density and biomass
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Author(s):  
Андрей Павлович Столяров

Изучены видовое разнообразие, пространственная и трофическая структура макробентосных сообществ сублиторали и нижних горизонтов литорали в 5-ти лагунных экосистемах Кандалакшского залива Белого моря. Всего в исследованных экосистемах было обнаружено 52 вида бентосных беспозвоночных животных и 6 видов морских трав и водорослей. В сублиторали наибольшим видовым разнообразием, общей плотностью и биомассой макробентоса характеризуется наиболее открытая к морю лагуна, расположенная на выходе из кутовой области Кислой губы, а наименьшим - наиболее закрытая и заиленная лагуна Никольской губы, где преобладали солоноватоводные и морские эвригалинные виды. Промежуточное положение занимали лагуна Ермолинской губы, лагуна, расположенная рядом с Ершовским озером и лагуна на Зеленом мысу. В нижней литорали общие показатели структуры сообщества макробентоса (общая плотность, биомасса и в меньшей степени видовое разнообразие) в отличие от сублиторали увеличивались от менее зарегулированных и открытых экосистем к более закрытым системам. Исключением является лагуна Никольской губы, значительное заиление которой приводит к существенному уменьшению видового разнообразия и снижению общей плотности и биомассы сообщества макробентоса. The species diversity, spatial and trophic structure of macrobenthos communities in the sublittoral and lower littoral horizons in five lagoon ecosystems of the Kandalaksha Bay of the White Sea have been studied. In total, 52 species of benthic invertebrates and 6 species of sea grasses and algae were found in the studied ecosystems. In the sublittoral zone, the highest species diversity, total density and biomass of macrobenthos is characterized by the lagoon most open to the sea, located at the exit from the innermost area of Kislaya Bay. The lowest diversity is found in the most closed and silted lagoon of Nikolskaya Bay, where brackish water and marine euryhaline species predominated. The lagoon of the Ermolinskaya Bay, the lagoon located next to the Ershov Lake and the lagoon on Cape Verde hold an intermediate position. In the lower littoral zone, the general indicators of the structure of the macrobenthos community (total density, biomass, and, to a lesser extent, species diversity), in contrast to the sublittoral one, increased from less regulated and open ecosystems to more closed systems. An exception is the lagoon of Nikolskaya Bay, the significant siltation of which leads to a significant decrease in species diversity and a decrease in the total density and biomass of the macrobenthos community.


2021 ◽  
Vol 288 (1965) ◽  
Author(s):  
D. Gómez-Gras ◽  
C. Linares ◽  
A. López-Sanz ◽  
R. Amate ◽  
J. B. Ledoux ◽  
...  

Understanding the resilience of temperate reefs to climate change requires exploring the recovery capacity of their habitat-forming species from recurrent marine heatwaves (MHWs). Here, we show that, in a Mediterranean highly enforced marine protected area established more than 40 years ago, habitat-forming octocoral populations that were first affected by a severe MHW in 2003 have not recovered after 15 years. Contrarily, they have followed collapse trajectories that have brought them to the brink of local ecological extinction. Since 2003, impacted populations of the red gorgonian Paramuricea clavata (Risso, 1826) and the red coral Corallium rubrum (Linnaeus, 1758) have followed different trends in terms of size structure, but a similar progressive reduction in density and biomass. Concurrently, recurrent MHWs were observed in the area during the 2003–2018 study period, which may have hindered populations recovery. The studied octocorals play a unique habitat-forming role in the coralligenous assemblages (i.e. reefs endemic to the Mediterranean Sea home to approximately 10% of its species). Therefore, our results underpin the great risk that recurrent MHWs pose for the long-term integrity and functioning of these emblematic temperate reefs.


2021 ◽  
Author(s):  
Qingju Xue ◽  
Ming Kong ◽  
Liqiang Xie ◽  
Tong Li ◽  
Mengna Liao ◽  
...  

Abstract Harmful cyanobacterial blooms are increasing in frequency and severity, which makes their toxic secondary metabolites of microcystins (MCs) have been widely studied, especially in their distribution and influence factors in different habitats. However, the distribution of MCs on the early growth stage of harmful cyanobacteria and its influence factors and risks are still largely unknown. Thus, in the present study, two reservoirs (Lutian Reservoir and Lake Haitang) with different trophic status in China have been studied weekly from March to May in 2018, when the cyanobacteria communities were just in the early growth stage, to investigate the variation of MCs concentration and the relationships between MCs and environmental parameters. During the investigation, Lutian Reservoir and Lake Haitang were found to be mesotrophic and light eutrophic, respectively. In Lutian Reservoir, the concentration of EMCs was obviously higher than that of IMCs with a mean value of 0.323 and 0.264 μg/L, respectively. Meanwhile, the concentration of EMCs also fluctuated more sharply than that of IMCs. Congeners of IMC-YR and EMC-LR were respectively dominant in total concentrations of IMCs and EMCs. Unsurprisingly, in Lake Haitang, the concentrations of IMC and EMC were both significantly higher than that in Lutian Reservoir with a mean concentration of 0.482 and 0.472 μg/L, respectively. Differently, the concentration of MC-YR was dominant in both IMCs and EMCs, followed by MC-LR. In correlation analysis, the IMCs were significantly and positively correlated with the density and biomass of phytoplankton phyla and potential MCs-producing cyanobacteria and the parameters of water temperature (WT), nutrients and organic matters. Similar results were also observed for EMCs. While the different variation of MCs in two reservoirs might be primarily caused by the differences in WT, nutrients (especially phosphorus), organic matters and the composition of MCs-producing cyanobacteria. In addition, the coexistence of the dominant species of Pseudoanabaena sp., which can produce taste-and-odor compound of 2-methylisoborneol (2-MIB), might have significant impacts on the concentration and toxicity of MCs. Our results suggested that the risks posed by MCs at the early growth stage of cyanobacteria should also deserve our attentions, especially in mesotrophic water bodies.


