scholarly journals Simulating the effects of phosphorus limitation in the Mississippi and Atchafalaya River plumes

2012 ◽  
Vol 9 (11) ◽  
pp. 4707-4723 ◽  
Author(s):  
A. Laurent ◽  
K. Fennel ◽  
J. Hu ◽  
R. Hetland
Keyword(s):  
Gulf Of Mexico ◽  
Primary Production ◽  
Inorganic Nitrogen ◽  
Circulation Model ◽  
Phosphorus Limitation ◽  
Early Summer ◽  
Nitrogen And Phosphorus ◽  
River Plumes ◽  
Northern Gulf Of Mexico ◽  
Plume Region

Abstract. The continental shelf of the northern Gulf of Mexico receives high dissolved inorganic nitrogen and phosphorus loads from the Mississippi and Atchafalaya rivers. The nutrient load results in high primary production in the river plumes and contributes to the development of hypoxia on the Louisiana shelf in summer. While phytoplankton growth is considered to be typically nitrogen-limited in marine waters, phosphorus limitation has been observed in this region during periods of peak river discharge in spring and early summer. Here we investigate the presence, spatio-temporal distribution and implications of phosphorus limitation in the plume region using a circulation model of the northern Gulf of Mexico coupled to a multi-nutrient ecosystem model. Results from a 7-yr simulation (2001–2007) compare well with several sources of observations and suggest that phosphorus limitation develops every year between the Mississippi and Atchafalaya deltas. Model simulations show that phosphorus limitation results in a delay and westward shift of a fraction of river-stimulated primary production. The consequence is a reduced flux of particulate organic matter to the sediment near the Mississippi delta, but slightly enhanced fluxes west of Atchafalaya Bay. Simulations with altered river phosphate concentrations (±50%) show that significant variation in the spatial extent of phosphorus limitation (±40% in July) results from changes in phosphate load.

scholarly journals Simulating the effects of phosphorus limitation in the Mississippi and Atchafalaya River plumes

2012 ◽  
Vol 9 (5) ◽  
pp. 5625-5657 ◽  
Author(s):  
A. Laurent ◽  
K. Fennel ◽  
J. Hu ◽  
R. Hetland
Keyword(s):  
Gulf Of Mexico ◽  
Primary Production ◽  
Inorganic Nitrogen ◽  
Circulation Model ◽  
Phosphorus Limitation ◽  
Early Summer ◽  
Nitrogen And Phosphorus ◽  
River Plumes ◽  
Northern Gulf Of Mexico ◽  
Plume Region

Abstract. The continental shelf of the northern Gulf of Mexico receives high dissolved inorganic nitrogen and phosphorus loads from the Mississippi and Atchafalaya rivers. The nutrient load results in high primary production in the river plumes and contributes to the development of hypoxia on the Texas-Louisiana shelf in summer. While phytoplankton growth is considered to be typically nitrogen-limited, phosphorus limitation has been observed in this region during periods of peak river discharge in spring and early summer. Here we investigate the presence, spatio-temporal distribution and implications of phosphorus limitation in the plume region using a circulation model of the northern Gulf of Mexico coupled to a multi-nutrient ecosystem model. Results from a 7 yr simulation (2001–2007) compare well with available observations and suggest that phosphorus limitation develops every year between the Mississippi and Atchafalaya deltas. Model simulations show that phosphorus limitation results in a delay and westward shift of a fraction of river-stimulated primary production. The consequence is a reduced flux of particulate organic matter to the sediment near the Mississippi delta, but enhanced fluxes westward in the Atchafalaya and far-field regions. Two discharge scenarios with altered river phosphate concentrations (±50 %) reveal a significant variation (±40 % in July) in the spatial extent of phosphorus limitation with changes in phosphate load.

scholarly journals A coupled physical-biological model of the Northern Gulf of Mexico shelf: model description, validation and analysis of phytoplankton variability

