Nutrient enhanced coastal ocean productivity in the north Gulf of Mexico: understanding the effects of nutrients on a coastal ecosystem

The continental shelf adjacent to the Mississippi River is a highly productive system, often referred to as the fertile fisheries crescent. This productivity is attributed to the effects of the river, especially nutrient delivery. In the later decades of the 2oth century, though, changes in the system were becoming evident. Nutrient loads were seen to be increasing and reports of hypoxia were becoming more frequent. During most recent summers, a broad area (up to 20,000 krn2) of near bottom, inner shelf waters immediately west of the Mississippi River delta becomes hypoxic (dissolved oxygen concentrations less than 2 mgll). In 1990, the Coastal Ocean Program of the National Oceanic and Atmospheric Administration initiated the Nutrient Enhanced Coastal Ocean Productivity (NECOP) study of this area to test the hypothesis that anthropogenic nutrient addition to the coastal ocean has contributed to coastal eutrophication with a significant impact on water quality. Three major goals of the study were to determine the degree to which coastal productivity in the region is enhanced by terrestrial nutrient input, to determine the impact of enhanced productivity on water quality, and to determine the fate of fixed carbon and its impact on living marine resources. The study involved 49 federal and academic scientists from 14 institutions and cost $9.7 million. Field work proceeded from 1990 through 1993 and analysis through 1996, although some analyses continue to this day. The Mississippi River system delivers, on average, 19,000 m3/s of water to the northern Gulf of Mexico. The major flood of the river system occurs in spring following snow melt in the upper drainage basin. This water reaches the Gulf of Mexico through the Mississippi River birdfoot delta and through the delta of the Atchafalaya River. Much of this water flows westward along the coast as a highly stratified coastal current, the Louisiana Coastal Current, isolated from the bottom by a strong halocline and from mid-shelf waters by a strong salinity front. This stratification maintains dissolved and particulate matter from the rivers, as well as recycled material, in a well-defined flow over the inner shelf. It also inhibits the downward mixing of oxygenated surface waters from the surface layer to the near bottom waters. This highly stratified flow is readily identifiable by its surface turbidity, as it carries much of the fine material delivered with the river discharge and resuspended by nearshore wave activity. A second significant contribution to the turbidity of the surface waters is due to phytoplankton in these waters. This turbidity reduces the solar radiation penetrating to depth through the water column. These two aspects of the coastal current, isolation of the inner shelf surface waters and maintenance of a turbid surface layer, precondition the waters for the development of near bottom summer hypoxia.

Effects of nutrients on the substrate biofilms in the integrated vertical-flow constructed wetland

A L9 orthogonal array design involving 3 factors (C6H12O6, KNO3 and NaH2PO4) and 3 levels for each (C6H12O6: 0.2, 0.4 or 0.8 g/L; KNO3: 0.4, 0.8 or 1.6 g/L, NaH2PO4: 0.05, 0.1 or 0.2 g/L), was used to study the effects of nutrients on dehydrogenase activity and polysaccharide content of substrate biofilms in the integrated vertical-flow constructed wetland (IVCW). Results showed that C6H12O6 and KNO3 were the main factors for dehydrogenase activity and polysaccharide content of biofilms, respectively. The combinations of three nutrients at different concentrations had different effects on dehydrogenase activity and polysaccharide content of biofilms. The optimal combination for dehydrogenase activity was obtained by locating the concentrations Of C6H12O6, KNO3 and NaH2PO4 at 0.2, 0.8 and 0.05 g, and the optimal combination for polysaccharide content was obtained by locating the concentrations Of C6H12O6, KNO3 and NaH2PO4 at 0.2, 0.4 and 0.2 g/L, respectively. The corresponding maximum activity and polysaccharide content were 5.40 mu g TF/g substrate/12 h and 3454.6 mu g/g substrate, respectively. These results would provide the laboratory foundation for optimizing the purification function of the wetland systems.

Daily dynamics of nutrients and chlorophyll a during a spring phytoplankton bloom in Xiangxi Bay of the Three Gorges Reservoir

We studied the daily dynamics of nutrients (total phosphorus [TP], total nitrogen [TN], and dissolved silicate [SiO2]) and chlorophyll a (chl a) during a spring bloom in Xiangxi Bay of the Three Gorges Reservoir in year 2005. According to the daily dynamics of chl a, the bloom occurred in two stages (23 February-25 March and 26 March-28 April). The concentration of SiO2 decreased at different layers of the water column with the development of the bloom. However, the decrease of SiO2 in the layers with high concentration of chl a was more dramatic than in the layers with low concentration of chl a. The concentration of TP was lowest value a few days after the peak of chl a during the first bloom period, and the lowest value of TN was found a few days after the peak of chl a during the second bloom period. Correlative analyses indicated that SiO2 and TP were limiting factors in the first bloom period, and SiO2 and TN were limiting factors in the second bloom period.

