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Climate-driven changes in carbon (C) cycling of forested ecosystems have the potential to alter long-term C sequestration and the global C balance. Prior studies have shown that C uptake and partitioning in response to hydrologic variation are system specific, suggesting that a comprehensive assessment is required for distinct ecosystems. Many sub-humid montane forest ecosystems in the US are projected to experience increased water limitation over the next decades and existing water-limited forests can be used as a model for how changes in the hydrologic cycle will impact such ecosystems more broadly. Toward that goal we monitored precipitation, net ecosystem exchange and lateral soil and stream C fluxes in three semi-arid to sub-humid montane forest catchments for several years (WY 2009–2013) to investigate how the amount and timing of water delivery affect C stores and fluxes. The key control on aqueous and gaseous C fluxes was the distribution of water between winter and summer precipitation, affecting ecosystem C uptake versus heterotrophic respiration. We furthermore assessed C stores in soil and above- and below-ground biomass to assess how spatial patterns in water availability influence C stores. Topographically-driven patterns in catchment wetness correlated with modeled soil C stores, reflecting both long-term trends in local C uptake as well as lateral redistribution of C leached from upslope organic soil horizons to convergent landscape positions. The results suggest that changes in the seasonality of precipitation from winter snow to summer rain will influence both the amount and the spatial distribution of soil C stores.

This study investigates the influence of water, carbon and energy fluxes on solute production and transport through the Jemez Critical Zone (CZ) and impacts on C-Q relationships over variable spatial and temporal scales. Chemical depletion-enrichment profiles of soils, combined with regolith thickness and groundwater data indicate the importance to stream hydrochemistry of incongruent dissolution of silicate minerals during deep bedrock weathering, which is primarily limited by water fluxes, in this highly fractured, young volcanic terrain. Under high flow conditions (e.g., spring snowmelt), wetting of soil and regolith surfaces and presence of organic acids promote mineral dissolution and provide a constant supply of base cations, Si, and DIC to soil water and groundwater. Mixing of waters from different hydrochemical reservoirs in the near stream environment during ‘wet' periods leads to the chemostatic behavior of DIC, base cations, and Si in stream flow. Metals transported by organic matter complexation (i.e., Ge, Al) and/or colloids (i.e., Al) during periods of soil saturation and lateral connectivity to the stream display a positive relationship with Q. Variable Si-Q relationships, under all but the highest flow conditions, can be explained by non-conservative transport and precipitation of clay minerals, which influences long- versus short-term Si weathering fluxes. By combining measurements of the CZ obtained across different spatial and temporal scales, we were able to constrain weathering processes in different hydrological reservoirs that may be flushed to the stream during hydrologic events, thereby informing C-Q relationships.

The critical zone (CZ) is the heterogeneous, near-surface layer of the planet that regulates life-sustaining resources. Previous research has demonstrated that a quantification of the influxes of effective energy and mass transfer (EEMT) to the CZ can predict its structure and function. In this study, we quantify how climate variability in the last 3 decades (1984–2012) has affected water availability and the temporal trends in EEMT. This study takes place in the 1200 km2 upper Jemez River basin in northern New Mexico. The analysis of climate, water availability, and EEMT was based on records from two high-elevation SNOTEL stations, PRISM data, catchment-scale discharge, and satellite-derived net primary productivity (MODIS). Results from this study indicated a decreasing trend in water availability, a reduction in forest productivity (4 g C m−2 per 10 mm of reduction in precipitation), and decreasing EEMT (1.2–1.3 MJ m2 decade−1). Although we do not know the timescales of CZ change, these results suggest an upward migration of CZ/ecosystem structure on the order of 100 m decade−1, and that decadal-scale differences in EEMT are similar to the differences between convergent/hydrologically subsidized and planar/divergent landscapes, which have been shown to be very different in vegetation and CZ structure.

The critical zone (CZ) can be conceptualized as an open system reactor that is continually transforming energy and water fluxes into an internal structural organization and dissipative products. In this study, we test a controlling factor on water transit times (WTT) and mineral weathering called Effective Energy and Mass Transfer (EEMT). We hypothesize that EEMT, quantified based on local climatic variables, can effectively predict WTT within—and mineral weathering products from—the CZ. This study tests whether EEMT or static landscape characteristics are good predictors of WTT, aqueous phase solutes, and silicate weathering products. Our study site is located around Redondo Peak, a rhyolitic volcanic resurgent dome, in northern New Mexico. At Redondo Peak, springs drain slopes along an energy gradient created by differences in terrain aspect. This investigation uses major solute concentrations, the calculated mineral mass undergoing dissolution, and the age tracer tritium and relates them quantitatively to EEMT and landscape characteristics. We found significant correlations between EEMT, WTT, and mineral weathering products. Significant correlations were observed between dissolved weathering products (Na+ and DIC), 3H concentrations, and maximum EEMT. In contrast, landscape characteristics such as contributing area of spring, slope gradient, elevation, and flow path length were not as effective predictive variables of WTT, solute concentrations, and mineral weathering products. These results highlight the interrelationship between landscape, hydrological, and biogeochemical processes and suggest that basic climatic data embodied in EEMT can be used to scale hydrological and hydrochemical responses in other sites.

