Primary Production Values Research Articles

A comparison of equations commonly used to calculate organic carbon content and marine palaeoproductivity from sediment data

Abstract A comparison is made of different methods for calculating total organic carbon (TOC) in deposits and marine primary productivity using sediment data. The calculation methods include both equations derived by pure regression analysis, and equations that include descriptions of processes such as carbon flux and burial efficiency. The results are compared with present-day measured values of total organic carbon and marine primary productivity, using measured sedimentation rate, dry bulk density and water depth. These measurements cover a large range of marine depositional environments, i.e. shallow to deep water, oxic to anoxic conditions, etc. Both TOC and productivity calculations show some consistent over- or under-prediction of computed values compared with the measured values, while some equations lead to unrealistic results. TOC calculations using process descriptions are influenced more by the choice of burial efficiency equation than by the choice of carbon flux equation. Productivity calculations are influenced by the choice of carbon flux equation. Calculations using measured values from a core show that productivity estimates vary by a factor of two.

Fluxes of particulate organic carbon in the East China Sea in summer

Abstract. To understand carbon cycling in marginal seas better, particulate organic carbon (POC) concentrations, POC fluxes and primary production (PP) were measured in the East China Sea (ECS) in summer 2007. Higher concentrations of POC were observed in the inner shelf, and lower POC values were found in the outer shelf. Similar to POC concentrations, elevated uncorrected POC fluxes (720–7300 mg C m−2 d−1) were found in the inner shelf, and lower POC fluxes (80–150 mg C m−2 d−1) were in the outer shelf, respectively. PP values (~ 340–3380 mg C m−2 d−1) had analogous distribution patterns to POC fluxes, while some of PP values were significantly lower than POC fluxes, suggesting that contributions of resuspended particles to POC fluxes need to be appropriately corrected. A vertical mixing model was used to correct effects of bottom sediment resuspension, and the lowest and highest corrected POC fluxes were in the outer shelf (58 ± 33 mg C m−2 d−1) and the inner shelf (785 ± 438 mg C m−2 d−1), respectively. The corrected POC fluxes (486 to 785 mg C m−2 d−1) in the inner shelf could be the minimum value because we could not exactly distinguish the effect of POC flux from Changjiang influence with turbid waters. The results suggest that 27–93% of the POC flux in the ECS might be from the contribution of resuspension of bottom sediments rather than from the actual biogenic carbon sinking flux. While the vertical mixing model is not a perfect model to solve sediment resuspension because it ignores biological degradation of sinking particles, Changjiang plume (or terrestrial) inputs and lateral transport, it makes significant progress in both correcting the resuspension problem and in assessing a reasonable quantitative estimate of POC flux in a marginal sea.

Biological response to typhoon in northern South China Sea: A case study of “Koppu”

Obviously increased phytoplankton biomass and primary production was observed via both in situ investigation and remote sensing analysis in the northern South China Sea during typhoon Koppu′s intrusion in September 2009. Sea surface temperature declined in both coastal and offshore area when Koppu arrived. In the offshore waters, stratification was weakened due to vertical mixing and sea surface temperature distribution pattern changed after the Koppu′s arrival. The in situ data showed that extreme high primary production (PP) value (35mgCm−3h−1) appeared near the Dan′gan Island indicating a potential algal bloom around the southern coastal waters of Hong Kong. Obviously increased nutrient loadings were also observed in the near-shore surface waters shortly after the typhoon′s arrival. According to both in situ observation and remote sensing results, it is suggested that PP in the offshore water was stimulated by extra vertical nutrient transport induced by Koppu; while the enhanced phytoplankton biomass and potential bloom along the coastal was mostly contributed by the increased Pearl River discharge after rainfall, which was also regulated by the typhoon event.

Экотоксикологический мониторинг арктических морей

For the first time the results of large-scale ecological and toxicological researches related to phytoplankton communities’ stability (ecological and toxicological monitoring) executed in the same season (summer period of succession) in all seas of Russian Arctic and Subarctic region — Baltic, White, Barents, Kara, Laptev, East Siberian, Chukchi and Bering Seas are presented. The experiments related to influence on primary production by copper’s (Cu) different concentrations were carried out in the conditions approached to natural ones during the voyages on Nikolay Kolomeytsev and Professor Shtokman research vessels. During 68 short-term toxicological onboard experiments the influence of some copper’s additives on the value of primary production of seas’ examined areas was studied.

