Sustainability of Gulf of Mexico Coastal Estuaries and Lagoons: Interactions with Hydrocarbon Production—A Review with a Look to the Future

Abstract

Here, we review the functioning and importance of deltaic coastal systems in the northern and southern Gulf of Mexico and how petroleum activities have impacted these two important systems. The Mississippi and Usumacinta-Grijalva Deltas are areas of high biological productivity and biodiversity that support the two largest fisheries in the Gulf. The north central Gulf receives inflow from the Mississippi river, the largest discharge in North America. The Mississippi Delta covers about 10,000 km². The Usumacinta-Grijalva River is the second highest freshwater input to the Gulf and discharges to the Usumacinta-Grijalva/Laguna de Terminos deltaic complex. These two areas are the largest petroleum producing regions in the Gulf, involving both inshore and offshore production. Petroleum activities impact coastal ecosystems in two important ways. In inshore areas dominated by coastal wetlands, there has been enormous physical disruption of the natural environment that affected hydrology and system functioning. In both inshore and offshore areas, spilled oil and release of high salinity produced water has led to widespread toxic pollution. Documentation of petroleum activity impacts on coastal marine ecosystems is much more advanced in the Mississippi Delta. Here, we describe how petroleum production impacts coastal ecosystems and discuss how restoration and management can restore the functioning of impacted coastal ecosystems.

1. Introduction

Coastal areas are characterized by several different types of systems; these include estuaries, river deltas, drowned river valleys, coastal lagoons, beaches, tidal flats, and coastal wetlands. Coastal wetlands, including marshes and mangroves, are among the most productive biological systems globally, and the largest areas of coastal wetlands occur in marine river deltas [1]. Deltaic ecosystems support important fisheries and high levels of biodiversity. Globally, coastal wetlands are most abundant in tropical areas and, secondarily, in the Arctic. Humans have lived in coastal areas for millennia and the majority of coastal megacities occur in the tropics, often in deltas [2].

Deltas are important economically. They support large fisheries and other natural resources and are often important ports supporting international trade. Deltas are often the site of petroleum production, reflecting millions of years of high biological productivity. Among deltas with significant petroleum production are the Rhine, Niger, Mekong, Ganges, and Amazon. In the Gulf of Mexico, there are numerous oil and gas fields associated with the Mississippi and Usumacinta-Grijalva Deltas. While petroleum producing areas are economically important, oil and gas activity has resulted in significant environmental degradation [3]. In this paper, we review the Mississippi and Usumacinta-Grijalva Deltas in terms of their ecological and economic importance and the impacts that petroleum production activities have had on these important systems. We then generalize our findings to deltas in other areas.

2. An Overview of Gulf of Mexico (GOM) Coastal Ecosystems

The Gulf of Mexico (GOM) is one of the largest semi-closed seas globally with an area of 564,000 square kilometers [4,5], bordered by the coasts of the USA, Mexico, and Cuba. The GOM receives inflow from the Caribbean via the Yucatan Channel. Outflow to the Atlantic Ocean is via the Strait of Florida, where it forms the Gulf Stream [5]. The GOM has a high diversity of coastal habitats that range from tropical and subtropical, to sub-temperate; however, these habitats will become entirely tropical by the end of the century due to climate change [6]. The southern GOM has a tropical climate with dry (spring), rainy (summer, autumn), and winter seasons [6,7]. By contrast, the northern GOM has more temperate seasons (winter, spring, summer and fall). There is a rich variety of coastal lagoons and estuaries in the GOM [6,8].

The coastal GOM is an area of great ecological value with a diversity of habitats. Coastal ecosystems include hypersaline lagoons, coral reefs, mangrove and marsh wetlands, estuaries, and deltas [9]. There are over 200 coastal systems including numerous productive coastal lagoons [4].

