Seasonal Nutrient Dynamics Research Articles

Comparative nutrient drawdown capacities of farmed kelps and implications of metabolic strategy and nutrient source.

Seaweed aquaculture, particularly kelp farming, is a popular topic as a potential solution for mitigating anthropogenic pollutants and enhancing coastal drawdown of carbon and nitrogen. Using a common garden approach, this study evaluated nutrient drawdown capacities of Alaria marginata (ribbon kelp) and Saccharina latissima (sugar kelp) across four commercial kelp farms in Southeast and Southcentral Alaska. Our findings show that A. marginata exhibited ~30% more carbon and 21% more nitrogen content compared to S. latissima. These results demonstrate the potential for A. marginata to serve as a more efficient species for nutrient drawdown into farmed kelp tissues (per unit biomass) for consideration of potential mitigative actions. The efficacy of this drawdown is likely to be driven by the careful pairing of kelp species with farming environment. Temporally, there was a noted increase in carbon content and a decline in nitrogen content from March to May for both species, consistent with known seasonal nutrient dynamics in coastal waters. Notably, differences in the carbon stable isotope signatures (δ13C) between the kelps may hint at variations in metabolic pathways and nutrient sourcing, particularly concerning the preferential assimilation of CO2 versus , and highlight the need for further work on this topic for applied macroalgal research.

Change in the Ecological Stoichiometry of Carex thunbergii in Response to Seasonal Dynamics and Environmental Factors in Shengjin Lake, China

Exploring the effects of environmental factors and plant physiological processes on plant nutrient stoichiometry is of great significance to understanding how wetland vegetation distributes and maintains function. However, we have a limited understanding of how the combination of plant communities and seasonality with soil physicochemical properties affects nutrient stoichiometry in wetland plants. In this study, we examined these factors in Carex thunbergii and soil across four types of plant communities dominant in the riparian zone of Shengjin Lake during the non−flooding periods of December 2020 and March 2021. In winter, the total foliar C, N, and P concentrations decreased along with an increase in plant coverage, which did not differ in spring. The C, N, C: P, and N: P of foliage significantly increased over the season, while soil C, N, C: P, and N: P significantly decreased over the season. Both in winter and spring, soil C and soil N decreased along with the increase of plant coverage. Our results suggest that both plant community and soil physicochemical properties have a significant influence on plant nutrient stoichiometry. This study improves our understanding of the seasonal dynamics of plant nutrients under different communities and soil physicochemical properties.

The life state of smooth vetch regulates the seasonal dynamics of microbial nutrient limitations in citrus orchards

AbstractCover crops improve soil fertility in orchard ecosystems, however, the response of soil microbial metabolism to fruit tree interactions with cover legumes at different stages of the life cycle remains uncertain, thereby limiting our understanding of the mechanisms that regulate nutrient cycling in orchards with cover crop management. Here, the characteristics of microbial energy (carbon, C) and nutrient (nitrogen, N or phosphorus, P) metabolism in the citrus rhizosphere and bulk soil in orchards were analyzed with two managements, that is, smooth vetch (Vicia villosa Roth var. glabresens Koch) cover and clean tillage, using an extracellular enzymatic stoichiometry model. Microbial C limitation was significantly reduced by cover during the vetch growing season owing to the resulting higher plant root C and soil organic C content. Competition for N between plants and microbes in the bulk soil might lead to significant microbial N limitation in covered orchards during the vetch‐decomposition season, presumably owing to a significant increase in citrus root N and a concomitant decrease in bulk soil total N. Partial least squares path modeling showed that citrus root nutrient contents negatively affected microbial C limitation, while soil nutrients negatively affected microbial relative nutrient limitation in covered orchards. Conversely, both effects were reversed by tillage. Smooth vetch cover mitigated microbial C limitation, and the microbial relative N/P limitation was also influenced by the life state of smooth vetch. Our study highlights the importance of changes in microbial metabolism driven by seasonal nutrient dynamics for understanding soil nutrient cycling and optimizing cover‐legumes management in orchards.