2021 ◽  
Vol 4 (4) ◽  
pp. 40-45
Author(s):  
Olabode O.S. ◽  
Oladapo O.S. ◽  
Ogunsola A. ◽  
Sangodele A.O.

Field experiments were carried out at the Teaching and Research Farm of the LadokeAkintola University of Technology, (LAUTECH), Ogbomoso to evaluate the effectiveness and determine the optimum rate of applying alternative herbicides to atrazine on maize plots in view of the current criticism against the herbicide. Five herbicides, namely; 3-maize force, Xtra force, Pre-maize Guard force (solution and pellet) at two rates (100% and 50% recommended rates) were compared with atrazine at full dose and 3 hoe-weeding in a Randomized complete Block Experiment with 3 replications. Maize, Variety OBA Super, maturing in 75 days, was planted at two plants per stand at a spacing of 75 x 50cm in two-year trials and maintained following the standard procedures. The herbicides were applied using a knapsack sprayer calibrated to deliver at 200liters/ha. Results showed that there were no significant differences (p=0.05) among the treatment and between the treatments and control with respect to seed germination, plant survival and other growth parameters. The highest grain yield (6757.3kg/ha) obtained with atrazine was not significantly different from those of other treatments and control. The effectiveness of the herbicides, measured using weed density and biomass, showed comparable effectiveness across the herbicides and atrazine. Furthermore, at a dosage of 50%, the herbicide’s effectiveness was highly comparable to those of atrazine at 100%. The implications of these findings were discussed.


Agronomy ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 2448
Author(s):  
Rana Nadeem Abbas ◽  
Asif Iqbal ◽  
Muhammad Aamir Iqbal ◽  
Omar M. Ali ◽  
Raees Ahmed ◽  
...  

Under the changing climate, fertilization regimes and weed infestation management in aromatic direct-seeded fine rice (DSR) remain vital for curbing environmental hazards and ensuring food security. A multi-year field study was undertaken to appraise the influence of fertilization techniques and weed-free periods on weed dynamics, nutrient uptake and paddy yield in a semi-arid environment. Treatments included two fertilization methods (broadcasting and side placement) and five weed-free durations (20, 30, 40, 50 post-seeding days, DAS) along with a weed-free crop for a whole season. Weed competition for a season-long crop (weedy check) was maintained for each fertilizer application method. Our results revealed that the side placement of fertilizers resulted in a significantly lower weed density and biomass, even under season-long weed competition. The highest paddy yield was recorded for a crop without weeds, while weed-free duration of up to 50 DAS followed it. The uptake of nitrogen (N), phosphorus (P) and potassium (K) for a weed-free duration of up to 50 DAS were only 19%, 9% and 8%, respectively, as compared to the weedy check. The uptake of N, P and K by weeds in the broadcast method was 18%, 30% and 24% higher, compared to side-placed fertilizers. The period of 20–50 DAS remained critical in DSR as far as weed control was concerned. Thus, the side placement of fertilizers and controlling weeds for up to 50 days after rice sowing can be recommended for general adoption in semi-arid agro-ecological conditions.


Weed Science ◽  
2021 ◽  
pp. 1-40
Author(s):  
Pinglei Gao ◽  
Aimei Hong ◽  
Min Han ◽  
Minghan Song ◽  
Yunhui Duan ◽  
...  

ABSTRACT As part of a long-term experiment to determine the impacts of composted manure and straw amendments (replacing 50% of chemical fertilizer with composted pig manure, wheat straw return combined with chemical fertilizer, and setting no fertilizer and chemical fertilizer-only as controls) on rice-associated weeds in a rice (Oryza sativa L.) - wheat (Triticum aestivum L.) rotation system, species richness, abundance, density, and biomass of weeds were assessed during years eight and nine. Fertilization decreased the species richness and total density of rice-associated weeds but increased their total biomass. The species richness and densities of broadleaf and sedge weeds decreased with fertilization, while species richness grass weeds increased only with straw return and density was not significantly affected. The shoot biomass per square meter of grass and broadleaf weeds were significantly higher with fertilization treatments than with the no fertilizer control, while that of sedge weeds declined with fertilizer application. With fertilization, the densities of monarch redstem (Ammannia baccifera L.) and smallflower umbrella sedge (Cyperus difformis L.) decreased, that of Chinese sprangletop [Leptochloa chinensis (L.) Nees] increased, and those of barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] and monochoria [Monochoria vaginalis (Burm. f.) C. Presl ex Kunth] were not significantly affected. Ammannia baccifera was the most abundant weed species in all treatments. Whereas composted pig manure plus fertilizer resulted in higher density of A. baccifera and lower shoot biomass per plant than chemical fertilizer only; wheat straw return plus chemical fertilizer caused lower density and shoot biomass of A. baccifera. Therefore, it may be possible that fertilization strategies that suppress specific weeds could be used as improved weed management program components in rice production systems.