Deegan et al. [10] analyzed 64 of the coastal systems around the GOM from Florida Bay to Laguna Conil in the State of Yucatan to investigate relationships among coastal vegetation, water budgets, river discharge, and fisheries. Fishery harvest and estuary areas were strongly related to freshwater input and physiography (Figure 1). The area of emergent vegetation was related to intertidal area and rainfall. Fishery harvest per unit area of open water was highly correlated with river discharge in the southern GOM. The study highlighted the distinctiveness of the Mississippi and Usumacinta-Grijalva Deltas. The north-western GOM near the U.S./Mexico and the northern Yucatan Peninsula are areas where annual precipitation consistently exceeds evaporation. The north-central and southern GOM are areas where there is high riverine input. The three highest river inputs, in order, are the Mississippi, Usumacinta-Grijalva and the Tombigbee (to Mobile Bay). Intertidal vegetation is highest in southern Florida, the Mississippi Delta, the upper Texas coast, and the Usumacinta-Grijalva Delta [10].

The Mississippi and Usumacinta-Grijalva Deltas stand out as areas with high wetland area, high rainfall and riverine input, and high fisheries. These areas also have the highest petroleum production in the GOM.

2.1. The Most Important Gulf of Mexico Estuaries and Coastal Lagoons

The circulation of the GOM includes a semi-permanent cyclonic gyre in Campeche Sound, and anticyclonic gyres which are shed by the Loop Current and move westward where they eventually dissipate. Discharge from the Mississippi, Grijalva, and Usumacinta Rivers is deflected to the west in both the southern and northern Gulf. The coast around the GOM is almost uniformly low-lying, with many narrow barrier islands, and is characterized by marshes, mangrove swamps and sandy beaches [11].

The Gulf region is important for offshore and inshore petroleum production for the U.S. and Mexico, generating a significant portion of total production for both countries. During 2023, oil production in the Mexican portion of the Gulf averaged 1.855 million barrels/day, with a total value of 109.94 billion pesos [12]. Mexican oil reserves are concentrated in the oil province of Cuencas del Sureste [13]. About half of U.S. petroleum refining and natural gas production is from the north-central Gulf coast. Marine transportation is a multi-billion-dollar industry centered mainly in New Orleans and Houston [14].

Seventy-three percent of coastal wetlands in the U.S. are found in the northern GOM and wetland loss is highest in this region [15]. Alteration of surface hydrology and petroleum production accounted for much of this loss [3,16,17]. The length of the Mexican shoreline is 1910 km and there is about 5767 km² of coastal lagoons. The Usumacinta-Grijalva and Papaloapan Rivers have the highest discharge in Mexico, and Laguna Madre (200,000 ha) and Laguna de Terminos (196,000 ha) are the largest coastal lagoons in the country. Important economic activities include fishing, tourism, ranching, agriculture, and oil extraction [18].

Mangroves cover 127,000 ha in the Laguna de Terminos. The economic value of the resources of the system was valued at 1.02 USD/ha/year for mangroves, 1193 USD/ha/year for water quality maintenance, and 1578 USD/ha/year for fisheries [19]. However, in 2001, Landsat analysis showed that mangrove cover in Terminos Lagoon had decreased to 79,546 ha [20].

2.1.1. Mississippi River Delta

The Mississippi River has a length of 3700 km with high fresh water and sediment discharge [21]. The Mississippi Basin covers 3.2 million km² and discharges to the GOM via the Mississippi and Atchafalaya Rivers [21] (Figure 2). There are important fisheries in the Mississippi River Delta and it is one of the largest coastal fisheries globally. Water quality in the river and coastal system is impacted by municipal effluent, industrial discharge, and agricultural runoff [22]. The value of ecosystem goods and services in coastal Louisiana is estimated at USD 12–47 billion annually. The value of natural capital ranges from USD 330 billion to USD 1.3 trillion [23].

Human activities have strongly impacted the Mississippi Delta, including building levees along the river that prevents riverine input to the deltaic plain, reclamation of wetlands, water pollution, and pervasive hydrologic disruption [25,26,27]. Oil and gas production began over a century ago. More than half of the petroleum production in Louisiana has come from the coastal area. Peak production of both oil and natural gas occurred around 1970 when over 500 million barrels of were produced. Petroleum production in the coastal zone came from more than 700 fields [27]. The Deepwater Horizon spill affected coastal marshes impacted salt marsh vegetation in the Mississippi Delta [28].

