Showing papers by "Michael N. Gooseff published in 2023"
TL;DR: In this paper , the authors quantified the amount of N stored in periphyton biomass and the hyporheic zone of a 5 km long McMurdo Dry Valleys stream corridor.
Abstract: In many temperate streams, biological uptake of N acts to attenuate the transport of excess N from allochthonous anthropogenic imports. Relatively few studies have determined how this N uptake relates to the magnitude of physical vs biological N storage in the stream corridor, especially for intermittent systems where allochthonous N imports are often low and N transport may only occur during brief periods of streamflow. Glacial meltwater streams in the McMurdo Dry Valleys of Antarctica provide an excellent setting to quantify autochthonous N-cycling and storage processes supported by abundant algal mats and well-connected hyporheic zones. We combined historic point-scale sediment and periphyton sample datasets with remote sensing-based modeling of periphyton coverage to estimate how much N was stored in periphyton biomass and the hyporheic zone of a 5-km long McMurdo Dry Valley stream corridor (>100,000 m2). We contextualized these N storage calculations by estimating the magnitude of annual N imports to and exports from the stream corridor based on >2 decades of streamflow and surface water data, source glacier ice cores and meltwater data, and past studies of local aeolian deposition and biological N fixation rates. We found that in this highly oligotrophic system, stream corridor-scale N storage was ∼1000× that of total annual N import or export fluxes. More than 90% of this temporarily stored N was autochthonous organic matter in the shallow (<10 cm) hyporheic zone, which acts as a reservoir that sustains N availability in the water column. Despite its location in a polar desert devoid of higher-order vegetation, area-normalized N storage (∼40 g N/m2) was greater than that reported for streams at lower latitudes (∼1–22 g N/m2). We also demonstrated that NH4+ sorption to stream sediment may be an important physicochemical N storage mechanism that responds to short-term fluctuations in streamflow and governs the mobility of inorganic N. Altogether, this research illustrates the importance of quantifying N storage within stream corridors when evaluating the significance of internal cycling and physical retention processes that modulate N availability.
1 citations
TL;DR: In this article , the authors used long-term (>60 years) climate reanalysis and river discharge observation data to assess longterm changes in discharge and their hydroclimatic drivers, which indicated that the recent increases in air temperature are directly related to these discharge changes.
Abstract: Arctic hydrology is experiencing rapid changes including earlier snow melt, permafrost degradation, increasing active layer depth, and reduced river ice, all of which are expected to lead to changes in stream flow regimes. Recently, long-term (>60 years) climate reanalysis and river discharge observation data have become available. We utilized these data to assess long-term changes in discharge and their hydroclimatic drivers. River discharge during the cold season (October–April) increased by 10% per decade. The most widespread discharge increase occurred in April (15% per decade), the month of ice break-up for the majority of basins. In October, when river ice formation generally begins, average monthly discharge increased by 7% per decade. Long-term air temperature increases in October and April increased the number of days above freezing (+1.1 d per decade) resulting in increased snow ablation (20% per decade) and decreased snow water equivalent (−12% per decade). Compared to the historical period (1960–1989), mean April and October air temperature in the recent period (1990–2019) have greater correlation with monthly discharge from 0.33 to 0.68 and 0.0–0.48, respectively. This indicates that the recent increases in air temperature are directly related to these discharge changes. Ubiquitous increases in cold and shoulder-season discharge demonstrate the scale at which hydrologic and biogeochemical fluxes are being altered in the Arctic.
1 citations
TL;DR: In this article , the authors explore the dynamics of temperature and DO at 10, 20, and 35 cm depth beneath the East River, Colorado, from July - October 2017 (relatively normal water year) and April to October 2018 (comparatively low flow year), enabled by distinctive, in-situ, high frequency (Δt = 5min) sensors that provided continuous time-series from the undisturbed study site over 14 months.
Abstract: Dissolved oxygen (DO) is critical for aquatic ecosystems, however, few studies have focused on the long-term DO dynamics in hyporheic zones, which are a function of both transport (hydrologic exchange between river and hyporheic zone) and uptake by biogeochemical reactions or respiration. We explore the dynamics of temperature and DO at 10, 20, and 35 cm depth beneath the East River, Colorado, from July - October 2017 (relatively normal water year) and April to October 2018 (comparatively low flow year), enabled by distinctive, in-situ, high frequency (Δt = 5min) sensors that provided continuous time-series from the undisturbed study site over 14 months. We expect that hyporheic DO, which has a regular daily fluctuation pattern, is supplied by the surface water (at all times we estimate downwelling) and that diurnal hyporheic DO temporal patterns should be aligned with diurnal hyporheic temperature patterns. However, this was not found to be the case. Hyporheic DO becomes depleted briefly at 20 and 35 cm depths in 2017, and at all 3 hyporheic depths for extended periods in 2018. Whereas diurnal temperature fluctuations have consistent timings of maxima and minima, hyporheic DO rarely has as regular a pattern, and daily ranges are inconsistent. Rainfall events caused some of these changes to diurnal hyporheic DO patterns without repeatable effects. Antecedent snowpack conditions influence streamflow dynamics and therefore hyporheic DO dynamics in this alpine river. These results also point to the strong and variable influence of hyporheic microbial communities regulating hyporheic DO.
TL;DR: In this article , a novel approach was proposed to manipulate experimental conditions and observe mass that is stored at timescales beyond the traditional reach-scale window of detection, leading to lower magnitudes of gross gains and losses in individual reaches.
