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Item Interpreting biogeochemical processes through the relationship between total alkalinity and dissolved inorganic carbon: Theoretical basis and limitations(Limnology and Oceanography Methods, 2024-03-14) Hang Yin; Xinping HuThe marine carbonate system is influenced by anthropogenic CO2 uptake, biogeochemical processes, and physical changes that involve freshwater input and removal. Two frequently used parameters to quantify seawater carbonate system are total alkalinity (TA) and total dissolved inorganic carbon (DIC). To account for the physical changes, both TA and DIC are usually normalized to a reference salinity (i.e., nTA and nDIC), and then the relationship between nTA and nDIC is used to identify major biogeochemical processes that regulate the carbonate system, based on process-specific reaction stoichiometry. However, the theoretical basis of this interpretation has not been holistically examined. In this study, we validated this method under idealized conditions and discussed the associated assumptions and limitations. Furthermore, we applied this method to interpret field TA and DIC data from a lagoonal estuary in the northwestern Gulf of Mexico. Our results demonstrated that evaluating field data that encompass multiple stations and time periods could be problematic. In addition, various combinations of biogeochemical processes can lead to the same nTA–nDIC relationship, even though the relative importance of each individual process may vary significantly. Therefore, the stoichiometric relationship relying solely on TA and DIC data is not a definitive approach for uncovering dominant biogeochemical processes. Instead, measurements of process-specific parameters are necessary.Item Sulfate enrichment in estuaries of the northwestern Gulf of Mexico: The potential effect of sulfide oxidation on carbonate chemistry under a changing climate(Limnology and Oceanography Letters, 2023-05-30) Yin, Hang; Hu, Xinping; Dias, LarissaWater quality parameters from 2000 to 2020 were used to identify the spatial and temporal sulfate variations in estuaries of the northwestern Gulf of Mexico. Sulfate enrichment relative to conservative mixing was found to be associated with a low river discharge period from 2012 to 2014 in all estuaries. Based on reaction stoichiometry, sedimentary sulfide oxidation holds significant potential for reducing the alkalinity in estuarine waters. However, during this extreme drought, alkalinity enrichment was also occasionally observed in some of the southern estuaries along with sulfate enrichment, and when alkalinity depletion occurred, the magnitude of depletion was usually much less than what would be expected based on sulfide oxidation alone. This discrepancy can be partially explained by carbonate dissolution and other proton removal pathways (e.g., Fe-oxide dissolution), and by the uncertainties in the model used to estimate alkalinity enrichment/depletion. Under a changing climate, the close coupling between river discharge variation and estuarine sulfate dynamics will significantly impact estuarine carbonate chemistry.Item Alkalinity distribution in the western North Atlantic Ocean margins(2010-08-13) Cai, Wei-Jun; Hu, Xinping; Huang, Wei-Jen; Jiang, Li-Qing; Wang, Yongchen; Peng, Tsung-Hung; Zhang, XinTotal alkalinity (TA) distribution and its relationship with salinity (S) along the western North Atlantic Ocean (wNAO) margins from the Labrador Sea to tropical areas are examined by this study. Based on the observed TA-S patterns, the mixing process that control alkalinity distribution in these areas can be categorized into a spectrum of patterns that are bracketed by two extreme mixing types, i.e., alongshore current dominated and river-dominated. Alongshore current-dominated mixing processes exhibit a segmented mixing line with a shared mid-salinity end-member. In such cases (i.e., Labrador Sea, Gulf of Maine, etc.), the y-intercept of the high salinity segment of the mixing line is generally higher than the local river alkalinity values, and it reflects the mixing history of the alongshore current. In contrast, in river-dominated mixing (Amazon River, Caribbean Sea, etc.), good linear relationships between alkalinity and salinity are generally observed, and the zero salinity intercepts of the TA-S regressions roughly match those of the regional river alkalinity values. TA-S mixing lines can be complicated by rapid changes in the river end-member value and by another river nearby with a different TA value (e.g., Mississippi-Atchafalaya/Gulf of Mexico). In the wNAO margins, regression intercepts and river end-member vale have a clear latitudinal distribution pattern, increasing from a low of ~300 mol kg-1 in the Amazon River plume to a