There is a large seasonal hypoxic zone on the continental shelf (dissolved oxygen < 2 mg per liter). The area of this zone has been as high as 22,700 km² in 2017 [29]. Hypoxia can affect growth rates, reproduction, diets, and habitat use by fish [27].

2.1.2. Terminos Lagoon

Terminos Lagoon in the state of Campeche (Figure 3) covers 2500 km², and it is the largest in the Gulf [30]. There are two tidal inlets (Puerto Real and Carmen) and the barrier island of Isla del Carmen. The population of the island is concentrated in Cd. del Carmen on the western end of the island. Trade winds induce a net east-to-west flow through the lagoon and about 40% of the flow that enters the eastern Puerto Real inlet leaves through the western Carmen inlet [31]. Three rivers discharge into the southern lagoon, namely, the Palizada, Chumpan, and Candelaria Rivers. The Palizada is a distributary of the Usumacinta-Grijalva River, which has a basin drainage area of 49,700 km². Mangroves occupy most of the shoreline of the lagoon. These are a nursery for a large fishery [31].

There are more than 84 families and 374 species of plants. Wildlife diversity is high, with about 1468 vertebrate species (aquatic and terrestrial). There are 30 vertebrate species endemic to the area [20]. Because of its high ecological and economic value, the Laguna de Terminos Protected Area for Fauna and Flora was established in 1994 [20,33,34].

Terminos Lagoon is a very important ecosystem for a number of reasons [33]:

(1)

There is high natural net primary productivity and secondary productivity;

(2)

Ecological diversity of the lagoon ecosystem is high in terms of species diversity, population assemblages, biogeochemical and ecological processes, and important critical habitats;

(3)

There are important fisheries for oysters and other shellfish, crustaceans, and fin fish;

(4)

There are important interactions with Campeche Sound through the tidal inlets, and among primary productivity, nekton community ecology and habitats;

(5)

The unique seasonality of environmental dynamics and hydrological and biological processes;

(6)

There are important annual changes in environmental behavior of the ecosystem;

(7)

The impacts of petroleum-related activities and petrochemical industries;

(8)

The incorporation of Laguna de Terminos in the natural protected areas system of Mexico;

(9)

The complex interactions among ecological and economic systems with governmental regulations and constraints;

(10)

The lack of inclusion of the idea of system functioning as a conceptual framework for sustainable management of the deltaic-lagoon systems [35].

There are three dominant mangrove species: black mangrove (Avicenia germinans L.) white mangrove (Laguncularia racemose Gaertn.f.), and red mangrove (Rhizophora mangle L.). Fisheries in Laguna de Terminos are strongly dependent on the area and production of mangroves [31]. Mangroves export organic materials and nutrients to adjacent aquatic systems in the lagoon and on the continental shelf. This enhances coastal productivity and trophic webs. A number of plant communities are associated with mangroves, including algal communities on the mangroves and adjacent sediments. This complex mangrove system is important in supporting important fisheries [36].

2.2. Socio-Environmental Characteristics of the Coastal Zone of the Gulf of Mexico

The GOM is an integrated system that forms an important conceptual framework for understanding and managing both natural and social systems in the Gulf region (Figure 4) [17].

Drivers are key natural and anthropogenic forcings [38]. Human activities impacting both social and natural systems of the Gulf include petroleum exploration and production, fishing, navigation, wetland reclamation, and water pollution. These interact with natural forcings, including tropical cyclones, water flow dynamics, and biogeochemistry. To help understand Gulf systems interactions, McKinney identified four major subsystems [17] (Figure 5): the ocean environment, coastal and marine ecosystems, socioeconomic interactions, and human health, which make up a socio-environmental system.