article Rareearthelements (REEs) were evaluatedaspotentialtracers of biogeochemicalweathering atpedon,hillslope, and catchment scales in the Jemez River Basin Critical Zone Observatory (JRB-CZO), Valles Caldera National Pre- serve, NM, USA. We investigated time series of REE patterns in precipitation, soil pore water, groundwater, and stream water, and related these data to REE composition of soil, rock and atmospheric dust. REE signatures in stream waters are dynamic, reflecting processes that occur along hydrologic flowpaths during transport to the stream, including organic matter complexation, primary and secondary mineral weathering, water/soil/bedrock interaction, and atmospheric deposition. Strong compositional similarities for the REE between soil waters and stream waters during the initial snowmelt are consistent with shallow subsurface flows to streams. Most (bio)

Stream water carbon (C) export is one important pathway for C loss from seasonally snow-covered mountain ecosystems and an assessment of overarching controls is necessary. However, such assessment is challenging because changes in water fluxes or flow paths, seasonal processes, as well as catchment specific characteristics play a role. For this study we elucidate the impact of: (i) changes in water flux (by comparing years of variable wetness), (ii) catchment aspect [north-facing (NF) vs. south-facing (SF)] and (iii) season (snowmelt vs. summer) on all forms of dissolved stream water C [dissolved organic C (DOC), chromophoric dissolved organic matter (CDOM) and dissolved inorganic C (DIC)] in forested catchments within the Valles Caldera National Preserve, New Mexico. The significant correlation between annual water and C fluxes (e.g. DOC r2 = 0.83, p < 0.02) confirms annual stream water discharge as the overarching control on C efflux, likely from a well-mixed ground water reservoir as indicated by previous research. However, CDOM exhibited a dominantly terrestrial fluorescence signature (59–71 %) year round, signaling a strong riparian and near stream soil control on CDOM composition. During snowmelt, the role of water as C transporter was superimposed on its control as C reservoir, when the NF stream transported significantly more soil C (40 % DOC, 56 % DIC) than the SF stream as a result of hillslope flushing. Inter-annual variations in winter precipitation were paramount in regulating annual stream C effluxes, e.g., reducing C effluxes three-fold after a dry (relative to wet) winter season. During the warmer summer months % dissolved oxygen saturation decreased, δ13CDIC increased and CDOM assumed a more microbial signature, consistent with heterotrophic respiration in the stream and riparian soils. As a result of stream C incubation and soil respiration, \( P_{{{\text{CO}}_{2} }} \) increased up to 12 times atmospheric values leading to substantial degassing.

Quantifying water exchange between a coastal wetland and the underlying groundwater is important for closing water, energy and chemical budgets. The coastal wetlandsoftheFlorida Everglades(USA)areattheforefront of a large hydrologic restoration project, and understanding of groundwater/surface-water interactions is needed to comprehend the effects of the project. Four independent techniques were used to identify water exchange at varying spatial and temporal scales in Taylor Slough, Everglades NationalPark.Thetechniquesincludedawater-budgetstudy and measurements of hydraulic head gradients, geochemical tracers, and temperature. During the 18-month study, the four methods converged as to the timing of groundwater discharge, typically between June and September, contem- poraneous with the wet season and increasing surface-water levels. These results were unexpected, as groundwater discharge was predicted to be greatest when surface-water levels were low, typically during the dry season. Either a time lag of 1-5months in the response of groundwater discharge to low surface-water levels or precipitation- induced groundwater discharge may explain the results. Groundwater discharge was a significant contributor (27%) to the surface water in Taylor Slough with greater rates of

[1] Long- and short-term changes in the spatial distribution of surface water phosphorus concentrations were assessed for the Everglades wetland (USA) from 12 years of monitoring data. Changes in phosphorus spatial distributions, before and after implementation of measures to reduce phosphorus, including stormwater treatment areas (STAs) and best management practices (BMPs), were used to evaluate the effect of the remediation strategies in the naturally oligotrophic wetland. Results showed a clear spatial and temporal gradient in phosphorus concentrations, with highest total phosphorus (TP) reaching 200 mg/L in the northern Water Conservation Areas (WCAs) because of canal inflow from the Everglades Agricultural Area (EAA). Long-term records of TP concentrations from 1995 to 2007 showed declines in Water Conservation Area WCA1 during the dry season (� 5.1%). Short-term changes (2003–2007) showed increasing trends in TP concentrations elsewhere in the Everglades, mainly in the southern areas: WCA3 and Everglades National Park (ENP). From 2003 to 2007, phosphorus increased by 7.4% per year in the ENP during the dry season. The area of the Everglades that exceeded the 10 mg/L surface water TP concentration ecological threshold was quantified and showed a long-term overall decline. However, except for the ENP, more than 65% of the Everglades surface area exceeded the 10 mg/L water quality threshold in 2007. During recent years, ENP and WCA3 surface areas that exceeded the alternative 15 mg/L annual geometric mean slightly increased, confirming the need to closely monitor these two regions.