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Disinfectant Byproducts Are the Most Common Water System Violations

In 2016, there were 2,733 public water supply systems in Missouri. In the previous post, I reported that 94.7% of the population received water from suppliers that had no violations of safe drinking water standards during the year (it has decreased from 95.7% in 2012). This means that 5.3% of the population was served by systems that did have a violation. As Missouri’s population in 2016 was 2,093,000, that means that almost 111,000 people were served water systems that had a violation during the year. This post looks into the nature of the violations.

In 2007 and 2010 there was an increase in the population affected by a violation. The cause in 2007 was an error in backwashing a filter at the Missouri American Water Company South Plant in St. Louis County. The error caused a spike in turbidity that lasted four minutes. During that time the water reached an estimated 24,578 customers, though no reports of illness were associated with this event. Even though only some customers were affected, federal documentation rules require that the entire service population be reported as exposed. In 2010, “the same phenomenon happened again.” (2012 Annual Compliance Report of Missouri Public Drinking Water, p. 4)

A violation does not indicate that public health was affected, but it creates the potential for a public health impact to occur. For this reason, violations are important administrative markers. The DNR monitors two broad kinds of violations. Water contaminants (chemicals and bacteria) can exceed their respective maximum concentration levels (health-based standards), or a water system can fail to meet adequate administrative standards (most often not performing and reporting the water quality tests required by law).

Figure 1 at right shows the percentage of the population served by community water systems that had different types of health-based violations in 2016. Violations of the Stage 1 & 2 DBP Rule were by far the most common, affecting about 3% of the population. (In the chart, Excel has rounded to the nearest full percent.) Figure 2 compares the data for 2013 and 2016.

(For larger view, click on figure.)

Figure 1. Data source: Missouri Department of Natural Resources, 2016.

Figure 2. Data source: Missouri Department of Natural Resources, 2016.

 

 

 

 

 

 

 

 

 

 

In previous years, the most common type of violation had to due with coliform bacteria. The text of the report indicates that in 2016 coliform contamination continued to represent the most common kind of violation. However, as shown in Figures 1 and 2, violations of the Stage 1 & 2 DBP Rule affected more of the population than did coliform contamination. Let me explain what this means.

Coliform bacteria are a family of bacteria that live naturally in the soil, and which also live naturally in the guts of many animals, including humans. Consequently, it is not uncommon for some coliform bacteria to get into water supplies. Most coliform bacteria are safe, but a few species of coliform bacteria (including some E. coli) can cause illness in humans. In addition, because they live in great numbers in the guts of humans and animals, their presence in large numbers serves as a sign of fecal contamination. Human and animal feces contain many species of harmful bacteria, and the presence of too many coliform bacteria serves as a marker that these other bacteria might be present, too.

Over the years, the EPA has lowered the maximum allowable level of coliform bacteria concentration in drinking water, and water systems have had to increase their treatment of the water to kill the bacteria. The treatment usually occurs in stages. Unfortunately water often contains organic matter, such as algae or dissolved plant material. If the water treatment is not done properly, the chemicals used to kill the bacteria react with the contaminants to form byproducts that can also be harmful. The Stage 1 & 2 DBP (Disinfectants and Disinfection ByProducts) Rule requires water systems to monitor the level of such byproducts in their water. Thus, it may be because water systems are using additional treatment to kill bacteria that decreasing coliform contamination and increasing violations of the Stage 1 & 2 DBP rule are occurring.

The presence of E. Coli or of other species of coliform bacteria remains the most serious violation, in the Department’s opinion. Thus, the presence of either results in a boil order. All water systems in Missouri are required to test for E. Coli. Nineteen systems received boil orders in 2016. That number has been moving mostly sideways since 2012, but represents a decrease from 32 in 2011. Most lasted for a few days up to two weeks, but some lasted for several months.

Seventy-four systems had chemical violations, almost all for trihalomethanes . Trihalomethanes are water treatment byproducts. They form if disinfectants used to treat the water (chlorine or bromine) react with matter that may be present in the water (e.g. decaying vegetation).

Eleven systems had violations involving excess radiological contaminants (down from 14 systems in 2012 and 16 systems in 2011). The problems came from several radiological elements, see the report for full details.

In 2016, 7 water systems had Surface Water Rule violations, the same as in 2013. All of the violations were for combined filter effluent turbidity. Systems must filter surface water to remove cryptosporidium, a parasite that causes diarrhea, and a violation of the turbidity rule means the filtering may not be adequate to remove the parasite.

As noted above, some of violations can be quite brief, and the threat they represent to public health can be small. However, the DNR puts a special focus on water systems that repeatedly fail to meet monitoring standards, and on those with a routine sample that tests positive for coliform, but which fail to submit follow-up or repeat samples as required.

As reported in the previous post, 38 water systems were listed as having had three or more major monitoring violations in 2016 (up from 27 systems in 2013). Many of them were in violation for many months. Figure 3 shows the list. Only 6 water systems had water that tested positive for excess coliform bacteria, but failed to provide the required follow-up samples for testing. This represents a decrease from 47 systems in 2013. Figure 4 shows the list.

Figure 3. Source: Missouri Department of Natural Resources, 2016.

Figure 4. Source: Missouri Department of Natural Resources, 2016.

 

 

 

 

 

 

 

 

 

 

 

 

Sources:

Missouri Department of Natural Resources. 2013 Annual Compliance Report of Missouri Public Drinking Water Systems. https://dnr.mo.gov/env/wpp/fyreports/index.html. Published 2014-11-18.

Missouri Department of Natural Resources. 2016. Annual Compliance Report of Missouri Public Water Systems. Downloaded 5/11/2018 from https://dnr.mo.gov/env/wpp/fyreports/index.html.
Missouri Census Data Center. Population Estimates for Missouri. Viewed online 6/28/2018 at http://mcdc.missouri.edu/trends/estimates.shtml.
Wikipedia contributors. (2018, May 15). Trihalomethane. In Wikipedia, The Free Encyclopedia. Retrieved 22:26, July 5, 2018, from https://en.wikipedia.org/w/index.php?title=Trihalomethane&oldid=841446641

Most Public Water Systems Met All Health-Based Regulations in 2016

The previous post reported that the Census of Missouri Public Water Systems – 2016 found 2,733 public water systems in Missouri, of which 2,720 were active. This post looks at Missouri’s 2016 Annual Compliance Report of Missouri Public Drinking Water Systems. It is the most recent summary report on Missouri’s public water systems. Additional detail about specific systems can be found in reports published by the systems themselves.