Over 15.8 million people, about 5% of the population of the U.S., inhabit the coast of the GOM (169). The coastal population along the Mexican Gulf is about 9.2 million people [39]. Natural resource-related economic activities are important for the GOM; however, growth and economic development have had an impact on the Gulf environment. In the U.S. portion of the Gulf, about 880,000 individuals work in the coastal economy, with an economic value of USD 117 billion annually [17]. Meanwhile, in Mexico’s Gulf coast, the value of economic activities is about 3.2 billion pesos annually, or about 22.6% of the national GDP [40].

Thus, the Gulf supports two of the most economically important activities for the two countries bordering most of the Gulf shoreline of both the U.S. and Mexico, including fisheries and petroleum production. About 17% of U.S. commercial fisheries and about 30% of recreational fishing occurs in the GOM. In 2017, the value of these fisheries amounted to nearly USD 12 billion [41]. In the Mexican GOM, fisheries are valued at 1.15 billion pesos [42]. Hydrocarbon extraction in the first three months of 2024 was valued at 822 million pesos [42].

3. Oil Sector in the Gulf of Mexico

3.1. Oil Production in the Northern Gulf of Mexico

Petroleum production in coastal Louisiana started early in the 20th century. Production for individual fields can last four to six decades or more, and the area is now in the last stage of production. The production cycle began with a rapid increase to a peak in about 1970, and then declined. Hydrocarbon production is correlated with wetland loss [43,44] (Figure 6). The production of high-salinity brine water was generally higher in the declining phase of petroleum production.

Petroleum activities cause direct and indirect impacts [16,43,46]. Dredging of canals and placement of spoil directly destroys wetlands. Indirect impacts include (1) pervasive change in hydrology; (2) increased subsidence of the land surface; (3) and impacts of toxic materials.

The impacts due to O&G production are evident when images of oil fields are viewed over time, as is indicated for two fields in the Mississippi Delta. Figure 7 and Figure 8 show wetland loss over time for two petroleum fields.

3.2. Oil Production in the Southern Gulf of Mexico

Oil was first produced in Tabasco and Veracruz between 1863 and 1938. Petróleos Mexicanos (PEMEX), the Mexican National Oil Company, was established in 1938. In 1976, offshore oil exploitation began in Campeche Sound with the Chac and Cantarell fields, which would become the main oil production region in the country. The latter field was the main hydrocarbon producer in the early 1980s, reaching a production of 3 million BBL oil/day [48]. However, Cantarell began to decline [49]. The history of hydrocarbon production of the Sound of Campeche is shown in Figure 9.

The daily oil production in 2024 was about 1.5 million barrels per day [50] which represented its lowest level of production since 1990. Moreover, the oil income declined by 14.5% (183,000 million pesos) in this period. Figure 10 shows the areas of petroleum production in the Mexican GOM [51].

There were 7705 active wells in the Mexican GOM in 2019 [53], with the highest production in the Campeche Sound area (Figure 11).

3.3. Impacts of Hydrocarbon Activities on Wetlands and Aquatic Ecosystems of the Gulf of Mexico

Oil and gas activities had produced a great number of oil spills and hydrocarbon-related accidents during exploration and exploitation activities (see Appendix A). In coastal Louisiana have resulted in significant impacts on the environment since the early 20th century, e.g., [3,16,27,54,55]. There are numerous oil and gas wells and an extensive pipeline network associated with production and transport of hydrocarbons, which affects every part of coastal Louisiana and the northern Gulf of Mexico (Figure 12a,b).

To understand the impacts of petroleum activities, it is necessary to understand that these activities and impacts occurred at a rate (decades) that was much higher than the rate of processes that developed and sustained the Mississippi River deltaic wetlands (hundreds to thousands of years) [26,56,57,58,59,60]. In less than a century, significant environmental changes have taken place in the Mississippi River deltaic wetlands due to petroleum production [3,16,44,61,62]. These activities have resulted in dramatic alteration of coastal systems and the intentional and accidental introduction of a variety of toxic materials into coastal wetlands [63,64,65], leading to coastal wetland loss and changes in ecosystem functioning [3,16,27,66,67].

