Christopher R. Farrow, Loong‐Tak Lim, Josef D. Ackerman
We examined the effects of riverbed roughness and turbulence (shear velocity, ) on propagule dispersion in the near‐field region (< 100 m) by releasing microbead models of larval and juvenile unionid mussels in tributaries of the Grand River (Ontario, Canada). The Conestogo River had the roughest bed and highest mean , followed by the Grand and Speed rivers. We predicted more downstream transport with higher velocities and that longitudinal dispersion coefficients (Kx) would match the patterns in roughness and . The Conestogo River had the highest downstream particle flux and Kx as predicted by simple empirical equations. Inconsistent with model predictions, however, the Grand River had the lowest particle flux and Kx. These differences were greater than expected based on the small differences in reach‐averaged mean velocities between the Grand and Conestogo rivers. This mismatch between Kx predicted by simple empirical models and those fit to an advection–diffusion model was related to the inertial properties of the flow in the advective zone (i.e., near field) of the reaches. Streamwise, lateral, and especially vertical velocities at drift nets were spatially heterogeneous within and among reaches, demonstrating the influence of the flow direction on particle flux. Although bulk fluid statistics provided a useful indication of how dispersal distances vary among rivers, our results suggest that near‐field dynamics can be complex, requiring high‐resolution bathymetry and velocity data for the development of improved advection–diffusion models. Care should be exercised in predicting the dispersal of particles at ecologically relevant spatial scales in rivers.
{"title":"Propagules go with the flow: Near‐field particle dispersion in reaches with different hydrodynamic conditions","authors":"Christopher R. Farrow, Loong‐Tak Lim, Josef D. Ackerman","doi":"10.1002/lno.12760","DOIUrl":"https://doi.org/10.1002/lno.12760","url":null,"abstract":"We examined the effects of riverbed roughness and turbulence (shear velocity, ) on propagule dispersion in the near‐field region (< 100 m) by releasing microbead models of larval and juvenile unionid mussels in tributaries of the Grand River (Ontario, Canada). The Conestogo River had the roughest bed and highest mean , followed by the Grand and Speed rivers. We predicted more downstream transport with higher velocities and that longitudinal dispersion coefficients (<jats:italic>K</jats:italic><jats:sub><jats:italic>x</jats:italic></jats:sub>) would match the patterns in roughness and . The Conestogo River had the highest downstream particle flux and <jats:italic>K</jats:italic><jats:sub><jats:italic>x</jats:italic></jats:sub> as predicted by simple empirical equations. Inconsistent with model predictions, however, the Grand River had the lowest particle flux and <jats:italic>K</jats:italic><jats:sub><jats:italic>x</jats:italic></jats:sub>. These differences were greater than expected based on the small differences in reach‐averaged mean velocities between the Grand and Conestogo rivers. This mismatch between <jats:italic>K</jats:italic><jats:sub><jats:italic>x</jats:italic></jats:sub> predicted by simple empirical models and those fit to an advection–diffusion model was related to the inertial properties of the flow in the advective zone (i.e., near field) of the reaches. Streamwise, lateral, and especially vertical velocities at drift nets were spatially heterogeneous within and among reaches, demonstrating the influence of the flow direction on particle flux. Although bulk fluid statistics provided a useful indication of how dispersal distances vary among rivers, our results suggest that near‐field dynamics can be complex, requiring high‐resolution bathymetry and velocity data for the development of improved advection–diffusion models. Care should be exercised in predicting the dispersal of particles at ecologically relevant spatial scales in rivers.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"27 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142867412","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Violaine Piton, Rafael Reiss, Ulrich Lemmin, Orlane Anneville, Gaël Many, Jérémy Keller, Valentin Kindschi, Htet Kyi Wynn, Serena Rasconi, Leslie Laine, David Andrew Barry
Diel Vertical Migration (DVM), a widespread zooplankton behavior in freshwater and marine systems, affects ecological interactions and biogeochemical cycles. In lakes, DVM has mainly been studied in the upper 50 m of the water column. However, based on acoustic and net sampling data collected in Lake Geneva, Switzerland (~ 309 m depth) during summer 2022, we demonstrate that DVM occurs down to ~ 125 m depth daily throughout the summer season. The daily descents terminated at around zenith when the Relative Rate of light Change (RRC) was the lowest, and the late afternoon ascent started when RRC values exceeded −0.005 s−1. DVM migration descent/ascent rates were asymmetric with faster mean upward rates () than downward rates (). Migration rates overall increased as summer progressed, corresponding to the intra‐seasonal increase in RRC. Cyclopoid copepods Cyclops prealpinus abundances correlated with the observed deep DVM and their migration responded to exogenous light cues. These new findings, which can also be expected to be relevant for other deep lakes, indicate that Lake Geneva's DVM greatly exceeds maximum migration depths previously reported for a lake. Thus, it is important to study zooplankton DVM dynamics throughout the entire water column in large, deep lakes since it plays an important role in buffering global climate change effects. Furthermore, it is suggested that present zooplankton DVM sampling protocols in large, deep lakes should be revised accordingly.
