Dating groundwater with dissolved silica and CFC concentrations in crystalline aquifers

Marçais, Jean; Gauvain, Alexandre; Labasque, Thierry; Abbott, Benjamin W.; Pinay, Gilles; Aquilina, Luc; Chabaux, François; Viville, Daniel; Dreuzy, Jean‐Raynald de

doi:10.1016/j.scitotenv.2018.04.196

Cited by 47 publications

(27 citation statements)

References 72 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition to data-driven approaches emphasis should also be put on robust estimations of water TT in catchments to constrain reaction rates. Recent studies present promising approaches to derive TTs in groundwater (Marcais et al, 2018;Kolbe et al, 2019) and at catchment scale (Jasechko et al, 2016;Yang et al, 2018a)…”

Section: Resultsmentioning

confidence: 99%

“…Consequently, the accretion pattern was intensified in the first decades, accompanied by an increase in CV C / CV Q . The resulting positive C-Q relationship on a seasonal basis was found in many agricultural catchments worldwide (e.g., Aubert et al, 2013;Martin et al, 2004;Mellander et al, 2014;Rodríguez-Blanco et al, 2015;Musolff et al, 2015). However, after several years of deeper migration of the N input, the catchment started to exhibit a chemostatic NO 3 export regime (after the 1990s), which was manifested in the decreasing CV C / CV Q ratio.…”

Section: Linking Effective Tts Concentrations and C-q Trajectories Wmentioning

confidence: 88%

See 1 more Smart Citation

Trajectories of nitrate input and output in three nested catchments along a land use gradient

Ehrhardt

Kumar

Fleckenstein

et al. 2019

Hydrol. Earth Syst. Sci.

View full text Add to dashboard Cite

Increased anthropogenic inputs of nitrogen (N) to the biosphere during the last few decades have resulted in increased groundwater and surface water concentrations of N (primarily as nitrate), posing a global problem. Although measures have been implemented to reduce N inputs, they have not always led to decreasing riverine nitrate concentrations and loads. This limited response to the measures can either be caused by the accumulation of organic N in the soils (biogeochemical legacy) -or by long travel times (TTs) of inorganic N to the streams (hydrological legacy). Here, we compare atmospheric and agricultural N inputs with longterm observations of riverine nitrate concentrations and loads in a central German mesoscale catchment with three nested subcatchments of increasing agricultural land use. Based on a data-driven approach, we assess jointly the N budget and the effective TTs of N through the soil and groundwater compartments. In combination with long-term trajectories of the C-Q relationships, we evaluate the potential for and the characteristics of an N legacy.We show that in the 40-year-long observation period, the catchment (270 km 2 ) with 60 % agricultural area received an N input of 53 437 t, while it exported 6592 t, indicating an overall retention of 88 %. Removal of N by denitrification could not sufficiently explain this imbalance. Log-normal travel time distributions (TTDs) that link the N input history to the riverine export differed seasonally, with modes spanning 7-22 years and the mean TTs being systematically shorter during the high-flow season as compared to low-flow conditions. Systematic shifts in the C-Q relationships were noticed over time that could be attributed to strong changes in N inputs resulting from agricultural intensification before 1989, the break-down of East German agriculture after 1989 and the seasonal differences in TTs. A chemostatic export regime of nitrate was only found after several years of stabilized N inputs. The changes in C-Q relationships suggest a dominance of the hydrological N legacy over the biogeochemical N fixation in the soils, as we expected to observe a stronger and even increasing dampening of the riverine N concentrations after sustained high N inputs. Our analyses reveal an imbalance between N input and output, long timelags and a lack of significant denitrification in the catchment. All these suggest that catchment management needs to address both a longer-term reduction of N inputs and shorterterm mitigation of today's high N loads. The latter may be covered by interventions triggering denitrification, such as hedgerows around agricultural fields, riparian buffers zones or constructed wetlands. Further joint analyses of N budgets and TTs covering a higher variety of catchments will provide a deeper insight into N trajectories and their controlling parameters.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Linking Effective Tts Concentrations and C-q Trajectories Wmentioning

confidence: 88%

Trajectories of nitrate input and output in three nested catchments along a land use gradient

Ehrhardt

Kumar

Fleckenstein

et al. 2019

Hydrol. Earth Syst. Sci.

View full text Add to dashboard Cite

show abstract

“…Though recognized as a planetary priority (Foley et al, 2011;Steffen et al, 2015;Le Moal et al, 2019), efforts to reduce eutrophication have had mixed results, partly because of two challenges that emerge at watershed scales (i.e., 1-10,000 km 2 ). First, it is difficult to quantify the overall residence time of nutrients in complex watersheds, which ranges from minutes to millennia as nutrients may be recycled or stored in plant biomass, soil, and groundwater (Jarvie et al, 2013;Sebilo et al, 2013;Marçais et al, 2018;Carey et al, 2019;Kolbe et al, 2019). Second, the capacity of ecosystems to remove or permanently retain nutrients via vertical processes such as denitrification or diagenesis is highly variable, and the socioecological drivers (e.g., watershed characteristics and agricultural practices) of nutrient removal are poorly understood (Pinay et al, 2015;Abbott et al, 2016;Dupas et al, 2018;Goyette et al, 2018;Jarvie et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Predicting Nutrient Incontinence in the Anthropocene at Watershed Scales

Frei

Abbott

Dupas

et al. 2020

Front. Environ. Sci.