high value between ~500-1100 mol kg-1 in the middle and high latitude margins. The highest value of ~2400 mol kg-1 is observed in the Mississippi River influenced areas. In addition to mixing control, biological processes such a calcification and benthic alkalinity production may also affect ocean margin alkalinity distribution. Therefore, deriving inorganic carbon system information in coastal oceans using alkalinity-salinity relationships, in particular, those of generic nature, may lead to significant errors.Item An assessment of ocean margin anaerobic processes on oceanic alkalinity budget(Global Biogeochem, 2011-07-08) Hu, Xinping; Cai, Wei-JunRecent interest in the ocean’s capacity to absorb atmospheric CO2 and buffer the accompanying “ocean acidification” has prompted discussions on the magnitude of ocean margin alkalinity production via anaerobic processes. However, available estimates are largely based on gross reaction rates or misconceptions regarding reaction stoichiometry. In this paper, we argue that net alkalinity gain does not result from the internal cycling of nitrogen and sulfur species or from the reduction of metal oxides. Instead, only the processes that involve permanent loss of anaerobic remineralization products, i.e., nitrogen gas from net denitrification and reduced sulfur (i.e., pyrite burial) from net sulfate reduction, could contribute to this anaerobic alkalinity production. Our revised estimate of net alkalinity production from anaerobic processes is on the order of 4–5 Tmol yr−1 in global ocean margins that include both continental shelves and oxygen minimum zones, significantly smaller than the previously estimated rate of 16–31 Tmol yr−1 . In addition, pyrite burial in coastal habitats (salt marshes, mangroves, and seagrass meadows) may contribute another 0.1–1.1 Tmol yr−1 , although their long‐term effect is not yet clear under current changing climate conditions and rising sea levels. Finally, we propose that these alkalinity production reactions can be viewed as “charge transfer” processes, in which negative charges of nitrate and sulfate ions are converted to those of bicarbonate along with a net loss of these oxidative anions.Item Microelectrode characterization of coral daytime interior pH and carbonate chemistry(Nature Communications, 2016-04-04) Cai, Wei-Jun; Ma, Yuening; Hopkinson, Brian M.; Grottoli, Andrea G.; Warner, Mark E.; Ding, Qian; Hu, Xinping; Yuan, Xiangchen; Schoepf, Verena; Xu, Hui; Han, Chenhua; Melman, Todd F.; Hoadley, Kenneth D.; Pettay, D. Tye; Matsui, Yohei; Baumann, Justin H.; Levas, Stephen; Ying, Ye; Wang, YongchenReliably predicting how coral calcification may respond to ocean acidification and warming depends on our understanding of coral calcification mechanisms. However, the concentration and speciation of dissolved inorganic carbon (DIC) inside corals remain unclear, as only pH has been measured while a necessary second parameter to constrain carbonate chemistry has been missing. Here we report the first carbonate ion concentration ([CO3 2 ]) measurements together with pH inside corals during the light period. We observe sharp increases in [CO3 2 ] and pH from the gastric cavity to the calcifying fluid, confirming the existence of a proton (H þ ) pumping mechanism. We also show that corals can achieve a high aragonite saturation state (Oarag) in the calcifying fluid by elevating pH while at the same time keeping [DIC] low. Such a mechanism may require less H þ -pumping and energy for upregulating pH compared with the high [DIC] scenario and thus may allow corals to be more resistant to climate change related stressors.Item Effect of Organic Alkalinity on Seawater Buffer Capacity: A Numerical Exploration(Springer Nature, 2020-04-20) Hu, XinpingOrganic alkalinity is a poorly understood component of total titration alkalinity in aquatic environments. Using a numerical method, the effects of organic acid (HOA) and its conjugate base (OA−) on seawater carbonate chemistry and buffer behaviors, as well as those in a hypothetical estuarine mixing zone, are explored under both closed- and open-system conditions. The simulation results show that HOA addition leads to pCO2 increase and pH decrease in a closed system when total dissolved inorganic carbon (DIC) remains the same. If opened to the atmosphere (pCO2=400 µatm), CO2 degassing and re-equilibration would cause depressed pH compared to the unperturbed seawater, but the seawater buffer to pH change [equation] indicates that weaker organic acid (i.e., higher pKa) results in higher bufer capacity (greater βDIC) than the unperturbed seawater. In comparison, OA− (with accompanying cations) in the form of net alkalinity addition leads to pCO2 decrease in a closed system. After re-equilibrating with the atmosphere, the