Ground water recharge is assumed to occur primarily at raised bog crests in northern peatlands, which are globally significant terrestrial carbon reservoirs. We synoptically surveyed vertical profiles of peat pore water δ18O and δ2H from a range of bog and fen landforms across the Glacial Lake Agassiz Peatlands, northern Minnesota. Contrary to our expectations, we find that local‐scale recharge penetrates to not only the basal peat at topographically high bog crests but also transitional Sphagnum lawns and low‐lying fen water tracks. Surface landscape characteristics appear to control the isotopic composition of the deeper pore waters (depths ≥0.5 m), which are partitioned into discrete ranges of δ18O on the basis of landform type (mean ± standard deviation for bog crests = −11.9 ± 0.4‰, lawns = −10.6 ± 0.1‰, fen water tracks = −8.8 ± 1.0‰). Fen water tracks have a shallow free‐water surface that is seasonally enriched by isotope fractionating evaporation, fingerprinting recharge to underlying pore waters at depths ≥3 m. Isotope mass balance calculations indicate on average 12% of the waters we sampled from the basal peat of the fen water tracks was lost to surface evaporation, which occurred prior to advection and dispersion into the underlying formation. These new data provide direct support for the hypothesis that methane production in deeper peat strata is fuelled by the downward transport of labile carbon substrates from the surface of northern peat basins. Copyright © 2013 John Wiley & Sons, Ltd.
Groundwater provides approximately one third of fresh water used by humans on the planet, but can be vulnerable to depletion during drought-particularly in large, regional aquifers that support irrigated agriculture (Aeschbach-Hertig & Gleeson, 2012;Taylor et al., 2013). Aquifer overdraft occurs where net outflows due to pumping exceed inflows from precipitation, surface-water recharge, and lateral flow, causing declines in groundwater levels and, in some extreme cases, land subsidence (Scanlon et al., 2012;Whittemore et al., 2016). Although physical relationships between pumping and groundwater-level decline have been observed and modeled in a variety of hydrogeologic settings (Butler et al., 2016;Faunt, 2009), effects of aquifer exploitation on water quality are often highly localized, difficult to extrapolate on regional scales, and have only been addressed in a handful of studies (e.g., Blaszyk & Gorski, 1981;Lambrakis & Kallergis, 2001;Nunes et al., 2021). California's Central Valley is a large (51,800 km 2 ), agricultural region that maintains high primary productivity under a semi-arid climate by irrigation from extensive surface-water diversions and groundwater pumpage (Faunt, 2009). Long-term groundwater depletion rates on the order of 2 km 3 yr −1 over the latter part of the 20th century can double during drought as pumpage increases to meet demand shortfalls from diminished surface-water flows (Famiglietti et al., 2011;Faunt et al., 2016). Drought-induced pumpage has precipitated dramatic groundwater-level declines and land subsidence in critically overdrafted groundwater basins within the San Joaquin Valley (SJV) subregion over the past 30 yr (Figure 1a; DWR, 2016DWR, , 2020. Recent work in the Central Valley has focused on vulnerability of shallow, domestic wells to supply failure during drought (Jasechko & Perrone, 2020;Pauloo et al., 2020), but little has been done to connect
Northern peatlands are an important source for greenhouse gases, but their capacity to produce methane remains uncertain under changing climatic conditions. We therefore analyzed a 43 year time series of the pore‐water chemistry to determine if long‐term shifts in precipitation altered the vertical transport of solutes within a large peat basin in northern Minnesota. These data suggest that rates of methane production can be finely tuned to multidecadal shifts in precipitation that drive the vertical penetration of labile carbon substrates within the Glacial Lake Agassiz Peatlands. Tritium and cation profiles demonstrate that only the upper meter of these peat deposits was flushed by downwardly moving recharge from 1965 to 1983 during a Transitional Dry‐to‐Moist Period. However, a shift to a moister climate after 1984 drove surface waters much deeper, largely flushing the pore waters of all bogs and fens to depths of 2 m. Labile carbon compounds were transported downward from the rhizosphere to the basal peat at this time producing a substantial enrichment of methane in Δ14C with respect to the solid‐phase peat from 1991 to 2008. These data indicate that labile carbon substrates can fuel deep production zones of methanogenesis that more than doubled in thickness across this large peat basin after 1984. Moreover, the entire peat profile apparently has the capacity to produce methane from labile carbon substrates depending on climate‐driven modes of solute transport. Future changes in precipitation may therefore play a central role in determining the source strength of peatlands in the global methane cycle.
