Ronald J. Avanzino

RETENTION AND TRANSPORT OF NUTRIENTS IN A THIRD-ORDER STREAM IN NORTHWESTERN CALIFORNIA: HYPORHEIC PROCESSES'

Chloride and nitrate were coinjected into the surface waters of a third—order stream for 20 d to examine solute retention, and the fate of nitrate during subsurface transport. A series of wells (shallow pits) 0.5—10 m from the adjacent channel were sampled to estimate the lateral interflow of water. Two subsurface return flows beneath the wetted channel were also examined. The conservative tracer (chloride) was hydrologically transported to all wells. Stream water was >88% of flow in wells <4 m from the wetted channel. The lowest percentage of stream water was 47% at a well 10 m perpendicular to the stream. Retention of solutes was greater in the hyporheic zone than in the channel under summer low—flow conditions. Nominal travel time (the interval required for chloride concentration to reach 50% of the plateau concentration) was variable by well location, indicating different flow paths and presumably permeability differences in subsurface gravels. Nominal travel time was M 24 h for wells <5 m from the we...

The role of water exchange between a stream channel and its hyporheic zone in nitrogen cycling at the terrestrial-aquatic interface

The subsurface riparian zone was examined as an ecotone with two interfaces. Inland is a terrestrial boundary, where transport of water and dissolved solutes is toward the channel and controlled by watershed hydrology. Streamside is an aquatic boundary, where exchange of surface water and dissolved solutes is bi-directional and flux is strongly influenced by channel hydraulics. Streamside, bi-directional exchange of water was qualitatively defined using biologically conservative tracers in a third order stream. In several experiments, penetration of surface water extended 18 m inland. Travel time of water from the channel to bankside sediments was highly variable. Subsurface chemical gradients were indirectly related to the travel time. Sites with long travel times tended to be low in nitrate and DO (dissolved oxygen) but high in ammonium and DOC (dissolved organic carbon). Sites with short travel times tended to be high in nitrate and DO but low in ammonium and DOC. Ammonium concentration of interstitial water also was influenced by sorption-desorption processes that involved clay minerals in hyporheic sediments. Denitrification potential in subsurface sediments increased with distance from the channel, and was limited by nitrate at inland sites and by DO in the channel sediments. Conversely, nitrification potential decreased with distance from the channel, and was limited by DO at inland sites and by ammonium at channel locations. Advection of water and dissolved oxygen away from the channel resulted in an oxidized subsurface habitat equivalent to that previously defined as the hyporheic zone. The hyporheic zone is viewed as stream habitat because of its high proportion of surface water and the occurrence of channel organisms. Beyond the channels hydrologic exchange zone, interstitial water is often chemically reduced. Interstitial water that has not previously entered the channel, groundwater, is viewed as a terrestrial component of the riparian ecotone. Thus, surface water habitats may extend under riparian vegetation, and terrestrial groundwater habitats may be found beneath the stream channel.

Retention and Transport of Nutrients in a Third‐Order Stream: Channel Processes

Chloride was injected as a conservative tracer with nitrate to examine nitrate retention (storage plus biotic uptake) and transport in a 327-m reach of a third-order stream draining a forested basin in northwestern California. Prior to injections, diel patterns of nutrient concentrations were measured under background conditions. Nitrate concentration of stream water increased downstream, indicating that the reach was a source of dissolved inorganic nitrogen to downstream communities under background, low-flow conditions, despite uptake by photoautotrophs. At the onset of continuous solute injection over a 10-d period, timing the passage of the solute front indicated that storage dominated nitrate retention. Instantaneous concentration differences at the base of the reach at hour 24 indicated that biotic uptake accounted for 13% of the nitrate amendment while hydrologic storage constituted 29%. Corrected for groundwater dilution (11.7%), saturation of the streams channel and hyporheic zones was not complete until 6.8 d of continuous injection. By day 3 nitrate retention was dominated by biotic processes. Biotic uptake was greatest during daylight hours indicating retention by photoautotrophs, but also occurred during darkness. After 10 d of continuous injection, mass balance calculations indicated that 29% of N (339 g) was retained from the total injected (1155 g), while the balance of injected nitrate was transported downstream. Storage of NO3-N was 117 g or 10% while biotic uptake was 222 g or 19%. Periphyton biomass on slides, chlorophyll a both on slides and on natural cobbles, and net community primary production all indicated a lag in periphyton response to nitrate amendment. Earliest indicators of a biotic response to nutrient amendment were decreases in both tissue C/N and epilithic respiration.

