Concentration‐discharge relationships in headwater streams of the Sierra Nevada, California

Abstract

We examined stream water concentration‐discharge relationships for eight small, forest watersheds ranging in elevation from 1485 to 2465 m in the southern Sierra Nevada. These headwater streams revealed nearly chemostatic behavior by current definitions for K+, Ca2+, Mg2+, Na+, Cl–, and SO42– in most cases but not for NH4+, NO3–, or ortho‐P. The latter ions were somewhat enriched during high flows. All ions studied showed a dilution process at lower flows (<50 L s−1) with the concentration‐discharge relationship being more chemostatic at higher flows. While previous studies in the Sierra Nevada have reported peak concentrations of NH4+, NO3–, and SO42– during snowmelt, the headwater systems of the Kings River Experimental Watersheds experience peak concentrations of these ions during the fall rains after the dry summer. These forested watersheds span the rain‐snow transition zone, are 49–228 ha in size, and have soils derived from granite. A statistically significant relationship between soils and stream water concentrations for ortho‐P, Ca2+, and Na+ strongly suggests that soil chemistry has a major influence on stream water chemistry. Factors controlling stream water NH4+, NO3–, and SO42– concentrations are less clear, but one possible source of spikes in these ions during storm events is input from O‐horizon runoff where high concentrations were measured. Overall, stream water concentration‐discharge relationships for these Sierran watersheds are similar to those found in other watershed systems (nearly chemostatic); however, the dominant processes controlling these relationships are probably localized because of different watershed characteristics like soil chemistry, vegetation cover, hydrologic flow paths, and weather patterns.

Seasonal dynamics and exports of elements from a first‐order stream to a large inland lake in Michigan

“…The C‐Q plots for Ca 2+ at the mid and upper and Na + at the upper flumes show a slight, though non‐significant dilution tendency. Overall, the abundance of strong dilution patterns (| b | > 0.2, except for Mg 2+ at upper flume where | b | = 0.1) at our site, contrast with findings by Godsey et al (), Hunsaker and Johnson (), and Kim et al (), who broadly observed base cations to have chemostatic or negative C‐Q relationships with slopes close to 0 (| b | < 0.1). In the Honeysuckle Creek watershed and across the local landscape, these major cations are present in the glacial parent materials and in soil exchangeable pools (Adams & Boyle, , ; Jin, Williams, Szramek, Walter, & Hamilton, ; Nave, Gough, Le Moine, & Nadelhoffer, ; Williams et al, ).…”

“…Although other researchers have found that many of the analytes they measured displayed chemostatic behaviour and had flat C‐Q shapes with slopes below | b | < 0.2 (Basu et al, ; Godsey et al, ; Hunsaker & Johnson, ; Kim, Dietrich, Thurnhoffer, Bishop, & Fung, ; Thompson et al, ), we found that all positive and negative Honeysuckle Creek C‐Q relationships, with the exception of Mg 2+ at the upper flume, were strongly significant with slopes greater than | b | > 0.2. Our results did generally agree with the findings of these researchers that solute concentrations vary less than discharge.…”

“…Cl − had lower CV C (20–30%) and chemostatic CV C /CV Q ratios at the mid and upper flumes compared to F − , which was more variable (CV C = 56–71%; no trend to slightly chemostatic CV C /CV Q ratio) but also measured at much lower concentrations. Musolff et al (), Hunsaker and Johnson (), and Moatar et al () also observed low variability chemostatic trends for Cl − .…”

“…With soil water NO 3 − concentrations an order of magnitude less than stream NO 3 − , it is likely that in‐stream or riparian zone biogeochemical processes and possibly precipitation are the primary sources of NO 3 − to the stream. In a forested watershed Duncan et al () observed a dilution pattern for NO 3 − when sampling at a weekly time step, however, high‐frequency sampling during storm events has revealed flushing of NO 3 − with concentrations increasing on the rising limb of storm hydrographs (Duncan et al, ; Hunsaker & Johnson, ; Inamdar et al, ). It is possible that similar phenomena could be occurring in our watershed as near‐stream NO 3 − sources are flushed out during storm events and due to the slow production of NO 3 − in those riparian areas, concentrations remain low and are diluted even further, especially during snow melt.…”

“…In contrast to the studies of larger watersheds where chemostatic C‐Q trends dominated for many analytes, studies that focused on smaller headwater catchments (80–162 ha) observed significant positive or negative C‐Q relationships for most analytes measured. Herndon et al (), Hoagland et al (), and Hunsaker and Johnson () did not necessarily observe the same C‐Q shape for all analytes, but they did observe significant C‐Q relationships for Mn, Ca 2+ , K + , Cl − , Fe, Al, DOC, and NO 3 − . Na + , Mg 2+ , SO 4 2− , and Si relationships that varied depending on study location.…”