Seasonal Production Patterns Research Articles

Seasonal patterns of methylmercury production, release, and degradation in profundal sediment of a hypereutrophic reservoir

Fuhrmann B, Beutel M, Ganguli P, Zhao L, Brower S, Funk A, Pasek J. 2021. Seasonal patterns of methylmercury production, release, and degradation in profundal sediment of a hypereutrophic reservoir. Lake Reserv Manage. 37:360–377. Profundal lake sediment is an important site of toxic methylmercury (MeHg) production by anaerobic bacteria. This study tracked sediment MeHg cycling in hypereutrophic Hodges Reservoir, in the United States. Sediment-associated MeHg was most elevated in the early spring during moderately reduced conditions. In the late spring, MeHg and iron were released into hypolimnetic water during the progression from iron-reducing to sulfate-reducing conditions at the sediment–water interface. A decrease in porewater sulfate in the early summer indicated enhanced sulfate-reducing bacteria (SRB) activity and was associated with sediment buildup of MeHg, likely due to enhanced sorption to iron sulfides. Depletion of sulfate in the sediment during the fall corresponded with a substantial decrease in both sediment and water-column MeHg, suggesting that methanogenic conditions led to enhanced MeHg degradation. Shortly afterward, MeHg increased in the hypolimnion, indicating an upward shift in the zone of SRB methylation. Our study suggests 2 “hot moments” of MeHg entry into the water column, where it is susceptible to uptake into the pelagic food web: a spring window of mildly reduced conditions that promote MeHg release from sediment, and a fall window where MeHg is produced in the upper hypolimnion. These hot moments may potentially be managed to lower mercury bioaccumulation via redox enhancement of the profundal zone with approaches such as bottom water oxygenation, which began operation in Hodges Reservoir in 2020. However, the complexity of biogeochemical responses to such management perturbations in regard to MeHg cycling makes it difficult to predict the ultimate effect of oxygenation on mercury bioaccumulation. Supplemental data for this article is available online at https://doi.org/10.1080/10402381.2021.1940397 .

Evidence for the Impact of Climate Change on Primary Producers in the Southern Ocean

Within the framework of the Marine Ecosystem Assessment for the Southern Ocean (MEASO), this paper brings together analyses of recent trends in phytoplankton biomass, primary production and irradiance at the base of the mixed layer in the Southern Ocean and summarises future projections. Satellite observations suggest that phytoplankton biomass in the mixed-layer has increased over the last 20 years in most (but not all) parts of the Southern Ocean, whereas primary production at the base of the mixed-layer has likely decreased over the same period. Different satellite models of primary production (Vertically Generalised versus Carbon Based Production Models) give different patterns and directions of recent change in net primary production (NPP). At present, the satellite record is not long enough to distinguish between trends and climate-related cycles in primary production. Over the next 100 years, Earth system models project increasing NPP in the water column in the MEASO northern and Antarctic zones but decreases in the Subantarctic zone. Low confidence in these projections arises from: (1) the difficulty in mapping supply mechanisms for key nutrients (silicate, iron); and (2) understanding the effects of multiple stressors (including irradiance, nutrients, temperature, pCO2, pH, grazing) on different species of Antarctic phytoplankton. Notwithstanding these uncertainties, there are likely to be changes to the seasonal patterns of production and the microbial community present over the next 50–100 years and these changes will have ecological consequences across Southern Ocean food-webs, especially on key species such as Antarctic krill and silverfish.

Dynamics of primary productivity in relation to submerged vegetation of a shallow, eutrophic lagoon: A field and mesocosm study.

