Nitrogen interception and export by experimental salt marsh plots exposed to chronic nutrient addition

Brin, Lindsay D.; Valiela, Iván; Goehringer, D. D.; Howes, Brian L.

doi:10.3354/meps08460

Cited by 47 publications

(38 citation statements)

References 36 publications

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“…Marshes can retain up to 95% of supplied N from dry fertilizer broadcast on the marsh surface or buried in the rooting zone as slow‐release granules (Brin et al. ). Based on estimates of net nitrate retention and nitrate concentrations measured in ebbing tidal water in the current study, ~50% of the nitrate added to the enriched creeks is exported on the following ebb tide (Drake et al.…”

Section: Discussionmentioning

confidence: 99%

Saltmarsh plant responses to eutrophication

Johnson¹,

Warren

Deegan

et al. 2016

Ecological Applications

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Abstract. In saltmarsh plant communities, bottom-up pressure from nutrient enrichment is predicted to increase productivity, alter community structure, decrease biodiversity, and alter ecosystem functioning. Previous work supporting these predictions has been based largely on short-term, plot-level (e.g., 1-300 m 2 ) studies, which may miss landscape-level phenomena that drive ecosystem-level responses. We implemented an ecosystem-scale, nine-year nutrient experiment to examine how saltmarsh plants respond to simulated conditions of coastal eutrophication. Our study differed from previous saltmarsh enrichment studies in that we applied realistic concentrations of nitrate (70-100 μM NO 3 − ), the most common form of coastal nutrient enrichment, via tidal water at the ecosystem scale (~60,000 m 2 creeksheds). Our enrichments added a total of 1,700 kg N·creek −1 ·yr −1 , which increased N loading 10-fold vs. reference creeks (low-marsh, 171 g N·m −2 ·yr −1 ; high-marsh, 19 g N·m −2 ·yr −1 ). Nutrients increased the shoot mass and height of low marsh, tall Spartina alterniflora; however, declines in stem density resulted in no consistent increase in aboveground biomass. High-marsh plants S. patens and stunted S. alterniflora did not respond consistently to enrichment. Nutrient enrichment did not shift community structure, contrary to the prediction of nutrient-driven dominance of S. alterniflora and Distichlis spicata over S. patens. Our mild responses may differ from the results of previous studies for a number of reasons. First, the limited response of the high marsh may be explained by loading rates orders of magnitude lower than previous work. Low loading rates in the high marsh reflect infrequent inundation, arguing that inundation patterns must be considered when predicting responses to estuarine eutrophication. Additionally, we applied nitrate instead of the typically used ammonium, which is energetically favored over nitrate for plant uptake. Thus, the form of nitrogen enrichment used, not just N-load, may be important in predicting plant responses. Overall, our results suggest that when coastal eutrophication is dominated by nitrate and delivered via flooding tidal water, aboveground saltmarsh plant responses may be limited despite moderate-to-high water-column N concentrations. Furthermore, we argue that the methodological limitations of nutrient studies must be considered when using results to inform management decisions about wetlands.

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Section: Discussionmentioning

confidence: 99%

Saltmarsh plant responses to eutrophication

Johnson¹,

Warren

Deegan

et al. 2016

Ecological Applications

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“…Salt marshes occupy the transition zone between marine and terrestrial ecosystems, and can retain or remove a large proportion of upslope N inputs that would otherwise enter the ocean (Seitzinger 1988, Nixon et al 1996, Brin et al 2010. Thus, these ecosystems play an important role as filters that mitigate the impacts of terrestrial N inputs on marine ecosystems (Valiela et al 2000, Mitsch et al 2001, Valiela and Cole 2002, Fisher and Acreman 2004.…”

Section: Introductionmentioning

confidence: 99%

Microbially mediated nitrogen retention and loss in a salt marsh soil

2015

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Abstract. Salt marshes currently play an important role as filters for upslope nitrogen (N) inputs. This could change in the future with sea level rise, warming and eutrophication, which are expected to favor monocultures over diverse plant communities. We explored patterns in gross N cycling, dissimilatory nitrate (NO 3 À ) reduction to ammonium (NH 4 þ ) (DNRA), and denitrification in a salt marsh soil under two typical redox conditions (aerobic and anaerobic), and in soils under plant communities manipulated to simulate potential future composition (forb and graminoid monocultures). Natural salt marsh soils exhibited high potential gross N mineralization rates, averaging 50.4 6 5.7 lg N g À1 d À1 under aerobic conditions; rates declined to 23.6 6 3.4 lg N g À1 d À1 under an N 2 headspace. Microbial NH 4 þ uptake and gross nitrification together accounted for only 14 % of gross N mineralization. Nitrogen retention via DNRA and microbial uptake greatly exceeded N losses via denitrification. Gross nitrification rates were greater in the forb and graminoid monocultures than in the control. This effect may be mediated by the lower plant biomass in the monocultures than in the control, which may have reduced competition between plants and nitrifiers for NH 4 þ . Soil NO 3 À concentrations and net nitrous oxide (N 2 O) fluxes were greatest for the forb monoculture, likely due to higher soil oxygen (O 2 ) concentrations in these plots. Our results suggest that salt marsh soils with a diverse plant community have high potential rates of N mineralization and microbial N retention, and the establishment of forb monocultures could lead to greater ecosystem N losses.

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“…In general, N 2 O emissions are considered detrimental as they increase atmospheric pollution. However, in coastal systems, denitrification leading to increased N 2 O efflux may be seen as environmentally beneficial, when this prevents the release of nitrate into the marine environment that can lead to eutrophication (Brin et al, 2010). There are very few studies concerning N 2 O emissions from freshwater or saltwater wetland soils (Poffenbarger et al, 2011).…”

Section: Introductionmentioning

confidence: 99%