Biomass mapping using forest type and structure derived from Landsat TM imagery

A method for mapping forest biomass was developed and tested on a study area in western Newfoundland, Canada. The method, BIOmass from Cluster Labeling Using Structure and Type (BioCLUST), involves: (i) hyperclustering a Landsat TM image, (ii) automatically labeling the clusters with information about forest type and structure, and (iii) applying stand-level equations that estimate biomass as a function of height and crown closure within forest species-type classes. BioCLUST was validated with biomass values measured at geo-referenced field plots and mapped across the study area using an existing forest management photo-inventory. Root mean square error (RMSE) values ranged from 43 to 79 tonnes/ha, and were lowest for intermediate height classes when validated with field plots. Overall bias was negative at 10 tonnes/ha compared with a negative bias of 3 tonnes/ha estimated for the photo-inventory. Validation of the biomass map gave RMSE values of 37–47 tonnes/ha and overall landscape biomass estimates within 0.4% of biomass mapped by the photo-inventory. BioCLUST offers an alternative to other biomass mapping methods when scene-specific plot data are limited and a photo-inventory is available for a representative portion of a Landsat scene.     

Use of voltammetric solid-state (micro)electrodes for studying biogeochemical processes: Laboratory measurements to real time measurements with an in situ electrochemical analyzer (ISEA)

Solid-state voltammetric (micro)electrodes have been used in a variety of environments to study biogeochemical processes. Here we show the wealth of information that has been obtained in the study of sediments, microbial mats, cultures and the water column including hydrothermal vents. Voltammetric analyzers have been developed to function with operator guidance and in unattended mode for temporal studies with an in situ electrochemical analyzer (ISEA). The electrodes can detect the presence (or absence) of a host of redox species and trace metals simultaneously. The multi-species capacity of the voltammetric electrode can be used to examine complex heterogeneous environments such as the root zone of salt marsh sediments. The data obtained with these systems clearly show that O₂ and Mn²⁺ profiles in marine sedimentary porewaters and in microbial biofilms on metal surfaces rarely overlap indicating that O₂ is not a direct oxidant for Mn²⁺. This lack of overlap was suggested originally by Joris Gieskes' group. In waters emanating from hydrothermal vents, Fe²⁺, H₂S and soluble molecular FeS clusters (FeS_aq) are detected indicating that the reactants for the pyrite formation reaction are H₂S and soluble molecular FeS clusters. Using the ISEA with electrodes at fixed positions, data collected continuously over three days near a Riftia pachyptila tubeworm field generally show that O₂ and H₂S anti-correlate and that H₂S and temperature generally correlate. Unlike sedimentary environments, the data clearly show that Riftia live in areas where both O₂ and H₂S co-exist so that its endosymbiont bacteria can perform chemosynthesis. However, physical mixing of diffuse flow vent waters with oceanic bottom waters above or to the side of the tubeworm field can dampen these correlations or even reverse them. Voltammetry is a powerful technique because it provides chemical speciation data (e.g.; oxidation state and different elemental compounds/ions) as well as quantitative data. Because (micro)organisms occupy environmental niches due to the system's chemistry, it is necessary to know chemical speciation. Voltammetric methods allow us to study how chemistry drives biology and how biology can affect chemistry for its own benefit.     

Multilayer analytic element modeling of radial collector wells

A new multilayer approach is presented for the modeling of ground water flow to radial collector wells. The approach allows for the inclusion of all aspects of the unique boundary condition along the lateral arms of a collector well, including skin effect and internal friction losses due to flow in the arms. The hydraulic conductivity may differ between horizontal layers within the aquifer, and vertical anisotropy can be taken into account. The approach is based on the multilayer analytic element method, such that regional flow and local three-dimensional detail may be simulated simultaneously and accurately within one regional model. Horizontal flow inside a layer is computed analytically, while vertical flow is approximated with a standard finite-difference scheme. Results obtained with the proposed approach compare well to results obtained with three-dimensional analytic element solutions for flow in unconfined aquifers. The presented approach may be applied to predict the yield of a collector well in a regional setting and to compute the origin and residence time, and thus the quality, of water pumped by the collector well. As an example, the addition of three lateral arms to a collector well that already has three laterals is investigated. The new arms are added at an elevation of 2 m above the existing laterals. The yield increase of the collector well is computed as a function of the lengths of the three new arms.     

Metal-organic complexation in the marine environment

We discuss the voltammetric methods that are used to assess metal-organic complexation in seawater. These consist of titration methods using anodic stripping voltammetry (ASV) and cathodic stripping voltammetry competitive ligand experiments (CSV-CLE). These approaches and a kinetic approach using CSV-CLE give similar information on the amount of excess ligand to metal in a sample and the conditional metal ligand stability constant for the excess ligand bound to the metal. CSV-CLE data using different ligands to measure Fe(III) organic complexes are similar. All these methods give conditional stability constants for which the side reaction coefficient for the metal can be corrected but not that for the ligand. Another approach, pseudovoltammetry, provides information on the actual metal-ligand complex(es) in a sample by doing ASV experiments where the deposition potential is varied more negatively in order to destroy the metal-ligand complex. This latter approach gives concentration information on each actual ligand bound to the metal as well as the thermodynamic stability constant of each complex in solution when compared to known metal-ligand complexes. In this case the side reaction coefficients for the metal and ligand are corrected. Thus, this method may not give identical information to the titration methods because the excess ligand in the sample may not be identical to some of the actual ligands binding the metal in the sample.     

