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River networks serve as conduits for dissolved organic matter (DOM) and carbon (DOC) from inland to coastal waters. Human activities and climate change are altering DOM sources, causing hydrological and biogeochemical shifts that impact DOC concentrations and changing the transport and transformation of DOM and DOC. Here, we synthesize current knowledge of changing DOM sources, DOC concentrations, and the associated hydrological and biogeochemical changes during transport along inland-to-coastal gradients, focusing on impacts to coastal and estuarine DOM and DOC. We project that continued land-use changes, hydrological management, and sea-level rise will result in more microbial and labile DOM, higher DOC concentrations, and an overall decoupling of DOC quantity and DOM quality. Understanding how these changes vary among river networks is essential to forecast coastal and estuarine water quality, ecosystem health, and global carbon cycling. 

Along low-elevation coastlines, sea-level rise (SLR) threatens to salinate ecosystems. To understand the effects of SLR and freshwater management on landscape carbon (C) exchange, we measured the net ecosystem exchange (NEE) of CO2 between subtropical wetland ecosystems and the atmosphere along a dynamic salinity gradient. Ecosystems were representative of freshwater marl prairies, brackish ecotones, and saline scrub mangrove forests in the southeastern Everglades. Patterns in NEE explained the landward movement of coastal wetlands, a process observed over the last 70 years. The capacity to capture C was greatest along the coast in the scrub mangrove (−294 ± 0.02 g C m−2 y−1) and declined inland into marl prairies (−47 ± 0.03 g C m−2 y−1). Low resilience to current conditions was evident in marl prairies, a result of the legacy impacts of water diversion throughout the greater Everglades. Although the southeastern Everglades captured approximately 115 metric tons of C in 2021, if the ecotone continues to advance at 25 m y−1 over the next century, we project a 12 % increase (16 mt C y−1) in net CO2 capture. Results emphasize that initial functional responses to changes in conditions may not accurately represent long-term outcomes and highlight the role of brackish ecotone communities as the frontline for climate- and management-induced shifts in coastal ecosystem structure and function. This is the first study to use disequilibrium dynamics to understand landscape-level transitions and their implications for C capture. 

This dataset contains field measurements taken during water sampling from 100 urban stream locations in the greater Miami, Florida metropolitan area. Field collection took place during five synoptic sampling events: Summer 2021 (Wet; July 8 to July 27), Fall 2021 (Wet; September 27 to October 7), Winter 2022 (Dry; January 3 to January 13), Spring 2022 (Dry; April 7 to April 23), and Summer 2022 (Wet; June 1 to June 13) to capture spatial and seasonal variation in stream conditions (specific conductivity, water temperature, dissolved oxygen, pH). Filtered stream samples were analyzed for dissolved organic carbon concentration and characteristics, available in a separate dataset. These data were collected as part of the Carbon in Urban Rivers Biogeochemistry (CURB) Project. Detailed field data and site data are published separately and can be linked using the “curbid” and “synoptic_event” columns in each dataset. 

This dataset contains dissolved organic carbon concentrations from surface water samples collected at 100 urban stream and canal locations in the greater Miami, Florida metropolitan area. Samples were collected five times across different seasons to capture spatial and seasonal variation in DOC concentration. These events include the wet seasons of 2021 and 2022, as well as the dry season of 2022, specifically: Summer 2021 (Wet; July 8 to July 27), Fall 2021 (Wet; September 27 to October 7), Winter 2022 (Dry; January 3 to January 13), Spring 2022 (Dry; April 7 to April 23), and Summer 2022 (Wet; June 1 to June 13). These data were collected as part of the Carbon in Urban Rivers Biogeochemistry (CURB) Project. Detailed field data and site data are published separately and can be linked using the “curbid” and “synoptic_event” columns in each dataset. 

This dataset contains dissolved organic matter (DOM) characteristics from surface water samples collected at 100 urban stream and canal locations in the greater Miami, Florida metropolitan area. Samples were collected five times across different seasons to capture spatial and seasonal variation in DOC concentration. These events include the wet seasons of 2021 and 2022, as well as the dry season of 2022, specifically: Summer 2021 (Wet; July 8 to July 27), Fall 2021 (Wet; September 27 to October 7), Winter 2022 (Dry; January 3 to January 13), Spring 2022 (Dry; April 7 to April 23), and Summer 2022 (Wet; June 1 to June 13). Fluorescent optical properties were measured on filtered water samples to understand the chemical composition of DOM. Excitation-Emission Matrices (EEMs) were measured using a Horiba Aqualog spectrometer. DOM characteristics were quantified using both standard fluorescence and absorbance metrics as well as through parallel factor (PARAFAC) analysis. These data were collected as part of the Carbon in Urban Rivers Biogeochemistry (CURB) Project. Detailed field data and site data are published separately and can be linked using the “curbid” and “synoptic_event” columns in each dataset. 

