Low Interannual Variability Research Articles

Temperature sensitivity of plant phenology in temperate and subtropical regions of China from 1850 to 2009

ABSTRACTPhenology can be used to track plant responses to climate change. In China, several studies have found the earlier trends of spring phenophases over the past 50 years. However, few studies put these phenological changes into historical perspective. Based on specific phenophases records from historical diaries and Chinese Phenological Observation Network, we developed spring phenology index (SPI) time series in temperate and subtropical regions of eastern China from 1850 to 2009. We firstly compare the temporal change of SPI and seasonal temperature anomaly. Subsequently, we search for common shifts in phenological and temperature time series by applying the moving t‐test method, and discuss temperature sensitivity of SPI by using the moving linear regression method for both regions. Results show that the SPI in temperate region revealed lower interannual variability than in subtropical region, while the seasonal temperature variability was higher in temperate region. In temperate region, the timing of significant shift towards earlier SPI (in 1979) coincides with the timing of shift in spring temperature time series. The temperature sensitivities of SPI differ among the two regions. The mean sensitivity of SPI to spring temperature in subtropical region (−3.7 days °C−1) is stronger than in temperate region (−2.5 days °C−1). The temperature sensitivity of SPI varies among consecutive 30‐year periods. In recent three decades, temperature sensitivity of spring phenophases became stronger in both regions.

How important and different are tropical rivers? — An overview

Tropical river systems, wherein much of the drainage basin experiences tropical climate are strongly influenced by the annual and inter-annual variations of the Inter-tropical Convergence Zone (ITCZ) and its derivative monsoonal winds. Rivers draining rainforests and those subjected to tropical monsoons typically demonstrate high runoff, but with notable exceptions. High rainfall intensities from burst weather events are common in the tropics. The release of rain-forming aerosols also appears to uniquely increase regional rainfall, but its geomorphic manifestation is hard to detect. Compared to other more temperate river systems, climate-driven tropical rivers do not appear to transport a disproportionate amount of particulate load to the world's oceans, and their warmer, less viscous waters are less competent. Tropical biogeochemical environments do appear to influence the sedimentary environment. Multiple-year hydrographs reveal that seasonality is a dominant feature of most tropical rivers, but the rivers of Papua New Guinea are somewhat unique being less seasonally modulated.Modeled riverine suspended sediment flux through global catchments is used in conjunction with observational data for 35 tropical basins to highlight key basin scaling relationships. A 50year, daily model simulation illuminates how precipitation, relief, lithology and drainage basin area affect sediment load, yield and concentration. Local sediment yield within the Amazon is highest near the Andes, but decreases towards the ocean as the river's discharge is diluted by water influxes from sediment-deprived rainforest tributaries. Bedload is strongly affected by the hydraulic gradient and discharge, and the interplay of these two parameters predicts foci of net bedload deposition or erosion. Rivers of the tropics have comparatively low inter-annual variation in sediment yield.

Effects of Animal Husbandry on Secondary Production and Trophic Efficiency at a Regional Scale

Agricultural systems are expected to have higher net secondary production (NSP) than natural systems as a result of higher trophic efficiency and lower interannual variability. These differences, however, have not been quantified across regional gradients. We compiled a dataset of herbivore biomass, consumption, NSP, annual precipitation, and aboveground net primary production (ANPP) for extensive livestock farms across a wide precipitation gradient in Argentina. We compared these data with worldwide published studies of natural systems. In a double-logarithmic scale, NSP of agricultural systems increased with ANPP from semiarid to subhumid systems and decreased from subhumid to humid systems, a response that contrasted with the linear positive increase of natural systems. Compared to natural systems dominated by homeotherms, E troph (NSP:ANPP) in agricultural systems in semiarid areas was 8 times higher, due to a 2 times higher E consump (Consumption:ANPP) and a 4 times higher E prod (NSP:Consumption). In subhumid areas, E troph was 46 times higher, due to a 13.7 times higher E consump and a 3.3 times higher E prod. In humid areas, E troph was 5 times higher, due to a 2.5 times higher E consump and a 2 times higher E prod. The interannual variation of herbivore biomass, a major determinant of NSP, was 60 % lower in agricultural than in natural systems dominated by homeotherms, and was decoupled from the variability of precipitation. Agricultural systems reach higher NSP by (1) diverting a major proportion of ANPP from the detritus to the grazing chain, (2) converting more efficiently consumption into NSP, and (3) stabilizing herbivore biomass across years.

