The Radiocarbon Method to Estimate Primary Production in Aquatic Environments

Diffusive limitation of C and nutrient uptake can be an important factor regulating metabolic processes in aquatic plants. Relationships between the flow regime and both primary productivity and nitrogenase activity (ethylene production) of coral reef algal components were studied via a productivity chamber that simulates oscillatory flow. Net primary productivity of algal turfs was increased significantly by flow speeds (steady flow equivalent) up to 16 cm s−1. The mode of water flow also was important; primary productivity of algal turfs increased by 21% under an oscillatory flow regime as compared to vortex flow created by stirring. Acanthophora spicifera exhibited increased primary productivity at flow speeds up to 10 cm s−1, while primary productivity of another rhodophyte, Coelothrix irregularis, increased up to 4 cm s−1. Rates of nitrogenase activity exhibited by algal turfs also were affected significantly by flow speed. These data indicate that diffusive limitation is important to varying degrees in reef algal turfs and macroalgae and suggest that primary productivity and rates of nitrogenase activity depend on ambient flow speeds and boundary‐layer dynamics.

All biological systems exist as a result of continual inputs of energy to maintain structure and order. At the scale of the ecosystem, most of this energy comes from sunlight, which is converted into the energy of organic matter in living biomass through the process of primary production, and from imports of organic matter from adjacent ecosystems. This import of energy in organic matter is, of course, dependent upon primary production in the “upstream” ecosystem. Thus, a critical aspect of understanding the functioning of an ecosystem is an accurate estimate of its rate of primary production.

The relationship between primary productivity and diversity has been demonstrated across taxa and spatial scales, but for organisms with biphasic life cycles, little research has examined whether productivity of larval and adult environments influence each life stage independently, or whether productivity of one life stage's environment outweighs the influence of the other. Experimental work demonstrates that tadpoles of stream-breeding anurans can exhibit a top-down influence on aquatic primary productivity (APP), but few studies have sought evidence of a bottom-up influence of primary productivity on anuran abundance, species richness and community composition, as seen in other organisms. We examined aquatic and terrestrial primary productivity in two forest types in Borneo, along with amphibian abundance, species richness, and community composition at larval and adult stages, to determine whether there is evidence for a bottom-up influence of APP on tadpole abundance and species richness across streams, and the relative importance of aquatic and terrestrial primary productivity on larval and adult phases of anurans. We predicted that adult richness, abundance, and community composition would be influenced by terrestrial primary productivity, but that tadpole richness, abundance, and community composition would be influenced by APP. Contrary to expectations, we did not find evidence that primary productivity, or variation thereof, predicts anuran richness at larval or adult stages. Further, no measure of primary productivity or its variation was a significant predictor of adult abundance, or of adult or tadpole community composition. For tadpoles, we found that in areas with low terrestrial primary productivity, abundance was positively related to APP, but in areas with high terrestrial primary productivity, abundance was negatively related to APP, suggesting a bottom-up influence of primary productivity on abundance in secondary forest, and a top-down influence of tadpoles on primary productivity in primary forest. Additional data are needed to better understand the ecological interactions between terrestrial primary productivity, aquatic primary productivity, and tadpole abundance.

Vertebrate populations throughout the circumpolar north often exhibit cyclic dynamics, and predation is generally considered to be a primary driver of these cycles in a variety of herbivore species. However, weather and climate play a role in entraining cycles over broad landscapes and may alter cyclic dynamics, although the mechanism by which these processes operate is uncertain. Experimental and observational work has suggested that weather influences primary productivity over multi-year time periods, suggesting a pathway through which weather and climate may influence cyclic herbivore dynamics. Using long-term monitoring data, we investigated the relationships among multi-year weather conditions, measures of primary productivity, and the abundance of two cyclic herbivore species: snowshoe hare and northern red-backed vole. We found that precipitation (rain and snow) and growing season temperatures were strongly associated with variation in primary productivity over multi-year time horizons. In turn, fourfold variation in the amplitude of both the hare and vole cycles observed in our study area corresponded to long-term changes in primary productivity. The congruence of our results for these two species suggests a general mechanism by which weather and climate might influence cyclic herbivore population dynamics. Our findings also suggested that the association between climate warming and the disappearance of cycles might be initiated by changes in primary productivity. This work provides an explanation for observed influences of weather and climate on primary productivity and population cycles and will help our collective understanding of how future climate warming may influence these ecological phenomena in the future.

