A chlorophyll time series for Narragansett Bay: Assessment of the potential effect of tidal phase on measurement

An 18-yr chlorophyll time series for Narragansett Bay based on weekly samples collected without regard to tidal phase revealed a long-term decrease in mean annual levels. The potential influence of neglecting tidal phase in the sampling strategy on measured chlorophyll and its apparent long-term decrease is evaluated. A two year data set (1995–1996) is used as a proxy for the 1973–1990 time series together with an observed relationship between continuous measurements of in situ chlorophyll fluorescence and accompanying tidal phase. The deviations in chlorophyll from long-term means relative to deviations from mean low water at the time of sample collection are also analyzed, as is the potential influence of tidally-induced advective increases or dilution on measured chlorophyll levels. The analyses, which compare the magnitude and trends in tidally adjusted and directly measured chlorophyll, indicate that semi-diurnal intratidal variations in chlorophyll had little apparent effect on the long-term and seasonal patterns and trends deduced from the chlorophyll measurements. Neither tidal advection of the chlorophyll gradient, nor bloom magnitude appear to compromise application of the model. The 18-yr decline in annual mean chlorophyll observed between 1973–1990 in narragansett Bay is considered to be a bonafide portrayal of actual events, and not an artifact of failure to consider tidal phase in the weekly sampling strategy. The results also suggest that intratidal variability in chlorophyll does not seriously confound its meaningful measurement and usefulness as a representative index of phytoplankton abundance at the permanent monitoring station established for Narragansett Bay. Nonetheless, there is need to refine and to incorporate temporal sampling strategies more closely attuned to the tempo of growth, grazing, and nutrient recycling which accompany estuarine phytoplankton dynamics.     

A comparison of the predictive potential of various vegetation indices for leaf chlorophyll content

Leaf chlorophyll is an important indicator of nutritional stress, photosynthetic capacity, and growth status of plants. Therefore, it is important to accurately estimate leaf chlorophyll content over a range of spatial and temporal scales. However, traditional methods for chlorophyll measurement mainly rely on chemical analysis, which is not universally applicable to dynamic monitoring of plants in large areas because it is time consuming and requires destructive measurements. Hyperspectral remote sensing has enormous potential for accurate retrieval of plant biochemical parameters. Therefore, it has become the most popular means to retrieve chlorophyll content, by establishing empirical relationships between different vegetation indices and chlorophyll content. In recent years, many vegetation indices have been developed for the inversion of chlorophyll content. Only the vegetation indices that are less affected by the external environment are used, in order to establish a strong and robust model. Therefore, it is very important to assess the anti-disturbance ability of different vegetation indices. In this paper, a new method is proposed to quantitatively assess the anti-disturbance ability of vegetation indices. The anti-disturbance ability of several vegetation indices that are commonly used for chlorophyll estimation was evaluated using this method. We concluded that the anti-disturbance ability of VogD, TCARI/OSAVI, and Datt99 is stronger than the other vegetation indices tested. However, if a vegetation index is not sensitive to chlorophyll content, predicting chlorophyll content holds no value even though it has a strong anti-disturbance ability. Therefore, we used the slope of the best fitting function between the vegetation index and chlorophyll content (defined as d(VI)/d(Chlorophyll content)) to measure the sensitivities of different indices to chlorophyll content. Finally, we found that TCARI/OSAVI was one of the best vegetation indices to estimate chlorophyll content at the leaf level. However, we have only considered three factors to evaluate the anti-disturbance ability of different vegetation indices, which is still far from enough because the canopy reflectance is affected by many factors. Therefore, we should account for more factors in the future.     

Climatic and Tidal Forcing of Hydrography and Chlorophyll Concentrations in the Columbia River Estuary

