Dark Soliton Solutions of Space-Time Fractional Sharma–Tasso–Olver and Potential Kadomtsev–Petviashvili Equations

Dark soliton solutions for space-time fractional Sharma–Tasso–Olver and space-time fractional potential Kadomtsev–Petviashvili equations are determined by using the properties of modified Riemann–Liouville derivative and fractional complex transform. After reducing both equations to nonlinear ODEs with constant coefficients, the tanh ansatz is substituted into the resultant nonlinear ODEs. The coefficients of the solutions in the ansatz are calculated by algebraic computer computations. Two different solutions are obtained for the Sharma–Tasso–Olver equation as only one solution for the potential Kadomtsev–Petviashvili equation. The solution profiles are demonstrated in 3D plots in finite domains of time and space.

Response of Phytoplankton Community Structure and Size- Fractionated Chlorophyll a in an Upwelling Simulation Experiment in the Western South China Sea

The South China Sea(SCS), which is the largest marginal sea in the western tropical Pacific, plays an important role in regional climate change. However, the research on the phytoplankton community structure(PCS) response to the upwelling remains inadequate. In January 2014, the upwelling simulation experiment was performed in the western SCS. Results indicate that the nutrient-rich bottom water not only increased the total Chlorophyll a(Chl a) concentrations, but would potentially altered the PCS. Due to new nutrients added, microphytoplankton had more sensitivity response to nutrient uptake than other phytoplankton groups. The variation of nutrients induced by formation, weakening and disappearance of upwelling resulted in phytoplankton species succession from cyanophyta to bacillariophyta. It may be the leading factor of the changes in PCS and size-fractionated Chl a. The initial concentration of DIP less than 0.1 μmol L-1 could not sustain the phytoplankton growth. This indicates that phosphorus may be the limiting factor in the western SCS.

Predicting the aquatic risk of realistic pesticide mixtures to species assemblages in Portuguese river basins

Although pesticide regulatory tools are mainly based on individual substances, aquatic ecosystems are usually exposed to multiple pesticides from their use on the variety of crops within the catchment of a river. This study estimated the impact of measured pesticide mixtures in surface waters from 2002 and 2008 within three important Portuguese river basins（＇Mondego＇, ＇Sado＇ and ＇Tejo＇） on primary producers, arthropods and fish by toxic pressure calculation. Species sensitivity distributions（SSDs）, in combination with mixture toxicity models, were applied. Considering the differences in the responses of the taxonomic groups as well as in the pesticide exposures that these organisms experience, variable acute multi-substance potentially affected fractions（ms PAFs） were obtained. The median msP AF for primary producers and arthropods in surface waters of all river basins exceeded 5%, the cut-off value used in the prospective SSD approach for deriving individual environmental quality standards. A ranking procedure identified various photosystem II inhibiting herbicides, with oxadiazon having the relatively largest toxic effects on primary producers, while the organophosphorus insecticides, chlorfenvinphos and chlorpyrifos, and the organochloride endosulfan had the largest effects on arthropods and fish, respectively. These results ensure compliance with European legislation with regard to ecological risk assessment and management of pesticides in surface waters.

Terrestrial ecosystem health under long-term metal inputs:modeling and risk assessment

Metal contamination of soils may pose long-term risks to ecosystem health if not proper-ly managed.Future projection of contamination trends,coupled with ecological assessment,is needed to assess such risks.This can be achieved by coupling dynamic models of soil metal accumulation and loss with risk assessment on the basis of projected metal levels.In this study,we modeled the long-term dy-namics of Cu,Zn,and Cd in agricultural topsoils of a northern Chinese catchment(Guanting reservoir)and related projected metal levels to 2060 to ecological risk.Past metal dynamics were simulated using historical metal inputs from atmospheric deposition,irrigation,fertilizers,and animal manures.Model-ing future dynamics was done using scenarios of projected metal input rates.Ecological risk assessment was done using the Potentially Affected Fraction(PAF)approach to estimate the combined toxic pressure due to the three metals.Modeled labile soil metals agreed well with measurements from monitoring in 2009 following adjustment of the porewater dissolved organic concentration.Metals were predicted to be largely retained in the topsoil.Projections were sensitive to changes in imposed soil pH,organic mat-ter,and porewater dissolved organic carbon.Modeling suggests that decreases in input rates to between 5%and 7.5%of 2009 levels are required to prevent further accumulation.Computed PAFs suggest zinc makes the greatest contribution to ecological risk.Under the most conservative estimate of PAF,the threshold of potential ecological risk was reached before 2060 in two of the three future input scenarios.