Monitoring Results – Annual Flow, Precipitation, TSS and Phosphorus: WY 2004-05
Study Overview and Background
Five USGS continuous monitoring stations within the 1,580 km2 Lower Fox Basin have been installed directly through the project. The following stations will provide 3 years of data beginning in October 2003 and ending September 30, 2006:
Stream flow and water-quality gaging stations were installed on three streams (Apple Creek, Ashwaubenon Creek and Baird Creek). A water-quality sampler was installed at Duck Creek. An acoustic velocity meter (AVM) and water-quality sampler were installed at East River . Stream flow measurements were made at all sites to determine stage–discharge relations. About 290 water-quality samples were collected during events and low flow conditions and analyzed for total suspended solids (TSS) and total phosphorus (TP) in 2005, compared to 480 samples in 2004. About 84 samples were analyzed for dissolved phosphorus (DP) in 2005, compared to 210 samples in 2004. The USGS computed daily TP and TSS loads for each stream, and will estimate DP loads. TSS concentrations have also been correlated with turbidity data from sondes operated by UW-Milwaukee. Four rain gauge-logger units were installed at the USGS stations by the USGS, and 12 tipping bucket rain gauges and loggers have been installed throughout the basin by UWGB.
1) Better understand cause/effect through event and continuous monitoring.
According to the Green Bay National Weather Service station (NWS), the second wettest May on historical record was recorded in 2004 (211 mm). With 3-times the normal precipitation, this rainfall was responsible for excessive runoff and loads in May and early June. However, total annual precipitation in WY2004 (813 mm) was only 10% above normal (741 mm). Annual precipitation in WY2005 at the Green Bay NWS was 719 mm, or 3% below normal. Annual stream flow ranged from 33 to 43% of total precipitation in 2004, compared to 14 to 23% in 2005. Stream flows estimated by the USGS during ice-affected periods in 2005 were adjusted downward based on area-weighted stream flow yields, precipitation and water balance requirements. Ice-affected flow was adjusted in Apple (annual change = -35%), Ashwaubenon (-27%) and Duck (-8.6%) creeks, which also affected constituent loads. Stream flows estimated by the USGS for Duck Creek during March 2004 were adjusted by assuming that the ice-affected period ended much earlier than assumed by the USGS, as observed by LFRWMP staff. This change also affected constituent loads in 2004 (annual change = +8.6%). Total stream flow during March accounted for 34 to 42% of the annual flow in both 2004 and 2005 from all sites except the East River in 2005 (23%).
Apple, Ashwaubenon and Baird Creeks had similar median TSS concentrations of approximately 127 mg/L in 2004, which is 2.5 times greater than the median value from previous studies. Much lower TSS concentrations of about 67 mg/L were determined for Duck Creek and East River; however, it should be noted that East River samples were typically composites of four samples per day. TSS concentrations were much lower in 2005. Median TSS concentrations of about 51 mg/L were observed at Apple, Ashwaubenon and Baird in 2005, and the median concentration was 30 mg/L at Duck Creek and 34 mg/L at East River . The maximum TSS concentrations ranged from 124 mg/L at East River to 6,180 mg/L at Ashwaubenon Creek in 2005.
High TP concentrations were found in all streams. In 2005, TP median concentrations ranged from 0.28 in Duck Creek to 0.70 mg/L in Ashwaubenon Creek. About 25% of Ashwaubenon Creek samples were greater than 0.93 mg/L. In 2004, TP median concentrations ranged from 0.27 in Duck Creek and East River , to 0.56 mg/L in Ashwaubenon Creek. Samples in excess of 2 mg/L TP have been collected from all sites, with a maximum of 7.0 mg/L from Ashwaubenon.
Annual median DP to TP fractions ranged from 49-57% in 2004. Median DP was 40-54% of TP during events and greater than 70% DP during low flow. Annual median DP to TP fractions ranged from 48% at Baird to 79% at Ashwaubenon in 2005. The mean DP in low flow samples collected from Ashwaubenon Creek (0.34 mg/L) in 2004-05 was significantly higher than from Apple, Baird or Duck (p<0.05). Further investigation may explain the cause for this difference. Discrete low flow samples were not collected from the East River .
Annual loads in 2004 were relatively large, and highly event driven: 13 days accounted for 80% of the TSS load and 67% of the TP load from Apple Creek. Baird Creek was less influenced by events: 13 days accounted for 67% of TSS and 52% of TP loads. Excluding Apple Creek, March, May and June accounted for 87-96% of the TSS load and 81-88% of the phosphorus load in the 2004 USGS water year. In contrast, the TSS total load in 2005 was less than 20% of the 2004 load. The TP load was less than 35% of the 2004 load. This difference was primarily due to wet soil conditions and high runoff and erosion in 2004, compared to relatively dry soil conditions and low runoff rates in 2005. Approximately 45-70% of the TSS and TP loads occurred in March 2005 at Apple, Baird and Duck Creeks.
As summarized in Table 1, annual TSS yields from Apple, Ashwaubenon and Baird were similar in 2004: 0.93, 0.70, 0.72 t/ha, respectively. TSS yields were 0.33 t/ha from Duck and 0.55 t/ha from the East River . Annual TP yields from Apple, Ashwaubenon and Baird were similar: 1.9, 2.0 and 2.3 kg/ha, respectively. TP yields were 1.1 kg/ha from Duck and 1.7 kg/ha from the East River (partial year). Stream flow and loads were much lower in 2005. Stream flow yields in 2005 ranged from 105 to 173 mm, and were about 30 to 50% of what they were in 2004. TSS yields in 2005 ranged from 0.06 to 0.20 t/ha, and were approximately 12 to 30% of what they were in 2004. TP yields in 2005 ranged from 0.44 to 0.79 kg/ha, and were about 20 to 44% of what they were in 2004. Baird Creek TSS and TP yields were similar to Duck Creek and the East River in 2005; whereas, yields were similar to Apple and Ashwaubenon in 2004.
WY 2004 and 2005 monitoring data from this project were published in the following USGS publications: Water Resources Data, Wisconsin, Water Years 2004 and 2005 Water-Data Reports WI-04-1 and WI-05-1, Middleton , WI