What are indicator organisms?

Scientists can help their communities better understand what’s in the water around them. When sewage leaks into lakes and rivers, the public can be exposed to harmful bacteria. Pontchartrain Conservancy monitors for fecal contamination by measuring three different indicator organisms: Enterococcus, Escherichia coli, and Fecal Coliform.

Indicator organisms allow for a reliable, safe, and easy assessment for the presence of fecal matter that could be present in water. The presence in water of E. coli, and often Enterococci, is direct evidence of fecal contamination from warm-blooded animals. Their presence indicates the possible presence of other pathogens.

The science behind the appropriateness of which indicator to use has evolved, and each method of quantification has its pros and cons.  In the 1960s, the U.S. Public Health Service recommended using fecal coliform bacteria as the primary indicator of water quality.  In 1968, the National Technical Advisory Committee translated the total coliform level to 400 fecal coliforms per 100 mL based on a ratio of total coliforms to fecal coliforms and then halved that number to 200 fecal coliforms per 100 mL.

In 2012, the US EPA published the 2012 Recreational Water Quality Criteria (2012 RWQC) which noted that the presence of fecal coliform bacteria are poor measures for the prediction of illness. This document establishes criteria for marine waters (Enterococcus) and fresh water (Enterococcus or E. coli).   

Risks

Water pollution caused by fecal contamination is a serious public health threat when recreating (primary contact recreation criteria). Fecal contamination can cause nausea, upset stomach, ear-aches, and rashes in swimmers. In worst case scenarios, it can even affect boaters who have limited direct contact with the water (secondary contact recreation). Failing infrastructure, wildlife, and even pets can be sources of fecal pollution.

Comparison of Measured FIB to Risk

EPA's evaluation of the bacteriological data indicated that using the fecal coliform indicator group at the maximum geometric mean of 200 per 100 mL recommended in Quality Criteria for Water would cause an estimated 8 illness per 1,000 swimmers at freshwater beaches and 19 illness per 1,000 swimmers at marine beaches. For historical comparisons, we continue to count sample fecal coliform densities for reference only.

The US EPA now recommends the use of Enterococcus as an indicator organism, which has been codified by the State of Louisiana for assessments. For primary contact recreation, defined as the recreational period of May 1 through October 31, the geometric mean density shall not exceed 35 colonies/100 mL, and no more than 10 percent of the individual samples in the data set shall exceed 130 Enterococci colonies/100 mL.

Pontchartrain Conservancy now utilizes the Beach Action Value (BAV), described in the 2012 Recreational Water Quality Criteria. The BAV value is a tool for determining a “do not exceed” value for beach notification purposes (such as advisories). For Enterococci, the BAV described in the 2012 RWQC is 70 CFU/100mL.

A Note on Methods

The 2012 RWQC use membrane filtration methods , which utilize a filter paper placed on media to isolate the FIB for counting. The water samples are filtered through a 0.45 µm filter paper and then grown on test-specific media (agar) at set temperatures for 24 hours. Colonies are counted under magnifying glass and reported as Colony Forming Units (or CFUs). These methods count a FIB population in a labor-intensive method that is considered the gold standard.

Pontchartrain Conservancy utilizes an analysis that is in less labor intensive and less costly. A laboratory incubates samples with specialized media, and through a patented method, incubates sealed trays with the sample distributed into water wells and incubated for 24 hours. Wells that contain FIB will fluoresce under an ultraviolet light; these wells are counted and compared to a data table for the Most Probable Number (MPN) of microorganisms.

There are pros and cons to the use of each method. The scientific literature suggests, however, that between the two methods, the MPN method over-estimates the sample population of FIB in water samples. From this standpoint, this method offers both lower cost of measurement and remains a more conservative estimator of FIB counts. While the 2012 RWQC utilizes CFU in the development of criteria, it is important to recognize that we do utilize different methods.

In the 5-year review of the 2012 RWQC, the EPA highlighted the need for molecular or genetic counting of FIB by quantitative polymerase chain reaction (qPCR). Molecular techniques are rapid and allow for day-of counting of FIB and assessment (compared to waiting at least 24 hours for the FIB to grow). The speed of this information, and improvements in both the techniques and capabilities of local laboratories, are likely to improve public health in the future. At some point in the future, there may be a change in the benchmark method for determining water quality safety.

Fecal coliform and Enterococcus are indicator organisms, which act as a proxy for the presence of pathogens.  Ideally, scientists use these microorganisms to assess the pollution of water.  Indicator organisms should be reliably detected in low numbers, rapidly, at low cost, and be non-pathogenic for laboratory technicians to work with. They should also be in greater numbers than pathogens and be unable to multiply in water.

Fecal coliform are considered to be non-spore forming, rod-shaped, microorganisms capable of metabolizing galactose by β-galactosidase – and these bacteria have been used to demonstrate gastrointestinal disease by fecal contamination since John Snow’s cholera study in 1855.

