Stream Chemistry Monitoring
Stream chemistry can be monitored for a variety of reasons. Ensuring human health, recreational opportunity, and wildife/environmental health are most common. It is often important to do monitoring before a problem is detected, so that changes can be detected if they do occur. Without background monitoring data, small changes may not be noticed until they grow in magnitude and become problems that pose serious risk and are more difficult to correct. If a specific issue is suspected, the testing becomes more focused and a network of monitoring sites may need to be established to determine the source of the pollutant.
A challenge of chemical monitoring is that pollutants in streams can be elusive. Some pollutants may be flushed into streams during only the first part of a rain event. Illegal discharges may occur only periodically. Pollutants that enter streams through improper sewage connections may only be detectable during dry periods. Water resource managers devise testing strategies to try to test for these elusive pollutants.
The simplest sampling strategy is carefully timed grab samples. Grab samples are one-time water samples captured by hand or perhaps an extendable pole with a cup on the end. The sample represents water from only one point in time. Automated equipment can be used to collect composite samples that integrate water over a longer period of time. Composite samples are a mixture of mini-samples taken at a specified time or flow interval. This integrates water captured, say, throughout a storm event.
Some typical parameters that are monitored in streams include:
pH is a measure of how basic or acidic the stream water is. Fish and other organisms require a pH range of 6.5 to 9.0 in order to be viable.
Conductivity is a measure of electrical conductivity based on the amount of dissolved matter (organic and inorganic) in stream water. High readings usually mean that the stream is receiving inputs from non-natural sources such as storm water runoff, failing septic systems, or agriculture.
Turbidity is a measure of solids suspended in the water. It is similar to total suspended solids, but is measured differently. Turbidity is measured by passing a beam of light through a water sample and measuring how much of that light is deflected by particles. Higher turbidity levels indicate poor water clarity. Minimally impacted streams in this ecoregion have a mean turbidity of 7.1 NTU.
Total Suspended Solids (TSS) is a measure of the amount of solids suspended in the water. TSS is composed of organic and inorganic materials suspended in the water column, and is measured by filtering the water and weighing the material filtered out. TSS is similar to turbidity because both are estimates of suspended particles. However, because turbidity measures the light-scattering characteristics of suspended materials and TSS measures their weight, these two water clarity measurements may yield different results.
Volatile Suspended Solids (VSS) is primarily the organic portions of the TSS, such as algae and detritus, and is often expressed as a percentage of TSS. If a large percentage of the TSS is volatile, algae and organic lake sediments dominate suspended materials.
Dissolved Oxygen is important for aquatic life and integral in several chemical processes. Ideally, dissolved oxygen levels fluctuate between 8 mg/l and 12 mg/l. If dissolved oxygen falls below 4 mg/l, fish kills can occur and phosphorus may be chemically released from sediment. Warm water temperatures and excessive decomposing organic matter both contribute to lower dissolved oxygen levels.
Total Phosphorus is a nutrient that is often the limiting factor in plant growth. Sources of phosphorus include decomposing organic matter, fertilizers, septic systems, animal wastes, eroded sediments, natural sources, and others. A single pound of phosphorus can result in 500 pounds of algae growth.
Chloride is a good indicator of human impacts on water resources because it is stable (not consumed in chemical or biological reactions), highly soluble, relatively unavailable from minerals in the quartz-rich Anoka Sand Plain Aquifer, and is commonly found in man-made substances such as cleaning products, certain fertilizers, and untreated sewage. Road salts are a widespread source of chloride contamination. Chlorides are a threat to stream biota at levels above about 230mg/l. Chloride is generally not itself a health threat to humans, but can be an indicator of other, more dangerous pollutants.
Salinity is a measure of dissolved salts. High salinity measurements may be the result of inputs from sources such as failing septic systems, spring runoff from roads and/or farm field runoff.
Temperature is needed to correct for other parameters. Aquatic life is also affected by temperature.
Fecal Coliform Bacteria are a group of microorganisms that live in the intestines of warm-blooded animals and are associated with feces. They are measured as an indicator of potential health risks to those exposed to the water.