{"title":"Identifying and quantifying unexpected deep zooplankton diel vertical migration in a large deep lake","authors":"Violaine Piton, Rafael Reiss, Ulrich Lemmin, Orlane Anneville, Gaël Many, Jérémy Keller, Valentin Kindschi, Htet Kyi Wynn, Serena Rasconi, Leslie Laine, David Andrew Barry","doi":"10.1002/lno.12736","DOIUrl":"https://doi.org/10.1002/lno.12736","url":null,"abstract":"Diel Vertical Migration (DVM), a widespread zooplankton behavior in freshwater and marine systems, affects ecological interactions and biogeochemical cycles. In lakes, DVM has mainly been studied in the upper 50 m of the water column. However, based on acoustic and net sampling data collected in Lake Geneva, Switzerland (~ 309 m depth) during summer 2022, we demonstrate that DVM occurs down to ~ 125 m depth daily throughout the summer season. The daily descents terminated at around zenith when the Relative Rate of light Change (RRC) was the lowest, and the late afternoon ascent started when RRC values exceeded −0.005 s<jats:sup>−1</jats:sup>. DVM migration descent/ascent rates were asymmetric with faster mean upward rates () than downward rates (). Migration rates overall increased as summer progressed, corresponding to the intra‐seasonal increase in RRC. Cyclopoid copepods <jats:italic>Cyclops prealpinus</jats:italic> abundances correlated with the observed deep DVM and their migration responded to exogenous light cues. These new findings, which can also be expected to be relevant for other deep lakes, indicate that Lake Geneva's DVM greatly exceeds maximum migration depths previously reported for a lake. Thus, it is important to study zooplankton DVM dynamics throughout the entire water column in large, deep lakes since it plays an important role in buffering global climate change effects. Furthermore, it is suggested that present zooplankton DVM sampling protocols in large, deep lakes should be revised accordingly.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"269 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142867409","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Valeria Jimenez, Sebastian Sudek, Charlotte Eckmann, Charles Bachy, Camille Poirier, Fabian Wittmers, Alyson E. Santoro, Michael J. Follows, Francisco P. Chavez, Irina Shilova, Alexandra Z. Worden
Marine eastern boundary current ecosystems, such as the California Current System (CCS), involve productive, mesotrophic transition zones. The CCS exhibits highly variable primary production (PP), yet factors driving the variability and underlying phytoplankton communities remain poorly understood. We integrated physicochemical and biological data from surface waters sampled during 10 CCS expeditions, spanning 13 yr, and resolved regimes with distinct phytoplankton communities. Additional to an oligotrophic regime (OR), mesotrophic waters beyond the coastal area partitioned into Meso‐High and Meso‐Low regimes, differing in nitrate concentrations and PP. The OR was dominated by Prochlorococcus High‐Light I (HLI), and eukaryotic phytoplankton were largely predatory mixotrophs. Eukaryotes dominated Meso‐Low and Meso‐High phytoplankton biomass. Within the Meso‐Low, Pelagomonas calceolata was important, and Prochlorococcus Low‐Light I (LLI) rose in prominence. In the Meso‐High, the picoprasinophyte Ostreococcus lucimarinus was abundant, and Synechococcus Clade IV was notable. The Meso‐High exhibited the highest PP (38 ± 16 mg C m−3 d−1; p < 0.01) and higher growth rates for photosynthetic eukaryotes (0.84 ± 0.02 d−1) than for Prochlorococcus (0.61 ± 0.01 d−1) and Synechococcus (0.31 ± 0.05 d−1). An experiment simulating seasonal oligotrophic seawater intrusion into the Meso‐High resulted in growth rates reaching 1.18 ± 0.10 d−1 (O. lucimarinus), 0.75 ± 0.21 d−1 (Prochlorococcus LLI), and 0.50 ± 0.04 d−1 (Synechococcus EPC2). Thus, variable PP is underpinned by distinct phytoplankton communities across CCS mesotrophic regimes, and their dynamic nature is influenced by the rapidity with which specific taxa respond to changing environmental conditions or possibly transient nutrient release from viral encounters. Future work should assess whether these dynamics are consistent across eastern boundary current ecosystems and over temporal variations.