Hydrographic patterns and chlorophyll concentrations in the Columbia River estuary were compared for spring and summer periods during 2004 through 2006. Riverine and oceanic sources of chlorophyll were evaluated at stations along a 27-km along-estuary transect in relation to time series of wind stress, river flow, and tidal stage. Patterns of chlorophyll concentration varied between seasons and years. In spring, the chlorophyll distribution was dominated by high concentrations from freshwater sources. Periods of increased stream flow limited riverine chlorophyll production. In summer, conversely, upwelling winds induced input of high-salinity water from the ocean to the estuary, and this water was often associated with relatively high chlorophyll concentrations. The frequency, duration, and intensity of upwelling events varied both seasonally and interannually, and this variation affected the timing and magnitude of coastally derived material imported to the estuary. The main source of chlorophyll thus varied from riverine in spring to coastal in summer. In both spring and summer seasons and among years, modulation of the spring/neap tidal cycle determined stratification, patterns of mixing, and the fate of (especially freshwater) phytoplankton. Spring tides had higher mixing and neap tides greater stratification, which affected the vertical distribution of chlorophyll. The Columbia River differs from the more tidally dominated coastal estuaries in the Pacific Northwest by its large riverine phytoplankton production and transfer of this biogenic material to the estuary and coastal ocean. However, all Pacific Northwest coastal estuaries investigated to date have exhibited advection of coastally derived chlorophyll during the upwelling season. This constitutes a fundamental difference between Pacific Northwest estuaries and systems not bounded by a coastal upwelling zone.     

Distribution and significance of chlorophyll derivatives and oxidation products during the spring phytoplankton bloom in the Celtic Sea April 2002

The abundances and distributions of chlorophyll a and its common transformation products have been profiled by high performance liquid chromatography during the disruption, re-establishment, growth and senescence of a phytoplankton bloom in the Celtic Sea during April 2002. Transformation products of chlorophyll a indicative of herbivory of the phytoplankton bloom have been identified using atmospheric pressure chemical ionisation liquid chromatography-multistage mass spectrometry and chlorophyll oxidation products, formed by autoxidation, are present in increasing abundance in samples collected during the later stages of bloom development. The formation of oxidation products during the earliest stages in the chlorophyll transformation pathway identifies water column processes as sources of these early intermediates in the formation of geologic aetioporphyrins and/or cycloalkanoporphyrins.     

中大西洋营养盐富集实验中浮游植物生长的营养盐限制作用

借助中国首次环球科学考察航次,在中大西洋航段现场对表层海水进行了添加N、P、Si的营养盐富集实验,通过实验过程中水体营养盐浓度、叶绿素a（Chl-a）浓度以及温度等参数的分析,探讨了实验海区浮游植物生长的营养盐限制作用。结果表明,添加N、P、Si都可造成实验水体中Chl-a浓度明显增大,且N对浮游植物生长的限制作用最明显,其次为P,Si的作用最弱。实验过程中水体N／P值的变化同叶绿素a浓度及浮游植物生长速度（R）没有可对比性,N／P值与后两者之间的相关性都差,可以认为水体中N／P值并不能单独限制浮游植物生长。实验水体温度同Chl-a浓度和R值间也缺乏相关性,表明水体温度同样不能控制浮游植物生长。     

Pigment analysis and spectral assessment of spruce trees undergoing forest decline in the NE United States and Germany

Measurement of photosynthetic pigments as ground truth for remotely sensed spectra of boreal communities was tested. Chlorophyll and carotenoid concentrations and ratios were obtained from needles of spruce trees which were healthy as well as those undergoing forest decline (Waldsterben) in Vermont (USA) and Baden-Württemberg (FR Germany). In needles of trees exhibiting forest decline symptoms, chlorophyll pigment concentrations were lower, chlorophyll b levels decreased relative to chlorophyll a, total chlorophyll (a + b) was less relative to total carotenoid, and percent of reflectance in the visible range was higher. Pigment and reflectance data differentiated between needles from healthy and declining sites. These results were compared to remotely sensed spectral data obtained by aircraft and satelitee. As a result of these initial comparisons, it appears that using photosynthetic pigments as ground truth for remotely sensed spectral data may be of value in developing techniques for differentiating undamaged and damaged tree canopies on a large spatial scale. Finally, similar pigment and reflectance properties characterized healthy and declining communities in both Vermont and Baden-Württemberg.     

Structures and profiles of novel sulfur-linked chlorophyll derivatives in an Antarctic lake sediment

High performance liquid chromatography-mass spectrometry has permitted the identification of a homologous series of novel alkylsulfide derivatives of chlorophyll a containing between one and five carbon atoms, in sediment from a coastal Antarctic lake. The sulfur-containing compounds are present in varying abundance in stratigraphic horizons representing a phase when the lake was a marine basin. Throughout this marine phase photic zone anoxia is recorded by the presence of bacteriochlorophyll c and d-derivatives. Distributional variations between sulfurised and non-sulfurised chlorophyll a-derivatives throughout the sediment section studied indicate that the extent of sulfurisation is not controlled by chlorophyll a abundance alone.     