resulting perturbed seawater has higher pH and βDIC than the unperturbed seawater. If river water has organic alkalinity, pH in the estuarine mixing zone is always lower than those caused by a mixing between organic alkalinity-free river (at constant total alkalinity) and ocean waters, regardless of the pKa values. On the other hand, organic alkalinity with higher pKa provides slightly greater βDIC in the mixing zone, and that with lower pKa either results in large CO2 oversaturation (closed system) or reduced βDIC (in mid to high salinity in the closed system or the entire mixing zone in the open system). Finally, despite the various effects on seawater buffer through either HOA or OA− addition, destruction of organic molecules including organic alkalinity via biogeochemical reactions should result in a net CO2 loss from seawater. Nevertheless, the significance of this organic alkalinity, especially that comes from organic acids that are not accounted for under the currently recognized “zero proton level” (Dickson in Deep Sea Res 28:609–623, 1981), remains unknown thus a potentially interesting and relevant research topic in studying oceanic alkalinity cycle.Item Timescales and Magnitude of Water Quality Change in Three Texas Estuaries Induced by Passage of Hurricane Harvey(Estuaries and Coasts, 2020-10-14) Walker, Lily M.; Montagna, Paul A.; Hu, Xinping; Wetz, Michael S.Tropical cyclones represent a substantial disturbance to water quality in coastal ecosystems via storm surge, winds, and flooding. However, evidence to date suggests that the impacts of tropical cyclones on water quality are generally short-lived (days-months) and that the magnitude of the disturbance is related to proximity to storm track. Discrete and continuous water samples were collected in three Texas estuaries before and after Hurricane Harvey made landfall in 2017. Of the three estuaries, the Guadalupe Estuary and its watershed received the highest rainfall totals and wind speeds. An ephemeral increase in salinity was observed (mean of 9.8 on 24 August 2017 to a peak of 32.1 on 26 August 2017) due to storm surge and was followed by a rapid decrease to < 1 as floodwaters reached the estuary. Salinity returned to pre-storm levels within 1 month. During the low salinity period, bottom water hypoxia developed and lasted for 9 days. In all three estuaries, there was an increase in inorganic nutrients post-Harvey, but the nutrients largely returned to pre-storm baseline levels by winter. The lack of long-term water quality impacts from Harvey despite its severity corroborates previous findings that estuarine water quality tends to return to baseline conditions within days to a few months after storm passage.Item Corrigendum: Disparate responses of carbonate system in two adjacent subtropical estuaries CV-5 to the influence of Hurricane Harvey - A case study(Frontiers in Marine Science, 2021-01-25) Hu, Xinping; Yao, Hongming; Staryk, Cory J.; McCutcheon, Melissa R.; Wetz, Michael S.; Walker, LilyItem Subtropical estuarine carbon budget under various hydrologic extremes and implications on the lateral carbon exchange from tidal wetlands(Elsevier, 2022-06-15) Yao, Hongming; Montagna, Paul A.; Wetz, Michael S.; Staryk, Corey J.; Hu, XinpingAs coastal areas become more vulnerable to climatic impacts, the need for understanding estuarine carbon budgets with sufficient spatiotemporal resolution arises. Under various hydrologic extremes ranging from drought to hurricane-induced flooding, a mass balance model was constructed for carbon fluxes and their variabilities in four estuaries along the northwestern Gulf of Mexico (nwGOM) coast over a four-year period (2014–2018). Loading of total organic carbon (TOC) and dissolved inorganic carbon (DIC) to estuaries included riverine discharge and lateral exchange from tidal wetlands. The lateral exchanges of TOC and DIC reached 4.5 ± 5.7 and 8.9 ± 1.4 mol·C·m−2·yr−1, accounting for 86.5% and 62.7% of total TOC and DIC inputs into these estuaries, respectively. A relatively high regional CO2 efflux (4.0 ± 0.7 mol·C·m−2·yr−1) was found, which was two times the average value in North American coastal estuaries reported in the literature. Oceanic export was the major pathway for losses of TOC (5.6 ± 1.7 mol·C·m−2·yr−1, 81.2% of total) and DIC (9.9 ± 2.9 mol·C·m−2·yr−1, 69.7% of total). The carbon budget exhibited high variability in response to hydrologic changes. For example, storm or hurricane induced flooding elevated CO2 efflux by 2–10 times in short periods of time. Flood following a drought also increased lateral TOC exchange (from -3.5 ± 4.7 to 67.8 ± 17.6 mmol·C·m−2·d−1) but decreased lateral DIC exchange (from 28.9 ± 3.5 to -7.1 ± 7.6 mmol·C·m−2·d−1). The large variability of carbon budgets highlights the