Nutrient uptake during low-level fertilization of a large, seventh-order oligotrophic river

Abstract

Uptake of nitrogen (total nitrogen (TN), NH4-N, and NO3-N) and phosphorus (total dissolved phosphorus (TDP) and total phosphorus (TP)) was quantified June through September 2009–2011 using whole-river fertilization in a seventh-order, P-limited river (Kootenai River, Idaho, USA), at discharges up to three orders of magnitude greater than previously studied. Mean uptake length (Sw) and uptake velocity (Vf) values were similar for dosed TDP and NH4; both had steep gradients indicating rapid uptake, while NO3-N did not. TP remained higher than reference levels. TN showed no clear pattern. Autotrophs accounted for 28% of daylight mean NO3-N uptake compared with 72% by heterotrophs. Nutrient uptake was strongly associated with chlorophyll accrual and epilithon growth rates. Mean midsummer epilithon growth and N rates roughly tripled late summer rates. TDP uptake length (Sw = 5.7 km) showed a slow increase with increasing stream order consistent with published findings. Mean TDP uptake velocity (Vf = 32 mm·min−1) was eight times greater than previously seen in smaller streams. Vf (10.9 ± 5 mm·min−1) and Sw (16.8. ± 7 km) for NO3-N increased with increasing river order and discharge.

Characterizing the phytoplankton and zooplankton communities in Kootenay Lake: a time series analysis of 24 years of nutrient addition

“…Given the ecological and societal responses to excessive nutrient loading in many lentic freshwater ecosystems, limnologists and aquatic ecologists have been studying and managing eutrophied rivers, lakes, and reservoirs over the past 50 years (Vollenweider 1968;National Academy of Sciences 1969;Schindler 1974;Anders and Ashley 2007). In contrast, attention in these fields and in fisheries management has only recently focused on techniques to mitigate cultural oligotrophication in waters across boreal and temperate regions that tend to be naturally oligotrophic (Ashley et al 1999;Stockner et al 2000;Anders and Ashley 2007;Hoyle et al 2014;Minshall et al 2014;Wilson et al 2018;Ward et al 2018). Nutrient addition has been increasingly studied and successfully used to mitigate reduced nutrient availability in Pacific salmon and steelhead-bearing streams in the Pacific Northwest, in part due to the reduction and elimination of historical marine derived nutrient subsidies from anadromous salmonids (Stockner 1987(Stockner , 2003Stockner and MacIsaac 1996;Ashley et al 1999;Gresh et al 2000;Kohler et al 2008Kohler et al , 2012.…”

“…Nutrient addition in Dworshak Reservoir (Wilson et al 2018), Idaho, involved only N following the success of the Kootenay Lake program (Bassett et al 2018). Although less common, nutrient addition has also been successfully used to increase artificially reduced biological productivity in large regulated temperate rivers, such as the Kootenai River, upstream in Idaho (Shafii et al 2010;Minshall et al 2014;Hoyle et al 2014;Watkins et al 2017;Ward et al 2018).…”

River management alters ecosystem metabolism in a large oligotrophic river

“…From 2014 to 2016, nitrate levels ranged between 1.0 to 1.5 mg/L in the Elk River near UN (Teck et al 2016). Downstream of Libby Dam, 2009 to 2011 summer nitrate concentrations ranged between 0.097 to 0.130 mg/L (Ward et al 2017). For 2009 to 2011 summers, total dissolved phosphorus concentrations were 0.0024 mg/L upstream of the phosphorus addition site, 0.0048 mg/L downstream of the phosphorus addition site, and then decreased to upstream concentrations by Rkm 267 (Ward et al 2017).…”

“…Downstream of Libby Dam, 2009 to 2011 summer nitrate concentrations ranged between 0.097 to 0.130 mg/L (Ward et al 2017). For 2009 to 2011 summers, total dissolved phosphorus concentrations were 0.0024 mg/L upstream of the phosphorus addition site, 0.0048 mg/L downstream of the phosphorus addition site, and then decreased to upstream concentrations by Rkm 267 (Ward et al 2017). RT and RP sections, between Libby Dam and the Moyie River confluence, are characterized by large cobble and gravel substrates, limited floodplain, and 2 to 3% macrophyte cover Table 1.…”

“…Historically, the Kootenai River has been ultraoligotrophic (Snyder and Minshall 2005). However, mining activity has increased nitrogen loading to the Elk River, Lake Koocanusa, and the Kootenai River since 2005 (Dessouki andRyan 2010, Teck et al 2016), and the river is now considered oligotrophic (Ward et al 2017). Phosphorus has been added to the Kootenai River at the Idaho-Montana border (276 Rkm) since 2006 to increase primary production and food resources available to declining fish populations (Hoyle 2012, Hoyle et al 2014, Minshall et al 2014.…”