Methods for physical separation and characterization of soil organic matter fractions

Turnover of soil organic matter (SOM) is coupled to the cycling of nutrients in soil through the activity of soil microorganisms. Biological availability of organic substrate in soil is related to the chemical quality of the organic material and to its degree of physical protection. SOM fractions can provide information on the turnover of organic matter (OM), provided the fractions can be related to functional or structural components in soil. Ultrasonication is commonly used to disrupt the soil structure prior to physical fractionation according to particle size, but may cause redistribution of OM among size fractions. The presence of mineral particles in size fractions can complicate estimations of OM turnover time within the fractions. Densiometric separation allows one to physically separate OM found within a specific size class from the heavier-density mineral particles. Nutrient contents and mineralization potential were determined for discrete size/density OM fractions isolated from within the macroaggregate structure of cultivated grassland soils. Eighteen percent of the total soil C and 25% of the total soil N in no-till soil was associated with fine-silt size particles having a density of 2.07-2.21 g/cm3 isolated from inside macroaggregates (enriched labile fraction or ELF). The amount of C and N sequestered in the ELF fraction decreased as the intensity of tillage increased. The specific rate of mineralization (mug net mineral N/mug total N in the fraction) for macroaggregate-derived ELF was not different for the three tillage treatments but was greater than for intact macroaggregates. The methods described here have improved our ability to quantitatively estimate SOM fractions, which in turn has increased our understanding of SOM dynamics in cultivated grassland systems.

Sources and preservation of organic matter in Plum Island salt marsh sediments (MA, USA): long-chain n-alkanes and stable carbon isotope compositions

Elemental (TOC, TN, C/N) and stable carbon isotopic (delta(13)C) compositions and n-alkane (nC(16-38)) concentrations were measured for Spartina alterniflora, a C-4 marsh grass, Typha latifolia, a C-3 marsh grass, and three sediment cores collected from middle and upper estuarine sites from the Plum Island salt marshes. Our results indicated that the organic matter preserved in the sediments was highly affected by the marsh plants that dominated the sampling sites. delta(13)C values of organic matter preserved in the upper fresh water site sediment were more negative (-23.0+/-0.3) as affected by the C-3 plants than the values of organic matter preserved in the sediments of middle (-18.9+/-0.8) and mud flat sites (-19.4+/-0.1) as influenced mainly by the C4 marsh plants. The distribution of n-alkanes measured in all sediments showed similar patterns as those determined in the marsh grasses S. alterniflora and T. latifolia, and nC(21) to nC(33) long-chain n-alkanes were the major compounds determined in all sediment samples. The strong odd-to-even carbon numbered n-alkane predominance was found in all three sediments and nC(29) was the most abundant homologue in all samples measured. Both delta(13)C compositions of organic matter and n-alkane distributions in these sediments indicate that the marsh plants could contribute significant amount of organic matter preserved in Plum Island salt marsh sediments. This suggests that salt marshes play an important role in the cycling of nutrients and organic carbon in the estuary and adjacent coastal waters. (C) 2003 Elsevier Ltd. All rights reserved.

Redox cycling of Ni-YSZ anode investigated by TPR technique

Effect of redox cycling on a Ni-YSZ anode prepared from 50 wt.% NiO and 50 wt.% YSZ was investigated by using temperature-programmed reduction (TPR), XRD and SEM techniques. XRD results showed that NiO was formed during re-oxidation. Both the XRD and TPR results depicted that the conversion of nickel to NiO depended on the re-oxidation temperature. The oxidation of Ni to NiO occurred quickly in the initial several minutes and then reached a quasi equilibrium. The TPR profiles tracing the redox cycling showed that it brought continuous changes in the NiO micro-structure at 800 degrees C, whereas at 600 degrees C it had only little effects on the reduction of NiO. Re-oxidation resulted in the formation of spongy aggregates of NiO crystallites. Redox cycling at 800 degrees C led to a continuous decrease in the primary crystallite size of NiO and a high dispersion of the Ni particles. A continuous expansion of the slice sample was observed in both of the oxidized and reduced states during the redox cycling at 800 degrees C, whereas this process did not occur during the redox cycling at 600 degrees C. (c) 2005 Elsevier B.V All rights reserved.

Absence of turnover and futile cycling of sucrose in leaves of Lolium temulentum L.: implications for metabolic compartmentation

Cairns, A. J., Gallagher, J. A. (2004). Absence of turnover and futile cycling of sucrose in leaves of Lolium temulentum L.: implications for metabolic compartmentation. Planta, 219 (5), 836-846. Sponsorship: BBSRC RAE2008