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pH

The pH of a lake or stream is a very important WQ parameter. Not only can pH directly affect aquatic life, it also controls other factors such as heavy metals that also impact aquatic habitats. The water quality standard for Wisconsin requires surface waters to be within a pH range of 6.5 – 9.0.

The pH of a stream is important because Many organisms are sensitive to relatively small changes in pH (> 0.5 units). Fish are unable to properly regulate salt concentrations within their bodies and essential suffer from osteoporosis when water drops to pH 5.5-5.0. Minnows and insect larva are especially sensitive to the effect of pH, and because these organisms support the entire aquatic food web, their pH sensitivity can have a dramatic effect on an entire ecosystem.

But pH does not always directly affect aquatic organisms—it can have indirect consequences too. For example, pH controls the solubility of potentially toxic metals such as aluminum. In neutral solutions, aluminum is “tied up” as an insoluble salt. At pH 5, however, aluminum becomes more soluble and bioaccumulates within aquatic organisms. Historically, this has been the basis for many of the problems associated with acidification of lakes and streams in Midwest and Northeast of the US.

Temperature

Temperature is another basic water quality parameter, but it is a bit complex because there is no single water quality criteria for temperature. Instead, temperature criteria are set based on whether the water body supports either a warm- or cold-water fishery. Generally, warm-water fisheries have an average daily summer temperatures >70oF (21 oC) and support warm water fish species like sunfish and largemouth bass. On the other hand, cold-water fisheries are generally <70 oF in the summer and are able to support trout and salmon populations.

Dissolved Oxygen

Molecular oxygen (O2) is required for the survival of nearly every living organism, even plants. While there is a significant amount of O2 in the atmosphere (21%), water can only contain a small amount of oxygen, making dissolved O2 (dO2) a very important water quality parameter.

Oxygen enters a water body through wave action caused by wind or through mixing of air and water caused by riffles in streams. In some instances, groundwater discharge can also contribute a significant amount of dissolved oxygen to a stream. The amount of oxygen dissolved in water is highly temperature dependent and therefore, has both a seasonal and a daily cycle. Cold water can hold more dissolved oxygen than warm water, so we tend to see higher dO2 levels in winter and early spring, when the water temperature is low. Conversely, in the summer and fall, dO2 levels are lower because the water temperature is typically higher.

The State of Wisconsin requires a minimum level of dO2 of 5 ppm in surface waters at all times. DO2 levels lower than 5 ppm are considered stressful for fish, while levels less than 3mg/L are too low to support fish populations. Low oxygen levels are usually caused by bacterial decomposition of organic matter. Sewage, industrial waste, or simply dying aquatic plants and algae provide food for bacterial populations, which in turn consume the dissolved oxygen resulting in a “dead zone”.

Turbidity

Turbidity describes the amount of suspended solids in a water sample, which makes water appear cloudy. Suspended solids are either abiotic materials like clays and silts, or they are living organisms such as algae and plankton. We often use turbidity as an indicator of increasing erosion within a watershed, and while this can be caused by land use practices such as construction and agriculture (including forestry), erosion is also a natural result of streambed channeling and development. Therefore, high turbidity levels do not necessarily indicate poor water quality and must be evaluated along side other water quality parameters.

While the obvious result of turbidity is simply cloudy water, turbidity also has a major, secondary impact on water quality—specifically the level of dissolved oxygen available for the aquatic ecosystem. Suspended particles can affect dO2 levels in two ways.

First, turbid water absorbs more solar radiation than clear water and increases water temperature. In turn, higher water temperature reduces the amount of oxygen that can dissolve in the water. This effect is also compounded by the fact that turbid water reduces the amount of sunlight penetrating into the water column, limiting the amount of photosynthetic oxygen being produced by aquatic plants and phytoplankton.

In addition to the temperature effect of turbidity, suspended solids are able to make nutrients, especially phosphates, more biologically available to aquatic algae. Algae growth is often limited by available phosphates keeping their growth ecologically balanced. Excess phosphates often cause algae blooms, and when they die, their decomposition consumes the available oxygen causing dO2 levels to drop.

Chloride

Chloride is a natural element found in a variety of sources and is necessary for normal biological function in all organisms. Many water quality programs in Wisconsin and Minnesota have begun to monitor chloride out of concern over road salt use, which is starting to impact surface waters in more urban areas. While road salt is an obvious chloride source, chloride is also an indicator for other land-use
practices affecting local watersheds. Leaky septic systems, poor manure management, and water softener discharges are all factors that contribute to chloride levels.

Chloride concentrations in freshwater naturally range between 0-100 ppm. State standards for chloride in surface water are quite variable and set based either on the aesthetics of drinking water (250 ppm Cl-, which is when water begins to taste salty) or on exposure levels associate with long-term toxicity to aquatic organisms (395 ppm for WI, 230 ppm for EPA). In general, chloride has a negative impact on all aquatic organisms, but it seems to have a greater affect on planktonic communities which support the entire aquatic food web. Chloride is a highly mobile contaminant and can also enter groundwater reserves used for drinking water supplies. Once present in drinking water, it can only be removed using reverse osmosis systems which are prohibitively expensive to implement in public water supplies.