Concentration and flux of total and dissolved phosphorus, total nitrogen, chloride, and total suspended solids for monitored tributaries of Lake Champlain, 1990-2012

Abstract

Annual and daily concentrations and fluxes of total and dissolved phosphorus, total nitrogen, chloride, and total suspended solids were estimated for 18 monitored tributaries to Lake Champlain by using the Weighted Regressions on Time, Discharge, and Seasons regression model. Estimates were made for 21 or 23 years, depending on data availability, for the purpose of providing timely and accessible summary reports as stipulated in the 2010 update to the Lake Champlain "Opportunities for Action" management plan. Estimates of concentration and flux were provided for each tributary based on (1) observed daily discharges and (2) a flow-normalizing procedure, which removed the random fluctuations of climate-related variability. The flux bias statistic, an indicator of the ability of the Weighted Regressions on Time, Discharge, and Season regression models to provide accurate representations of flux, showed acceptable bias (less than ±10 percent) for 68 out of 72 models for total and dissolved phosphorus, total nitrogen, and chloride. Six out of 18 models for total suspended solids had moderate bias (between 10 and 30 percent), an expected result given the frequently nonlinear relation between total suspended solids and discharge. One model for total suspended solids with a very high bias was influenced by a single extreme value; however, removal of that value, although reducing the bias substantially, had little effect on annual fluxes.

Phosphorus Characterization and Contribution from Eroding Streambank Soils of Vermont's Lake Champlain Basin

“…Average storm‐event concentrations for AB and IB from 2008 through 2010 were 48 and 60 µg L −1 TP and 32 and 402 mg L −1 total suspended solids (TSS), respectively (Bartlett and Bowden, 2014). The LP has been continually monitored near its outlet since 2004 and, for the top 45% of flow days during 2008 through 2010 (to be comparable to the AB and IB data), the average concentrations were 77 µg L −1 TP and 32 mg L −1 TSS (Medalie, 2014).…”

“…In two of the streams, we were able to estimate the portion of each stream's total sediment load and TP that was potentially derived from streambank erosion. For the entire LP, we used available daily TSS monitoring data (Medalie, 2014) and estimated that streambank erosion was equivalent to 23% of the observed total sediment export over the study time period (May 2005 to May 2007). If we calculate TP loss for the entire stream using our mean TP concentration and the 3‐yr streambank erosion estimate (2368 Mg), the potential TP input from streambanks was 5.8% of the TP export measured by Medalie (2014).…”

“…Allen Brook had seasonal TSS and TP monitoring from 2008 through 2010 (Bartlett and Bowden, 2014). We prorated the seasonal export to annual export by using daily Winooski River data for the same dates (Medalie, 2014) and calculated potential streambank contributions of 92% of the observed TSS and 30% of the observed TP. These are relatively high values but not out of the range reported by others (DeWolfe et al, 2004; Langendoen et al, 2012).…”

Impact of an Extreme Storm Event on River Corridor Bank Erosion and Phosphorus Mobilization in a Mountainous Watershed in the Northeastern United States

“…These estimates are both similar in magnitude to our 17.6 × 10 3 Mg of stream bank erosion (Table ). The annual suspended sediment export from the Winooski for 2011, the year of Irene, was 4 times higher than the average of the prior 19 years (Medalie, ).…”

“…The Mad River watershed (Figure ) comprises a relatively small area of the Lake Champlain basin, but similar extreme flows were observed throughout the upper Winooski River sub‐basin (Olson, ). Sediment (TSS) discharge at the mouth of the Winooski for 29 August 2011 (the day after Irene entered Vermont) was 126 × 10 3 Mg, which is higher than the average annual export from 1992 to 2012 (excluding 2011) of 113 × 10 3 Mg (Medalie, ). Similar high sediment discharges were seen in two of the major watersheds of the northeastern United States—the Hudson and Connecticut Rivers.…”