Determination of the source regions for surface to stratosphere transport: An Eulerian backtracking approach

A wide range of inverse problems in atmospheric transport and chemistry can be solved within the Eulerian backtracking framework. Here it is shown how a new and accurate numerical implementation can be used as an alternative to Lagrangian back trajectory methods in a wide class of process studies. As a key example, the question of how the (time‐averaged) stratospheric flux of a finite lifetime chemical species depends upon the location(s) of its surface source(s) is addressed. The resulting sensitivity maps are demonstrated to be robust features of the global atmospheric circulation, with relatively low interannual variability. The maps serve as an at‐a‐glance resource for policymakers wishing to compare the likely impact of proposed emission locations for very short lived halogenated species on the total loading of stratospheric chlorine and bromine.

Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements

Abstract. This study aims to determine the mineral contribution to PM10 in the central Mediterranean Sea, based on 7 yr of daily PM10 samplings made on the island of Lampedusa (35.5° N, 12.6° E). The chemical composition of the PM10 samples was determined by ion chromatography for the main ions, and, on selected samples, by particle-induced X-ray emission (PIXE) for the total content of crustal markers. Aerosol optical depth measurements were carried out in parallel to the PM10 sampling. The average PM10 concentration at Lampedusa over the period June 2004–December 2010 is 31.5 μg m−3, with low interannual variability. The annual means are below the EU annual standard for PM10, but 9.9% of the total number of daily data exceeds the daily threshold value established by the European Commission for PM (50 μg m−3, European Community, EC/30/1999). The Saharan dust contribution to PM10 was derived by calculating the contribution of Al, Si, Fe, Ti, non-sea-salt (nss) Ca, nssNa, and nssK oxides in samples in which PIXE data were available. Cases in which crustal content exceeded the 75th percentile of the crustal oxide content distribution were identified as elevated dust events. Using this threshold, we obtained 175 events. Fifty-five elevated dust events (31.6%) displayed PM10 higher than 50 μg m−3, with dust contributing by 33% on average. The crustal contribution to PM10 has an annual average value of 5.42 μg m−3, and reaches a value as high as 67.9 μg m−3 (corresponding to 49% of PM10) during an intense Saharan dust event. The crustal content estimated from a single tracer, such as Al or Ca, is in good agreement with the one calculated as the sum of the metal oxides. Conversely, larger crustal contents are derived by applying the EU guidelines for demonstration and subtraction of exceedances in PM10 levels due to high background of natural aerosol. The crustal aerosol amount and contribution to PM10 showed a very small seasonal dependence; conversely, the dust columnar burden displays an evident annual cycle, with a strong summer maximum (monthly average aerosol optical depth at 500 nm up to 0.28 in June–August). We found that 71.3% of the dust events identified from optical properties over the atmospheric column display a high dust content at the ground level. Conversely, the remaining 28.7% of cases present a negligible or small impact on the surface aerosol composition due to the transport processes over the Mediterranean Sea, where dust frequently travels above the marine boundary layer, especially in summer. Based on backward trajectories, two regions, one in Algeria–Tunisia, and one in Libya, are identified as main source areas for intense dust episodes occurring mainly in autumn and winter. Data on the bulk composition of mineral aerosol arising from these two source areas are scarce; results on characteristic ratios between elements show somewhat higher values of Ca / Al and (Ca + Mg) / Fe (2.5 ± 1.0, and 4.7 ± 2.0, respectively) for Algeria–Tunisia than for Libyan origin (Ca / Al = 1.9 ± 0.7 and (Ca + Mg) / Fe = 3.3 ± 1.1).

Influence of Leaf Area Index Prescriptions on Simulations of Heat, Moisture, and Carbon Fluxes