Aquatic ecosystems nowadays are under constant pressure, either from recent or historical events. In most systems with increased nutrient supply, submerged macrophytes got replaced by another stable state, dominated by phytoplankton as main primary producer. Yet, reducing the nutrient supply did not yield the aimed goal of restored habitats for submerged macrophytes in systems worldwide. The question arises, why submerged macrophytes do not re-colonize, and if they are actually competitive. Therefore, primary production assays were conducted in ex-situ bentho-pelagic mesocosms and compared to the actual ecosystem, a turbid brackish lagoon of the southern Baltic Sea. Mesocosm were either manipulated to be colonized by macrophytes, or stayed phytoplankton dominated. Oxygen evolution was monitored over a period of five months in 5 min (mesocosms) to 10 min (ecosystem) intervals. Surface and depth-integrated production was calculated to analyse seasonal and areal resolved production patterns. It was found that macrophyte mesocosms were more stable, when considering only surface O2 production. However, calculating depth-integrated production resulted in net-heterotrophy in both shallow mesocosms approaches and the actual ecosystem. This heterotrophy is likely mediated by sediment respiration and POC accumulation in mesocosms, and a low share of productive to respiring water column in the actual ecosystem. Therefore, it seems unlikely that macrophytes will re-settle, as constant net-heterotrophy may allow for high-nutrient turnover at sediment-water interfaces and within the water column, favouring phytoplankton. These results will assist decision makers in developing more effective restoration measures that can mitigate the negative effects of eutrophication on ecosystem function and services.

Climate and Socioeconomic Factors Drive Irrigated Agriculture Dynamics in the Lower Colorado River Basin

The Colorado River Basin (CRB) includes seven states and provides municipal and industrial water to millions of people across all major southwestern cities both inside and outside the basin. Agriculture is the largest part of the CRB economy and crop production depends on irrigation, which accounts for about 74% of the total water demand cross the region. A better understanding of irrigation water demands is critically needed as temperatures continue to rise and drought intensifies, potentially leading to water shortages across the region. Yet, past research on irrigation dynamics has generally utilized relatively low spatiotemporal resolution datasets and has often overlooked the relationship between climate and management decisions such as land fallowing, i.e., the practice of leaving cultivated land idle for a growing season. Here, we produced annual estimates of fallow and active cropland extent at high spatial resolution (30 m) from 2001 to 2017 by applying the fallow-land algorithm based on neighborhood and temporal anomalies (FANTA). We specifically focused on diverse CRB agricultural regions: the lower Colorado River planning (LCRP) area and the Pinal and Phoenix active management areas (PPAMA). Utilizing ground observations collected in 2014 and 2017, we found an overall classification accuracy of 88.9% and 87.2% for LCRP and PPAMA, respectively. We then quantified how factors such as climate, district water rights, and market value influenced: (1) annual fallow and active cropland extent and (2) annual cropland productivity, approximated by integrated growing season NDVI (iNDVI). We found that for the LCRP, a region of winter cropping and senior (i.e., preferential) water rights, active cropland productivity was positively correlated with cool-season average vapor pressure deficit (R = 0.72; p < 0.01). By contrast, for the PPAMA, a region of summer cropping and junior water rights, annual fallow and active cropland extent was positively correlated with cool-season aridity (precipitation/potential evapotranspiration) (R = 0.46; p < 0.05), and active cropland productivity was positively correlated with warm-season aridity (precipitation/potential evapotranspiration) (R = 0.42; p < 0.01). We also found that PPAMA cropland productivity was more sensitive to aridity when crop prices were low, potentially due to the influence of market value on management decisions. Our analysis highlights how biophysical (e.g., temperature and precipitation) and socioeconomic (e.g., water rights and crop market value) factors interact to explain seasonal patterns of cropland extent, water use and productivity. These findings indicate that increasing aridity across the region may result in reduced cropland productivity and increased land fallowing for some regions, particularly those with junior water rights.

Time Series Model to Forecast the Pricing of Dairy Products

Seasonal patterns and patterns of food production are linked with each other, which contributes to have a significant impact on the economy of a country. Seasons and food production patterns are linked with each other. Because of this, it is of the utmost importance to establish projections about the production of food patterns that are sensitive to variations in the climate, which will ultimately result in satisfied customers and successful production. Because of this, it is vital to establish trustworthy techniques of dairy production forecasting in order to prevent a shortage of dairy production in an industry. As a result, the purpose of this study is to construct a model that is capable of reliably predicting the price of dairy products in relation to changes in the climate. In the course of the research for the thesis, Ireland will serve as the case study, and a mix of time series and machine learning models will be utilized in order to make price predictions. A time series of data relating to dairy production from the year 1990 to 2019 is extracted and utilized as a data source for dairy products. This data source will be used until the year 2019. The work that was actually done for the proposed paper makes use of the entire dataset for training purposes and makes use of the pricing list for the previous year for the testing phase. These are then utilized as variables in order to assess product yields as well as product losses. The implementation, on the other hand, is based on the principles of time series as well as four machine learning algorithms, specifically ARIMA, ARIMA Garch, SEM, and SARIMA. In compared to the results of other models, it was shown that the SARIMA model produced superior results. In addition, the findings were computed on the basis of an assessment matrix that took into account the root mean square error.