Differences in phytoplankton community composition along a riverine to freshwater tidal continuum was an important factor affecting the primary productivity and quantity of phytoplankton biomass available to the San Francisco Estuary food web downstream. The relative contribution of riverine and freshwater tidal phytoplankton was determined using measurements of primary productivity, respiration, and phytoplankton species composition along a riverine to freshwater tidal gradient in the San Joaquin River, one of two major rivers that flow into the San Francisco Estuary. Chl a-specific net primary productivity was greater in the freshwater tidal habitat and was correlated with both a higher growth efficiency and maximum growth potential compared with the river upstream. Cluster analysis indicated these differences in growth parameters were associated with differences in species composition, with greater percent diatom and green algal species biomass upstream and flagellate biomass downstream. Correlation between the chl a specific net productivity and phytoplankton species composition suggested the downstream shift from riverine diatom and green algal species to flagellate species contributed to the seaward increase in net primary productivity. Environmental conditions, such as specific conductance and water transparency, may have influenced primary productivity along the riverine to freshwater tidal continuum through their effect on both species composition and growth rate. Data suggest light was not the sole controlling factor for primary productivity in this highly turbid estuary; phytoplankton growth rate did not increase when riverine plankton communities from low light conditions upstream were exposed to higher light conditions downstream. This study suggests that the availability of phytoplankton biomass to the estuarine food web may be influenced by management of both phytoplankton growth and community composition along the riverine to freshwater tidal continuum.

Abstract. Polar systems are undersampled due to the difficulty of sampling remote and challenging environments; however, these systems are critical components of global biogeochemical cycles. Measurements on primary productivity in specific areas can quantify the input of organic matter to food webs and so are of critical ecological importance as well. However, long-term measurements using the same methodology are available only for a few polar systems. Primary productivity measurements using 14C-uptake incubations from the Ross Sea, Antarctica, are synthesized, along with chlorophyll concentrations at the same depths and locations. A total of 19 independent cruises were completed and 449 stations occupied where measurements of primary productivity (each with seven depths) were completed. The incubations used the same basic simulated in situ methodology for all. Integrated water column productivity for all stations averaged 1.10 ± 1.20 g C m−2 d−1, and the maximum was 13.1 g C m−2 d−1. Annual productivity calculated from the means throughout the growing season equalled 146 g C m−2 yr−1. The mean chlorophyll concentration in the euphotic zone (the 1 % irradiance level) was 2.85 ± 2.68 mg m−3 (maximum observed concentration was 19.1 mg m−3). Maximum photosynthetic rates above the 30 % isolume (normalized to chlorophyll) averaged 0.98 ± 0.71 mg C (mg chl)−1 h−1, similar to the maximum rate found in photosynthesis–irradiance measurements. Productivity measurements are consistent with the temporal patterns of biomass found previously, with biomass and productivity peaking in late December; mixed layers were at a minimum at this time as well. Estimates of plankton composition also suggest that pre-January productivity was largely driven by the haptophyte Phaeocystis antarctica and summer productivity by diatoms. The data set (https://doi.org/10.26008/1912/bco-dmo.863815.2, Smith, 2021) will be useful for a comparison to other Antarctic regions and provide a basis for refined bio-optical models of regional primary productivity and biogeochemical models for the Southern Ocean.

While terrestrial biomes are routinely defined by their dominant vegetation structure and coupled primary productivity regimes, connecting primary productivity regimes with the properties of aquatic vegetation in rivers is uncommon. Gross primary production (GPP) and ecosystem respiration (ER) indicate riverine ecosystem processes that are useful for monitoring river response to human alterations, global change, and restoration, but how aquatic vegetation structure and biomass influence GPP and ER is poorly known. We related patterns in the time series of daily GPP and ER to submerged aquatic vegetation biomass at 11 reaches on the Klamath River, California, downstream of four dams prior to their removal in 2024. Rooted macrophytes dominated vegetation assemblages at upriver sites and transitioned to filamentous algae downriver. Fluxes of GPP and ER were high compared to those of other rivers, with the magnitude and timing of mean ER, mean GPP, peak GPP, GPP variability, and green-up varying among sites. While total autotrophic biomass correlated strongly with mean summer GPP ( 0.80), evidence of macrophytes driving mean summer GPP was weaker ( 0.60). Relationships between mean summer ER and macrophyte biomass and total autotrophic biomass ( 0.93 and 0.87, respectively) were stronger than relationships between biomass and GPP. This strong relationship between ER and biomass was due to ER increasing late in summer, possibly because respiration of autotrophic biomass produced earlier in the season, or from vegetation structure creating patches of increased respiration of imported or stored carbon. Assessments of relationships between submerged aquatic vegetation and river metabolism may help inform predictions about changing ecosystem structure and function that influence water quality, including ecosystem response to the removal of four large hydroelectric dams on the Klamath River.