Relationship between methanesulfonate (MS−) in atmospheric particulate and remotely sensed phytoplankton activity in oligo-mesotrophic central Mediterranean Sea

The coupling between oceanic and atmospheric sulfur cycles is fundamental for the understanding of the role of sulfate particles as potential climate regulators. We discuss existing relationships among methanesulfonate (MS− – one of the end products of oxidation of biogenic dimethylsulfide – DMS) in the atmospheric particulate, phytoplankton biomass, and remotely-sensed activity in the central Mediterranean. The MS− concentration in the aerosol particles is based on PM10 sampling (from 2005 to 2008) of atmospheric aerosols at the island of Lampedusa (35.5°N, 12.6°E) in the central Mediterranean Sea.The marine primary production in the sea sector surrounding the sampling site is obtained by using Ocean Color remote sensed data (SeaWiFS, MODIS-Aqua). In particular, primary production is calculated using a bio-optical model of sea reflectance and a Wavelength-Depth-Resolved Model (WDRM), fed by elaborated satellite data (chlorophyll concentration in the euphotic layer – Chl, sea surface temperature) and daily solar surface irradiance measurements.The multi-year evolution of MS− atmospheric concentration shows a well-defined seasonal cycle with a summer maximum, corresponding to the annual peak of solar radiation and a minimum of phytoplankton biomass (expressed as Chl).Statistically significant linear relationships between monthly means of atmospheric MS− and both the phytoplankton productivity index PB (r2 = 0.84, p < 0.001) and the solar radiation dose (SRD; r2 = 0.87, p < 0.001) in the upper mixed layer of the sea around Lampedusa are found. These correlations are mainly driven by the common seasonal pattern and suggest that DMS production in the marine surface layer is mainly related to the phytoplankton physiology. High values of PB are also the expression of stressed cells. The main stress factors in Mediterranean Sea during summer are high irradiance and shallow depth of the upper mixed layer, which lead to enhanced DMS emissions and higher MS− amounts in the atmosphere.During spring 2005 high biomass and primary productivity values are observed in February and April, just one month before the peaks of atmospheric MS− (March and May). The occurrence of anomalously high values at this time is hypothesized to be related to the negative phase of the North Atlantic Oscillation, and to related oceanic and atmospheric processes. The possible role of the taxonomic composition of phytoplankton assemblages is also discussed.

Annual budget and seasonal variation of aboveground and belowground net primary productivity in a lowland dipterocarp forest in Borneo

AbstractTropical forests are thought to have among the highest values of net primary productivity (NPP) on Earth, but comprehensive data on NPP have rarely been collected for tropical forests, especially outside of the Neotropics. In this study, we quantify aboveground and belowground NPP, along with additional environmental factors over a 1–2 year period in a lowland dipterocarp forest in Borneo. The site is characterized by high annual rainfall and typically no month of the year when the forest is under water stress. We estimated the total NPP to be 15.89 ± 0.90 Mg C ha−1 yr−1 (mean ± standard error) for a forest plot on clay soils and 12.79 ± 0.68 Mg C ha−1 yr−1 for a forest plot on sandy loam soils. Of this productivity, the allocation to aboveground NPP is 81.8 ± 6.0%/80.4 ± 6.0% and to belowground NPP is 18.2 ± 3.7%/19.6 ± 2.6% on clay and sandy loam, respectively. Fine root productivity (NPPfine roots) shows stronger seasonal variation relative to other components of NPP. There is evidence suggesting interannual variation in NPPfine roots, leaf flush, NPPlitterfall, and NPPACW. This is the first attempt to describe how the biomass of a Bornean tropical forest is allocated to the various components of NPP over the seasonal cycle. The study highlights the marked seasonality of a tropical forest even under largely aseasonal environmental conditions, as well as the important effect of contrasting seasonality on different soil types.

The global NPP dependence on ENSO: La Niña and the extraordinary year of 2011

Global ecosystems remove about 25% of anthropogenic CO2 emissions; however, the response of the land sink to climate variability and change is not yet fully understood. In 2011, the highest global value of net primary production (NPP) since 2000 was registered on the Moderate Resolution Imaging Spectroradiometer record, together with the highest value on the Carbon Dioxide Information Analysis Center record of carbon land sink strength since 1959. Here we show that El Niño/Southern Oscillation (ENSO) is responsible for much of the variability observed in the land sink and that the high NPP anomaly observed in 2011 was largely influenced by the strongest La Niña since the 1970s that lasted from late 2010 to early 2012. ENSO explains more than 40% of global NPP variability, mainly driven by the response of Southern Hemisphere ecosystems, particularly in tropical and subtropical regions. Water availability, controlled by temperature and precipitation anomalies, appears to be the main factor driving the regional response of NPP to ENSO.

