Interannual Variability Of Primary Production Research Articles

Interannual Variability of Primary Production in the East Siberian Sea

Interannual variability (2002–2018) of primary production, surface seawater temperature (T0), photosynthetically active radiation (PAR) and ice cover area in the East Siberian Sea (ESS) was studied based on the data of the MODIS-Aqua ocean color scanner. The annual total primary production (PPtot) decreased by 1.7 TgC over 17 years. The multi-year negative trend in PPtot was 0.1 TgC y–1 (1.38% y–1). The decrease in PPtot was accompanied by the decrease in the area-specific primary production (IPP). Over the investigated period the annual mean IPP decreased by 13 mgC m–2 d–1. The multi-year negative trend in IPP was 0.76 mgC m–2 d–1 y–1 (0.84% y–1). The decrease in PPtot and IPP was accompanied by statistically insignificant increase in T0 (R2 = 0.09) and statistically significant decline in PAR (R2 = 0.29). Over the 17 years, T0 in ESS increased by 0.68°С (0.04°С y–1 or 3.2% y–1) and PAR declined by 3.4 Ein m–2 d–1 (0.2 Ein m–2 d–1 y–1 or 1.9% y–1). The ice-free area slightly diminished during the study period (R2 = 0.10) by 64.94×103 km2. The statistically insignificant negative multi-year trend in the ESS ice-free area was 3.82 × 103 km2 y–1 (0.87% y–1). Long-term variability in PPtot in ESS from 2002 to 2018 depended not only on the decrease in the ice cover but also on PAR level and IPP.

Seasonal to Inter-Annual Variability of Primary Production in Chesapeake Bay: Prospects to Reverse Eutrophication and Change Trophic Classification

Estuarine-coastal ecosystems are rich areas of the global ocean with elevated rates of organic matter production supporting major fisheries. Net and gross primary production (NPP, GPP) are essential properties of these ecosystems, characterized by high spatial, seasonal, and inter-annual variability associated with climatic effects on hydrology. Over 20 years ago, Nixon defined the trophic classification of marine ecosystems based on annual phytoplankton primary production (APPP), with categories ranging from “oligotrophic” to “hypertrophic”. Source data consisting of shipboard measurements of NPP and GPP from 1982 to 2004 for Chesapeake Bay in the mid-Atlantic region of the United States supported estimates of APPP from 300 to 500 g C m−2 yr−1, corresponding to “eutrophic” to “hypertrophic” categories. Here, we developed generalized additive models (GAM) to interpolate the limited spatio-temporal resolution of source data. Principal goals were: (1) to develop predictive models of NPP and GPP calibrated to source data (1982 to 2004); (2) to apply the models to historical (1960s, 1970s) and monitoring (1985 to 2015) data with adjustments for nutrient loadings and climatic effects; (3) to estimate APPP from model predictions of NPP; (4) to test effects of simulated reductions of phytoplankton biomass or nutrient loadings on trophic classification based on APPP. Simulated 40% decreases of euphotic-layer chl-a or TN and NO2 + NO3 loadings led to decreasing APPP sufficient to change trophic classification from “eutrophic’ to “mesotrophic” for oligohaline (OH) and polyhaline (PH) salinity zones, and from “hypertrophic” to “eutrophic” for the mesohaline (MH) salinity zone of the bay. These findings show that improved water quality is attainable with sustained reversal of nutrient over-enrichment sufficient to decrease phytoplankton biomass and APPP.

Interannual Variability of Primary Production in the Laptev Sea

Studies of the interannual variability of primary production, surface water temperature, photosynthetically active radiation, and sea ice cover in the Laptev Sea were performed based on MODIS-Aqua data (2002–2018). For a 17-year period, a statistically significant positive trend of surface temperature (R2 = 0.27) and a negative trend of photosynthetically active radiation (R2 = 0.24) were established. For the investigated period, the average annual water temperature in the Laptev Sea increased by 1.38°C and photosynthetically active radiation decreased by 3.4 Ein m–2 d–1. The ice-free water area extended insignificantly (0.15% y–1). The total primary production declined by 1.87 TgC or by 1.4% y–1. This decline was accompanied by a decrease in area-specific primary production. For the investigated period, the average annual area-specific primary production values declined by 37.4 mgC m–2 d–1 or by 1.6% y–1. The presented results suggest that changes in Laptev Sea primary productivity for the last 17 years were mainly caused by a decrease in photosynthetically active radiation and area-specific primary production rather than the dynamics of the sea ice cover.