Seasonal variations in viral distribution, dynamics, and viral-mediated host mortality in the Arabian Sea

Viruses are key players in the marine ecosystem. It is critical to study specific viral processes and their inter-relationship with various biotic and abiotic variables to quantify their impact on the marine environment. This study investigates the influence of seasonality on viral distribution and their mediated processes in the coastal region of the southeastern Arabian Sea (India) for two consecutive years (2014 and 2015). Water samples were collected from four sampling stations, S1, S2, S3 and S4, in the southeastern Arabian Sea on a monthly basis. Samples were analyzed for the variations in viral abundance, viral production, and viral-induced host mortality covering three seasons namely, pre-monsoon, monsoon and post-monsoon. Viruses and bacteria were enumerated by epifluorescence microscopy following staining with SYBR Green I and viral production was estimated using viral dilution method. Seasonal variations in viral-mediated mortality and microzooplankton grazing mortality of phytoplankton hosts were estimated by modified dilution method. The results revealed a pronounced seasonal pattern of viral abundance (0.04–4.03 × 107 viruses mL−1) and viral production (0.71 × 1010–4.94 × 1010 L−1d−1). The observed high viral-induced mortality of prokaryotes (25.85%) and phytoplankton (7.98–28.9%) during the pre-monsoon season was eventually linked to high viral abundance and production rates. Viral-mediated processes were essentially linked to host density and water temperature. Transmission electron microscopy analysis revealed that myoviruses and non-tailed viruses were dominant in the study region with rod-shaped bacteria being more susceptible to viral infection. The results indicated the prevalence of seasonally induced active viral processes in this tropical marine ecosystem which may significantly contribute to rapid recycling of nutrients in this region.

Remarkable Similarity in Timing of Absorptive Fine-Root Production Across 11 Diverse Temperate Tree Species in a Common Garden.

Long-term minirhizotron observations of absorptive fine roots provide insights into seasonal patterns of belowground root production and carbon dynamics. Our objective was to compare root dynamics over time across mature individuals of 11 temperate trees species: five evergreen and six deciduous. We analyzed the timing and growth on 1st-and 2nd-order roots in minirhizotron images down to a vertical depth of 35 cm, as well as monthly and total annual length production. Production patterns were related to total annual precipitation of the actual and previous year of root production over 6 years. The main or largest peak of annual fine-root production occurred between June and September for almost all species and years. In most years, when peaks occurred, the timing of peak root production was synchronized across all species. A linear mixed model revealed significant differences in monthly fine-root length production across species in certain years (species x year, P < 0.0001), which was strongly influenced by three tree species. Total annual root production was much higher in 2000–2002, when there was above-average rainfall in the previous year, compared with production in 2005–2007, which followed years of lower-than-average rainfall (2003–2006). Compared to the wetter period all species experienced a decline of at least 75% in annual production in the drier years. Total annual root length production was more strongly associated with previous year’s (P < 0.001) compared with the actual year’s precipitation (P = 0.003). Remarkably similar timing of monthly absorptive fine-root growth can occur across multiple species of diverse phylogeny and leaf habit in a given year, suggesting a strong influence of extrinsic factors on absorptive fine-root growth. The influence of previous year precipitation on annual absorptive fine-root growth underscores the importance of legacy effects in biological responses and suggests that a growth response of temperate trees to extreme precipitation or drought events can be exacerbated across years.

