Evaluating the Role of Missisquoi Bay Subaqueous Soils for Carbon Storage.

Eutrophication associated with high concentrations of phosphorus originating from the agricultural land surrounding Missisquoi Bay has raised concerns about its influence on submersed aquatic vegetation and the overall health of Lake Champlain. Subaqueous soils play an important role in nutrient management, sedimentation, submersed aquatic vegetation and water quality. The objectives of this study were to (i) characterize physical and chemical properties of subaqueous soils within a portion of Missisquoi Bay based on ground-penetrating radar (GPR) and soil analysis; and (ii) assess relationships among the subaqueous soil-landscapes based on digital soil mapping (DSM) techniques and analysis of the distribution of radar facies and submersed aquatic vegetation (SAV). Coarse Stratified Sediment and Lacustrine Silt radar facies covered 51 and 41% of the study area and were associated with Delta/Nearshore and Lakebed/Bay Bottom subaqueous soil-landscape units, respectively. The sediment composition and stratification of the Coarse Stratified Sediment radar facies reflected the direct influence of depositional events associated with the Missisquoi River delta. This was also confirmed by the observed decrease of P with distance from the delta from 125 to 66 mg kg-1 within this facies. The Lacustrine Silt radar facies occurred in relatively deep waters in low-energy depositional areas away from the direct influence of delta depositions. Highest P concentrations of 683 and 990.7 mg kg-1 were also associated with this facies. Only 7% of the bay area was covered by Organic Soil Material radar facies and was associated with Fringing Peatland subaqueous soil-landscape unit. Less than 1% of the bay area was underlain by exposed bedrock. Soils cores confirmed the identity of the radar facies. The majority of the SAV was associated with Delta/Nearshore and Fringing Peatland subaqueous soil-landscape units, which occur under relatively shallow waters.