Temporal variability of nitrate concentration in a schist aquifer and transfer to surface waters

Pauwels, Hélène; Lachassagne, Patrick; Bordenave, Pierre; Foucher, Jean-Claude; Martelat, Anne

doi:10.1016/s0883-2927(00)00062-7

Cited by 43 publications

(23 citation statements)

References 14 publications

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“…In such a case, nitrate transfer is controlled by water table fluctuation, which induces variation of the hydrological flowpath contribution to the stream discharge (Schnabel et al, 1993;Petry et al, 2002). According to these authors, during winter, high nitrate concentration in streamwater results from higher contribution of nitrate-rich hillslope shallow groundwater, whereas during summer streamwater mainly comes from denitrified bottomland groundwater (Altman and Parizek, 1995;Hill, 1996) and deep fractured aquifers (Pauwels et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

Seasonal and interannual variations of nitrate and chloride in stream waters related to spatial and temporal patterns of groundwater concentrations in agricultural catchments

Martin¹,

Aquilina

Gascuel‐Odoux³

et al. 2004

Hydrological Processes

122

109

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Abstract:Nitrate concentrations in streamwater of agricultural catchments often exhibit interannual variations, which are supposed to result from land-use changes, as well as seasonal variations mainly explained by the effect of hydrological and biogeochemical cycles. In catchments on impervious bedrock, seasonal variations of nitrate concentrations in streamwater are usually characterized by higher nitrate concentrations in winter than in summer. However, intermediate or inverse cycles with higher concentrations in summer are sometimes observed. An experimental study was carried out to assess the mechanisms that determine the seasonal cycles of streamwater nitrate concentrations in intensive agricultural catchments. Temporal and spatial patterns of groundwater concentrations were investigated in two adjacent catchments located in south-western Brittany (France), characterized by different seasonal variations of streamwater nitrate concentrations. Wells were drilled across the hillslope at depths ranging from 1Ð5 to 20 m. Dynamics of the water table were monitored and the groundwater nitrate and chloride concentrations were measured weekly over 2 years. Results highlighted that groundwater was partitioned into downslope domains, where denitrification induced lower nitrate concentrations than into mid-slope and upslope domains. For one catchment, high subsurface flow with high nitrate concentrations during high water periods and active denitrification during low water periods explained the higher streamwater nitrate concentrations in winter than in summer. For the other catchment, the high contribution of groundwater with high nitrate concentrations smoothed or inverted this trend. Increasing bromide/chloride ratio and nitrate concentrations with depth argued for an effect of past agricultural pressure on this catchment. The relative contribution of flows in time and correlatively the spatial origin of waters, function of the depth and the location on the hillslope, and their chemical characteristics control seasonal cycles of streamwater nitrate concentrations and can influence their interannual trends.

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Section: Introductionmentioning

confidence: 99%

Seasonal and interannual variations of nitrate and chloride in stream waters related to spatial and temporal patterns of groundwater concentrations in agricultural catchments

Martin¹,

Aquilina

Gascuel‐Odoux³

et al. 2004

Hydrological Processes

122

109

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“…The mechanisms responsible for nitrate transport from the groundwater to the river are well documented in Brittany (Dia et al 2000;Molenat et al 2002;Cle´ment et al 2003;Martin et al 2004). Heterotrophic and autotrophic denitrification processes in groundwater have also been quantified in different contexts (Mariotti 1986;Wassenaar 1995;Montgomery et al 1997;Pauwels et al 2001). The organic top soil horizons are usually considered as highly biogeochemically reactive.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Biogeochemical Activities in the Soil and Unsaturated Zone of Weathered Granite