Seasonal Patterns of Denitrification and N2O Production in a Southern New England Salt Marsh

Denitrification removes reactive nitrogen (N) from ecosystems by transforming nitrate (NO3−) to dinitrogen (N2) gas. Incomplete denitrification produces nitrous oxide (N2O), a potent greenhouse gas. In salt marshes, denitrification, N2O production, and N2O yield (the fraction of denitrification that produces N2O) have implications for N load reduction and greenhouse gas emissions. We collected soil cores from three salt marsh zones (low marsh, high marsh, and invasive Phragmites australis) on five sampling dates that spanned the growing season (May through October) to quantify seasonal patterns of potential denitrification, N2O production, and N2O yield. Potential denitrification peaked at the beginning and end of the growing season, with rates several times higher in May and October than in June, but we found no significant differences among salt marsh zones. In contrast, seasonal patterns of potential N2O production depended on marsh zone; N2O production was aseasonal in high marsh and P. australis zones, but in the low marsh, N2O production was lower in July compared to all other months sampled. In this salt marsh, seasonal variation of potential denitrification and N2O production was greater than spatial variation over the marsh zones, highlighting the importance of understanding temporal patterns of salt marsh N cycling.

Management Practices of Pasture, Range and Grazing Reserves for Livestock Production in the Tropics: A Review

The objective of the paper was to review management practices of pasture, range and grazing reserves in order to ensure steady supply of feed and promote sustainable livestock productivity in the tropics. Grazing management deals with such questions as how long should animals stay in one area and how long they should stay off it; which animals should graze what pasture; how many animals should graze together and what other activities should be integrated with grazing. Grazing management and stocking rate are the two most important variables affecting herbage production, seasonal pattern of production, herbage quality and botanical composition. Farm animals require nutrients to support body maintenance, reproduction, lactation, and growth. The nutritional needs of livestock vary according to breed, age, sex, class, stage of production, performance level and weight. Physiological and environmental stressors, such as sickness and weather, can also influence nutritional requirements. Ruminant animals, especially cattle, sheep and goats are natural grazers and possess remarkable ability to digest plant carbohydrates that is generally indigestible by most other mammals. It is natural then to assume that, grazing is the best way to supply a nutrient-dense diet to ruminant animals. Pasture land with high quality grass-legume can meet energy requirements of growing or lactating ruminants in the wet season. Energy supplementation on pasture helps in maintaining high grains and milk production. High quality forages have the ability to supply all the energy needed to maintain highly-productive ruminants throughout the growing season, but only when managed intensively. Legume-grass pastures have protein content greater than 18% during the vegetative stage. Feed resources that contain minerals include; range or pasture plants, harvested forages, concentrates and mineral supplements. The levels of minerals in plants are a function of interaction between several factors which include soil type, plant species, stage of maturity, dry matter yield, grazing management and climate. Forage conservation and preservation should be highly encouraged among farmers especially during the wet season where the feed resources are in abundant supply.

Striking seasonal pattern of primary production in the river-dominated ocean margin of the northern South China Sea (NSCS-RiOMar) revealed by new field and remotely sensed data

Seasonal patterns of phytoplankton biomass and primary production (PP) are important features characterizing a marine ecosystem. The South China Sea (SCS) has been arbitrarily illustrated as an ecosystem with low PP in summer and high PP in winter. However, there is an emerging consensus about a lack of unity of PP seasonality in the SCS even in the northern SCS shelf-sea. Through analysis of the distributions of the remotely sensed colored dissolved organic matter absorption coefficient, a river-dominated ocean margin in the northern SCS (NSCS-RiOMar) with the 50 m isobath as its southeastern boundary has been defined. The difference in PP seasonality between the NSCS-RiOMar and the whole shelf-sea was evaluated by both the measured and the remotely sensed depth-integrated primary production (ΣPP). A diagnostic analysis found that euphotic depth and a function of the half-saturation light intensity accounted for the seasonal variation of ΣPP in the NSCS-RiOMar. Accordingly, the Platt and Sathyendranath (1993) model plus the nearest neighbor method and the semi-analytical estimates of euphotic depth were used to compute the remotely sensed ΣPP. The average ΣPP in the NSCS-RiOMar were 1146.4, 1604.7, 979.5, and 891.3 mg C m−2 d−1 in spring, summer, autumn, and winter, respectively, contrasted with small seasonal variations in the whole shelf-sea. The unimodal ΣPP peak was in June-July in accordance with the peak of Pearl River discharge. This result was striking because previous remote sensing studies all showed the reversed seasonal pattern of ΣPP in both the NSCS-RiOMar and the whole shelf-sea. The annual PP was estimated to be 33.5 ± 2.3 Mt C yr−1 and 56.2 ± 3.2 Mt C yr−1 in the NSCS-RiOMar and the whole shelf-sea, respectively. The nutrients inputted by the China Coastal Current might account for 4–23% of ΣPP in the NSCS-RiOMar between December and February.