Alkaline phosphatase activity in an equatorial coral reef ecosystem unrelated to seasonal nutrient dynamics

Alkaline phosphatase activity in an equatorial coral reef ecosystem unrelated to seasonal nutrient dynamics

Dynamic Change Characteristics of Litter and Nutrient Return in Subtropical Evergreen Broad-Leaved Forest in Different Extreme Weather Disturbance Years in Ailao Mountain, Yunnan Province

By studying the dynamic change characteristics of litter production, composition, nutrient content, and return amount of different components in different extreme weather interference years of Ailao Mountain evergreen broad-leaved forest, the paper provides theoretical support for the post-disaster nutrient cycle, ecological recovery, and sustainable development of the subtropical mid-mountain humid evergreen broad-leaved forest. Square litter collectors were randomly set up to collect litter. After drying to a constant mass, we calculated the seasonal and annual litter volume and the contents of organic carbon (C), total nitrogen (N), total phosphorus (P), total potassium (k), total sulfur (S), total calcium (Ca), and total magnesium (Mg). Finally, the nutrient return amount is comprehensively calculated according to the litter amount and element content. We tracked dynamic changes in litter quantity, nutrient composition, and nutrient components across different years. The results showed that the amount of litter from 2005 to 2015 was 7704–8818 kg·hm−2, and the order of magnitude was: 2005 (normal year) > 2015 (extreme snow and ice weather interference) > 2010 (extreme drought weather interference); the composition mainly included branches, leaves, fruit (flowers), and other components (bark, moss, lichen, etc.), of which the proportion of leaves was the largest, accounting for 41.70%–61.52%; The monthly changes and total amounts in different years exhibited single or double peak changes, and the monthly litter components in different years showed significant seasonality. In this study, the nutrient content of litter was higher than that of litter branches each year. The total amount of litter and the nutrient concentration of each component are C, Ca, N, K, Mg, S, and P, from large to small. The order of nutrient return in different years was the same as that of litter, and the returns of nutrients in litter leaves were greater than that of litter branches. The ratio of nutrient returns of litter and litter branches from 2005 to 2010 was 2.03, 1.23, and 3.69, respectively. The research shows that the litter decreased correspondingly under the extreme weather disturbance, and the impact of the extreme dry weather disturbance was greater than that of the extreme ice and snow weather disturbance. However, the evergreen broad-leaved forest in the study area recovers well after being disturbed. The annual litter amount and nutrient return amount is similar to that of evergreen broad-leaved forests in the same latitude and normal years in other subtropical regions. The decomposition rate and seasonal dynamics of litter nutrients are not greatly affected by extreme weather.

Factors affecting the seasonal succession of phytoplankton functional groups in a tropical floodplain reservoir in Vietnam

Abstract Phytoplankton communities can be classified into different groups based on physiological, morphological, and ecological functions. In this study, the responses of phytoplankton functional groups (PFGs) to physicochemical variables and hydraulic regimes were investigated and used as ecological indicators in the Tri An Reservoir (TAR), a eutrophic tropical floodplain reservoir located in southern Vietnam. Altogether, 148 phytoplankton taxa were identified and assigned to 16 PFGs; the four predominant PFG groups were M (Microcystis spp.), MP (filamentous cyanobacteria: Oscillatoria spp., and some other diatoms: Gomphonema angustatum, Navicula sp.), J (green algae: Coelastrum spp., Cosmarium spp., Pediastrum spp., Scenedesmus spp., Staurastrum spp., Tetradesmus spp., Tetraëdron spp., and Xanthidium spp.), and P (Closterium spp., Aulacoseira granulata, Fragilaria spp., Pinnularia spp., and Desmidium baileyi). The average PFG biovolume ranged from 79.6 ± 20.2 to 230.1 ± 69.1 mg/L with M being the dominant group. The trophic state index (TSI) indicated that the water condition was light-eutrophic to hyper-eutrophic. It was found that the large water level fluctuation resulted in seasonal nutrient dynamics, with higher nutrient concentrations and higher turbidity during the low water level period and vice versa. The redundancy analysis (RDA) indicated that the nutrient concentrations, water level fluctuation, and mixing regimes were critical factors in the PFG selection in the TAR. Therefore, we assumed that water level fluctuation management coupled with biological competition have the potential to control toxic cyanobacteria in the TAR. In conclusion, the PFGs are suitable for examining the effects of environmental conditions on phytoplankton dynamics in tropical floodplain reservoirs, but their sensitivity to long-term changes in water quality and eutrophication requires further investigation.

