Effects of benthic algae on release of soluble reactive phosphorus from sediments: a radioisotope tracing study

To evaluate the effect of benthic algae on soluble reactive phosphorus（SRP） release from sediments in shallow lakes, experiments on SRP release with and without benthic algae in sediment cores and an experiment on SRP uptake by benthic algae were conducted using the radioisotope（32P） tracing method. The dissolved oxygen（DO） concentration in sediment cores was also investigated. The results show that benthic algae effectively reduce the release of SRP from sediments to overlying water. The uptake of SRP by benthic algae, which is the direct way in which benthic algae affect the SRP release from sediments, is low in filtered water and increases with the SRP concentration. However, in the experiment, the increased uptake rate lasted for a short time（in one hour）, and after that it returned to a low rate. Benthic algae make the DO concentration and the oxic layer thickness increased, which can indirectly reduce the SRP release from sediments. These findings indicate that benthic algae can reduce the SRP release from sediments in both direct and indirect ways. It seems that the indirect way also plays an important role in reducing the SRP release from sediments.

Potential influence of overwintering benthic algae on water quality

Overwintering benthic algae not only directly impact drinking water safety, but also affect the algae recruitment in warm spring seasons. Thus, understanding the characteristics of overwintering benthic algae can provide scientific references for formulating preventative strategies of reasonable water resource. However, they have received less attention. In this study, the spatiotemporal variation of benthic algae and their harmful secondary metabolites were studied from autumn to summer in Qingcaosha Reservoir. Benthic algae(picophytobenthos accounting for 55.42%) had a high biomass during overwintering, and the groups of overwintering benthic algae included pico-Cyanobacteria, pico-Cryptomonas, pico-Chlorophyta, pico-Diatoms, Cyanobacteria, Chlorophyta, Cryptomonas and Diatoms, which were consistent with the planktonic algae species in warm seasons. In oligotrophic or mesotrophic water bodies, micronutrients of iron and manganese were key nutrient factors influencing the biomass of benthic algae. Furthermore, picophytobenthos were important potential contributors of harmful secondary metabolites. The content of microcystins, anatoxin-a, geosmin and 2-methylisoborneol in sediment were 15.75 μg/kg ·FW, 48.16 μg/kg ·FW, 3.91 ng/kg ·FW, and 11.76 ng/kg ·FW during winter, which had potential to be released into water bodies to impact water quality. These findings indicate that water quality monitoring programs need to consider sediment in winter as a potential source of toxins and preventative measures to prevent excessive proliferation of algae should be implemented in winter.

New Benthic Fossils from the Late Ediacaran Strata of Southwestern China

The Jiangchuan Biota from the Jiucheng Member(Mb.)of the Dengying Formation(Fm.),discovered in Jiangchuan,eastern Yunnan,China,is marked by copious macrofossils at the apex of the Ediacaran strata.This fauna features benthic algae with varied holdfasts and other fossils of indeterminate taxonomic affinity and is compositionally unique compared to the Shibantan and Gaojiashan biotas of the Dengying Fm.and the Miaohe and Wenghui biotas of the Doushantuo Fm.,elsewhere in China.One novel benthic saccular macroalgal fossil,named here Houjiashania yuxiensis gen.and sp.nov.,from the Jiangchuan Biota is based on fossils that are sausage-shaped,elongate,tubular,ranging from 0.3 to 4 cm in length,and up to 0.8 cm in diameter.One terminus is blunt and rounded to an obtuse angle,the other is bent with a spread-out surface resembling a holdfast,suggesting a three-dimensional thallus.Thin,stipe-shaped outgrowths,likely vestiges of sessile saccular life forms,are prevalent in macroalgal fossils of analogous size and shape,as well as present brown algae Scytosiphonaceae,such as Colpomenia and Dactylosiphon.The new findings augment the diversity of benthic algae,such as those known from the Early Neoproterozoic Longfengshan Biota in North China.The benthic algal macrofossils in the Jiucheng Mb.add to knowledge of Late Ediacaran metaphyte diversification and offer more clues about the evolutionary positioning of primitive macroalgae.The co-occurrence of numerous planktonic and benthic multicellular algae and planktonic microbes might have facilitated ecologically the more extensive later Cambrian explosion evidenced by the Chengjiang Biota in Yunnan.

The age and quality of pond bottom soil affect water quality and production of Pangasius hypophthalmus in the tropical environment

Pangasius hypophthalmus is the most cultured freshwater fish by smallholder farmers in Indonesia.One of the main challenges in the production is the highly weathered and infertile soils on the bottom of a pond that influences aquaculture productivity.This work investigated the effects of pond age on soil quality,water quality,benthic algae population,and P.hypophthalmus production.We carried out a field experiment in a randomized design with pond age of 4 levels:Ponds aged 0-5 years(P1),6-10 years(P2),11-15 years(P3),and 16-20 years(P4).The soil is a Typic Palaeudult(Ultisol),and fish were grown for three months.The results showed that the chemical soil quality parameters and soil organic matter content increased linearly with pond age,resulting in the enhancement of water quality parameters.The increase in nitrate and phosphate directly affected benthic algae richness.These,in turn,in the highest fish production in P3,6.4 kg/m^(2),specific growth rate was 3.76%/d,survival rate of 66.7%,and feed conversion ratio of 1.8%.Linear correlation coefficients indicated that the contents of total N,total P,and organic carbon in the bottom soil of the pond were related to the increase in phosphate,nitrate,and organic matter content in pond water.Total N content,total P,carbon organic matter,C/N ratio,and CEC value in pond bottom soil significantly correlated to Pangus fish production.C/N ratio,CEC value in pond bottom soil,and CO_(2)concentration in pond water significantly correlated to fish survival rate.Multiple linear regression indicated that fish production was significantly related to the pond age,water NH3,total alkalinity,and soil total P and C/N ratio(R^(2)=0.99,P<0.001).Increased soil C/N ratio caused a negative effect on fish production.The results suggested that old-aged ponds,with proper management,act as a nutrient sink,resulting in increased aquaculture production.The implementation of the best practices will benefit the Pangus culture in the tropical environment.