Seasonal to Inter-Annual Variability of Primary Production in Chesapeake Bay: Prospects to Reverse Eutrophication and Change Trophic Classification

Seasonal to Inter-Annual Variability of Primary Production in Chesapeake Bay: Prospects to Reverse Eutrophication and Change Trophic Classification

Interannual variability in primary production and shelf-offshore transport of nutrients along the northeast Pacific Ocean margin

A 33-year hindcast (1979–2011) of a regional circulation-ecosystem model is used to examine interannual variability of primary production and cross-shelf transport of nutrients and phytoplankton along the British Columbia and Washington coast. Linkages between simulated primary production anomalies and forcing are explored through correlations to local upwelling winds, outflow from the Juan de Fuca Strait estuarine circulation, and two indices of Pacific Ocean basin-scale variability, the Pacific Decadal Oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO). The dominant large scale pattern of interannual variability of primary production is correlated to the NPGO but not the PDO. In the shelf region, negative primary production anomalies appear to be primarily associated with El Niño events. Along the northern shelves (between ~48.6 and 53. 9°N), time-series of annual primary production anomalies are significantly correlated with upwelling winds whereas farther south (between 46 and 48.6°N) the anomalies are correlated with nitrate outflow from the Juan de Fuca Strait. Model results indicate that coastal waters off Vancouver Island are rich in nutrients, so phytoplankton growth in this region are less limited by nitrate than on the Washington coast. Off Vancouver Island, surface phytoplankton and nitrate are exported out of the continental shelf by horizontal advection during the upwelling season. In addition, at specific sites along the coast (off Brooks Peninsula and at the southern tip of Haida Gwaii), eddies and jets carry surface nutrient and phytoplankton seaward, increasing primary production offshore.

Coupled 1-D physical–biological model study of phytoplankton production at two contrasting time-series stations in the western North Pacific

A vertical one-dimensional physical–biological model is applied to clarify the mechanisms controlling the seasonality and interannual variability of primary production in the surface layer at two contrasting time-series stations, K2 (in the subarctic gyre) and S1 (in the subtropical gyre), in the western North Pacific. Using forcing based on realistic atmospheric and oceanic data, the model reproduces seasonal differences in the degree to which different controlling factors affect primary production between these two stations, primarily as a result of differences in the physical environment. At station K2, light intensity is an important factor controlling primary production in summer. After April, the mixed layer depth (MLD) becomes shallow, resulting in higher average light intensity, and the water column remains stratified until September; these sustain high primary production during this period. In contrast, at station S1, the supply of nutrients via entrainment is vital to sustaining production, because light intensity remains sufficient throughout the year. In summer, the relationship between nutricline depth and euphotic layer is a controlling factor. The simulations forced by the different atmospheric conditions for each year, respectively, show different MLD. In the 2012 simulation, the deep winter MLD (200 m) enhances primary production in the surface layer as compared to the other two years (2010 and 2011) simulations.

Interannual variability of primary production and dissolved organic nitrogen storage in the North Pacific Subtropical Gyre

The upper ocean primary production measurements from the Hawaii Ocean Time series (HOT) at Station ALOHA in the North Pacific Subtropical Gyre showed substantial variability over the last two decades. The annual average primary production varied within a limited range over 1991–1998, significantly increased in 1999–2000 and then gradually decreased afterwards. This variability was investigated using a one‐dimensional ecosystem model. The long‐term HOT observations were used to constrain the model by prescribing physical forcings and lower boundary conditions and optimizing the model parameters against data using data assimilation. The model reproduced the general interannual pattern in the observed primary production, and mesoscale variability in vertical velocity was identified as a major contributing factor to the interannual variability in the simulation. Several strong upwelling events occurred in 1999, which brought up nitrate at rates several times higher than other years and elevated the model primary production. Our model results suggested a hypothesis for the observed interannual variability pattern of primary production at Station ALOHA: Part of the upwelled nitrate input in 1999 was converted to and accumulated as semilabile dissolved organic nitrogen (DON), and subsequent recycling of this semilabile DON supported enhanced primary productivity for the next several years as the semilabile DON perturbation was gradually removed via export.

