Water quality response to a pulsed‐flow event on the Mokelumne river, California

Abstract

Controlled water releases from reservoirs (i.e. artificial floods) are used as a management technique to remove fine sediments and detrital materials from spawning gravels, mobilize gravel bars and clear encroaching brush from stream banks. The effects of a managed release event on water quality were investigated on the lower Mokelumne River in the western Sierra Nevada, California. The managed release was characterized by an increase in flow over a 4-day period (from 11 to 57 m 3 s À1 ). Automatic pump samplers were used to collect samples for water quality from 0.7, 16.4, 37.4 and 54.4 km below Camanche Dam. These sampling sites provided water quality data for three distinct stream reaches: a gravel and sand-textured substrate reach (0.7-16.4 km), a reach characterized by lentic conditions associated with a small reservoir (16.4-37.4 km), and fine sand and silt-textured substrate reach (37.4-54.4 km). Water samples were analysed for total suspended solids (TSS), total nitrogen, ammonium (NH 4 -N), nitrate (NO 3 -N), total phosphorus, soluble reactive phosphorus (SRP), dissolved organic carbon (DOC), foecal coliforms and E. coli. Chemographs for all constituents exhibited spikes in concentration with each increase in streamflow for the rising limb. Fluxes of TSS, total P and total N released from the 0.7 to 16.4 km reach were 322, 0.32 and 0.70 Mg, respectively. The small reservoir acted as a sink for particulate materials retaining about 50% of TSS, 48% of total P and 43% of total N. However, the reservoir acted as a source of dissolved nutrients (NO 3 -N ¼ 0.28 Mg and SRP ¼ 0.055 Mg). The stream reach below the reservoir (37.4 to 54.4 km) was a source of particulate materials, dissolved nutrients and bacteria, possibly due to agricultural and urban inputs.

The upside-down river: Reservoirs, algal blooms, and tributaries affect temporal and spatial patterns in nitrogen and phosphorus in the Klamath River, USA

“…Many studies have shown that rivers can act as sinks of P during low flows, and sources of P during high flows (Haggard et al, 2001;Henson et al, 2009;Kronvang et al, 1999). High flows have been shown to agitate sediments and stimulate the release of P (Johnson et al, 1976) as well as provide increased load capacity (Keup, 1968).…”

Sediment can be a reservoir for coliform bacteria released into streams

“…Most reports of sediment coliforms and resuspension phenomena come from study sites where there are large benthic disturbances such as dredging (Grimes, 1975), from coastal and estuarine studies where tidal forces, recreational uses, or controlled water releases from reservoirs can cause relatively large shifts in drag forces on the sediment Crabill et al, 1999;Henson et al, 2007;Pettibone et al, 1996;Solo-Gabriele et al, 2000), or from studies in which the bed sediment was disturbed by artificial flooding or mechanical sediment disturbance (Bai and Lung, 2005;McDonald et al, 1982;Nagels et al, 2002;Sherer et al, 1988). Direct comparisons of water and sediment coliform counts over a long period of time at natural, undisturbed stream systems have not been performed.…”

Dissolved organic carbon delivery from managed flow releases in a montane snowmelt river

“…Whilst our results clearly show that DOC concentration was not related to discharge during Jindabyne Dam releases (Fig. 5), the literature report inconsistent relationships between DOC concentration and discharge in dam tailwaters, with DOC concentration increasing with discharge below some dams (Henson et al 2007;Ulseth and Hall 2015), and an insignificant relationship below others (Ulseth and Hall 2015). Although Henson et al (2007) and Ulseth and Hall (2015) do not specify the spatial extent of riparian and floodplain inundation in their studies, it is possible that the relatively small area inundated by the dam releases in our study precluded large changes in DOC concentration, as only the lower river benches were wetted.…”

“…Managed flow releases delivered from reservoirs are therefore likely to provide a different quantity and quality of DOC compared to the natural events they are intended to simulate, potentially influencing carbon flow through the downstream aquatic ecosystem. Few studies have examined DOC delivery from managed flow releases in detail, although Henson et al (2007) reported a pulse in DOC concentration from 0.5 to 3.6 mg L -1 up to 54 km downstream of Camanche Dam on the rising limb of a managed flow release on the Mokelumne River, California.…”