Ditching Nutrients: Roadside Drainage Networks are Hotspots for Microbial Nitrogen Removal. Issue 7 (2nd July 2021)

• Record Type: Journal Article
• Authors: Tatariw, Corianne; Mason, Olivia U.; Mortazavi, Behzad
• Is Part Of: Journal of geophysical research. Volume 126:Issue 7(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-02
• Subjects: roadside ditch -- denitrification -- anammox -- land use change -- nitrogen removal; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2020JG006115
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: Human‐made stormwater control systems are biogeochemical hotspots, but construction and management may result in homogenization of their ecosystem structure. Roadside ditches are a ubiquitous part of the landscape, yet few studies have quantified their biogeochemical potential. We conducted a study to determine (a) nitrate (NO3 − ) removal potential through rate measurements and (b) microbial community structure using 16S rRNA gene (iTag) sequencing in roadside ditches draining predominantly forested, urban, and agricultural watersheds surrounding Mobile Bay, AL (USA). We found that nitrogen (N) removal rates by denitrification and anammox dominated over N‐retention by dissimilatory nitrate reduction to ammonium, accounting for upwards of 89% of NO3 − reduction on average. There were no differences in soil characteristics between land use types, but denitrification potential rates in forested ditches were less than half of those in urban and agricultural ditches, possibly as a result of differences in vegetation management. Microbial alpha and beta diversity were largely homogenous across the three land use types. However, indicator species analysis revealed putative ammonia oxidizers ( Nitrososphaeraceae and Nitrosomonadaceae ), nitrate reducers (Gaiellales), and nitrous oxide reducers ( Myxococcales ) as significant groups in urban and agricultural ditches. We conclude that land use effects on N‐removal in these constructed drainage networks are mediated through key microbial groups and ditch vegetation management strategies. Further, roadside ditches have significant potential for reactive N removal in the landscape. Plain Language Summary: Humans have increased the amount of the nutrient nitrogen in the environment, resulting in issues such as harmful algal blooms and dead zones in coastal waters. Excess nitrogen can be removed from the environment by different microbial process. While microbial nitrogen removal occurs in many ecosystems, those that are vegetated with fluctuating water levels, such as wetlands, are very well suited for nitrogen removal. Like wetlands, roadside ditches have fluctuating water levels, and are likely to be vegetated, but little is known about their capacity for nitrogen removal. We measured microbial nitrogen removal rates and examined microbial community structure (i.e., "who's there") to see how well roadside ditches remove nitrogen. We found that ditches have nitrogen removal rates comparable to those of many natural ecosystems, including wetlands and rivers. Nitrogen removal potential was higher in ditches located in regions with more human activity, such as where cities and farms are located, which were also characterized by more microbes that are able to process nitrogen. Overall, our study shows that roadside ditches may be important areas for removing nitrogen in the environment. Key Points: Dissimilatory nitrate reduction was dominated by denitrification and anammox, rather than dissimilatory nitrate reduction to ammonium Removal rates were higher in urban and agriculture dominated catchments Nitrogen‐cycling microbes were indicators of urban and agricultural land use