Short-Term and Interannual Variability in Primary Production in the Low-Salinity Zone of the San Francisco Estuary

We measured primary production during spring–summer 2006–2007 to determine the carbon supply to the low-salinity pelagic food web of the San Francisco Estuary (SFE). Weekly or biweekly samples were taken at three stations of fixed salinity for size-fractionated primary production and biomass, both as chlorophyll and from biovolume based on counts. Error variance in productivity estimates arose mainly from the depth integration of 14C uptake, showing the importance of productivity measurements at high light levels for estimates of depth-integrated production. Temporal and spatial variability in production were surprisingly small. Combining data from this study with long-term monitoring data, productivity and biomass were variable in time and salinity but without persistent patterns and with infrequent blooms. Production within the low-salinity zone was unresponsive to variation in freshwater flow, in contrast to findings in other estuaries where nutrient loading drives variability in production and other regions of the SFE where production responds to residence time or to stratification. Estimated annual primary production was only 25 and 31 g C m−2 year−1 during 2006 and 2007, only half of it in cells >5 μm. These results imply that phytoplankton provided poor food web support for higher trophic levels, probably contributing to the long-term decline in fish abundance in the brackish to freshwater region of the estuary.

Marine primary production in the Canadian Arctic, 1956, 1961–1963

Marine primary productivity studies pursued in the Canadian Arctic in 1961–1963, using standard techniques (oxygen and carbon-14) of the time, showed that maximum production developed rapidly in July at 5-m depth under very low light intensities and under intact but melting sea ice. The time of maximum production was correlated with depths of snow in spring. Low production levels were found in August in those years and estimated in 1956. Nitrate exhaustion occurred before maximum production and was followed by rapid sinking of chlorophyll and productivity and reduction of assimilation numbers. Gross production values greatly exceeded net production values in 1961–1963, and gross production in 2 years was about double that of a third year, which may be due to different initial conditions of nutrient concentrations in the euphotic zone. Interannual variability in primary production may be the result of changes in water masses in the surface layer, as driven by atmospheric pressure patterns.

Drivers of inter-annual variability in Net Ecosystem Exchange in a semi-arid savanna ecosystem, South Africa

Abstract. Inter-annual variability in primary production and ecosystem respiration was explored using eddy-covariance data at a semi-arid savanna site in the Kruger Park, South Africa. New methods of extrapolating night-time respiration to the entire day and filling gaps in eddy-covariance data in semi-arid systems were developed. Net ecosystem exchange (NEE) in these systems occurs as pulses associated with rainfall events, a pattern not well-represented in current standard gap-filling procedures developed primarily for temperate flux sites. They furthermore do not take into account the decrease in respiration at high soil temperatures. An artificial neural network (ANN) model incorporating these features predicted measured fluxes accurately (MAE 0.42 gC/m2/day), and was able to represent the seasonal patterns of photosynthesis and respiration at the site. The amount of green leaf area (indexed using satellite-derived estimates of fractional interception of photosynthetically active radiation fAPAR), and the timing and magnitude of rainfall events, were the two most important predictors used in the ANN model. These drivers were also identified by multiple linear regressions (MLR), with strong interactive effects. The annual integral of the filled NEE data was found to range from −138 to +155 g C/m2/y over the 5 year eddy covariance measurement period. When applied to a 25 year time series of meteorological data, the ANN model predicts an annual mean NEE of 75(±105) g C/m2/y. The main correlates of this inter-annual variability were found to be variation in the amount of absorbed photosynthetically active radiation (APAR), length of the growing season, and number of days in the year when moisture was available in the soil.

Primary production of Inner Mongolia, China, between 1982 and 1999 estimated by a satellite data-driven light use efficiency model

