Jia-Zhong Zhang

Potential availability of sedimentary phosphorus to sediment resuspension in Florida Bay

the central bay. The spatial pattern of TSP is consistent with distribution of both seagrass and phytoplankton that are limited by available phosphorus in Florida Bay. Among the five pools, the authigenic carbonate fluorapatite, biogenic apatite and CaCO3-bound phosphorus account for the largest fraction (45%) of TSP, of which inorganic phosphorus is the dominant form, and organic phosphorus accounts for about 30% in the western and north central regions and less than 10% in other areas of Florida Bay. The second largest pools are the refractory organic phosphorus (24% of TSP) and reductant-soluble inorganic phosphorus (19% of TSP). Readily exchangeable phosphorus accounts for 8% of TSP, of which organic phosphorus is 60%. Detrital apatite phosphorus of igneous or metamorphic origin represents the smallest fraction, only 5% of TSP. Spatial distribution of phosphorus and iron in sediments indicates that external sources of these two essential plant nutrients to Florida Bay are spatially separated with phosphorus introduced by west coast waters across the western margin of Florida Bay and iron from freshwater flow into the eastern region. INDEX TERMS: 1030 Geochemistry: Geochemical cycles (0330); 1050 Geochemistry: Marine geochemistry (4835, 4850); 4805 Oceanography: Biological and Chemical: Biogeochemical cycles (1615); 4845 Oceanography: Biological and Chemical: Nutrients and nutrient cycling; KEYWORDS: Florida Bay, phosphorus, sediment

Speciation and fluxes of nutrients (N, P, Si) from the upper Yukon River

[1]xa0Water samples were collected from the Yukon River near the Stevens Village Station from May to September 2002 and analyzed for nutrients (N, P, and Si) in dissolved, particulate, organic, and inorganic forms to examine temporal variations in nutrient concentrations, fluxes, and phase partitioning. Both NO3 and PO4 concentrations in the Yukon River were much lower than those of world rivers, with an average concentration of 2.43 ± 0.63 μM-N and 0.053 ± 0.040 μM-P, respectively. Si(OH)4 concentrations were more comparable to those of world rivers, with an average concentration of 82 ± 21 μM-Si. Integrated annual fluxes were 2.4 × 108 mole-NO3, 3.4 × 106 mole-PO4, and 8.7 × 109 mole-Si(OH)4, respectively. Nutrient discharge during the river ice open season contributed 73 to 95% of the annual flux depending on nutrient species. Within the total N pool transported by the Yukon River, dissolved inorganic N comprised 7 ± 4% and particulate N made up 25 ± 10%, while dissolved organic N (DON) was the dominant N species (with an average of 67 ± 10%). In contrast, P was predominantly partitioned in the particulate phase (with an average of 94 ± 6%), leaving 4 ± 5% of the total P in the dissolved organic phase and ∼2 ± 1% in the dissolved inorganic phase. The partitioning of N and P indicates that the transformation between dissolved and particulate or inorganic and organic phases may play a critical role in controlling the flux of bioavailable nutrients and thus the nutrient dynamics in the Yukon River Basin and its coastal region. Nutrient specific fluxes normalized to drainage area in the Yukon River Basin were 0.57 mmole/m2/yr for NO3, 0.012 mmole/m2/yr for PO4, and ∼19 mmole/m2/yr for Si(OH)4, respectively. The relatively low specific fluxes of NO3 and PO4 in the Yukon River Basin reflect its pristine status or little anthropogenic influence, whereas cold climate in the Arctic/subarctic region may be responsible for its lower Si(OH)4 specific flux, in agreement with a general trend of increasing Si specific flux with decreasing latitude in global river systems. A warming climate and thus deeper permafrost active layer in the Yukon River watershed would likely enhance the export flux of nutrients into the Bering Sea.

Shipboard Fluorometric Flow Analyzer for High-Resolution Underway Measurement of Ammonium in Seawater

A shipboard fluorometric flow analyzer has been developed for near-real-time, high-resolution underway measurement of ammonium in seawater. The fluorometric method is based on the reaction of ammonium with o-phthaldialdehyde (OPA) and sulfite. The reagents used in this method have been modified to suit seawater analysis. This method shows no refractive index and salinity effect from seawater samples. The potential interferences in seawater have been studied, and their effects have been reduced. The instrument response is linear over a wide range of ammonium concentration. The limit of detection of 1.1 nM was estimated in laboratory using ammonium standards prepared in distilled water. It should be noted that application of this method to low-level ammonium measurement requires a correction of interference species, such as amino acids. The sample throughput is 3600 h(-1). The system can be used for both freshwater and seawater samples and has been used to monitor the distribution of ammonium in Florida coastal waters around an oceanic wastewater outfall.

