Elevated nutrient inputs to marshes differentially impact carbon and nitrogen cycling in two northern Gulf of Mexico saltmarsh plants

Ledford, Taylor; Tatariw, Corianne; Mason, Olivia U.

doi:10.1007/s10533-020-00656-9

Cited by 19 publications

(15 citation statements)

References 75 publications

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“…As hypothesized, the constructed marshes were net CO 2 sinks with similar rates to the reference marsh, suggesting that ecosystem CO 2 exchange is tightly coupled to plant biomass recovery and can therefore occur a few decades after construction. Further, GEP and

{ER}_{{CO}_{2}}

were comparable to other natural marshes in the Mobile Bay region (Wilson et al 2015; Starr et al 2018; Ledford et al 2020), including marshes comprised of different plant species than in this study. Although CO 2 exchanges showed a faster trajectory of recovery than what has been shown in other studies (Moreno‐Mateos et al 2012), we still measured lower sediment %OM, which is consistent with prior findings that OM recovery can lag for decades following construction or restoration (Craft et al 2003).…”

Section: Discussionsupporting

confidence: 81%

“…Average annual ecosystem respiration (

{ER}_{{CO}_{2}}

) versus average annual gross ecosystem production (GEP) from various marshes around Mobile Bay. Small open circles represent

{ER}_{{CO}_{2}}

: GEP ratios from natural marshes located at Dauphin Island (DI), AL, Dog River, AL, Grand Bay (GB), AL, Point Aux Pins (PP), AL, and Week's Bay (WB), AL collected previously from Wilson et al (2015), Starr et al (2018), and Ledford et al (2020). In marshes where two vegetation types were observed (Dauphin Island, Grand Bay, and Point Aux Pins), rates were averaged by vegetation type ( Juncus and Spartina ).…”

Section: Resultsmentioning

confidence: 99%

“…Grayscale open triangles represent the

{ER}_{{CO}_{2}}

: GEP ratios from the reference natural marsh (black), CON‐1 (white), and CON‐2 (gray) from the current study in Fowl River, AL. Points inside the gray box indicate plots that were amended with N and P from Dauphin Island, AL from Ledford et al (2020). Error bars represent means ± 1SE and the dashed line shows the 1:1 ratio.…”

Section: Resultsmentioning

confidence: 99%

“…In contrast, both extractable and pore‐water NH 4 + were comparable across marshes, which suggest the ammonium pool may be fed by high N remineralization in constructed marshes and not tidal delivery. In general, coastal marsh productivity is nutrient (N and P) limited (Gallagher 1975; Valiela et al 1975; Patrick & Delaune 1976; Haines 1979; Mendelssohn 1979; Buresh et al 1980; Cargill & Jefferies 1980; Cavalieri & Huang 1981; Darby & Turner 2008; Davis et al 2017; Ledford et al 2020), and inorganic forms of N (NO 3 − , NO 2 − , and NH 4 + ) are strong drivers of plant growth and productivity (Hachiya & Sakakibara 2017). Particularly, NH 4 + can be more bioavailable to plants in anaerobic soils compared to NO 3 − and NO 2 − (Miller & Cramer 2005).…”

Section: Discussionmentioning

confidence: 99%

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Ecosystem carbon exchange and nitrogen removal rates in two 33‐year‐old constructed salt marshes are similar to those in a nearby natural marsh

Ledford

Tatariw

Starr

et al. 2021

Restoration Ecology

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Human activities have led to 1–2% of coastal wetlands lost per year globally, with subsequent losses in ecosystem services such as nutrient filtering and carbon sequestration. Wetland construction is used to mitigate losses of marsh cover and services resulting from human impacts in coastal areas. Though marsh structure can recover relatively quickly (i.e., <10 years) after construction, there are often long‐term lags in the recovery of ecosystem functions in constructed marshes. We conducted a year‐long study comparing seasonal plant productivity, ecosystem respiration (ERCO2), denitrification, and dissimilatory nitrate reduction to ammonium (DNRA) between two 33‐year‐old constructed marshes (CON‐1, CON‐2) and a nearby natural reference marsh (NAT). We found that CON‐1 and CON‐2 were structurally similar to NAT (i.e., plant aboveground and belowground biomass did not differ). Likewise, gross ecosystem productivity (GEP), ERCO2, and net ecosystem exchange (NEE) were similar across all marshes. Further, DNRA and denitrification were similar across marshes, with the exception of greater denitrification rates at CON‐2 than at the other two sites. While pore‐water ammonium concentrations were similar across all marshes, organic matter (OM) content, pore‐water phosphate, nitrate + nitrite, and hydrogen sulfide concentrations were greater in NAT than CON‐1 and CON‐2. Collectively, this work suggests that current marsh construction practices could be a suitable tool for recovering plant structure and some ecosystem functions. However, the lag in recovery of pore‐water nutrient stocks and OM content also suggests that some biogeochemical functions may take longer than a few decades to fully recover in constructed marshes.