Seasonal patterns of reproduction and production in Nili-Ravi buffaloes

Records of Nili-Ravi buffalo maintained at ICAR-Central Institute for Research on Buffaloes, sub-campus Nabha for the period 2009–2018, were analysed with the aim to study the effect of season on various reproductive and productive parameters. Seasons were categorized as follows: winter –Nov. to Feb.; summer – Mar. to Jun.; and rainy – Jul. to Oct. The average temperature ranged from as high as 32.3°C in summer to as low as 18.4°C in winter. The average humidity ranged from as low as 28.2% in summer to as high as 52.8% in rainy season. Data of 4,203 estruses during this period revealed significant effect on estrus expression with lower expression in summer, and highest during winter. A significant reduction in estrus detection efficiency during summer and rainy seasons as compared to winter was recorded. The conception rate was significantly higher during winter as compared to summer and rainy season. During this period, 1,398 calvings were recorded. It was observed that buffaloes that calved in summer tended to have highest calving to first service interval as well as service period (135 and 167 d, respectively) and lowest in rainy season (78 and 114 d, respectively). The wet and herd averages were significantly higher in winter as compared to summer and rainy. Animals that calved in rainy season had significantly lower lactation length (299±13 d) as compared to summer (373±13 d) and winter (320±17 d). It may be concluded that high temperature and humidity during summer and rainy season exert negative effect on reproductive and productive performance in Nili-Ravi buffaloes.

Production of Fungal Mycelia in a Temperate Coniferous Forest Shows Distinct Seasonal Patterns.

In temperate forests, climate seasonality restricts the photosynthetic activity of primary producers to the warm season from spring to autumn, while the cold season with temperatures below the freezing point represents a period of strongly reduced plant activity. Although soil microorganisms are active all-year-round, their expressions show seasonal patterns. This is especially visible on the ectomycorrhizal fungi, the most abundant guild of fungi in coniferous forests. We quantified the production of fungal mycelia using ingrowth sandbags in the organic layer of soil in temperate coniferous forest and analysed the composition of fungal communities in four consecutive seasons. We show that fungal biomass production is as low as 0.029 µg g−1 of sand in December–March, while it reaches 0.122 µg g−1 in June–September. The majority of fungi show distinct patterns of seasonal mycelial production, with most ectomycorrhizal fungi colonising ingrowth bags in the spring or summer, while the autumn and winter colonisation was mostly due to moulds. Our results indicate that fungal taxa differ in their seasonal patterns of mycelial production. Although fungal biomass turnover appears all-year-round, its rates are much faster in the period of plant activity than in the cold season.

Seasonal patterns of fine root dynamics and their contribution to net primary production in hinoki cypress (Chamaecyparis obtusa) and konara oak (Quercus serrata) forests

Key messageFine root and litterfall are major contributor of NPP and fine root production may reflect forest productivity in a warm-temperate forest in Japan.Forest ecosystems play an important role as the major carbon sink on land, with fine root dynamics and litterfall representing major carbon fluxes. The objectives of this research were to estimate NPP including annual fine root production values, to investigate fine root dynamics and the relationships between above– and belowground organs in konara oak (Quercus serrata) and hinoki cypress (Chamaecyparis obtusa) forests. Litterfall was collected seasonally for 1 year from June 2013. The ingrowth core method and the sequential soil core method were applied with a root litterbag experiment to estimate fine root (< 2 mm) production (FRP), mortality (FRM), and decomposition (FRD) for 1 year (from 2013 to 2014), using the continuous inflow estimate method and the simplified decision matrix. The total NPP ranged from 8.2 to 13.9 (t ha− 1 yr− 1), and the sum of aboveground litterfall and FRP accounted for 60% of the total NPP on average, confirming the significance of above- and belowground litter for the forest NPP as a source of detritus for the decomposer system. In hinoki cypress stand, fine root biomass peaked in the end of winter while fine root necromass showed the highest peak in late summer. In konara oak stand, only very fine root (< 0.05 mm) biomass and necromass demonstrated significant seasonal patterns. The seasonal patterns of fine root production did not differ between forest types and root diameter classes. We found a possible relationship between above- and belowground production and fine root production tended to be high in productive forests. This study improves our understanding of different patterns of carbon dynamics between temperate broadleaved and coniferous forest ecosystems.