Primary production in the Sulu Sea

The Sulu Sea, located between Borneo and the Philippines, is separated from the surrounding ocean by two chains of islands. There are no passages below 500 m depth and the basin, which at the deepest is 5,000m, is filled with warm low oxygen water. The near surface chlorophyll concentration has been examined with the aid of ocean colour sensors on board satellites. Direct comparisons between a field observation of chlorophyll and its remotely sensed values from OCTS (Ocean Colour Temperature Scanner) are found to be in satisfactory agreement. An 8-month time series of chlorophyll near the centre of the Sulu Sea has been used to show that the chlorophyll level is significantly higher than the level in the adjacent South China Sea. This was most pronounced at the period of change between the monsoons. The greater primary productivity may provide the explanation for the higher deposition rate of carbon in the Sulu Sea. Although the Sulu Sea is more productive than the adjacent South China Sea, the central area can still be classified as a desert. Estimates of the new primary production in the central Sulu Sea seem to be just sufficient to support the current fishery.     

An instrument system for high-speed mapping of chlorophyll a and physico-chemical variables in surface waters

A device incorporating microprocessor control and flow-through sampling permits high-speed measurements of chlorophyll a, and physical and chemical variables in aquatic systems. Continuous sampling of chlorophyll a, conductivity, temperature, salinity, incident photosynthetically active radiation (PAR), underwater PAR, and pH facilitates multiple correlations and mapping of variables at both small and large spatial scales. The instrument is portable and can be installed in a small boat for “rapid response” sampling of large areas. The low-voltage DC power requirement and shallow draft make the device especially suitable for work in shallow coastal areas, tidal creeks, bayous, and physically complex aquatic landscapes where larger vessels cannot be operated. Examples of applications of the instrument are discussed. In Fourleague Bay, Louisiana, a shallow estuary on the Gulf of Mexico, we were able to detect horizontal chlorophyll a structure and transient fronts map spatial variations on the scale of a few meters to several kilometers, and follow movements of chlorophyll features through the estuary. These patterns were often not apparent when sampled at discrete stations.     

北冰洋沉积物和海水叶绿素α浓度分布的区域性特征

2003年夏季中国第二次北极科学考察期间,在北冰洋楚科奇海陆架、楚科奇海台、陆坡流区、门捷列夫海岭和加拿大海盆等不同区域进行了200 m以浅海水和部分观察站沉积物表层叶绿素a浓度的现场观测。结果表明,观测水体叶绿素α浓度变化范围为0.002～39.008 μg/dm3。表层浓度分布范围为0.037～4.644 μg/dm3,平均值为0.612 μg/dm3;高叶绿素α浓度出现在水深20～30 m的次表层水。叶绿素α浓度分布具有明显的区域性特征,水柱平均浓度的次序为楚科奇海陆架区>陆坡流区>楚科奇海台区>加拿大海盆区>门捷列夫海岭区。表层沉积物叶绿素α浓度从未能检出～3.978 μg/g(湿重),平均浓度为0.954 μg/g(湿重),表现为沉积物表层的浓度高于下层,陆架和陆坡流区的浓度高于海岭区以及海台和海盆区的分布特征。     

Factors Determining the Location of the Chlorophyll Maximum and the Fate of Algal Production within the Tidal Freshwater James River

Longitudinal variation in factors affecting phytoplankton production were analyzed to better understand the mechanisms that cause the formation of a chlorophyll maximum within the tidal freshwater James River. Phytoplankton production was two- to threefold higher in the region where persistent elevated chlorophyll concentrations occurred. Near this site, the morphology of the James transitions from a narrow, deep channel to a broad expanse with shallow areas adjoining the main channel. Shallower depths resulted in greater average irradiance within the water column and suggest that release from light limitation was the principal factor accounting for the location of the chlorophyll maximum. Grazing rates were low indicating that little of the algal production was directly consumed by zooplankton. Low exploitation by zooplankton was attributed to poor food quality due to high concentrations of non-algal particulate matter and potential presence of cyanobacteria. Metabolism data suggest that two thirds of net primary production was respired in the vicinity of the chlorophyll maximum and one third was exported via fluvial and tidal advection. Comparison of water column and ecosystem metabolism indicates that the bulk of respiration occurred within the sediments and that sedimentation was the dominant loss process for phytoplankton.     