Abstract: Stream solute tracers are commonly injected to assess transport and transformation in study reaches, but results are biased toward the shortest and fastest storage locations. While this bias has been understood for decades, the impact of an experimental constraint on our understanding has yet to be considered. Here, we ask how different our understanding of reach‐ and segment‐scale transport would be if our empirical limits were extended. We demonstrate a novel approach to manipulate experimental conditions and observe mass that is stored at timescales beyond the traditional reach‐scale window of detection. We are able to explain the fate of an average of 26% of solute tracer mass that would have been considered as “lost” in a traditional study design across our 14 replicates, extending our detection limits to characterize flowpaths that would have been previously unmeasured. We demonstrate how this formerly lost mass leads to predicting lower magnitudes of gross gains and losses in individual reaches, and ultimately show that the network turnover we infer from solute tracers represents an upper limit on actual, expected behavior. Finally, we review the evolution of tracer studies and their interpretation including this approach and provide a proposed future direction to extend empirical studies to not‐before‐seen timescales.
TL;DR: In this article , a combined approach of hydrometric monitoring, geochemical characterization, and end-member mixing analysis (EMMA) was used to assess hydrologic connectivity between areas with high upslope accumulation and the stream.
Abstract: Montane ecoregions are important vehicles for downstream hydrologic function, but their dynamics are relatively understudied compared to alpine and subalpine catchments in the western United States. Montane catchments experience shifts in precipitation inputs seasonally, which results in spatiotemporal differences in source area contributions to the stream. We collected hydrometric and geochemical data between 2018 and 2021 from a 2.65 km2 semi-arid headwater catchment in the Front Range of Colorado, USA. Using a combined approach of hydrometric monitoring, geochemical characterization, and end-member mixing analysis (EMMA), we assess hydrologic connectivity between areas with high upslope accumulation and the stream. Within our study area, high upslope accumulation area corresponded to alluvial/ colluvial fans wherein we focused instrumentation and water sample collection. Using observed rainfall, and multiyear measurements of groundwater levels, soil moisture, and streamflow, we observed distinct hydrologic seasons within our catchment characterized by snowmelt during the spring, rainstorms during the summer, and a return to baseflow during the fall. Within this framework, we found that source areas to streamflow shift with longitudinal distance downstream, and among hydrologic seasons. Notably, our EMMA results indicate that contributions from upstream source areas become less important than lateral inputs from spring snowmelt into the fall return to baseflow. This was most pronounced at the upper catchment where upstream contributions to streamflow decreased up to 33.3% between spring and fall. These results suggest that streamflow is maintained by local source areas contributing laterally and vertically. Our results reflect dynamic shifts in hydrologic connectivity in space and in time, which are increasingly important to land and water resource management given rapid climate changes within the western United States.
DOI•
01 Mar 2023
TL;DR: In this article , the authors examined the geochemical signature of meltwater on glaciers in the McMurdo Dry Valleys of Antarctica, the largest ice-free area on the continent, characterized by alpine glaciers flowing into broad, rocky valleys.
Abstract: Glaciers form the headwaters of many watersheds and, in arid polar environments, can provide the vast majority of water to downstream systems. Headwater watersheds are critically important for setting the chemistry for downstream systems, yet we know comparatively little about the patterns and processes that generate the geochemical signature of meltwater on glacier surfaces. Here, we focus on glaciers in the McMurdo Dry Valleys of Antarctica, the largest ice‐free area on the continent, characterized by alpine glaciers flowing into broad, rocky valleys. We examine patterns from the coast inland, accumulation to ablation zones, laterally across individual glaciers, and through the zone of meltwater generation. We directly compare solutes to sediment concentrations, a major source of dissolved solutes. Our findings agree with previous work that the overall meltwater chemistry of a given glacier is a product of local sediment sources and regional wind patterns: foehn winds moving from the ice sheet to the coast and on‐shore sea breezes. Further, these patterns hold across an individual glacier. Finally, we find that the ice chemistry and sediment profiles reflect freeze‐thaw and melt processes that occur at depth. This indicates that the transport and weathering of sediment in the ice profile likely has a strong influence on supra‐ and proglacial stream chemistry. This new understanding strengthens connections between physical and geochemical processes in cold‐based polar glacier environments and helps us better understand the processes driving landscape and ecosystem connectivity.
TL;DR: In this paper, the authors quantify the soil moisture content of soils throughout the Fryxell basin using multispectral satellite remote sensing techniques and demonstrate that ecologically relevant abundances of liquid water are common across the landscape throughout the austral summer.
Abstract: Available soil moisture is thought to be the limiting factor for most ecosystem processes in the cold polar desert of the McMurdo Dry Valleys (MDVs) of Antarctica. Previous studies have shown that microfauna throughout the MDVs are capable of biological activity when sufficient soil moisture is available (~2–10% gravimetric water content), but few studies have attempted to quantify the distribution, abundance, and frequency of soil moisture on scales beyond that of traditional field work or local field investigations. In this study, we present our work to quantify the soil moisture content of soils throughout the Fryxell basin using multispectral satellite remote sensing techniques. Our efforts demonstrate that ecologically relevant abundances of liquid water are common across the landscape throughout the austral summer. On average, the Fryxell basin of Taylor Valley is modeled as containing 1.5 ± 0.5% gravimetric water content (GWC) across its non-fluvial landscape with ~23% of the landscape experiencing an average GWC > 2% throughout the study period, which is the observed limit of soil nematode activity. These results indicate that liquid water in the soils of the MDVs may be more abundant than previously thought, and that the distribution and availability of liquid water is dependent on both soil properties and the distribution of water sources. These results can also help to identify ecological hotspots in the harsh polar Antarctic environment and serve as a baseline for detecting future changes in the soil hydrological regime.