Sources of phosphorus to the Carson River upstream from Lahontan Reservoir, Nevada and California, Water Years 2001-02

Groundwater contributions to excessive algal growth in the East Fork Carson River, Carson Valley, west-central Nevada, 2010 and 2012

“…The ratio of orthophosphate to total phosphorus concentration ranged from 0.35 to 0.69 with a median of 0.54, indicating 54 percent of the total phosphorus was orthophosphate. These results vary from findings of Alvarez and Seiler (2004) who found much lower ratios in July and August of 2002 at a site on EFCR at Muller Lane, just downstream from SDT, even though streamflow conditions were similar. The N:P ratio at all three stream sites in July, September, and October 2010 indicated potential nitrogen limitation; in other words, periphyton productivity may have been limited by the amount of nitrogen available for uptake.…”

“…The ratio of orthophosphate to total phosphorus ranged from 0.25 to 0.47 with a median of 0.32 in stream samples collected in 2012. These results indicate the majority of total phosphorus was from particulate phosphorus and are consistent with the findings of Alvarez and Seiler (2004). For phosphorus species, only total phosphorus and orthophosphate were measured in water samples, and for this study, particulate phosphorus is estimated as total phosphorus minus orthophosphate.…”

“…For phosphorus species, only total phosphorus and orthophosphate were measured in water samples, and for this study, particulate phosphorus is estimated as total phosphorus minus orthophosphate. Particulate phosphorus defined this way includes phosphorus bound to clays, minerals, and decaying organic matter; phosphorus incorporated into living tissue; and phosphorus in dissolved non-orthophosphate forms (Alvarez and Seiler, 2004).…”

“…However, higher stream nutrient concentrations at SUT in August 2012 (table 19) likely were the result of upstream urban runoff from the towns of Minden and Gardnerville and irrigation return flow from agricultural land in the surrounding area that enter the EFCR from the Cottonwood Slough tributary (Alvarez and Seiler, 2004). In the summers of 2001 and 2002, three samples were collected from Cottonwood Slough at the mouth of the EFCR and had orthophosphate concentrations ranging from 0.07 to 0.1 mg/L as P and total nitrate plus nitrite concentrations of 0.1 mg/L as N (Alvarez and Seiler, 2004). If similar nutrient concentrations existed in this tributary during 2012, Cottonwood Slough may have been an upstream source of nutrient concentrations available for uptake by algae and influenced the higher algal biomass conditions observed at SUT.…”