An autonomous batch analyzer for the determination of trace ammonium in natural waters using fluorometric detection

An autonomous batch analyzer (ABA) is described for the measurement of ammonium in natural waters. The system combines previously described batch analysis and continuous flow analysis methods. With its simpler design, the system is robust, flexible, inexpensive, and requires minimal maintenance. The sampling frequency is ca. 8 h−1 and the limit of detection ca. 1 nM which is comparable to the most sensitive flow through or batch analysis methods previously described. Reproducibility is 0.6% (n = 10) at an ammonium level of 200 nM. There are three working ranges: 5–1000 nM, 20–4000 nM, and 0.2–25 μM. In addition, the system produces a calibration curve by autodilution from a single stock standard solution with the same accuracy as traditional manual calibration methods. Representative field data and comparisons with standard EPA methods confirm the utility of the ABA.

Methyl bromide cycling in a warm‐core eddy of the North Atlantic Ocean

[1]xa0We conducted a detailed investigation of the evolution of methyl bromide concentrations, degradation rates, and ventilation rates for 26 days in a naturally contained, warm-core eddy of the North Atlantic Ocean. This is the first study of the oceanic cycling of methyl bromide in a natural, contained system with a complete suite of supporting measurements of physical and chemical variables. Methyl bromide concentrations in the mixed layer ranged from 2.3 to 4.2 nmol m−3, degradation rates ranged from 0.1 to 0.9 nmol m−3 d−1, net sea-to-air exchange rates ranged from 0 to 0.5 nmol m−3 d−1, and net loss rates through the thermocline were less than 0.1 nmol m−3 d−1. From a mass balance for methyl bromide in the mixed layer, we calculated production rates ranging from <0.1 to 1.3 nmol m−3 d−1. The median of this range, 0.48 nmol m−3 d−1, is higher than the ∼0.15 nmol m−3 d−1 necessary to maintain the reported global oceanic emission of 56 Gg yr−1. This is reasonable, because our study area was supersaturated in methyl bromide, whereas the ocean as a whole is undersaturated.

A simple, effective mixing chamber used in conjunction with a syringe pump for flow analysis.

A simple, effective mixing chamber used in conjunction with a syringe pump for flow analysis is described and evaluated. A mixing chamber was constructed using a conventional 5mL pipette tip and its performance compared with a widely used mixing coil. The results demonstrate that the mixing coil does not rapidly and completely mix solutions. Utilizing a configuration that reversed solution positions in the chamber with each mixing cycle, the proposed mixing chamber achieved complete mixing in a significantly shorter time than the mixing coil. The influence of injected sample volume on absorbance signals was evaluated by calculating an S(1/2) value for the system. As tested with a minimal rinse, the system has no discernable carryover. Testing this new approach in our previously described silicate measurement system resulted in a more than twofold improvement in sensitivity.

An estimate of diapycnal nutrient fluxes to the euphotic zone in the Florida Straits

A recent hydrographic survey of the Florida Current at 27°N revealed an enhanced upward flux of nutrients along the Florida coast. Geostrophic flow of the Gulf Stream through the narrow Florida Straits causes an uplift of the nutricline toward its western edge, shoaling the mixed layers into the base of the euphotic zone. At a nearshore station, nitrate, phosphate, and silicate concentrations reached 19, 1.4, and 10u2009µM, respectively, at a water depth of 27u2009m. Furthermore, nutrient vertical gradients below the mixed layer increased with decreasing seafloor depth toward the Florida coast. The estimated vertical eddy diffusive nutrient fluxes across diapycnal surfaces reached 0.40–83.7, 0.03–6.24, and 0.24–45.5u2009mmolu2009m−2 d−1 for nitrate, phosphate, and silicate, respectively, along the shore. Estimated fluxes span a wide range due to the range of diffusivity measured. The lower end of estimated fluxes are comparable to open ocean values, but higher end of estimates are two orders of magnitude greater than those observed in open ocean. The diapycnal nutrient fluxes declined rapidly offshore as a result of decreasing vertical gradients of nutrient concentration.