Abstract Leaf area index (LAI), the total one-sided surface area of leaf per ground surface area, is a key component of land surface models. The authors investigate the influence of differing, plausible LAI prescriptions on heat, moisture, and carbon fluxes simulated by the Community Atmosphere Biosphere Land Exchange version 1.4b (CABLEv1.4b) model over the Australian continent. A 15-member ensemble monthly LAI dataset is generated using the Moderate Resolution Imaging Spectroradiometer (MODIS) LAI product and gridded observations of temperature and precipitation. Offline simulations lasting 29 years (1980–2008) are carried out at 25-km resolution with the composite monthly means from the MODIS LAI product (control simulation) and compared with simulations using each of the 15-member ensemble monthly varying LAI datasets generated. The imposed changes in LAI did not strongly influence the sensible and latent fluxes, but the carbon fluxes were more strongly affected. Croplands showed the largest sensitivity in gross primary production with differences ranging from −90% to 60%. Plant function types (PFTs) with high absolute LAI and low interannual variability, such as evergreen broadleaf trees, showed the least response to the different LAI prescriptions, while those with lower absolute LAI and higher interannual variability, such as croplands, were more sensitive. The authors show that reliance on a single LAI prescription may not accurately reflect the uncertainty in the simulation of terrestrial carbon fluxes, especially for PFTs with high interannual variability. The study highlights that accurate representation of LAI in land surface models is key to the simulation of the terrestrial carbon cycle. Hence, this will become critical in quantifying the uncertainty in future changes in primary production.

Human Migration, Protected Areas, and Conservation Outreach in Tanzania

A recent discussion debates the extent of human in-migration around protected areas (PAs) in the tropics. One proposed argument is that rural migrants move to bordering areas to access conservation outreach benefits. A counter proposal maintains that PAs have largely negative effects on local populations and that outreach initiatives even if successful present insufficient benefits to drive in-migration. Using data from Tanzania, we examined merits of statistical tests and spatial methods used previously to evaluate migration near PAs and applied hierarchical modeling with appropriate controls for demographic and geographic factors to advance the debate. Areas bordering national parks in Tanzania did not have elevated rates of in-migration. Low baseline population density and high vegetation productivity with low interannual variation rather than conservation outreach explained observed migration patterns. More generally we argue that to produce results of conservation policy significance, analyses must be conducted at appropriate scales, and we caution against use of demographic data without appropriate controls when drawing conclusions about migration dynamics.

Integrating Land Change Science and Savanna Fire Models in West Africa

Fire is a key component of many land use systems and a determinant of land change. There is a growing concern that climate change will cause more catastrophic fires, but in many areas the impacts will be mediated by human land use practices. In African savannas, for example, fires are frequent and research finds low inter-annual variability in burned areas in places with highly variable rainfall. This regularity of fire suggests that African regimes are humanized, meaning that they are governed by human practices more than climate variation. Although these fire regimes are stable, they vary greatly over space. This paper will determine the reasons for two distinctly different fire regimes in Mali by integrating land change and savanna fire science. The study takes a two pronged approach to examine the causes of fire regimes and the reasons they change. It tests the notion that land cover (not land use) governs fire regimes by combining long term burn scar and vegetation analysis with local interviews. Results indicate that efforts to link fire and land change science, need to focus more on subtle differences in land cover, landscape pattern and human practices, than on drought, land use or fire policy.

Effects of lakes and reservoirs on annual river nitrogen, phosphorus, and sediment export in agricultural and forested landscapes

AbstractRecently, effects of lakes and reservoirs on river nutrient export have been incorporated into landscape biogeochemical models. Because annual export varies with precipitation, there is a need to examine the biogeochemical role of lakes and reservoirs over time frames that incorporate interannual variability in precipitation. We examined long‐term (~20 years) time series of river export (annual mass yield, Y, and flow‐weighted mean annual concentration, C) for total nitrogen (TN), total phosphorus (TP), and total suspended sediment (TSS) from 54 catchments in Wisconsin, USA. Catchments were classified as small agricultural, large agricultural, and forested by use of a cluster analysis, and these varied in lentic coverage (percentage of catchment lake or reservoir water that was connected to river network). Mean annual export and interannual variability (CV) of export (for both Y and C) were higher in agricultural catchments relative to forested catchments for TP, TN, and TSS. In both agricultural and forested settings, mean and maximum annual TN yields were lower in the presence of lakes and reservoirs, suggesting lentic denitrification or N burial. There was also evidence of long‐term lentic TP and TSS retention, especially when viewed in terms of maximum annual yield, suggesting sedimentation during high loading years. Lentic catchments had lower interannual variability in export. For TP and TSS, interannual variability in mass yield was often >50% higher than interannual variability in water yield, whereas TN variability more closely followed water (discharge) variability. Our results indicate that long‐term mass export through rivers depends on interacting terrestrial, aquatic, and meteorological factors in which the presence of lakes and reservoirs can reduce the magnitude of export, stabilize interannual variability in export, as well as introduce export time lags. Copyright © 2013 John Wiley & Sons, Ltd.