2011 ◽  
Vol 8 (7) ◽  
pp. 1881-1899 ◽  
Author(s):  
K. Fennel ◽  
R. Hetland ◽  
Y. Feng ◽  
S. DiMarco
Keyword(s):  
Organic Matter ◽  
Gulf Of Mexico ◽  
Primary Production ◽  
River System ◽  
Phytoplankton Growth ◽  
Biological Model ◽  
Model Description ◽  
Ecological Gradient ◽  
Northern Gulf Of Mexico ◽  
Plume Region

Abstract. The Texas-Louisiana shelf in the Northern Gulf of Mexico receives large inputs of nutrients and freshwater from the Mississippi/Atchafalaya River system. The nutrients stimulate high rates of primary production in the river plume, which contributes to the development of a large and recurring hypoxic area in summer, but the mechanistic links between hypoxia and river discharge of freshwater and nutrients are complex as the accumulation and vertical export of organic matter, the establishment and maintenance of vertical stratification, and the microbial degradation of organic matter are controlled by a non-linear interplay of factors. Unraveling these interactions will have to rely on a combination of observations and models. Here we present results from a realistic, 3-dimensional, physical-biological model with focus on a quantification of nutrient-stimulated phytoplankton growth, its variability and the fate of this organic matter. We demonstrate that the model realistically reproduces many features of observed nitrate and phytoplankton dynamics including observed property distributions and rates. We then contrast the environmental factors and phytoplankton source and sink terms characteristic of three model subregions that represent an ecological gradient from eutrophic to oligotrophic conditions. We analyze specifically the reasons behind the counterintuitive observation that primary production in the light-limited plume region near the Mississippi River delta is positively correlated with river nutrient input, and find that, while primary production and phytoplankton biomass are positively correlated with nutrient load, phytoplankton growth rate is not. This suggests that accumulation of biomass in this region is not primarily controlled bottom up by nutrient-stimulation, but top down by systematic differences in the loss processes.

scholarly journals A coupled physical-biological model of the Northern Gulf of Mexico shelf: model description, validation and analysis of phytoplankton variability

2011 ◽  
Vol 8 (1) ◽  
pp. 121-156 ◽  
Author(s):  
K. Fennel ◽  
R. Hetland ◽  
Y. Feng ◽  
S. DiMarco
Keyword(s):  
Organic Matter ◽  
Gulf Of Mexico ◽  
Primary Production ◽  
Mississippi River ◽  
River System ◽  
Biological Model ◽  
Model Description ◽  
Ecological Gradient ◽  
Northern Gulf Of Mexico ◽  
Plume Region

Abstract. The Texas-Louisiana shelf in the Northern Gulf of Mexico receives large inputs of nutrients and freshwater from the Mississippi/Atchafalaya River system. The nutrients stimulate high rates of primary production in the river plume, which contributes to the development of a large and recurring hypoxic area in summer. The mechanistic links between hypoxia and river discharge of freshwater and nutrients are complex as the accumulation and vertical export of organic matter, the establishment and maintenance of vertical stratification, and the microbial degradation of organic matter are controlled by a non-linear interplay of factors. We present results from a realistic, 3-dimensional, physical-biological model that includes the processes thought to be of first order importance to hypoxia formation and demonstrate that the model realistically reproduces many features of observed nitrate and phytoplankton dynamics including observed property distributions and rates. We then contrast the environmental factors and phytoplankton source and sink terms characteristic of three model subregions that represent an ecological gradient from eutrophic to oligotrophic conditions. We analyze specifically the reasons behind the counterintuitive observation that primary production in the light-limited plume region near the Mississippi River delta is positively correlated with river nutrient input. We find that, while primary production and phytoplankton biomass are positively correlated with nutrient load, phytoplankton growth rate is not. This suggests that accumulation of biomass in this region is not primarily controlled bottom up by nutrient-stimulation, but top down by systematic differences in the loss processes. We hypothesize that increased retention of river water in high discharge years explains this phenomenon.

scholarly journals N and P as ultimate and proximate limiting nutrients in the northern Gulf of Mexico: Implications for hypoxia reduction strategies

2017 ◽  
Author(s):  
Katja Fennel ◽  
Arnaud Laurent
Keyword(s):  
Gulf Of Mexico ◽  
Primary Production ◽  
Statistical Regression ◽  
Nutrient Inputs ◽  
Nutrient Reduction ◽  
Total N ◽  
Northern Gulf Of Mexico ◽  
P Limitation ◽  
Hypoxic Area ◽  
Reduction Strategies

