a pH meter.

    The other parameter used to characterize a lake's acidification condition is alkalinity. Personnel can measure alkalinity in the field by using a test kit. The procedure involves monitoring the changes in pH of a water sample as an acid is dripped into i t. Personnel calculate alkalinity based on the amount of acid it took to reach an end point pH.

    The end point pH for determining alkalinity varies according to the approximate actual alkalinity of the sample.

    When titrating, the end point pH can be determined in two basic ways:

  • by using a pH meter; or
  • by mixing a standard indicator solution into the sample and watching for a color change that will occur when the desired end point pH is reached.



    There are several kits on the market that can be used to measure alkalinity. Each kit has its own procedures that should be followed carefully.

    As with pH, the objectives of the monitoring program and the data quality requirements of the program customers will guide the decision on which test kit to purchase.

    The Gran analysis method is an alternative technique for charac terizing a lake's acidification condition. Commonly used in scien tific studies of acidic deposition, the method provides information, referred to as acid neutralizing capacity because it includes carbonate, bicarbonate, and hydroxide alkalinity plus the additional buff ering capacity of organic acids and other compounds. 

    Monitoring Bacteria at Bathing Beaches

    A wide variety of disease-causing organisms can be transmitted to humans at bathing beaches. Sources of pathogens include sewage, runoff from animal or wildfowl areas, and even swimmers themselves.

    Because of the risk of waterborne disease, it is good public health practice to test beaches periodically during the swimming season. Public health officials usually monitor for the presence of one or more indicator organisms as part of a regular sampling program. The relative abun dance of an indicator organism found in a water sample serves as a warning for the likely presence of other, more dangerous pathogens in the water.

    The indicator organisms most often used to indicate sanitary conditions at bathing beaches are:

  • fecal coliform bacteria; and
  • enterococcus bacteria. Coliforms belong to the enteric bacteria group, Enterobacteriaceae, which consists of various species found in the environment and in the intestinal tract of warm-blooded animals. Fecal coliforms are the part of the coliform group that are derived from th e feces of warm-blooded animals. The fecal test differentiates between coliforms of fecal origin and those from other sources.



    Enterococcus are a subset of the fecal coliform group. Like fecal coliforms, they, too, indicate fecal contamination by warm-blooded animals. They are useful because they are found only in certain animals. Examination of the ratio of fecal coliform to ent erococcus can, there fore, indicate whether the bacterial pollution is from humans or animals.

    Most public health officials recommend weekly testing of swimming beach areas. Sampling should occur at one or more sampling sites in water three to four feet deep. A sterilized sampling bottle should be prepared by the laboratory.

    The number of sites needed will vary with the length and configuration of the beach. One site is generally adequate if the beach shoreline is 300 linear feet or less. If the shoreline is between 300 and 700 linear feet, a minimum of two sites is recommend ed. A beach shoreline greater than 700 feet requires three or more sample sites.

    There are six steps in most basic procedures:

  • Remove the cap from a sterile collection bottle without touching the inside of the cap or the inside of the bottle.
  • Grip the bottle at the base and plunge it in a downward motion into the water to a depth of 12 to 18 inches.
  • Using a forward sweeping motion (so water is not washed over the hand into the bottle), invert the bottle and bring it to the surface.
  • Empty it slightly to leave approximately one inch of air at the top.
  • Re-cap the container, then label and store it at a temperature between 39° and 45° F.
  • Transport the bottle to the laboratory as soon as possible after sampling.



    Sampling for bacteria at beaches should be conducted under the auspices of the local health department. Analysis should be done at a certified laboratory. If a problem is found, program officials should notify health authorities for follow-up testing and mitigation activities.

    The sampling protocol for monitoring bacteria concentrations at natural bathing beaches will also vary according to program objectives and the requirements of data users who, in many instances, are officials of the local health department. Most health dep artments have strict criteria and procedures that must be followed when sampling for indicator organ isms like fecal coliform or enterococcus bacteria. The  sampling protocol, therefore, must follow the protocol used by the health depart ment.