Groundwater nitrogen processing in Northern Gulf of Mexico restored marshes
Groundwater nitrogen processing was examined in a restored black needlerush (Juncus roemerianus) marsh to assess its potential for removing land-derived nitrogen pollution. Two restoration designs, one initially planted at 50% cover (half density plots) and the other one at 100% cover (full density...
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| Published in: | Journal of environmental management 2015-03, Vol.150, p.206-215 |
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| Main Authors: | , , , |
| Format: | Article |
| Language: | eng |
| Subjects: | |
| Online Access: | Get full text |
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| Summary: | Groundwater nitrogen processing was examined in a restored black needlerush (Juncus roemerianus) marsh to assess its potential for removing land-derived nitrogen pollution. Two restoration designs, one initially planted at 50% cover (half density plots) and the other one at 100% cover (full density plots), were compared with non-vegetated controls. The introduction via groundwater of a NO3− solution with a conservative tracer (Br−) and labeled isotopically (15N) allowed calculation of nitrogen removal in the plots following two methods. The first method used changes in the ratio [NOx]:[Br−] as the groundwater plume traveled through the plot, and the second method relied on balancing 15N input with 15N export. Both methods showed ≈97% of the N from the simulated groundwater plume was removed (i.e. not delivered to the open waters of the adjacent estuary) in vegetated plots and ≈86% was removed in non-vegetated controls. The most dominant routes of N removal from the introduced solution were N2 production and assimilation into macrophyte biomass, which were similar in magnitude for the vegetated plots, whereas N2 production dominated in the unvegetated plots. The majority of N removed from the introduced solution occurred in the first 30 cm the solution traveled in the vegetated treatments. In addition, ambient porewater concentrations of dissolved inorganic nitrogen (DIN) were similar between full and half density plots, but lower than the non-vegetated control (≈8.5× and 7.5×), suggesting full and half density plots removed more DIN than non-vegetated plots. These results suggest that restoring marshes by planting 50% of the area may be a more cost-effective restoration design in terms of mitigating land-derived nutrient pollution than planting 100% of the area since it requires less effort and cost while removing similar quantities of N.
•We tested nitrogen processing in 2 restored marsh designs and unvegetated areas.•The restoration designs were 50% and 100% initial planting density.•Both designs removed similar amounts of nitrogen and more than unvegetated areas.•N2 production and plant uptake were responsible for most nitrogen removal.•Planting at 50% density is more cost-effective for nitrogen removal. |
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| ISSN: | 0301-4797 1095-8630 |