Abstract. The occurrence of hypoxia in coastal oceans is a growing problem worldwide and clearly linked to anthropogenic nutrient inputs. While the need for reducing anthropogenic nutrient loads is generally accepted, it is costly and thus requires scientifically sound nutrient-reduction strategies. Issues under debate include the relative importance of nitrogen (N) and phosphorus (P), and the magnitude of reduction requirements. The largest anthropogenically induced hypoxic area in North American coastal waters (of 15,000 ± 5,000 km2) forms every summer in the northern Gulf of Mexico where the Mississippi and Atchafalaya Rivers deliver large amounts of freshwater and nutrients to the shelf. A 2001 plan for reducing this hypoxic area by nutrient management in the watershed called for a reduction of N loads. Evidence of P limitation during the time of hypoxia formation has arisen since then, and has opened up the discussion about single versus dual nutrient reduction strategies for this system. Here we report the first systematic analysis of the effects of single and dual nutrient load reductions from a spatially explicit physical-biogeochemical model for the northern Gulf of Mexico. The model has been shown previously to skillfully represent the processes important for hypoxic formation. Our analysis of an ensemble of simulations with stepwise reductions in N, P and N&P loads provides insight into the effects of both nutrients on primary production and hypoxia, and allows us to estimate what nutrient reductions would be required for single and dual nutrient reduction strategies to reach the hypoxia target. Our results show that, despite temporary P limitation, N is the ultimate limiting nutrient for primary production in this system. Nevertheless, a reduction in P load would reduce hypoxia because primary production in the region where density stratification is conducive to hypoxia development, but reduction in N load have a bigger effect. Our simulations show that, at present loads, the system is saturated with N, in the sense that the sensitivity of primary production and hypoxia to N load is much lower than it would be at lower N loads. We estimate that reduction of 63 % ± 18 % in total N load or 48 % ± 21 % in total N&P load are necessary to reach a hypoxic area of 5,000 km2, which is consistent with previous estimates from statistical regression models and highly simplified mechanistic models.

scholarly journals Modeling ocean circulation and biogeochemical variability in the Gulf of Mexico

2013 ◽  
Vol 10 (11) ◽  
pp. 7219-7234 ◽  
Author(s):  
Z. Xue ◽  
R. He ◽  
K. Fennel ◽  
W.-J. Cai ◽  
S. Lohrenz ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Ocean Circulation ◽  
Function Analysis ◽  
Inorganic Nitrogen ◽  
Circulation Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Open Boundary ◽  
Biogeochemical Model ◽  
Open Boundary Conditions

Abstract. A three-dimensional coupled physical-biogeochemical model is applied to simulate and examine temporal and spatial variability of circulation and biogeochemical cycling in the Gulf of Mexico (GoM). The model is driven by realistic atmospheric forcing, open boundary conditions from a data assimilative global ocean circulation model, and observed freshwater and terrestrial nitrogen input from major rivers. A 7 yr model hindcast (2004–2010) was performed, and validated against satellite observed sea surface height, surface chlorophyll, and in situ observations including coastal sea level, ocean temperature, salinity, and dissolved inorganic nitrogen (DIN) concentration. The model hindcast revealed clear seasonality in DIN, phytoplankton and zooplankton distributions in the GoM. An empirical orthogonal function analysis indicated a phase-locked pattern among DIN, phytoplankton and zooplankton concentrations. The GoM shelf nitrogen budget was also quantified, revealing that on an annual basis the DIN input is largely balanced by the removal through denitrification (an equivalent of ~ 80% of DIN input) and offshore exports to the deep ocean (an equivalent of ~ 17% of DIN input).

scholarly journals Kilometer-scale larval dispersal processes predict metapopulation connectivity pathways for Paramuricea biscaya in the northern Gulf of Mexico

