Saltwater intrusion and soil carbon loss: Testing effects of salinity and phosphorus loading on microbial functions in experimental freshwater wetlands

Servais, Shelby; Kominoski, John S.; Charles, Sean P.; Gaiser, Evelyn E.; Mazzei, Viviana; Troxler, Tiffany G.; Wilson, Benjamin J.

doi:10.1016/j.geoderma.2018.11.013

Cited by 55 publications

(59 citation statements)

References 51 publications

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“…, Servais et al. ). In addition, we saw higher DOC content in the surface water, indicating that this newly produced belowground DOC may also be diffusing or leaching into the water column (Appendix : Table ).…”

Section: Discussionmentioning

confidence: 98%

“…As roots die, DOC can be leached abiotically out of the soil and usually provides an additional energy source for bacteria (Pinney et al 2000). However, we saw a decrease in soil CO 2 efflux with increased salinity, which means that the microbial community was likely too stressed to use this newly available energy source (Schimel et al 2007, Servais et al 2019). In addition, we saw higher DOC content in the surface water, indicating that this newly produced belowground DOC may also be diffusing or leaching into the water column (Appendix S1: Table S2).…”

Section: Effects Of Salinity On Plant Biomass and C Fluxmentioning

confidence: 93%

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Phosphorus alleviation of salinity stress: effects of saltwater intrusion on an Everglades freshwater peat marsh

Wilson

Servais

Charles

et al. 2019

Ecology

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Saltwater intrusion and salinization of coastal wetlands around the world are becoming a pressing issue due to sea level rise. Here, we assessed how a freshwater coastal wetland ecosystem responds to saltwater intrusion. In wetland mesocosms, we continuously exposed Cladium jamaicense Crantz (sawgrass) plants and their peat soil collected from a freshwater marsh to two factors associated with saltwater intrusion in karstic ecosystems: elevated loading of salinity and phosphorus (P) inputs. We took repeated measures using a 2 × 2 factorial experimental design (n = 6) with treatments composed of elevated salinity (~9 ppt), P loading (14.66 μmol P/d), or a combination of both. We measured changes in water physicochemistry, ecosystem productivity, and plant biomass change over two years to assess monthly and two‐year responses to saltwater intrusion. In the short‐term, plants exhibited positive growth responses with simulated saltwater intrusion (salinity + P), driven by increased P availability. Despite relatively high salinity levels for a freshwater marsh (~9 ppt), gross ecosystem productivity (GEP), net ecosystem productivity (NEP), and aboveground biomass were significantly higher in the elevated salinity + P treated monoliths compared to the freshwater controls. Salinity stress became evident after extended exposure. Although still higher than freshwater controls, GEP and NEP were significantly lower in the elevated salinity + P treatment than the +P treatment after two years. However, elevated salinity decreased live root biomass regardless of whether P was added. Our results suggest that saltwater intrusion into karstic freshwater wetlands may initially act as a subsidy by stimulating aboveground primary productivity of marsh plants. However, chronic exposure to elevated salinity results in plant stress, negatively impacting belowground peat soil structure and stability through a reduction in plant roots.

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Section: Discussionmentioning

confidence: 98%

Section: Effects Of Salinity On Plant Biomass and C Fluxmentioning

confidence: 93%

Phosphorus alleviation of salinity stress: effects of saltwater intrusion on an Everglades freshwater peat marsh

Wilson

Servais

Charles

et al. 2019

Ecology

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“…Because nitrite, nitrate, ammonium, TP, and SRP concentrations in fresh and salt source waters were not significantly different, our S treatment did not provide N or P subsidies (Servais et al. , Wilson et al. ).…”

Section: Discussionmentioning

confidence: 99%

“…There was no significant difference between canal and Florida Bay water pH, DOC, DIN,

{NO}_{3}^{-}

{NO}_{2}^{-}

{NH}_{4}^{+}

, TP, or SRP (Servais et al. , Wilson et al. ).…”

Section: Methodsmentioning

confidence: 99%

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Periphyton as an indicator of saltwater intrusion into freshwater wetlands: insights from experimental manipulations

