Seasonal and Morphological Controls on Nitrate Retention in Arctic Deltas

Estimates of nitrate loading to the Arctic Ocean are limited by the lack of field observations within deltas partly due to logistical constraints. To overcome this limitation, we use a remote sensing framework to estimate retention of nitrate in Arctic deltas. We achieve this by coupling hydrological and biogeochemical process models at the network scale for five major Arctic deltas. Binary masks of delta channels were used to simulate flow direction and magnitude through networks. Models were parameterized using historical and seasonal observations. Simulated nitrate retention ranged from 2.9% to 15% of the incoming load. Retention rates were largest during winter but smallest during spring conditions when increased discharges export large nitrate masses to the coast. Under future climate scenarios, retention rates fall by similar to 1%-10%. Arctic deltas have an important effect on the magnitude of nitrate entering Arctic seas and the inclusion of processing in deltas can improve flux estimates.

Automated summary

The lack of field observations in Arctic deltas limits the estimation of nitrate loading to the Arctic Ocean due to logistical constraints. To overcome this, a remote sensing framework was used to estimate nitrate retention in Arctic deltas, by coupling hydrological and biogeochemical process models at the network scale. Binary masks of delta channels were used to simulate flow direction and magnitude, and models were parameterized using historical and seasonal observations. Simulated nitrate retention ranged from 2.9% to 15% of the incoming load, with the highest retention rates during winter and the lowest during spring conditions. Under future climate scenarios, retention rates are expected to decrease by approximately 1%-10%.