importance of high-resolution spatiotemporal coverage under different hydrologic conditions, and the importance of carbon contribution from tidal wetlands to coastal carbon cycling.Item Coral disease outbreak at the remote Flower Garden Banks, Gulf of Mexico(Frontiers in Marine Science, 2023-01-26) Johnston, Michelle; Studivan, Michael; Enochs, Ian; Correa, Adrienne; Besemer, Nicole; Eckert, Ryan; Edwards, Kimberly; Hannum, Ryan; Hu, Xinping; Nuttall, Marissa; O'Connell, Kelley; Palacio-Castro, Ana; Schmahl, George; Sturm, Alexis; Ushijima, Blake; Voss, JoshuaEast and West Flower Garden Bank (FGB) are part of Flower Garden Banks National Marine Sanctuary (FGBNMS) in the northwest Gulf of Mexico. This geographically-isolated reef system contains extensive coral communities with the highest coral cover (>50%) in the continental United States due, in part, to their remoteness and depth, and have historically exhibited low incidence of coral disease and bleaching despite ocean warming. Yet in late August 2022, disease-like lesions on seven coral species were reported during routine monitoring surveys on East and West FGB (2.1–2.6% prevalence). A series of rapid response cruises were conducted in September and October 2022 focused on 1) characterizing signs and epidemiological aspects of the disease across FGB and within long-term monitoring sites, 2) treating affected coral colonies with Base 2B plus amoxicillin, and 3) collecting baseline images through photostations and photomosaics. Marginal and/or multi-focal lesions and tissue loss were observed, often associated with substantial fish and invertebrate predation, affecting the dominant coral species Pseudodiploria strigosa (7–8% lesion prevalence), Colpophyllia natans (11–18%), and Orbicella spp. (1%). Characterizing this disease event during its early epidemic phase at East and West FGB provides a critical opportunity to observe how coral disease functions in a relatively healthy coral ecosystem versus on reefs chronically affected by various stressors (e.g., Caribbean reefs adjacent to urban centers). Insights into the etiology, spread, and impacts of the disease can ultimately inform efforts to mitigate its effects on coral communities.Item A biogeochemical alkalinity sink in a shallow, semiarid estuary of the Northwestern Gulf of Mexico(Aquatic Geochemistry, 2022-12-08) Dias, Larissa; Hu, Xinping; Yin, HangEstuarine total alkalinity (TA), which buffers against acidification, is temporally and spatially variable and regulated by complex, interacting hydrologic and biogeochemical processes. During periods of net evaporation (drought), the Mission-Aransas Estuary (MAE) of the northwestern Gulf of Mexico experienced TA losses beyond what can be attributed to calcification. The contribution of sedimentary oxidation of reduced sulfur to the TA loss was examined in this study. Water column samples were collected from five stations within MAE and analyzed for salinity, TA, and calcium ion concentrations. Sediment samples from four of these monitoring stations and one additional station within MAE were collected and incubated between 2018 and 2021. TA, calcium, magnesium, and sulfate ion concentrations were analyzed for these incubations. Production of sulfate along with TA consumption (or production) beyond what can be attributed to calcification (or carbonate dissolution) was observed. These results suggest that oxidation of reduced sulfur consumed TA in MAE during droughts. We estimate that the upper limit of TA consumption due to reduced sulfur oxidation can be as much as 4.60 × 108 mol day−1 in MAE. This biogeochemical TA sink may be present in other similar subtropical, freshwater-starved estuaries around the world.Item Ocean acidification in the Gulf of Mexico: Drivers, impacts, and unknowns(Progress in Oceanography, 2022-10-04) Osborne, Emily; Hu, Xinping; Hall, Emily; Yates, Kimberly; Vreeland-Dawson, Jennifer; Shamberger, Katie; Barbero, Leticia; Hernandez-Ayon, J. Martin; Gomez, Fabian; Hicks, Tacey; Xu, Yuan-Yuan; McCutcheon, Melissa; Acquafredda, Michael; Chapa-Balcorta, Cecilia; Norzagaray, Orion; Pierrot, Denis; Munoz-Caravaca, Alain; Dobson, Kerri; Williams, Nancy; Rabalais, Nancy; Dash, PadmanavaOcean acidification (OA) has resulted in global-scale changes in ocean chemistry, which can disturb marine organisms and ecosystems. Despite its extensively populated coastline, many marine-dependent communities, and valuable economies, the Gulf of Mexico (GOM) remains a relatively understudied region with respect to acidification. In general, the warm waters of the GOM are better buffered from acidification compared to higher latitude seas, yet long-term acidification has been documented in several GOM regions. OA within the GOM is recognized as spatially variable, particularly