Microbial biomass and numbers of denitrifiers related to macropore channels in agricultural and forest soils

Transport and reduction of nitrate in clayey till underneath forest and arable land

“…The profiles reveals two to three orders of magnitude higher concentration of nitrate reducing bacteria (6A), and 2-10 times higher concentrations of water-soluble organic carbon (6B) at the agricultural site than at the forest site. This is in agreement with Vinther et al (1999) who found that the numbers of denitrifying bacteria and nitrate reducing bacteria were very low ( < 10 4 cells g À 1 soil) in the same forest soil as studied in this investigation as compared to the 10 5 -10 6 cells g À 1 soil which is generally found in agricultural soils. Further, Vinther et al (1999) found that the numbers of denitrifying bacteria and the content of ATP were significantly higher along macropore channels than in the matrix soil, and that the low concentration of DOC in the forest soil was a limiting factor for the denitrification.…”

“…This is in agreement with Vinther et al (1999) who found that the numbers of denitrifying bacteria and nitrate reducing bacteria were very low ( < 10 4 cells g À 1 soil) in the same forest soil as studied in this investigation as compared to the 10 5 -10 6 cells g À 1 soil which is generally found in agricultural soils. Further, Vinther et al (1999) found that the numbers of denitrifying bacteria and the content of ATP were significantly higher along macropore channels than in the matrix soil, and that the low concentration of DOC in the forest soil was a limiting factor for the denitrification. This is in accordance with Burford and Bremner (1976) who found a linear relationship between denitrification capacity, defined as the evolution of gaseous nitrogen over 7 days from samples amended with nitrate, and soil content of watersoluble carbon.…”

“…Similarly, the effluent solution from the column experiments (se below) were analysed for dissolved organic carbon (DOC) and ATP. Nitrate reducing bacteria were enumerated as described by Vinther et al (1999). The soil samples for the study were collected in autumn immediately after harvest from the agricultural site and in winter from the forest site.…”

“…Canadell et al, 1996;Jørgensen et al, 1998aJørgensen et al, ,b, 2002Vinther et al, 1999;Jensen et al, 1999). The occurrence of this sub-environment is visually apparent in most sub-soil profiles of oxidized till as a distinct bleached pattern of local chemical alteration along macropore walls (microsites) extending from the root zone and sometimes down to 10 m depth or more (e.g.…”

A random walk solution for modeling solute transport with network reactions and multi-rate mass transfer in heterogeneous systems: Impact of biofilms

“…Also, the natural occurrence of preferential flow channels in porous media (typically represented as a mobile region in the multirate model) favors the movement of groundwater and dissolved elements through certain pathways, which typically harbor larger bacterial densities and microbial activities compare to the adjacent porous media (Pivetz and Steenhuis, 1995;Mallawatantri et al, 1996;Rubol et al, 2014). In fact, Vinther et al (1999) and Bundt et al (2001) found that both substrate availability and nutrient supply are largest in preferential flow paths, enhancing bacterial biomass and associated microbial processes. Similar processes occur at a smaller scale where contaminants may diffuse into stagnant water (intraaggregate or dead-end pores) or/and inside biofilms attached to the aquifer soil surface.…”