Seasonal Dynamics of Dry Matter Accumulation and Nutrients in a Mature Miscanthus × giganteus Stand in the Lower Silesia Region of Poland

Biomass from M. × giganteus has great promise for use within the bioeconomy sectors, but to maximise environmental benefits, crops must produce high yields while minimising energetically costly inputs. Complex interactions between soil conditions, climatic variations, plant maturity and genotype influence yields and nutrient dynamics, which in turn impacts crop sustainability. To investigate the flux of growth and nutrients in response to a changing environment, M. × giganteus was grown in southwest Poland and sampled monthly (June–November) from 2010 to 2012. Measurements examined the interaction between plant growth and leaf development, and nutrient (N, P, K, Ca and Mg) concentrations of rhizomes, stems and leaves. The three growth years studied were markedly different for growth and meteorological conditions. Between 2010 and 2011, above ground biomass yield increased significantly from 16.5 ± 0.4 t ha−1 to 20.1 ± 0.5 t ha−1. The 2012 rhizome weights at the beginning of the growth season were halved due to extreme frost; however, resulting yield was similar (19.9 ± 0.6 5 t ha−1). Final yield from all three years were successfully predicted using MISCANFOR, and modelling indicated crop yield was water-limited. The seasonal flux of N and K from rhizome to stems and leaves then back to the rhizome at the onset of senescence was as expected in 2010 and 2011. In 2012, no such trend was evident especially for N suggesting different macronutrient sources from rhizome and soil improves the resilience of perennial crop yield across a range of diverse growth conditions.

Seasonal nutrient dynamics in the P depleted Eastern Mediterranean Sea

The Eastern Mediterranean Sea (EMS), is ultra-oligotrophic with unusual anti-estuarine circulation. It is P depleted and the limited enrichment studies which have been carried out, suggest seasonal changes in nutrient limitation. In this study high sensitivity dissolved nutrients (and associated parameters) were determined monthly over an annual cycle at a pelagic location in the SE Levantine basin. Nitrate & Nitrite (Nox) concentrations were high (300–500 nM) during the winter mixing period and enabled a concurrent phytoplankton increase in which larger picoeukaryotes and eukaryotes were dominant. After the thermal stratification of the water column commenced, Nox decreased through early summer transition period to low values (generally 50 nM or less) in the late summer. DIP remained at low nM concentrations the entire year while DOP decreased from 40 nM in winter to 30 nM in summer.. Prochlorococcus, the smallest picocyanobacteria, that does not typically utilize nitrate, dominated during the summer when both Nox and DIP concentrations were lowest. Ammonium concentrations were low (10–100 nM) with no systematic changes with season or depth. As a result, the DIN:DIP ratios were high (20–825) in winter and low (2–66) in summer, showing that these ratios vary seasonally. The dynamics of nutrient availability combined with the temporal changes in total chlorophyll and the altered dominance of the predominant phytoplankton species (i.e. nitrate-metabolizing Synechococcus during winter versus the smaller Prochlorococcus abundant in summer), leads to our hypothesis that the seasonal change in DIN:DIP indicates a switch from P limitation in winter during the annual phytoplankton increase to N&P or even N limitation in summer. Export Production (172 mmol N m−2 y−1) determined from the calculated loss of Nox from the photic zone, was similar to previous estimates in the EMS. Our results in terms of seasonally changing nutrient dynamics and resulting productivity confirm that the EMS has many of the characteristics found in P starved ocean gyre systems.

Seasonal dynamics of energy and nutrients of Pinus koraiensis seedlings in different successional stages of broadleaved Korean pine forest in Changbai Mountain, China.