Declining biological production as a part of an ongoing land degradation process is considered a severe environmental problem in the dry northern and northwestern regions of China. The aim of this study is to develop and adapt a satellite data-driven gross primary production model called Lund University light use efficiency model (LULUE) to temperate conditions in order to map gross primary production (GPP) for the Grasslands of Inner Mongolia Autonomous Region (IMAR), China, from 1982 to 1999. The water stress factor included in the original model has been complemented with two temperature stress factors. In addition, algorithms that allocate the proportions of C3/C4 photosynthetic pathways used by plants and that compute temperature-based C3 maximum efficiency values have been incorporated in the model. The applied light use efficiency (LUE) model is using time series of the Normalized Difference Vegetation Index (NDVI), CLouds from AVHRR (CLAVR) from the 8-km resolution NOAA Pathfinder Land Data Set (PAL). Quasi-daily rainfall and monthly minimum and maximum temperatures, together with soil texture information, are used to compute water limitations to plant growth. The model treats bare soil evaporation and actual transpiration separately, a refinement that is more biophysically realistic, and leads to enhanced precision in our water stress term, especially across vegetation gradients. Based on ground measurements of net primary production (NPP) at one site, the LULUE reproduces the variability of primary production better than CENTURY or NDVI alone. Mean annual GPP between 1982 and 1999 range from about 100 g/m 2 in desert regions in the west to about 4000 g/m 2 in the northeast of IMAR, and the coefficient of variation for GPP is highest near the margins of the deserts in the west where rainfall is erratic. Linear trends fitted through the 18-year time series reveal that the western regions have encountered no change, while a large area in the center of the IMAR shows marked increases in GPP. In the northeast, negative trends in GPP are noted and coincide with rainfall trends. Though the high inter-annual variability in primary production undermines the identification of significant trends, we could not isolate any general decline in grassland primary production.

Revisited ecosystem model (MODECOGeL) of the Ligurian Sea: seasonal and interannual variability due to atmospheric forcing

A one-dimensional coupled hydrodynamical–biological model, MODèle d' ECOsystème du G.H.E.R. et du L.O.V. (MODECOGeL), of the water column is developed and applied to the Ligurian Sea (North Western Mediterranean). It is an extended and improved version of the model presented by Lacroix and Nival [J. Mar. Syst. 16 (1998) 23]. The hydrodynamic model is a 1D version of the 3D turbulent closure G.H.E.R. model, which takes into account momentum and heat surface fluxes computed from a real meteorological data set. The ecosystem model is defined by a nitrogen cycle described by 12 biological state variables including several plankton size classes and an explicit description of the bacterial loop. One data set coming from the FRONTAL missions is used to initialise and validate the model. To assess the impact of the interannual variability of the meteorological conditions on the ecosystem dynamics, the coupled model is run with 4-year real meteorological conditions (October 1984–September 1988). The model estimated percentages of the interannual variability of the annual mean biomass of phytoplankton, zooplankton and bacteria respectively of 31.0%, 16.2% and 16.3%. The contribution of the zooplankton related to the total plankton biomass (phytoplankton, zooplankton and bacteria) has been found to be the most sensitive to the meteorological conditions variations (21%), followed by the phytoplankton (12%) and finally, by the bacteria (5%). The model estimated percentages of interannual variability of the annual gross primary production, the annual mean f-ratio and the annual bacterial production respectively of 27.9%, 18.5% and 13.4% although the interannual variability of the real winds conditions is only of 11.3%. Due to the more windy and less sunny conditions prevailing during the years “1985–1986” and “1986–1987”, the annual primary production was found higher than during the years “1984–1985” and “1987–1988”. The bacterial production is always greater than the primary production, showing the importance of the bacteria in such an oligotrophic environment. On a seasonal scale, the highest interannual variability of the primary production and the f-ratio is found in spring like for the wind intensity.

Time-Dependent Modeling of the Baltic Entrance Area. 1. Quantification of Circulation and Residence Times in the Kattegat and the Straits of the Baltic Sill

