SUSPENDED SEDIMENT TRANSPORT THROUGH THE MENDENHALL GLACIER WATERSHED PRELIMINARY RESULTS

Our goals were to measure the relative contributions of glacier and non-glacier sources of suspended sediment delivered into Mendenhall Lake. We also wanted to determine the contribution of suspended sediments in basal meltwater from the Mendenhall glacier. Lake depths of >80m at the glacier terminus make subglacial sediment contributions difficult to measure directly. Suspended sediment samples were collected using automated samplers between June and November 2001. One hundred ml samples were collected every 6 hours from a glacier-fed stream (Nugget Ck) and two nonglacier streams (Steep Ck. and Unnamed Ck) draining into proglacial Mendenhall Lake in Juneau, AK. In addition, suspended sediments were collected from the Mendenhall River below the lake outlet. Water samples were processed through millipore filters and weighed for silt and clay content. Preliminary results comparing suspended sediment concentrations against USGS discharge data point to a positive relationship between the concentrations of suspended sediments and the volume of glacial meltwater discharge. Suspended sediments concentrations from nonglacial source streams (Steep Creek, Mt McGinnis drainage) were 0.001-0.04 mgl-1. Samples from Nugget Creek and Mendenhall River, both glacier fed streams, yielded 0.1-.02 mgl-1. Surface lake samples showed a concentration of 0.1 mgl-1. Comparison of suspended sediment concentrations measured at streams flowing into proglacial Mendenhall Lake with outflow samples suggest that glacial meltwater is the predominant source of suspended sediments into this system. Continuing this work for another year will allow us to measure the annual concentration of glacier-contributed suspended sediment in this watershed and to estimate Mendenhall glacier erosion rates.