But, EPA studies suggest that fecal coliform is a poor-predictor of gastrointestinal disease, and recommended the use of Enterococcus or Escherichia coli.  E. coli is a common microbial species found in fecal coliform methods, and is more specific to fecal pollution.  Enterococcus is a non-spore forming, spherical bacteria found in the large quantities in the human intestinal tract, and it is a salt-hardy microorganism, and can withstand salt pressure more readily than E. coli or fecal coliform species.

The 2012 Recreational Water Quality Criteria (RWQC) published by the US EPA provided guidance for Enterococcus and E. coli, and the Louisiana Department of Environmental Quality updated the water quality criteria to reflect this change. Pontchartrain Conservancy still samples and analyzes for fecal coliform, but we now only highlight when Enterococcus values exceed the Beach Action Value of 70 CFU/100mL to be consistent with the 2012 RWQC.  You might notice a difference between the values reported when comparing fecal coliform and Enterococcus.  A direct comparison of fecal coliform and Enterococcus isn’t possible, its equivalent to comparing apples and oranges.

If you have further questions, reach out to us at waterquality@scienceforourcoast.org

What is salinity?

Salinity is the measurement of salt dissolved in water. Salinity is usually measured in parts per thousand (reported as “ppt”). The average ocean salinity is 35 ppt: this means that in every kilogram of seawater (1000 grams), 35 grams are dissolved salt. Waters are considered fresh if they have less than 2 ppt.

Because the water in estuaries is a mixture of fresh water and ocean water, the salinity in most estuaries is less than the open ocean. Salinity in an estuary varies based on location in the estuary, the daily tides, and the volume of fresh water flowing into the estuary. However, salinity can also vary with depth: salt water is denser than fresh water. Because of this salt and fresh water may not mix, and salt water ‘wedges’ can form on the bottom of lakes and rivers. In our estuary, salinity levels are generally highest near the Rigolets passes, where flow from the Gulf of Mexico enters, and lowest near the confluence of the rivers on the Northshore, where freshwater flows into Lake Pontchartrain.

How do we measure salinity?

To determine the concentration of salinity, we use a meter that measures the ability of water to conduct a current. This property of water is called conductivity, and it increases with higher concentrations of dissolved ions. Because these conductive ions come from dissolved salts, water with higher salinity will conduct electricity better than water with no dissolved salt. Salinity can also be determined with three other methods: evaporation, titration, and refractometer.

Salinity in the Pontchartrain Estuary

Over the last 30 years that we have been monitoring water quality, the salinity in Lake Pontchartrain has changed. In 1998, the USGS Environmental Atlas for the Pontchartrain Basin reported a mean salinity of 13 ppt, with an increasing trend at the Seabrook Bridge. Since then, salinity in the lake has dropped. Closure of the Mississippi River-Gulf Outlet and openings of the Bonnet Carré Spillway have contributed to a freshening of the salinity across the basin, which averaged less than 1 ppt in 2018. Since 2017, we have observed that salinity decreases when the spillway opens and increases with strong easterly winds.

Salinity will continue to be an important water quality parameter because it can determine what species of fish and plants grow and thrive in an area. Although freshening salinities are changing the distribution of sport-fish and shrimp across the region, reduced salinity in the basin makes cypress plantings and swamp forest restoration possible. Swamp restoration is vital for rebuilding our defense against storm surge.

Why is temperature important?

Because temperature influences almost every other water quality parameter, it is one of the most important abiotic factors in an ecosystem. And considered on its own, temperature can affect the way aquatic plants and organisms metabolize and reproduce. Higher temperatures can result in higher metabolic rates, and that can quickly deplete oxygen in an aquatic ecosystem.

Here's how:

Higher temperatures cause metabolic rates to increase, accelerating both growth and decay of aquatic life. Metabolic rate is the amount of energy an organism expends over time, and as it increases so too does the amount of oxygen an organism requires. Decomposition is also demanding of oxygen. Further compounding this effect, higher temperatures make it harder for oxygen to dissolve in water meaning there is less available oxygen for aquatic life. So in an environment where both growth and decay are accelerated, and oxygen is not as readily dissolved into water, the concentration of DO can fall precipitously.

Additionally, extreme temperatures above 35°C, can begin to breakdown the biological enzymes necessary for a functioning metabolism. If broken down, aquatic organisms will be less able to process nutrients, and likely die. A drastic change in temperature can also affect the survival of eggs and nymphs.

What can change temperature?

Natural mechanisms and human actions can influence the temperature of an aquatic ecosystem.

Natural sources, such as sunlight radiation and the atmosphere can transfer heat to a water body. While sunlight transfers thermal energy into a water body, the atmosphere can absorb heat from or transfer heat into water, depending on the difference in temperature. If the waterbody is warmer than the air, heat will be pulled out of it and into the atmosphere. If the scenario is flipped and the ambient temperature is warmer than the water body, heat will be transferred into the water. Depending on the amount of their flow, tributaries feeding warmer or cooler water into a lake can also cause changes in temperature.