Ammonium sorption to channel and riparian sediments: A transient storage pool for dissolved inorganic nitrogen

Sediment (0.5 mm–2.0 mm grain size) was incubated in nylon bags (200 μm mesh) below the water table in the channel and in two transects of shallow wells perpendicular to the banks (to 18 m) of a third-order stream during August, 1987. One transect of wells drained steep old-growth forest, and the other a steep 23 year-old clear-cut partially regenerated in alder. At approximately 6-week intervals between October, 1987, and June, 1988, bags were retrieved. Total exchangeable ammonium was determined on sediment, and dissolved oxygen, nitrate and ammonium were determined in stream and well water. Exchangeable ammonium ranged from 10 μeq/100 g of sediment in the stream where nitrification potential and subsurface exchange with stream water were high, to 115 μeq/100 g sediment 18 m inland where channel water-groundwater mixing and nitrification potential were both low. Sorbed ammonium was highest during summer/autumn base flow and lowest during winter storm flow. Both channel and well water contained measurable dissolved oxygen at all times. Ammonium concentration was typically < 10 μg-N/L in channel water, increased with distance inland, but did not exceed 365 μg-N/L at any site. Nitrate concentration was typically higher in well water than channel water. Nitrate levels increased dramatically in wells at the base of the clear-cut following the onset of autumn rains. The results indicate a potential for temporary storage of ammonium on riparian sediments which may influence biotic nitrogen cycling, and alter the timing and form of dissolved inorganic nitrogen transport from the watershed.

Long‐term frozen storage of stream water samples for dissolved orthophosphate, nitrate plus nitrite, and ammonia analysis

Many researchers have used freezing as an effective, short-term, water sample preservation method for subsequent nutrient analysis. In this study, filtered samples held at −16±2°C for 4–8 years were reanalyzed for orthophosphate, nitrate plus nitrite, and ammonia. Orthophosphate and ammonia concentrations decreased by 0.2 μg P/L and 5 μg N/L, respectively, at mean concentrations of 69.4 μg P/L and 246 μg N/L. Nitrate plus nitrite increased by 1.1 μg N/L at a mean concentration of 139.1 μg N/L. An anaerobic well sample proved to be unsuitable for freezing because it lost significant amounts of orthophosphate during the freezing process. None of the differences observed over long periods of frozen storage were more than twice the estimated standard deviation of the analytical methods used in the study. The small changes observed demonstrate the effectiveness of frozen storage as a means of nutrient preservation in water samples that are unaffected by the freezing process itself.

In situ retention-transport response to nitrate loading and storm discharge in a third-order stream

Nitrate retention was assayed in a 264-m reach of a third-order stream, Little Lost Man Creek, Humboldt County, California, USA. Nitrate budgets (24-48 hours) were calculated under background conditions, and during four other intervals of modified nitrate concentration caused by nutrient amendment or storm-enhanced discharge. Under background, low-flow conditions, the reach was a source of nitrate to downstream communities. Retention during the first 36 hours of nitrate amendment was dominated by storage in the hyporheic zone and later by biotic uptake as storage zones became saturated (plateau concentration). The increase in net retention caused by increased nitrate concentration decreased output/input (O/I) ratio from 1.11 before amendment to 0.61 after 36 hours, and to 0.86 after transient storage zones were filled. Dilution, caused by a nearly four-fold increase in discharge, increased biotic retention and also export as previously stored nitrate leached from the hyporheic zone into the channel. Nitrate continued to leach from the hyporheic zone seven days after the amendment ended. This type of response may enhance biotic nutrient cycling by providing waters of higher nutrient concentration to partially scoured epilithic surfaces following reset of the benthic community by a major storm.

Phosphorus and Nitrogen Legacy in a Restoration Wetland, Upper Klamath Lake, Oregon

The effects of sediment, ground-water, and surface-water processes on the timing, quantity, and mechanisms of N and P fluxes were investigated in the Wood River Wetland 5–7 years after agricultural practices ceased and seasonal and permanent wetland hydrologies were restored. Nutrient concentrations in standing water largely reflected ground water in winter, the largest annual water source in the closedbasin wetland. High concentrations of total P (22 mg L−1) and total N (30 mg L−1) accumulated in summer when water temperature, air temperature, and evapotranspiration were highest. High positive benthic fluxes of soluble reactive P and ammonium (NH4+-N) were measured in two sections of the study area in June and August, averaging 46 and 24 mg m−2 d−1, respectively. Nonetheless, a wetland mass balance simultaneously indicated a net loss of P and N by assimilation, denitrification (1.1–10.1 mg N m−2 h−1), or solute repartitioning. High nutrient concentrations pose a risk for water quality management. Shifts in the timing and magnitude of water inflows and outflows may improve biogeochemical function and water quality by optimizing seed germination and aquatic plant distribution, which would be especially important if the Wood River Wetland was reconnected with hyper-eutrophic Agency Lake.