We examined the seasonal variations of growth and nutrient accumulation of two-year-old Korean pine (Pinus koraiensis) seedlings in the primary broadleaved Korean pine forest (primary forest) and poplar birch forest (secondary forest) in Changbai Mountain. The seasonal changes of photosynthetically active radiation (PAR), seedling biomass, nonstructural carbohydrate (NSC), total nitrogen (N), and total phosphorus (P) were measured in both forests. The effects of understory light and its seasonal variations in both forests on the growth and nutrient accumulation of understory Korean pine seedlings were also explored. The results showed that the seasonal variations of monthly cumulative PAR under both forests showed a double-peak pattern. In summer, light conditions under the two forests were poor because of the closed canopy. In spring and autumn, light conditions were better due to the deciduous characteristics of canopy broadleaved trees, with light conditions under the secondary forest being obviously better than that of the primary forest. The seasonal variations of biomass, NSC, total N and total P concentrations of Korean pine seedlings in the primary and secondary forests were basically consistent with that of understory light. All those variables increased significantly in spring and autumn, and decreased in summer. In spring, starch concentration increased. In summer, starch and soluble sugar concentrations decreased gradually, and touched bottom in August. In autumn, soluble sugar concentration increased significantly. The biomass and NSC concentration of seedlings under secondary forest were significantly higher than those under primary forest in spring and autumn, but without difference in summer. Therefore, the diffe-rence of understory light conditions in spring and autumn between the two forests might be the key factor driving nutrient accumulation, growth and regeneration of Korean pine seedlings.

Seasonal dynamics of soil nutrients and microbial activity due to colonization by bracken ferns (Pteridium aquilinum (L.) Kuhn) in a pine forest

Bracken (Pteridium aquilinum) is an aggressive colonizer of disturbed and other successional habitats in temperate forests. However, little is known about how bracken colonization modifies soil microbial activity and nutrient cycling. We questioned whether bracken presence alters soil nutrient pools and soil microbial respiration throughout a growing season and whether this effect depends on the size of the bracken patch. To answer these questions, we sampled the soil in bracken patches of different sizes (large, medium and small) and in the surrounding pine forest (paired sampling design) in summer, autumn, winter and spring. We analyzed the samples to determine nutrient contents (C, N and P) and soil microbial respiration. Patch size did not influence soil microbial activity or nutrient pools. Bracken acted as nutrient sink for N pools through the growing season and as source or sink for C and P pools depending on season. Moreover, the effect on nutrient pools did not depend on bracken characteristics (area, density or height). Bracken presence enhanced soil microbial respiration proportionally to patch area. The control that bracken exerts over nutrient pools may determine the successful (or otherwise) establishment of other plant species. This contributes to making bracken a successful colonizer as no particular population threshold (area, density) has to be reached before nutrients becomes limiting to other plant species.

Spatiotemporal distribution of canopy litter and nutrient resorption in a chronosequence of different development stages of Cunninghamia lanceolata in southeast China

Canopy litter is an important component of coarse woody debris (CWD), which affects nutrient and carbon cycling in forest ecosystems. For marcescent plant species (characterized by dead branches and leaves remaining in the canopy for several years before abscission), nutrient resorption from senescing leaves is an important nutrient conservation strategy. However, investigating the ecological function of canopy litter is challenging due to its limited accessibility and also the heterogeneous canopy microclimate in terms of light transmission, temperature and moisture. We studied the spatiotemporal distribution of canopy litter mass and seasonal dynamics of leaf nutrients and nutrient resorption during senescence in the canopy along a chronosequence of Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] plantations in southeast China. The dry mass weight of dead branches and dead leaves in the canopy significantly increased with stand stage (14.6, 14.2, and 17.4 t ha−1 for young, middle-aged, and mature stands respectively), accounting for high proportions of total aboveground litter of 85.7%, 79.1% and 80.0%, respectively, along with annual litterfall production (2.44, 3.75, and 4.34 t ha−1, respectively). The canopy height distribution of dead branches and leaves also increased with stand age, ranging from 0 to 4 m in young stands, 3–8 m in middle-aged stands, to 4–10 m in mature stands. The seasonal pattern of canopy litter mass was the inverse of litterfall production: canopy litter mass peaked, while litterfall production was lowest in winter. Mean N, P, K, and Mg nutrient resorption efficiencies across stands at each stage were 53.8–58.9%, 64.0–68.9%, 85.0–90.2%, and 46.5–56.6%, respectively, while Ca was not retranslocated from senescing leaves. In summary, Chinese fir plantations retain large amounts of dead branches and leaves in the canopy from which at least ~50% of the nutrients N, P, K and Mg are recycled, representing an important nutrient conservation strategy that has evolved to adapt to nutrient-limited habitats. Canopy litter therefore plays an important role in these forest plantation ecosystems and should be protected instead of being removed from the canopy to the forest floor.