Variable fluorescence techniques are increasingly used to assess phytoplankton photosynthesis. All fluorescence techniques and models for photosynthetic electron transport rates (ETRs) are amplitude‐based and are subject to errors, especially when phytoplankton growth is nutrient‐limited. Here we develop a new, kinetic‐based approach to measure, directly and in absolute units, ETRs and to estimate growth rates in phytoplankton. We applied this approach to investigate the effects of nitrogen limitation on phytoplankton photophysiology and growth rates. Nutrient stress leads to a decrease in the quantum yield of photochemistry in Photosystem II (Fv/Fm); however, the relationship between Fv/Fm and growth rates is highly nonlinear, which makes it impossible to quantify the reduction in phytoplankton growth rates from Fv/Fm alone. In contrast, the decline in growth rates under nitrogen stress was proportional to the decrease in kinetic‐based photosynthetic rates. Our analysis suggests the kinetic fluorescence measurements markedly improve the accuracy of ETR measurements, as compared to classical amplitude‐based measurements. Fluorescence‐based methods for primary production rely on measurements of ETRs and then conversion to carbon fixation rates by using the electron yields of carbon fixation. The electron yields exhibit 10‐fold variability in natural phytoplankton communities and are strongly affected by nutrient limitation. Our results reveal that a decrease in the growth rates and the electron yields of carbon fixation is driven by, and can be quantified from, a decrease in photosynthetic turnover rates. We propose an algorithm to deduce the electron yields of carbon fixation, which greatly improve fluorescence‐based measurements of primary production and growth rates.

Eutrophication is a serious environmental and economic problem in coastal marine ecosystems worldwide. It has recently been recommended that measurements of primary productivity, being a sensitive and accurate indicator of eutrophication, should be mandatory when monitoring and assessing the ecological status of coastal waters. The units of primary productivity chosen for eutrophication assessment will be very important because not all measures of primary productivity vary monotonically (or even straightforwardly) with changes in aquatic fertility. Volumetric expressions of primary productivity (rates of carbon fixation per unit volume of seawater) may prove to be the most sensitive and most reliable measures to use when evaluating the eutrophication status of coastal marine ecosystems. Another potential measure of primary productivity, the light-saturated rate of photosynthesis per unit Chlorophyll a (P:BChl) ratio, is unsuitable for the assessment of aquatic ecosystem responses to nutrient enrichment.

