Retrospective Analysis of Midsummer Hypoxic Area and Volume in the Northern Gulf of Mexico, 1985–2011

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 &pm; 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 % &pm; 18 % in total N load or 48 % &pm; 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.

The impact of alternative nutrient kinetics and computational grid size on model predicted primary production and hypoxic area in the northern Gulf of Mexico

Environmental Modelling & Software ◽

10.1016/j.envsoft.2020.104661 ◽

2020 ◽

Vol 126 ◽

pp. 104661

Author(s):

James J. Pauer ◽

Wilson Melendez ◽

Timothy J. Feist ◽

John C. Lehrter ◽

Brenda Rashleigh ◽

...

Keyword(s):

Gulf Of Mexico ◽

Primary Production ◽

Computational Grid ◽

Grid Size ◽

Northern Gulf Of Mexico ◽

Hypoxic Area ◽

The Impact

Hypoxic volume is more responsive than hypoxic area to nutrient load reductions in the northern Gulf of Mexico—and it matters to fish and fisheries

Environmental Research Letters ◽

10.1088/1748-9326/aaf938 ◽

2019 ◽

Vol 14 (2) ◽

pp. 024012 ◽

Cited By ~ 7

Author(s):

Donald Scavia ◽

Dubravko Justić ◽

Daniel R Obenour ◽

J Kevin Craig ◽

Lixia Wang

Keyword(s):

Gulf Of Mexico ◽

Nutrient Load ◽

Northern Gulf Of Mexico ◽

Hypoxic Area ◽

Hypoxic Volume

Ensemble modeling informs hypoxia management in the northern Gulf of Mexico

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1705293114 ◽

2017 ◽

Vol 114 (33) ◽

pp. 8823-8828 ◽

Cited By ~ 38

Author(s):

Donald Scavia ◽

Isabella Bertani ◽

Daniel R. Obenour ◽

R. Eugene Turner ◽

David R. Forrest ◽

...

Keyword(s):

Gulf Of Mexico ◽

Mississippi River ◽

Task Force ◽

Weather Conditions ◽

Nitrogen Loading ◽

Load Reduction ◽

Nutrient Inputs ◽

Northern Gulf Of Mexico ◽

Water Column Stratification ◽

Hypoxic Area

A large region of low-dissolved-oxygen bottom waters (hypoxia) forms nearly every summer in the northern Gulf of Mexico because of nutrient inputs from the Mississippi River Basin and water column stratification. Policymakers developed goals to reduce the area of hypoxic extent because of its ecological, economic, and commercial fisheries impacts. However, the goals remain elusive after 30 y of research and monitoring and 15 y of goal-setting and assessment because there has been little change in river nitrogen concentrations. An intergovernmental Task Force recently extended to 2035 the deadline for achieving the goal of a 5,000-km2 5-y average hypoxic zone and set an interim load target of a 20% reduction of the spring nitrogen loading from the Mississippi River by 2025 as part of their adaptive management process. The Task Force has asked modelers to reassess the loading reduction required to achieve the 2035 goal and to determine the effect of the 20% interim load reduction. Here, we address both questions using a probabilistic ensemble of four substantially different hypoxia models. Our results indicate that, under typical weather conditions, a 59% reduction in Mississippi River nitrogen load is required to reduce hypoxic area to 5,000 km2. The interim goal of a 20% load reduction is expected to produce an 18% reduction in hypoxic area over the long term. However, due to substantial interannual variability, a 25% load reduction is required before there is 95% certainty of observing any hypoxic area reduction between consecutive 5-y assessment periods.

Daily hypoxia forecasting and uncertainty assessment via Bayesian mechanistic model for the Northern Gulf of Mexico

10.5194/hess-2021-207 ◽

2021 ◽

Author(s):

Alexey Katin ◽

Dario Del Giudice ◽

Daniel R. Obenour

Keyword(s):

