Variance In Primary Production Research Articles

Nutricline adjustment by internal tidal beam generation enhances primary production in idealized numerical models

When the barotropic tide encounters variable bathymetry, fluctuating flow along a topographic slope generates baroclinic tides, or internal tides. There is growing evidence that these internal tides can affect primary production in the euphotic zone, though the dominant mechanisms are unclear. Internal tides move passive phytoplankton through an exponentially varying light field, enhancing primary production near the base of the euphotic zone. In addition internal tides also increase primary production through vertical nutrient advection into the euphotic zone. Topographically generated internal tides can be separated into two regimes: 1) the often highly nonlinear near-field regime where tidal beams are observed and 2) the more linear far-field regime. This study examines the primary production response to these internal tide processes using the Regional Ocean Modeling System (ROMS) coupled to a simple Nutrient, Phytoplankton, Zooplankton, Detritus (NPZD) model configured for an oligotrophic system with the nutricline positioned below 50 m depth. These idealized simulations generate internal tide beams with an oscillating, horizontal body force at the M2 tidal frequency that is applied to domains with a bathymetric step and uniform stratification. Sensitivity of the primary production response to the energy content of the tidal beam is obtained by adjusting the height and slope of the bathymetric step. Simulation results reveal that primary production intensifies along tidal beams due to the local enhancement of parcel vertical displacement (light effect) and nutrient advective flux divergence (nutrient effect). In the near-field regime across the range of step heights and slopes in this study, the nutrient effect is an order of magnitude larger and explains 92% of the variance in primary production versus only 14% for the light effect. The geometry of the generating feature sets the kinematics of the tidal beam. The light effect is limited in the euphotic zone across our domains because realized changes in light experienced over a tidal cycle are small relative to the amount of light available at a particular depth. In contrast, the magnitude of the nutrient effect increases more substantially with tidal beam energy.

Estimating the Suitability for the Reintroduced Arabian Oryx (Oryx leucoryx, Pallas 1777) of Two Desert Environments by NIRS-Aided Fecal Chemistry

The re-introduction paradigm is that Arabian Oryx (Oryx leucoryx) herds adjust the size of their home ranges depending on the availability of vegetation, which is directly related to rainfall. In Israel, Arabian oryx were released in two hyper-arid sites: the Arava Valley and in the Paran wilderness, belonging to the Sudanese and the Saharo–Arabian biogeographic zones, respectively. While post-release survival was similar in both, reproductive success in the Paran wilderness reintroduction site was extremely low, resulting in an acute decline of the reintroduced population over time. The hypothesis that impaired nutrition might be associated with this finding was assessed with near-infrared spectroscopy (NIRS)-aided chemistry of monthly sampled fecal pellets, used as remote sensing evidence of ingested diets, throughout a year. Fecal nitrogen (FN), used as an estimate of nutritional status, was consistently higher in the Arava. Grass was never the sole or even a major dietary component. The dietary contribution of tannin-rich browse was high and steady all year-round in the Arava and increased steadily in Paran from winter to summer, corresponding to the period of availability of Acacia raddiana pods in both regions. The oryx in Paran had a home-range that was ten-fold, compared to the Arava, suggesting less feed availability. Acacia browsing may mitigate the effects of temporal variance in primary production. Under such conditions, oryx should be preferably released in areas that support significant acacia stands.

Deciphering the past to inform the future: preparing for the next (“really big”) extreme event

Climate change will bring more extremes in temperature and precipitation that will impact productivity and ecosystem resilience throughout agroecosystems worldwide. Historical events can be used to identify drivers that impact future events. A catastrophic drought in the US in the 1930s resulted in an abrupt boundary between areas severely impacted by the Dust Bowl and areas that were less severely affected. Historical primary production data confirmed the location of this boundary at the border between two states (Nebraska and Iowa). Local drivers of weather and soils explained production responses across the boundary before and after the drought (1926–1948). During the drought, however, features at the landscape scale (soil properties and wind velocities) and regional scale (the Missouri River, its floodplain, and the nearby Loess Hills) explained most of the observed variance in primary production. The impact of future extreme events may be affected by land surface properties that either accentuate or ameliorate the effects of these events. Consideration of large‐scale geomorphic processes may be necessary to interpret and manage for catastrophic events.

Phytoplankton composition, photosynthesis and primary production during different hydrographic conditions at the Northwest Iberian upwelling system

The major hydrographic conditions along the NW Iberian Peninsula are upwelling and poleward current. Changes in prevailing winds create transitional hydrographic states such as down- welling, stratification and upwelling-downwelling relaxation. Four cruises were undertaken between 44.25 and 41.14° N during spring, summer and winter, when there was a clear demarcation of these hydrographic conditions. We studied the effects of hydrography on phytoplankton species composi- tion, photophysiology, light limitation and primary production (PP) derived from broad-band and spectral models. PP was significantly higher during upwelling (F3, 49 = 99.41, p < 0.001; mean 2595 ± 213 mgC m -2 d -1 ) compared with all other hydrographic conditions. The poleward current had the lowest PP (214 ± 22 mgC m -2 d -1 ). PP calculated using the spectral model (∑ PPPUR) was greater than PP from the broad-band model (∑ PPPAR), especially when southerly winds prevailed, and during stratified conditions when the chlorophyll maximum was deeper, irradiance levels were lower and most of the phytoplankton biomass was below the light limitation depth. During northerly winds, chl a was the single most important variable influencing the calculation of PP and the difference between ∑ PPPAR and ∑ PPPUR was small, since most of the phytoplankton biomass occurred above the light limitation depth, in saturating irradiance. Variations in hydrography were intrinsically linked to changes in phytoplankton species composition, photophysiology and PP. Over the whole region 89% of the variance in maximum photosynthetic rate Pm B was explained by daily mean spectral irradiance, biomass of flagellates and cyanobacteria and 75% of the variance in PP was explained by the along- shore Ekman transport component (Qy), cyanobacteria and diatom biomass. Qy alone explained 52% of the variance in PP over the shelf, which was also coupled with variations in Pm B and the biomass of diatoms and flagellates. At oceanic locations there was no relation between Qy and PP (r 2 = 7%), and PP co-varied with Pm B and the biomass of cyanobacteria.