Day et al. [16] summarized the impacts of petroleum-related activities on coastal systems in coastal Louisiana, and we review their findings and put them into the context of the southern Gulf of Mexico.

3.3.1. Canals

There are over 700 petroleum fields in coastal Louisiana with thousands of wells, resulting in thousands of kilometers of canals. Canal dredging and spoil placement caused pervasive change in surface hydrology. Canals are generally straight and deeper than natural tidal channels. Increasing canal density causes a loss of natural channels in a process known as channel theft [3,16]. Canal networks are often interconnected and lead to saltwater intrusion into fresher wetlands [27,55,67,68,69,70,71,72,73,74], which leads to decreased productivity and mortality of wetlands [71,75,76,77]. Saltwater intrusion causes stress and mortality of low-salinity and fresh wetlands [77] and rapid decomposition of freshwater peats [78] in a process called marsh collapse. This causes vegetation stress and mortality and vulnerability to erosion [78,79].

3.3.2. Spoil Banks

Spoil banks along dredged canals impede sheet flow over wetlands, reducing exchange of water, sediments, chemicals, and organisms. Wetlands become impounded or semi-impounded by canals and have fewer but longer-duration flooding events. Spoil banks trap water in semi-impounded areas, which negatively impacts wetlands [27,61,66,73,75,80,81,82,83,84,85,86,87,88,89,90,91,92,93]. Because of reduced water exchange due to spoil banks, most water input only occurs when water levels are increased, as happens during strong storms. This leads to longer-duration flooding because water cannot flow unimpeded over the spoil banks [56,80,86,90,94]. The combination of reduced sediment input and lower productivity by wetlands reduces the rate of vertical accretion, which has been measured to be up to five times lower than in non-impounded wetlands [54,83,86,95,96,97]. Spoil banks, however, are not permanent because they sink due to subsidence and compaction, and many disappear completely over time. However, by the time the spoil banks disappear, most of the wetlands surrounding the spoil banks have converted to open water [3,26].

3.3.3. Alteration of Surface Hydrology through Cumulative Impacts

As noted above, tidal wetlands depend on unrestricted tidal exchange to maintain their health. Altered hydrology stresses wetlands due to decreased water exchange [27,56,61,67,73,74,89,91,98,99,100].

Oil and gas canals widen over time due to undercutting of spoil banks, edge, erosion, and sloughing and this leads to additional loss of wetlands [91,98]. The weight of spoil banks can cause compaction parallel to spoil banks. Loss of wetlands is due to a combination of subsidence, reduced water exchange, and reduced sediment input [47]. Nichols reported that the weight of the spoil compacted soils creating a barrier to groundwater movement [101]. This loss of surface elevation is termed shallow subsidence [100].

Oil and gas canals are deeper and straighter than tidal channels that are shallow and sinuous [27]. As canal density increases, natural channel density is lower (Figure 13 and Figure 14) [80,102]. This process, known as channel theft, alters natural hydrology because oil and gas canals are more efficient than natural shallow channels [99]. Oil and gas canals may also connect water bodies that were not previously connected, causing changes in local hydrologic patterns [99].

3.3.4. Enhanced Subsidence Due to Petroleum Extraction

Reduced sediment input in combination with reduced vegetation productivity causes an increase in rates of surficial subsidence. In addition, petroleum withdrawal leads to deep subsidence. This occurs in two phases: first as the petroleum reservoir compacts due to petroleum withdrawal, and then in the bounding shales as water slowly leaks into the reservoir and is pumped out [3,16,46,104] (Figure 15). The second phase can continue for several decades after most production ceases.

3.4. Impacts of Petroleum on Marine Resources and Ecosystems

Petroleum toxicity depends on the chemical makeup of the oil [105]. Two types of oil are produced in Campeche Sound: heavy oil (Maya) and light oil (Itsmo). Each one has specific characteristics that influence their behavior, such as weathering processes, the risk and impact that each has on biodiversity, the environment (toxicity and bioaccumulation), and the rapidity of damages. In Campeche Sound, high temperatures favor oil evaporation and photooxidation, which can remove more than half of spilled oil. Other characteristics are precipitation that can convey oil from land to rivers, lagoons, and coastal zones. Additionally, local wind patterns may accelerate the oil dispersion, emulsification, and biodegradation [106].