Gulf Of Mexico ◽

Mechanistic Model ◽

Summer Season ◽

Nitrogen Loading ◽

Mechanistic Modeling ◽

Seasonal Forecasts ◽

Meteorological Model ◽

Forecast Performance ◽

Northern Gulf Of Mexico ◽

Hypoxic Area

Abstract. Low bottom water dissolved oxygen conditions (hypoxia) occur almost every summer in the northern Gulf of Mexico due to a combination of nutrient loadings and water column stratification. Several models have been used to forecast the midsummer hypoxic area based on spring nitrogen loading from major rivers. However, sub-seasonal forecasts are needed to fully characterize the dynamics of hypoxia over the summer season, which is important for informing fisheries and ecosystem management. Here, we present an approach to forecast hypoxic conditions at daily resolution through Bayesian mechanistic modeling that allows for rigorous uncertainty quantification. Within this framework, we develop and test different representations and projections of hydro-meteorological model inputs. We find that May precipitation over the Mississippi River Basin is a key predictor of summer discharge and loading that substantially improves forecast performance. Accounting for spring wind conditions also improves forecast performance, though to a lesser extent. The proposed approach generates forecasts for two different sections of the Louisiana–Texas shelf (east and west), and it explains about 50 % of the variability in total hypoxic area when tested against historical observations (1985−2016). Results also show how forecast uncertainties build over the summer season, with longer lead times from the nominal forecast release date of 31 May, due to increasing stochasticity in riverine and meteorological inputs. Consequently, the portion of overall forecast variance associated with uncertainties in data inputs increases from 26 % to 41 % from June–July to August–September, respectively. Overall, the study demonstrates a unique approach to assessing and reducing uncertainties in dynamic hypoxia forecasting.

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

Biogeosciences ◽

10.5194/bg-15-3121-2018 ◽

2018 ◽

Vol 15 (10) ◽

pp. 3121-3131 ◽

Cited By ~ 12

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 long-standing and growing problem worldwide and is 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) as well as the magnitude of the reduction requirements. The largest anthropogenically induced hypoxic area in North American coastal waters (of 15 000 ± 5000 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. Since then evidence of P limitation during the time of hypoxia formation has arisen, and a dual nutrient-reduction strategy for this system has been endorsed. 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 and P loads provides insight into the effects of both nutrients on primary production and hypoxia, and it 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 is P limited in the region where density stratification is conducive to hypoxia development, but reductions in N load have a bigger effect. Our simulations show that, at present loads, the system is almost 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 reductions of 63±18 % in total N load or 48±21 % in total N and P load are necessary to reach a hypoxic area of 5000 km2, which is consistent with previous estimates from statistical regression models and highly simplified mechanistic models.

A Scenario and Forecast Model for Gulf of Mexico Hypoxic Area and Volume

Environmental Science & Technology ◽

10.1021/es4025035 ◽

2013 ◽

Vol 47 (18) ◽

pp. 10423-10428 ◽

Cited By ~ 33

Author(s):

Donald Scavia ◽

Mary Anne Evans ◽

Daniel R. Obenour

Keyword(s):

Gulf Of Mexico ◽

Forecast Model ◽

Hypoxic Area ◽

Area And Volume

Effects of hypoxia on habitat quality of pelagic planktivorous fishes in the northern Gulf of Mexico

Marine Ecology Progress Series ◽

10.3354/meps10768 ◽

2014 ◽

Vol 505 ◽

pp. 209-226 ◽

Cited By ~ 17

Author(s):

H Zhang ◽

DM Mason ◽

CA Stow ◽

AT Adamack ◽

SB Brandt ◽

...

Keyword(s):

Gulf Of Mexico ◽

Habitat Quality ◽

Northern Gulf Of Mexico

Exploration of real-time satellite measurements to advance hurricane intensity prediction in the northern Gulf of Mexico

OCEANS 2009 ◽

10.23919/oceans.2009.5422158 ◽

2009 ◽

Author(s):

Nan Walker ◽

Robert Leben ◽

Steven Anderson ◽

Alaric Haag ◽

Chet Pilley ◽

...

Keyword(s):

Gulf Of Mexico ◽

Real Time ◽

Satellite Measurements ◽

Hurricane Intensity ◽

Northern Gulf Of Mexico ◽

Intensity Prediction

Potential for Relocation to Alter the Incubation Environment and Productivity of Sea Turtle Nests in the Northern Gulf of Mexico

Chelonian Conservation and Biology ◽

10.2744/ccb-1306.1 ◽

2018 ◽

Vol 17 (2) ◽

pp. 252 ◽

Cited By ~ 1

Author(s):

Matthew Ware ◽

Mariana M.P.B. Fuentes

Keyword(s):

Gulf Of Mexico ◽

Sea Turtle ◽

Northern Gulf Of Mexico