As combined sewer systems and centralized wastewater treatment facilities age, many communities in the world are challenged by management of combined sewer overflow (CSO). Constructed wetlands are considered to be one of the green infrastructure solutions to CSOs in the US. Despite the wide application of constructed wetlands to different types of wastewaters, the stochastic and intermittent nature of CSO presents challenges for design and performance assessment of constructed wetlands. This paper reviews the application status of CSO constructed wetlands in the US, assesses the benefits of CSO constructed wetlands, identifies challenges to designing CSO constructed wetlands, and proposes design considerations. This review finds that constructed wetlands are effective in CSO treatment and relatively less expensive to build than comparable grey infrastructure. Constructed wetlands not only remove pollutants, but also mitigate the event-associated flow regime. The design challenges include incorporating considerations of green infrastructure into permit requirements, determining design capacity for highly variable flows, requiring pretreatment, OPEN ACCESSWater 2014, 6 3363 and needing adaptive design and intensive monitoring. Simultaneous monitoring of flow rate and water quality at both the inflow and outflow of CSO constructed wetlands is required for performance assessment and needed to support design, but is rarely available.
Up to 850 billion gallons of untreated combined sewer overflow (CSO) is discharged into waters of the United States each year. Recent changes in CSO management policy support green infrastructure (GI) technologies as "front of the pipe" approaches to discharge mitigation by detention/reduction of urban stormwater runoff. Constructed wetlands for CSO treatment have been considered among suites of GI solutions. However, these wetlands differ fundamentally from other GI technologies in that they are "end of the pipe" treatment systems that discharge from a point source, and are therefore regulated in the U.S. under the National Pollution Discharge Elimination System (NPDES). We use a comparative regulatory analysis to examine the U.S. policy framework for CSO treatment wetlands. We find in all cases that permitting authorities have used best professional judgment to determine effluent limits and compliance monitoring requirements, referencing technology and water quality-based standards originally developed for traditional "grey" treatment systems. A qualitative comparison with Europe shows less stringent regulatory requirements, perhaps due to institutionalized design parameters. We recommend that permitting authorities develop technical guidance documents for OPEN ACCESS Sustainability 2014, 6 2393 evaluation of "green" CSO treatment systems that account for their unique operational concerns and benefits with respect to sustainable development.
Although northern peatlands represent a globally significant reservoir for carbon, considerable uncertainty exists concerning solute transport systems within large (>1000 km 2) peat deposits. We therefore delineated geochemical gradients linked to groundwater recharge and discharge along a 6 km transect within the 1200 km 2 Red Lake Peatland of northwestern Minnesota. We used ratios of Ca/Mg and 87 Sr/ 86 Sr to distinguish discharge of calcareous groundwater (~1.4 and 0.7155, respectively) to the peatland from the mineral substratum along a topographic gradient from a bog crest downslope to an internal fen water track and bog islands. In contrast, the stable isotopes of the porewaters (δ 18 O from-12.8 ‰ to-7.8 ‰) show that the active pore-spaces in these peat profiles has been flushed by recharge from the near-surface peat. We hypothesize that back-diffusion of groundwater-derived solutes from the peat matrix to active pore-spaces has allowed the geochemical signal from paleo-hydrogeologic discharge to persist into the current regime of dilute recharge. This effect has not been observed previously on the landform-scale and has important implications for carbon cycling in peatlands.
Map showing locations of water districts and major infrastructure for surface-water conveyance in the northern Sierra Nevada foothills domestic-supply aquifer assessment study units, 2015-17, California Groundwater Ambient Monitoring and Assessment Program Priority Basin Project ....13 6. Map showing locations of grid cells, groundwater grid sites, and the understanding site sampled for the northern Sierra Nevada foothills domestic-supply aquifer assessment study units, 2015-17, California Groundwater Ambient Monitoring and Assessment Program Priority Basin Project ....16 vi 7. Map showing locations of grid cells for the northern Sierra Nevada foothills domestic-supply aquifer assessment study units, 2015-17, California Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project; public-supply wells used for the comparative assessment of domestic wells with public-supply wells from the Sierra Nevada Regional GAMA assessment
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