A public water system is one that provides water to at least 15 service connections, or to an average of at least 25 people for at least 60 days each year. Community Systems (CWS) supply water to the same population year-round. Non-Transient Non-Community Water Systems (NTNCWS) supply water to at least 25 of the same people at least 6 months per year, but not year-round. An example might be a school that has its own water system. Transient Non-Community Water Systems (TNCWS) provide water in places where people do not remain for long periods of time. Examples might include gas stations or campgrounds that have their own water systems.

The amount of treatment that water must receive differs depending on the source of the water. Surface water and underground water under the direct influence of surface water are more vulnerable to contamination, so they receive more treatment. Underground water from aquifers not under the direct influence of surface water tend to contain water that is heavily filtered by the rock through which it seeps. Sometimes, the seepage is so slow that the water is old, predating most forms of modern contamination.

Figure 1. Source: Missouri Department of Natural Resources, 2016.

Figure 2. Source: Missouri Department of Natural Resources, 2016.

 

 

 

 

 

 

 

 

Figure 1 shows the percentage of population served by community water systems that meet all health-based requirements by year. Figure 2 shows the number of violations involving E. Coli or acute contamination levels. Non-compliance can result from many factors from broken pipes, to human error, to systems that are inadequate in the first place. The EPA goal is for 95% of the public water systems in a state to have no health-based violations in a year. In 2016, Missouri had 94.7% compliance. That is close to the goal, but it is a decrease from over 95% in 2013. The chart shows no general trend, but in some years the compliance rate appears to slip significantly. The last 3 years have all been below the EPA goal.

The number of violations for E. coli and acute MCL violations (maximum contaminant level violations – also mostly due to coliform contamination) peaked in 2008 and had another bad year is 2011. Since 2012, it has mostly been moving sideways. In 2016, there were 19 violations.

Ninety-four-point-seven percent is a high mark – you would have been happy to score 94.7% on tests at school, wouldn’t you? Since Missouri’s population in 2016 was 2,093,000, however, it means that water systems serving almost 111,000 people had a health-based violation. (Missouri Census Data Center)

In 2016, 38 public water systems had 3 or more “major monitoring violations” of the rules to protect against coliform contamination. That is an increase from 27 in 2013. Monitoring violations are a concern because hinders the Department of Natural Resources’s ability to determine if the drinking water is safe, especially if the monitoring violation occurs multiple times.

In 2016, however, there were only 6 major “repeat monitoring violations,” down from 41 in 2013. A repeat monitoring violation occurs when If a routine sample from a public water system tests positive for coliform bacteria, then the system is required to submit a second test to confirm the finding, and to conduct follow up testing to ensure that the problem is eliminated. A repeat monitoring violation occurs when the system fails to submit the repeat testing or follow up testing.

None of these violatios mean that people were actually sickened, the report does not address that issue. It does mean, however, that a potential vulnerability occurred, and that continuing work needs to be done to ensure that Missourians have safe drinking water.

The next post will look into the nature of the violations that occurred.

Sources:

Missouri Census Data Center. Population Estimates for Missouri. Viewed online 6/28/2018 at http://mcdc.missouri.edu/trends/estimates.shtml.

Missouri Department of Natural Resources. 2016. Annual Compliance Report of Missouri Public Water Systems. Downloaded 5/11/2018 from https://dnr.mo.gov/env/wpp/fyreports/index.html.

Census of Public Water Systems, 2018

Each year the Missouri Department of Natural Resources publishes the Census of Missouri Public Water Systems. I reported on the 2013 census here, and the 2014 census here, and the 2015 census here. This post reports on the 2016-2018 censuses. The census provides basic information about the number and type of public water systems in the state, plus information on each system that includes the source of its water, the type of treatment it gives the water, and a chemical analysis of the water that covers 16 inorganic chemicals.

The EPA defines a public water system as one that provides water for human consumption to at least 15 service connections or that serves an average of at least 25 people for at least 60 days a year. It classifies public water systems in three categories. Community Water Systems (CWS) supply water to the same population year-round. Non-Transient Non-Community Water Systems (NTNCWS) supplies water to at least 25 of the same people at least 6 months per year, but not year-round. An example might be a school that has its own water system. A Transient Non-Community Water System (TNCWS) provides water in a place where people do not remain for long periods of time. Examples might include gas stations or campgrounds that have their own water systems. Not included in the report are private systems, such as a privately owned well that provides water only to its owner.

Table 1 shows the number of public water systems in Missouri by category. In 2018 there were 2,732 public water systems in Missouri, about 52% of which were community water systems. The numbers have not changed greatly over the years.

Table 1.

Table 1. Data source: Missouri Department of Natural Resources, 2013 through 2018.

A primary water system is one that obtains water from a well, infiltration gallery, lake, reservoir, river, spring, or stream. A secondary water system is one that obtains its water from an approved water system, and distributes it to consumers. (Missouri 10 CSR 60-2015, Definitions) For instance, in 2018 the St. Louis City Public Water System was a primary system. It obtained 100% of its water from surface water supplies, and treated the water itself. On the other hand, the Kirkwood Public Water System was a secondary system. It purchased 100% of its water from Missouri American Water, which treated the water before selling it to Kirkwood. Kirkwood only distributes the water.

In 2018, about 78% of Missouri public water systems were primary systems, and they served about 79% of the population. Table 2 shows the number of systems by water source, and Table 3 shows the population served by each type.

Table 2.

Table 2. Data source: Missouri Department of Natural Resources, 2013 through 2018.

Table 3.

Table 3. Data source: Missouri Department of Natural Resources, 2013 through 2018.

Groundwater means groundwater that is not directly influenced by the surface water above it. The groundwater is isolated from surface groundwater by thick layers of rock or sediment that filter the ground water before it reaches the groundwater aquifer. Such groundwater is often considered less vulnerable to pollution by chemicals and organic waste. Groundwater Under Direct Influence refers to groundwater that is not protected from the surface water above it, and which consequently contains groundwater contaminants, such as chemicals, insects, microorganisms, algae, or turbidity. This kind of water requires more extensive treatment before it is fit for use. So does surface water. Groundwater is a limited resource, however, that sometimes takes hundreds, if not thousands, of years to percolate into underground aquifers. Overuse can deplete it. (See here.)

In 2018, groundwater systems constituted 84.5% of the total number of systems, but they served only 37.1% of the population. On the other hand, surface systems constituted 15.2% of the systems, but served 62.4% of the population. Table 3 shows the population served by water source.

Most of the water systems in Missouri source their water from groundwater, only a few from ground water under direct influence. However, the source serving the largest population is surface water. Specifically, the Missouri River is the water source for much of the Kansas City and St. Louis metropolitan areas. More than half of Missouri’s population is served by water either from the Missouri River Alluvial Aquifer or water from the river itself.