两种用于作物冠层叶绿素含量提取的改进光谱指数

在深入探讨目前广泛使用的提取叶绿素含量的植被指数的光谱响应机制基础上,利用PROSPECT+SAIL模型模拟的作物冠层反射率样本数据对比分析了这些植被指数对叶绿素含量变化的敏感性差异,包括PSSRa、PSSRb、PSNDa、PSNDb、NPCI、PRI、MCARI和TVI等.结果表明,上述植被指数或对土壤背景变化敏感,或受高值LAI影响趋于饱和,对作物叶绿素含量反演效果均不理想.提出了4种基于TVI和MCARI的改进植被指数MTVI1、MTVI2、MCARI1和MCARI2,揭示了它们对土壤背景和LAI不敏感,对叶绿素含量变化更为敏感的光谱机制,并根据实验数据对其进行验证.实验表明,改进的植被指数MTVI2和MCARI2是作物冠层叶绿素含量较好的预测器,可据此建立作物冠层叶绿素含量反演模型.     

Refining habitat requirements of submersed aquatic vegetation: Role of optical models

A model of the spectral diffuse attenuation coefficient of downwelling irradiance was constructed for Chincoteague Bay, Maryland, and the Rhode River, Maryland. The model is written in terms of absorption spectra of dissolved yellow substance, the chlorophyll-specific absorption of phytoplankton, and absorption and scattering by particulate matter (expressed as turbidity). Based on published light requirements for submersed aquatic vegetation (SAV) in Chesapeake Bay, the model is used to calculate the range of water-quality conditions that permit survival of SAV at various depths. Because the model is spectrally based, it can be used to calculate the attenuation of either photosynthetically active radiation (PAR, equally weighted quanta from 400 nm to 700 nm) or photosyntheticallyusable radiation (PUR, the integral of the quantum spectrum weighted by the pigment absorption spectrum of SAV). PUR is a more accurate measurement of light that can be absorbed by SAV and it is more strongly affected by phytoplankton chlorophyll in the water column than is PAR. For estuaries in which light attenuation is dominated by turbidity and chlorophyll, the model delimits regions in which turbidity alone (chlorophyll <10 μg 1^?1), chlorophyll alone (turbidity <1 NTU) or both factors (chlorophyll >10 μg 1^?1, turbidity >1 NTU) must be reduced to improve survival depths for SAV.     

Calculating optical water quality targets to restore and protect submersed aquatic vegetation: Overcoming problems in partitioning the diffuse attenuation coefficient for photosynthetically active radiation

Submersed aquatic vegetation (SAV) is an important component of shallow water estuarine systems that has declined drastically in recent decades. SAV has particularly high light requirements, and losses of SAV have, in many cases, been attributed to increased light attenuation in the water column, frequently due to coastal eutrophication. The desire to restore these valuable habitats to their historical levels has created the need for a simple but accurate management tool for translating light requirements into water quality targets capable of supporting SAV communities. A procedure for calculating water quality targets for concentrations of chlorophyll and total suspended solids (TSS) is derived, based on representing the diffuse attenuation coefficient for photosynthetically active radiation, K_d(PAR), as a linear function of contributions due to water plus colored dissolved organic matter (CDOM), chlorophyll, and TSS. It is assumed that K_d(PAR) conforms to the Lambert-Beer law. Target concentrations are determined as the intersection of a line representing intended reduction of TSS and chlorophyll by management actions, with another line describing the dependence of TSS on chlorophyll at a constant value of K_d(PAR). The validity of applying the Lambert-Beer law to K_d(PAR) in estuarine waters was tested by comparing the performance of a linear model of K_d(PAR) with data simulated using a more realistic model of light attenuation. The linear regression model tended to underestimate K_d(PAR) at high light attenuation, resulting in erroneous predictions of target concentrations at shallow restoration depths. The errors result more from the wide spectral bandwidth of PAR, than from irrecoverable nonlinearities in the diffuse attenuation coefficient per se. In spite of the failure of the Lambert-Beer law applied to K_d(PAR), the variation of TSS with chlorophyll at constant K_d(PAR) determined by the more mechanistic attenuation model was, nevertheless, highly linear. Use of the management tool based on intersecting lines is still possible, but coefficients in the line describing the dependence of TSS on chlorophyll at constant K_d(PAR) must be determined empirically by application of an optical model suitably calibrated for the region of interest. An example application of the procedure to data from the Rhode River, Maryland, indicates that approximately 15% reduction in both TSS and chlorophyll concentrations, or 50% reduction in chlorophyll alone, will be needed to restore conditions for growth of SAV to levels that existed in the late 1960s.     

