WHERE ARE THE TROUT IN HARDWOOD CREEK? A STORY OF LLAMAS, CARP AND TMDL EXCEEDANCE IN A GLACIATED TERRAIN

Hardwood Creek flows on the till plain of the Grantsburg Sublobe 15 miles north of downtown St. Paul, Minnesota. The creek is fed by groundwater recharging on the Superior Lobe lateral moraine immediately to the east. The watershed is relatively low and flat with several high diversity wetlands and tamarack bogs. Despite its location in an area of relatively light development along with cool water temperatures the dissolved oxygen levels in the creek are too low support much more than rough fish. The small hobby farms, primarily horses with some llamas, scattered throughout the watershed would not appear to produce high loads of organic carbon.

Low dissolved oxygen levels in the stream may be the result of highly reduced groundwater feeding numerous springs and seeps. This low oxygen inflow is exacerbated by the low stream gradient (<1ft/mile) with few riffles to mix in atmospheric oxygen. Groundwater in underlying outwash sands is confined by 20 feet of compacted tills of the Des Moines Lobe at gradients exceeding 0.1 ft/ft. This large gradient produces diffuse groundwater flow with significant contact with organics in the till and overlying peat deposits. Springs and seeps along Hardwood Creek are often denoted by iron precipitates. Cation and anion analyses from monitoring wells and the main stream flow were used to delineate the contribution of groundwater to Hardwood Creek. Total Maximum Daily Loads (TMDLs) designed for higher gradient streams without large contributions of reduced groundwater may not be applicable to this system.