The report “Net primary production of a forest ecosystem with experimental CO2 by enrichment” by E.H. DeLucia et al. (14 May, p. [1177][1]) provides excellent and much-needed experimental work on the responses of the terrestrial biosphere to elevated atmospheric carbon dioxide (CO2). However, we are concerned about the report's last statement (also appearing in the abstract), which extrapolates measurements of net primary production (NPP) from this one experiment to the world's forests as a whole, suggesting that they could absorb as much as 50% of the projected fossil fuel emissions of CO2 in 2050. This projection gives a misleading, perhaps erroneous, picture of the role of the terrestrial biosphere in the global carbon cycle. First, NPP is not the appropriate measurement to apply when considering the net uptake (or release) of CO2 by the terrestrial biosphere on a biome or larger spatial scale and over several decades. The most appropriate concept is net biome production (NBP) ([1][2]), which includes not only NPP, but also losses of carbon resulting from heterotrophic respiration, fires, insect-induced mortality, logging, and other natural and human-induced disturbances ([2][3]). In contrast to global terrestrial NPP, which is about 60 picograms of carbon per year, global terrestrial NBP is about ± 1 or 2 picograms per year. Second, there is considerable difficulty in extrapolating up in time and space from a single experiment based on a step-change in CO2 concentration over a young, rapidly growing stand of trees, as noted by the authors of the report immediately before the final statement. Third, applying the same methodology for extrapolation as used in this report, we conclude that the world's forests should now be taking up at least 3 picograms of carbon per year of fossil-fuel emissions. This is significantly higher than current estimates of terrestrial carbon sequestration [for example, ([3][4])] and is inconsistent with atmospheric inverse calculations, as well as with estimates of oceanic carbon uptake. In the current, post-Kyoto international political climate, scientific statements about the behavior of the terrestrial carbon cycle must be made with care, especially extrapolations from stand-level experiments or observations. 1. [↵][5]1. J.N. Galloway, 2. J.M. Melillo 1. E.D. Schulze, 2. M. Heimann , in Asian Change in the Context of Global Change, J.N. Galloway, J.M. Melillo, Eds. (Cambridge Univ. Press, Cambridge, 1998), pp. 145-161 (No. 3, IGBP Book Series,. 2. [↵][6]1. IGBP Terrestrial Carbon Working Group , Science 280, 1393 (1998). [OpenUrl][7][Abstract/FREE Full Text][8] 3. [↵][9]1. D.S. Schimel , Global Change Biol. 1, 77 (1995). [OpenUrl][10] # Effect on the Biosphere of Elevated Atmospheric CO2 {#article-title-2} NPP is the difference between total, annually integrated photosynthesis (gross primary production) and plant respiration and therefore represents the rate of carbon uptake from the atmosphere by ecosystems ([1][2]). By assuming that all forests of the world are similar to our young, fast-growing stand of loblolly pine, we attempted to constrain an estimate of the maximum net increment of NPP when the atmosphere contains 560 parts per million of CO2. Our value for forest uptake, 50% of the anticipated CO2 emissions from fossil fuels in the year 2050, indicates that forests will not solve the global warming problem for us. And, as Bolin et al. indicate, actual long-term carbon storage will be much less than NPP, owing to the activity of soil microbes, fires, human land-use changes, and so forth, which act to return CO2 to the atmosphere. 1. 1. W.H. Schlesinger , Biogeochemistry (Academic Press, San Diego, CA, 1997). [1]: /lookup/doi/10.1126/science.284.5417.1177 [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: #xref-ref-1-1 View reference 1 in text [6]: #xref-ref-2-1 View reference 2 in text [7]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.issn%253D0036-8075%26rft.aulast%253DIGBP%2BTerrestrial%2BCarbon%2BWorking%2BGroup%26rft.auinit1%253D%2B%26rft.volume%253D280%26rft.issue%253D5368%26rft.spage%253D1393%26rft.epage%253D1394%26rft.atitle%253DCLIMATE%253A%2B%2BThe%2BTerrestrial%2BCarbon%2BCycle%253A%2BImplications%2Bfor%2Bthe%2BKyoto%2BProtocol%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.280.5368.1393%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [8]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEzOiIyODAvNTM2OC8xMzkzIjtzOjQ6ImF0b20iO3M6MjU6Ii9zY2kvMjg1LzU0MzUvMTg0OS45LmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ== [9]: #xref-ref-3-1 View reference 3 in text [10]: {openurl}?query=rft.jtitle%253DGlobal%2BChange%2BBiol.%26rft.volume%253D1%26rft.spage%253D77%26rft.atitle%253DGLOBAL%2BCHANGE%2BBIOL%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx

Resulting from synecological studies in some areas of the southern North Sea, a contradiction becomes evident between measurements of primary production and determinations of the activities consuming organic matter. In the Southern Bight, the consumption in 10 times higher than the production. This means that the primary production has been underestimated, and/or the consumption over-estimated. In order to discuss the validity of the methods used for determining the respiration activities, some results are presented: (a) during a 24-h cycle at the Sluice-Dock of Ostend, the variations of the oxygen concentration in the water are explained by the measured activities and diffusion fluxes; (b) two different methods are shown to give comparable results: the initial rate of oxygen consumption and the anaplerotic fixation of CO2. The other possible sources of error lie mainly in the extrapolations ones has to make in order to establish a general budget: (a) extrapolation in time is very difficult because of important variations of organic matter and respiration activities to be observed during a 24-h cycle; (b) extrapolation in function of the depth does not seem very difficult in the case of shallow, entirely mixed water masses. No argument was found against the validity of the methods used for the determination of respiration activities. Therefore, the question remains open as to which parameters are over-estimated or under-estimated by actual methods.

