Muddy Waters: Unintentional Consequences of Blue Carbon Research Obscure Our Understanding of Organic Carbon Dynamics in Seagrass Ecosystems

The recent surge in research on organic carbon sequestration by seagrass ecosystems has begun to reveal the complexity of the carbon cycle within these ecosystems. In this prospective we discuss two areas of investigation that require further scrutiny: (1) why organic carbon is stabilized in seagrass sediments, and (2) how long organic carbon resides within these sediments. By delving into these topics, pointing out current pitfalls, and highlighting methodological advances, our motive is to focus future efforts and provide a frame work to manage the complexity found within the diverse seagrass bioregions. The high rate of seagrass degradation and loss, coupled with increasing atmospheric CO2 concentrations gives precedence to these lines of research, which require rigorous reevaluation if we are to substantially advance our understanding of OC dynamics in seagrass ecosystems

Unusually Warm Summer Temperatures Exacerbate Population and Plant Level Response of Posidonia oceanica to Anthropogenic Nutrient Stress

Posidonia oceanica is a key foundation species in the Mediterranean providing valuable ecosystem services. However, this species is particularly vulnerable towards high coastal nutrient inputs and the rising frequency of intense summer heat waves, but their combined effect in situ has received little attention so far. Here, we investigated the effects of in situ nutrient addition during an unusually warm summer over a 4-month period, comparing different morphological, physiological and biochemical population metrics of seagrass meadows growing in protected areas (Ischia) with meadows already exposed to significant anthropogenic pressure (Baia – Gulf of Pozzuoli). Our study highlights that the effects of warmer than usual summer temperatures on the population level of seagrass meadows can be exacerbated if the plants are already exposed to higher anthropogenic pressures. Morphological and population level indicators mainly changed over time, possibly impacted by season and the warmer temperatures, and displayed more pronounced reductions in seagrasses from impacted sites. The additional nutrient supply had even more deleterious effects, as shown by a decrease in approximately 67% in cover in fertilized plots at high impacted sites and 33% at low impacted sites. Moreover, while rhizome starch concentration showed a seasonal increase in plants from low impacted sites it displayed a trend of a 27% decrease in fertilized plots of the high impacted sites. Epiphyte biomass was approximately four-fold higher on leaves of plants growing in impacted sites and even doubled with the additional nutrient input. Predicting and anticipating stress in P. oceanica is of crucial importance for conservation and management efforts, given the limited colonizing and reproductive ability and extremely slow growth of this ecosystem engineer. Our results suggest that monitoring efforts should focus especially on leaf area index (LAI), carbohydrate concentrations in the rhizomes, and epiphyte cover on leaves as indicators of the onset of stress in Posidonia oceanica, which can be used by decision makers to take appropriate measures before damage to the ecosystem becomes irreversible, minimize future human interference and strengthen the resilience of these important ecosystems

Impacts of residential fertilizer ordinances on Florida lacustrine water quality

Abstract Despite the assumption that residential fertilizer ordinances improve regional water quality, their impacts across space and time largely remain unknown. Here, we analyze changes in water quality of lakes throughout the State of Florida from 1987 to 2018, comparing trends in water quality parameters before and after implementation of county‐wide fertilizer ordinances. We used a large dataset of publicly collected water quality data and linear mixed models to analyze ordinance impacts on total nitrogen, total phosphorus, chlorophyll a, and Secchi depth across 160 lakes throughout Florida. We further analyze water quality impacts relative to the type of ordinance (winter fertilizer ban, summer ban, nonseasonal ban, no ban). We found fertilizer ordinances favorably impacted lacustrine water quality, and winter (dry season) fertilizer bans had the greatest effect across all water quality metrics. Results of this study can be used to support the effectiveness of fertilizer ordinances across humid tropical and subtropical climate regions

Muddy waters: Unintentional consequences of blue carbon research obscure our understanding of organic carbon dynamics in seagrass ecosystems

