Periphytic Biofilm, which comprised of algae, bacteria and nutrients, is widespread in shallow water-sediment system. Howerver, it is unclear for its roles in N cycle, especially in the most complex denitrification process. This restricts the simulation of denitrification rate and N budget calculation.

According to a new research published in Water Resources Research, Yongqiu Xia, an Associate Professor in the Institute of Soil Sciences, Chinese Academy of Sciences,  along with his team revealed the secret between  periphytic Biofilm and denitrification process

Denitrification was one of the most challenging nitrogen cycling processes to quantify due to complex interactions among influencing factors. Xia and the group of researchers noticed that even though this subject was studied and researched by quite a few, yet it accounted for the greatest uncertainty in their understanding of the N cycle at any given scale.

One of the challenges they faced in improving denitrification models was to gauge the consequence when each factor directly affected denitrification and how each factor indirectly impacted denitrification via interactions with other factors.

An in-depth and innovative study allowed them to understand the importances of those omnipresent periphytic biofilms on denitrification.

They did so by dividing the water-sediment into three parts (water column, sediment, and periphytic biofilm). In addition to the above, the potential factors too were divided into three categories (N species, periphytic biofilm characteristics, and bacterial denitrifiers and nitrifiers). Structural equation modelling (SEM) was used for both methods.

(Figure. A shallow water-sediment showing sediment, periphyton, and water components and a diagram illustrating their denitrification process.)

After some analysis, Xia and the team found that periphytic biofilm exerted a great control over the net denitrification except for factors of N species and sediment interface.

The study pointed that periphytic biofilm increased net denitrification directly as well as indirectly through the pH, the dissolved oxygen, dissolved organic carbon, and N concentrations in the water column and sediment.

The research findings were that “the overall contribution of periphytic biofilm to net denitrification was less than that of the sediment but greater than that of the water column”. The study laid stress how one should incorporate bacterial denitrifier and nitrifier genes and periphytic biofilm characteristics during model construction to make an preciser prediction of denitrification in a shallow and stagnant water-sediment system.

Based on the total effects of the models, their findings revealed there were 26% improvements of the performances if microbial predictors was included in denitrification model, while  periphytic biofilm enhanced the explanatory power of the model by another ~15%.

Their findings are important to undstand the mechanism of N cycle in shallow water-sediment system. In the past, periphytic biofilm was never taken into account in denitrification process and modelling framework. Obviously this study filled this data gap and was critical for reducing the uncertainty associated with the magnitude of denitrification.

The findings have great implications in nutrient management of stagnant water systems, such as measures aimed at reducing N fertilizer losses in paddy fields and improving N removal in constructed wetlands. The growth of periphytic biofilm should be restricted to reduce denitrification loss from paddy rice. While in constructed wetlands, periphytic biofilm is recommended to increase denitrification rate and remove excess N in the system.

Xia concluded this research by leaving scope for scientists who want to study this process in the future. He suggested that more incubation experiments with large variations in bacterial diversity and denitrifier gene abundance should be brought about in experimentation to achieve a better simulation. Furthermore, he also recommended that since the vast majority of periphytic communities are eukaryotic algae, studies in the future should take this factor into consideration and incorporate characteristics of eukaryotic algae into denitrification model building.

The study by Yongqiu Xia and his team shows his intellect in handling a complex subject. Their research findings will be of great importance in both understanding mechanism of N cycling and nutrient management of shallow water-sediment system.

Original Source: Improving Denitrification Models by Including Bacterial and Periphytic Biofilm in a Shallow Water‐Sediment System (https://doi.org/10.1029/2018WR022919)

About the Author: Yongqiu Xia

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