within the coastal zone where numerous physical and biogeochemical processes contribute to carbonate chemistry dynamics. The historical progression of OA within the entire GOM is difficult to assess because only a few dedicated long-term monitoring sites have recently been established, and full-water column observations are limited. However, environmental drivers on smaller scales that affect GOM acidification were found to include freshwater, nutrient, and carbonate discharge from large rivers; ocean warming, circulation and residence times; and episodic extreme weather events. GOM marine ecosystems provide essential services, including coastline protection and carbon dioxide removal, and habitats for many marine species that are economically and ecologically important. However, organismal and ecosystem responses to OA are not well constrained for the GOM due to a lack of studies examining the specific effects of OA on regionally relevant species under contemporary and projected conditions. Tackling the vast number of remaining scientific unknowns in this region can be coordinated through regional capacity networks, such as the Gulf of Mexico Coastal Acidification Network (GCAN), working to achieve a system-wide understanding of Gulf OA and its impacts. Here we synthesize the current peer-reviewed literature on GOM acidification across the ocean-estuarine continuum and identify critical knowledge, research, and monitoring gaps that limit our current understanding of environmental, ecological, and socioeconomic impacts from acidification.Item Aragonite saturation states in estuaries along a climate gradient in the northwestern Gulf of Mexico(Frontiers in Environmental Science, 2022-10-10) Hu, Xinping; Yao, Hongming; McCutcheon, Melissa; Dias, Larissa; Staryk, Cory; Wetz, Michael; Montagna, PaulIn the northwestern Gulf of Mexico (nwGOM), the coastal climate shifts abruptly from the humid northeast to the semiarid southwest within a narrow latitudinal range. The climate effect plays an important role in controlling freshwater discharge into the shallow estuaries in this region. In addition to diminishing freshwater runoff down the coast, evaporation also increases substantially. Hence, these estuaries show increasing salinity along the coastline due to the large difference in freshwater inflow balance (river runoff and precipitation minus evaporation and diversion). However, this spatial gradient can be disrupted by intense storm events as a copious amount of precipitation leads to river flooding, which can cause temporary freshening of these systems in extreme cases, in addition to freshwater-induced ephemeral stratification. We examined estuarine water aragonite saturation state (Ωarag) data collected between 2014 and 2018, covering a period of contrasting hydrological conditions, from the initial drought to multiple flooding events, including a brief period that was influenced by a category 4 hurricane. Based on freshwater availability, these estuaries exhibited a diminishing Ωarag fluctuation from the most freshwater enriched Guadalupe Estuary to the most freshwaterstarved Nueces Estuary. While Ωarag values were usually much higher than the threshold level (Ωarag = 1), brief freshwater discharge events and subsequent low oxygen levels in the lower water column led to episodic corrosive conditions. Based on previously obtained Ωarag temporal trends and Ωarag values obtained in this study, we estimated the time of emergence (ToE) for Ωarag. Not only did estuaries show decreasing ToE with diminishing freshwater availability but the sub-embayments of individual estuaries that had a less freshwater influence also had shorter ToE. This spatial pattern suggests that planning coastal restoration efforts, especially for shellfish organisms, should emphasize areas with longer ToE.Item Seasonal Mixing and Biological Controls of the Carbonate System in a River-Dominated Continental Shelf Subject to Eutrophication and Hypoxia in the Northern Gulf of Mexico(Frontiers in Marine Science, 2021-03-26) Huang, Wei-Jen; Cai, Wei-Jun; Hu, XinpingLarge rivers export a large amount of dissolved inorganic carbon (DIC) and nutrients to continental shelves; and subsequent river-to-sea mixing, eutrophication, and seasonal hypoxia (dissolved oxygen < 2 mg⋅L–1) can further modify DIC and nutrient distributions and fluxes. However, quantitative studies of seasonal carbonate variations on shelves are still insufficient. We collected total alkalinity (TA), DIC, and NO3– data from nine cruises conducted between 2006 and 2010 on the northern Gulf of Mexico continental shelf, an area strongly influenced by the Mississippi and Atchafalaya Rivers. We applied a three-end-member model (based on salinity and potential alkalinity) to our data to remove