A comparison of primary production models in an area of high mesoscale variability (South Shetland Islands, Antarctica)

Three types of primary productivity (PP) models were evaluated in a mesoscale area around the South Shetland Islands (Antarctica). Input variables were: phytoplankton carbon biomass, Chlorophyll a, sea water temperature, daily irradiance, among others, collected in situ during an oceanographic cruise (COUPLING, January 2010). Models of the first type were based on Chl a measurements: the widely used model VGPM (Behrenfeld and Falkowski, 1997) and a derived version developed for the Western Antarctic Peninsula (Dierssen et al., 2000). The second type included two models based on phytoplankton carbon biomass: one developed for the whole Southern Ocean (Arrigo et al., 2008) and one based on the Metabolic Theory of Ecology developed by López-Urrutia et al. (2006), being the first time that a model with these features is used for Antarctic waters. The third type was an updated version of the carbon-based model CbPM (first described by Behrenfeld et al. (2005)) based on the Chl a/carbon biomass ratio modulation. The degree of agreement among the results between the different types of models turned out to be low (>30% of difference), but high within models of the same type (<10% of difference). Biomass-based model predictions differed the most from those estimated by the other two types. The differences in PP estimates were primarily attributed to the different ways these models treat the phytoplankton assemblage, along with the difference in input variables. Among the five models evaluated, the output from the modified version of the CbPM showed the lowest bias (0.55) being the most realistic. It made a special attempt to detect the factors controlling phytoplankton physiological state, showing a nutrient limitation towards the Drake area similar to the one observed for the in situ PP values.

Effect of Degradation Intensity on Grassland Ecosystem Services in the Alpine Region of Qinghai-Tibetan Plateau, China

The deterioration of alpine grassland has great impact on ecosystem services in the alpine region of Qinghai-Tibetan Plateau. However, the effect of grassland degradation on ecosystem services and the consequence of grassland deterioration on economic loss still remains a mystery. So, in this study, we assessed four types of ecosystem services following the Millennium Ecosystem Assessment classification, along a degradation gradient. Five sites of alpine grassland at different levels of degradation were investigated in Guoluo Prefecture of Qinghai Province, China. The species composition, aboveground biomass, soil total organic carbon (TOC), and soil total nitrogen (TN) were tested to evaluate major ecological services of the alpine grassland. We estimated the value of primary production, carbon storage, nitrogen recycling, and plant diversity. The results show the ecosystem services of alpine grassland varied along the degradation gradient. The ecosystem services of degraded grassland (moderate, heavy and severe) were all significantly lower than non-degraded grassland. Interestingly, the lightly degraded grassland provided more economic benefit from carbon maintenance and nutrient sequestration compared to non-degraded. Due to the destruction of the alpine grassland, the economic loss associated with decrease of biomass in 2008 was $198/ha. Until 2008, the economic loss caused by carbon emissions and nitrogen loss on severely degraded grassland was up to $8 033/ha and $13 315/ha, respectively. Urgent actions are required to maintain or promote the ecosystem services of alpine grassland in the Qinghai-Tibetan Plateau.

Spawning site selection by European anchovy (Engraulis encrasicolus) in relation to oceanographic conditions in the Strait of Sicily

AbstractEuropean anchovy egg occurrence and density data from summer surveys (1998–2007) and oceanographic data were examined to study the mechanisms that control the spatial distribution of anchovy spawning habitat in the Strait of Sicily. Quotient analysis indicated habitat preference for temperature (18–19°C), bottom depth (50–100 m), water column stability (13–14 cycle h−1), fluorescence (0.10–0.15 μg m−3 Chl a), salinity (37.5–37.6 PSU), current speed (0.20–0.25 m s−1) and density (26.7–26.8 kg m−3, σt). Canonical discriminant analysis identified temperature, column stability and fluorescence as major drivers of anchovy spawning habitat. Three of the 4 years which had lower egg abundance were warmer years, with low values of primary productivity. A geostrophic current flowing through the Strait (the Atlantic Ionic Stream, AIS) was confirmed as the main source of environmental variability in structuring the anchovy spawning ground by its influence on both the oceanography and distribution of anchovy eggs. This 10‐yr data series demonstrates recurrent but also variable patterns of oceanographic flows and egg distribution. A lack of freshwater flow in this area appears to depress productivity in the region, but certain and variable combinations of environmental conditions can elevate production in some sub‐areas in most years or other sub‐areas in fewer years. These temporal and spatial patterns are consistent with an ocean triad theory postulating that processes of oceanographic enrichment, concentration, and retention may help predict fishery yields.