Assessment of the Skill of Coupled Physical–Biogeochemical Models in the NW Mediterranean

Numerical modelling is a key tool to complement the current physical and biogeochemical observational datasets. It is essential for understanding the role of oceanographic processes on marine food webs and producing climate change projections of variables affecting key ecosystem functions. In this work we evaluate the horizontal and vertical patterns of four state-of-the-art coupled physical-biogeochemical models, three of them already published. Two of the models include data assimilation, physical and/or biological, and two do not. Simulations are compared to the most exhaustive dataset of in situ observations in the North Western Mediterranean, built ad hoc for this work, comprising gliders, conventional CTD surveys and complemented with satellite observations. The analyses are performed both in the whole domain and in four sub-regions (Catalan Shelf, Ebro Delta, Mallorca Channel and Ibiza Channel), characterized by a priori divergent primary production dynamics and driving mechanisms. Overall, existing models offer a reasonable representation of physical processes including stratification, surface temperature and surface currents, but it is shown that relatively small differences among them can lead to large differences in the response of biogeochemical variables. Our results show that all models are able to reproduce the main seasonal patterns of primary production both at the upper layer and at the Deep Chlorophyll Maximum (DCM), as well as the differential behaviour of the four sub-regions. However, there are significant discrepancies in the local variability of the intensity of the winter mixing, phytoplankton blooms or the intensity and depth of the DCM. All model runs show markedly contrasting patterns of interannual phytoplankton biomass in all four sub-regions. This lack of robustness should dissuade end-users from using them to fill gaps in time series observations without assessing their appropriateness. Finally, we discuss the usability of these models for different applications in marine ecology, including fisheries oceanography.

Seasonal patterns of near-bottom chlorophyll fluorescence in the eastern Chukchi Sea: 2010–2019

The Chukchi Sea consists of a broad, shallow (<45 m) shelf that is seasonally (November–July) covered by sea ice. This study characterizes the seasonal patterns of near-bottom primary production using moored instruments measuring chlorophyll fluorescence, oxygen, nitrate, and photosynthetically active radiation. From 2010 to 2018, moorings were deployed at multiple sites each year. Instruments were restricted to within 10 m of the seafloor due to ice keels, which can reach 30 m below the surface in this region. Near-bottom blooms were common at all mooring sites. The bloom onset directly followed ice retreat whereas the end of the bloom followed loss of light in September. The intensity of light at the seafloor (~40 m deep) was similar to levels observed under 1–2 m thick ice floes in the spring/early summer, and was sufficient to support photosynthesis near the seafloor, utilizing nitrate and producing oxygen. We hypothesize that the near bottom bloom originated from aggregates of ice algae that sank during ice retreat. As a consequence of climate warming and earlier ice retreat, we predict that the near-bottom bloom onset will occur earlier, but the timing of the end of the near-bottom bloom will remain the same pending a sufficient nutrient supply. The Chukchi Sea is highly productive even though the growing season is short. This production is promoted by a shallow seafloor, which allows multiple production layers (surface open water, bottom of the mixed layer, under-ice algae, and disassociated ice algae which settles near the seafloor). We term this the Multiple Production Layers (MPL) hypothesis.