Recent lake ice‐out phenology within and among lake districts of Alaska, U.S.A

The timing of ice‐out in high latitudes is a fundamental threshold for lake ecosystems and an indicator of climate change. In lake‐rich regions, the loss of ice cover also plays a key role in landscape and climatic processes. Thus, there is a need to understand lake ice phenology at multiple scales. In this study, we observed ice‐out timing on 55 large lakes in 11 lake districts across Alaska from 2007 to 2012 using satellite imagery. Sensor networks in two lake districts validated satellite observations and provided comparison with smaller lakes. Over this 6 yr period, the mean lake ice‐out for all lakes was 27 May and ranged from 07 May in Kenai to 06 July in Arctic Coastal Plain lake districts with relatively low inter‐annual variability. Approximately 80% of the variation in ice‐out timing was explained by the date of 0°C air temperature isotherm and lake area. Shoreline irregularity, watershed area, and river connectivity explained additional variation in some districts. Coherence in ice‐out timing within the lakes of each district was consistently strong over this 6 yr period, ranging from r‐values of 0.5 to 0.9. Inter‐district analysis of coherence also showed synchronous ice‐out patterns with the exception of the two arctic coastal districts where ice‐out occurs later (June‐July) and climatology is sea‐ice influenced. These patterns of lake ice phenology provide a spatially extensive baseline describing short‐term temporal variability, which will help decipher longer term trends in ice phenology and aid in representing the role of lake ice in land and climate models in northern landscapes.

Resistance of the size structure of the fish community to ecological perturbations in a large river ecosystem

Summary Frequency distributions of log‐scaled abundance and body size for aquatic biota, including fish, yield size spectra that provide gross estimates of food‐web capacity (number of individuals supported by the food web indexed by the midpoint height or y‐intercept) and ecological efficiency (rate of decreasing organismal abundance with increasing body size as indicated by the size‐spectra slope). Size spectra are known to respond in predictable fashion to exploitation by commercial (marine) fisheries, but there has been relatively little research of size spectra in freshwater systems and less evaluation of how community size‐structure responds to the wider array of ecological perturbations prevalent in freshwater systems. We used a 29‐year experimental gillnet data set to test the responses of food‐web capacity and ecological efficiency (as indexed by size spectra) of a large river fish community to variations in predatory demand (population expansion of double‐crested cormorant, Phalacrocorax auritus) and perturbations affecting primary production (reductions in total phosphorus and warming summer water temperature). Fish community capacity (size‐spectra elevation) and ecological efficiency (size‐spectra slope) showed low interannual variation (coefficients of variation 5.6 and 15.4%, respectively). Though highly stable, food‐web capacity decreased over time concurrent with declining total phosphorus concentrations and increasing cormorant abundance. Interannual variation in ecological efficiency was not related to the measured perturbations. Relative abundance of the core species that comprised 95% of the community remained relatively consistent over time. The fish community size‐structure was also stable and resistant to ecological perturbation. However, we found measurable changes in the composition of secondary species, and these were associated with an increase in cormorant abundance and decrease in total phosphorus. The lack of change in core community species representation and in overall size structure suggest community‐level compensatory mechanisms were operating.

Simulating the effects of global climate change on Atlantic croaker population dynamics in the mid-Atlantic Region

Projecting global climate change (GCC) effects on fish populations has primarily focused on temperature, while non-temperature effects are rarely simulated. In this study, we used a non-linear matrix population projection model of Atlantic croaker (Micropogonias undulatus) in the mid-Atlantic Bight to illustrate how global climate change effects, in addition to temperature, can be incorporated into population projections. The model was a multiple time step, stage-within-age matrix projection model with two nursery regions (Virginia and North Carolina estuaries) for young-of-the-year (YOY, egg to age-1) life stage development and a single ocean spatial box for adults. Late juvenile mortality was density-dependent and calibrated to generate a spawner-recruit relationship similar to observed values. Model simulations were for 160 years. Global climate change effects were estimated for 2020, 2050, and 2080, which resulted in three new sets of parameter values of the matrix model. The first 40 years of the 160 years were baseline, followed by 40 years of 2020 parameter values, 40 years of 2050 values, and 40 years of 2080 values. Changes in the parameters of the matrix model were based on changes in annual and seasonal temperatures generated by global circulation models, as well as presumed changes in precipitation causing increased hypoxia, increased variability in salinity, rising sea level, and changes in ocean circulation causing increased northward and offshore transport. Global climate change resulted in increased croaker abundance with lower inter-annual variability. Sensitivity analysis with each GCC effect imposed singly showed that the increase in croaker abundance under GCC was due to the complex suite of positive and negative responses across multiple life stages. The major positive response was due to warmer temperatures, and the major negative effects were due to increased variability in salinity, increased offshore transport, and sea level rise. A second sensitivity analysis showed that important, but highly uncertain, effects produced smoothly increasing population responses with increasing magnitude. We discuss how effects other than temperature can be important to projecting population responses to GCC, and the strengths and weaknesses of our analysis. Our analysis demonstrates how a variety of GCC-related effects can be incorporated into traditional population models; what is needed is sufficient empirical information to quantify the effects in terms of growth, mortality, movement, and reproduction.