the contribution of physical mixing to DIC and nitrate distribution patterns and to derive the net in situ removal of DIC and nitrate (ΔDIC and ΔNO3–, respectively). Systematic analyses demonstrated that the seasonal net DIC removal in the near-surface water was strong during summer and weak in winter. The peak in net DIC production in the near-bottom, subsurface waters of the inner and middle sections of the shelf occurred between July and September; it was coupled, but with a time lag, to the peak in the net DIC removal that occurred in the near-surface waters in June. A similar 2-month delay (i.e., January vs. November) could also be observed between their minima. A detailed examination of the relationship between ΔDIC and ΔNO3– demonstrates that net biological activity was the dominant factor of DIC removal and addition. Other effects, such as air–sea CO2 gas exchange, wetland exports, CaCO3 precipitation, and a regional variation of the Redfield ratio, were relatively minor. We suggest that the delayed coupling between eutrophic surface and hypoxic bottom waters reported here may also be seen in the carbon and nutrient cycles of other nutrient-rich, river-dominated ocean margins worldwide.Item Temporal variability and driving factors of the carbonate system in the Aransas Ship Channel, TX, USA: a time series study(Biogeosciences, 2021-08-09) McCutcheon, Melissa R.; Yao, Hongming; Staryk, Cory J.; Hu, XinpingThe coastal ocean is affected by an array of co-occurring biogeochemical and anthropogenic processes, resulting in substantial heterogeneity in water chemistry, including carbonate chemistry parameters such as pH and partial pressure of CO2 (pCO2). To better understand coastal and estuarine acidification and air-sea CO2 fluxes, it is important to study baseline variability and driving factors of carbonate chemistry. Using both discrete bottle sample collection (2014–2020) and hourly sensor measurements (2016–2017), we explored temporal variability, from diel to interannual scales, in the carbonate system (specifically pH and pCO2) at the Aransas Ship Channel located in the northwestern Gulf of Mexico. Using other co-located environmental sensors, we also explored the driving factors of that variability. Both sampling methods demonstrated significant seasonal variability at the location, with highest pH (lowest pCO2) in the winter and lowest pH (highest pCO2) in the summer. Significant diel variability was also evident from sensor data, but the time of day with elevated pCO2 and depressed pH was not consistent across the entire monitoring period, sometimes reversing from what would be expected from a biological signal. Though seasonal and diel fluctuations were smaller than many other areas previously studied, carbonate chemistry parameters were among the most important environmental parameters for distinguishing between time of day and between seasons. It is evident that temperature, biological activity, freshwater inflow, and tide level (despite the small tidal range) are all important controls on the system, with different controls dominating at different timescales. The results suggest that the controlling factors of the carbonate system may not be exerted equally on both pH and pCO2 on diel timescales, causing separation of their diel or tidal relationships during certain seasons. Despite known temporal variability on shorter timescales, discrete sampling was generally representative of the average carbonate system and average air-sea CO2 flux on a seasonal and annual basis when compared with sensor data.Item Integrating High-Resolution Coastal Acidification Monitoring Data Across Seven United States Estuaries(Frontiers in Marine Science, 2021-08-19) Rosenau, Nicholas A.; Galavotti, Holly; Yates, Kimberly K.; Bohlen, Curtis C.; Hunt, Christopher W.; Liebman, Matthew; Brown, Cheryl A.; Pacella, Stephen R.; Largier, John L.; Nielsen, Karina J.; Hu, Xinping; McCutcheon, Melissa R.; Vasslides, James M.; Poach, Matthew; Ford, Tom; Johnston, Karina; Steele, AlexBeginning in 2015, the United States Environmental Protection Agency’s (EPA’s) National Estuary Program (NEP) started a collaboration with partners in seven estuaries along the East Coast (Barnegat Bay; Casco Bay), West Coast (Santa Monica Bay; San Francisco Bay; Tillamook Bay), and the Gulf of Mexico (GOM) Coast (Tampa Bay; Mission-Aransas Estuary) of the United States to expand the use of autonomous monitoring of partial pressure of carbon dioxide (pCO2) and pH. Analysis of high-frequency (hourly to sub-hourly) coastal acidification data including pCO2, pH, temperature, salinity, and dissolved oxygen (DO) indicate that the sensors effectively captured key parameter measurements under challenging environmental conditions, allowing for an initial characterization