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1. Submarine Groundwater Discharge Alters Benthic Community Composition and Functional Diversity on Coral Reefs

   https://doi.org/10.3390/d17030161  

   Barnas, Danielle M; Zeff, Maya; Silbiger, Nyssa J (March 2025, Diversity)

   Coral reefs experience numerous natural and anthropogenic environmental gradients that alter biophysical conditions and affect biodiversity. While many studies have focused on drivers of reef biodiversity using traditional diversity metrics (e.g., species richness, diversity, evenness), less is known about how environmental variability may influence functional diversity. In this study, we tested the impact of submarine groundwater discharge (SGD) on taxonomic and functional diversity metrics in Mo‘orea, French Polynesia. SGD is the expulsion of terrestrial fresh or recirculated seawater into marine environments and is associated with reduced temperatures, pH, and salinity and elevated nutrient levels. Using a regression approach along the SGD gradient, we found that taxon and functional-entity richness displayed unimodal relationships to SGD parameters, primarily nitrate + nitrite and phosphate variability, with peak richness at moderate SGD for stony coral and the full benthic community. Macroalgae showed this unimodal pattern for functional-entity but not taxonomic richness. Functional community composition (presence and abundance of functional entities) increased along the gradient, while taxonomic composition showed a nonlinear relationship to SGD-related parameters. SGD is a common feature of many coastal ecosystems globally and therefore may be more important to structuring benthic functional diversity than previously thought. Further, studying community shifts through a functional-trait lens may provide important insights into the roles of community functions on ecosystem processes and stability, leading to improved management strategies. 

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2. Long‐term nutrient enrichment, mowing, and ditch drainage interact in the dynamics of a wetland plant community

   https://doi.org/10.1002/ecs2.3252  

   Goodwillie, Carol; McCoy, Michael W.; Peralta, Ariane L. (October 2020, Ecosphere)

   Abstract Fertilization studies have elucidated basic principles of the role of nutrients in shaping plant communities and demonstrated the potential effects of anthropogenic nutrient deposition. Yet less is known about how these effects are mediated by interacting ecological factors, particularly in nutrient‐poor wetland habitats. In a long‐term experiment in a coastal plain wetland, we examined how fertilization and mowing affected the diversity and composition of a plant community as it reestablished after major disturbance. A drainage ditch in proximity to the experimental plots allowed us also to consider the influence of hydrology and its interactions with nutrient addition. Fertilization decreased species richness, with wetland specialist species showing especially great losses, and several lines of evidence suggest that the effect was mediated by competition for light. Altered hydrology via ditch drainage had effects that were similar to fertilization, with more rapidly draining plots showing lower diversity and decreased abundance of wetland species. Plant community diversity and dynamics were influenced by complex interactions between fertilization, disturbance, and hydrology. The negative effect of fertilization on species richness was initially mitigated by mowing, but in later years was more evident in mowed than in unmowed plots. In the absence of disturbance, nutrient addition increased the rate of transition to primarily woody communities. Similarly, drained plots experienced increased rates of succession compared to wetter plots. Our results suggest that these interactions need to be considered to understand the potential effects of anthropogenic nutrient addition and hydrologic alterations to wetland ecosystems. 

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3. Year-around survey and manipulation experiments reveal differential sensitivities of soil prokaryotic and fungal communities to saltwater intrusion in Florida Everglades wetlands

   https://doi.org/10.1016/j.scitotenv.2022.159865  

   Zhao, Jun; Chakrabarti, Seemanti; Chambers, Randolph; Weisenhorn, Pamela; Travieso, Rafael; Stumpf, Sandro; Standen, Emily; Briceno, Henry; Troxler, Tiffany; Gaiser, Evelyn; et al (February 2023, Science of The Total Environment)

