Fig. 1.

Locations of the five study areas (dots) within their larger drainage basins (shaded areas): DR2, within the Yakima River Basin; Valley Creek within the Upper Mississippi River Basin; Maple Creek within the Eastern Platte River Basin; Leary Weber within the White River Basin; and Morgan Creek within the Delmarva Peninsula.

 


Fig. 2.

Nitrate concentration (mg/L as N) box plots for streams (SW) and upland groundwater (GW) for each study area. Overland flow (OV), stream-bed pore water (PW), riparian (RP), springs (SP), and tile drain (TD) data are given for selected study areas. Samples were collected from 2002 to 2004. Boxplots with different statistical designation letters have mean ranks that are significantly different (P < 0.05). All concentrations are dissolved.

 


Fig. 3.

Orthophosphate concentration (mg/L as P) box plots for streams (SW) and upland groundwater (GW) for each study area. Overland flow (OV), stream-bed pore water (PW), riparian (RP), springs (SP), and tile drain (TD) data are given for selected study areas. Box plots with different statistical designation letters have mean ranks that are significantly different (P < 0.05). All concentrations are dissolved.

 


Fig. 4.

Estimated fraction of stream nitrate and orthophosphate load that is derived from base flow vs. the base flow index of the stream (based on data from October 2002–September 2004). Dashed line shows 1:1 relation between BFI and the fraction of total load derived from base flow.

 


Fig. 5.

Nitrate concentrations (mg/L as N) in surface water are plotted against base flow index values determined for the day of sampling for Morgan Creek (top), DR2 (middle) and Valley Creek (bottom). On the right side of each figure box plots show nitrate concentrations in groundwater by compartment: PW, stream-bed pore water; RP, riparian zone; GW, upland groundwater; SP, springs. See Fig. 2 or 3 for box plot explanation.