15 January 2013

Africa: Using Insects to Measure Water Quality


Odume Oghenekaro Nelson is a Nigerian student who entered the RISE program at Rhodes University in Grahamstown, South Africa, in 2009.

Since then he has become adept in the use of a new approach in testing water quality based on the presence or condition of certain aquatic insects. Unlike traditional chemical methods of detecting water pollutants, the use of an insect-based technique promises a more accurate and complete picture of ecosystem health.

Nelson's early studies of aquatic insects, which are now complete, earned him an MSc degree in 2011. He has decided to continue this work at the PhD level, expanding the scope of his work to include the water policies formulated by the South African Department of Water Affairs.

His MSc research was accomplished along the Swartkops River that flows through Port Elizabeth and into the Indian Ocean. He chose the Swartkops for its proximity to his university in Grahamstown, and for its hydrological, ecological, and recreational importance to the Eastern Cape region.

The entire Swartkops catchment area, in which about 1 million people live, is subjected to both industrial and agricultural pollution, as is the 12-mile estuarine segment where it broadens, slows, and flows through Port Elizabeth. Activities that degrade its water quality along the way include sand and clay mining, sewage treatment, a salt works, a tannery, multiple discharges from a large industrial area along the river just upstream from the tidal reach, and a large storm water canal system.

Nelson found that traditional chemical techniques for testing water quality did not give accurate or meaningful readings, especially for chemicals that were not on the testing list or that were present in very small amounts. More important, chemical testing gave virtually no information about organisms inhabiting the water, changes in animal and plant communities, and other features that determine the ecological health of rivers.

The presence (or absence) of organisms such as insects, on the other hand, can reveal a great deal about the environment. Those he studied first were small, slender flies of the common family Chironomidae, often known as non-biting midges. While the adult midges superficially resemble mosquitoes, the larvae are the familiar reddish bloodworms found in the river muds of many climates.

Both the adult and larval phases of chironomids provide important food for countless species of predators world-wide, including fishes, dragonflies, toads, beetles, swallows, bats, newts, and others. Because of their importance to many other organisms, their own health is fundamental to overall environmental function.

Members of the Chironomidae family have long been known to prefer relatively clean to polluted water, so that their presence alone provides a rough indication of water quality. When some of these sensitive species are exposed to even small, sub-lethal doses of certain pollutants, however, they show deformities of the mentum, or mouthparts.

Although these deformities may not be noticeable to the non-expert, Nelson has learned to see them as reliable and sensitive indicators of water quality. During his MSc research he learned to identify even slight changes in the mouthparts of chironomids exposed to pollutants, especially the cadmium, chromium, copper, or zinc used in the mining and automotive industries. In such environments, he found, certain mouthparts would be missing, fused, or duplicated, and he developed particular water-quality indexes based on such changes.

He has also studied other insects that can be used to create water quality indices. One is the EPT index, which includes the insect orders Ephemeroptera (mayflies), Placoptera (stoneflies), and Tricoptera (caddisflies). He has also worked with the SASS index, or South African Scoring System, and the ASPT index, for the Average Score Per Taxon (a taxon is a taxonomic unit, such as a genus, order, or family).

Yet another index is the ETOC, which includes the Ephemeroptera and Tricoptera of the EPT index plus the Odonata (dragonflies) and Coleoptera (beetles). In all, he has experimented with about 19 such indices in the Swartkops. Some were sensitive not only to heavy metals, but also to nutrient pollution caused by wastewater and agriculture, or to general pollution that may contain organic compounds, pesticides, nutrients, and other pollutants.

Nelson used a "multi-layered" approach in applying these indicators. In the first layer he compared the baseline (clean-water) insect community with various insect communities that indicate pollution.

In the second layer, which he called multi-metric, he tested river water against all 19 metrics. At the third level, he looked for mouthpart deformities. Learning to apply these three stages of evaluation earned Nelson his MSc "With Distinction," along with a series of publications, three of them in international journals, including the Elsevier journal Physics and Chemistry of the Earth.

In moving to the PhD stage of his work, Nelson and his supervisor, Prof. Tally Palmer of Rhodes University, began to study how the new insect tools could be useful in strengthening two pieces of water legislation in South Africa: the National Water Act (NWA) and the Water Services Act (WSA). The NWA created two strategies: (1) Resource Directed Measures, or RDM, which were designed to protect environmental resources; and (2) Source Directed Controls, or SDC, which were designed to regulate use of water resources through licensing, authorizing, and permitting. For example, companies intending to discharge mine wastes into waterways must comply with limits specified by the SDC.

The Water Services Act, or WSA, sets out strategies to provide water services and sanitation to the public, with two programs for doing so. The first is the Blue Drop certification program, which regulates the structure and management of drinking water systems. The second is the Green Drop program, which regulates the infrastructure by which wastewater is treated before discharge into a river.

The Green Drop program had many good features, says Nelson, but because it depends on traditional chemical techniques for evaluating water quality, it did not succeed in raising environmental water quality. When Nelson and Prof. Palmer had studied their new techniques, they decided to present them to the people in positions to use them: the administrators of the Nelson Mandela Bay Municipality, in Port Elizabeth, and the nearby Sundays River Valley Municipality, a key citrus growing area. They presented their findings, and after some initial confusion about the concept, the administrators agreed to help with additional testing.

"What we wanted to do," said Nelson, "was to get these two pieces of legislation - the National Water Act and the Water Services Act - to relate to each other. We needed metrics that were sensitive enough to make them both work better. The question we posed was, if we treat our wastewater, and find it is compliant at the discharge point, does that protect our resources in the river? At the present moment, wastewater compliance is measured only chemically. If it's below the chemical limit, everyone says, that's fine. But that tells us nothing about the health of the ecosystem."

What Nelson proposed to the municipalities was to test the wastewater by the insect-based techniques after wastewater treatment. When the municipalities agreed, he selected a particular wastewater plant. In July 2012, he laid out a series of nine small test streams (20 feet long and 6 inches wide) that allow the treated effluent to flow through them en route to the river.

The test streams began running in August, and sampling began in November 2012. The effluent from the plant to the first three streams was treated with the customary amount of chlorine to kill bacteria (i.e., 100 percent effluent concentration); the effluent in the second three streams was diluted with dechlorinated tap water to give a 50 percent concentration of the original effluent; and the last three streams received only dechlorinated tap water . The wastewater will be allowed to run through the streams for at least six months, with regular sampling of insects. At the same times, the river itself will also be sampled.

Nelson will also make the sampling more accurate by moving from simple analysis of species to analysis of traits (features) within each species. "What we are after," he said, "is a trait-based approach for monitoring water pollution in South Africa. We want to measure multiple insect traits: body size, shape, level of hemoglobin, respiration mode, diet, feeding methods, mobility, and rate of dispersal as the larvae emerge as adults. All these tell us something about the health of the species, and the ecosystem. We will make up our own specific index using these traits. This will tell us what traits allow the insects to survive, and how they are affected by pollution."

He acknowledges that there are limitations to the use of insects. For one, the aquatic immature stages of the insects are often difficult to identify. Also, the chironomid index can be used only when chironomid species live in the water to be sampled. And some individual insects have different responses to pollutants than others, so that multiple species - and indexes - are needed.

"We know we'll have problems to fix," he said. "But I am optimistic that we can fix them. The good thing is that these new indexes give us a way to bridge the needs of the National Water Act and the Water Services Act. One is trying to protect the environment, and one is trying to protect the quality of the water for the people who use it. What we are doing protects both at once."

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