Hydrocarbon pollution in the marine environment is associated with exploration, production, marine and submarine transportation, shipment, disembarkation operations, and accidents such as spills from submarine oil pipelines, tanker accidents, platform spills, and explosions [106]. Moreover, there are other hydrocarbons sources from industrial loading and unloading, municipal discharges, runoff from rivers to the coastal zone, atmospheric deposition, and chronic and discrete leakage of “chapopoteras” from natural marine outcrops.

When oil is spilled, weathering occurs [107]. The main processes involved in weathering are dispersion, phytolysis, emulsification, evaporation, adsorption, sedimentation, and biodegradation [107].

Total concentrations of PAHs in coastal lagoons and organisms, especially oysters, in lagoons of the GOM exceeded permitted limits in several areas (

Table 1. Average concentrations of total, high-, and low-molecular-weight polycyclic aromatic hydrocarbons (PAHs) in coastal lagoons and bays of the Atlantic coast of Mexico. N.R. = Not reported. Source: [107].

Lagoon/Bay	PAH	LMW 1	HMW 2
	(mg/g)	(mg/g)	(mg/g)
Chetumal	2.34	0.27	2.17
Sian Ka’An	1.16	0.55	0.8
Salada	6.65	0.21	6.44
Llano	5.00	0.31	4.69
Mandinga	5.68	0.8	4.88
La Mancha	6.73	0.39	6.34
Pueblo Viejo	3.81	1.12	2.08
Tamiahua	3.42	0.88	2.54
Tampamachoco	4.48	1.21	3.27
Mecoacan	0.95	N.R.	N.R.
Carmen	1.31	N.R.	N.R.
Machona	1.85	N.R.	N.R.
“High” U.S.A.	2.40
Critical	35.0

¹ LMW = low-molecular-weight PAHs. ² HMW = high-molecular-weight PAHs.

and

Table 2. Average concentrations of polycyclic aromatic hydrocarbons (PAHs) in Crasostrea virginica and A. assimilis in coastal lagoons and bays of the Atlantic coast of Mexico. Source: [107].

Lagoon/Bay	PAH (ng/g)	Organism
Carmen	232	C. virginica
Machona	404	C. virginica
Mecoacan	219	C. virginica
Terminos	1900	C. virginica
Chetumal	77,000	A. assimilis
Mean STP	536	C. virginica

) [107].

The impact of hydrocarbons depends on a number of factors including toxicity, contact between vegetation and animals and oil, species, frequency of oil contact, seasonality, brine impacts, and cleanup [105]. Figure 16 summarizes these impacts.

Results from emissions of greenhouse gases from cumulative O&G production from 1960–2019 were calculated by Llano and Flores [109]. For this period, cumulative oil production was 41,602 MMb, while natural gas cumulative production was 76,803 thousand million cubic feet (MMMcf). Extraction, processing, and use of these hydrocarbons have resulted in at least 23,959.60 million tons of carbon dioxide equivalents, calculated with the methodology of the Climate Accountability Institute (

Table 3. Marine and terrestrial emissions of greenhouse gases resulting from cumulative production of gas and oil in Mexico 1960–2019. Source: [109].

Activity			Shallow Waters	Land	Total
			Tons of CO2e
Extraction	Natural Gas	Fugitive (Methane)	282.31	568.49	850.8
		Venting	38.83	78.18	117.01
		Burning	2.36	4.76	7.12
		Internal use as fuel	80.62	162.34	242.96
		Subtotal gas	404.12	813.77	1217.89
	Crude oil	Fugitive (Methane)	427.83	196.24	624.07
		Venting	40.6	18.62	59.22
		Burning	168.84	77.45	246.29
		Subtotal oil	637.27	292.31	929.58
		Subtotal extraction	1041.39	1106.08	2147.47
Processing	Natural Gas	Processing	26.5	53.37	79.88
	Crude oil	Processing	1494.46	685.49	2179.95
		Subtotal processing	1520.96	738.86	2259.82
Combustion	Natural Gas	Combustion	1360.90	2740.42	4101.31
	Crude oil	Combustion	10,592.39	4858.61	15,451.00
		Subtotal combustion	11,953.29	7599.02	19,552.31
		Total	14,515.64	9443.96	23,959.60

). The largest emissions volume came from hydrocarbon processing and combustion, estimated as 91% of the total emissions, with 9% coming from the extraction phase generated directly for the oil fields.