2021 ◽  
Author(s):  
Guangpeng Liu ◽  
Annalisa Bracco ◽  
Andrea M. Quattrini ◽  
Santiago Herrera
Keyword(s):  
Gulf Of Mexico ◽  
Ocean Circulation ◽  
Larval Dispersal ◽  
Circulation Model ◽  
Physical Models ◽  
Genetic Connectivity ◽  
Connectivity Pattern ◽  
Dispersal Pattern ◽  
Long Distance ◽  
Northern Gulf Of Mexico

AbstractFine-scale larval dispersal and connectivity processes are key to species survival, growth, recovery and adaptation under rapidly changing disturbances. Quantifying both are required to develop any effective management strategy. In the present work, we examine the dispersal pattern and potential connectivity of a common deep-water coral, Paramuricea biscaya, found in the northern Gulf of Mexico by evaluating predictions of physical models with estimates of genetic connectivity. While genetic approaches provide estimates of realized connectivity, they do not provide information on the dispersal process. Physical circulation models can now achieve kilometer-scale resolution sufficient to provide detailed insight into the pathways and scales of larval dispersal. A high-resolution regional ocean circulation model is integrated for 2015 and its advective pathways are compared with the outcome of the genetic connectivity estimates of corals collected at six locations over the continental slope at depths comprised between 1000 and 3000 meters. Furthermore, the likely interannual variability is extrapolated using ocean hindcasts available for this basin. The general connectivity pattern exhibits a dispersal trend from east to west following 1000 to 2000-meter isobaths, corresponding to the overall westward near-bottom circulation. The connectivity networks predicted by our model were mostly congruent with the estimated genetic connectivity patterns. Our results show that although dispersal distances of 100 km or less are common, depth differences between tens to a few hundred meters can effectively limit larval dispersal. A probabilistic graphic model suggests that stepping-stone dispersal mediated by intermediate sites provides a likely mechanism for long-distance connectivity between the populations separated by distances of 300 km or greater, such as those found in the DeSoto and Keathley canyons.

scholarly journals Kilometer-Scale Larval Dispersal Processes Predict Metapopulation Connectivity Pathways for Paramuricea biscaya in the Northern Gulf of Mexico

2021 ◽  
Vol 8 ◽  
Author(s):  
Guangpeng Liu ◽  
Annalisa Bracco ◽  
Andrea M. Quattrini ◽  
Santiago Herrera
Keyword(s):  
Gulf Of Mexico ◽  
Ocean Circulation ◽  
Larval Dispersal ◽  
Circulation Model ◽  
Physical Models ◽  
Genetic Connectivity ◽  
Connectivity Pattern ◽  
Dispersal Pattern ◽  
Long Distance ◽  
Northern Gulf Of Mexico

Fine-scale larval dispersal and connectivity processes are key to species survival, growth, recovery and adaptation under rapidly changing disturbances. Quantifying both are required to develop any effective management strategy. In the present work, we examine the dispersal pattern and potential connectivity of a common deep-water coral, Paramuricea biscaya, found in the northern Gulf of Mexico by evaluating predictions of physical models with estimates of genetic connectivity. While genetic approaches provide estimates of realized connectivity, they do not provide information on the dispersal process. Physical circulation models can now achieve kilometer-scale resolution sufficient to provide detailed insight into the pathways and scales of larval dispersal. A high-resolution regional ocean circulation model is integrated for 2015 and its advective pathways are compared with the outcome of the genetic connectivity estimates of corals collected at six locations over the continental slope at depths comprised between 1,000 and 3,000 m. Furthermore, the likely interannual variability is extrapolated using ocean hindcasts available for this basin. The general connectivity pattern exhibits a dispersal trend from east to west following 1,000 to 2,000-m isobaths, corresponding to the overall westward near-bottom circulation. The connectivity networks predicted by our model were mostly congruent with the estimated genetic connectivity patterns. Our results show that although dispersal distances of 100 km or less are common, depth differences between tens to a few hundred meters can effectively limit larval dispersal. A probabilistic graphic model suggests that stepping-stone dispersal mediated by intermediate sites provides a likely mechanism for long-distance connectivity between the populations separated by distances of 300 km or greater, such as those found in the DeSoto and Keathley canyons.

Sign in / Sign up

Export Citation Format

Share Document