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SDI in the Great Plains​

Oligochaete Worms Invade SDI System?

Mahbub Alam1, Steve Cringan2, & Wendell Nicholas3

Several taxa of aquatic invertebrates were present in the flushed water from a newly established Subsurface Drip Irrigation (SDI) system. Among them were oligochaete worms (essentially very small aquatic earthworms), larval chironomidae (very early instar midgefly larvae), nymphal insects (very early instar hemipterans, true bugs, probably aquatic), and a few representatives of the groups rotifera and protozoa. The oligochaetes constituted upwards of 90 percent of the biomass in the flush sample and are much larger in size than the other organisms present. These are soft bodied, but may cause orifice clogging from organic materials exudated or decomposed from dead organisms.

All of the observed groups of organisms present in the flush sample represent a typical fauna of habitats such as wet ditches, stream or lake bottoms. They may be found on and in the sediment of stream and ditch bottoms as well as within the interstial spaces of sand, gravel or sediments beneath the upper surface of the stream or ditch floor.

The oligochaete worms appeared to be reproductively mature and full adult size approximately 10 millimeters (0.4 inches) in length with a diameter of approximately 0.2-0.25 millimeters (0.008 to 0.01 inches). Variation in the size of the oligochaetes was not observed suggesting that growth may be rapid to adult size. There were sexually mature individuals present although not all individuals observed had the appearance of sexual maturity. They may also be capable of asexual reproduction. The eggs would probably be on the order of one quarter of adult diameter or smaller (0.05-0.06 millimeter or 0.002 inches). Aquatic oligochaete worms are not a well known group of organisms either in terms of their systematics or their life histories.

It is suspected that the existing old main pipeline, which was incorporated to the system, is the source. But by the process of deduction, it is now suspected that the pore or slit outlet size of the irrigation drip tubes may not block the migration of the worms during periods of disuse with a saturated zone around the emitter opening. The emitter pore size for laterals of 1 3/8" diameter with 24" emitter spacing is large enough to permit entry of these organisms. The tortuous pathway leading to the emitter of the drip tube would provide little obstacle to the worms compared to its movement within the interstial spaces found between soil particles in stream or ditch bottoms. It certainly seems plausible that the worms and other organisms could be entering the system during disuse and in the case of the oligochaetes, actually reproducing and thriving within the system.

The majority of the biomass in the flush sample was of soft-bodied organisms. It is expected that the hazard of clogging outlet orifices would be minimal relative to organisms with a hard or chitinous exoskeleton. Periodic flushing to clear the system along with shock chlorination would seem to be adequate for maintaining the system. It may be useful to periodically filter some of the flushed water as a means of monitoring the system.

The SDI system at Big Bow, Kansas was flushed and chlorinated using gas chlorinator. The injection rate was 20 ppm. The mixture was left inside the system to over winter. This will provide greater contact time. The system will be flushed with fresh water next spring before the irrigation season starts.

Questions about this information may be directed to Mahbub Alam, Extension Agriculture Engineer & Irrigation specialist, (620) 275-9164, e-mail, malam@ksu.edu

1. Extension Agriculture Engineer, K-State Research & Extension
2. Environmental Scientist, KDHE, Kansas
3. SDI System Owner, Big Bow, Kansas