Brine Production

Discharge of produced water, aka brine, causes serious environmental impacts. This is a sedimentary water that can be up to 150 million years old. Its composition varies in different oil fields, but it may contain oil, sulfates, bicarbonates, hydrogen sulfur, cyanide, carbon dioxide, heavy metals (cadmium, arsenic, chrome, lead, mercury, vanadium, and zinc), and other toxic compounds [110].

The disposal of high-salinity brine into the environment has both short- and long-term negative impacts. It can cause groundwater and soil pollution, since this water is high in salinity, and heavy metals and other pollutants can infiltrate into the soil and groundwater. Brine production can lead to air pollution if it is disposed of through evaporation tanks. In the long term, these elements can result in acid rain, respiratory diseases, and other health problems [110].

Brine production has been a major problem in the Mississippi Delta. Prior to its banning in 1997, large quantities of brine were released into the natural environment [111]. Much more brine is produced than oil and it is much more toxic than oil [112]. Brine includes many toxic compounds in addition to having high salinity [113,114] (

Table 4. Common components of produced water resulting from oil and gas production in the Mississippi Delta. Source: Data taken from [115].

Category	Constituent
Metals	Aluminum, Antimony, Arsenic, Barium, Boron, Cadmium, Gold, Iron, Mercury, Chromium, Copper, Lead, Zinc, Nickel, Platinum, Silver, Strontium, Tin, Magnesium, Molybdenum, Tiitanium, Thallium, Vanadium
Naturally Occurring Radioactive Materials	Radium-226, Radium-228
Monocyclic Aromatic Hydrocarbons	Benzene, Benzoic acid, Chlorobenzene, Di-n-butyl phthalate, Toluene, Ethlybenzene, Isopropylbenzene, n-Propylbenzene, p-chloro-m-cresol, Xylenes
Polycyclic Aromatic Hydrocarbons	Acenaphthene, Anthracene, Benzo(a)anthracene, Cyrsene, Dibenzothiophenes, Fluoranthene, Flourene, Napththalene, Benzo(a)pyrene
Miscellaneous Organic Chemicals	Phenols, Bis(2-ethylhexyl)phthalate, Oil and grease
Miscellaneous Other Components	Calcium, Potassium, Radon, Sodium chloride, Total dissolved solids, Ammonia, Bromides, Sulfates, Sulfides

).

The impacts of brine on coastal ecosystems in the Mississippi has been studied in detail [116]. Produced water can have salinities up to 300 ppt [63,65,117], which is toxic to most coastal organisms [108]. In the western Mississippi Delta, thousands of acres of sawgrass (Cladium jamacansis) marsh were killed due to discharge of produced water and the area subsequently converted to open water due to decomposition of soil organic matter and subsidence [118,119]. Produced water also contains hydrocarbons that are toxic to coastal organisms [115].

4. Discussion and Conclusions

Determining the extent of damage to coastal system due to oil and gas activity depends on knowledge of the condition of the system both prior to and after impacts. This knowledge is much more advanced in the northern GOM compared to the southern GOM. This makes assessing vulnerability and adequately determining the scale of the damage more difficult. Thus, there is a need for additional research on gathering information on the functioning of coastal systems on which contingency planning can be formulated.