海洋东部边界流生态系统，如加利福尼亚流系统（CCS），涉及生产性中营养化过渡带。CCS显示出高度可变的初级生产（PP），然而驱动变异的因素和潜在的浮游植物群落仍然知之甚少。我们整合了在10次CCS考察中采集的地表水的物理化学和生物数据，跨越13年，并解决了不同浮游植物群落的制度。除了低营养状态（OR）外，沿海地区以外的中营养水域分为中高和中低状态，硝酸盐浓度和PP不同。OR由原绿球藻高光I （HLI）主导，真核浮游植物主要是掠食性混合营养生物。中低和中高浮游植物生物量以真核生物为主。在中低温菌群中，绿单胞菌（Pelagomonas calceolata）占有重要地位，低光照I原绿球藻（Prochlorococcus Low‐Light I， LLI）的地位上升。在中高海拔地区，有大量的裸色红葡萄球菌和IV系聚球菌。Meso‐High表现出最高的PP(38±16 mg C m−3 d−1)；p & lt;光合真核生物的生长速率（0.84±0.02 d - 1）高于原绿球藻（0.61±0.01 d - 1）和聚球藻（0.31±0.05 d - 1）。模拟季节性低营养海水入侵中高河段的实验结果显示，藻体的生长速率分别为1.18±0.10 d - 1 （O. lucimarinus）、0.75±0.21 d - 1（原绿球藻LLI）和0.50±0.04 d - 1（聚球藻EPC2）。因此，可变的PP是由不同的浮游植物群落支撑的，它们的动态性质受到特定分类群对不断变化的环境条件或可能从病毒遭遇中短暂释放营养物质的反应速度的影响。未来的工作应该评估这些动态是否在东部边界洋流生态系统和时间变化上是一致的。
{"title":"Distinct phytoplankton assemblages underlie hotspots of primary production in the eastern North Pacific Ocean","authors":"Valeria Jimenez, Sebastian Sudek, Charlotte Eckmann, Charles Bachy, Camille Poirier, Fabian Wittmers, Alyson E. Santoro, Michael J. Follows, Francisco P. Chavez, Irina Shilova, Alexandra Z. Worden","doi":"10.1002/lno.12771","DOIUrl":"https://doi.org/10.1002/lno.12771","url":null,"abstract":"Marine eastern boundary current ecosystems, such as the California Current System (CCS), involve productive, mesotrophic transition zones. The CCS exhibits highly variable primary production (PP), yet factors driving the variability and underlying phytoplankton communities remain poorly understood. We integrated physicochemical and biological data from surface waters sampled during 10 CCS expeditions, spanning 13 yr, and resolved regimes with distinct phytoplankton communities. Additional to an oligotrophic regime (OR), mesotrophic waters beyond the coastal area partitioned into Meso‐High and Meso‐Low regimes, differing in nitrate concentrations and PP. The OR was dominated by <jats:italic>Prochlorococcus</jats:italic> High‐Light I (HLI), and eukaryotic phytoplankton were largely predatory mixotrophs. Eukaryotes dominated Meso‐Low and Meso‐High phytoplankton biomass. Within the Meso‐Low, <jats:italic>Pelagomonas calceolata</jats:italic> was important, and <jats:italic>Prochlorococcus</jats:italic> Low‐Light I (LLI) rose in prominence. In the Meso‐High, the picoprasinophyte <jats:italic>Ostreococcus lucimarinus</jats:italic> was abundant, and <jats:italic>Synechococcus</jats:italic> Clade IV was notable. The Meso‐High exhibited the highest PP (38 ± 16 mg C m<jats:sup>−3</jats:sup> d<jats:sup>−1</jats:sup>; <jats:italic>p</jats:italic> < 0.01) and higher growth rates for photosynthetic eukaryotes (0.84 ± 0.02 d<jats:sup>−1</jats:sup>) than for <jats:italic>Prochlorococcus</jats:italic> (0.61 ± 0.01 d<jats:sup>−1</jats:sup>) and <jats:italic>Synechococcus</jats:italic> (0.31 ± 0.05 d<jats:sup>−1</jats:sup>). An experiment simulating seasonal oligotrophic seawater intrusion into the Meso‐High resulted in growth rates reaching 1.18 ± 0.10 d<jats:sup>−1</jats:sup> (<jats:italic>O. lucimarinus</jats:italic>), 0.75 ± 0.21 d<jats:sup>−1</jats:sup> (<jats:italic>Prochlorococcus</jats:italic> LLI), and 0.50 ± 0.04 d<jats:sup>−1</jats:sup> (<jats:italic>Synechococcus</jats:italic> EPC2). Thus, variable PP is underpinned by distinct phytoplankton communities across CCS mesotrophic regimes, and their dynamic nature is influenced by the rapidity with which specific taxa respond to changing environmental conditions or possibly transient nutrient release from viral encounters. Future work should assess whether these dynamics are consistent across eastern boundary current ecosystems and over temporal variations.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"7 6 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142867411","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jens Boyen, María T. Rodríguez, Bruno Vlaeminck, Patrick Fink, Pascal I. Hablützel, Marleen De Troch
Greenhouse gas emissions lead to ocean warming and acidification, negatively impacting marine organisms and their functioning, including long‐chain polyunsaturated fatty acid (LC‐PUFA) production by marine microalgae. Copepods, primary consumers of microalgae, possess a unique capacity for endogenous LC‐PUFA biosynthesis, possibly enabling them to cope with reduced dietary LC‐PUFA availabilities. However, this capacity may be itself impacted by changing oceanographic conditions. In this study, we conducted a laboratory experiment to evaluate the combined effects of warming (+3°C), acidification (−0.4 pH), and dietary LC‐PUFA deficiency on the fatty acid composition and LC‐PUFA biosynthesis (measured by quantitative RT‐PCR) of the benthic harpacticoid copepod Platychelipus littoralis (Brady, 1880). We hypothesized increased LC‐PUFA biosynthesis under all drivers compensating for LC‐PUFA reductions. Lipid profiles of copepods exposed to multiple stressors contained shorter‐chained and more saturated fatty acids. While copepods maintained base‐line relative concentrations of the physiologically important LC‐PUFA docosahexaenoic acid (DHA) on an LC‐PUFA deficient diet at ambient temperatures, DHA concentrations decreased significantly with higher temperatures. Expression of the DHA biosynthesis genes Δ4 front‐end desaturase and elovl1a increased under dietary LC‐PUFA deficiency but did not exceed base‐line levels when simultaneously exposed to acidification. Expression of Δ4 front‐end desaturase and multiple elongases correlated positively with C18 precursor concentrations and negatively with those of LC‐PUFAs such as DHA, indicating their role as LC‐PUFA biosynthesis enzymes. Overall, our findings suggest that ocean warming and acidification may impede benthic copepods' LC‐PUFA biosynthesis capacity under reduced dietary inputs, limiting their contribution toward global LC‐PUFA availability for higher trophic levels.
