Selection of areas for restoration should be based on cost‐effectiveness analysis to attain the maximum benefit with a limited budget and overcome the traditional ad hoc allocation of funds for ...restoration projects. Restoration projects need to be planned on the basis of ecological knowledge and economic and social constraints. We devised a novel approach for selecting cost‐effective areas for restoration on the basis of biodiversity and potential provision of 3 ecosystem services: carbon storage, water depuration, and coastal protection. We used Marxan, a spatial prioritization tool, to balance the provision of ecosystem services against the cost of restoration. We tested this approach in a mangrove ecosystem in the Caribbean. Our approach efficiently selected restoration areas that at low cost were compatible with biodiversity targets and that maximized the provision of one or more ecosystem services. Choosing areas for restoration of mangroves on the basis carbon storage potential, largely guaranteed the restoration of biodiversity and other ecosystem services.
Coastal wetlands can have exceptionally large carbon (C) stocks and their protection and restoration would constitute an effective mitigation strategy to climate change. Inclusion of coastal ...ecosystems in mitigation strategies requires quantification of carbon stocks in order to calculate emissions or sequestration through time. In this study, we quantified the ecosystem C stocks of coastal wetlands of the Sian Ka'an Biosphere Reserve (SKBR) in the Yucatan Peninsula, Mexico. We stratified the SKBR into different vegetation types (tall, medium and dwarf mangroves, and marshes), and examined relationships of environmental variables with C stocks. At nine sites within SKBR, we quantified ecosystem C stocks through measurement of above and belowground biomass, downed wood, and soil C. Additionally, we measured nitrogen (N) and phosphorus (P) from the soil and interstitial salinity. Tall mangroves had the highest C stocks (987±338 Mg ha(-1)) followed by medium mangroves (623±41 Mg ha(-1)), dwarf mangroves (381±52 Mg ha(-1)) and marshes (177±73 Mg ha(-1)). At all sites, soil C comprised the majority of the ecosystem C stocks (78-99%). Highest C stocks were measured in soils that were relatively low in salinity, high in P and low in N∶P, suggesting that P limits C sequestration and accumulation potential. In this karstic area, coastal wetlands, especially mangroves, are important C stocks. At the landscape scale, the coastal wetlands of Sian Ka'an covering ≈172,176 ha may store 43.2 to 58.0 million Mg of C.
In nutrient-poor landscapes, external nutrient subsidies are important for sustaining local production. Seabirds can transport marine nutrients in the form of guano to terrestrial and coastal ...ecosystems where they can relieve nutrient limitation. We assessed whether seabirds provide nutrient subsidies to mangrove islands that are strongly limited by phosphorus (P) in the Yucatan Peninsula. Our hypotheses were: (1) seabirds transport nutrients to mangrove islands, (2) mangroves use marine-derived nutrients and (3) nutrient inputs are higher during the nesting season. We chose 6 mangrove islands within a coastal lagoon: 2 with no birds, 2 with temporary birds and 2 with permanent bird colonies. On each, we measured forest structure and soil characteristics (P, pH, salinity and organic matter) for 3 seasons (dry, wet and trade wind season). We collected leaves (green and senescent) to determine P content and resorption efficiency as a measurement of nutrient limitation. Green leaves were also sampled for δ13C and δ15N to determine nutrient origin. Results show that islands with permanent bird colonies have the highest soil nutrients, which are used by the mangrove trees and relieve some of their nutrient limitation. Nutrient inputs were homogenously distributed through the sediment column, although a decrease in P and an increase in the N:P ratio in the first 20 cm suggests bacterial consumption. Bird nutrient inputs are seasonal, with highest inputs during the nesting season. This study shows an example in which marine-derived nutrients could be important for production of coastal mangrove islands.