The persistence and stability of fish assemblages within eelgrass meadows (Zostera marina) on the Pacific coast of Canada

The persistence and stability of fish assemblages found in 34 eelgrass (Zostera marina) meadows along the British Columbia coast was examined from 2004 to 2011. Assemblage persistence (nontrending species composition) and assemblage stability (constancy in abundance over time) were assessed using a time-lag regression method that tests for temporal turnover within short time series. Overall, 85% of the fish assemblages persisted, and 80% of the assemblages exhibited stability in abundance over the 8-year study. Environmental conditions in 33 of 34 meadows did not change substantially over the 8 years, and the low interannual variability may have contributed to the high persistence and stability of the fish assemblages. The lack of temporal turnover in relatively undisturbed eelgrass fish assemblage properties is a critical element for effective monitoring of coastal ecosystem integrity.

Interannual changes in the zooplankton community structure on the southeastern Bering Sea shelf during summers of 1994–2009

On the southeastern Bering Sea shelf, mesozooplankton plays an important role in material transfer between primary producers and fisheries resources. The biomass of mesozooplankton in this region is known to vary annually, but little is known about annual changes in community structure and species composition. In the present study, regional and long-term changes in abundance, biomass and community structure of copepods and chaetognaths on the shelf were evaluated based on NORPAC net samples collected during summers of 1994–2009. During the study period, regime shifts occurred from high interannual variability regime (1994–1999) to low interannual variability regime with high temperature (2000–2005), then to a low interannual variability regime with low temperature (2007–2009). A total of 24 calanoid copepod species belonging to 21 genera were identified from samples. Copepod abundance ranged from 150 to 834,486inds.m−2, was greatest on the Middle shelf, and was higher in cold years, than in warm years. Copepod biomass ranged from 0.013 to 150gDMm-2, and was also higher in cold years than in warm years. Based on the results of cluster analysis, the copepod community was divided into six groups (A–F). The regional and interannual distributions of each group were distinct. Interannual changes in abundance of the dominant copepod on the Outer shelf and Middle shelf were highly significant (p<0.0001), and their abundances were negatively correlated with temperature and salinity. Interannual changes in copepod community that occurred between cold and warm years are thought to have been caused by differences in the magnitude and timing of the spring phytoplankton bloom between the two regimes. Abundance and biomass of the chaetognath Parasagitta elegans ranged from 30 to 15,180inds.m-2 and from 11 to 1559mgDMm−2, respectively. Chaetognath abundance was significantly correlated with the abundance of the dominant copepods (p<0.0001). Differences in cold and warm years may also affect recruitment of walleye pollock. We conclude that on the southeastern Bering Sea shelf, the magnitude and timing of primary production, which is related to climate change, may significantly affect how it is transferred through the food web.

Assessing the performance of Intergovernmental Panel on Climate Change AR5 climate models in simulating and projecting wind speeds over China

The ability of nine current generation (Coupled Model Intercomparison Project Phase 5, CMIP‐5) coupled atmosphere‐ocean general circulation models (AOGCMs) to accurately simulate the near‐surface wind climate over China is evaluated by comparing output from the historical period (1971–2005) with an observational data set and reanalysis output. Results suggest the AOGCMs show substantial positive bias in the mean 10 m wind speed relative to observations and the ERA‐40, National Centers for Environmental Prediction–Department of Energy, and National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis. Given that the models generally produce the upper level geopotential height gradients comparatively well, it is postulated that one major reason for the discrepancy between observed and modeled wind fields is the surface characterization used in the AOGCMs. All models exhibit lower interannual variability than reanalysis data and observations, and none of the models reproduce the recent decline in wind speed that is manifest in the near‐surface observations. The wind speed of individual model runs during the historical period does not exhibit much influence from the initial atmospheric conditions. The output for the current century from seven of the AOGCMs is examined relative to the historical wind climate. The results indicate that spatial fields of wind speed at the end of the 21st century are very similar to those of the last 35 years with comparatively little response to the precise representative concentration pathway scenario applied.

