| Keywords: |
Eutrophication, High flow events, Iron, Nutrient loading, phosphorus, Seasonality, Snowmelt, Spring runoff, Suspended sediment |
| Abstract: |
Spring runoff often comprises the majority
of annual discharge and riverine phosphorus (P) export
due to sustained high flow, and the magnitude of
spring runoff can be a strong predictor of receiving
water summer harmful algal bloom severity. Yet the
loading of reactive forms of P during this time period
remains poorly-characterized in time, space and
geochemical partitioning. Here, we explore the
hypothesis that riverine dissolved and suspended
sediment P loads during spring runoff have a particularly
high proportion of potentially reactive species
due to unique hydrologic pathways and P association
with iron (Fe).The concentration, distribution and
temporal dynamics of dissolved P (DP), dissolved and
colloidal Fe, and redox sensitive suspended sediment
P (RSP) and Fe during spring runoff and summer
storms were compared in forested and agricultural
catchments of the same watershed. The dominant
carrier of RSP was Fe (oxy)hydroxides across land
cover and season, but Fe (oxy)hydroxide particles and
colloids in agricultural catchments were strongly
enriched in RSP and DP during spring runoff and
summer storms, particularly at the onset of snowmelt.
In 2014, 83% of DP and 74% of RSP were delivered to
Missisquoi Bay during spring runoff. Suspended
sediment was significantly more redox sensitive than
typically input to limnological models, suggesting that
the reactivity of this load may be systematically
underestimated. Changes in the timing, provenance
and severity of spring runoff associated with climate
or land cover change will have dramatic impacts on
total riverine P loads and their potential reactivity in
receiving water ecosystems.
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