{"title":"Temperature, pH, and diet interactively affect biosynthesis of polyunsaturated fatty acids in a benthic harpacticoid copepod","authors":"Jens Boyen, María T. Rodríguez, Bruno Vlaeminck, Patrick Fink, Pascal I. Hablützel, Marleen De Troch","doi":"10.1002/lno.12763","DOIUrl":"https://doi.org/10.1002/lno.12763","url":null,"abstract":"Greenhouse gas emissions lead to ocean warming and acidification, negatively impacting marine organisms and their functioning, including long‐chain polyunsaturated fatty acid (LC‐PUFA) production by marine microalgae. Copepods, primary consumers of microalgae, possess a unique capacity for endogenous LC‐PUFA biosynthesis, possibly enabling them to cope with reduced dietary LC‐PUFA availabilities. However, this capacity may be itself impacted by changing oceanographic conditions. In this study, we conducted a laboratory experiment to evaluate the combined effects of warming (+3°C), acidification (−0.4 pH), and dietary LC‐PUFA deficiency on the fatty acid composition and LC‐PUFA biosynthesis (measured by quantitative RT‐PCR) of the benthic harpacticoid copepod <jats:italic>Platychelipus littoralis</jats:italic> (Brady, 1880). We hypothesized increased LC‐PUFA biosynthesis under all drivers compensating for LC‐PUFA reductions. Lipid profiles of copepods exposed to multiple stressors contained shorter‐chained and more saturated fatty acids. While copepods maintained base‐line relative concentrations of the physiologically important LC‐PUFA docosahexaenoic acid (DHA) on an LC‐PUFA deficient diet at ambient temperatures, DHA concentrations decreased significantly with higher temperatures. Expression of the DHA biosynthesis genes Δ4 front‐end desaturase and elovl1a increased under dietary LC‐PUFA deficiency but did not exceed base‐line levels when simultaneously exposed to acidification. Expression of Δ4 front‐end desaturase and multiple elongases correlated positively with C<jats:sub>18</jats:sub> precursor concentrations and negatively with those of LC‐PUFAs such as DHA, indicating their role as LC‐PUFA biosynthesis enzymes. Overall, our findings suggest that ocean warming and acidification may impede benthic copepods' LC‐PUFA biosynthesis capacity under reduced dietary inputs, limiting their contribution toward global LC‐PUFA availability for higher trophic levels.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"29 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142867410","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Audrey N. Thellman, Tammy Wooster, Heather Malcom, Emma J. Rosi, Emily S. Bernhardt
Recent observations document increased abundance of algae in the headwater streams of Hubbard Brook Experimental Forest (HBEF). It is possible that this “greening up” of HBEF streams may be due to climate change, with rising temperatures, altering terrestrial phenology, and shifting hydrologic regimes. Alternatively, stream “greening” could be from the slow recovery of stream chemistry after decades of acid rain, which has led to rising pH, declining concentrations of toxic Al3+, and low solute concentrations. Four years of weekly algal measurements on artificial moss and ceramic tiles, along with six nutrient enrichment experiments, revealed new insights about the interactions between these two autotrophs. We found that in protected weir ponds and in stream channels, algal biomass was higher on artificial moss substrates than on tiles—with this effect amplified in the stream channels. These results suggest that bryophytes can provide physical protection from flood scour or may trap nutrients to support algal growth. In stream channels, algal biomass was higher in well‐lit habitats and time periods indicating strong light limitation. We only measured nitrogen and phosphorus limitation of algal biomass in nutrient enrichment experiments conducted within weir ponds, with higher light availability and lower flow. By comparison, results from the remaining four instream experiments provided little evidence for nutrient limitation, with only one trial showing increased algal growth in response to nutrient addition. The most striking implication of our study is the role of bryophytes in providing refugia, and potentially nutrients, to algae in shaded and oligotrophic headwater streams.