Source:

Missouri Department of Natural Resources. 2013. 2013 Census of Missouri Public Water Systems. Downloaded 2018-06-13 from https://dnr.mo.gov/env/wpp/census.htm.

Missouri Department of Natural Resources. 2014. 2014 Census of Missouri Public Water Systems. Downloaded 2018-06-13 from https://dnr.mo.gov/env/wpp/census.htm.

Missouri Department of Natural Resources. 2015. Census of Missouri Public Water Systems, 2015. Downloaded 2018-06-13 from https://dnr.mo.gov/env/wpp/census.htm.

Missouri Department of Natural Resources. 2016. 2016 Census of Missouri Public Water Systems. Downloaded 2018-06-13 from https://dnr.mo.gov/env/wpp/census.htm.

Missouri Department of Natural Resources. 2017. 2017 Census of Missouri Public Water Systems. Downloaded 2018-06-13 from https://dnr.mo.gov/env/wpp/census.htm.

Missouri Department of Natural Resources. 2018. 2018 Census of Missouri Public Water Systems. Downloaded 2018-06-13 from https://dnr.mo.gov/env/wpp/census.htm.

Say Goodby to Saline Lakes


“Many of the world’s saline lakes are shrinking at alarming rates, reducing waterbird habitat and economic benefits while threatening human health.”


So begins a recent report in Nature Geoscience.

Figure 1. Major Saline Lakes Across the World. Source: Wurtsbaugh et al, 2017.

Saline lakes, also known as salt lakes, are landlocked bodies of water with a concentration of dissolved minerals several times higher than in freshwater lakes, sometimes even higher than in the ocean. The largest in the world is the Caspian Sea, but other well known saline lakes include the Dead Sea and the Great Salt Lake. Two dozen of the world’s most important saline lakes are shown in Figure 1. The larger blue dots indicate those that formerly had a surface area larger than 250 square kilometers (larger than a circular lake about 18 miles across).

Wayne Wurtsbaugh and his associates looked at the volume of water in 6 saline lakes. The sample is loaded towards the United States, but includes two in Central Asia:

  • The Aral Sea (Kazakhstan and Uzbekistan)
  • The Dead Sea (Israel,  Jordan, and Palestine)
  • The Great Salt Lake (Utah, United States)
  • Lake Urmia (Iran)
  • Owens Lake (California, United States)
  • Walker Lake (Nevada, United States)

Figure 2. Percent Decline in Volume of 6 Saline Lakes. Source: Wurtsbaugh et al, 2017.

Figure 2 shows the loss of water in the 6 lakes over time, with some lakes going back to 1875. Every one of them has experienced a dramatic loss.

The Dead Sea has experienced the lowest percentage loss, the reason being that it is a very deep lake (Maximum depth 978 ft.) Despite that fact, the surface of the lake has dropped 28 feet, and it has been divided in two. (Wikipedia 2018b, Wurtsbaugh et al, 2017).

Starting in 1913, the streams that fed Owens Lake in California were diverted to provide water to Los Angeles. (See my post on California’s water supply, here. For movie buffs, this is also the subject of the famous movie Chinatown.) The lake has been almost completely drained, and is now mostly a dry lake (salt flat). (Wikipedia 2018c)

Figure 2. The Aral Sea in 2014. Source: NASA 2014.

Perhaps the “poster child” for what can happen to dry lakes is the Aral Sea. Formerly one of the largest lakes in the world, with a surface area of 26,300 square miles (almost the size of Lake Superior), water diversion has turned it into several small lakes, plus a whole lot of dry lake bed (salt flat). Figure 2 shows the Aral Sea in 2014, with the gray line showing the former extent of the lake. (Micklin 2007, Wikipedia 2018a, NASA 2014)

The demise of these lakes has not been caused primarily by a decline in precipitation, but rather by diversion of water for human consumption. In some cases, the consumption has been to provide potable water for large population, as in the case with Owens Lake and Los Angeles. In other cases, it has been to provide irrigation water for crops, as in the case with the Aral Sea.

Many aquatic species live in saline lakes, and the lake’s demise obviously devastates them. In addition, the survival of many species of migratory birds depends on an unbroken chain of places they can stop and refuel on their long journeys. Break the chain in even one place, and their survival is threatened. Saline lakes are one of the places birds stop during migration, and draining the lakes threatens to break the chain.

In addition, when saline lakes are emptied, what remains behind is a fine, salty dust that is laced with heavy metals and pesticide residue that drained into the lake over many years. It is picked up by the wind and blown for miles. Posts in this blog have discussed the health threats represented by airborne particulates, and the damage done by this salty dust has been well documented around the Aral Sea. Aerial photographs revealed salt plumes extending as much as 500 km. (310 miles) from the lake. It is considered an essential factor in the region’s high incidence of both acute and chronic illness. (Micklin 2007)

Of these lakes, the 2 with the highest percentage of remaining water are the Dead Sea and the Great Salt Lake. Wurtsburgh et al conclude that the key to conserving these lakes is to provide the river inflow needed to restore and sustain them. Otherwise, these once important lakes will remain (become) nothing but a choking dust in the wind.

Sources:

Micklin, Philip. 2007. The Aral Sea Disaster. Annual Review of Earth and Planetary Sciences. 35:47-72. Available online at http://www.annualreviews.org/action/doSearch?SeriesKey=earth&AllField=Micklin&startPage=&ContribAuthorStored=Micklin%2C%20Philip.NASA. 2014.

NASA. 2014. ”The Aral Sea Loses Its Eastern Lobe.” Earth Observatory. Downloaded 2018-01-04 from https://earthobservatory.nasa.gov/IOTD/view.php?id=84437.

Wikipedia. 2018a. “Aral Sea.” Wikipedia. Viewed online 2018-01-04 at https://en.wikipedia.org/wiki/Aral_Sea.

Wikipedia. 2018b. “Dead Sea.” Wikipedia. Viewed online 2018-01-04 at https://en.wikipedia.org/wiki/Dead_Sea.

Wikiepedia. 2018c. “Owens Lake.” Wikipedia. Viewed online 2018-01-04 at https://en.wikipedia.org/wiki/Owens_Lake.

Wurtsbaugh, Wayne, Craig Miller, Sarah Null, Justin DeRose, Peter Wilcock, Maura Hahnenberger, Frank Howe, and Johnnie Moore. 2017. Nature Geoscience, Vol 10. DOI: 10.1038/NGEO3052. Available online at www.nature.com/naturegeoscience.

Does Southwest Missouri Face a Future Water Shortage?


Southwest Missouri faces a water crisis. If nothing is done, demand will exceed current supply by 2030. However, sufficient additional water to meet demand through 2060 appears to be available, and could be accessed at a relatively low cost. Whether doing so would impact the regions ecosystem is not known.


