Sediment source analysis in the Linganore Creek watershed, Maryland, USA, using the sediment fingerprinting approach: 2008 to 2010

Purpose: Fine-grained sediment is an important pollutant in
streams and estuaries, including the Chesapeake Bay in the
USA. The objective of this study was to determine the sources
of fine-grained sediment using the sediment fingerprinting
approach in the Linganore Creek watershed, a tributary to
the Chesapeake Bay.

Materials and methods: The sediment fingerprinting approach
was used in the agricultural and forested, 147-km 2
Linganore Creek watershed, Maryland from 1 August 2008 to 31 December
2010 to determine the relative percentage contribution from
different potential sources of fine-grained sediment. Fine-grained suspended sediment samples (<63 μm) were collected
during storm events in Linganore Creek using an automatic
sampler and manual isokinetic samplers. Source samples were
collected from 40 stream bank sites, 24 agricultural (cropland and
pasture) sites, and 19 forested sites. Suspended sediment and
source samples were analyzed for elements and stable isotopes.

Results and discussion: Results of sediment fingerprinting for
194 samples collected in 36 separate storm events indicate that
stream banks contributed 53% of the annual fine-grained
suspended sediment load, agriculture contributed 44%, and
forests contributed 3%. Peak flows and sediment loads of the
storms correlate to stream bank erosion. The highest peak
flows occurred in the winter and, along with freeze–thaw
activity, contributed to winter months showing the highest
rate of stream bank erosion. Peak flow was negatively correlated to sediment sources from agricultural lands which had
the greatest contribution in non-winter months. Caution
should be observed when trying to interpret the relation between sediment sources and individual storms using the sediment fingerprinting approach. Because the sediment fingerprinting results from individual storms may not include the temporal aspects of the sourced sediment, sediment that is in
storage from previous events, remobilized and sampled during
the current event, will reflect previous storm characteristics.
Stream bank sediment is delivered directly to the channel
during an event, whereas the delivery of upland sediment to
the stream is lower due to storage on hillslopes and/or in
channels, sediment from stream banks are more likely to be
related to the characteristics of the sampled storm event.

Conclusions: Stream banks and agricultural lands are both
important sources of fine-grained sediment in the Linganore
Creek watershed. Peak flows and sediment loads for the 36
storms show a significant relation to sediment sources from
stream bank erosion. Attempting to link upland sediment
sources to flow and seasonal characteristics is difficult since
much of the upland sediment eroded in an event goes into
storage. By averaging sediment sources over several storms, it
may be possible to determine not only the sediment sources
that are directly contributed during the current event but also
sediment from previous events that was in storage and
remobilized.