Human influence on water temperature usually comes as discharge from industrial and municipal facilities. For example, a power plant must cool generation equipment overheating during the production of electricity. Often, they pull water from a nearby source like a stream or river, to absorb heat and cool it down. As a result, the water cools the power plant equipment, but it returns to its original source warmer. The introduction of even slightly warmer water into a cooler aquatic environment can produce the negative consequences mentioned previously.

A similar example includes storm water runoff from parking lots, or areas paved with asphalt. On hot summer days, afternoon rain showers can carry heat away from these surfaces and into nearby waters.

What is water visibility?

Water visibility is a measure of how far down light can penetrate through the water column. Clear waters are characterized by low concentrations of suspended soil particles and/or algae, whereas turbid waters are marked by high levels of suspended particles that cloud visibility by absorbing and scattering light. Because water clarity is closely related to light penetration, it has important implications for the diversity and productivity of aquatic life that a system can support.

For example, clearer water allows more sunlight to reach submerged aquatic vegetation. The vegetation, in turn, produces oxygen, provides habitat for fish and shellfish and provides food for waterfowl, fish and mammals. Additionally, clear waters are generally valued for aesthetic and recreational purposes. Water clarity can vary naturally due to tides, storm events, wind patterns and changes in sunlight.

Why do we measure water visibility?

When human activities upstream and in the watershed increase soil erosion and nutrient inputs beyond natural conditions, water clarity can be reduced. In addition to limiting the appeal of waters for swimming and other recreational uses, the sediments and nutrients that reduce clarity can also be harmful to aquatic ecosystems by smothering nearshore habitats, burying benthic communities and changing algal growth patterns.

Turbidity in the Pontchartrain Estuary

In the past, we've seen increased turbidity play a critical part in destroying the health of Lake Pontchartrain. In fact, the lake's condition was the catalyst for the creation of our organization. Clamshell dredging negatively impacted the ecology of the lake in two ways. First, the act of dredging stirred up settled solids like sand and silt, re-suspending them in the water column and increasing turbidity. Second, it removed the lake's main filter feeder, the Rangia Clam. Rangia clams are crucial for preserving the lake's water clarity because they filter water and scrub it for nutrients. Anything abiotic, like sediment, is expelled from the clam and coated in a slime film. The film coating weighs the abiotic particles down, making them settle faster and reducing turbidity in the lake.

Currently, we are trying to fully understand the effects that opening the Bonnet Carrée Spillway has on the water quality of the lake. When the Army Corps opens the control structure, fresh and muddy Mississippi River water flows into the Pontchartrain Estuary. We know this will cause changes in the composition of the water, that are measurable through the water quality parameters we monitor. We collect water quality data year-round to help surrounding communities better understand the changes seen in the Lake Pontchartrain Estuary.

How does PC measure water visibility?

We utilize a tool called a Secchi disk. A Secchi disk is a black and white disk that is lowered by hand into the water to the depth at which it vanishes from sight. The distance to vanishing is then recorded. The clearer the water, the greater the distance.

What is Dissolved Oxygen?

Surprise! There's oxygen in water, and it's not just in the form of H₂O.

We know that oxygen and hydrogen can form a compound called water, but what happens when oxygen is all by itself? Oxygen molecules that are not bonded to any other element are considered "free" or non-compound elements. When free oxygen (O₂) is present in water, we call it Dissolved Oxygen (DO). In its free form, DO is available for fish and aquatic plants to breathe in, much like humans take in oxygen from the air.

Oxygen can be introduced into water through the air or as the byproduct of photosynthesis. From the air, free oxygen can slowly dissolve across the water's surface or enter through aeration (e.g. wind or tide-driven waves, waterfalls, streams). Humans can also increase the amount of DO in a waterbody by aerating mechanically. Such is the case with fish tank air pumps or large dams. Other factors like depth, temperature, and salinity also affect DO concentrations.

Why is measuring dissolved oxygen important?

Dissolved oxygen is a critical resource for aquatic organisms and a necessary ingredient in decomposing biological pollution such as wastewater runoff, monitoring the changes in DO can help inform us of the health of an aquatic ecosystem. A balanced level of dissolved oxygen is important for the organisms living in our water like fish, invertebrates, bacteria, and plants.

Dangerously high levels of DO can occur in areas where forces of aeration are high, like at the foot of a waterfall or near a hydropower dam. Similarly, algal blooms can produce high levels of DO through rapid photosynthesis. Consequently, fish can develop a deadly gas bubble disease. 

Too little DO can also pose a threat to aquatic life. Dissolved oxygen levels can fall drastically in over productive waters. For example, an over productive waterbody may contain more organisms than it can support, or in the case of an algal bloom die off, the rate of oxygen-demanding decomposition may require more DO than available. Likewise, pollution from wastewater and sewage runoff can deplete DO, because it will require free oxygen to decompose. As a result, the area will become anoxic, or without oxygen, and be unable to support most aquatic life.