In the previous post, I reported that current stresses on water supply along the Missouri River depend primarily on human decisions about how to manage competing demands for the river’s water. The future effects of climate change are not yet known.

What about regions of the state that don’t depend on the Missouri River for their water supply? Are demands projected to exceed supply?

To answer that question, we must start by distinguishing between water resources and water supply. Water resources consist of the total water available in a region. Water supply is the amount of water that the infrastructure is capable of delivering.

Water resources consist of surface water and groundwater. Some regions of the state depend primarily on surface water. In fact, surface water supplies 8 of Missouri’s 10 largest cities, and 62% of the state’s total water consumption (44% from the Missouri River alone). Groundwater supplies about 38% of Missouri’s water consumption. Some regions, however, rely more heavily on groundwater, especially in the southern part of the state.

Figure 1. Southwest Missouri Counties Expected to Experience a Future Water Shortage. Source: Adapted from a map at Wikimedia Commons.

No region of the state is currently experiencing a sustained shortfall in water supply compared to demand. Perhaps the region most likely to experience one in the future is a 16 county area in Southwest Missouri. Figure 1 shows a map of the 16 counties.

The region has historically depended primarily on groundwater, as it is underlain by the Ozark Aquifer. Aquifer levels fluctuate depending on how much precipitation occurs to recharge them. In addition, over-pumping can deplete the water supply in a local region of the aquifer faster that water can flow in to replace it, causing a cone of depression. It can leave neighboring wells high and dry, but does not affect the whole aquifer. Severe over-pumping from multiple sources can deplete the entire aquifer, which is occurring in California.

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Figure 2. Missouri Population Density. Source: Tri-State Water Coalition.

The region’s constraints on water supply have occurred because of growth. Figure 2 is a map of population density in Missouri. It shows that Southwest Missouri is one of the more densely populated regions.

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Figure 3. Source: Tri-State Water Resource Coalition.

Figure 3 shows that from 1990-2000 the region was the fastest growing in the state. Between 2000 and 2010, the trend continued, with Christian County growing an astounding 43% and Taney County growing by 30%.

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Figure 4. Source: Tri-State Water Resource Coalition

The result has been over-pumping, and Figure 4 shows the results. In Southwest Missouri, most areas have experienced some decrease in the groundwater level. A few regions in Green County (the City of Springfield), Jasper County (the City of Joplin), and Stone and Taney Counties (the Branson area) have experienced cones of depression, dropping the water table more than 300 feet. The worst affected area is the large red area on the left side of the map. It is in Oklahoma, centered on Miami, OK.

Using a mid-level growth forecast, studies have calculated that current water resources will be overrun by demand by 2030. Even reducing demand through conservation would only meet needs through 2040.

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Figure 5. Projected Water Demand and Supply by 2060 in a Drought Year. Source: Tri-State Water Resource Coalition.

The region has significant surface water resources, however, and could supplement its water supply. Three significant reservoirs could supply water to the region: Stockton Lake, Table Rock Lake, and Lake Taneycomo. The first two are operated by the U.S. Army Corps of Engineers, and the latter is owned and operated by Empire District Electric Company. These organizations would have to approve the reallocation of water, but the water is there. Figure 5 shows projected available supply and demand if surface water resources were tapped. It would require the construction of pipelines and pumping stations, but the dams and reservoirs already exist.

Climate change is not projected to cause a decrease in precipitation in the region. The worst drought on record occurred in the 1950s, and if anything, the trend in precipitation has increased slightly since 1895. The temperature is projected to increase significantly, however. If increased temperature were to lead to less water reaching the aquifer to recharge it, then it could have implications for the regions water supply. But so far, those projections have not yet been calculated.

Unfortunately, none of the reports I contacted discuss the environmental impacts that the increasing demand for water will place on the ecosystem in the region. In fact, so far as I could tell, possible effects were not even considered. Will dropping water tables cause springs, creeks, and rivers to go dry? Will reallocation of the water from the regions reservoirs affect the health of the White and Osage Rivers? Will subsidence occur? These effects have occurred elsewhere, why Missouri would expect to be immune from them? But I just don’t know.

Thus, it appears that Southwest Missouri does face a water crisis. If nothing is done, demand will exceed current supply by 2030. However, sufficient additional water to meet demand through 2060 appears to be available, and could be accessed at a relatively low cost. Whether doing so would impact the regions ecosystem is not known.

Sources:

Missouri Department of Natural Resources. Springfield Plateau Groundwater Province. Downloaded 5/23/2017 from https://dnr.mo.gov/geology/wrc/groundwater/education/provinces/springfieldplatprovince.htm?/env/wrc/groundwater/education/provinces/springfieldplatprovince.htm.

State of Missouri and U.S. Army Corps of Engineers. 2012. Southwest Missouri Water Resource Study – Phase I. Downloaded 5/23/2017 from http://www.swl.usace.army.mil/Portals/50/docs/planningandenvironmental/Phase%20I%20-%20Southwest%20Missouri%20Water%20Study%20Final%20Report%20.pdf.

State of Missouri and U.S. Army Corps of Engineers. 2014. Southwest Missouri Water Resource Study – Phase II. Downloaded 5/23/2017 from http://tristatewater.org/wp-content/uploads/2014/11/Phase-II-FINAL-Southwest-Missouri-Supply-Availability-Report-Final_March_2014-from-Mike-Beezhold-9-16-14.pdf.

Tri-State Water Resource Coalition. 2015. Securing Water for Southwest Missouri. Downloaded 5/30/2017 from https://waterways.org/wordpress1/wp-content/uploads/2015/05/Securing-Water-for-Southwest-Missouris-Future.pdf.

Will Climate Change Affect Water Supply on the Missouri River?


How climate change will affect water supply from the Missouri River is not yet known. Current problems with Missouri River water supply principally affect the barge transportation industry, and the agricultural and industrial clients that use it to transport their goods and supplies.


The Missouri River is important for Missouri. More than half of Missouri residents get their drinking water from the Missouri River or the alluvial aquifer it directly feeds. Not only that, the river’s water is used for agricultural irrigation, for industry, to support barge traffic along the Missouri and Mississippi Rivers, for recreation, and to support the ecosystems that depend on the river for their survival.

Figure 1. Dams and Other Locations Along the Missouri River. Source: Google Earth.

In the previous post, I reported that the snowpack in the western United States has declined by 23%, and it is forecast to decline more by 2038. The eastern border of the study area forms the western boundary of the Missouri River Basin. Will the changing western snowpack impact the Missouri River’s ability to supply Missouri’s needs?