Climate and human modifications, including restoration, are changing freshwater availability in wetland ecosystems. Changes in spatiotemporal variability in water depth can influence biogeochemistry and aquatic metabolism (net ecosystem productivity, gross primary productivity [GPP], and ecosystem respiration [ER]). In subtropical wetlands, flocculent organic matter (floc) is a dominant form of organic matter made up of periphyton, macrophytes, and microbes. How changes in water depth with climate and human modifications of subtropical wetlands influence biogeochemistry and the metabolism of floc is uncertain and necessary to understand the consequences for carbon (C) cycling. We collected seasonal floc samples from shorter‐hydroperiod marshes (Taylor Slough Panhandle [TS/Ph]) and longer‐hydroperiod marshes (Shark River Slough [SRS]) in Everglades National Park (Florida, U.S.A.). We measured floc‐specific metabolism and biogeochemistry during the wet (May–November) and dry seasons (December–April) when marsh conditions differed in water depth, photosynthetically active radiation (PAR), floc chlorophylla, bulk density, and C and nutrients. Floc biogeochemistry was driven by hydrologic changes in water depth, while floc metabolism was influenced by floc biogeochemistry and PAR in both marshes. Floc‐specific metabolism was more net heterotrophic (GPP < ER) in TS/Ph than in SRS, driven by floc bulk density, total nitrogen, total C, total phosphorus, and total inorganic C. Increasing water depths with freshwater restoration may drive higher rates of C loss in shallower compared to deeper marshes. Understanding how hydrologic changes affect organic matter lability and respiration is important in managing C storage in ecosystems. 

Abstract Leaf litter in coastal wetlands lays the foundation for carbon storage, and the creation of coastal wetland soils. As climate change alters the biogeochemical conditions and macrophyte composition of coastal wetlands, a better understanding of the interactions between microbial communities, changing chemistry, and leaf litter is required to understand the dynamics of coastal litter breakdown in changing wetlands. Coastal wetlands are dynamic systems with shifting biogeochemical conditions, with both tidal and seasonal redox fluctuations, and marine subsidies to inland habitats. Here, we investigated gene expression associated with various microbial redox pathways to understand how changing conditions are affecting the benthic microbial communities responsible for litter breakdown in coastal wetlands. We performed a reciprocal transplant of leaf litter from four distinct plant species along freshwater‐to‐marine gradients in the Florida Coastal Everglades, tracking changes in environmental and litter biogeochemistry, as well as benthic microbial gene expression associated with varying redox conditions, carbon degradation, and phosphorus acquisition. Early litter breakdown varied primarily by species, with highest breakdown in coastal species, regardless of the site they were at during breakdown, while microbial gene expression showed a strong seasonal relationship between sulfate cycling and salinity, and was not correlated with breakdown rates. The effect of salinity is likely a combination of direct effects, and indirect effects from associated marine subsidies. We found a positive correlation between sulfate uptake and salinity during January with higher freshwater inputs to coastal areas. However, we found a peak of dissimilatory sulfate reduction at intermediate salinity during April when freshwater inputs to coastal sites are lower. The combination of these two results suggests that sulfate acquisition is limiting to microbes when freshwater inputs are high, but that when marine influence increases and sulfate becomes more available, dissimilatory sulfate reduction becomes a key microbial process. As marine influence in coastal wetlands increases with climate change, our study suggests that sulfate dynamics will become increasingly important to microbial communities colonizing decomposing leaf litter. 

