Variation of microorganisms in drip irrigation systems using high-sand surface water

Using high-sand surface water in agricultural irrigation has become an alternative way to release groundwater stress. Although drip irrigation is considered as the most appropriate irrigation method for high-sand water application, as it is precise and controllable, it easily leads to emitter dogging. The clogging issue couldn't be well controlled if merely focused on the sand size and concentration. Therefore, figuring out whether microorganisms significantly affect the clogging process is important for appropriate high-sand water utilization. Based on these, the phospholipid fatty acids (PLFAs) was applied as the biological indicator of the microorganisms, and an in-site drip irrigation experiment using eight types of flat emitters was carried out. The results indicated that there were more than 10 types of PLFAs in emitter clogging substances using high-sand water, brackish water and their 1:1 mixed water in volume. As PLFAs contents showed significant positive linear correlations with emitter clogging degree (CD) (R-2 > 0.89, p < 0.05), it demonstrated that microorganism variations directly affected emitter clogging process. Among the PLFAs obtained, Pseudomonas 16:0 and heavy pyrolysis hydrogen Bacillus 18:0 were the PLFAs those fully distributed during the clogging process, which occupied 66.0%-87.0% of the total contents of PLFAs, and they both displayed significant linear correlations with CD (R-2 > 0.72, p < 0.05). Therefore, they were considered as the critical bacteria to emitter clogging. Their competition and the effects on the other types of PLFAs determined the evolution and variation characteristics of the microorganism community, and the ecological parameters of microorganism community (including diversity, evenness and dominance indexes) all had significant quadratic patterns with CD (R-2 > 0.56, p < 0.05). Although mixing high-sand water and brackish water in equal volume reduced both the sediment and salinity in the water source, the PLFAs obviously increased and resulted in the more intense biological clogging process and thus enhanced the physical-chemical-biological coupling effects. Consequently, the operating cycle of mixed water treatment decreased by 8.9%-22.0%. The results in this paper aim to provide theoretical references to drip irrigation emitter clogging mechanism using high-sand surface water and to offer guidelines for appropriate high-sand water utilization in agriculture.