Determination of groundwater discharge into a sand and gravel bottom river: a comparison of chloride dilution and seepage meter techniques

The extent of mixing berween groundwater and surfaee water varies in stream eatehments. In eatehments with high alluvial eonduetiviry, steep hydraulie gradients, and relatively low groundwater pressure gradients, the extent of surfaee water penetration into the aq uifer is large an d the shallow subsurfaee water ean eonsist almost emirely of stream water. In eomrast, eatehmems with large verrieal groundwater pressure gradiems or fine bed sedimems have restricted surfaee water penetration and shallow porewater eonsists primarily of groundwater. 1-;lydrologie and biologie retemion assoeiated with stream water penetration imo the bed ean signifieantly affeet solute eomposition and coneentration in stream and shallow groundwater. Stream eatehmems with large hydrologie exehange zones rend to have a greater influenee on the solure eomposition of stream water than eatehmems with small hydrologie exehange zones (VALETI et al. 1996, MULHOLLAND et al. I 997). Hydrologie and biologie retention also will influenee the solute eomposition of groundwater in stream eatehmems where rhe water immediately below the bed is predominantly groundwater. For example, seasonal variations in stream water ehemistty of the Shingobee River indieate that mierobial proeesses in the hydrologie exehange zone have a signifieam impaet on inorganie N ehemistry of groundwater diseharge (DuFF et al. 1996). The purpose of this study was to eompare estimates of groundwater diseharge by rwo methods. The first teehnique, ehloride dilurion, was used to determine the magnitude of flow inerease in the rota! reaeh. The seeond teehnique, seepage meter flux, was used to determine the variability of groundwater diseharge assoeiated with streambed heterogeneity within the reaeh. Determining the volume and ehemieal composition of various groundwater sourees is a eritieal first step for ealculating mass balanee for the reaeh. Mass balanee is a eommon proeedure for dedueing the proeesses responsible for nutriem transformations from measured ehanges in load. To aeeurately ealculate mass balanees, it is neeessary to determine volume and ehemieal eomposition of major groundwater sourees, including diffuse and foeused groundwater diseharge and bankside seeps.

Nutrients contributed by ‘old’ and ‘new’ ground water to the Shingobee River MN, USA

Groundwater-dominated rivers have special characteristics that influence their hydrology, geomorphology, chemistry and ecology. Common hydrologic features associated with groundwater-dominated rivers include maintenance of low flows and stability of temperature and flow regime. Regionally, high groundwater discharge buffers seasonal changes in water temperature, especially in northern climates where the annual temperature range is large (PoWER et al. 1999). Within si tes, large temperature variation can occur laterally, providing local habitat warming in winter or cooling in summer (WEBB & ZHANG, 1999). Chemically, groundwater-dominated rivers often have stable water quality, low turbidity and high bicarbonate and nitrate (WARD et al. 1999). Al! o f these properties can strongly influence the ecology of groundwater-dominated streams and rivers.

Nutrient chemistry, transformation and release in riparian groundwater seep discharge during the final meter of subsurface transport, Minnesota, USA

Groundwater discharges into streams either directly through the stream bed or indirectly via bankside seeps. Literature reports have long indicated that prior to becoming surface water, riparian groundwater can undergo significant nitrate retention (LoWRANCE et al. 1984, PETERJOHN & CoRRELL 1984, JAcoBs & ÜILLIAM 1985, LowRANCE 1992, HILL 1996), especially where shallow impermeable sediments or other aquicludes force it into biotically active riparian habitats (JAcoBS & ÜILLIAM 1985, JoRDAN et al. 1993, CEY et al. 1999, HILL et al. 2000). More recently, perfusion studies using intact sediment cores have indicated significant nutrient transformations, including coupled nitrification-denitrification during the subchannel discharge of groundwater (SHEIBLEY et al. 2003a). Numerical modeling of these transformations indicated that they can exert significant control on surface water chemistry (SHEIBLEY et al. 2003b). Equivalent nutrient transformations in bankside riparian seeps and their contribution to surface water remain little studied. While riparian seep inputs are rare in most streams, they can be common in groundwater-dominated drainages. ÜENEREUX et al. (2002) used mixing models to demonstrate that interbasin transfer of regional groundwater could contribute significantly to surface water discharge and chemistry in lowland Costa Rica. At the same site, PRINGLE et al. (1990, 1993), PRINGLE & TRISKA (1991) and TRISKA et al. (2006) identified a zone of high soluble reactive phosphorus (SRP) increase in the Rio Salto in Costa Rica based on its presence in adjacent seeps and springs. These seeps and springs emerged along a gradient break and boundary between 2 historic lava flows. We examined nutrient contribution and seasonal nutrient chemistry of eleven riparian bank seeps for 2 years along a 600-m reach of a groundwater dominated stream in north-central Minnesota, U.S.A. Our objective was to determine riparian seep contribution to stream discharge and to identify nutrient transformations as groundwater emerged at the seep surface during the final meter of subsurface transport.