|BAKER, BETH - Mississippi State University|
|KROGER, ROBERT - Mississippi State University|
|CZARNECKI, JOBY - Mississippi State University|
Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2015
Publication Date: N/A
Interpretive Summary: Reducing runoff water inputs, specifically runoff nutrients, is a key goal from farms employing nutrient best management plans in regions impacting large bodies of water, such as the Gulf of Mexico. One approach to reduce nutrient runoff is through the use of low-grade weirs, which can slow water down thus causing a “ponding” effect in drainage ditches. The purpose of this ponding effect is to cause the conversion of these nutrients to forms which will not transport horizontally or vertically through the soil profile. To date the biological processes involved in these weirs are unknown. This study aimed to determine the effect these weirs have on the microbial population of these drainage ditches. Overall, it was shown that the process is complex with many genes activated and microbial populations were induced by the soil C inputs. This study demonstrated the most effective sampling approach to understanding these environments, particularly given their heterogeneity.
Technical Abstract: Enhancing wetland characteristics in agricultural drainage ditches with the use of low-grade weirs, has been identified as a potential best management practice (BMP) to mitigate nutrient runoff from agriculture landscapes. This study examined microbe community abundance and diversity involved in denitrification in agricultural drainage systems fitted with low-grade weirs. Appropriate sampling scales of microbial communities were investigated using 16S rRNA, as well as denitrification functional genes nosZ, nirS, and nirK via qPCR and T-RFLP analysis. Genes 16S rRNA, nosZ and nirS were all successfully detected in soil samples, while nirK was below the detection limit (5,000 GU/g soil) throughout the study. Utilizing a combination of all sampling regimes was found to be most effective in capturing microbial community patterns without capturing too much noise from environmental heterogeneity, as ANOVA results revealed no significant differences in 16S rRNA or nirS between predetermined sampling scales (p>0.05). A Pearson correlation matrix confirmed that 16S rRNA and nosZ gene abundances were positively correlated with soil C, N, and moisture, while nirS abundance was only positively correlated with soil C and soil moisture. This highlights the potential for wetland-like characteristics to be recovered in agricultural drainage systems, as implementing weirs in these systems is observed to enhance soil moisture and conditions for N remediation. This study provides the basis for additional investigations of these unique environments in the Mississippi Alluvial Valley and a starting point for adaptive management to enhance environments for microbial communities towards bioremediation goals.