The answer is complicated. Precipitation in the Upper Missouri River Basin has historically fallen mostly as snow, building a winter snowpack that slowly melts during the spring. The snowmelt is gathered into reservoirs created by 6 large dams along the Missouri River, plus more than 40 smaller ones on tributaries. The 6 large dams begin at the Gavin’s Point Dam on the Nebraska-South Dakota border, and extend upriver to the Ft. Peck Dam in Montana. (See Figure 1.) The result is that water flow below the reservoirs is largely controlled by man, not nature.

Figure 2. Data source: Wikipedia.

The annual water yield from the Missouri River is small compared to the size of its basin. The data is given in Figure 2, where the red columns represent the length of the rivers, and the blue line represents their average discharge. No other river in the USA serves such a large basin with so little water. In drought years it is already too small to fully meet all of the demands that are put on it, resulting in conflict over how to manage the river, and over which values to give priority. The conflict has primarily been between up-river interests, which would like to see water allocated to support irrigation, drinking water, and mitigation in their states during periods of drought, and down-river interests, which would like to see water released to support commercial navigation on the river.

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Figure 3. Source: Hansen Professional Services, Inc. 2011.

In 2004, the Army Corps of Engineers changed the rules by which the river is operated to reduce water releases during drought. During drought years, this better supports up-stream interests, but results in a shorter season during which the river can support barge traffic. The result has been a decrease in annual tonnage moved on the river (Figure 3).

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Figure 4. Well Drilling in Western North Dakota. Source: Vanosdall 2013.

In addition, development in the Upper Missouri Basin has increased water demand in that region. A prime example would be the development of the oil and gas reserves in North Dakota. Well drilling uses large quantities of water. (See Figure 4). Given that the water yield from the Missouri River is already too small to fully support all of the demands placed on it, any increase in demand is bound to constrain supply even further.

The constraints discussed above, however, are all man-made constraints. How will climate change and the declining western snowpack affect all of this?

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Source: National Centers for Environmental Information.

The snowpack decline has occurred because of increasing temperature, not decreasing precipitation. Figures 5 repeats a chart I published in January 2016, showing that precipitation has increased in the region over time.

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Figure 6. Source: Melillo 2014.

Figure 6 shows that the 2011 National Climate Assessment projects that the annual flow on the Missouri River will actually increase by about 15% by 2070. However, more precipitation will fall as rain instead of snow, and the snow that does fall will melt sooner. This means that more water will enter the reservoirs during winter and early spring, and less during late spring and summer. In addition, increased temperature will increase evaporation from the river and reservoirs, and it will increase water consumption by crops, leading to earlier and increased demand for water. There is a potential mismatch between when the water is available and when it is needed.

The question will be whether it will be possible to manage the reservoirs successfully under the new conditions. When looking at the water situation in California (here), we discovered that water authorities expected climate change to create reservoir management problems that would result in an increased water deficit during the summer and autumn. It is possible that the reservoirs along the Missouri will encounter similar problems, but it is not certain.

One potential difference is that California has multiple, relatively short rivers, leading to only one large reservoir per river, and perhaps one or two small feeder reservoirs. The Missouri River, however, is a single long river. It has 6 large reservoirs chained along it, plus at least 40 feeder reservoirs on tributaries. This may give managers flexibility in managing the river that is not possible in California.

Five separate water resource studies have been undertaken to determine how climate change will impact the ability of the Missouri River to meet the demands placed on it. Unfortunately, they have not all been completed, and I can find no comprehensive analysis.

For the time being, problems with water supply on the Missouri River involve human decisions about how to manage the river. To date, in the State of Missouri they have primarily impacted the barge industry, plus the farmers and industries that depend on the barge industry to transport their goods and supplies.

Sources:

Drew, John, and Karen Rouse. 2006. “Missouri Water in High Demand.” Missouri Resources, Winter, 2006. Downloaded 5/31/2017 from https://dnr.mo.gov/geology/wrc/docs/Water-InHighDemand.pdf?/env/wrc/docs/Water-InHighDemand.pdf.

Bureau of Reclamation. 2016. Basin Report: Missouri River. Downloaded 5/25/2017 from https://www.usbr.gov/climate/secure/docs/2016secure/factsheet/MissouriRiverBasinFactSheet.pdf.

Bureau of Reclamation. 2016. SECURE Water Act Section 9503(c) – Reclamation Climate Change and Water. Prepared for United States Congress. Denver, CO: Bureau of Reclamation, Policy and Administration. Downloaded 5/25/2017 from https://www.usbr.gov/climate/secure.

Hanson Professional Services, Inc. 2011. Missouri River Historic Timeline and Navigation Service Cycle. Missouri River Freight Corridor Assessment and Development Plan. Downloaded 5/31/2017 from https://library.modot.mo.gov/rdt/reports/tryy1018.

Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, 841 pp. doi:10.7930/J0Z31WJ2. Available online at http://nca2014.globalchange.gov.

Vanosdall, Tiffany. 2013. Missouri River Water Supply. US Army Corps of Engineers. Downloaded 6/1/2017 from https://denr.sd.gov/coewatersupply22Apr2013.pdf.

Wikipedia. List of U.S. Rivers by Discharge. Data retrieved online 5/31/2017 at https://en.wikipedia.org/wiki/List_of_U.S._rivers_by_discharge.

Declining Snowpack in the American West


The snowpack over the western United States has declined about 23% since 1981. It is projected to decline more in the future.


I have written a number of posts about the looming water deficit in California due to a projected decline in the snowpack on the Sierra Nevada mountains. Is something similar projected to occur throughout the entire western United States?

Figure 1. Change in Snow Water Equivalent at SNOTEL Stations, 1955-2016. Source: Mote and Sharp 2016, in Environmental Protection Agency, 2016.

Yes. Studies find that the water content of the snowpack throughout the West has already declined 23%, and it is expected to decline more, perhaps up to 30% by 2038.

This decline is not occurring via a decrease in precipitation. Indeed, to date precipitation across the West has actually increased slightly. The decline is occurring due to increased temperature. Some precipitation that used to fall as snow now falls as rain, and the snow that does fall melts more quickly.

Mote and Sharp studied the snow water equivalent* of the snowpack in April from 1955-2016 at SNOWTEL measuring stations operated by the U.S. Natural Resource Conservation Service. Figure 1 shows a map of the stations, with blue dots representing stations where the snowpack increased and orange dots representing stations where the snowpack declined. The size of the dots represent the magnitude of change.

It is easy to see that the vast majority showed declines in the snowpack, in many cases by as much as 80%. Overall, Mote and Sharp computed that there had been an average 23% decline in the western snowpack since 1955.