Continental shelves are the most productive areas in the seas with the strongest implications for global nitrogen cycling. The Yucatán shelf (YS) is the largest shelf in the Gulf of Mexico (GoM); ...however, its nitrogen budget has not been quantified. This is largely due to the lack of significant spatio-temporal in situ measurements and the complexity of the shelf dynamics, including coastal upwelling, coastal-trapped waves (CTWs), and influence of the Yucatán Current (YC) via bottom Ekman transport and dynamic uplift. In this paper, we investigate and quantify the nitrogen budget of dissolved inorganic nitrogen (DIN) and particulate organic nitrogen (PON) in the YS using a 9-year output from a coupled physical–biogeochemical model of the GoM. The sum of DIN and PON is here referred to as total nitrogen (TN). Results indicate that the main entrance of DIN is through its southern (continental) and eastern margins. The TN is then advected to the deep oligotrophic Bay of Campeche and central GoM. It is also shown that the inner shelf (bounded by the 50 m isobath) is “efficient” in terms of TN, since all DIN imported into this shelf is consumed by the phytoplankton. Submarine groundwater discharges (SGDs) contribute 20 % of the TN, while denitrification removes up to 53 % of TN that enters into the inner shelf. The high-frequency variability of the TN fluxes in the southern margin is modulated by fluxes from the YC due to enhanced bottom Ekman transport when the YC leans against the shelf break (250 m isobath) on the eastern margin. This current–topography interaction can help to maintain the upwelling of Cape Catoche, uplifting nutrient-rich water into the euphotic layer. The export of TN at both western and northwestern margins is modulated by CTWs with a mean period of about 10 d in agreement with recent observational and modelling studies.
The coastal environment of the Yucatan Peninsula (SE, Mexico) includes a wide variety of ecosystems ranging from mangroves to coral reefs, resulting in a heterogeneous landscape. Specifically, the ...marine system is characterized by environmental differences which respond to regional and local forcing functions such as marine currents and groundwater discharges (GD). Such functional characteristics were used here to define four subregions across the Yucatan coast and diagnose the health status of this coastal marine ecosystem. To achieve this goal, we conducted an analysis and integration of water quality variables, an eutrophic assessment, evaluated changes in submerged aquatic vegetation (SAV), and analyzed the community structure and distribution of harmful phytoplankton. The first step was to determine the reference values for each subregion based on data previously collected from 2002 to 2006 along the coast of Yucatan, 200
m offshore. The trophic index (TRIX) and Canadian index for aquatic life (CCMEWQI) were used to diagnose each subregion and then the ASSETS approach was conducted for Dzilam and Progreso, sampling localities on each end of the health status continuum (those with the best and worst conditions). Overall, results indicated that the marine coastal ecosystem of Yucatan is in good condition; however, differences were observed between subregions that can be attributed to local forcing functions and human impacts. Specifically, the central region (zone HZII, Progreso-Telchac) showed symptoms of initial eutrophication due to nutrient inputs from human activities. The eastern region (zone HZ III, Dzilam-Las Bocas) showed a meso-eutrophic condition linked to natural groundwater discharges, while the other two subregions western (zone HZI Celestun-Palmar) and caribbean (zone HZ IV Ria Lagartos-El Cuyo) exhibited symptoms of oligo-mesotrophic condition. These findings may be considered baseline information for coastal ecosystem monitoring programs in Yucatan, and the approach used could be replicated for other coastal areas.
The influence of coastal submarine groundwater discharges (SGD) on the distribution and abundance of seagrass meadows was investigated. In 2012, hydrological variability, nutrient variability in ...sediments and the biotic characteristics of two seagrass beds, one with SGD present and one without, were studied. Findings showed that SGD inputs were related with one dominant seagrass species. To further understand this, a generalized additive model (GAM) was used to explore the relationship between seagrass biomass and environment conditions (water and sediment variables). Salinity range (21–35.5 PSU) was the most influential variable (85%), explaining why
H. wrightii
was the sole plant species present at the SGD site. At the site without SGD, GAM could not be performed since environmental variables could not explain a total variance of > 60%. This research shows the relevance of monitoring SGD inputs in coastal karstic areas since they significantly affect biotic characteristics of seagrass beds.
Mangrove ecosystems can function as a habitat for many juvenile marine fish species, with provisions of food and refuge. Seemingly, these ecosystems have been extensively reduced due to anthropogenic ...activity, as is widespread land use and road construction along the coastline. Nonetheless, much needed restoration efforts have increased tremendously over time. This study analyzes fish community, and the manner in which habitats in the mangrove ecosystem are used, comparing two mangrove zones, a conserved zone (healthier state) and one undergoing restoration. Hydrologically, no significant differences were registered (KW p>0.05). Of the 24 species registered, marine species were dominant in the conserved zone and estuarine species dominant in the restoration zone. Juvenile fishes were more abundant in the conserved mangrove zone, with a higher proportion of adults found in the restoration zone. According to Hutcheson’s t test, fish diversity showed significant statistical differences between sites combined with distinct climatic seasons. The Canonical Correspondence Analysis (CCA) indicated a relationship between secondary freshwater species Floridichthys polyommus and Cyprinodon artifrons and greater salinity and temperature, whereas marine species had a higher relationship with well oxygenated sites. A high number of marine fish species in juvenile stage in the conserved area may relate to mangroves functioning as nurseries. This can serve as a useful indicator by managers taking an integral approach to evaluate and monitor present and future mangrove restoration programs and pathways.