Voltammetric methods of sulfate ion analysis in natural waters

Sulfate anion can be measured in waters of widely varying salinity by polarography and amperometry. Polarography is the preferred method because it allows for measurement of sulfate in the 50-ppm range. The polarographic method is rapid, precise, and can be adapted for smaller sample volumes by simple modification of the sample preparation. We report a precision of 0.17% on I.A.P.S.O. standard seawater and 0.90% on 50-ppm samples. Amperometry requires more time overall for analyses because it is a titrimetric method, but it also is a precise technique (0.28% on I.A.P.S.O. standard seawater). Both techniques do not require any unusual sample preparation and are easily performed in most laboratories.     

The influence of sulfides on soluble organic-Fe(III) in anoxic sediment porewaters

Solid and colloidal iron oxides are commonly involved in early diagenesis. More readily available soluble Fe(III) should accelerate the cycling of iron (Fe) and sulfur (S) in sediments. Experiments with synthetic solutions (Taillefert et al. 2000) showed that soluble Fe(III) (i.e., <50 nm diameter) reacts at a mercury voltammetric electrode at circumneutral pH if it is complexed by an organic ligand. The reactivity of soluble organic-Fe(III) with sulfide is greatly increased compared to its solid equivalent (e.g., amorphous hydrous iron oxides or goethite). We report here data from two different creeks of the Hackensack Meadowlands District (New Jersey) collected with solid state Au/Hg voltammetric microelectrodes and other conventional techniques, which confirm the existence of soluble organic-Fe(III) in sediments and its interaction with sulfide. Chemical profiles in these two anoxic sediments show the interaction between iron and sulfur during early diagenesis. Soluble organic-Fe(III) and Fe(II) are dominant in a creek where sulfide is negligible. This dominance suggests that the reductive dissolution of iron oxides goes through the dissolution of solid Fe(III), then reduction to Fe(II), or that soluble organic-Fe(III) is formed by chemical or microbial oxidation of organic-Fe(II) complexes. In a creek sediment where sulfide occurs in significant concentration, the reductive dissolution of Fe(III) is followed by formation of FeS_(aq), which further precipitates. Dissolved sulfide may influence the fate of soluble organic-Fe(III), but the pH may be the key variable behind this process. The high reactivity of soluble organic-Fe(III) and its mobility may result in the shifting of local reactions, at depths where other electron acceptors are used. These data also suggest that estuarine and coastal sediments may not always be at steady state.     

Kinetics of the Abiotic Reduction of Polymeric Manganese Dioxide by Nitrite: An Anaerobic Nitrification Reaction

Manganese oxides are strong environmental oxidants recently found to be involvedin the nitrogen cycle. Of the several possible reactions with reduced nitrogen species,the reduction of MnO₂ by nitrite has only received marginal attention. Yet, this reaction might explain why nitrification can occur in the absence of O₂, observed in both sediments and water columns. We have determined the stoichiometry of this reaction, as well as the chemical kinetics and the activation parameters, using a soluble polymeric form of MnO₂. The reaction rate decreases with increasing pH and decreasing temperature. The reaction is first order in each reactant with a second order rate constant (k) = 493 M^-1 min^-1 at 21.5 °C and pH = 5.00. The energy of activation (Ea = 9.370 kJ/mole) and the entropy of activation ( S = -169.5 J/mole) show the reaction to be associative and diffusion controlled, occurring via an inner-sphere mechanism, likely with O atom transfer from MnO₂ to HNO₂. The reaction is proton assisted and slowsdown at pH 5.5 where NO₂ ^- and MnO₂ (unprotonated and negatively charged) become the dominant species. In natural waters and sediments where anaerobic nitrification has been observed the pH is higher than this. Thus, the thermodynamically favorable reaction will likely proceed by microbial mediation.     

Tidal and seasonal variations of sulfate ion in a New Jersey marsh system

Sulfate variations during a tidal cycle were investigated at three sites in a highly polluted tidal marsh. Sulfate- chlorinity relationships were determined in the light of fluctuations in temperature, dissolved oxygen and pH. The relationships were found to be seasonal in nature, being affected by temperature and rainfall effects on biologic productivity. Both reduction of sulfate ion to a sulfide species and oxidation of sulfide species to the sulfate ion were found to occur. Consideration of the sulfide oxidation process suggests the possibility that metals precipitated as sulfides may be mobilized and redistributed in the marsh system.