Abstract The particulate organic matter buried in carbonate-rich seagrass ecosystems is an important blue carbon reservoir. While carbonate sediments are affected by alkalinity produced or consumed in seagrass-mediated biogeochemical processes, little is known about the corresponding impact on organic matter. A portion of particulate organic matter is carbonate-associated organic matter. Here, we explore its biogeochemistry in a carbonate seagrass meadow in central Florida Bay, USA. We couple inorganic stable isotope analyses (δ³⁴S, δ¹⁸O) with a molecular characterization of dissolved and carbonate associated organic matter (21 tesla Fourier-transform ion cyclotron resonance mass spectrometry). We find that carbonate-associated molecular formulas are highly sulfurized compared to surface water dissolved organic matter, with multiple sulfurization pathways at play. Furthermore, 97% of the formula abundance of surface water dissolved organic matter is shared with carbonate-associated organic matter, indicating connectivity between these two pools. We estimate that 9.2% of the particulate organic matter is carbonate-associated, and readily exchangeable with the broader aquatic system as the sediment dissolves and reprecipitates. 

Water column nutrient concentrations and autotrophy in oligotrophic ecosystems are sensitive to eutrophication and other long-term environmental changes and disturbances. Disturbance can be defined as an event or process that changes the structure and response of an ecosystem to other environmental drivers. The role disturbance plays in regulating ecosystem functions is challenging because the effect of the disturbance can vary in magnitude, duration, and extent spatially and temporally. We measured changes in total nitrogen (TN), dissolved inorganic nutrient (DIN), total phosphorus (TP), soluble reactive phosphorus (SRP), total organic carbon (TOC), and chlorophyll-a (Chl-a) concentrations throughout the Everglades, Florida Bay, and the Florida Keys. This region has been subjected to a variety of natural and anthropogenic disturbances including tropical storms, fires, eutrophication, and rapid increases in water levels from sea-level rise and freshwater restoration. We hypothesized that the rate of change in water quality would be greatest in the coastal ecotone where disturbance frequencies and marine P concentrations are highest, and in freshwater marshes closest to hydrologic changes from restoration. We applied trend analyses on multi-decadal data (1996–2019) collected from 461 locations distributed from inland freshwater Everglades (ridge and slough) to outer marine reefs along the Florida Keys, USA. Total Organic Carbon decreased throughout the study area and was the only parameter with a systematic trend throughout the study area. All other parameters had spatially heterogeneous patterns in long-term trends. Results indicate more variability across a large spatial and temporal extent associated with changes in biogeochemical indicators and water quality conditions. Chemical and biological changes in oligotrophic ecosystems are important indicators of environmental change, and our regional ridge-to-reef assessment revealed ecosystem-specific responses to both long-term environmental changes and disturbance legacies. 

This dataset package encompasses measurements from field surveys of mangrove regeneration, porewater variables, and light conditions across six mangrove sites in the coastal Everglades. The goal of this project was to quantify mangrove regeneration of seedlings and saplings in mid- and downstream locations within three estuaries in Everglades National Park, Florida, USA. We assessed the effects of porewater variables and light conditions on the observed regeneration patterns. The package includes seven datasets: FCE1268_Porewater: Contains measurements of porewater salinity, sulfide, ammonia, nitrite, orthophosphate, and nitrate at a 30 cm depth. Porewater surveys were conducted biannually from 09-10-2020 to 05-17-2022. See also similar porewater data for Florida Coastal Everglades (FCE) long-term sites in data packages knb-lter-fce.1169 and knb-lter-fce.1171, which contain data for SRS-5 and SRS-6, available in the FCE LTER website's data catalog or the EDI repository. FCE1268_Foliar_Nutrient_Content dataset, collected in August 2022, includes measurements of foliar nutrient content (total carbon, total nitrogen, and total phosphorus) for three mangrove species (A. germinans, L. racemosa, R. mangle) of two life stages—seedlings (height < 1 m) and saplings (height ≥ 1 m and Diameter at Breast Height (DBH) < 2.5 cm). FCE1268_Light contains light intensity (foot-candle) measurements taken at 1-hour intervals from 09-18-2020 to 08-29-2022 at mangrove sites and converted photosynthetic active radiation values from an outdoor mesocosm experiment. FCE1268_Sapling_Density provides biannual count measurements of individuals at the sapling plot level (4 m^-2) within each site from 07-09-2020 to 08-29-2022. FCE1268_Seedling_Density contains biannual count measurements of individuals at the seedling plot level (m^-2) within each site from 07-07-2020 to 08-29-2022. FCE1268_Sapling_Regeneration contains height, crown area, and stem elongation measurements of tagged sapling individuals at the plot level (4 m^-2) from 07-09-2020 to 08-29-2022. FCE1268_Seedling_Regeneration contains height, crown area, and stem elongation measurements of tagged seedling individuals at the plot level (m^-2) from 07-07-2020 to 08-29-2022. Data collection for all datasets is complete.