The following data was collected by students involved in programming at the Bayfront Center for Maritime Studies as well as schools that participated in the Environmental Rediscoveries program.
June 2000
July 2000
August 2000
September 2000
October 2000
Each water quality parameter that is measured indicates something important about the ecosystem of Presque Isle Bay. Each of these factors are limiting, that is, each has a maximum and a minimum value, above or below which life for many species cannot continue. The four parameters (temperature, dissolved oxygen, conductivity and pH) were measured using a Hydrolab®.
Temperature directly affects the rate of biological activities. Every organism has an upper and lower tolerance limit for temperature and a certain temperature range that they prefer. Most organisms will try and remain near the center of their range. Water forms temperature layers at different depths through a process called thermal stratification; however Presque Isle Bay does not stratify and the temperature is relatively uniform throughout. Lake Erie does stratify. The upper, warmer layer is the epilimnion; the layer of transition from warmer to colder waters is the thermocline (represented by a drop in temperature of 1°C for every increase in depth of 1 meter); and the lower, colder layer is the hypolimnion, which has a relatively uniform temperature. A rapid increase or decrease in temperature can have a negative impact on aquatic life.
Dissolved oxygen: Oxygen is one of the most important environmental factors in aquatic systems. The atmosphere contains approximately 20 percent oxygen in the gaseous state but is typically found in lower amounts in aquatic environments. The oxygen found in the water is dissolved in solution and therefore is less available to the organisms. The relative amount of dissolved oxygen in aquatic environments is measured in parts per million (ppm). The amount of dissolved oxygen in the water can potentially become a limiting factor for many organisms. For example, most fish need dissolved oxygen levels of 6 ppm to survive, however, some species like carp and catfish can survive at levels as low as 4 ppm.
Conductivity is directly related to the amount of chemical ions in the water. Dissolved solids present in the water exist as ions and their solution can conduct an electrical current. A high conductivity reading implies that there are a lot of ions present in the water and is associated with fertile lakes; a lower conductivity implies fewer ions present and is associated with relatively infertile lakes. Metals such as aluminum, copper, magnesium and mercury exist as ions in the water. The higher the conductivity reading, the higher level of metals that will more likely be found. The conductivity does not say which metals are present, simply that there are metal ions in the water.
pH expresses the concentration of hydrogen ions in an solution on a scale that runs from 0 to 14. On this scale 7 is neutral; below 7 is acidic; and above 7 is basic. The scale is exponential; i.e., the concentration of hydrogen ions at pH 6 is actually 10 times that of pH 7. An example of a basic solution is Alka-Seltzer dissolved in water. It has a pH greater than 7.0 since it is composed of sodium bicarbonate, a basic substance. It is used to neutralize the acid in your stomach which has a pH well below 7.0. Aquatic organisms can be very sensitive to pH fluctuations, with most aquatic organisms preferring a pH around 7. Some fish species can tolerate pH levels as low as 5.0; however, most do best in ranges of 6.5 to 9.0. Mayfly nymphs are very sensitive to pH, if the pH were to drop as low as 5.0 it could wipe out their entire population.