The need for better understanding of the effects of O&G activities is evidenced by the extensive development of petroleum exploration and extraction in coastal waters and wetlands in both the Mississippi Delta, and the Sound of Campeche, and the adjacent Usumacinta-Grijalva Delta. There are over 700 fields in the northern Gulf, and a similar number are located in the southern Gulf. In addition, there are thousands of kilometers of canals. Production of petroleum can last for six decades or more. However, most fields are aging, and many are no longer active. Production peaked in the northern Gulf in about 1970. Brine production was highest during the second half of the production history of the fields. Wetland loss generally followed oil production, with peak loss occurring about the same time as the petroleum peak.

Petroleum production caused environmental impacts via three main mechanisms, namely, pervasive alteration of surface hydrology, increased sinking or subsidence of coastal environments due to oil and gas production, and the introduction of toxic materials, including oil and produced water. The cumulative impact of interconnected canals and spoil banks led to wetland loss, reduction in water interchange between water bodies, and wetland channel theft and saltwater intrusion. All of these factors lead to shallow subsidence. Spoil banks also disappear over time as they sink.

Production of petroleum also leads to deep subsidence in both the petroleum reservoirs and in the bounding shales [120]. This also leads to induced faulting. Wetland loss can last for several decades after a field is no longer productive. Deep subsidence is often greater than shallow subsidence.

High-salinity brine water, with salinity up to 300 ppt, was released to coastal ecosystems for decades before being banned in 1997 for the Mississippi Delta. This brine is more toxic than oil because of the variety of hydrocarbon, heavy metals, and radioactive materials. Produced water discharge is still allowed in the southern Gulf of Mexico. Both brine and oil are toxic to a range of organisms in coastal waters.

5. Future Directions

The UN Ocean Decade (2021–2030) aims to focus on Sustainable Development Goal 14 addressing the sustainable use of ocean resources. Agenda 2030 promotes sustainable management of oceans by 2030. Of the United Nations seven Ocean Decade Outcomes, there are three that are most applicable to the GOM and its hydrocarbon production. The findings in the GOM are applicable to petroleum production in deltas and coastal wetlands in other coastal areas. The findings in the GOM are applicable to petroleum production in deltas and coastal wetlands in other coastal areas.

• A clean ocean; eliminating sources of pollution;
• Management for healthy coastal resources;
• Maintaining a productive ocean for sustainable food production and ocean economy (https://oceandecade.org/vision-mission/, accessed on 30 July 2024).

Following the Deepwater Horizon disaster oil spill the U.S. government established a half-billion-dollar program addressing human health, protection of natural systems, and improving the safety of the oil industry following the Deepwater Horizon disaster oil spill [121]. However, the petroleum industry continues to be economically important and current levels of production are higher than at the time of the disaster. Much production in now in deep water. Dealing with infrastructure from the declining inshore industry is an important challenge [122].

On the other hand, Mexico’s O&G production is being promoted by the 2018–2024 federal administration, despite international climate change agreements. The Energy Reform Law and an Energy Transition Law aims to decrease O&G production and increase the use of clean energy. We encourage that the new federal administration will promote clean energy sources.

O&G production is just one economic sector that depends on the coastal zone. Other activities that contribute to the Gulf’s economy in both countries are fisheries, navigation, industry, and tourism. However, the Gulf coast is changing constantly. This effect is dramatic in coastal Louisiana [122]. In Mexico, the coastal zones of Tabasco and Campeche, especially Carmen Island and Terminos Lagoon, will be extensively flooded due to sea-level rise, with some ecosystems, such as mangroves, likely being completely lost, leading to out-migration to safer places. Oil and gas impacts make these problems worse. Planning for the future depends on understanding the future climate and related impacts to provide decision-makers with the best science for climate resilience policies. It is important to understand that resilience varies for coastal communities and this inequality acts synergistically with other manifestations of inequality, for example, wealth, access to education, and public services.

Problems associated with the disruptions caused by climate change, the energy transition, and environmental degradation are becoming more apparent in the Gulf of Mexico. We need new approaches to address these issues. As Augustine said “If we can get it right in this unique and challenging setting, we can use that experience to inform the path forward for the nation and the world” [122]. The findings in GOM will prove valuable to other coastal areas with petroleum production.