Aromatic Rich Natural Organic Matter Increases Growth and Reduces Nickel Toxicity in a Wild Daphnia Hybrid

Natural organic matter (NOM) is on the rise across the Shield. Its heterogeneous, amalgamate nature makes each NOM source potentially unique. Relatively little is known about the direct effects distinct NOM sources have on daphniids, or the varying protection NOM provides against metal toxicity –specifically Ni. I show that NOM from different natural sources increases growth rates and decreases time to maturation of Daphnia to various degrees. These changes relate to aromatic content of NOM isolates, the mechanism most likely being a hormonal effect or mild oxidative stress. Aromatic content (representing phenolic groups) is also positively related to Ni mitigation for those isolates with specific UV absorbance below 19.3 cm2mg-1. Incorporating NOM aromatic content into a predictive model improves the relationship between predicted and measured LC50s by 5%. I demonstrate that structural differences between NOM isolates relating to aromatic content play a major role in their effects on Daphnia.