Primary production and consumption of organic matter in the southern North Sea during the spring bloom of 1975

Aquatic mosses are important primary producers in High-Arctic lakes, but little information is available on their contribution to the overall production in these lakes. In order to predict effects of climate change on whole-lake ecosystem characteristics, more knowledge is needed on the role of moss in primary production, the extent of nutrient limitation of moss primary production and whether moss serves as food resource for secondary producers. In this study, we conducted an in situ growth experiment of an aquatic moss in a High-Arctic lake in NE Greenland and used these data to determine annual net production of this moss in the whole lake. We also measured tissue-N and tissue-P in order to assess nutrient limitation of moss production, measured in situ decomposition rates by litter bag experiments over 1 year and assessed the role of moss as food source by analysing stable isotope 15N and 13C of relevant organism groups in the lake. Net primary production of moss was 1.3 gC m−2 year−1 and constituted 23 % of the total benthic primary production and 18 % of the total lake primary production. Stoichiometric assessments suggested N and P limitation of moss growth. On average, 15 % of the standing biomass was decomposed per year. Our results also indicate that moss is not directly used as food resource by herbivores, but the most abundant herbivore, Lepidurus arcticus, is feeding on the epiphytic biofilm on the moss. Moss biomass is instead incorporated into the microbial decomposer pathway. All together, the study shows that moss plays an important ecological role as primary producer in High-Arctic lakes and functions as substrate for periphytic biofilm that serves as food resource for important herbivore invertebrates.

Although most pasture growth models simulate many above‐ and belowground components of the plant community, calibration and validation are usually based only on periodic measurements of aboveground forage yield. This research used daily measurements of gross primary productivity (GPP) to validate the photosynthesis subroutine of the Integrated Farm System Model (IFSM). The model was calibrated for a pasture grazed by beef cattle (Bos taurus) in 2003, then validated with data from 2004 through 2006. Predicted and observed annual yield differed by 14 ± 9%, whereas predicted GPP differed from observed GPP by only 7 ± 3%. Seasonal trends in GPP were also adequately simulated, although a slight overestimation in the spring and early‐summer and underestimation in the later half of the year occurred. Overestimation occurred when wintertime temperatures were above freezing or when N availability was high following fertilizer application. Late‐season underestimation was related to low soil N availability which resulted from excessive N uptake by plants earlier in the year. Only minor adjustments in model structure were needed to improve simulation of GPP. Most adjustments involved changes in parameter values, many of which are often difficult to find or lacking in the literature. Refinement of models to accurately simulate the seasonal distribution of physiological parameters such as GPP will help ensure that model structures correctly represent the true dynamics of C assimilation and pasture growth.

The purpose of this paper is to upscale tower measurements of net primary productivity (NPP) to the Boreal Ecosystem‐Atmosphere Study (BOREAS) study region by means of remote sensing and modeling. The Boreal Ecosystem Productivity Simulator (BEPS) with a new daily canopy photosynthesis model was first tested in one coniferous and one deciduous site. The simultaneous CO2 flux measurements above and below the tree canopy made it possible to isolate daily net primary productivity of the tree canopy for model validation. Soil water holding capacity and gridded daily meteorological data for the region were used as inputs to BEPS, in addition to 1 km resolution land cover and leaf area index (LAI) maps derived from the advanced very high resolution radiometer (AVHRR) data. NPP statistics for the various cover types in the BOREAS region and in the southern study area (SSA) and the northern study area (NSA) are presented. Strong dependence of NPP on LAI was found for the three major cover types: coniferous forest, deciduous forest and cropland. Since BEPS can compute total photosynthetically active radiation absorbed by the canopy in each pixel, light use efficiencies for NPP and gross primary productivity could also be analyzed. From the model results, the following area‐averaged statistics were obtained for 1994: (1) mean NPP for the BOREAS region of 217 g C m−2 yr−1; (2) mean NPP of forests (excluding burnt areas in the region) equal to 234 g C m−2 yr−1; (3) mean NPP for the SSA and the NSA of 297 and 238 g C m−2 yr−1, respectively; and (4) mean light use efficiency for NPP equal to 0.40, 0.20, and 0.33 g C (MJ APAR)−1 for deciduous forest, coniferous forest, and crops, respectively.