Spatial patterns and seasonal dynamics of foliar nutrients in 5-year-old Betula alnoides plantations

Spatial distribution and season-induced variations in foliar nutrients of tree crowns play key roles in growth, and nutrient retranslocation and resorption from leaves are important mechanisms for trees to cope with sites of diversified fertility. Seasonal dynamics and spatial patterns of foliar macronutrients (Nitrogen (N), Phosphorus (P) and Potassium (K)) as well as nutrient retranslocation and resorption in a series of crown layers were examined in 5-year-old Betula alnoides plantations using a spacing trial (2500 (2 m × 2 m, spacing), 1667 (2 m × 3 m), 1250 (2 m × 4 m), 1111 (3 m × 3 m), 833 (3 m × 4 m) and 625 (4 m × 4 m) stems·ha−1) in south China. Significant effects of planting density on foliar nutrient concentrations and nutrient retranslocation and resorption were absent during a whole seasonal cycle or in each season. Both foliar total P and K concentrations increased significantly with increasing crown depth, whereas an obvious trend was not observed for foliar total N concentration. The season with the lowest foliar nutrient concentration varied with the elements, i.e. summer (Jul) for N, winter (Jan) for P and spring (Apr) for K, whereas the highest was observed in autumn (Oct) for all these macronutrient elements. Among crown layers, differences in nutrient concentrations were much lower in the high growth seasons from October to April than those in other seasons. There were significant differences among crown layers in N and P retranslocation efficiency rather than in nutrient resorption efficiency. Significant differences were absent in both retranslocation and resorption efficiencies of K. The highest nutrient retranslocation efficiency was found in the crown layer 2–3 m above ground level for N and 3–4 m for P. The absence of considerable differences among spacing treatments and crown layers mentioned above might be due to the weak early intra-specific competition induced by planting density, soil fertility or fertilization and nutrient demands of this species. These findings could provide suggestions for implementing proper pruning treatments, improving fertilization regimes and other related forest managements for B. alnoides and even other valuable timber species in the tropical and warm sub-tropical regions.

Seasonal responses of nutrient to hydrology and biology in the southern Yellow Sea

Seasonal nutrient dynamics regulated by hydrological and biological variables in the southern Yellow Sea (SYS) were studied based on the datasets collected during four cruises: spring (April 28-May 10, 2014), summer (August 17-September 22, 2015), autumn (November 7–17, 2014) and winter (January 13-February 1, 2016). In the present study, by dividing the study area into three distinct current-dominated subregions based on T-S distribution, cluster analysis, and principal components analysis (PCA), we revealed that the response mechanisms of nutrients to physical and biological processes were important. Among all factors, the physical processes, mainly including the Yellow Sea Cold Water Mass (YSCWM) onset, the Changjiang (Yangtze) Diluted water (CDW) and Taiwan Warm Current (TWC) intrusion and the Yellow Sea Warm Current (YSWC) invasion, were the principal driving force, which significantly changed the inherent balance of nutrient structure. Meanwhile, biological depletion was also a significant factor, especially in the stratified seasons, even though its impact on the nutrient structure could be balanced by vigorous water exchange or vertical mixing. The regional variation of nutrient regime and the regulatory mechanism behind it were revealed at the same time. The coastal area showed strong signs of potential P limitation as a result of excessive dissolved inorganic nitrogen (DIN) entering via terrestrial runoff and anthropogenic activities. The 32 °N transect, which is adjacent to the boundary of the SYS and the East China Sea (ECS), showed varying hydrological features due to the strong intrusion of CDW and TWC. Therefore, P or Si were the main limiting factor for the development of algal biomass. The central study area possessed a comparatively stable water column with the specific existence of the YSCWM present at the bottom, thus acting as a potential nutrient pool. Hence, we hypothesized that the offshore side of the study area tended to be more P and N co-limited, whereas the nutrient cycles in the nearshore side showed significant seasonal and regional variations, which corresponded to the change in physical oceanographic processes and algal biomass.