   Global sea-level rise is transforming coastal ecosystems, especially freshwater wetlands, in part due to increased episodic or chronic saltwater exposure, leading to shifts in biogeochemistry, plant- and microbial communities, as well as ecological services. Yet, it is still difficult to predict how soil microbial communities respond to the saltwater exposure because of poorly understood microbial sensitivity within complex wetland soil microbial communities, as well as the high spatial and temporal heterogeneity of wetland soils and saltwater exposure. To address this, we first conducted a two-year survey of microbial community structure and bottom water chemistry in submerged surface soils from 14 wetland sites across the Florida Everglades. We identified ecosystem-specific microbial biomarker taxa primarily associated with variation in salinity. Bacterial, archaeal and fungal community composition differed between freshwater, mangrove, and marine seagrass meadow sites, irrespective of soil type or season. Especially, methanogens, putative denitrifying methanotrophs and sulfate reducers shifted in relative abundance and/or composition between wetland types. Methanogens and putative denitrifying methanotrophs declined in relative abundance from freshwater to marine wetlands, whereas sulfate reducers showed the opposite trend. A four-year experimental simulation of saltwater intrusion in a pristine freshwater site and a previously saltwater-impacted site corroborated the highest sensitivity and relative increase of sulfate reducers, as well as taxon-specific sensitivity of methanogens, in response to continuously pulsing of saltwater treatment. Collectively, these results suggest that besides increased salinity, saltwater-mediated increased sulfate availability leads to displacement of methanogens by sulfate reducers even at low or temporal salt exposure. These changes of microbial composition could affect organic matter degradation pathways in coastal freshwater wetlands exposed to sea-level rise, with potential consequences, such as loss of stored soil organic carbon. 

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4. Data for: Drainage impacts on the productivity of wetland species Spartina alterniflora and Salicornia pacifica

   https://doi.org/10.5061/dryad.5qfttdzc1  

   Watson, Elizabeth; Chernesky, Kylie; Njie, Daouda; Champlin, Lena; Swenson Perger, Darci; University, Drexel (January 2023, Dryad)

   Coastal wetlands display ecohydrological zonation such that vertical differences of plant zones are driven by varying groundwater levels over tidal cycles. It is unclear how variable levels of tidal drainage directly impact biotic and abiotic factors in coastal wetland ecosystems. To determine the impacts of drainage levels, simulated tides in mesocosms with varying degrees of drainage were created with Spartina alterniflora, the salt marsh coastal ecosystem dominant species on the United States Atlantic Coast, and Salicornia pacifica, the Pacific Coast dominant. We measured biomass production and photosynthesis as indicators of plant health, and we also measured soil and porewater characteristics to help interpret patterns of productivity. These measures included above and belowground biomass, porewater pH, salinity, ammonium concentration, sulfide concentration, soil redox potential, net ecosystem exchange, photosynthesis rate, respiration rate, and methane flux. We found the greatest plant production in soils with intermediate drainage levels, with production values that were 13.7% higher for S. alterniflora and 57.7% higher for S. pacifica in the intermediate flooding levels than found in more inundated and more drained conditions. Understanding how drainage impacts plant species is important for predicting wetland resilience to sea level rise, as increasing water levels alter ecohydrological zonation. 

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5. Experimental warming weakens positive plant diversity effects on pitfall trap sampled ant diversity.

   Clark, A. (April 2022, Soil organisms)

   Abstract Ants are important components of many terrestrial ecosystems because of their high abundance, their central position in food webs, and because they can strongly influence ecosystem properties such as soil aeration, nutrient cycling, and plant community composition. Moreover, ants are also known to respond strongly to changes in environmental and biological conditions. In particular, two major anthropogenic environmental impacts – climate change and the loss of primary producers – may have interactive effects on ant communities. To examine this potential interaction, we quantified pitfall trap sampled ant diversity and activity across a fully factorial experiment manipulating temperature and grassland plant species richness at the Cedar Creek Ecosystem Science Reserve in Minnesota, USA. Consistent with previous arthropod studies, we found a significant increase in sampled ant diversity in plots with higher sown plant species richness, such that plots with the largest number of plant species also had the highest sampled ant diversity. However, the strength of this relationship declined significantly in experimentally warmed subplots, especially when considered for higher aggregated spatial scales of samples. Taken together, these results suggest that the positive effects of plant diversity on sampled ant diversity may be partially undermined under warmer conditions. 

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