Total mercury, methylmercury, phosphate, and sulfate inputs to a bog ecosystem from herring gull (Larus smithsoniansus) guano.

Avian biovector transport is an important mechanism for the movement of contaminants and nutrients to remote locations, usually bird colonies, through excretion, molting and decomposition of carcasses. Methylmercury (MeHg) is a bioaccumulative neurotoxin and endocrine disruptor which is present in many remote ecosystems. We collected guano samples biweekly from a herring gull (Larus smithsoniansus) colony over two summers and analyzed MeHg, total mercury (THg), water-extractable phosphate (PO43-) and sulfate (SO42-). Concentrations of THg in guano declined through the summer months while %MeHg significantly increased (ranging from 12% to 100% of THg), suggesting a switch in diet as gull nutritional needs or food availability changed through the summer. The percentage of PO43- in dry guano increased throughout the summer (ranging from 2.8% to 4.4% of dry weight) and SO42- varied throughout the season (ranging from 0.1% to 0.8% of dry weight). These data indicate that gulls are transporting considerable amounts of MeHg, PO43-, and likely other contaminants to Big Meadow Bog, Nova Scotia.