Showing papers by "Daniel M. Alongi published in 2005"
TL;DR: In this article, the authors examined sediment accumulation and microbial mineralization at three Kandelia candel forests spanning the intertidal zone along the south coastline of the heavily urbanized Jiulongljiang Estuary, Fujian Province, China.
Abstract: Rates of sediment accumulation and microbial mineralization were examined at three Kandelia candel forests spanning the intertidal zone along the south coastline of the heavily urbanized Jiulongljiang Estuary, Fujian Province, China. Mass sediment accumulation rates were rapid (range: 10–62 kg m −2 y −1 ) but decreased from the low- to the high-intertidal zone. High levels of radionuclides suggest that these sediments originate from erosion of agricultural soils within the catchment. Mineralization of sediment carbon and nitrogen was correspondingly rapid, with total rate of mineralization ranging from 135 to 191 mol C m −2 y −1 and 9 to 11 mol N m −2 y −1 ; rates were faster in summer than in autumn/winter. Rates of mineralization efficiency (70–93% for C; 69–92% for N) increased, as burial efficiency (7–30% for C; 8–31% for N) decreased, from the low-to the high-intertidal mangroves. Sulphate reduction was the dominant metabolic pathway to a depth of 1 m, with rates (19–281 mmol S m −2 d −1 ) exceeding those measured in other intertidal deposits. There is some evidence that Fe and Mn reduction-oxidation cycles are coupled to the activities of live roots within the 0–40 cm depth horizon. Oxic respiration accounted for 5–12% of total carbon mineralization. Methane flux was slow and highly variable when detectable (range: 5–66 μmol CH 4 m −2 d −1 ). Nitrous oxide flux was also highly variable, but within the range (1.6–106.5 μmol N 2 O m −2 d −1 ) measured in other intertidal sediments. Rates of denitrification were rapid, ranging from 1106 to 3780 μmol N 2 m −2 d −1 , and equating to 11–20% of total sediment nitrogen inputs. Denitrification was supported by rapid NH 4 release within surface deposits (range: 3.6–6.1 mmol m −2 d −1 ). Our results support the notion that mangrove forests are net accumulation sites for sediment and associated elements within estuaries, especially Kandelia candel forests receiving significant inputs as a direct result of intense human activity along the south China coast.
244 citations
TL;DR: Analysis of current data suggests that microbial communities in coastal waters and in unconsolidated sediments metabolise nutrients equivalent to the entire dissolved and particulate nutrient load debouched from land, helping to explain why coral reefs on the middle and outer shelf have remained relatively unscathed despite a significant increase in sediment delivery.
150 citations
TL;DR: NUE in R. stylosa correlated inversely with mature leaf N and P content, implying that NUE in this species is maximized by the synthesis of low-nutrient leaves, i.e. a nutrient retention strategy, whereas such does not appear to be the case for A. marina.
95 citations
TL;DR: Human-induced disturbance creates a sharp zonation of dry, hypersaline soil overlying less saline, wetter soil, suppressing surface microbial and root growth in mangroves of the Vellar–Coleroon estuarine complex, southeast India, partly explaining why mangrove are stunted.
Abstract: Large areas of mangroves in India are heavily disturbed by cattle grazing, hypersalinity, and other human-induced impacts. In two disturbed Avicennia marina forests and two undisturbed A. marina and Rhizophora apiculata forests in the Pichavaram mangroves of the Vellar–Coleroon estuarine complex, southeast India, we measured the rates and pathways of microbial decomposition of soil organic matter to determine if human impact is altering biogeochemical activity within these stands. Rates of total carbon oxidation (TCOX) were higher in the undisturbed A. marina forest (mean 199 mol C m−2 year−1) than in the two impacted stands (43 and 79 mol C m−2 year−1); rates of total carbon oxidation in the R. apiculata forest averaged 75 mol C m−2 year−1. Sulphate reduction (range 21–319 mmol S m−2 day−1) was the major decomposition pathway (65–85% of TCOX), except at the most disturbed forest (30% of TCOX). Rates of sulphate reduction at all sites peaked in sub-surface soils to a depth of about 1 m, leading to little carbon burial (3–5% of total C input). There was some evidence of measurable iron and manganese reduction in association with tree roots. Rates of microbial activity were rapid in comparison with rates measured in other mangrove soils, reflecting high rates of phytoplankton production and organic matter retention in this lagoon. Human-induced disturbance creates a sharp zonation of dry, hypersaline soil overlying less saline, wetter soil, suppressing surface microbial and root growth. We conclude that this vertical alteration of soil characteristics and biogeochemistry shifts the cycling of nutrients between trees and microbes to a disequilibrium state, partly explaining why mangroves are stunted in these declining forests.
54 citations