Phytoplankton biomass, cell diameter, and species composition in the low salinity zone of Northern San Francisco Bay estuary

Phytoplankton chlorophyll a concentration, biovolume, cell diameter, and species composition differed across the narrow, low salinity zone between 0.6‰ to 4‰ and may influence copepod food availability in the northern San Francisco Bay Estuary. The highest chlorophyll a concentrations (range 3.2–12.3 μg 1^?1), widest cell diameters (>5 μm diam), highest diatom densities and highest production rates of >10 μm diam cells occurred at the landward edge of the salinity zone in April during a strong spring tide and May during a strong neap tide. Near optimum predator/prey ratios, large prey estimated spherical diameters, and high chlorophyll a concentrations suggest these phytoplankton communities provided good food quantity and quality for the most abundant copepods, Eurytemora affinis, Sinocalanus doerrii, and Pseudodiaptomus forbesi. At the center of the zone, chlorophyll a concentrations, diatom densities, and production rates of >10 μm diam cells were lower and cell diameters were smaller than upstream. Downstream transport was accompanied by accumulation of phytoplankton with depth and tide; maximum biomass occurred on spring tide. The lowest chlorophyll a concentrations (1.4–3.6 μg 1^?) and consistently high densities (3,000–4,000 cells ml^?1) of <5 μm diam cells occurred at the seaward edge of the zone, where the green alga Nannochloris spp. and the bluegreen alga Synechococcus spp. were the most abundant phytoplankton. Low chlorophyll a concentrations and production rates of >10 μm diam cells, small prey estimated spherical diameters, and high predator/prey ratios suggested the seaward edge of the zone had poor phytoplankton food for copepodids and adult copepods. The seaward decrease in phytoplankton chlorophyll a concentration and cell diameter and shift in species composition in the low salinity zone were probably a function of an estuary-wide decrease in chlorophyll a concentration, cell diameter, and diatom density since the early 1980s that was enhanced in the low salinity zone by clam herbivory after 1987. *** DIRECT SUPPORT *** A01BY090 00008     

Origin and significance of 13-hydroxychlorophyll derivatives in sediments

The authenticity of hydroxychlorophyll derivatives in sediments has been verified by subjecting pure chlorophyll preparations to the extraction method used for sediments. Model studies of chlorophyll autoxidation reveal hydroxychlorophyll as the major product formed in the presence of hydrogen peroxide. Its stability to further oxidation implies that hydroxychlorophyll derivatives are not precursors of aetioporphyrins and are more likely to produce cycloalkanoporphyrins via the processes of diagenesis. The occurrence of 13²-hydroxyphaeophytin a throughout a sediment core from Loch Ness confirms it to be a widespread chlorophyll oxidation product formed during early diagenesis. Profiles of hydroxychlorophyll derivatives in a sediment core from an Antarctic lake demonstrate their potential for use as markers of oxidation processes in palaeoenvironmental assessment.     

An investigation of the dissolved free amino acids and their relation to phytoplankton cell density in the Damariscotta River estuary,Maine

The DFAA composition was analyzed over the course of one year, along with salinity, temperature, phytoplankton nutrients, chlorophyll and cell counts. Stepwise multiple linear regression on all variables indicated that the total dissolved free amino acids were only directly related to individual amino acid variations, and not the other variables measured. In the prediction of cell density, only silicate and chlorophyll were significant predictors. Individual amino acids may be more significant in blooms of a single species.     

Seasonal variation of chlorophyll and primary productivity in central Arabian Sea: A macrocalibrated upper ocean ecosystem model

Seasonal variation of chlorophyll has been of considerable interest on account of the effect of photosynthesis on ocean-atmosphere carbon exchange. It can be predicted by a dynamical system model of the marine ecosystem coupled with a physical oceanographic model. There is however a major difficulty in the calibration of contemporary ecosystem models on account of sparse data and a large number of model parameters. This paper reports a new approach of macrocalibration in which values of six parameters are determined by examining in detail the seasonal variation of chlorophyll and primary productivity keeping in view the observations of two Indian JGOFS cruises. Both switching and non-switching versions of grazing functions are used in a 7-component FDM model. Detailed simulations are reported for one station (16°N, 65°E). They show the effects of dependence of grazing preference on prey density on the behaviour of the ecosystem. The results of the simulation also provide a partial basis for developing correlations of primary production with chlorophyll and sediment flux.     

