Variability of in‐stream and riparian storage in a beaded arctic stream

The extent and variability of water storage and residence times throughout the open water season in beaded arctic streams are poorly understood. Data collected in Imnavait Creek, a beaded stream located north of the Brooks Range in Alaska, were used to better understand the effects of in‐pool and riparian storage on heat and mass movement through beaded streams. Temperature data of high spatial resolution within the pools and surrounding sediments were used with volumetric discharge and electrical conductivity to identify storage areas within the pools, banks, and other marshy areas within the riparian zone, including subsurface flow paths that connect the pools. These subsurface flows were found to alter water conductivity and the character of dissolved organic matter (DOM) in short reaches (10 s of m) while influencing the chemistry of downstream pools. During low flow periods, persistent stratification occurred within the pools due to absorption of solar radiation by DOM coupled with permafrost below and low wind stress at the pool surface. Additionally, one of the shallow pools (<0.5 m depth) remained stratified during higher flow periods and lower radiation inputs due to dense subsurface flows entering the bottom of the pools. This consistent separation of surface and bottom water masses in each pool will increase the travel times through this and similar arctic watersheds, and therefore will affect the evolution of water chemistry and material export. Copyright © 2011 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93522/1/hyp8323.pd

The Role of Headwater Streams in Downstream Water Quality1

Knowledge of headwater influences on the water-quality and flow conditions of downstream waters is essential to water-resource management at all governmental levels; this includes recent court decisions on the jurisdiction of the Federal Clean Water Act (CWA) over upland areas that contribute to larger downstream water bodies. We review current watershed research and use a water-quality model to investigate headwater influences on downstream receiving waters. Our evaluations demonstrate the intrinsic connections of headwaters to landscape processes and downstream waters through their influence on the supply, transport, and fate of water and solutes in watersheds. Hydrological processes in headwater catchments control the recharge of subsurface water stores, flow paths, and residence times of water throughout landscapes. The dynamic coupling of hydrological and biogeochemical processes in upland streams further controls the chemical form, timing, and longitudinal distances of solute transport to downstream waters. We apply the spatially explicit, mass-balance watershed model SPARROW to consider transport and transformations of water and nutrients throughout stream networks in the northeastern United States. We simulate fluxes of nitrogen, a primary nutrient that is a water-quality concern for acidification of streams and lakes and eutrophication of coastal waters, and refine the model structure to include literature observations of nitrogen removal in streams and lakes. We quantify nitrogen transport from headwaters to downstream navigable waters, where headwaters are defined within the model as first-order, perennial streams that include flow and nitrogen contributions from smaller, intermittent and ephemeral streams. We find that first-order headwaters contribute approximately 70% of the mean-annual water volume and 65% of the nitrogen flux in second-order streams. Their contributions to mean water volume and nitrogen flux decline only marginally to about 55% and 40% in fourth- and higher-order rivers that include navigable waters and their tributaries. These results underscore the profound influence that headwater areas have on shaping downstream water quantity and water quality. The results have relevance to water-resource management and regulatory decisions and potentially broaden understanding of the spatial extent of Federal CWA jurisdiction in U.S. waters

Beavers affect carbon biogeochemistry : both short-term and long-term processes are involved.

With the recent population increase in beavers (Castor spp.), a considerable amount of new riparian habitat has been created in the Holarctic. We evaluated how beaver‐induced floods affect carbon (C) dynamics in the beaver ponds and in the water‐atmosphere and riparian zone interfaces. Beaver disturbance affects soil organic C storage by decreasing or increasing it, resulting in a redistribution of C. Upon flooding, the concentration of dissolved organic carbon (DOC) increases in the water. This C can be released into the atmosphere, it can settle down to the bottom sediments, it can be sequestered by vegetation, or it can be transported downstream. The carbon dioxide (CO2) emissions vary between 0.14 and 11.2 g CO2 m−2 day−1, averaging 4.9 CO2 g m−2 day−1. The methane (CH4) emissions vary too, from 27 mg m−2 day−1 to 919 mg m−2 day−1, averaging 222 mg CH4 m−2 day−1. Globally, C emission from beaver ponds in the form of CH4 and CO2 may be 3.33–4.62 Tg (teragram, 1012 g) year−1. The yearly short‐term sedimentation rates in beaver ponds vary between 0.4 and 47 cm year−1, and individual ponds contain 9–6355 m3 of sediment. The approximate global estimate for yearly C sedimentation is 3.8 Tg C; beaver ponds globally contain 380 Tg sedimented C. After being formed, beaver pond deposits can remain for millennia. Both C sequestration and CO2 and CH4 emissions in ponds of various ages should be taken into account when considering the net effect of beavers on the C dynamics. With present estimates, beaver ponds globally range from a sink (−0.47 Tg year−1) to a source (0.82 Tg year−1) of C. More research is needed with continuous flux measurements and from ponds of different ages. Likewise, there is a need for more studies in Eurasia to understand the effect of beaver on C biogeochemistry.Peer reviewe