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{ER}_{{CO}_{2}}

Section: Discussionsupporting

confidence: 81%

“…Average annual ecosystem respiration (

{ER}_{{CO}_{2}}

) versus average annual gross ecosystem production (GEP) from various marshes around Mobile Bay. Small open circles represent

{ER}_{{CO}_{2}}

Section: Resultsmentioning

confidence: 99%

“…Grayscale open triangles represent the

{ER}_{{CO}_{2}}

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Ecosystem carbon exchange and nitrogen removal rates in two 33‐year‐old constructed salt marshes are similar to those in a nearby natural marsh

Ledford

Tatariw

Starr

et al. 2021

Restoration Ecology

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“…Soil extractable NH 4 + was determined fluorometrically with a Turner Designs 7200‐002 fluorometer equipped with a CDOM/NH4 UV module (Holmes et al 1999: Protocol B). Porewater NO 3 − concentrations in the region are typically low and do not show spatial variability (Wilson et al 2015; Ledford et al 2020), so extractable NO 3 − was not measured in this study.…”

Section: Methodsmentioning

confidence: 89%

Nitrate reduction capacity is limited by belowground plant recovery in a 32‐year‐old created salt marsh

Tatariw

Mortazavi

Starr

et al. 2020

Restoration Ecology

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Human activities have decreased global salt marsh surface area with a subsequent loss in the ecosystem functions they provide. The creation of marshes in terrestrial systems has been used to mitigate this loss in marsh cover. Although these constructed marshes may rapidly recover ecosystem structure, biogeochemical processes may be slow to recover. We compared denitrification and dissimilatory nitrate reduction to ammonium (DNRA) rates between a 32‐year‐old excavation‐created salt marsh (CON‐2) and a nearby natural reference salt marsh (NAT) to assess the recovery of ecosystem function. These process rates were measured at 5 cm increments to a depth of 25 cm to assess how plant rooting depth and organic matter accumulation impact N‐cycling. We found that, for both marshes, denitrification and DNRA declined with depth with the highest rates occurring in the top 10 cm. In both systems, N‐retention by DNRA accounted for upwards of 75% of nitrate reduction, but denitrification and DNRA rates were nearly 2× and 3× higher in NAT than CON‐2, respectively. Organic matter was 6× lower in CON‐2, likely due to limited plant belowground biomass production. However, there was no response to glucose additions, suggesting that the microbial functional community, not substrate limitation, limited nitrate reduction recovery. Response ratios showed that denitrification in CON‐2 recovered in surficial sediments where belowground biomass was highest, even though biomass recovery was minimal. This indicates that although recovery of ecosystem function was constrained, it occurred on a faster trajectory than that of ecosystem structure.

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Labile organic matter promotes nitrogen retention in natural and constructed gulf coast marshes

Starr,

Mortazavi,

Tatariw

et al. 2024

Biogeochemistry

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Coastal marshes mitigate allochthonous nitrogen (N) inputs to adjacent marine habitat; however, their extent is declining rapidly. As a result, marsh restoration and construction have become a major foci of wetland management. Constructed marshes can quickly reach similar plant biomass to natural marshes, but biogeochemical functions like N removal and retention can take decades to reach functional equivalency, often due to lags in organic matter (OM) pools development in newly constructed marshes. We compared denitrification and dissimilatory nitrate reduction to ammonium (DNRA) rates in a 32 year-old constructed marsh and adjacent reference marsh in the Northern Gulf of Mexico. Marsh sediments packed into 3 mm “thin discs” were subjected to three OM quality treatments (no OM addition, labile OM, or recalcitrant OM) and two N treatments (ambient nitrate or elevated nitrate) during a 13 day incubation. We found that OM addition, rather than marsh type or nitrate treatment, was the most important driver of nitrate reduction, increasing both denitrification and DNRA and promoting DNRA over denitrification in both marshes. Fungal and bacterial biomass were higher in the natural marsh across treatments, but recalcitrant OM increased fungal biomass in the constructed marsh, suggesting OM-limitation of fungal growth. We found that constructed marshes are capable of similar denitrification and DNRA as natural marshes after 30 years, and that labile OM addition promotes N retention in both natural and constructed marshes. Graphical Abstract Conceptual figure highlighting the findings of this experiment. Under control treatment with no C addition (bottom panel), constructed and natural marshes have similar rates of both DNRA and denitrification. The natural marsh has higher fungal and bacterial biomass, while fungal biomass is not detectable in the constructed marsh. Under labile OM additions (upper left panel), rates of both DNRA and denitrification are increased and DNRA becomes favored over denitrification in both marshes. Recalcitrant OM additions (upper right) increase denitrification, but do not affect DNRA or % denitrification. The addition of recalcitrant OM also increases the detectability of fungal biomass in the constructed marsh.

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Elevated nutrient inputs to marshes differentially impact carbon and nitrogen cycling in two northern Gulf of Mexico saltmarsh plants

Cited by 19 publications

References 75 publications

Ecosystem carbon exchange and nitrogen removal rates in two 33‐year‐old constructed salt marshes are similar to those in a nearby natural marsh

Ecosystem carbon exchange and nitrogen removal rates in two 33‐year‐old constructed salt marshes are similar to those in a nearby natural marsh

Nitrate reduction capacity is limited by belowground plant recovery in a 32‐year‐old created salt marsh

Labile organic matter promotes nitrogen retention in natural and constructed gulf coast marshes

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