Wednesday, July 6, 2022

DCD found in summer streams

Research carried out by University of Otago research fellow Dr Marc Schallenberg indicates dicyandiamide (DCD) could have long term impacts on some New Zealand waterways. His paper “Occurrence of the Agricultural Nitrification Inhibitor, Dicyandiamide, in Surface Waters and its Effects on Nitrogen Dynamics in an Experimental Aquatic System” was published in the international journal Agriculture, Ecosystems and Environment late last year and is the first research on how DCD affects waterways. On October 20 and November 11, 2008, Schallenberg and masters student Ian Smith, from the United States, took 15 water samples from the Taieri Plain drains and streams upstream of the Waipori/Lake Waihola wetlands. The waterways were fed wholly or partly by shallow groundwater seepage, springs, surface runoff and some were tidal. On January 21, 2009, the pair again took water samples from the same sites except for four which had dried up. In almost all of the sites where water samples were taken, DCD was found at each sampling. “We knew farmers were using DCD on farms on the Taieri in the spring and we expected to find it in the waterways then but not in the summer,” Schallenberg said.

Ammonium levels were measured as well and in most of the water samples, the more DCD that was present, the more ammonium, suggesting DCD was influencing the nitrogen (N) cycle by blocking nitrification in the waterways as it does on land.

Schallenberg and Smith also conducted laboratory experiments using sediment and water from a non-tidal part of a Taieri wetland and showed the presence of DCD did disrupt the naturally occurring nitrification process in water, causing a build-up of ammonium.

“While DCD in low concentrations is probably not toxic to aquatic organisms, ammonium is toxic, especially for trout,” he said.  

“Native fish, such as eels, are fairly robust to ammonium in their adult stages but I’m not sure how ammonium affects them at other stages of their life cycle.”

Waterways which contained little N would probably not be affected by DCD.

“DCD may only be a problem if ammonium is already in the water. DCD disrupts the process of microbial nitrification and so prevents the conversion of ammonium to less-toxic nitrate by naturally occurring beneficial bacteria.”

Ammonium occurs in waterways from a variety of sources – from bird and fish excrement and decomposing organic matter, to deep groundwater passing through ancient decaying plant matter.

Schallenberg said he hoped to be able to do further research on the effects of DCD in waterways.

“The only other research in waterways done on DCD that I know about was in rice paddies. That’s why I wanted to look into it. We know what it does on land but how does it affect waterways?”

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