Sea surface temperature gradients, baroclinicity, and vegetation gradients in the sea

We describe the results of an analysis of the 1984 CalCOFI data set, in which sea surface temperature (SST) gradients were found to be well correlated to isopycnal slope (baroclinicity) at the mesoscale. A link was established between the SST gradients and gradients of integral biomass [mg chlorophyll (Chl) a m−2] and integral primary production (mg C m−2day−1). The water column photosynthetic efficiency, Ψ, was calculated by combining the CalCOFI data base with satellite-based estimates of the surface irradiance. It was found that Ψ was rather stable, but not constant, for a wide range of isopycnal slopes, in which integrated nitrate concentrations varied by up to 500×. Variability in Ψ was most strongly dependent on calendar date, with the highest values in winter months and the lowest values in the summer, which was probably due to an effect of day length or irradiance. The relationship between baroclinicity and SST gradients was highly scale dependent; from 0 to 200 km, the data were randomly distributed, then as the length scales exceeded 400 km, the relationship between baroclinicity and the SST gradient showed a significantly negative slope, with steadily improving correlation coefficient. Such relationships for individual cruises generally showed improved correlation over the generic annual relationship, which highlights the dynamic hydrography of the region. Baroclinicity/SST gradient relationships also improved in waters of increasing depth. A technique is described for calculating net integral biomass or production gradients from SST imagery. The gradients in biomass and productivity showed increasingly strong ties to isopycnal slope at larger size scales. Although this topic has long been described by oceanographers, this paper is the first to demonstrate a quantitative coupling between baroclinicity and primary production gradients as a function of length scale. Also significant is the observation that the relationships between baroclinicity versus gradients of integral chlorophyll or integral productivity are consistent over seasons and over an area exceeding 1 million km2. We conclude that for satellite algorithms to account for >50% of the variance in primary production, the nutrient term must be considered. Information on baroclinicity is relevant to estimates of the along-isopycnal nutrient flux to the euphotic zone. Merging this with the more traditional light-based estimates of photosynthesis will improve algorithm performance since the methods utilize entirely independent sources of information.

Remote sensing of primary production—II. A semi-analytical algorithm based on pigments, temperature and light

A semi-analytical algorithm for estimating integrated primary production is described which uses pigment, temperature and light data. The algorithm was designed using 648 stations of data from the California Cooperative Fisheries Investigations and the Southern California Bight Study. Pigment and temperature values were used to describe maximum photosynthesis in the surface waters. A model for the vertical distribution of chlorophyll was devised which simplifies the estimation of those pigments too deep for the satellite to detect. Quantum yield, light utilization efficiency, and chlorophyll-specific light utilization efficiency were described and parameterized for inclusion in the algorithm. Variance in the photosynthetic yield term was typically the largest. Some of the variance could be partitioned as nutrient effects and inter-cruise variability. Algorithm performance could be increased considerably by using one or two stations as “calibration” stations for each area of about 300,000 km 2 (and deleting such stations from subsequent analysis). Using ship data as input, the uncalibrated algorithm explained about 35% of the variance in primary production whereas the calibrated algorithm accounted for 58% of the variance. Using satellite data as input, the uncalibrated and calibrated algorithm accounted for 35 and 48% of the variance in primary production, respectively. Of the algorithm examined in Parts I and II of this series, the semi-analytical algorithm described here explains the most variance and comes the closest to a 1:1 ratio of predicted to observed production.

Polymixis and algal production in a tropical lake: latitudinal effects on the seasonality of photosynthesis

SUMMARY. 1. Phytoplankton production was measured during 1981–82 in Bahia de Puno. a large polymictic system that is part of LakeTiticaca in the tropical Andes (Peru‐Bolivia), Photosynthesis followed aweak seasonal pattern through each 12‐month cycle but the largestvariations occurrud between years.2. The large temporal variations in productivity appeared to becontrolled by biological events rather than by the direct effeets ofseasonal or aseasonal physical processes. Major shifts in production overthe 2‐year period were attributable to the proportional abundance andactivity of N2‐fixing blue‐green algae. Production was uncorrelated withthe seasonal radiation cycle.3. In vivo fluorescence and photosynthetic assays revealed largechanges in phytoplankton community structure over time and depth.The shifts in vertical structure were associated with changes in transparency and water column stabilily.Physiological as well as floristiceffects dictated the variations in fluorescence per unit chlorophyll a.4. An analysis of twenty‐seven primary productivity data sets fromdifferent latitudes shtiwed that Bahia dc Puno resembled other tropicallakes in its relatively weak coupling between algal photosynthesis andseasonal variations in light. Productivity in the temperate zone correlated with the annual cycle of incoming radiation while the tropicalproduction data did not. For many of the tropical lakes, but fewtemperate lakes, the between‐month variance in primary production wassignificantly higher than the between‐month variance for incomingradiation. There was a significant positive relationship between maximum production variance explained hy light (maximum r2 for each dataset) and latitude.5. As in many tropical lakes. Bahia de Puno experiences moderatelylarge variations in algal photosynthesis.The muted seasonal cycle of light explains only a small portion of the total variation In productivity, and other factors such as weuther‐related events are disproportionately important.