Unintended consequences of mitigating agricultural run-off: Changes to symbiotic bacterial communities of resident isopods

Background/Question/Methods

Phosphorus (P) is an essential nutrient applied to agricultural fields to improve crop biomass. Much of this P is unused by the plants, runs off of fields, and enters waterways. Increased P in waterways can lead to harmful algal blooms and ecosystem deterioration. Iron slag and drinking water filter residues (DWFR) adsorb P and can be applied to areas of high agricultural runoff such as adjacent drainage ditches or tile outlets, potentially lessening nutrient runoff. It is unknown however if the application of such materials may have unintended effects on the biological communities within these habitats. To that end, we assessed symbiotic bacterial communities found in and on aquatic isopods (Family Asellidae) inhabiting a drainage ditch treated with iron slag and DWFR. We collected isopods upstream and downstream of these mitigation treatments (Nf64) and extracted total genomic DNA from each. We utilized terminal restriction fragment length polymorphism (TRFLP) analysis of PCR amplified bacterial DNA (16S rRNA gene region) to evaluate isopod bacterial community structure across the sites before and after P mitigation treatment application.

Results/Conclusions

TRFLP analyses indicated that both iron slag and DWFR treatments altered isopod bacterial community structures (Iron slag: PERMANOVA F(1,29)=3.89, p=0.006; DWFR: PERMANOVA F(2,33)=3.69, p=0.0006). Changes in these bacterial communities as a result of the P mitigation treatment may be to the detriment of isopod health. Additional study is warranted to determine what components of the bacterial communities were altered and if these altered bacterial communities of the isopods result in decreased host fitness.