Colored Bell Pepper Yields from Cultivars Grown in High Tunnels in Northern New England

High tunnels can facilitate production of ripe colored bell peppers (Capsicum annuum) in locations with short growing seasons by extending the length of the growing season and protecting fruit from biotic and abiotic stressors. We grew 10 cultivars of bell pepper over 3 years in a high tunnel in Durham, NH. Yields of marketable colored fruit ranged from 1576 to 2285 g/plant in 2015, from 1194 to 1839 g/plant in 2016, and 1471 to 2358 g/plant in 2017. Significant differences in marketable yield among cultivars existed only in 2015 and 2017. Of the 10 cultivars evaluated, those developed for controlled environments produced greater marketable yields than those developed for production in the field or unheated tunnels (P &lt; 0.0001). The seasonal production patterns were similar among cultivars in all 3 years: a single peak in production occurred between 159 and 175 days after seeding, followed by much lower but steady production until frost ended each growing season. Our results demonstrate that reasonable yields of colored bell peppers can be produced in high tunnels in locations with short growing seasons. We suggest that further work may be needed to identify optimal pruning and canopy management strategies to maximize yields and fruit quality.

Carbon and Nutrient Inputs by Litterfall in Evergreen and Deciduous Forests in Korea

Knowledge about carbon and nutrient fluxes by litterfall is important for understanding nutrient cycling in geologically unique ecosystems. However, the determination of forest litterfall production patterns is difficult due to many biophysical factors influencing the process. In this study, we (1) quantified the litterfall production and carbon and nutrient fluxes in warm-temperate evergreen forest stands in Jeju Gotjawal and (2) compared these values to those of a typical cool-temperate deciduous forest stand by forest types and climate differences. Litterfall from evergreen broadleaved forests at Cheongsu (CS) and Seonheul (SHb), a mixed forest at Seonheul (SHm) in Jeju Gotjawal, and a deciduous broadleaved forest at Chungnam National University Forest (CNU) was collected for a full two years using litter traps. Samples were sorted into leaves, twigs, barks, seeds, and unidentified materials, and then weighed and measured for C, N, P, K, Ca, and Mg fluxes by litterfall. Results showed that the mean annual litterfall (846.3 g m−2, average of CS, SHb, and SHm) at Jeju Gotjawal was similar to that of CNU (885.5 g m−2), but varied by site in Jeju Gotjawal: CS (933.1 g m−2) was significantly higher than the average of SHb and SHm (802.9 g m−2). Seasonal patterns of litterfall production differed by forest types; evergreen broadleaved forests showed a bimodal peak in fall and spring while deciduous broadleaved forests showed a unimodal peak in fall. Jeju Gotjawal had significantly higher total macronutrient concentrations and contents (except for K) than CNU and they also varied by site in Jeju Gotjawal: CS had higher N, P, Ca, and Mg contents than SHb and SHm. We conclude that litterfall production and nutrient fluxes differed by forest stand as influenced by forest types and climate. Further, our findings are important for understanding carbon and nutrient dynamics in the geologically unique ecosystem of Jeju Gotjawal and other areas with similar characteristics.

Seasonal patterns of benthic-pelagic coupling in oyster habitats

Oysters enhance benthic-pelagic coupling in coastal systems by moving large quantities of suspended particulates to the sediments, stimulating biogeochemical processes. Recent research efforts have focused on quantifying the impact of oysters on coastal biogeochemical cycling, yet there is little consensus on how oysters influence processes across systems. A potential driver of this variance is availability of organic material suspended in the water column and subsequent loading to sediment by oysters. Here, we measured fluxes of sediment di-nitrogen (N2-N), ammonium (NH4+), combined nitrate-nitrite (NOx), and phosphate (PO43-) in spring, summer, and fall at 2 oyster reefs and 1 farm in a temperate estuary (Narragansett Bay, Rhode Island). We then linked these fluxes with patterns of water column primary production. Nitrogen removal from the system was highest in spring, when we detected net sediment denitrification (48.8 µmol N2-N m-2 h-1) following a winter-spring diatom bloom. In contrast, we measured sediment N2 fixation in fall (-44.8 µmol N2-N m-2 h-1) at rates nearly equivalent to spring denitrification. In the summer, we measured a nearly net zero sediment N2-N flux (-2.7 µmol N2-N m-2 h-1). Recycling of nitrogen to the water column was consistent across seasons, composed almost exclusively of NH4+. These results demonstrate that sediment nitrogen cycling in oyster habitats is dynamic and can change rapidly based on seasonal patterns of productivity. At carrying capacity, the impact of oysters on nitrogen cycling is large and should be considered during efforts to increase oyster populations through aquaculture or reef restoration.