An integrated assessment of business risk for pasture-based dairy farm systems intensification

The increasing cost/price pressures on Australian dairy farmers mean that they will need to increase on-farm productivity by producing more milk per ha from home-grown forage. Since there is a limit to the potential yield from pasture an innovative intensification system that integrates pasture and forage crops has been developed. This complementary forages system (CFS) has shown to increase milk production per ha from home-grown forage beyond pasture potential. An integrated modelling approach was used to assess the business risk of this system and compare it to a system with increased use of concentrates, the pasture plus grain (PG) system and to the initial situation, the Base system. First, based on the results of a 2-year CFS farmlet study, the systems’ milk production, forage and supplements consumption were simulated for a 140ha farm using a decision support model. Second, the systems’ operating profit was calculated using a whole-farm budgeting approach. Third, the effect of inter-annual variation in key variables related to operating profit was assessed using a stochastic budgeting technique to calculate cumulative probability of profit as a measure of business risk. The selected variables were: price of milk, concentrates, urea fertiliser and irrigation water and yields of pasture and forage crops. The inter-annual variability of these yields was simulated for 100years of daily weather data assuming limited irrigation using validated biophysical simulation models. The sum of the forage crops yields had a lower inter-annual variability than pasture yields, which were more closely associated to annual rainfall. This lower variability was due to the high water use efficiency of maize, prioritized in the irrigation. The risk analysis showed that milk price was the variable with the highest impact on operating profit followed by forage yields, whereas urea fertiliser had the lowest effect. When integrating all variables, PG showed the highest business risk, followed by Base and CFS, respectively. Very high standards were assumed for the management of forage crops, pastures and feeding and therefore these results may not apply to all dairy farmers. However, this integrative systems analysis approach highlighted the potential of intensification alternatives with a diversified home-grown forage base to reduce business risk compared to systems based on only pasture and increased use of concentrates.

Factors controlling interannual variability of vertical organic matter export and phytoplankton bloom dynamics – a numerical case-study for the NW Mediterranean Sea

Abstract. Mid-latitude spring blooms of phytoplankton show considerable year-to-year variability in timing, spatial extent and intensity. It is still unclear to what degree the bloom variability is connected to the magnitude of the vertical flux of organic matter. A coupled three-dimensional hydrodynamic-biogeochemical model is used to relate interannual variability in phytoplankton spring-bloom dynamics to variability in the vertical export of organic matter in the NW Mediterranean Sea. Simulation results from 2001 to 2010, validated against remote-sensing chlorophyll, show marked interannual variability in both timing and shape of the bloom. Model results show a tendency for the bloom to start later after cold and windy winters. However, the onset of the bloom occurs often when the mixed layer is still several hundred metres deep while the heat flux is already approaching zero and turbulent mixing is low. Frequency and intensity of wind episodes control both the timing and development of the bloom and the consequent export flux of organic matter. The wintertime flux is greater than zero and shows relatively low interannual variability. The magnitude of the interannual variability is mainly determined in March when the frequency of windy days positively correlates with the export flux. Frequent wind-driven mixing episodes act to increase the export flux and, at the same time, to interrupt the bloom. Perhaps counterintuitively, our analysis shows that years with discontinuous, low-chlorophyll blooms are likely to have higher export flux than years with intense uninterrupted blooms. The NW Mediterranean shows strong analogy with the North Atlantic section within the same latitude range. Hence, our results may also be applicable to this quantitatively more important area of the world ocean.