The impact of land-cover change on flood peaks in peatland basins

In headwater peatlands, saturation-excess overland flow is a dominant source of river discharge. Human modifications to headwater peatlands result in vegetation cover change but there is a lack of understanding about how the spatial distribution of such change impacts flood peaks. A fully distributed version of TOPMODEL with an overland flow velocity module was used to simulate flood response for three upland peat basins. Bare peat strips adjacent to channels resulted in a higher and faster flow peak; for a 20 mm/hr rainfall event, with bare riparian zones covering 10% of the basin area, peaks were increased, compared to the current hydrograph, by 12.8%, 1.8% and 19.6% in the three basins. High density Sphagnum ground cover over the same riparian zones reduced flow peaks (e.g. by 10.1%, 1.8% and 13.4% for the 20 mm hr-1 event) compared to the current hydrograph. With similar total areas of land-cover change, the size of randomly located patches of changed cover had no effect on peak flow for patch sizes up to 40000 m2. However, cover changes on gentle slope areas generally resulted in a larger change in peak flow when compared with the same changes on steeper slopes. Considering all results for the same proportion of catchment area that undergoes change, land-cover change along narrow riparian buffer strips had the highest impact on river flow. Thus, the protection and revegetation of damaged riparian areas in upland peat catchments may be highly beneficial for flood management

Nitrogen solutes in an Adirondack forested wetland: importance of dissolved organic nitrogen.

yr −1 respectively, less than flux estimates using biweekly plus storm and snowmelt sampling. DON flux was 18 mol ha −1 yr −1 greater using only biweekly sampling. These differences are probably not of ecological significance relative to the total flux of N from the watershed (349 mol ha −1 yr −1 ). Dissolved organic N concentrations were positively related to discharge during both the dormant (R 2 = 0.31; P &lt; 0.01) and growing season (R 2 = 0.09; P &lt; 0.01). There was no significant relationship between NO − 3 concentration and discharge during the dormant season, but a significant negative relationship was found during the growing season (R 2 = 0.29; P &lt; 0.01). Biotic controls in the growing season appeared to have had a larger impact on stream water NO − 3 concentrations than on DON concentrations. Arbutus Lake had a major impact on stream water N concentrations of the four landscape positions sampled, suggesting the need to quantify within lake processes to interpret N solute losses and patterns in watershed-lake systems. 16

A field-based study of soil water and groundwater nitrate release in an Andirondack forested watershed

[1] Nitrate (NO 3 À ) movement was studied using a combination of isotopic, chemical, and hydrometric data within the 135 ha Archer Creek watershed in the Adirondack Mountains of New York from January 1995 to December 1996. This research was conducted to identify sources of stream water NO 3 À and the mechanisms that deliver NO 3 À to the stream to test two hypotheses: (1) Soil water NO 3 À concentrations are highest after dry periods and subsequently lower with each storm. (2) Stream water NO 3 À concentrations are controlled by groundwater during growing season low flows and by soil water during the dormant season and during storms. Antecedent moisture conditions and season had little effect on mean soil water NO 3 À concentrations before storms (range of 1.1-5.1 mmol L À1 throughout the study). High soil water NO 3 À concentrations (up to 136 mmol L À1 ) were found only at the watershed ridge top during the 1996 snowmelt and early summer. Results from isotopic hydrograph separations and chemical end-member mixing analysis showed that soil water and till groundwater dominated stream base flow and storm flow during six monitored storms. Near-stream wetland groundwater and event water contributed little to streamflow during most conditions. Near-stream groundwater contributions to streamflow were significant only during very low base flow (&lt;0.05 mm h À1 ) during the summer and fall. Highest stream water NO 3 À concentrations coincided with peaks in the till groundwater contribution according to isotopic hydrograph separations using d 18 O and chloride as conservative tracers. A conceptualization of streamflow generation and watershed NO 3 À release is described in which hillslope hollows are the principal zones of soil water and till groundwater mixing in the watershed and till groundwater is the main source of stream water NO 3 À during both base flow and storms