Movement patterns and habitat use during incubation and chick-rearing of Cory's shearwaters (Calonectris diomedea diomedea) (Aves: Vertebrata) from Central Mediterranean: influence of seascape and breeding stage

We analysed the patterns of movement and habitat use of Cory's shearwaters (Calonectris diomedea diomedea) from two colonies in the central Mediterranean Sea: the island of Linosa and the Tremiti Archipelago. The colony of Linosa is placed in a rather pelagic environment, being about 160 km distant from the coasts of both Sicily and Tunisia, while the colony of Tremiti is rather near to the coast of the Adriatic Sea, being only 25 km from the Italian coast. Field work during incubation was carried out at both colonies and throughout chick-rearing only at Linosa. We aimed to test first whether birds from the two colonies differ significantly in habitat use, and secondly whether constraints during incubation and chick-rearing lead birds to explore different habitats. Trip duration was correlated with the farthest distance covered in both colonies and, for Linosa birds, it decreased at the start of chick-rearing but increased later. During incubation the expanse of explored areas did not differ between the colonies, but for Tremiti these were generally characterized by higher average primary production and shallower waters than those for Linosa. Furthermore, during the incubation period Linosa birds explored areas with higher values of primary production and shallower waters than during chick-rearing. Chick-rearing is therefore likely to constrain birds to use sub-optimal areas closer to their colony due to the intense pressures of chick provisioning. Our data indicate that conservation efforts should therefore aim not only to protect the best foraging areas but also to conserve areas closer to the colonies, which will be profitable enough to provide adult birds with sufficient food for chick-rearing.

Satellite-derived multi-year trend in primary production in the Arctic Ocean

Spaceborne one month averaged data, predominantly from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and partly from the Moderate Resolution Imaging Spectroradiometer (MODIS), were used to investigate changes in primary production (PP) by phytoplankton in the Arctic Ocean from 1998 to 2010. Several PP retrieval algorithms were tested against the collected in situ data, and it was shown that the algorithm by Behrenfeld and Falkowski gave the best results (with the coefficient of correlation, r, equal to 0.8 and 0.75, respectively, for the pelagic and shelf zones). Based on the performed test, the Behrenfeld and Falkowski algorithm was further applied for determining both the annual PP in the Arctic and the PP trend over the above-mentioned time period. Results of our analysis indicate that PP in the Arctic has increased by ˜15.9% over 13 years (1998–2010). This finding, as well as the absolute annual values of PP remotely quantified in the present study, is at odds with analogous numerical assessments by other workers. These disagreements are thought to be due to differences in the applied methodologies of satellite data processing such as cloud masking and determination of phytoplankton concentration within (1) overcast areas and (2) areas of massive growth of coccolithophores as well as (3) in the shelf zone prone to a significant influence of land and river run-off.

Dataset of CarboEastAsia and uncertainties in the CO2 budget evaluation caused by different data processing

The datasets of net ecosystem CO2 exchange (NEE) were acquired from 21 forests, 3 grasslands, and 3 croplands in the eastern part of Asia based on the eddy covariance measurements of the international joint program, CarboEastAsia. The program was conducted by three networks in Asia, ChinaFLUX, JapanFlux, and KoFlux, to quantify, synthesize, and understand the carbon budget of the eastern part of Asia. An intercomparison was conducted for NEE estimated by three gap-filling procedures adopted by ChinaFLUX, JapanFlux, and KoFlux to test the range of uncertainty in the estimation of NEE. The overall comparison indicated good agreement among the procedures in the seasonal patterns of NEE, although a bias was observed in dormant seasons depending on the different criteria of data screening. Based on the gap-filled datasets, the magnitude and seasonality of the carbon budget were compared among various biome types, phenology, and stress conditions throughout Asia. The annual values of gross primary production and ecosystem respiration were almost proportional to the annual air temperature. Forest management, including clear-cutting, plantation, and artificial drainage, was significant and obviously affected the annual carbon uptake within the forests. Agricultural management resulted in notable seasonal patterns in the crop sites. The dataset obtained from a variety of biome types would be an essential source of knowledge for ecosystem science as well as a valuable validation dataset for modeling and remote sensing to upscale the carbon budget estimations in Asia.