{"title":"Stream bryophytes promote “cryptic” productivity in highly oligotrophic headwaters","authors":"Audrey N. Thellman, Tammy Wooster, Heather Malcom, Emma J. Rosi, Emily S. Bernhardt","doi":"10.1002/lno.12741","DOIUrl":"https://doi.org/10.1002/lno.12741","url":null,"abstract":"Recent observations document increased abundance of algae in the headwater streams of Hubbard Brook Experimental Forest (HBEF). It is possible that this “greening up” of HBEF streams may be due to climate change, with rising temperatures, altering terrestrial phenology, and shifting hydrologic regimes. Alternatively, stream “greening” could be from the slow recovery of stream chemistry after decades of acid rain, which has led to rising pH, declining concentrations of toxic Al<jats:sup>3+</jats:sup>, and low solute concentrations. Four years of weekly algal measurements on artificial moss and ceramic tiles, along with six nutrient enrichment experiments, revealed new insights about the interactions between these two autotrophs. We found that in protected weir ponds and in stream channels, algal biomass was higher on artificial moss substrates than on tiles—with this effect amplified in the stream channels. These results suggest that bryophytes can provide physical protection from flood scour or may trap nutrients to support algal growth. In stream channels, algal biomass was higher in well‐lit habitats and time periods indicating strong light limitation. We only measured nitrogen and phosphorus limitation of algal biomass in nutrient enrichment experiments conducted within weir ponds, with higher light availability and lower flow. By comparison, results from the remaining four instream experiments provided little evidence for nutrient limitation, with only one trial showing increased algal growth in response to nutrient addition. The most striking implication of our study is the role of bryophytes in providing refugia, and potentially nutrients, to algae in shaded and oligotrophic headwater streams.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"56 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142832567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ian T. Black, Maria T. Kavanaugh, Clare E. Reimers
Marine heatwave (MHW) events have led to acute decreases in primary production and phytoplankton biomass in the surface ocean, particularly at the mid latitudes. In the Northeast Pacific, these anomalous events have occasionally encroached onto the Oregon shelf during the ecologically important summer upwelling season. Increased temperatures reduce the density of offshore waters, and as a MHW is present offshore, coincident downwelling or relaxation may transport warmer waters inshore. As an event persists, new upwelling‐driven blooms may be prevented from extending further offshore. This work focuses on MHWs and coincident events that occurred off Oregon during the summers of 2015–2023. In late summer 2015 and 2019, both documented MHW years, coastal phytoplankton biomass extended on average 6 and 9 km offshore of the shelf break along the Newport Hydrographic Line, respectively. During years not influenced by anomalous warming, coastal biomass extended over 34 km offshore of the shelf break. Reduced biomass also occurs with reduced upwelling transport and nutrient flux during these anomalous warm periods. However, the enhanced front associated with a MHW aids in the compression of phytoplankton closer to shore. Over shorter events, heatwaves propagating far inshore also coincide with reduced chlorophyll a and sea‐surface density at select cross‐shelf locations, further supporting a physical displacement mechanism. Paired with the physiological impacts on communities, heatwave‐reinforced physical confinement of blooms over the inner‐shelf may have a measurable effect on the gravitational flux and alongshore transport of particulate organic carbon.
{"title":"Bloom compression alongside marine heatwaves contemporary with the Oregon upwelling season","authors":"Ian T. Black, Maria T. Kavanaugh, Clare E. Reimers","doi":"10.1002/lno.12757","DOIUrl":"https://doi.org/10.1002/lno.12757","url":null,"abstract":"Marine heatwave (MHW) events have led to acute decreases in primary production and phytoplankton biomass in the surface ocean, particularly at the mid latitudes. In the Northeast Pacific, these anomalous events have occasionally encroached onto the Oregon shelf during the ecologically important summer upwelling season. Increased temperatures reduce the density of offshore waters, and as a MHW is present offshore, coincident downwelling or relaxation may transport warmer waters inshore. As an event persists, new upwelling‐driven blooms may be prevented from extending further offshore. This work focuses on MHWs and coincident events that occurred off Oregon during the summers of 2015–2023. In late summer 2015 and 2019, both documented MHW years, coastal phytoplankton biomass extended on average 6 and 9 km offshore of the shelf break along the Newport Hydrographic Line, respectively. During years not influenced by anomalous warming, coastal biomass extended over 34 km offshore of the shelf break. Reduced biomass also occurs with reduced upwelling transport and nutrient flux during these anomalous warm periods. However, the enhanced front associated with a MHW aids in the compression of phytoplankton closer to shore. Over shorter events, heatwaves propagating far inshore also coincide with reduced chlorophyll <jats:italic>a</jats:italic> and sea‐surface density at select cross‐shelf locations, further supporting a physical displacement mechanism. Paired with the physiological impacts on communities, heatwave‐reinforced physical confinement of blooms over the inner‐shelf may have a measurable effect on the gravitational flux and alongshore transport of particulate organic carbon.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"21 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142832636","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Bofu Zheng, Weifeng (Gordon) Zhang, Rubao Ji, Rachel H. R. Stanley, E. Taylor Crockford, Diana N. Fontaine, Emily E. Peacock, Tatiana A. Rynearson, Heidi M. Sosik
In aquatic ecosystems, allochthonous nutrient transport to the euphotic zone is an important process that fuels new production. Here, we use high‐resolution physical and biogeochemical observations from five summers to estimate the mean vertical nitrate flux, and thus new production over the Northeast U.S. Shelf (NES). We find that the summertime nitrate field is primarily controlled by biological uptake and physical advection–diffusion processes, above and below the 1% light level depth, respectively. We estimate the vertical nitrate flux to be 8.2 ± 5.3 × 10−6 mmol N m−2 s−1 for the mid‐shelf and 12.6 ± 8.6 × 10−6 mmol N m−2 s−1 for the outer shelf. Furthermore, we show that the new production to total primary production ratio (i.e., the f‐ratio), consistently ranges between 10% and 15% under summer conditions on the NES. Two independent approaches—nitrate flux‐based new production and O2/Ar‐based net community production—corroborate the robustness of the f‐ratio estimation. Since ~ 85% of the total primary production is fueled by recycled nutrients over sufficiently broad spatial and temporal scales, less than 15% of the organic matter produced in summer is available for export from the NES euphotic zone. Our direct quantification of new production not only provides more precise details about key processes for NES food webs and ecosystem function, but also demonstrates the potential of this approach to be applied to other similar datasets to understand nutrient and carbon cycling in the global ocean.