Mangrove deforestation threatens to release large stores of carbon from soils that are vulnerable to oxidation. Carbon stored in deep soils is not measured in national carbon inventories. Thus, ...policies on emission reductions have likely underestimated the contribution of mangrove deforestation to national emissions. Here, we estimate that emissions from deforestation and degradation of mangroves in Mexico are 31 times greater than the values used to determine national emission reduction targets for the Paris Agreement. Thus, Mexico has vastly undervaluated the potential of mangrove protection to reduce its emissions. Accounting for carbon emissions from mangrove soils should greatly increase the priority of mangrove forests to receive funding for protection under carbon trading programs.
Mangrove ecosystems may be a source of organic carbon and nutrients to adjacent coastal systems on one hand and provide a sedimentary sink for organic carbon on the other. The balance between these ...two functions may be sensitive to both natural and anthropogenically induced variability, yet these effects have not been thoroughly evaluated in mangrove ecosystems. We determine organic matter sources and carbon burial rates over the past 160 years in three lagoons on the Yucatan Peninsula, Mexico. Carbon isotopes and C/N elemental ratios are utilized to trace the three sources contributing to sedimentary organic matter, mangroves, seagrasses and phytoplankton, while nitrogen isotopes are used to elucidate potential post-depositional biogeochemical transformations in mangrove lagoon sediments. All three organic matter sources contribute to organic carbon burial. Phytoplankton and mangroves are the dominant sources of organic matter in lagoon bank sediments and seagrasses are a significant source to central lagoon sediments. Organic carbon burial rates are higher at the lagoon fringes, where mangrove vegetation dominates, than in seagrass-dominated mid-lagoon areas. A reduction in mangrove contribution to the sedimentary organic matter pool concurrent with reduced total organic carbon burial rates is observed in the recent past at all three lagoons studied. Natural cycles in sediment organic matter source over the past 160 years are observed in a high-resolution core. These fluctuations correspond to climatic variability in this region, as recorded in deep-sea foraminiferal assemblages. Additional work is required in order to differentiate between recent anthropogenic perturbations and natural variability in organic carbon sources and burial rates within these ecosystems.
Methane concentrations in the water column and emissions to the atmosphere were determined for three tropical coastal lagoons surrounded by mangrove forests on the Yucatán Peninsula, Mexico. Surface ...water dissolved methane was sampled at different seasons over a period of 2 years in areas representing a wide range of salinities and anthropogenic impacts. The highest surface water methane concentrations (up to 8378 nM) were measured in a polluted canal associated with Terminos Lagoon. In Chelem Lagoon, methane concentrations were typically lower, except in the polluted harbor area (1796 nM). In the relatively pristine Celestún Lagoon, surface water methane concentrations ranged from 41 to 2551 nM. Methane concentrations were negatively correlated with salinity in Celestún, while in Chelem and Terminos high methane concentrations were associated with areas of known pollution inputs, irrespective of salinity. The diffusive methane flux from surface lagoon water to the atmosphere ranged from 0.0023 to 15 mmol CH4 m−2 d−1. Flux chamber measurements revealed that direct methane release as ebullition was up to 3 orders of magnitude greater than measured diffusive flux. Coastal mangrove lagoons may therefore be an important natural source of methane to the atmosphere despite their relatively high salinity. Pollution inputs are likely to substantially enhance this flux. Additional statistically rigorous data collected globally are needed to better consider methane fluxes from mangrove‐surrounded coastal areas in response to sea level changes and anthropogenic pollution in order to refine projections of future atmospheric methane budgets.
Key Points
Elevated surface water and porewater methane concentrations were measured throughout the lagoons despite moderate to marine salinities
Pollution inputs are likely to substantially enhance methane concentrations and fluxes in mangrove‐surrounded lagoon systems
Ebullition is an important yet under quantified process of methane emissions in the shallow tidally influenced mangrove‐lagoon systems
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