et al. 2005

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International audienceThis study, based on field and laboratory work, investigates the biogeochemical activity below the organic top soil horizons, particularly the potential for nitrate removal processes in the deep vadose zone (1–2.5 m depth) of a weathered granite. An experimental site located in the Kerbernez agricultural catchment (Brittany) has been equipped with ceramic cups from 0.5 to 2.5 m depth since November 2001. This arrangement allowed collection of water samples from the soil profile and the upper part of the unsaturated weathered granite. Samples were analysed twice a month for chloride, nitrate and sulphate concentrations over a period of 2.5 years. Laboratory measurements were carried out on three soil horizons and four weathered granite facies sampled in October 2003 for hydrolasic activity, potential nitrification, potential denitrification and batch experiments to study nutrient dynamics. Anion analyses in the field show that the nitrate and chloride concentrations were linearly correlated at each depth. The nitrate/chloride ratio decreased with depth in the upper part of the weathered granite from 4.93 to 2.82. This suggests that nitrate was removed during its vertical transport in the unsaturated zone. The laboratory experiments show that the bacterial activity decreased with depth. However, a significant potential for biogeochemical reactions exists below the organic soil layers. The denitrification rates obtained in the laboratory were significant, up to 800 ng N h−1 g−1 after about 100 h of incubation for the most reactive weathered granite facies. These rates agree with effective rates usually measured in riparian zones, but they were 50 times higher than those observed in the field. This difference suggests that the denitrification processes occurring in the field were spatially limited to localised anaerobic microsites, where the bacterial activities are controlled by the availability of N and C substrate. Finally, the laboratory measurements lead us to assume that heterotrophic denitrification was clearly the predominant process occurring in the field because of the good correlation between nitrate concentration variation and carbon content (r = −0.94). Moreover, the slight increase in sulphate concentrations observed in the field and in the laboratory was insufficient to explain the complete removal of nitrate

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“…However, agricultural activities diminish in the fall season and there are further increases in precipitation, which result in flushing of the aquifer or dilution of well water by the rainwater (Iqbal, 2002) to cause lower NO 3 concentration. Similarly, the dry season can lead to a high concentration of contaminants in well water (Pauwels et al, 2001;Vinten and Dunn, 2001). Although it is a rainy season in July in the PRD, the NO 3 concentration is higher than it is in spring, implying that septic tanks around wells are an important effect factor for groundwater.…”

Section: Characteristics Of Ec No 3 In Groundwater and Identificatiomentioning

confidence: 99%

Impact of septic tank systems on local groundwater quality and water supply in the Pearl River Delta, China: case study

Tang

Chen³

et al. 2007

Hydrological Processes

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Abstract:Located at southern coast of China, the Pearl River Delta (PRD) is facing serious water problems in both quantity and quality after its rapid urbanization in the last decade. Most remarkably, the local groundwater, that was used to be the source of drinking water before the urbanization was polluted due to poor management of the septic tanks. In order to study the effects of suburban development on local groundwater flow and water quality in the PRD region, Fengcun of Guangzhou has been chosen as the study area. In Fengcun, drinking water was groundwater before the 1990s, but now piped reservoir water is used by each family because the groundwater has been polluted. This study clarifies the source and process of the groundwater pollution from septic tanks using isotopic and geochemical characteristics, especially nitrate (NO 3 ) concentrations. Water samples were collected from the wells and ponds in Fengcun in March and July 2005 and in July 2006. Based on the pe-pH diagram, NO 3 and ammonium of groundwater are from the effect of human activities, rather than from nitrification and ammonification of N 2 . NO 3 pollution of groundwater is from point sources, and NO 3 concentrations decrease from northeast to southwest. Groundwater is polluted rapidly by the leakage of septic tanks. NO 3 concentrations of pollution sources were lower than 20 mg l 1 in March 2005, but had increased to about 120 mg l 1 in July 2006. This implies that groundwater protection should be strengthened in rural areas of the PRD.

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Temporal variability of nitrate concentration in a schist aquifer and transfer to surface waters

Cited by 43 publications

References 14 publications

Seasonal and interannual variations of nitrate and chloride in stream waters related to spatial and temporal patterns of groundwater concentrations in agricultural catchments

Seasonal and interannual variations of nitrate and chloride in stream waters related to spatial and temporal patterns of groundwater concentrations in agricultural catchments

Investigation of Biogeochemical Activities in the Soil and Unsaturated Zone of Weathered Granite

Impact of septic tank systems on local groundwater quality and water supply in the Pearl River Delta, China: case study

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