在水生生态系统中，向透光层输送异源营养物质是促进新产量的一个重要过程。在这里，我们利用五个夏季的高分辨率物理和生物地球化学观测数据来估算硝酸盐的平均垂直通量，从而估算美国东北部大陆架（NES）的新产量。我们发现，夏季硝酸盐场主要由生物吸收和物理平流-扩散过程控制，分别位于 1%光照深度以上和以下。我们估计中大陆架的垂直硝酸盐通量为 8.2 ± 5.3 × 10-6 mmol N m-2 s-1，外大陆架为 12.6 ± 8.6 × 10-6 mmol N m-2 s-1。此外，我们还发现，在夏季条件下，NES 的新产量与总初级产量之比（即 f 比）始终介于 10% 与 15% 之间。两种独立的方法--基于硝酸盐通量的新产量和基于 O2/Ar 的群落净产量--证实了 f 比率估算的稳健性。由于初级生产总量的约 85% 是由足够宽的时空尺度上的循环营养物质提供的，因此夏季产生的有机物中只有不到 15% 可用于从 NES 的透光层输出。我们对新生成物的直接量化不仅为近海生态系统食物网和生态系统功能的关键过程提供了更精确的细节，而且还证明了这种方法应用于其他类似数据集以了解全球海洋养分和碳循环的潜力。
{"title":"Vertical nitrate flux fuels new production over summertime Northeast U.S. Shelf","authors":"Bofu Zheng, Weifeng (Gordon) Zhang, Rubao Ji, Rachel H. R. Stanley, E. Taylor Crockford, Diana N. Fontaine, Emily E. Peacock, Tatiana A. Rynearson, Heidi M. Sosik","doi":"10.1002/lno.12765","DOIUrl":"https://doi.org/10.1002/lno.12765","url":null,"abstract":"In aquatic ecosystems, allochthonous nutrient transport to the euphotic zone is an important process that fuels new production. Here, we use high‐resolution physical and biogeochemical observations from five summers to estimate the mean vertical nitrate flux, and thus new production over the Northeast U.S. Shelf (NES). We find that the summertime nitrate field is primarily controlled by biological uptake and physical advection–diffusion processes, above and below the 1% light level depth, respectively. We estimate the vertical nitrate flux to be 8.2 ± 5.3 × 10<jats:sup>−6</jats:sup> mmol N m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> for the mid‐shelf and 12.6 ± 8.6 × 10<jats:sup>−6</jats:sup> mmol N m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> for the outer shelf. Furthermore, we show that the new production to total primary production ratio (i.e., the f‐ratio), consistently ranges between 10% and 15% under summer conditions on the NES. Two independent approaches—nitrate flux‐based new production and O<jats:sub>2</jats:sub>/Ar‐based net community production—corroborate the robustness of the f‐ratio estimation. Since ~ 85% of the total primary production is fueled by recycled nutrients over sufficiently broad spatial and temporal scales, less than 15% of the organic matter produced in summer is available for export from the NES euphotic zone. Our direct quantification of new production not only provides more precise details about key processes for NES food webs and ecosystem function, but also demonstrates the potential of this approach to be applied to other similar datasets to understand nutrient and carbon cycling in the global ocean.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"76 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142832570","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Christopher W. Hunt, Joseph E. Salisbury, Xuewu Liu, Robert H. Byrne
The capacity of aquatic systems to buffer acidification depends on the sum contributions of various chemical species to total alkalinity (TA). Major TA contributors are inorganic, with carbonate and bicarbonate considered the most important. However, growing evidence shows that many rivers, estuaries, and coastal waters contain dissolved organic molecules with charge sites that create organic alkalinity (OrgAlk). This study describes the first comparison of (1) OrgAlk distributions and (2) acid–base properties in contrasting estuary‐plume systems: the Pleasant (Maine, USA) and the St. John (New Brunswick, CA). The substantial concentrations of OrgAlk in each estuary were sometimes not conservative with salinity and typically associated with very low pH. Two approaches to OrgAlk measurement showed consistent differences, indicating acid–base characteristics inconsistent with the TA definition. The OrgAlk fraction of TA ranged from 78% at low salinity to less than 0.4% in the coastal ocean endmember. Modeling of titration data identified three groups of organic charge sites, with mean acid–base dissociation constants (pKa) of 4.2 (± 0.5), 5.9 (± 0.7) and 8.5 (± 0.2). These represented 21% (± 9%), 8% (± 5%), and 71% (± 11%) of titrated organic charge groups. Including OrgAlk, pKa, and titrated organic charge groups in carbonate system calculations improved estimates of pH. However, low and medium salinity, organic‐rich samples demonstrated persistent offsets in calculated pH, even using dissolved inorganic carbon and CO2 partial pressure as inputs. These offsets show the ongoing challenge of carbonate system intercomparisons in organic rich systems whereby new techniques and further investigations are needed to fully account for OrgAlk in TA titrations.