A prognostic model for the estuarine circulation in the Baltic entrance area is described. The model is based on the work by Stigebrandt (1983) and is built of a number of flow-regulating physical processes and forced by oceanic sea level, local meteorological conditions, and freshwater supply to the Baltic. It resolves the horizontal variations by dividing the entrance area into 7 sub-basins. The vertical stratification in each sub-basin evolves with time due to mixing, diffusion, and water exchange with adjacent basins. Instead of using a fixed vertical grid, the stratification is described by a variable number of layers created by inflowing water and by a pycnocline retreat near the surface. The model is a highly cost-effective tool compared to high-resolution 3D-models since computations are 105–106 times faster. Still, the model reproduces the stratification on time-scales longer than a few days as verified by comparison with observed time-series. The magnitude of the simulated average estuarine circulation conforms well to independent estimates of the water exchange. The model is used to quantify the temporal and horizontal variability of circulation, mixing, and diffusion. Long-term average rate of work against the buoyancy forces by entrainment and diffusion is calculated for each sub-basin. The highest rates of work against the buoyancy forces by diffusion are found in the northern Kattegat and in the Fehmarn Belt while the lowest rate is found in the Oresund. The total mixing in terms of transformation of water masses is also quantified. The average residence times for surface and deep water are estimated for each subbasin. Residence times longer than 1 mo are found in Fehmarn Belt and in the deep water of southern Kattegat. In other parts of Kattegat and the Samso Belt the residence times are 1 to 2 wk for surface water and 2 to 3 wk for deep water. The age of the water is defined as the time spent since a particular water mass was in contact with either the sea surface or with the vertical model boundaries has been estimated. By comparing the age distribution in the Kattegat with observations of oxygen concentration, it is concluded that the variability of the ventilation of deeper layers is of less importance to the occurrence of low oxygen concentrations compared to other factors such as interannual variability in primary production.

Seasonal and interannual variability in primary production and particle flux at Station ALOHA

A 5-year time-series study of primary production and euphotic-zone particle export in the subtropical North Pacific Ocean near Hawaii (Sta. ALOHA, 22°45′N, 158°W) with measurements collected at approximately monthly intervals has revealed significant variability in both ecosystem processes. Depth-integrated (0–200 m) primary production averaged 463 mg C m −2 day −1 ( s = 156, n = 54) or 14.1 mol C m −2 year −1. This mean value is greater than estimates for the North Pacific Ocean gyre made prior to 1984, but conforms to data obtained since the advent of trace metal-clean techniques. Daily rates of primary productivity at Sta. ALOHA exhibited interannual variability including a nearly 3-year sustained increase during the period 1990–1992 that coincided with a prolonged El Nifio-Southern Oscillation (ENSO) event. Export production, defined as the particulate carbon (PC) flux measured at the 150 m reference depth, also varied considerably during the initial 5 years of the ongoing field experiment. The PC flux averaged 29 mg C m −2 day −1 ( s = 11, n = 43) or 0.88 mol Cm −2 year −1. A 5-fold variation between the minimum and maximum fluxes, measured in any given year, was observed. During the first 3 years of this program (1989–1991), a pattern was resolved that included two major export events per annum one centered in late winter and the other in late summer. After 1991, export production exhibited a systematic decrease with time during the prolonged ENSO event. When expressed as a percentage of the contemporaneous primary production, PC export ranged from 2 to 16.9%, with a 5-year mean of 6.7% ( s = 3.3, n = 40). Contrary to existing empirical models, contemporaneous primary production and PC flux were poorly correlated, and during the ENSO period they exhibited a significant inverse correlation. This unexpected decoupling of particle production and flux has numerous implications for oceanic biogeochemical cycles and for the response of the ocean to environmental perturbations.

Interannual Variability in Primary Production in Tallgrass Prairie: Climate, Soil Moisture, Topographic Position, and Fire as Determinants of Aboveground Biomass

Interannual Variability in Primary Production in Tallgrass Prairie: Climate, Soil Moisture, Topographic Position, and Fire as Determinants of Aboveground Biomass

Interannual fluctuations in primary production: Meteorological forcing at two subalpine lakes

Meteorological factors are associated with most of the interannual variability in primary production at both Castle Lake, California (41°N, 122°W) and Lake Tahoe, California‐Nevada (39°N, 120°W). At Castle Lake, extreme values of annual primary production, either much higher or lower than the long‐term average, are likely to occur during the phenomenon of El Niño/Southern Oscillation. Two plausible pathways for the impacts of these large‐scale climate events at Castle Lake were identified: winter snowfall, acting through its effect on the snow‐ice pack and timing of the spring thaw; and total precipitation, acting through its effect on outwash rates. In contrast, no influence of large‐scale climate events is apparent at Lake Tahoe, but a plausible pathway involving the impact of synoptic‐scale phenomena on interannual variation was identified: local weather events occurring in the late winter‐early spring period near the time of minimal stratification, acting through their effect on the depth of spring mixing. The difference between the two lakes can be attributed to absence of an ice cover and long hydraulic retention time at Lake Tahoe. Time‐series models that incorporate meteorological information adequately forecast primary production at both lakes.