of daily to seasonal trends in carbonate chemistry across a range of estuarine settings. Multi-year monitoring showed that across all water bodies temperature and pCO2 covaried, suggesting that pCO2 variability was governed, in part, by seasonal temperature changes with average pCO2 being lower in cooler, winter months and higher in warmer, summer months. Furthermore, the timing of seasonal shifts towards increasing (or decreasing) pCO2 varied by location and appears to be related to regional climate conditions. Specifically, pCO2 increases began earlier in the year in warmer water, lower latitude water bodies in the GOM (Tampa Bay; Mission-Aransas Estuary) as compared with cooler water, higher latitude water bodies in the northeast (Barnegat Bay; Casco Bay), and upwelling-influenced West Coast water bodies (Tillamook Bay; Santa Monica Bay; San Francisco Bay). Results suggest that both thermal and non-thermal influences are important drivers of pCO2 in Tampa Bay and Mission-Aransas Estuary. Conversely, non-thermal processes, most notably the biogeochemical structure of coastal upwelling, appear to be largely responsible for the observed pCO2 values in West Coast water bodies. The co-occurrence of high salinity, high pCO2, low DO, and low temperature water in Santa Monica Bay and San Francisco Bay characterize the coastal upwelling paradigm that is also evident in Tillamook Bay when upwelling dominates freshwater runoff and local processes. These data demonstrate that high-quality carbonate chemistry observations can be recorded from estuarine environments using autonomous sensors originally designed for open-ocean settings.Item Effects of climate change on metabolite accumulation in freshwater and marine cyanobacteria(Elsevier Inc., 2021-09-02) Huang, I-Shuo; Hu, Xinping; Abdulla, Hussain; Zimba, Paul V.Global climate change and anthropogenic nutrient inputs are responsible for increased frequency of cyanobacterial blooms that potentially contain 55 classes of bioactive metabolites. This study investigated the effects of CO2 availability and concomittant pH levels on two cyanobacteria that produce microcystins: a marine cf. Synechocystis sp. and a freshwater Microcystis aeruginosa. Cyanobacterial strains were semi-continuously cultured in mesotrophic growth media at pH 7.5, 7.8, 8.2, and 8.5 via a combination of CO2 addition and control of alkalinity. The cell concentration between treatments was not significantly different and nutrient availability was not limited. Concentration of most known cyanobacterial bioactive metabolites in both cyanobacterial strains increased as CO2 increased. At pH 7.8, bioactive metabolite intracellular concentration in M. aeruginosa and Synechocystis was 1.5 and 1.2 times greater than the other three treatments, respectively. Intracellular concentration of microginin in M. aeruginosa at pH 7.5 was reduced by 90% compared to the other three treatments. Intracellular concentration of microcyclamide-bistratamide B was lower in M. aeruginosa and higher in Synechocystis at elevated CO2 concentration. M. aeruginosa products were more diverse metabolites than Synechocystis. The diversity of accumulated metabolites in M. aeruginosa increased as CO2 increased, whereas the metabolite diversity in Synechocystis decreased as pH decreased. Overall, intracellular concentration of bioactive metabolites was higher at greater CO2 concentrations; marine and freshwater cyanobacteria had different allocation products when exposed to differing CO2 environments.Item Best Practice Data Standards for Discrete Chemical Oceanographic Observations(Frontiers in Marine Science, 2022-01-21) Jiang, Li-Qing; Pierrot, Denis; Wanninkhof, Rik; Feely, Richard A.; Tilbrook, Bronte; Alin, Simone; Barbero, Leticia; Byrne, Robert H.; Carter, Brendan R.; Dickson, Andrew G.; Gattuso, Jean-Pierre; Greeley, Dana; Hoppema, Mario; Humphreys, Matthew P.; Karstensen, Johannes; Lange, Nico; Lauvset, Siv K.; Lewis, Ernie R.; Olsen, Are; Pérez, Fiz F.; Sabine, Christopher; Sharp, Jonathan D.; Tanhua, Toste; Trull, Thomas W.; Velo, Anton; Allegra, Andrew J.; Barker, Paul; Burger, Eugene; Cai, Wei-Jun; Chen, Chen-Tung A.; Cross, Jessica; Garcia, Hernan; Hernandez-Ayon, Jose Martin; Hu, Xinping; Kozyr, Alex; Langdon, Chris; Lee, Kitack; Salisbury, Joe; Wang, Zhaohui Aleck; Xue, LiangEffective data management plays a key role in oceanographic research as cruise-based data, collected from different laboratories and expeditions, are commonly compiled to investigate regional to global oceanographic processes. Here we describe new and updated best practice data standards for discrete chemical oceanographic observations, specifically those dealing with column header abbreviations, quality control flags, missing value indicators, and standardized