and draining of the reservoir for irrigation purposes. While the extensive wetlands 

 influenced by the presence of the dike may act as a sink for organic matter and nutrients, 

 periodic drops in the water table caused by irrigation withdrawal may result in increased 

 decomposition of stored organic matter and releases of nutrients (Mitsch and Gosselink, 

 1986). 



Similarly, Station 8 is located downstream from the natural confluence of Dutchman 

 Creek which is recharged by water from the extensive wetlands that have formed below 

 the dike. Discharge at this station is the highest on the lower reaches of the Creek, which 

 indicates the influence of subsurface water recharge by groundwater, despite significant 

 withdrawals for irrigation. As a result of increased flow, Lost Creek carries its highest 

 mean load of TN (37.2 kg/day) in this reach, despite a drop in TN concentrations. 



Kjeldahl nitrogen levels (Fig. 7) were highly variable for most sites, with Station 

 6 on Dutchman Creek having the highest mean concentration of 363 ppb. Station 9, near 

 the creek's mouth had the second highest mean value of 290 ppb. Peak daily values 

 exceeded 280 ppb for all sites with maximum levels at Stations 6 (860 ppb) and 8 (850 

 ppb). Highest levels for all sites occurred during peak runoff in May and June. 



Total nitrogen levels (Fig. 8) at Stations 1-4 were all approximately 200 ppb. 

 Due mostly to the high levels of nitrate/nitrite recorded for Stations 5 through 9, total 

 mtrogen levels exhibit a similar pattern with a sharp increase in TN in the area above and 

 in Dutchman Creek. Dutchman had the highest levels of TN with a mean of 950 ppb and 

 a maximum value of 1360 ppb on 6/24/99. Mean values near the mouth of Lost Creek 

 were 470 ppb TN, with a maximum value of 740 ppb. On most sample dates, Station 9 

 exceeded the VNRP target of 300 ppb TN. 



Average TN loads of all stations (Fig. 9) were within range of Station 1 . Station 8 

 had the highest average loads of 37 kg/day TN. Lost Creek's TN loads relative to Clark 

 Fork River loads are summarized in Table 4. From 1989-1999 summer mean TN load for 

 Lost Creek near its mouth varied from 12-31 kg/day which is 11-18% of the Clark Fork 

 River TN load just above Lost Creek. Mean loading of nitrate/nitrite represented nearly 

 half Lost Creek's TN load at mouth and 23-44% of the Clark Fork's nitrate loads. 

 Amazingly, on 5/13/99, Lost Creek's nitrate load equaled the load earned by the river 

 (-40 kg/day). 



Although average 1999 loads of TN at the confluence were within the range of 

 historic values (Table 4), nitrate levels were higher in 1999 and comprised a greater 

 proportion of the total nitrogen concentration than in prior sampling years. Again, this 

 may be a result of applying Anaconda's wastewater in the Lost Creek basin, which began 

 in 1994. Prior to that, Anaconda pumped its wastewater into the Opportunity Ponds 

 which would have contributed nutrients to the headwaters of the Clark Fork. However, 

 mean nitrate concentrations in the Clark Fork River appear higher (if only slightly) in 

 1999 than 1989-1990. 