 

Figure 2. Observed and Modeled Change in Snowpack. Source: Fyfe, et al, 2017.

Fyfe and his colleagues conducted climate modeling to try to determine whether the decline in the snowpack was due to natural causes or human causes. Figure 2 shows the results in a rather complicated graph. Let’s unpack it. The computer models ran from 1950 to 2010. The dashed black line shows the observed trend in the snow water content. The solid blue line shows the projected snow water content if only natural climate causes are included in the model. It doesn’t fit the observed trend very well. The solid black line shows the projected snow water content if both natural and human climate causes are included in the model. It fits the observed data quite closely. (The pink and green lines show data from analyses using other sets of data and need not concern us here. The gray band and blue dotted lines show statistical confidence levels for the computer simulations, and also need not concern us here.)

The simulation that included both natural and human causes agreed with the observed data, but the one that included only natural causes did not. The authors concluded that natural causes could not explain the loss of snowpack in the West. A combination of human and natural causes could explain it.

Figure 3. Projected Short-Term Change in Snowpack. Source: Fyfe, et al, 2017.

Fyfe and his colleagues also conducted a suite of climate models to project snowpack loss into the future. The results are shown in Figure 3. In this graph, the y-axis represents the actual snow water content of the snowpack, not the change. The blue line represents the computer model that projected the least snowpack loss in 2030, and the red line represents the computer model that projected the most loss. It is common practice among climate modelers to run a suite of projections, and when this is done, the average of them is often also presented, and it is often taken as likely to be the most accurate. In Figure 3, the average of the projections is represented by the black line.

It is easy to see that the trend in all of the lines is down. There is considerable variation from point-to-point in the red and blue lines, indicating that the projections expect there to be considerable variability in the snowpack from year-to-year. The black line is pretty smooth, however, as might be expected from an average of several analyses, and it has a consistent downward trend. The losses in snowpack in some of the projections ran as high as 60%, though average loss across the suite of projections was about 30%.

A 30% decline in the snowpack does not sound so dire; after all the projections are for a 60% loss of snowpack in California (see here). However, that projection was for the end of the century. This projection is for 2038; that’s only 20 years from now.

Some may wonder about how little snow water equivalent is shown on the y-axis of Figure 3. In the 1990s, the snowpack maxed-out each year at only 6+ cm. of snow water equivalent. In thinking about this number, remember two things: first, a centimeter of water represents somewhere between 3 and 20 centimeters of snow, with an average value being somewhere around 10 cm. Thus, 6 cm. of snow water equivalent would roughly equal 60 cm. of snow, or 23.6 inches. Thus, the average depth of the snowpack was about 2 feet. Second, remember that the measurements were averaged across hundreds of locations; some were high and received a great deal of snow, but some were relatively low (low altitude means more rain, less snow), or were located in areas that don’t receive much precipitation of any kind.

Much of Missouri depends on the Missouri River as a water supply, including both Kansas City and St. Louis. The Missouri River gets much of its water from the western snowpack. A declining snowpack may, or may not, have implications for our water supply, depending on whether the reservoirs along the Missouri River can accommodate the shift toward earlier snowmelt and increased rain. I will look at this issue in the next post.

*   Snow water equivalent: Different types of snow hold different amounts of water. Thus, scientists don’t just measure how deep the snow is. Rather, at a given location they take a representative sample of the snowpack and melt it, thereby determining how much water it holds. This is the snowpack’s snow water equivalent at that given location. April is generally when the snowpack is at its maximum.

Sources:

Environmental Protection Agency. 2016. Climate Change Indicators in the United States: Snowpack. Retrieved online 5/22/2017 at https://www.epa.gov/sites/production/files/2016-08/documents/print_snowpack-2016.pdf.

Fyfe, John, Chris Kerksen, Lawrence Mudryk, Gregory Flato, Benjamin Santer, Neil Swart, Noah Molotch, Xuebin Zhang, Hui Wan, Vivek Arora, John Scinocca, and Yanjun Jiao. 2017. “Large Near-Term Projected Snowpack Loss Over the Western United States.” Nature Communications, DOI: 10.1038/ncomms14996. Retrieved online 5/14/2017 at https://www.nature.com/articles/ncomms14996.

California Drought Emergency Officially Over

Gov. Jerry Brown officially declared California’s drought emergency over on Friday, April 7. It was a fitting ending to one of the worst episodes in California’s drought-laden history.

Or was it? The next two posts update California’s water situation. This one focuses on the current short-term situation. The next one focuses on the future, with an eye toward the future impact of climate change. I have personal reasons for following California’s water situation – I have family living there. But in addition, California is the most populous state in the Union, it has the largest economy of any state, and the state grows a ridiculously large fraction of our food. What happens in California affects us here in Missouri.

Figure 1. California Snowpack, 3/31/2017. Source: California Department of Water Resources.

Is the short-term drought truly over? Yes, I think so. The vast majority of California’s precipitation falls during the winter, and the snowpack that builds up in the Sierra Nevada Mountains serves as California’s largest “reservoir.” As it melts, it not only releases water that represents about 30% of the state’s water supply, but it also feeds water into the underground aquifers that provide groundwater to much of the state. Thus, the size of the snowpack is the most important factor in determining California’s water status. California measures the water content of the snowpack electronically and manually. The measurements around April 1 are considered the most important, as that is when the snowpack is typically at its largest. Figure 1 shows the report for this year. Statewide, the water content of the snowpack was 164% of average for the date, almost 2/3 larger than average. The water content was significantly above average in all three regions of the snowpack, North, Central, and South.

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I follow the snow report at Mammoth Mountain Ski Resort to provide a specific example of the snow conditions. Figure 2 shows that through March, Mammoth received over 500 inches of snow, one of the highest totals in the record going back to 1969-70. The column for 2016-17 has very large blue and orange sections, indicating that the majority of the snow fell in January and February. Figure 3 confirms the impression. It charts the amount of snowfall at Mammoth during each month of the 2016-17 snow season, and compares it to the average for that month across all years. You can see that both January and February were monster snow months, especially January. By March, snowfall had already fallen below average. I wouldn’t make too much of this fact, one month doesn’t make a trend.

Figure 2. Source: Mammoth Mountain Ski Resort.

Figure 3. Data source: Mammoth Mountain Ski Resort.

 

 

 

 

 

 

 

 

 

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Figure 4. Source: California Data Exchange Center.

California also stores water in man-made reservoirs. Figure 4 show the condition of 12 especially important ones on March 31. Most were above their historical average for that date, and many were approaching their maximum capacity. Those who follow this blog know that the Oroville Reservoir actually received so much water that it damaged both the main and emergency spillways, threatening collapse of the dam and requiring evacuation of thousands of people down stream. (See here.)

