M. Bilala, b, c, A. Jaffrezica,b,c*, Pourcher A.M.d, C. Waltera,b,c,
a
Agrocampus Ouest , UMR1069, Soil Agro and HydroSystem, F-35000 Rennes, France
b
INRA, UMR1069 Soil Agro and HydroSystem, F-35000 Rennes, France
c
Université européenne de Bretagne, France d CEMAGREF, 17 av. de Cucillé 35044 Rennes
*Corresponding author. Dr. Anne Jaffrezic: anne.jaffrezic@agrocampus-ouest.fr Tel.: (33) (0)2 23 48 54 20 - Fax (33) (0)2 23 48 54 30
Abstract
Fluorescence properties of dissolved organic matter (DOM) were used to characterize the diffuse DOM pollution by pig slurry and cow manure. A simulating runoff experiment was conducted on a microplot of 1m² a few hours after farming waste spreading. Three repetitions for each treatment (control, pig slurry and cow manure at agronomic rates) were tested in April 2008.
A rainfall simulation was conducted with intensity of 67 mm.h-1. Cumulated runoff was about 16 L for each plot. Regional integration was applied on fluorescence measurements. Ratio bio:geo (biochemical fluorescence in the region I, II and IV / geochemical fluorescence (humic/fulvic like- fluorescence, region III and V) and ratio III/V (humic-like fluorescence) discriminated the farm wastes DOM from soil source. The fluorescence properties on first runoff samples from farming waste amended soils were identical to those measured on raw farming waste. This indicated that a spring storm event which occurred a few hours after the spreading lead to transfer of DOM from farming waste. The ratios bio:geo and III:V were significantly higher than those measured in control in the first 6L runoff in pig slurry treatment and in all the runoff samples collected in two repetition on cow manure. However in the last cow manure simulation replicate, DOM transfer was from soil source. Region V also discriminated the soil DOM with significantly higher fluorescence from the farming wastes. It was impossible to discriminate pig slurry from cow manure contamination since fluorescence properties measured on cow faeces were identical to pig slurry. Air drying treatment modifies the fluorescence properties of the farming waste. To detect farm waste contamination in stream, fresh effluent analysis dataset have to be investigated to explore the variability of the farming wastes fluorescence properties.
Key words: farm wastes, Pig slurry, cow manure, rainfall simulation, runoff, fluorescence
Introduction
In modern agricultural systems, the widespread use of farm wastes fertilization serve as a valuable source of crops nutrients (Moral et al., 2005) and a mean of alternative source of chemical fertilizers which cause excess nitrates and phosphorous loads in the catchment streams (Granger et al., 2010) during intense rainfall events. Water contamination can be aggravated if rainfall event occur shortly after the supply of farm manures and transport the DOM towards the stream by modifying the water pathways via surface runoff or preferential flow via tile draining (Royer et al., 2007a; Hernes et al., 2008; Naden et al., 2009).
The excess DOM production pollutes the natural resource water quality. In the French legislation, [DOC] concentration in superficial water should be under 10 mgL-1 during 95% of sampling time for drinking water supplies. Moreover, DOM act as a vector in the transport of pesticides, metals and viruses etc towards streams (Williams et al., 2005; Song et al., 2008). In the literature, there is scarcity of knowledge about the net impact of different farm manures supply on the DOM production in soil if rainfall coincides with the fertilization time. The new directive on Bathing water quality 2006/7/EC (Anonymous, 2006) strengthens the concept of bathing water management by introducing bathing water profiles designed to identify pollution sources in bathing waters and of other surface waters in the catchment area of bathing water concerned. One of the major sources of fecal pollution which may contaminate bathing waters is associated with the practice of land spreading of animal wastes, especially in intensive agricultural areas such as Brittany (France). It is well know that cattle and pig manures contain pathogenic microorganisms (Guan and Holley, 2003; Omisakin et al., 2003) and that land spreading of manure constitutes a human health risk (Thaddeus et al., 2008). It is thus important to use methods to identify livestock contamination in surface water and to discriminate cow manure from ping slurry contamination.
Identifying sources of contamination required the development of tracers of DOM. EEM Fluorescence spectroscopy appears as a interesting tool and has been applied to trace diffuse agricultural pollution from dairy slurry spreading on intensively-farmed grasslands (Naden et al., 2009). Excitation-emission matrix spectra (EEM fluorescence) are obtained by incrementation of excitation and registration of emission spectra. Four major peaks are generally observed in DOM samples. However, in this current study, instead of taking few
wavelengths (<250 nm) and shorter emission wavelengths (<380 nm) are related to simple aromatic proteins such as tyrosine and tryptophan (Regions I and II). Peaks at intermediate excitation wavelengths (250–340 nm) and shorter emission wavelengths (<380 nm) are related to soluble microbial by-product-like material (Region IV) while peaks located at the excitation wavelengths (230–300 nm) and the emission wavelengths (380-575 nm) represent humic acid-like substances (Region III). Peaks at longer excitation wavelengths (>300 nm) and longer emission wavelengths (>380 nm) are related to fulvic acid-like organics (Region V). Relative importance of these peaks or region had been used to trace DOM from diverse sources. Baker (2002) has demonstrated that intense ratio tryptophane-like to fulvic/humic like fluorescence are higher in farming wastes compared to stream water. Naden et al., (2009) also used the ratio of indices of tryptophane-like and fulvic/humic like fluorescence (TI:FI) to distinguish incindental losses of dairy slurry in drainage waters.
In the presented study, we (i) investigated the impact of pig slurry and cow manure wastes on the production of dissolved organic mater during spring storm events by analysing runoff water quality by simulation (ii) test the potential of fluorescence spectroscopy as tracer of farm manure DOM during three rainfall simulation events, and finally try to discriminate between pig and cow manure contamination in runoff water.