@article{fdi:010055818,
  title = {{L}ong term monitoring of the chemical composition of precipitation and wet deposition fluxes over three {S}ahelian savannas},
  author = {{L}aouali, {D}. and {G}aly-{L}acaux, {C}. and {D}iop, {B}. and {D}elon, {C}. and {O}range, {D}idier and {L}acaux, {J}. {P}. and {A}kpo, {A}. and {L}avenu, {F}. and {G}ardrat, {E}. and {C}astera, {P}.},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he purpose of this study is to analyze a long term database of the chemical composition of precipitation at three {A}frican dry savanna sites in the {S}ahel. {T}he precipitation samples were collected during the monsoon season at {A}goufou (15 degrees 20'{N}, 01 degrees 29'{W}, {M}ali) from 2004 to 2006, {B}anizoumbou (13 degrees 31'{N}, 02 degrees 38'{E}, {N}iger) from 1994 to 2009 and {K}atibougou (12 degrees 56'{N}, 07 degrees 32' {W}, {M}ali) from 1997 to 2008. p{H} and major inorganic and organic ions in precipitation were analyzed by ionic chromatography. {A} characterization of mean precipitation chemistry with the associated wet deposition fluxes for each species is presented. {T}he first important result is that interannual variability of all volume-weighted mean ({VWM}) concentrations is low, ranging between +/- 5% and +/- 25%. {A}cidity in dry savannas is low and indicates the strong alkaline nature of the precipitation. {T}he average annual p{H} at {A}goufou is 6.28, 5.75 at {B}anizoumbou and 5.54 at {K}atibougou. {T}his result is correlated with the important terrigenous contribution measured in the chemical content of precipitation, implying acidity neutralization by mineral species such as {C}a2+ and {NH}4+. {M}g2+ and {K}+ are found to play a minor role in neutralization. {E}nrichment factor calculations for {C}a2+, {SO}42-, {K}+ and {M}g2+ with respect to the sea reference reveal a significant influence of {S}aharan and {S}ahelian crustal sources. {VWM} concentrations of these species dominate the composition of measured precipitation. {A}n estimation of the potential particulate and gas contribution to the total precipitation composition is given for each site: {A}t {A}goufou, the mean relative contribution in rainwater is 80% for particles and 20% for gases, while at the {B}anizoumbou and {K}atibougou sites, results indicate 70% for particles and 30% for gases. {T}he high particulate phase contribution to precipitation emphasizes the importance of multiphase processes between gases and particles in the atmospheric chemistry typical of {A}frican semi-arid savanna ecosystems. {T}he second highest contribution is nitrogenous, with high {VWM} concentrations of {NO}3- and {NH}4+ measured at the three sites. {M}onthly evolution of {NO}3- and {NH}4+ concentrations are studied in relation to gaseous emission sources in the {S}ahelian region, i.e. biogenic soil emission and ammonia sources from animals. {T}he calculated wet nitrogen deposition flux presents a regular increase throughout the wet season at the three sites. {R}esults suggest total mean nitrogen deposition fluxes of 1.80 kg {N} ha(-1) yr(-1) at {A}goufou, 2.10 kg {N} ha(-1) yr(-1) at {B}anizoumbou, and 3.30 kg {N} ha(-1) yr(-1) at {K}atibougou. {T}he marine contribution is lower, 23% at {A}goufou, 17% at {B}anizoumbou and 13% at {K}atibougou. {T}he last contribution concerns organic acidity, which ranges from 5% at {A}goufou, 10% at {B}anizoumbou to 14% at {K}atibougou. {T}errigenous and marine contributions present a negative gradient, whereas nitrogenous and organic contributions a positive gradient along the {S}ahelian transect defined by {A}goufou-{B}anizoumbou-{K}atibougou.},
  keywords = {{A}frican semi-arid ecosystems ; {M}ineral species ; {N}itrogenous compounds ; {N}eutralization factor ; {A}tmospheric chemistry ; {S}ahelian savannas},
  booktitle = {},
  journal = {{A}tmospheric {E}nvironment},
  volume = {50},
  numero = {},
  pages = {314--327},
  ISSN = {1352-2310},
  year = {2012},
  DOI = {10.1016/j.atmosenv.2011.12.004},
  URL = {https://www.documentation.ird.fr/hor/fdi:010055818},
}