Mazzei

Wilson

Servais

et al. 2020

Ecological Applications

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Saltwater intrusion has particularly large impacts on karstic wetlands of the Caribbean Basin due to their porous, carbonate bedrock and low elevation. Increases in salinity and phosphorus (P) accompanying saltwater intrusion into these freshwater, P‐limited wetlands are expected to alter biogeochemical cycles along with the structure and function of plant and algal communities. Calcareous periphyton is a characteristic feature of karstic wetlands and plays a central role in trophic dynamics, carbon storage, and nutrient cycling. Periphyton is extremely sensitive to water quality and quantity, but the effects of saltwater intrusion on these microbial mats remain to be understood. We conducted an ex situ mesocosm experiment to test the independent and combined effects of elevated salinity and P on the productivity, nutrient content, and diatom composition of calcareous periphyton from the Florida Everglades. We measured periphyton total carbon, nitrogen, and P concentrations and used settlement plates to measure periphyton accumulation rates and diatom species composition. The light and dark bottle method was used to measure periphyton productivity and respiration. We found that exposure to ~1 g P·m−2·yr−1 significantly increased periphyton mat total P concentrations, but had no effect on any other response variable. Mats exposed to elevated salinity (~22 kg salt·m−2·yr−1) had significantly lower total carbon and tended to have lower biomass and reduced productivity and respiration rates; however, mats exposed to salinity and P simultaneously had greater gross and net productivity. We found strong diatom species dissimilarity between fresh‐ and saltwater‐treated periphyton, while P additions only elicited compositional changes in periphyton also treated with saltwater. This study contributes to our understanding of how the ecologically important calcareous periphyton mats unique to karstic, freshwater wetlands respond to increased salinity and P caused saltwater intrusion and provides a guide to diatom indicator taxa for these two important environmental drivers.

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Saltwater and phosphorus drive unique soil biogeochemical processes in freshwater and brackish wetland mesocosms

et al. 2021

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Coastal ecosystems are exposed to saltwater intrusion but differential effects on biogeochemical cycling are uncertain. We tested how elevated salinity and phosphorus (P) individually and interactively affect microbial activities and biogeochemical cycling in freshwater and brackish wetland soils. In experimental mesocosms, we added crossed gradients of elevated concentrations of soluble reactive P (SRP) (0, 20, 40, 60, 80 μg/L) and salinity (0, 4, 7, 12, 16 ppt) to freshwater and brackish peat soils (10, 14, 17, 22, 26 ppt) for 35 d. We quantified changes in water chemistry [dissolved organic carbon (DOC), ammonium (NH4+), nitrate + nitrite (N + N), SRP concentrations], soil microbial extracellular enzyme activities, respiration rates, microbial biomass C, and soil chemistry (%C, %N, %P, C:N, C:P, N:P). DOC, NH4+, and SRP increased in freshwater but decreased in brackish mesocosms with elevated salinity. DOC similarly decreased in brackish mesocosms with added P, and N + N decreased with elevated salinity in both freshwater and brackish mesocosms. In freshwater soils, water column P uptake occurred only in the absence of elevated salinity and when P was above 40 µg/L. Freshwater microbial EEAs, respiration rates, and microbial biomass C were consistently higher compared to those from brackish soils, and soil phosphatase activities and microbial respiration rates in freshwater soils decreased with elevated salinity. Elevated salinity increased arylsulfatase activities and microbial biomass C in brackish soils, and elevated P increased microbial respiration rates in brackish soils. Freshwater soil %C, %N, %P decreased and C:P and N:P increased with elevated salinity. Elevated P increased %C and C:N in freshwater soils and increased %P but decreased C:P and N:P in brackish soils. Freshwater soils released more C and nutrients than brackish soils when exposed to elevated salinity, and both soils were less responsive to elevated P than expected. Freshwater soils became more nutrient‐depleted with elevated salinity, whereas brackish soils were unaffected by salinity but increased P uptake. Microbial activities in freshwater soils were inhibited by elevated salinity and unaffected by added P, but brackish soil microbial activities slightly increased with elevated salinity and P.

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Saltwater intrusion and soil carbon loss: Testing effects of salinity and phosphorus loading on microbial functions in experimental freshwater wetlands

Cited by 55 publications

References 51 publications

Phosphorus alleviation of salinity stress: effects of saltwater intrusion on an Everglades freshwater peat marsh

Phosphorus alleviation of salinity stress: effects of saltwater intrusion on an Everglades freshwater peat marsh

Periphyton as an indicator of saltwater intrusion into freshwater wetlands: insights from experimental manipulations

Saltwater and phosphorus drive unique soil biogeochemical processes in freshwater and brackish wetland mesocosms

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