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An inside look at the science of cleaning up and fixing the mess of marine pollution

Little “Bugs” Can Spread Big Pollution Through Contaminated Rivers

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This is a post by the NOAA Restoration Center’s Lauren Senkyr.

When we think of natural resources harmed by pesticides, toxic chemicals, and oil spills, most of us probably envision soaring birds or adorable river otters.  Some of us may consider creatures below the water’s surface, like the salmon and other fish that the more charismatic animals eat, and that we like to eat ourselves. But it’s rare that we spend much time imagining what contamination means for the smaller organisms that we don’t see, or can’t see without a microscope.

Mayfly aquatic insect on river bottom.

A mayfly, pictured above, is an important component in the diet of salmon and other fish. (NOAA)

The tiny creatures that live in the “benthos”—the mud, sand, and stones at the bottoms of rivers—are called benthic macroinvertebrates. Sometimes mistakenly called “bugs,” the benthic macroinvertebrate community actually includes a variety of animals like snails, clams, and worms, in addition to insects like mayflies, caddisflies, and midges. They play several important roles in an ecosystem. They help cycle and filter nutrients and they are a major food source for fish and other animals.

Though we don’t see them often, benthic macroinvertebrates play an extremely important role in river ecosystems. In polluted rivers, such as the lower 10 miles of the Willamette River in Portland, Oregon, these creatures serve as food web pathways for legacy contaminants like PCBs and DDT. Because benthic macroinvertebrates live and feed in close contact with contaminated muck, they are prone to accumulation of contaminants in their bodies.  They are, in turn, eaten by predators and it is in this way that contaminants move “up” through the food web to larger, more easily recognizable animals such as sturgeon, mink, and bald eagles.

Some of the ways contaminants can move through the food chain in the Willamette River.

Some of the ways contaminants can move through the food chain in the Willamette River. (Portland Harbor Trustee Council)

The image above depicts some of the pathways that contaminants follow as they move up through the food web in Oregon’s Portland Harbor. Benthic macroinvertebrates are at the bottom of the food web. They are eaten by larger animals, like salmon, sturgeon, and bass. Those fish are then eaten by birds (like osprey and eagle), mammals (like mink), and people.

An illustration showing how concentrations of the pesticide DDT biomagnify 10 million times as they move up the food chain from macroinvertebrates to fish to birds of prey.

An illustration showing how concentrations of the pesticide DDT biomagnify 10 million times as they move up the food chain from macroinvertebrates to fish to birds of prey. (U.S. Fish and Wildlife Service)

As PCB and DDT contamination makes its way up the food chain through these organisms, it is stored in their fat and biomagnified, meaning that the level of contamination you find in a large organism like an osprey is many times more than what you would find in a single water-dwelling insect. This is because an osprey eats many fish in its lifetime, and each of those fish eats many benthic macroinvertebrates.

Therefore, a relatively small amount of contamination in a single insect accumulates to a large amount of contamination in a bird or mammal that may have never eaten an insect directly.  The graphic to the right was developed by the U.S. Fish and Wildlife Service to illustrate how DDT concentrations biomagnify 10 million times as they move up the food chain.

Benthic macroinvertebrates can be used by people to assess water quality. Certain types of benthic macroinvertebrates cannot tolerate pollution, whereas others are extremely tolerant of it.  For example, if you were to turn over a few stones in a Northwest streambed and find caddisfly nymphs (pictured below encased in tiny pebbles), you would have an indication of good water quality. Caddisflies are very sensitive to poor water quality conditions.

Caddisfly nymphs encased in tiny pebbles on a river bottom.

Caddisfly nymphs encased in tiny pebbles on a river bottom are indicators of high water quality. (NOAA)

Surveys in Portland Harbor have shown that we have a pretty simple and uniform benthic macroinvertebrate population in the area. As you might expect, it is mostly made up of pollution-tolerant species. NOAA Restoration Center staff are leading restoration planning efforts at Portland Harbor and it is our hope that once cleanup and restoration projects are completed, we will see a more diverse assemblage of benthic macroinvertebrates in the Lower Willamette River.

Lauren SenkyrLauren Senkyr is a Habitat Restoration Specialist with NOAA’s Restoration Center.  Based out of Portland, Ore., she works on restoration planning and community outreach for the Portland Harbor Superfund site as well as other habitat restoration efforts throughout the state of Oregon.

Author: Office of Response and Restoration

The National Ocean Service's Office of Response and Restoration (OR&R) provides scientific solutions for marine pollution. A part of the National Oceanic and Atmospheric Administration (NOAA), OR&R is a center of expertise in preparing for, evaluating, and responding to threats to coastal environments. These threats could be oil and chemical spills, releases from hazardous waste sites, or marine debris.

2 thoughts on “Little “Bugs” Can Spread Big Pollution Through Contaminated Rivers

  1. The state of Oregon is using PREDATOR, and STRESSOR assessment in coastrange salmon streams to clarify macroinvertebrate assemblage shifts. Many stream segments in the Siuslaw watershed have shown potential impairment of macroinvetebrate populations. The state appears to be fixated on attributing these shifts on fine sediment as the cause, or at least as the primary cause. The little that I have studied the issues involved suggest that it may be premature to claim fine seds. ODEQ relies heavily upon the 303d list as the main indicator of potential stream water quality impairment, and then this information biases the potential assessment. The 303d list, based mainly on data from LASAR database, is obviously very incomplete assessment of water quality. Very many toxic contaminant NPS pollutants have been ignored due to political biases for 303d listings. Since very little data usually exists for toxic contaminants on stream segments, the state does not allocate funding for toxics assessment during prioritization processes. This is a classic catch 22,that greatly limits natural resource management environmental assessment in the field… therefore suspected pollution never gets clarified. The water responsible agencies fear the reactions of the legislators, that usually ellicit funding reductions for other good work the agencies are still able to do if they make ‘waves’ by wanting to fund pointedly investigative water quality monitoring for any of these pollution sources identified. This dynamic is very limiting for the salmon habitat restoration processes that huge sums of money are used for.

  2. Toxic metal pollution oin the Siuslaw watershed could easily be responsible for the biocriteria listings due to reduction of metal pollution intollerant species. Many sources of anthropogenic lead pollution are identified by field managers, secriptive reports have been submitted, and funding for water sampling has been denied because preliminary sampling was indicative of toxic pollution sourcing problems. It seems scientifically, ecologically, and fiscally irresponsible to ignore the obvoius sources and the preliminary assessments indicating the need for pointedly investigative followup testing to definitively assess these water quality impairment risks. The funding prioritization process is misinformed, and salmon habitat improvement suffers.
    Details are available.

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