Water ◽  
2021 ◽  
Vol 13 (22) ◽  
pp. 3155
Author(s):  
Shumin Liu ◽  
Fengbin Zhao ◽  
Xin Fang

Phytoplankton and bacterioplankton play a vital role in the structure and function of aquatic ecosystems, and their activity is closely linked to water eutrophication. However, few researchers have considered the temporal and spatial succession of phytoplankton and bacterioplankton, and their responses to environmental factors. The temporal and spatial succession of bacterioplankton and their ecological interaction with phytoplankton and water quality were analyzed using 16S rDNA high-throughput sequencing for their identification, and the functions of bacterioplankton were predicted. The results showed that the dominant classes of bacterioplankton in the Qingcaosha Reservoir were Gammaproteobacteria, Alphaproteobacteria, Actinomycetes, Acidimicrobiia, and Cyanobacteria. In addition, the Shannon diversity indexes were compared, and the results showed significant temporal differences based on monthly averaged value, although no significant spatial difference. The community structure was found to be mainly influenced by phytoplankton density and biomass, dissolved oxygen, and electrical conductivity. The presence of Pseudomonas and Legionella was positively correlated with that of Pseudanabaena sp., and Sphingomonas and Paragonimus with Melosira granulata. On the contrary, the presence of Planctomycetes was negatively correlated with Melosira granulata, as was Deinococcus-Thermus with Cyclotella sp. The relative abundance of denitrifying bacteria decreased from April to December, while the abundance of nitrogen-fixing bacteria increased. This study provides a scientific basis for understanding the ecological interactions between bacteria, algae, and water quality in reservoir ecosystems.


2021 ◽  
pp. 1-23
Author(s):  
Clint W. Beiermann ◽  
Cody F. Creech ◽  
Stevan Z. Knezevic ◽  
Amit J. Jhala ◽  
Robert Harveson ◽  
...  

Abstract Late-emerging summer annual weeds are difficult to control in dry bean production fields. Dry bean is a poor competitor with weeds, due to its slow rate of growth and delayed canopy formation. Palmer amaranth is particularly difficult to control due to season-long emergence and resistance to acetolactate synthase (ALS)-inhibiting herbicides. Dry bean growers rely on PPI and preemergence residual herbicides for the foundation of their weed control programs; however, postemergence herbicides are often needed for season-long weed control. The objective of this experiment was to evaluate effect of planting date and herbicide program on late-season weed control in dry bean in western Nebraska. Field experiments were conducted in 2017 and 2018 near Scottsbluff, Nebraska. The experiment was arranged in a split-plot design, with planting date and herbicide program as main-plot and sub-plot factor, respectively. Delayed planting was represented by a delay of 15 days after standard planting time. The treatments EPTC + ethalfluralin, EPTC + ethalfluralin fb imazamox + bentazon, and pendimethalin + dimethenamid-P fb imazamox + bentazon, resulted in the lowest Palmer amaranth density three weeks after treatment (WAT) and the highest dry bean yield. The imazamox + bentazon treatment provided poor Palmer amaranth control and did not consistently result in Palmer amaranth density and biomass reduction, compared to the non-treated control. In 2018, the delayed planting treatment had reduced Palmer amaranth biomass with the pendimethalin + dimethenamid-P treatment, as compared to standard planting. Delaying planting did not reduce dry bean yield and had limited benefit in improving weed control in dry bean.


2021 ◽  
Vol 8 ◽  
Author(s):  
Anguo Zhang ◽  
Hongjun Li ◽  
Xiaolong Yang ◽  
Lili Wang ◽  
Yangchun Gao ◽  
...  

In this study, the release effects of the buried clam Meretrix meretrix in a northern estuary of China (Shuangtaizi Estuary) was assessed in terms of population ecology and genetic variability by using longer-term monitoring data from 2011 (used as the baseline data) to 2018. A total of 2.4 × 108 hatchery juveniles were released from 2012 to 2014, and follow-up monitoring survey of the growth, distribution, density, and biomass of M. meretrix population was carried out. Results showed a temporary spike in the population of M. meretrix, and the population underwent considerable year-to-year fluctuations in total abundance and biomass. Meanwhile, the age structure of the populations from 2011 to 2018 is still an unstable expanding type. Genetic analysis based on 10 polymorphic microsatellite markers revealed no significant genetic differentiation and weak genetic structures between years but higher genetic diversities in 2014–2018 than in the initial period (2013) of stock restoration. Our study suggests that effective policies for management and conservation to restore M. meretrix population by local governments are still needed in the long run.


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