Seasonal and Tidal Dynamics of Nutrients and Chlorophyll a Concentration in Water at the Sundarbans Mangrove Ecosystems of Bangladesh

The seasonal and tidal variations of physicochemical parameters, nutrient concentrations and chlorophyll a concentration from the water of Passur river and Koromjol canal in the Sundarbans mangrove ecosystems were investigated during March 2018 to February 2019. Samples were collected from five sampling stations during March, August and November where these months were considered as pre-monsoon, monsoon and post-monsoon seasons, respectively. The nutrients NH3-N, NO3-N, PO4-P, SO4 and Chlorophyll a concentrations were found 0.001 to 0.09, 3.5 to 50, 0.06 to 5.4, 30 to 272 and 0.18 to 1.75 mg/L, respectively, during high tides, and 0.001 to 0.39, 4.2 to 47, 0.1 to 2.75, 20 to 179 and 0.218 to 1.88 mg/L, respectively, during low tides. The NO3-N was very high than suitable limit during both tides at monsoon and post-monsoon season. The PO4-P was found moderately high during both tides at all stations. The SO4 was found to be 187.8 and 76.87 mg/L during high tide, and 135.4 and 95.73 mg/L during low tides in pre-monsoon and post-monsoon, respectively, that were very high than water quality standards. The Passur river and the Koromjol canal were fluctuating seasonally and tidally in some magnitude and their variations can alter the water quality as well as the density and distribution of living organisms.

The importance of nutrient hotspots for grazing ungulates in a Miombo ecosystem, Tanzania.

While movement patterns of grazing ungulates are strongly dependent on forage quality their use of nutrient hotspots such as termite mounds or grazing lawns has rarely been quantified, especially in savanna ecosystems where soil-nutrient quality is low. Additionally, few experiments have been conducted to determine the role of termite mound- and grazing lawn-derived soils in improving forage quality in the field. We studied wild ungulate grazing activities around ten termite mounds, six grazing lawns and their respective control sites in a Miombo system of Issa Valley, western Tanzania, in the same system. We used indirect observations (i.e., dung, tracks) to identify seasonal and spatial variations in habitat use of various wild mammalian grazers. Grazer visitation rates were nine and three times higher on termite mounds and grazing lawns, respectively, compared to control sites. During the rainy season, termite mounds were more frequently used than grazing lawns while the latter were used more often during the dry season. In an additional pot experiment with soils derived from different areas, we found that Cynodon dactylon in termite mound-derived soils had twice as high Nitrogen and Phosphorous contents and biomass compared to grasses planted in grazing lawn soils and control site soils. We highlight that both termite mounds and grazing lawns play a significant role in influencing seasonal nutrient dynamics, forage nutrient quality, habitat selectivity, and, hence, grazing activities and movement patterns of wild ungulate grazers in savannas. We conclude that termite mounds and grazing lawns are important for habitat heterogeneity in otherwise nutrient–poor savanna systems.

Seasonal dynamics of nutrients and organic matter in urban stream

The study presents the results of water quality evaluation in the Setun River watershed, located entirely within the limits of the Moscow City. Multiple point and non-point sources of pollution cause the nutrient and organic matter content of the river and its tributaries to significantly differ from the natural background. Maximum nitrogen and phosphorus concentrations were observed at the upper reaches of the river during the summer low flow due to the landfill impact. Because of the extreme nutrient pollution at the river’s upper course, subsequent water inflow, even from significantly polluted tributaries, has a diluting effect, and the nutrient concentration decreases downstream. The effect of urbanization on the organic matter content is reflected in elevated COD and BOD values that exceed the national environmental guidelines. Seasonal dynamics of organic matter content includes increased organic matter during snowmelt and its relatively low content during summer.

Seasonal dynamics of carbonate chemistry, nutrients and CO2 uptake in a sub-Arctic fjord