calculation of certain properties. These data standards have been developed with the goals of improving the current practices of the scientific community and promoting their international usage. These guidelines are intended to standardize data files for data sharing and submission into permanent archives. They will facilitate future quality control and synthesis efforts and lead to better data interpretation. In turn, this will promote research in ocean biogeochemistry, such as studies of carbon cycling and ocean acidification, on regional to global scales. These best practice standards are not mandatory. Agencies, institutes, universities, or research vessels can continue using different data standards if it is important for them to maintain historical consistency. However, it is hoped that they will be adopted as widely as possible to facilitate consistency and to achieve the goals stated above.Item Long-Term Trends in Estuarine Carbonate Chemistry in the Northwestern Gulf of Mexico(Frontiers in Marine Science, 2022-03-03) McCutcheon, Melissa R.; Hu, XinpingA four-decade dataset that spans seven estuaries along a latitudinal gradient in the northwestern Gulf of Mexico and includes measurements of pH and total alkalinity was used to calculate partial pressure of CO2 (pCO2), dissolved inorganic carbon (DIC), saturation state of aragonite (ΩAr), and a buffer factor (βDIC, which measures the response of proton concentration or pH to DIC concentration change) and examine long-term trends and spatial patterns in these parameters. With the notable exception of the northernmost and southernmost estuaries (and selected stations near freshwater input), these estuaries have generally experienced long-term increases in pCO2 and decreases in DIC, ΩAr, and βDIC, with the magnitude of change generally increasing from north to south. At all stations with increasing pCO2, the rate of increase exceeded the rate of increase in atmospheric pCO2, indicating that these estuaries have become a greater source of CO2 to the atmosphere over the last few decades. The decreases in ΩAr have yet to cause ΩAr to near undersaturation, but even the observed decreases may have the potential to decrease calcification rates in important estuarine calcifiers like oysters. The decreases in βDIC directly indicate that these estuaries have experienced continually greater change in pH in the context of ocean acidification.Item Temporal variability and driving factors of the carbonate system in the Aransas Ship Channel, TX, USA: a time series study(Copernicus Publications, 2021-08-09) McCutcheon, Melissa R.; Yao, Hongming; Staryk, Cory J.; Hu, XinpingThe coastal ocean is affected by an array of co-occurring biogeochemical and anthropogenic processes, resulting in substantial heterogeneity in water chemistry, including carbonate chemistry parameters such as pH and partial pressure of CO2 (pCO2). To better understand coastal and estuarine acidification and air-sea CO2 fluxes, it is important to study baseline variability and driving factors of carbonate chemistry. Using both discrete bottle sample collection (2014–2020) and hourly sensor measurements (2016–2017), we explored temporal variability, from diel to interannual scales, in the carbonate system (specifically pH and pCO2) at the Aransas Ship Channel located in the northwestern Gulf of Mexico. Using other co-located environmental sensors, we also explored the driving factors of that variability. Both sampling methods demonstrated significant seasonal variability at the location, with highest pH (lowest pCO2) in the winter and lowest pH (highest pCO2) in the summer. Significant diel variability was also evident from sensor data, but the time of day with elevated pCO2 and depressed pH was not consistent across the entire monitoring period, sometimes reversing from what would be expected from a biological signal. Though seasonal and diel fluctuations were smaller than many other areas previously studied, carbonate chemistry parameters were among the most important environmental parameters for distinguishing between time of day and between seasons. It is evident that temperature, biological activity, freshwater inflow, and tide level (despite the small tidal range) are all important controls on the system, with different controls dominating at different timescales. The results suggest that the controlling factors of the carbonate system may not be exerted equally on both pH and pCO2 on diel timescales, causing separation of their diel or tidal relationships during certain seasons. Despite known temporal variability on shorter timescales, discrete sampling was generally representative of the average carbonate system and average air-sea CO2 flux on a seasonal and annual basis when compared with sensor data.