Thesis (Ph. D.)--University of Rhode Island, 2005. / Typescript. Includes bibliographical references (leaves 253-257).

Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 142-152). Also available on the World Wide Web.

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Terrestrial ecosystems provide a substantial carbon sink that helps mitigate climate change, sequestering roughly 30% of anthropogenic carbon emissions annually. However, the long-term future of this sink is not well understood. In this dissertation, I use satellite remote sensing, in-situ measurements, and models to improve understanding of the nature and magnitude of spatial and temporal variation in the primary productivity of Eastern Deciduous Forests of the United States. In my first research chapter, I use remote sensing to model to the phenology of two key variables that control forest productivity: leaf area index (LAI) and the fraction of absorbed photosynthetically active radiation (fAPAR). Results show that the relationship between remotely sensed vegetation indices and both LAI and fAPAR is strongly influenced by systematic variation in near infrared reflectance arising from seasonal changes in canopy shadow fraction that are independent of physical changes in forest canopy properties. In my second research chapter, I use estimates of gross primary production (GPP) derived from eddy covariance measurements at four temperate deciduous sites to model the phenology and controls on light use efficiency (LUE) within and across sites. Results show that multiple modes of variation in incoming radiation dominate daily and seasonal variation in LUE, and provide a refined basis for understanding how variability in environmental controls affect LUE and how the strength of these drivers change throughout the growing season. In my third research chapter, I use the long-term record of Landsat imagery, in-situ phenological observations, and estimates of GPP derived from eddy covariance measurements at two temperate deciduous forest sites to investigate how phenology controls interannual variability in GPP at these sites. Results demonstrate that phenology metrics derived from remote sensing are consistent with in-situ measurements, and that interaction between the timing of growing season anomalies and incoming radiation explains a significant proportion of interannual variation in GPP. Taken together, results from this dissertation demonstrate how variation in phenology and LUE control variation in deciduous forest productivity, which is essential for reducing uncertainty in how future climate changes will impact the carbon budget of deciduous forest ecosystems.

Rates of primary production and community metabolism were monitored over a one year period using the diurnal oxygen method. Certain physico-chemical parameters were also measured, and autotrophic standing crops were estimated. An in-depth study was made of the phytoplankton community and various diversity indicies were calculated. Simple correlations were run between all parameters measured (biotic and abiotic), and their inter-relationships examined. Multiple linear regression analyses were used to develop equations predictive of production and community metabolism. Bluegreen algae were the dominant phytoplankters with blooms occurring in late summer and fall. Yearly mean production was approximately 21 kcal per meter square per day with a mean photosynthetic efficiency of 1.2 per cent. Of the various parameters measured turbidity and water temperature were most important in determining rates of primary production.

Leaf traits have long been used to classify and characterise species in natural ecosystems. In addition, leaf traits provide important information about plants’ strategies for the use of resources and can be used to improve our understanding of ecosystem level processes such as nutrient cycling and carbon allocation. To explore the linkages between leaf traits and productivity, we worked in two resource-limited ecosystems (a grassland and a forest), and used leaf traits to understand how species respond to changes in available resources and their relationship to ecosystem processes. We worked in a species rich limestone-grassland located in central England, which has been subjected to long-term climatic manipulation (winter warming, summer drought and extra summer rainfall). We characterised species composition in terms of their identity, abundance and leaf structural properties (nitrogen content and leaf mass per area (LMA)) in the main treatments and the control. We found that change in species abundance was the most important factor to understand the differences in productivity (above ground biomass and total foliar nitrogen). We then measured CO2 exchange at ecosystem level, using a chamber technique, and assessed the treatments’ effect on the gross primary productivity (GPP) and ecosystem respiration (Reco). GPP and Reco were controlled by soil moisture and above ground biomass but also influenced by the conditions experienced during the growing season prior to the measuring period. Our second location was a post-disturbance chronosequence in a seasonally dry tropical forest in Costa Rica and we used leaf level gas exchange measurements to explore the role of nitrogen (N) and phosphorus (P) on the temporal-spatial variation of photosynthesis of dominant species. We found that photosynthetic efficiency was strongly linked to leaf N and P content, but that there was an important seasonal pattern on this relationship likely associated to P remobilization. Additionally we found seasonal changes in resources (water, nutrients) had a larger impact on the photosynthetic parameters than changes along the chronosequence. The two ecosystems studied for this thesis are contrasting in their physiognomy, species composition and climate, but are also characterised by species whose structural traits (high LMA and high C:N ratio) are likely to have a significant impact on the nutrient cycling processes. We learned that leaf traits provide important information about species strategies and their usage of resources and they can also aid to address questions at ecosystem level in time and space, either through simple aggregation or as emergent properties. Additionally, the traits explored are important input information to up-scale processes from leaf to the ecosystem level, a step needed to address the effect changes in resources will have on the seasonally dry tropical forest and grasslands, which represent a significant fraction of the total global carbon storage.