Temporal variability in taxonomic completeness of stream macroinvertebrate assemblages

Natural temporal variation in biological assemblages is generally acknowledged, but rarely controlled for in existing bioassessment approaches. Many bioassessment methods ignore the variation of assemblage structure through time and, thus, lack a process to evaluate the effects of natural temporal variation on their outcomes. We used an 11-y data set from 24 near-pristine reference streams (validation sites) and a 5-y data set from 10 streams exposed to human disturbance (test sites) in northern Finland to examine: 1) the amount of interannual variation in macroinvertebrate communities in both types of streams measured as variation in taxonomic completeness (i.e., ratio of observed/expected taxa; O/E ratio), and 2) how temporal variability affects bioassessment outcomes. Most of the variation in O/E values was explained by stream type (validation or test). Interannual variation in O/E was low at both validation and test sites, a result supporting the assumption of high constancy of biological assemblages through time. Temporal variation in O/E at validation sites was related to climatic factors (regional precipitation) and to some local environmental variables, e.g., substratum heterogeneity. Communities in validation and test sites responded differentially to climatic variation. The low interannual variation in O/E suggests that 1-y data from reference sites can be extrapolated across years relatively safely, but climatically extreme years may be problematic. Temporal variability in O/E was low at both types of sites, but it was still high enough to result in variable ecological status assessments across years, mainly at test sites with lower O/E ratios. Thus, at test sites, use of only 1-y data may cause erroneous management decisions, and accurate assessment of the biological quality of test sites might require repeated sampling over several years.

A century of hydrological variability and trends in the Fraser River Basin

This study examines the 1911–2010 variability and trends in annual streamflow at 139 sites across the Fraser River Basin (FRB) of British Columbia (BC), Canada. The Fraser River is the largest Canadian waterway flowing to the Pacific Ocean and is one of the world’s greatest salmon rivers. Our analyses reveal high runoff rates and low interannual variability in alpine and coastal rivers, and low runoff rates and high interannual variability in most streams in BC’s interior. The interannual variability in streamflow is also low in rivers such as the Adams, Chilko, Quesnel and Stuart where the principal salmon runs of the Fraser River occur. A trend analysis shows a spatially coherent signal with increasing interannual variability in streamflow across the FRB in recent decades, most notably in spring and summer. The upward trend in the coefficient of variation in annual runoff coincides with a period of near-normal annual runoff for the Fraser River at Hope. The interannual variability in streamflow is greater in regulated rather than natural systems; however, it is unclear whether it is predominantly flow regulation that leads to these observed differences. Environmental changes such as rising air temperatures, more frequent polarity changes in large-scale climate teleconnections such as El Niño-Southern Oscillation and Pacific Decadal Oscillation, and retreating glaciers may be contributing to the greater range in annual runoff fluctuations across the FRB. This has implications for ecological processes throughout the basin, for example affecting migrating and spawning salmon, a keystone species vital to First Nations communities as well as to commercial and recreational fisheries. To exemplify this linkage between variable flows and biological responses, the unusual FRB runoff anomalies observed in 2010 are discussed in the context of that year’s sockeye salmon run. As the climate continues to warm, greater variability in annual streamflow, and hence in hydrological extremes, may influence ecological processes and human usage throughout the FRB in the 21st century.

Tree-ring based PDSI reconstruction since 1853 AD in the source of the Fenhe river basin, Shanxi province, China

A robust tree-ring-width chronology was developed from two Pinus tabulaeformis sampling sites in the source of the Fenhe River, Shanxi Province, China. Based on the tree-ring-width indices, a 157-year long Palmer Drought Severity Index (PDSI) was reconstructed, which explains 53.7% of the variance of the modeled PDSI over the common period 1957-2008. The drought periods in the study area include 1914–1931 and 1970 to the present, whereas the wet periods were 1866-1892 and 1932–1969. The drought of 1914–1931 was a severe long-lasting drought with a low inter-annual variability, and the drought of 1970–2009 was an overall long-term drought with a high inter-annual variability. The period of 1866-1892 is a continuously wet period with a low inter-annual variability and the period of 1932–1969 is an overall long-term wet period with a high inter-annual variability. The reconstructed PDSI series in the source of the Fenhe River shows synchronous variations with the regional drought/wetness indices. Spatial correlation analyses indicate that the higher correlations lie exclusively in the Fenhe River Basin. This indicates that the reconstructed PDSI has regional representativeness and can represent the drought history of the entire Fenhe River Basin to some extent. Furthermore, the reconstructed PDSI matches with the variability of the per unit yield of summer grain crops in Shanxi Province very well and they have significant correlation. From a long-term perspective the reconstructed PDSI series could supply scientific and valuable information to the water resources management and then help the sustainable development in agricultural production, economic development, and ecosystem balance.