High nutrient and sediment loads of the temporary river El Albujón related to human induced soil erosion (SE-Spain, Murcia)

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1 High nutrient and sediment loads of the temporary river El Albujón related to human induced soil erosion (SE-Spain, Murcia) Kretschmer S. 1), Höke S. 2), Burghardt W. 3) 1) 2) 3) University of Duisburg-Essen, FB9 Soil Technology, Essen, Germany 1) Tel.: 0049 (0) ) 3) Keywords: temporary waters, phosphorus-loss, water erosion, Mar Menor, Albujon 1) Introduction The Mediterranean is characterized by water scarcity and low river flow during summer months and flood events in autumn and winter. Temporary rivers are widespread in the Mediterranean but scarcely investigated. The increasing human induced landscape destruction and the intense agricultural use affect the sensitive hydrology of such temporary rivers. Heavy rainstorms in autumn and winter generate a sudden surface runoff, called "first flush", with high nutrient and sediment loads. These shock loadings affect marine or limnic ecosystems and human water resources. Actually the water availability per person and year is decreasing in all Mediterranean countries (HOFRICHTER, 2002), for that reason integrated water management is of great importance. The European project "Evaluation and Improvement of water quality models for application to temporary waters in Southern European Catchments" (Acronym: tempqsim) is aimed at creating efficient tools for water management in European Mediterranean regions. An improved management and a better knowledge about behavior of temporary river catchments are necessary for the implementation of the European Water Framework Directive. The tempqsim-project s consortium consists on 14 participating institutions with hydrologists, biologists and soil scientists which are investigating water quality and sediment processes of eight temporary river catchments for an improved hydrological modeling. One of the eight catchments is located in SE-Spain, Murcia. The present paper will introduce to this catchment by describing the current situation of the river El Albujón. 2) Study area Study area is the catchment of the temporary river El Albujón. It is located in the south-east of Spain, in the region Murcia (figure 1). The climate is the typical semiarid Mediterranean. One of Europe s driest locations (Cabo de Gata, 122 mm yr -1 ; HOFRICHTER, 2002) is situated very near to the Albujón study catchment. The river El Albujón discharges to the lagoon Mar Menor, which is a hypersaline coastal lagoon of 135 km² surface area and 3-4 m of depth. The lagoon s catchment 1

The Campo de Cartagena is formed by Quarternary material which is only occasionally interrupted by volcanic outcrops and enclosed by mountains.

2 is a wide plain (1440 km²), called Campo de Cartagena, with low inclination towards sea level. It is a hydrological unit with six main water courses, which are dry most of the year (ALONSO-ZARZA et al. 1998). The Campo de Cartagena is formed by Quarternary material which is only occasionally interrupted by volcanic outcrops and enclosed by mountains. The main soil types are calciorthid and cambiorthid Aridisole (CNIG, 1992). The Campo de Cartagena has a surface area of ha. The main land use is horticulture (16300 ha, 54 %) and citrus (8700 ha, 29%). Other land uses are green houses (1900 ha, 6 %) and fruit trees (1200 ha, 4 %). Spain Murcia Figure 1: Location of the study catchment El Albujón in SE-Spain, Murcia. The Albujón river discharges into the Mar Menor. Two sample sites are located at the river Albujón, one sample site is located at the tributary Azohía. Within the Albujón catchment three areas were surveyed. At two of these areas the river sediments were sampled along river cross sections. One cross section is located at the River El Albujón and the second cross section is located at the tributary Azohía (figure 1). During the sampling time in September 2003 these two investigated cross sections looked as follows: (a) The Albujón-cross section is situated in the downstream region of the river channel El Albujón, where the river course is a straightened channel. In September 2003, during the sampling campaign the stream bed was covered by reed. Groundwater discharge was creating 2

lentic water pools but no runoff water occurred. The sediment was water saturated and anoxic at a depth >15 cm. Fields of cropland border both riparian sides.