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Figure 5. Elevation of the Surface of Lake Mead. Source: water-data.com.

In addition, Southern California receives the lion’s share of water drawn from the Colorado River, thus the status of Lake Mead, the largest reservoir on the Colorado, is important to the state. A study in 2008 found that there was a 50% chance the reservoir would go dry by 2021. On March 31, Lake Mead was at 1088.26 feet above sea level. (This doesn’t mean there were that many feet of water in the reservoir, Hoover Dam isn’t that tall. Rather, it represents how many feet above sea level the surface of the water was. Lake Mead’s maximum depth is 532 feet.) The current level represents 41.38% of capacity. Figure 5 shows the level of the lake over time. You can see that the line tends to go up with the spring snowmelt, and down during the rest of the year. This year it is up very slightly year-over-year, but the trend has been relentlessly down since 2000.

The conclusion seems inescapable: for this year at least, California has plenty of water. The short-term drought is over. One year doesn’t make a climate trend, however. In the next post I will consider the implications of this wet winter for California’s water situation going into the future.

Sources

Barnett, Tim, and David Pierce. 2008. “When Will Lake Mead Go Dry?” Water Resources Research, 44, W03201. Retrieved online at http://www.image.ucar.edu/idag/Papers/PapersIDAGsubtask2.4/Barnett1.pdf.

CA.GOV. Governor Brown Lifts Drought Emergency, Retains Prohibition on Wasteful Practices. Viewed online 4/10/2017 at https://www.gov.ca.gov/home.php.

California Data Exchange Center. Conditions for Major Reservoirs: 31-Mar-2017. Viewed online at http://cdec.water.ca.gov/cdecapp/resapp/getResGraphsMain.action.

California Department of Water Resources. Snow Water Equivalents (inches) for 3/30/2017. Viewed online 3/31/2017 at http://cdec.water.ca.gov/cgi-progs/snowsurvey_sno/DLYSWEQ.

Mammoth Mountain Ski Resort. Snow Conditions and Weather, Extended Snow History. Data downloaded 4/2/2017 from http://www.mammothmountain.com/winter/mountain-information/mountain-information/snow-conditions-and-weather.

water-data.com. “Lake Mead Daily Lake Levels.” Downloaded 4/5/2017 from http://graphs.water-data.com/lakemead/.

Missouri Fish Advisory for 2017

Table 1. Source: Missouri Department of Health and Senior Services, 2017.

Eating fish is thought to have healthful benefits, including cognitive benefits for the young and a reduction in the risk of cardiovascular disease in adults. However, environmental toxins limit the amount of fish you should eat. The principle of bioaccumulation, which explains why, was reviewed in the previous post.

Whether fish are safe to eat depends on the water where they were caught. The Missouri Department of Health and Senior Services publishes a report identifying lakes, rivers, and streams where environmental contamination requires a fish advisory. This post looks at the report for 2017.

Table 1 lists the bodies of water for which fish advisories have been issued, the species of fish affected, the sizes of fish affected, the contaminants, and the limit that should be observed (serving advice).

Looking at the table, the toxins include chlordane, lead, mercury, and PCBs. In some cases the fish are safe to eat once weekly, in other cases only once monthly, and in some cases they should not be eaten at all. Several species from rivers near Missouri’s old lead belt tend not to be safe at all. I’ve posted on the Big River previously (here).

The advisories are separated into those that apply to all consumers, and those that apply to “sensitive populations.” Please look at who is included under “sensitive populations”: children younger than 13 and women who are either pregnant, nursing, or of childbearing age. Wow, that is a huge portion of the population! For them, there is no fish caught in any body of water in the United States that is safe to consume more than once weekly. And for them, several important species of game fish caught in Missouri waters should only be consumed once monthly.

Figure 1. Source: Missouri Department of Health and Senior Services.

Figure 1 shows a map of the affected bodies of water. Looking at the bodies of water affected, you can see that they cover a lot of territory: the entire lengths of the Mississippi and Missouri Rivers in the state, the major portion of the Big River, the Blue River, Clearwater Lake (ironic, no?), and Montrose Lake.

The contaminants of concern listed by the Missouri report include chlordane, PCBs (polychlorinated biphenyls), lead, and methylmercury. Chlordane was an insecticide. It was widely used as a termite control in residences, and it was used widely on crops. Starting in 1988, sales of chlordane were banned in the United States. However, chlordane persists in the environment. It adheres to soil particles in the ground and very slowly dissolves into groundwater, where it migrates to rivers and lakes. Once in the water of rivers and lakes, it bioaccumulates. That is why, even though banned in 1988, it is still a contaminant of concern in Missouri fish. Elevated levels of chlordane in the blood are associated with an increased risk of cognitive decline, prostate cancer, type-2 diabetes, and obesity. According to the Missouri report, levels of chlordane are gradually decreasing, but remain a concern in some bodies of water.

PCBs are a family of chemicals that were once widely used as insulating and cooling liquids in electrical mechanisms. PCBs were banned in the United States in 1979, however they are extremely long-lived compounds, and it is estimated that 40% of all PCB ever manufactured remain in use. Toxicity varies among specific chemicals in the family. Exposure to PCBs is capable of causing a variety of health effects, including rashes, reduced immune function, poor cognitive development in children, liver damage, and increased risk of cancer. PCBs in the environment generally enter bodies of water, where they enter the bodies of aquatic species and bioaccumulate up the food chain. According to the Missouri report, levels of PCB are gradually decreasing, but remain a concern in some bodies of water.

Lead is a heavy metal that was once heavily mined in Missouri. Lead mining continues, and as recently as 2014, more lead was released into the environment in Missouri than any other toxic chemical. (See here.) Lead used to be released into the environment through the inclusion of tetraethyl lead in gasoline, and through lead paint. Both of those uses have been banned in the United States. Today, lead enters the environment through mine tailings. Thus, it is of greatest concern in locations that either have or had significant lead mining activities (portions of Southeastern Missouri, for instance). Tailings containing lead were (are) dumped on the ground. From the tailings lead washes into nearby bodies of water, where it is ingested by aquatic species and then bioaccumulates. Lead is readily absorbed by living tissue. It affects almost every organ and system in the body. At high levels it can be immediately dangerous to life and health. At lower levels, symptoms include abdominal pain, weakness in fingers, wrists, and ankles, blood pressure increases, miscarriage, delayed puberty, and cognitive impairment.