Changing patterns of pasture production in south-eastern Australia from 1960 to 2015

The seasonal pattern of pasture production and its variability from year to year are important for pasture-based livestock production systems in south-eastern Australia because they influence key strategic decisions such as stocking rate and timing of the reproductive cycle. In this study, the effects of observed climate variations over the period 1960–2015 on pasture growth patterns were investigated by using a biophysical modelling approach. Pasture growth rates were simulated using DairyMod biophysical software at five sites ranging from high-rainfall, cool temperate at Elliott in Tasmania to medium-rainfall, warm temperate at Wagga Wagga in southern New South Wales. Annual pasture yields showed a small increasing rate of 50 kg DM/ha.year at Elliott and 40 kg DM/ha.year at Ellinbank (P &amp;lt; 0.05), whereas other sites showed no significant trend over time. A cross-site analysis of seasonal average pasture growth rates predicted under four different discrete periods of 14 years each showed that winter growth has increased steadily through time (P = 0.001), and spring pasture growth rate has decreased (P &amp;lt; 0.001) in 2002–15 compared with the earlier periods. Year-to-year pasture yield variability (coefficient of variation) during autumn and spring seasons has also increased (P &amp;lt; 0.05) across sites in the period 2002–15 compared with 1998–2001. At each site, the number of spring days with water stress (growth limiting factor_water &amp;lt;0.7) was ~10 times greater than the number of days with temperature stress (growth limiting factor_temperature &amp;lt;0.7). There was an increase in the number of days with water stress at Wagga Wagga, and increased heat stress at Wagga Wagga and Hamilton (P &amp;lt; 0.05) in the most recent period. These results highlight the importance of incorporating more heat-tolerant and deep-rooting cultivars into pasture-based production system. Although previous studies of climate-change impact have predicted increasing winter growth rates and a contraction of the spring growing season in the future (2030), this study provides clear evidence that these changes are already occurring under the observed climate in south-eastern Australia.

Aboveground biomass and seasonal patterns of aboveground net primary productivity in five bamboo species in northern Laos

Abstract Aims Accurate estimates of bamboo biomass and net primary productivity (NPP) are required to evaluate the carbon sequestration potential of bamboo forests. However, relevant data that are important for climate change mitigation, have rarely been collected in regions outside of East Asia and India. Information on seasonal patterns of NPP and its components will enable the quantification of factors that influence the carbon balance in bamboo forests. In this study, we quantified the aboveground biomass (AGB) and aboveground NPP of five major bamboo species in northern Laos using monthly data collected over a 12-month period. Methods All live culms in 10, 2 m × 2 m plots (for one monopodial bamboo species: Indosasa sinica) and 30 clumps per species (for four sympodial bamboo species: Bambusa tulda, Cephalostachyum virgatum, Dendrocalamus membranaceus and Gigantochloa sp.) were numbered and measured at breast height. We set 10 or 20 litter traps per species to collect litterfall. Censuses of dead and recruited culms and litterfall collection were performed once per month for 12 months. Important Findings The AGB was highest in I. sinica (59.87 Mg ha−1) and lowest in C. virgatum (11.54 Mg ha−1), and was mostly below the plausible global range for bamboos (32–256 Mg ha−1). The sympatric distribution of multiple bamboo species at the study sites may have suppressed the AGB in four of the five studied species. The aboveground NPP estimates were between 3.43 and 14.25 Mg ha−1 yr−1; those for D. membranaceus (8.20 Mg ha−1 yr−1) and I. sinica (14.25 Mg ha−1 yr−1) were comparable to mean global estimates for temperate evergreen forests (8.78 Mg ha−1 yr−1) and tropical moist forests (10.56 Mg ha−1 yr−1). High culm recruitment rates (15.20–23.39% yr−1) were major contributors to aboveground NPP estimates. Seasonal patterns of aboveground NPP were largely influenced by the phenology of the new culms. In the four sympodial bamboo species, new culms began to emerge following the onset of persistent rainfall, mainly in July and August. However, the sprouting of new culms in the monopodial species I. sinica followed a trend of increasing temperatures, mainly in March and April. Thus, our results indicate that bamboos have considerable potential for sequestering carbon in northern Laos, but that this potential may be affected by climate change.