{"title":"Organic alkalinity distributions, characteristics, and application to carbonate system calculations in estuarine and coastal systems","authors":"Christopher W. Hunt, Joseph E. Salisbury, Xuewu Liu, Robert H. Byrne","doi":"10.1002/lno.12761","DOIUrl":"https://doi.org/10.1002/lno.12761","url":null,"abstract":"The capacity of aquatic systems to buffer acidification depends on the sum contributions of various chemical species to total alkalinity (TA). Major TA contributors are inorganic, with carbonate and bicarbonate considered the most important. However, growing evidence shows that many rivers, estuaries, and coastal waters contain dissolved organic molecules with charge sites that create organic alkalinity (OrgAlk). This study describes the first comparison of (1) OrgAlk distributions and (2) acid–base properties in contrasting estuary‐plume systems: the Pleasant (Maine, USA) and the St. John (New Brunswick, CA). The substantial concentrations of OrgAlk in each estuary were sometimes not conservative with salinity and typically associated with very low pH. Two approaches to OrgAlk measurement showed consistent differences, indicating acid–base characteristics inconsistent with the TA definition. The OrgAlk fraction of TA ranged from 78% at low salinity to less than 0.4% in the coastal ocean endmember. Modeling of titration data identified three groups of organic charge sites, with mean acid–base dissociation constants (pK<jats:sub>a</jats:sub>) of 4.2 (± 0.5), 5.9 (± 0.7) and 8.5 (± 0.2). These represented 21% (± 9%), 8% (± 5%), and 71% (± 11%) of titrated organic charge groups. Including OrgAlk, pK<jats:sub>a</jats:sub>, and titrated organic charge groups in carbonate system calculations improved estimates of pH. However, low and medium salinity, organic‐rich samples demonstrated persistent offsets in calculated pH, even using dissolved inorganic carbon and CO<jats:sub>2</jats:sub> partial pressure as inputs. These offsets show the ongoing challenge of carbonate system intercomparisons in organic rich systems whereby new techniques and further investigations are needed to fully account for OrgAlk in TA titrations.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"47 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142832639","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dan Yang, Asger Buur Jensen, Brian K. Sorrell, Hans Brix, Franziska Eller
Saline wetlands play a crucial role in climate regulation through their robust cooling effect, attributed to rapid carbon sequestration and minimal methane production. However, a comprehensive understanding of the mechanisms controlling their greenhouse gas (GHG) balance is lacking, particularly in salt marshes that are fully or partially submerged due to rising sea levels. We conducted a controlled manipulative experiment to test the effect of water levels on GHG emissions, including four water table levels: ‐10, 0, +5 cm and a fluctuating water table. We used soil cores from a Spartina anglica‐dominated salt marsh and examined the CO2 and CH4 fluxes over a growing season. Daylight CO2 uptake and dark CO2 emission were highest at the ‐10cm water table, while CH4 emissions were lowest at this water table. CO2 and CH4 fluxes were primarily driven by air and water temperature and solar irradiance. Our results indicate that salt marshes with near‐surface water levels (‐10 to 5 cm) function as potent CO2 sinks and minor sources of CH4 during the growing season. The high photosynthetic carbon assimilation combined with low CH4 fluxes resulted in a Global Warming Potential value of ‐326 g CO2eq m−2 on a 100‐year scale. Our study accounted for CH4 fluxes, CO2 uptake and emission together, and identified the mechanisms controlling CO2 and CH4 exchange. This approach is crucial for evaluating the potential of saline tidal wetlands as net carbon sinks and for developing scientifically sound climate mitigation policies.