Mercury enters the environment from many sources. One important source is coal. When coal is burned, it is emitted up the flue. Though the amount in any lump of coal is tiny, so much coal is burned to produce energy that tons and tons are emitted every year. The mercury falls out of the atmosphere, where it gets washed into bodies of water. There, it is converted by microbes into methylmercury, which is then ingested into aquatic species, and it bioaccumulates. In children a high level of methylmercury has been associated with language and memory deficits, reduced IQ, and learning disabilities. In adults, it has been associated with an increased risk of cardiovascular disease and autoimmune conditions.

It seems to me that for all of these contaminants, the situation may be slowly improving, though it is still problematic. The persistence of these contaminants in the environment, in many cases decades after their manufacture was banned, demonstrates an important environmental principle: the environmental problems you create may not go away quickly. They are likely to remain with you for a long, long time.

Sources:

Missouri Department of Health and Senior Services. 2017. 2017 Missouri Fish Advisory: A Guide to Eating Missouri Fish. Downloaded 3/9/17 from http://www.health.mo.gov/fishadvisory.

Wikipedia. Chlordane. Viewed online 3/15/2017 at https://en.wikipedia.org/wiki/Chlordane.

Wikipedia. Lead. Viewed online 3/15/2017 at https://en.wikipedia.org/wiki/Lead.

Wikipedia. Methylmercury. Viewed online 3/15/2017 at https://en.wikipedia.org/wiki/Methylmercury.

Wikipedia. Polychlorinated biphenyl. Viewed online 3/15/2017 at https://en.wikipedia.org/wiki/Polychlorinated_biphenyl.

Environmental Toxins Limit Fish Consumption

Eating fish may be good for you, or it may poison you. (Pick one)

In the 1970s, researchers reported that native people living in Greenland (Inuits) had very low rates of heart disease compared with counterparts living in Denmark. Scientists attributed these health benefits to the consumption of fish and sea mammals containing high levels of long-chain polyunsaturated fatty acids. Recently, however, research has questioned the accuracy of these early studies, as more recent research shows that the rate of heart disease and heart attack among the Inuit are similar to those in non-Inuit populations. Thus, there has been some question regarding how strong the association is between reduced risk of cardiovascular disease and fish consumption. The situation reminds me of one of my favorite sayings: It ain’t what we don’t know that’s gonna hurt us, it’s what we do know that just ain’t so.

Over the years, thousands of research studies have been conducted, with the result that the consumption of fish is included in most dietary guidelines. The benefits are primarily considered to be the previously mentioned reduction in the risk of coronary heart disease in adults, but also an improvement in cognitive development in infants and young children.

The current dietary guidelines in the USA have moved away from the concept of the minimum daily requirement. Instead they describe recommended patterns of healthy eating. The recommendation for seafood has not changed, however: 8 oz. of seafood per week. (Dietary Guidelines, p. 18)

It is generally recognized, however, that some fish species contain significant levels of contaminants. These contaminants include a number of really nasty poisons, including chlordane, polychlorinated biphenyls (PCBs), lead, and methylmercury. These compounds can be toxic even in very small amounts, and they are bioaccumlative.

Bioaccumulation is an important concept in understanding environmental toxins. The basic idea is that even tiny amounts of toxin can build up in the body. Here’s how: at any given feeding, a toxin may be eaten in such tiny amounts that there is no immediate effect on the animal that consumes it. However, it is absorbed by the body, and it is not readily eliminated by natural processes. Thus, over time, the amount in the body builds up each time the animal eats a little more.

Imagine a lake. Mercury emitted by coal-burning power plants falls into the lake, where microbes convert it to methylmercury. Algae living in the lake take in some of that methylmercury. Along comes a tiny fish fry, and it eats some of that algae. Now with each mouthful of algae, the fish fry ingests a dose of methylmercury. And it starts to build up. How many mouthfuls of algae does a fish fry eat? I don’t know, but it is quite a lot. Now, along comes a medium-sized fish, and it eats the fish fry. With one bite, it has ingested not just a tiny amount of methylmercury, but all the methylmercury that built up in the body of the fish fry during its lifetime. How many fish fry does a medium-sized fish eat? I don’t know, but it is quite a few, and the medium-sized fish ingests all of the methylmercury built up in the bodies of each fish it eats. Now, along comes a large fish, and it eats the medium-sized fish. With one bite, it has ingested not just a tiny amount of mercury, but all the methylmercury built up in the body of the medium-sized fish. How many medium-sized fish does a large fish eat? I don’t know, but it is quite a few, and the large fish ingests all of the methylmercury built up in the bodies of each fish it eats.

Now, let’s imagine that our fish are living in a Missouri lake. Along comes a fisherman, and he catches one fish per week and eats it. That will be 52 fish per year. Now, I don’t know what the actual numbers are, but let us assume that a fish fry eats 1,000 individual alga, while a medium-sized fish eats 100 fry, and a large fish eats 100 medium-sized fish. These estimates may be wildly wrong, but the point is to illustrate the principle of bioaccumulation, and they will allow us to do so.

Using the estimates above, each fish fry will ingest the methlymercury contained in 1,000 algae; each medium-sized fish will ingest the amount contained in 100,000 algae; each large fish will ingest the amount contained in 10 million algae, and in a year, our fisherman will ingest the amount contained in 520 million algae. If he continues for 10 years, he will consume the amount contained in 5.2 billion algae.

Over time, the amount of methylmercury in our fisherman’s body will build up, perhaps eventually reaching the point where it starts to poison him.

Now, my presentation is over-simplified; in real life bioaccumulation is much more complex. Further, the numbers I chose for my progression were totally arbitrary. Nonetheless, they illustrate the basic idea of bioaccumulation. And the principle applies not only to methylmercury, but also to lead, PCBs, and dioxins.

The result is that, however good for you eating fish may be in theory, there are limits due to environmental contaminants. The next post will look at what those limits are in Missouri.

Sources:

Committee on a Framework for Assessing the Health, Environmental, and Social Effects of the Food System; Food and Nutrition Board; Board on Agriculture and Natural Resources; Institute of Medicine; National Research Council; Nesheim MC, Oria M, Yih PT, editors. A Framework for Assessing Effects of the Food System. Washington (DC): National Academies Press (US); 2015 Jun 17. ANNEX 1, DIETARY RECOMMENDATIONS FOR FISH CONSUMPTION. Available from: https://www.ncbi.nlm.nih.gov/books/NBK305180.

Missouri Department of Health and Senior Services. 2017. 2017 Missouri Fish Advisory: A Guide to Eating Missouri Fish. Downloaded 3/9/17 from www.health.mo.gov/fishadvisory.

U.S. Department of Health and Human Services and U.S. Department of Agriculture.
2015–2020 Dietary Guidelines for Americans. 8th Edition. December 2015. Available at http://health.gov/dietaryguidelines/2015/guidelines.