Monitoring Components Overview
In order to obtain sufficient data about a waterbody, water quality monitoring must be conducted at least once per month from April or May through October or November. During each of these monitoring trips, the following data is collected:
Water Clarity (Secchi Disk)
Water clarity is one of the most fundamental aspects of lake health because it suggests the abundance of algae and therefore the abundance of nutrients in the lake. In addition, water clarity determines the depth of warming by sunlight and therefore the process of seasonal thermal stratification.
Water clarity is measured at the deep spot using a Secchi disk and a view scope.
Several parameters are measured at the deep spot in the lake at one-meter depth increments from the surface to the lake bottom.
- Temperature – causes thermal stratification, that is, the layers of upper warm water and deeper cooler water. This layering is a fundamental aspect of lakes that governs many of the important processes that occur over the course of a year.
- Dissolved Oxygen – the amount of dissolved oxygen in the water directly influences nutrient concentrations. When dissolved oxygen in the bottom water falls below 1mg/L (becomes anoxic), the process of internal loading occurs, in which nutrients previously trapped in the bottom sediment are released into the water.
- Conductivity (conductance) – measures the concentration of all ionic materials in the water, derived from watershed weathering and runoff. Conductance is an indirect way of estimating the influence of both stormwater runoff and septic system effluents, as both sources are rich in salts that contain the ions that are factored into the conductance value. Conductance is not a trophic indicator because it does support algae and plant growth.
- Light, pH, and Oxydation Reduction Potential – additional secondary parameters that help determine water quality and lake health.
In most cases, nutrients are the primary factor used for determining water quality. High levels of nutrients such as total phosphorus and total nitrogen lead to an increase in plant and algae growth and a decrease in water clarity.
Water samples are collected at specific depths, usually the top, middle, and bottom of the water column at the deep spot in the lake. The samples are analyzed for the presence and concentration of nutrients such as total phosphorus, total nitrogen, and ammonia.
Planktonic algae are microscopic organisms that are suspended in the water column and, at high concentrations, cause a greenish tint to the water. Algae flourishes in water with high phosphorus concentrations.
Algae samples are collected using a 3-meter integrated sampler. The samples are later analyzed to identify algae species and count the concentration of algae within the sample.
Zooplankton are microscopic organisms that are found in both saltwater and freshwater ecosystems. They are an important component of lakes because they consume some species of algae and because they are a vital food source for many species of young fish.
Plankton samples are collected using a fine-mesh tow net. Back at the lab, the plankton species within the samples are identified and counted.
Aquatic Plant Survey
Aquatic plant surveys are vital for identifying the presence and abundance of plant species in the lake and, most importantly, searching for invasive species. It is important to survey the lake regularly because the earlier an invasive species is discovered, the easier it is to eliminate from the lake.
During an aquatic plant survey, the entire shoreline of the waterbody is observed out to the depth at which plants stop growing. Species abundance and density assessments are made along the length of the shore.