盐碱地由于其快速的碳固存和极少的甲烷产生而具有强大的冷却效应，在气候调节中发挥着至关重要的作用。然而，对控制其温室气体（GHG）平衡的机制缺乏全面的了解，特别是在由于海平面上升而完全或部分淹没的盐沼中。我们进行了一项控制操纵实验，以测试水位对温室气体排放的影响，包括四种地下水位：- 10、0、+5厘米和波动的地下水位。我们使用了一个以米草属植物为主的盐沼的土壤岩心，研究了一个生长季节的CO2和CH4通量。日光CO2吸收和黑暗CO2排放在‐10cm地下水位处最高，而CH4排放在此地下水位处最低。CO2和CH4通量主要受空气和水温以及太阳辐照度的驱动。我们的研究结果表明，在生长季节，近地表水位（- 10至5 cm）的盐沼是有效的CO2汇和少量CH4源。高光合碳同化加上低CH4通量导致100年尺度上的全球变暖潜势值为‐326 g CO2eq m−2。我们的研究将CH4通量、CO2吸收和排放结合起来，确定了控制CO2和CH4交换的机制。这一方法对于评估咸水潮汐湿地作为净碳汇的潜力和制定科学合理的气候缓解政策至关重要。
{"title":"Rising water levels increase CH4 emissions and decrease CO2 exchange in a temperate salt marsh","authors":"Dan Yang, Asger Buur Jensen, Brian K. Sorrell, Hans Brix, Franziska Eller","doi":"10.1002/lno.12742","DOIUrl":"https://doi.org/10.1002/lno.12742","url":null,"abstract":"Saline wetlands play a crucial role in climate regulation through their robust cooling effect, attributed to rapid carbon sequestration and minimal methane production. However, a comprehensive understanding of the mechanisms controlling their greenhouse gas (GHG) balance is lacking, particularly in salt marshes that are fully or partially submerged due to rising sea levels. We conducted a controlled manipulative experiment to test the effect of water levels on GHG emissions, including four water table levels: ‐10, 0, +5 cm and a fluctuating water table. We used soil cores from a <jats:italic>Spartina anglica</jats:italic>‐dominated salt marsh and examined the CO<jats:sub>2</jats:sub> and CH<jats:sub>4</jats:sub> fluxes over a growing season. Daylight CO<jats:sub>2</jats:sub> uptake and dark CO<jats:sub>2</jats:sub> emission were highest at the ‐10cm water table, while CH<jats:sub>4</jats:sub> emissions were lowest at this water table. CO<jats:sub>2</jats:sub> and CH<jats:sub>4</jats:sub> fluxes were primarily driven by air and water temperature and solar irradiance. Our results indicate that salt marshes with near‐surface water levels (‐10 to 5 cm) function as potent CO<jats:sub>2</jats:sub> sinks and minor sources of CH<jats:sub>4</jats:sub> during the growing season. The high photosynthetic carbon assimilation combined with low CH<jats:sub>4</jats:sub> fluxes resulted in a Global Warming Potential value of ‐326 g CO<jats:sub>2</jats:sub>eq m<jats:sup>−2</jats:sup> on a 100‐year scale. Our study accounted for CH<jats:sub>4</jats:sub> fluxes, CO<jats:sub>2</jats:sub> uptake and emission together, and identified the mechanisms controlling CO<jats:sub>2</jats:sub> and CH<jats:sub>4</jats:sub> exchange. This approach is crucial for evaluating the potential of saline tidal wetlands as net carbon sinks and for developing scientifically sound climate mitigation policies.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"38 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142809334","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Melissa Steinman, Moritz S. Schmid, Robert K. Cowen, Su Sponaugle, Kelly R. Sutherland, Anne W. Thompson
Doliolids have a unique ability to impact the marine microbial community through bloom events and filter feeding. Their predation on large eukaryotic microorganisms is established and evidence of predation on smaller prokaryotic microorganisms is beginning to emerge. We studied the association between microorganisms and wild‐caught doliolids in the Northern California Current system. Doliolids were collected during bloom events identified at three different shelf locations with variable upwelling intensity. We discovered doliolids were associated with a range of prokaryotic microbial functional groups, which included free‐living pelagic Archaea, SAR11, and picocyanobacteria. The results suggest the possibility that doliolids could feed on the smallest members of the microbial community, expanding our understanding of doliolid feeding and microbial mortality. Given the ability of doliolids to clear large portions of seawater by filtration and their high abundance in this system, we suggest that doliolids could be an important player in shaping the microbial community structure of the Northern California Current system.
{"title":"The microorganisms associated with doliolids in a productive coastal upwelling system","authors":"Melissa Steinman, Moritz S. Schmid, Robert K. Cowen, Su Sponaugle, Kelly R. Sutherland, Anne W. Thompson","doi":"10.1002/lno.12748","DOIUrl":"https://doi.org/10.1002/lno.12748","url":null,"abstract":"Doliolids have a unique ability to impact the marine microbial community through bloom events and filter feeding. Their predation on large eukaryotic microorganisms is established and evidence of predation on smaller prokaryotic microorganisms is beginning to emerge. We studied the association between microorganisms and wild‐caught doliolids in the Northern California Current system. Doliolids were collected during bloom events identified at three different shelf locations with variable upwelling intensity. We discovered doliolids were associated with a range of prokaryotic microbial functional groups, which included free‐living pelagic Archaea, SAR11, and picocyanobacteria. The results suggest the possibility that doliolids could feed on the smallest members of the microbial community, expanding our understanding of doliolid feeding and microbial mortality. Given the ability of doliolids to clear large portions of seawater by filtration and their high abundance in this system, we suggest that doliolids could be an important player in shaping the microbial community structure of the Northern California Current system.","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"32 1","pages":""},"PeriodicalIF":4.5,"publicationDate":"2024-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142788609","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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