The overall aim of the study was to provide better insights to the ecological role and impact of cyanobacteria in Baltic Sea (BS) bay, coastal and open sea areas. Biomass and heterocyst development of diazotrophic, heterocystous cyanobacteria were monitored over several years simultaneously as physical parameters such as nutrients and temperature. Nitrogen fixation was estimated as well as its transfer in the BS food web. Even after decades of debate there is still controversy whether eutrophication of lakes and estuaries/coastal areas should be managed by reducing phosphorus only or also nitrogen. Central to this debate is whether nitrogen fixation by cyanobacteria can replace shortages of combined nitrogen quickly enough to make phosphorus the limiting nutrient and nitrogen removal pointless or even harmful. Also, it is not clear if available combined nitrogen inhibits heterocystous cyanobacterial nitrogen fixation and if it is used for their growth in situ. A large ecosystem-wide experiment started in Himmerfjärden bay in year 1997, where the N-loadings and release depth from a modern sewage treatment plant (STP), located in the inner part of the bay, were modulated. The STP creates a steep gradient of nutrients and stable nitrogen isotopes, which can be used to study uptake of combined nitrogen, as well as biomass development and primary productivity. A 35-year long data series was used to achieve good insights into phytoplankton development and primary productivity in the Baltic Sea over the last couple of decades. These in vivo long time series, based on monitoring data, in combination with shorter series (2-3 seasons, including measurements of colony stoichiometry and stable isotopes), have resulted in a unique meta-dataset, allowing for high-resolution observations into the role of the cyanobacteria in the Baltic Sea ecosystem. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

In this study, the relationship of above-ground net primary productivity (ANPP) with precipitation using the enhanced vegetation index (EVI) from satellite data as surrogate for ANPP was assessed. To use EVI as a proxy for ANPP we extracted the satellite data from areas with uniform vegetation in a 2x2 km area for the multi-site approach.In the multi-site analysis in the United States our results showed a strong exponential relationship between iEVI and annual precipitation across the sites and climate regimes studied. We found convergence of all sites toward common and maximum rain use efficiency under the water-limited conditions represented by the driest year at each site. Measures of inter-annual variability in iEVI with rainfall variation across biomes were similar to that reported by Knapp and Smith (2001) in which the more herbaceous dominant sites were found to be most sensitive to interannual variations in precipitation with no relationships found in woodland sites.The relationship was also evaluated in the southern hemisphere using a multi-site analysis with information from satellite TRMM for precipitation and MOD13Q1 from MODIS for EVI values at calendar and hydrologic year periods. The tested sites were located across the 6 major land cover types inAustralia, obtained from MODIS MCD12Q1 product and used to compare the relationship across different biomes. The results showed significant agreement between the annual iEVI and annual precipitation across the biomes involved in this study showing non-significant differences between the calendar and hydrologic years for the 24 sites across different climatic conditions.At the regional scale we also assessed the ANPP-precipitation relationship across all of Australia. Precipitation data from TRMM was obtained at 0.25x0.25 degrees spatial resolution and monthly temporal resolution and EVI values were obtained from the CGM (Climate Grid Modeling) MOD13C1-16-days and 5.6km temporal and spatial resolutions, respectively. Our results were in fair agreement with those from our first two studies and previous research and provided specific insights regarding the use iEVI as a proxy for productivity over extended regions as well as its combination with data sets from TRMM sensor for precipitation data.

Under steady state conditions where the rate of biological oxygen production is balanced by oxygen evasion to the atmosphere, net community production (NCP) can be estimated from mixed layer oxygen/argon measurements. This method is effective in the open ocean but not in coastal zones where upwelling of low oxygen water violates the simple steady state assumption. Since these upwelling regions are highly productive, excluding them can lead to significant underestimations of global productivity. Here, I use a quasi-2D version of the Regional Ocean Modelling System (ROMS), including oxygen and argon as prognostic variables, to model the relationship between NCP and the sea-to-air flux of biological oxygen in a coastal upwelling system. The relationship between the sea-to-air flux of biological oxygen and NCP is poorest near the shore during upwelling favourable winds when waters that are undersaturated in oxygen reach the surface and depress the oxygen/argon ratio. I averaged NCP temporally and spatially over the residence time with respect to gas exchange and the Lagrangian motion of a water parcel. I found that the maximum distance travelled (∼25 km) over this time period indicated a distance from the upwelling plume at which much of the the low oxygen signal is erased. When the sea-to-air flux of biological oxygen was below 20 mmol m−2 day−1, NCP was usually also found in that range. Above that range the sea-to-air flux of biological oxygen is a lower bound for NCP. NCP occurring below the mixed layer can affect the sea-to-air flux of biological oxygen either by entrainment or diffusion into the mixed layer causing an overestimation of NCP, but this process had a minimal effect on most of my model data. Removing values with mixed layers deeper than 25 m improves the estimation, although further studies may reveal that this depth should be adjusted based on mean wind forcing. / Graduate / 0415

Production dynamics in the phytoplankton community of a mesotrophic Texas reservoir were measured weekly over a four month period using 14C incubation and ATP assay methodologies. Assimilation values of 14C ranged from 0.2 to 45 ug C 1 hr1 - . Significant positive and occasionally negative changes in biomass (i.e. viable organic carbon) were observed in short term (4 hr) in situ incubations juxtapo-sitioned with the 14C experiments; viable organic carbon production, estimated with the ATP assay, ranged from -25 to +50 ug C 1l1hr1. Carbon assimilation and biomass changes did not correlate in either short term (4-5 hr.) or over the study period (6 months). However, weekly biomass trends were predicted by relative positive or negative biomass changes in the short term incubations. Biomass measurements gave a more sensitive insight into production dynamics in the phytoplankton community than did carbon assimilation measurements.