The recent surge in research on organic carbon sequestration by seagrass ecosystems has begun to reveal the complexity of the carbon cycle within these ecosystems. In this prospective we discuss two areas of investigation that require further scrutiny: (1) why organic carbon is stabilized in seagrass sediments, and (2) how long organic carbon resides within these sediments. By delving into these topics, pointing out current pitfalls, and highlighting methodological advances, our motive is to focus future efforts and provide a frame work to manage the complexity found within the diverse seagrass bioregions. The high rate of seagrass degradation and loss, coupled with increasing atmospheric CO2 concentrations gives precedence to these lines of research, which require rigorous reevaluation if we are to substantially advance our understanding of OC dynamics in seagrass ecosystems

Las marismas de marea andaluzas como sumidero y almacén de carbono orgánico

En el marco del proyecto Life Blue Natura evaluamos la variabilidad horizontal de las reservas y flujos de carbono orgánico en las marismas del Odiel y Bahía de Cádiz. Los muestreos se centraron en captar la variabilidad en función de la influencia mareal (marisma baja, media y alta) diagnosticada por las bandas de vegetación. Se muestrearon 13 estaciones en cada una de las localidades, en un total de 34 catas de entre 21 y 259 cm de longitud y 24 muestras de biomasa. Las reservas medias de carbono orgánico en el primer metro de suelo de marisma saludable se estiman en Stock1m= 333 ± 74 (DE) t CO2 ha-1, pero los depósitos de carbono continúan en profundidad, y estimamos que las reservas podrían ser un 12-112% mayores. La Variabilidad espacial en la riqueza (%Corg) y densidad de Corg no era significativa entre localidades (ANOVA anidada), pero sí entre estaciones con distinta influencia mareal ( p< 10-4). %Corg y Densidad Corg eran mayores en la marisma media que en las demás ( p< 10-4). Además, la Densidad Corg era mayor en los lodazales de marisma baja no vegetada, que en la marisma baja vegetada y la marisma alta (p< 10-3 y 10-4). Con sedimentos mas jóvenes, las marismas inundadas diariamente, y en especial la marisma media, son el reactor de secuestro de carbono más intenso del ecosistema, tanto a escala secular (flujo100a= 2,24 ± 0,47 (DE) t CO2 ha-1 año-1), como a la del periodo que tarda en acumular el primer metro (flujo1m= 1,17 ± 0,14 (DE) t CO2 ha-1 año-1 en 360 y 494 años, en Odiel y los Toruños, respectivamente). En la marisma media el Stock1m era (442 ± 173 (DE) t CO2 ha-1) mayor que en baja no vegetada (343 ± 79 (DE) t CO2ha-1), la baja vegetada por S. maritima (259 ± 40 (DE) t CO2 ha-1) y la alta (270 ± 77 (DE) t CO2 ha-1), donde fueron similares entre sí. El Stock1m de la única estación submareal (caño) era similar al de la marisma baja (249 ± 31 (DE) t CO2 ha-1). Sin embargo, el carbono orgánico en las marismas altas es más antiguo, producto de la maduración de la materia orgánica acumulada durante milenios, y de la compactación del suelo, que hace que el intervalo temporal abarcado en las reservas del primer metro de suelo sea mayor. El Corg se acumuló en el suelo de la marisma a una tasa promedio de flujo100a= 1,3 ± 0,9 (DE) t CO2 ha-1 año-1, aunque dicha tasa varía desde valores negativos en 2 estaciones donde se ha detectado erosión, hasta 2,6 t CO2 ha-1 año-1 en la marisma media del Odiel. Extrapolando con las cartografías de marismas, estimamos que las marismas saludables de Odiel y Cádiz contienen 2,7 ± 0.1 (DE) Mt de CO2 en sus suelos y que han secuestrado unas 8,1 ± 0,3 kt CO2 al año en los últimos 100 años. Las marismas de Andalucía tendrían un Stock1m 19,5 ± 5,6(DE) Mt CO2, y en el último siglo han secuestrado 68,6 ± 36,4(DE) kt CO2 por año