Chlorophyll modulation of mixed layer thermodynamics in a mixed-layer isopycnal General Circulation Model — An example from Arabian Sea and equatorial Pacific

Western tropical Indian Ocean, Arabian Sea, and the equatorial Pacific are known as regions of intense bio-chemical-physical interactions: the Arabian Sea has the largest phytoplankton bloom with seasonal signal, while the equatorial Pacific bloom is perennial with quasi-permanent upwelling. Here, we studied three dimensional ocean thermodynamics comparing recent ocean observation with ocean general circulation model (OPYC) experiment combined with remotely sensed chlorophyll pigment concentrations from the Coastal Zone Color Scanner (CZCS). Using solar radiation parameterization representing observations that a higher abundance of chlorophyll increases absorption of solar irradiance and heating rate in the upper ocean, we showed that the mixed layer thickness decreases more than they would be under clear water conditions. These changes in the model mixed layer were consistent with Joint Global Ocean Flux Study (JGOFS) observations during the 1994-1995 Arabian Sea experiment and epi-fluorescence microscopy (EFM) on samples collected during Equatorial Pacific Ocean Climate Study (EPOCS) in November, 1988. In the Arabian Sea, as the chlorophyll concentrations peak in October (3 mg/m³) after the summer plankton bloom induced by coastal upwelling, the chlorophyll induced biological heating enhanced the sea surface temperature (SST) by as much as 0.6‡C and sub-layer temperature decreases and sub-layer thickness increases. In the equatorial Pacific, modest concentrations of chlorophyll less than 0.3 mg/m³ is enough to introduce a meridional differential heating, which results in reducing the equatorial mixed layer thickness to more than 20 m. The anomalous meridional tilting of the mixed layer bottom enhances off equatorial westward geostrophic currents. Consequently, the equatorial undercurrent transports more water from west to east. We proposed that these numerical model experiments with use of satellite andin situ ocean observations are consistent under three dimensional ocean circulation theory combined with solar radiation transfer process.     

Field spectroscopy and radiative transfer modelling to assess impacts of petroleum pollution on biophysical and biochemical parameters of the Amazon rainforest

Biophysical and biochemical plant foliage parameters play a key role in assessing vegetation health. Those plant parameters determine the spectral reflectance and transmittance properties of vegetation; therefore, hyperspectral remote sensing, particularly imaging spectroscopy, can provide estimates of leaf and canopy chemical properties. Based on the relationship between spectral response and biochemical/biophysical properties of the leaves and canopies, the PROSPECT radiative transfer model simulates the interaction of light with leaves. In this study, more than 1100 leaf samples from the Amazon forest of Ecuador were collected at several study sites, some of which are affected by petroleum pollution, and across the vertical profile of the forest. For every sample, field spectroscopy at leaf level was conducted with a spectroradiometer. The goal of this study was to assess leaf optical properties of polluted and unpolluted rainforest canopies across the vertical profile and identify vegetation stress expressed in changes of biophysical and biochemical properties of vegetation. An ANOVA followed by Holme’s multiple comparisons of means and a principal component analysis showed that photosynthetic pigments, chlorophyll and carotenoids have significantly lower levels across the vertical profile of the forest, particularly in sites affected by petroleum pollution. On the other hand, foliar water content showed significantly higher levels in the polluted site. Those findings are symptoms of vegetation stress caused by reduced photosynthetic activity and consequently decreased transpiration and water-use efficiency of the plants. Cross-comparison between SPAD-502 chlorophyll content meter index and chlorophyll content showed strong positive correlation coefficients (r = 0.71 and r ² = 0.51) which suggests that using the SPAD-502 chlorophyll index itself is sensitive enough to detect vegetation stress in a multispecies tropical forest. Therefore, the SPAD-502 can be used to assess chlorophyll content of vegetation across polluted and non-polluted sites at different canopy layers. The results presented in this paper contribute to the very limited literature on field spectroscopy and radiative transfer models applied to the vertical profile of the Amazon forest.