An Efficient Tide-Surge Interaction Model for the Coast of Bangladesh

The numerical method of lines(MOLs)in coordination with the classical fourth-order Runge Kutta(RK(4,4))method is used to solve shallow water equations(SWEs)for foreseeing water levels owing to the nonlinear interaction of tide and surge accompanying with a storm along the coast of Bangladesh.The SWEs are developed by extending the body forces with tide generating forces(TGFs).Spatial variables of the SWEs along with the boundary conditions are approximated by means of finite difference technique on an Arakawa C-grid to attain a system of ordinary differential equations(ODEs)of initial valued in time,which are being solved with the aid of the RK(4,4)method.Nested grid technique is adopted to solve coastal complexities closely with least computational cost.A stable tidal solution in the region of our choice is produced by applying the tidal forcing with the major tidal constituent M2(lunar semi-diurnal)along the southern open-sea boundary of the outer scheme.Numerical experimentations are carried out to simulate water levels generated by the cyclonic storm AILA along the coast of Bangladesh.The model simulated results are found to be in a reasonable agreement with the limited available reported data and observations.

Biochar amendment alters the partitioning of nitrate reduction by significantly enhancing DNRA in a paddy field

Using 15N tracer technique,we investigated the potential rates of denitrification,anaerobic ammonium oxidation,dis-similatory nitrate reduction to ammonium(DNRA),and their partitioning among nitrate reduction,as well as the N_(2)O emission rates in a paddy soil receiving various biochar(0%,0.03%,0.1%,0.5%,and 1.0%;w/w)and straw(0.1%)over six consecutive years.Results showed that except for the 1.0%amendment treatment,biochar significantly(P<0.05)increased denitrification rates by 10.19‒75.96%compared with non-biochar amended treatment,and that biochar significantly(P<0.05)increased DNRA rates by 1.63‒6.84 folds relative to non-biochar amended treatment.Conse-quently,biochar shifted more NO3-partitioning toward DNRA process,as suggested by the increased DNRA/(denitri-fication+DNRA)ratios from 1.60 to 13.18%.On the other hand,biochar significantly(P<0.05)reduced N_(2)O emission rates by 61.86-97.65%accompanied by a significant decrease in N_(2)O/(N_(2)O+N_(2))ratios(65.29-98.39%),indicating bio-char amendment facilitated the reduction of N_(2)O to N_(2).The promoting effects of biochar on DNRA rates and DNRA/(denitrification+DNRA)ratios were attributed to the increased carbon availability and the altered nitrate reducer communities.Collectively,our study suggests that biochar amendment in the paddy soil is helpful for N conservation by favoring nitrate partitioning toward DNRA process,which deepens our understanding of how biochar mediates N cycling in the paddy field.