Environmental change can have a significant impact on biogeochemical cycles at high latitudes and be particularly important in ecologically valuable fjord ecosystems. Seasonality in biogeochemical cycling in a sub-Arctic fjord of northern Norway (Kaldfjorden) was investigated from October 2016 to September 2018. Monthly changes in total inorganic carbon (CT), alkalinity (AT), major nutrients and calcium carbonate saturation (Ω) were driven by freshwater discharge, biological production and mixing with subsurface carbon-rich coastal water. Stable oxygen isotope ratios indicated that meteoric water (snow melt, river runoff, precipitation) had stratified and freshened surface waters, contributing to 81% of the monthly CT deficit in the surface layer. The timing and magnitude of freshwater inputs played an important role in Ω variability, reducing AT and CT by dilution. This dilution effect was strongly counteracted by the opposing effect of primary production that dominated surface water Ω seasonality. The spring phytoplankton bloom rapidly depleted nitrate and CT to drive highest Ω (~2.3) in surface waters. Calcification reduced AT and CT, which accounted for 21% of the monthly decrease in Ω during a coccolithophore bloom. Freshwater runoff contributed CT, AT and silicates of terrestrial origin to the fjord. Lowest surface water Ω (~1.6) resulted from organic matter remineralisation and mixing into subsurface water during winter and spring. Surface waters were undersaturated with respect to atmospheric CO2, resulting in modest uptake of –0.32 ± 0.03 mol C m–2 yr–1. Net community production estimated from carbon drawdown was 14 ± 2 g C m–2 yr–1 during the productive season. Kaldfjorden currently functions as an atmospheric CO2 sink of 3.9 ± 0.3 g C m–2 yr–1. Time-series data are vital to better understand the processes and natural variability affecting biogeochemical cycling in dynamic coastal regions and thus better predict the impact of future changes on important fjord ecosystems.

Biogeochemical asynchrony: Ecosystem drivers of seasonal concentration regimes across the Great Lakes Basin

AbstractChanges in seasonal nutrient dynamics are occurring across a range of climates and land use types. Although it is known that seasonal patterns in nutrient availability are key drivers of both stream metabolism and eutrophication, there has been little success in developing a comprehensive understanding of seasonal variations in nutrient export across watersheds or of the relationship between nutrient seasonality and watershed characteristics. In the present study, we have used concentration and discharge data from more than 200 stations across U.S. and Canadian watersheds to identify (1) archetypal seasonal concentration regimes for nitrate, soluble reactive phosphorus (SRP), and total phosphorus, and (2) dominant watershed controls on these regimes across a gradient of climate, land use, and topography. Our analysis shows that less impacted watersheds, with more forested and wetland area, most commonly exhibit concentration regimes that are in phase with discharge, with concentration lows occurring during summer low‐flow periods. Agricultural watersheds also commonly exhibit in‐phase behavior, though the seasonality is usually muted compared to that seen in less impacted areas. With increasing urban area, however, nutrient concentrations frequently become essentially aseasonal or even exhibit clearly out‐of‐phase behavior. In addition, our data indicate that seasonal SRP concentration patterns may be strongly influenced by proximal controls such as the presence of dams and reservoirs. In all, these results suggest that human activity is significantly altering nutrient concentration regimes, with large potential consequences for both in‐stream metabolism and eutrophication risk in downstream waterbodies.

Seasonal and Tidal Dynamics of Nutrients and Chlorophyll a Concentration in Water at the Sundarbans Mangrove Ecosystems of Bangladesh

Seasonal and Tidal Dynamics of Nutrients and Chlorophyll a Concentration in Water at the Sundarbans Mangrove Ecosystems of Bangladesh

Change in ecological stoichiometry of Carex brevicuspis in response to seasonal dynamics and elevation in Dongting Lake, China

Plant nutrient stoichiometry is affected by both environmental factors and plant physiological processes. However, we know little about how small elevation gradients (influencing e.g. flooding regimes) and seasonality combine with soil physicochemical properties to influence nutrient stoichiometry in wetland plants. In this study, we examined these factors in Carex brevicuspis at Dongting Lake, China, during the non‐flooding periods in March, May and December of 2015 and February of 2016. We found that total foliar C concentration increased as elevation increased, especially during December 2015 and February 2016. At the low‐elevation site, total foliar C concentration decreased over the season, whereas it first increased and then decreased over time at higher elevations. Foliar total N and P concentrations decreased from March to May and subsequently increased throughout the season, and these concentrations were always much higher at the low‐elevation site. The C:N and C:P ratios first increased and then decreased over the season, while increasing with rising elevation. The N:P ratio was lower at the low‐elevation site, especially during May 2015 and February 2016; its variation over time differed across the elevations. A canonical correspondence analysis revealed that soil organic C, total N and soil nitrate N are important for determining C. brevicuspis stoichiometry. Our results suggest that both elevation and plant life stage have a significant influence on plant stoichiometry. This study improves our understanding of the seasonal dynamics of plant nutrients under different geographical conditions.