Self Cite

View full text Add to dashboard Cite

Quantifying nutrient attenuation at watershed scales requires long-term water chemistry data, water discharge, and detailed nutrient input chronicles. Consequently, nutrient attenuation estimates are largely limited to long-term research areas or modeling studies, constraining understanding of the ecological characteristics controlling nutrient attenuation and complicating efforts to protect or restore water quality in developed and developing regions. Here, we combined long-term data and a broad suite of biogeochemical parameters from 49 watersheds in northwestern France to test how well instantaneous measurements can predict nitrogen (N) and phosphorus (P) attenuation at watershed scales. We evaluated 13 biogeochemical and 12 hydrological proxies of hydrological flowpaths, residence time, and biogeochemical transformation. Across the 49 watersheds, nutrient attenuation ranged from 88 to −2% for N and 99-96% for P. The strongest biogeochemical proxies of N attenuation were NO − 3 isotopes, rare earth elements (REEs), radon, and turbidity, together explaining 75% of observed variation. For P attenuation, REEs, NO − 3 isotopes, molecular weight of dissolved organic matter, and radon were the strongest proxies, but only explained 27% of observed variation. However, a single hydrological parameter-annual runoff-explained 91% of N attenuation and the relative abundance of schist bedrock explained 56% of P attenuation. We discuss how runoff both controls and reflects watershed hydrology, biogeochemistry, and nutrient attenuation. For example, runoff was correlated with long-term decreases in nutrient concentration, demonstrating how leakier watersheds recover more quickly from nutrient saturation. Given the immense fertilization capacity of modern society, we propose that eutrophication can only be solved by reducing nutrient inputs, though hydrochemical proxies can provide valuable information on where to carry out essential food production activities.

show abstract

“…Silica has often been considered relatively immune to disruption by human activities because geochemical drivers, such as bedrock lithology, hydrology, and climate, strongly influence its biogeochemistry Dürr et al, 2011). During the past few decades, a greater appreciation of the silica cycle's sensitivity to human perturbation has emerged, through recognition that silica export to the global oceans can be influenced by river damming (Humborg et al, 2000), nutrient overenrichment (Conley et al, 1993), permafrost thaw from climatic warming (Frey & McClelland, 2009;Guo et al, 2004;Smedberg et al, 2006), and recently, watershed land use (Carey & Fulweiler, 2012a, 2012bConley et al, 2008;Marçais et al, 2018;Struyf et al, 2010). Urbanization and agricultural land cover influence silica turnover and flux (Carey & Fulweiler, 2016;Clymans et al, 2011;Maguire & Fulweiler, 2016Vandevenne et al, 2012), but little work has focused on wildfire as a disruptor of silica transfer between terrestrial and aquatic systems.…”

Section: Introductionmentioning

confidence: 99%

Plant Uptake Offsets Silica Release From a Large Arctic Tundra Wildfire

2019

Self Cite

View full text Add to dashboard Cite

Rapid climate change at high latitudes is projected to increase wildfire extent in tundra ecosystems by up to fivefold by the end of the century. Tundra wildfire could alter terrestrial silica (SiO 2 ) cycling by restructuring surface vegetation and by deepening the seasonally thawed active layer. These changes could influence the availability of silica in terrestrial permafrost ecosystems and alter lateral exports to downstream marine waters, where silica is often a limiting nutrient. In this context, we investigated the effects of the largest Arctic tundra fire in recent times on plant and peat amorphous silica content and dissolved silica concentration in streams. Ten years after the fire, vegetation in burned areas had 73% more silica in aboveground biomass compared to adjacent, unburned areas. This increase in plant silica was attributable to significantly higher plant silica concentration in bryophytes and increased prevalence of silica-rich gramminoids in burned areas. Tundra fire redistributed peat silica, with burned areas containing significantly higher amorphous silica concentrations in the O-layer, but 29% less silica in peat overall due to shallower peat depth post burn. Despite these dramatic differences in terrestrial silica dynamics, dissolved silica concentration in tributaries draining burned catchments did not differ from unburned catchments, potentially due to the increased uptake by terrestrial vegetation. Together, these results suggest that tundra wildfire enhances terrestrial availability of silica via permafrost degradation and associated weathering, but that changes in lateral silica export may depend on vegetation uptake during the first decade of postwildfire succession. Plain Language SummaryClimate change in the Arctic is leading to more frequent and severe wildfire in Arctic tundra ecosystems. Studying the silica (SiO2) cycle in Arctic ecosystems is important because the amount of silica exported from land to sea can control uptake by marine primary producers in Arctic coastal waters. We investigated how tundra wildfire affects silica cycling by returning to a large Arctic wildfire 10 years after the burn to collect samples of stream water, vegetation, and peat. We found that plants growing on burned landscapes contained 73% more silica in their aboveground biomass compared to unburned areas nearby. While the fire thawed permafrost underneath it, we did not observe increased levels of silica in streams draining burned areas. This pattern indicates that elevated rates of silica uptake via plants may prevent increased silica export to marine waters following tundra wildfire. We conclude that the effect of tundra fire on silica cycling depends on the recovery trajectories of terrestrial and aquatic ecosystems in the Arctic.

show abstract

Dating groundwater with dissolved silica and CFC concentrations in crystalline aquifers

Cited by 47 publications

References 72 publications

Trajectories of nitrate input and output in three nested catchments along a land use gradient

Trajectories of nitrate input and output in three nested catchments along a land use gradient

Predicting Nutrient Incontinence in the Anthropocene at Watershed Scales

Plant Uptake Offsets Silica Release From a Large Arctic Tundra Wildfire

Contact Info

Product

Resources

About