Development and application of a phytoplankton primary production model for well-mixed lakes

For estimations of the ecological state of a lake and its future trends, data on seasonal and long-term variations of primary production are most necessary. The methods of in situ measurements of production are time consuming, rather complicated, and very expensive. Bio-optical model calculations provide a good alternative here. A semi-empirical model for estimating phytoplankton primary production (Arst et al., 2008, Aquatic Biology, Vol. 3, No. 1, pp. 19-30) allows calculating the vertical profiles and areal (integrated over water column) values of primary production using chlorophyll a concentration, incident irradiance, and light attenuation coefficient in the water. In the present study this model was developed further by elaborating its automated version. It enables performing rapid and greatly replicated estimations of the circumstantial variability of phytoplankton primary production at hourly intervals from morning to evening and as daily and monthly sums based on a table of initial parameters and depths. For demonstrating the practical application of the model we calculated primary production in two large eutrophic North-European lakes (Vortsjarv and Peipsi), using a database collected during four warm months in 2009 (123 days in both lakes).

Balancing trade-offs between biodiversity and production in the re-design of rangeland landscapes

The conflict that exists between the competing needs of biological conservation and pastoral production is well recognised but few studies have examined these conflicts due to their complexity and the uncertainty that surrounds these relationships. The development of a Bayesian network model that examines the trade-offs between the conservation value of the landscape for a range of taxa (flora, mammals, birds and herpetofauna) and its primary production value under alternative land uses is described. The model emphasises structural diversity of vegetation and ecosystem productivity as key drivers of both biodiversity and agricultural production. Simple scenarios, used to examine the influence of different land uses on multiple components of biodiversity and agricultural productivity, demonstrated the potential for the analysis of the trade-offs associated with alternative landscape designs. The potential of the model, as a planning or policy development tool for land management agencies or regional Natural Resource Management bodies, at multiple scales, is identified.

Trophic interactions, ecosystem structure and function in the southern Yellow Sea

The southern Yellow Sea is an important fishing ground, providing abundant fishery resources. However, overfishing and climate change have caused a decline in the resource and damaged the ecosystem. We developed an ecosystem model to analyze the trophic interactions and ecosystem structure and function to guide sustainable development of the ecosystem. A trophic mass-balance model of the southern Yellow Sea during 2000–2001 was constructed using Ecopath with Ecosim software. We defined 22 important functional groups and studied their diet composition. The trophic levels of fish, shrimp, crabs, and cephalopods were between 2.78 and 4.39, and the mean trophic level of the fisheries was 3.24. The trophic flows within the food web occurred primarily in the lower trophic levels. The mean trophic transfer efficiency was 8.1%, of which 7.1% was from primary producers and 9.3% was from detritus within the ecosystem. The transfer efficiency between trophic levels II to III to IV to V to >V was 5.0%, 5.7%, 18.5%, and 19.7%–20.4%, respectively. Of the total flow, phytoplankton contributed 61% and detritus contributed 39%. Fishing is defined as a top predator within the ecosystem, and has a negative impact on most commercial species. Moreover, the ecosystem had a high gross efficiency of the fishery and a high value of primary production required to sustain the fishery. Together, our data suggest there is high fishing pressure in the southern Yellow Sea. Based on analysis of Odum’s ecological parameters, this ecosystem was at an immature stage. Our results provide some insights into the structure and development of this ecosystem.

