Lakes as buffers of stream dissolved organic matter (DOM) variability: Temporal patterns of DOM characteristics in mountain stream-lake systems

Abstract

[1] Lakes within fluvial networks may affect dissolved organic matter (DOM) dynamics in streams by dampening spring DOM snowmelt flushing responses and/or by increasing summer DOM production. We assessed the temporal variability of dissolved organic carbon (DOC) concentration and DOM characteristics (specific ultraviolet absorbance (SUVA 254 ); DOC:dissolved organic nitrogen (DOC:DON)), as well as DOC export in seven paired lake inflows and outflows in the Sawtooth Mountain lake district, Idaho. We hypothesized that lakes would decrease stream DOM temporal variability and increase DOM export as a result of autotrophic production. We correlated DOM variability with landscape factors to evaluate potential drivers of DOM temporal patterns (measured as coefficient of variation). Coefficients of variation were 40-90% higher in lake inflows than outflows for DOC concentrations, characteristics, and DOC:DON. Increases in DOC concentrations on the ascending limb of the snowmelt hydrograph were greater in lake inflows than outflows, and on average mean DOC flux occurred 5.4 days earlier in the inflows than for the outflows. During base flow, mean outflow DOC concentrations were 1.7 times greater than inflows, and six outflows had higher annual export than inflows. Combined, these results illustrate that lakes alter the magnitude, timing and temporal variation of DOM concentration and characteristics exported from subalpine watersheds. This buffering effect results from a seasonal shift in the balance between hydrological versus biological controls on DOC dynamics, where lakes act as a sink during the spring when hydrologic controls dominate watershed DOM transport and act as a DOM source during summer.

Dam tailwaters compound the effects of reservoirs on the longitudinal transport of organic carbon in an arid river

“…In comparison, peak concentrations of OC coincided with peak discharge below Fontenelle reservoir, which was likely driven by a combination of factors including dam operations and longer residence time of water in the reservoir relative to the river. For instance, a similar finding of peak OC concentration with peak discharge was found below natural alpine lakes in Idaho, USA, which was attributed to residence time of the lake (Goodman et al, 2011). Riverine DOC sources, and therefore bioavailability and composition, can be seasonally dependent.…”

“…Reservoirs on rivers may trap particulate OC (POC) (Friedl and Wüest, 2002;Downing et al, 2008;Tranvik et al, 2009) and transform and produce dissolved OC (DOC) (Mash et al, 2004;Knoll et al, 2013). Increased water residence time (Vörösmarty et al, 1997;Sabo et al, 2010) allows for OC to be respired, incorporated into microbial production, or buried while production of autochthonous or microbial DOC increases (Mash et al, 2004;Knoll et al, 2013).…”

Nitrogen Fluxes Into, Out Of, and Within a Virginia Permaculture Livestock Farm

“…The relative importance of DON in the Timbercreek Farm pond's outflow changed seasonally; in the winter, DON was 10-30% of the TDN flux and in the summer and fall, 40-50% of the TDN (Chaffin 2016). A similar study found that both dissolved organic matter and DON increased in a pond's outflow in the summer (Goodman et al 2011). This seasonal pattern suggests that primary production (and subsequent decomposition) is important in controlling DON:DIN ratios in the pond's outflow (Chaffin 2016).…”

“…Naturally occurring lakes are often sinks of DIN, but sources of DON (Goodman et al 2011). DON fluxes into and out of agricultural impoundments are often highly variable (Powers et al 2013).…”

“…Naturally occurring lakes are a significant N sink (Seitzinger et al 2002, Mulholland et al 2008, Goodman et al 2011. Like lakes, reservoirs are also N sinks (Powers et al 2014); however, because the physical parameters of impoundments, primarily lake morphology and residence time, make them distinct from natural lakes (Thornton et al 1990), the magnitude and relative importance of N pathways may be different.…”