Geology topics

V. H. Rivera-Monroy

Publications and source records attributed to V. H. Rivera-Monroy.

4 recordsLinked to original sources

USGS2020

Estuarine submerged aquatic vegetation habitat provides organic carbon storage across a shifting landscape

Submerged aquatic vegetation (SAV) thrives across the estuarine salinity gradient providing valuable ecosystem services. Within the saline portion of estuaries, seagrass areas are frequently cited as hotspots for their role in capturing and retaining organic carbon (C org ). Non-seagrass SAV, located in the fresh to brackish estuarine areas, may also retain significant soil C org , yet their role remains unquantified. Given rapidly occurring landscape and salinity changes due to human and natural disturbances, landscape level carbon pool estimates from estuarine SAV habitat blue carbon estimates are needed. We assessed C org stocks in SAV habitat soils from estuarine freshwater to saline habitats (interior deltaic) to saline barrier islands (Chandeleur Island) within the Mississippi River Delta Plain (MRDP), Louisiana, USA. SAV habitats contain C org stocks equivalent to those reported for other estuarine vegetation types (seagrass, salt marsh, mangrove). Interior deltaic SAV C org stocks (231.6 ± 19.5 Mg C org ha −1 ) were similar across the salinity gradient, and significantly higher than at barrier island sites (56.6 ± 10.4 Mg C org ha −1 ). Within the MRDP, shallow water SAV habitat covers up to an estimated 28,000 ha, indicating that soil C org storage is potentially 6.4 ± 0.1 Tg representing an unaccounted C org pool. Extrapolated across Louisiana, and the Gulf of Mexico, this represents a major unaccounted pool of soil C org . As marshes continue to erode, the ability of coastal SAV habitat to offset some of the lost carbon sequestration may be valuable. Our estimates of C org sequestration rates indicated that conversion of eroding marsh to potential SAV habitat may help to offset the reduction of C org sequestration rates. Across Louisiana, we estimated SAV to offset this loss by as much as 79,000 Mg C yr −1 between the 1960s and 2000s.

Louisiana↗

USGS2006

Evaluating the relative contributions of hydroperiod and soil fertility on growth of south Florida mangroves

Low and high water periods create contrasting challenges for trees inhabiting periodically flooded wetlands. Low to moderate flood durations and frequencies may bring nutrient subsidies, while greater hydroperiods can be energetically stressful because of oxygen deficiency. We tested the hypothesis that hydroperiod affects the growth of mangrove seedlings and saplings in a greenhouse experiment by varying flood duration while keeping salinity and soil fertility constant. We measured the growth of mangrove trees along a hydroperiod gradient over a two-year period by tracking fine-scale diameter increment. Greenhouse growth studies indicated that under a full range of annual flood durations (0-8760 h/year), hydroperiod alone exerted a significant influence on growth for one species, Laguncularia racemosa, when flooding was imposed for two growing seasons. Field evaluations, on the other hand, indicated that increased flood duration may provide nutrient subsidies for tree growth. Diameter growth was related curvilinearly to site hydroperiod, including flood duration and frequency, as well as to salinity and soil fertility. An analysis of soil physico-chemical parameters suggests that phosphorus fertility, which was also linked directly to hydroperiod, is likely to influence growth on south Florida mangrove sites. The physical removal of phosphorus by greater flood frequencies from upland sources and/or addition of phosphorus from tidal flooding balanced against increased soil aeration and reduced water deficits may be an extremely important growth determinant for south Florida mangroves. ?? Springer 2006.

Hydrobiologia↗

USGS1996

A 7 year record of above-ground net primary production in a southeastern Mexican mangrove forest

Spatial and temporal variations in net above-ground primary production (NPP) and litter turnover rate were studied, from 1987 to 1993, in a mangrove forest bordering Laguna de Terminos, Mexico. NPP, the sum of total litter fall and wood production, was measured over the entire study period in three zones in a basin forest: zone I, where Rhizophora mangle (red mangrove) occurs but Avicennia germinans (black mangrove) is the dominant species; zone II, a scrub forest of A. germinans ; zone III, where larger A. germinans trees occur. In 1991, a fringe zone dominated by A. germinans and R. mangle was added to the study. Three distinctive climatic seasons occur in the region: rainy, dry, and cold front (locally named ‘nortes’). Average total litter fall in the fringe zone (793 g m −2 year −1 ) was significantly higher than in the basin forest (496, 307, and 410 g m −2 year −1 for basin zones I, II, and III, respectively). All zones showed significant differences among seasons with the norte season having significantly lower litter fall. Litter turnover rates were about 7 months in zones I and II and 10 months in zone III, reflecting the low tidal range that occurs in the basin forest. Low litter turnover rates in the basin forest were reflected in a high organic matter standing crop. Annual average stem growth was significantly higher in zones I and III (1.27 and 1.36 kg per tree year −1 , respectively) than in zone II (0.62 kg per tree year −1 ). Above-ground NPP rates in the basin forest (399–695 g m −2 year −1 ) were lower than in fringe and riverine forests, reflecting patterns of litter fall and wood production. There was no seasonal variation in soil salinity but the basin forest had significantly higher soil salinity than the fringe forest. Spatially, mean soil salinity was inversely related to litter fall. Long-term patterns in soil salinity, precipitation and air temperature explained 74% of the inter-annual litter fall variability. Over the 7 year study, productivity in zone II was more variable than in zones I and III, and productivity (litter fall and wood growth) were less variable than litter standing crop and turnover.

Campeche↗

USGS1995

Direct denitrification in mangrove sediments in Terminos Lagoon, Mexico

Rates of direct denitrification were measured using 15 N isotope tchniques in intact sediment cores from fringe and basin mangroves in Terminos Lagoon, Mexico. Sediments were injected with 15 NO 3 - and the distribution of 15 N was measured over time in the head space, overlying water, and sediments. Experiments included an investigation of spatial variation in denitrification rates by comparing results from the fringe and basin mangroves in the rainy season (July 1991); a second experiment was to determine the effect of 3 different NO 3 - concentrations (25, 100, 200 umol core -1 15 N-KNO 3 - ) on denitrification rates and was performed in the fringe mangrove during the 'Norte' season (January 1992). Highest 15 N-N 2 fluxes were measured in the fringe mangrove at 9.4 umol m -2 h -1 , while denitrification rates in the basin mangrove ranged from 1.9 to 4.5 umol m -2 h -1 . 15 N-N 2 fluxes in sediment cores from the fringe mangrove were significantly higher (4.5 to 7.7 umol m -2 h -1 ) in cores enriched with 200 umol core -1 15 N-KNO 3 - compared to cores enriched with 25 and 100 umol core -1 15 N-KNO 3 - (<1 umol m -2 h -1 ). Most of the applied 15 N was recovered as particulate nitrogen in the sediment and a small fraction reduced to NH 4 + in both experiments. The low denitrification rates observed in the fringe and basin mangroves indicate that the capacity for sediment denitrification is limited by low NO 3 - availability. Previous nutrient exchange studies concluded that the fringe mangrove was a 'sink' of NO 3 - since sediment uptake of NO 3 - was assumed lost through denitrification. Results from this study show <10% of sediment NO 3 - uptake in fringe mangroves may be lost to denitrification; the remainder being immobilized in the sediment.

Terminos Lagoon↗