Effects of shrimp pond water on phytoplankton: importance of salinity and trophic status of the receiving environment

Aquaculture generates a large load of effluents rich in organic matter and nutrients that may be introduced into the environment. This study aimed to assess in a microcosm experiment, the effect of shrimp pond water mixed with Patos Lagoon estuary water on phytoplankton chlorophyll a and primary production, simulating two salinities. Chlorophyll a, dissolved inorganic nutrients and primary production were measured in two experiments. In Harvest I, salinity of shrimp pond and environment water was similar, and chlorophyll a showed different trends over time, according to the amount of nitrogen available. In Harvest II, with different salinities and high nutrient concentrations in environment water, chlorophyll a levels showed a similar increasing trend over time in all mixtures. Net primary production showed differences among treatments in the first sampling in Harvest I, but not in the second, whereas no differences were observed among treatments in Harvest II. We conclude that shrimp pond effluent can lead to short-term variations in chlorophyll a and primary production levels, with similar salinities. Salinity differences result in lower chlorophyll a and primary production values than expected according to the nutrient input. Differences in salinity can be an important management strategy to choose the best harvest period.

Estimates of New and Total Productivity in Central Long Island Sound from In Situ Measurements of Nitrate and Dissolved Oxygen

Biogeochemical cycles in estuaries are regulated by a diverse set of physical and biological variables that operate over a variety of time scales. Using in situ optical sensors, we conducted a high-frequency time-series study of several biogeochemical parameters at a mooring in central Long Island Sound from May to August 2010. During this period, we documented well-defined diel cycles in nitrate concentration that were correlated to dissolved oxygen, wind stress, tidal mixing, and irradiance. By filtering the data to separate the nitrate time series into various signal components, we estimated the amount of variation that could be ascribed to each process. Primary production and surface wind stress explained 59 and 19 %, respectively, of the variation in nitrate concentrations. Less frequent physical forcings, including large-magnitude wind events and spring tides, served to decouple the relationship between oxygen, nitrate, and sunlight on about one quarter of study days. Daytime nitrate minima and dissolved oxygen maxima occurred nearly simultaneously on the majority (>80 %) of days during the study period; both were strongly correlated with the daily peak in irradiance. Nighttime nitrate maxima reflected a pattern in which surface-layer stocks were depleted each afternoon and recharged the following night. Changes in nitrate concentrations were used to generate daily estimates of new primary production (182 ± 37 mg C m−2 day−1) and the f ratio (0.25), i.e., the ratio of production based on nitrate to total production. These estimates, the first of their kind in Long Island Sound, were compared to values of community respiration, primary productivity, and net ecosystem metabolism, which were derived from in situ measurements of oxygen concentration. Daily averages of the three metabolic parameters were 1,660 ± 431, 2,080 ± 419, and 429 ± 203 mg C m−2 day−1, respectively. While the system remained weakly autotrophic over the duration of the study period, we observed very large day-to-day differences in the f ratio and in the various metabolic parameters.

The relationship between satellite-derived primary production and vertical mixing and atmospheric inputs in the Yellow Sea cold water mass

This study examined the spatiotemporal distribution of primary production and its relationship with climatic and environmental factors in the south Yellow Sea Cold Water Mass (YSCWM) from January 1998 to December 2007. Primary production was estimated from satellite ocean color data. The annual primary production cycle was characterized by two peaks: a larger one in April (spring) and a smaller one in November (fall). The first empirical orthogonal function (EOF) mode of monthly primary production showed that two peaks occurred separately in spring and fall most years and two high primary production regions appeared in the middle of the YSCWM. The first EOF mode of monthly and spring primary production revealed a high primary production value in spring 2006. Correlation and multiple linear regression analyses suggested that primary production was influenced by the mixed layer depth (MLD), upward sea water velocity, aerosol index, and precipitation. The consistency between the first EOF mode of spring primary production and the aerosol index suggested that Asian dust events are important in the interannual variation of primary production in spring, especially in 2006.

Assessment of MODIS imagery to track light-use efficiency in a water-limited Mediterranean pine forest

Daily values of gross primary production (GPP) derived from an eddy-covariance flux tower have been used to analyze the information content of the MODIS Photochemical Reflectance Index (PRI) on the light-use efficiency (ε). The study has been conducted in a Mediterranean Pinus pinaster forest showing summer water stress. Advanced processing techniques have been used to analyze the effect of various external factors on ε and PRI temporal variations. The intra-annual correlation between these two variables has been found to be mostly attributable to concurrent variations in sun and view zenith angles. The PRI has been normalized from these angular effects (NPRI), and its ability to track ecosystem ε response to prolonged summer water limitations has been analyzed. The observed shift between ε and NPRI reveals that, for the study area and at MODIS spatial resolution, NPRI is informative on changes in pigments and canopy structure related to the vegetation response to prolonged water stress.