Suplee M.W.,520 East 6th Ave. |
Flynn K.F.,520 East 6th Ave. |
Chapra S.C.,Tufts University
Journal of the American Water Resources Association | Year: 2015
Nitrogen and phosphorus criteria were developed for 233 km of the Yellowstone River, one of the first cases where a mechanistic model has been used to derive large river numeric nutrient criteria. A water quality model and a companion model which simulates lateral algal biomass across transects were used to simulate effects of increasing nutrients on five variables (dissolved oxygen, total organic carbon, total dissolved gas, pH, and benthic algal biomass in depths ≤1 m). Incremental increases in nutrients were evaluated relative to their impact on predefined thresholds for each variable; the first variable to exceed a threshold set the nutrient criteria. Simulations were made at a low flow, the 14Q5 (lowest average 14 consecutive day flow, July-September, recurring one in five years), which was derived using benthic algae growth curves and EPA guidance on excursion frequency. An extant climate dataset with an annual recurrence was used, and tributary water quality and flows were coincident with the river's 10 lowest flow years. The river had different sensitivities to nutrients longitudinally, pH being the most sensitive variable in the upstream reach and algal biomass in the lower. Model-based criteria for the Yellowstone River are as follows: between the Bighorn and Powder river confluences, 55 μg TP/l and 655 μg TN/l; from the Powder River confluence to Montana state line, 95 μg TP/l and 815 μg TN/l. Pros and cons of using steady-state models to derive river nutrient criteria are discussed. © 2014 American Water Resources Association.
Suplee M.W.,520 East 6th Ave. |
Watson V.,University of Montana |
Dodds W.K.,Kansas State University |
Shirley C.,520 East 6th Ave.
Journal of the American Water Resources Association | Year: 2012
Nutrient pollution is an ongoing concern in rivers. Although nutrient targets have been proposed for rivers, little is known about long-term success of programs to decrease river nutrients and algal biomass. Twelve years of summer data (1998-2009) collected along 383km of the Clark Fork River were analyzed to ascertain whether a basin-wide nutrient reduction program lowered ambient total nitrogen (TN) and total phosphorus (TP) concentrations, and bottom-attached algal biomass. Target nutrient and algal biomass levels were established for the program in 1998. Significant declines were observed in TP but not TN along the entire river. Downstream of the city of Missoula, TP declined below a literature-derived TP saturation breakpoint and met program targets after 2005; TN was below targets since 2007. Algal biomass also declined significantly below Missoula. Trends there likely relate to the city's wastewater facility upgrades, despite its 20% population increase. Upstream of Missoula, nutrient reductions were less substantial; still, TP and TN declined toward saturation breakpoints, but no significant reductions in algal biomass occurred, and program targets were not met. The largest P-load reduction to the river was from a basin-wide phosphate laundry detergent ban set 10years before, in 1989. We document that nutrient reductions in rivers can be successful in controlling algal biomass, but require achievement of concentrations below saturation and likely close to natural background. © 2012 American Water Resources Association.