3 lentic water pools but no runoff water occurred. The sediment was water saturated and anoxic at a depth >15 cm. Fields of cropland border both riparian sides. (b) The Azohía-cross section is situated at the Azohía channel, a tributary of El Albujón. It is bordered by horticulture fields which are sloping to the channel. In September 2003 no discharge, no moisture and no reed occurred, but very dry stream sediments and scrubs characterized the channel bed in the investigated area. (c) In the third study area a horticulture field was surveyed. The land use (horticulture) of the surveyed field represents 54 % of the whole area of Campo de Cartagena. During this field campaign in February 2004 this field (figure 3; 5.74 ha of surface area) was sampled and erosion was mapped. The sampling area is located nearby the Albujón channel at the midpart of the study catchment (figure 1). The field is sloping gently towards the Albujón channel and is affected by rill erosion and heavy stream bank erosion occurred between the field margin and the river channel (figure 4). 3) Methods The cross section sampling included the channel bed and the stream banks, as well as soil and dust sampling on cropland and field paths. Soils and sediments were sampled with metal ring kits in depth of 0-2 cm, 2-5 cm, 5-10 cm and cm (figure 2). The cross section survey was in September Figure 2: Sampling design along a river cross section. 3

At the third study site the topsoil was sampled upslope, midslope and at base of slope by average sampling (ten times) at 0-10 cm and 10-20 cm depth with a core device.

$Bulk density and water content of soil and sediment samples were determined gravimetrically. The fraction of inorganic phosphorus was measured by extracting air dried soil with 0.$

4 At the third study site the topsoil was sampled upslope, midslope and at base of slope by average sampling (ten times) at 0-10 cm and cm depth with a core device. The stream bank erosion between the field margin and the river channel (figure 4) was mapped with global positioning system (GPS) and the volume of erosion loss was estimated by metric measurement. Bulk density and water content of soil and sediment samples were determined gravimetrically. The fraction of inorganic phosphorus was measured by extracting air dried soil with 0.5 M H 2 SO 4 (SCHINNER et al., 1996). To obtain the fraction of total Phosphorus, first the soil was ignited at 550 C in order to incinerate organic matter. After ignition the total phosphorus was extracted with 0.5 M H 2 SO 4. After extraction and filtration the phosphorus content was analyzed with the colorimetric Mo-blue method (SCHINNER et al., 1996). The analyses were carried out at fine material < 2 mm. Figure 4: Figure 3: Overirrigation and stream bank erosion at the Albujón river channel. Overirrigation, downhill ploughing and rill erosion at a crop field (same site as Fig.4) 4) Results Table 1 shows phosphorus concentrations (total, inorganic and organic) as minimum, maximum and mean values in various materials (soil, sediment and dust). The results of the cross section sampling show that P-concentrations in soils are higher than in the dust and in the channel bed sediments. The values of the sediment-p have a wide range (for example: sediment of 0-20 cm depth, n=15, P= mg kg -1 ). 4

5 Table 1: Phosphorus concentrations of soil, sediment and dust (mg kg C dry soil). Cross section sampling main channel Albujón tributary Azohía Depth n P total P inorganic P organic [cm] [mg kg -1 ] [mg kg -1 ] [mg kg -1 ] min max mean min max mean min max mean soil dust sediment soil dust sediment Crop land survey field soil upslope midslope Base of slope silted crust The results of the crop field survey show that P-concentrations are increasing in downward direction ( mg kg -1 at the upper part of the field in 0-20 cm of depth, versus mg kg -1 at the lower part of the field in 0-20 cm of depth, table 1). For interpreting the results it is better to have a look on the spatial distribution of phosphorus concentrations along the river cross sections (figures 5 and 6) as follows: (a) Albujón cross section: Figure 5 shows the cross section at the Albujón channel with P total - concentrations [mg kg -1 ] at different sampling depth. The topsoil of the crop fields have very high concentrations of phosphorus (>1000 mg kg -1 ). The field paths between crop field and channel have a dust layer with considerably high P-concentrations ( mg kg -1 ). Dust and sediment within the channel are less concentrated, with one striking exception: at one site under a dense reed stock there occur the highest P-concentration (1220 mg kg -1 ), but this hot spot of P-content occurs only within the upper two centimetres. This material has a much higher silt content (clayey silt; clay: 13 %, silt: 72 %, sand: 15 %) than the surrounding material within the cross section. The grain size distribution of the field soil is a clayey loam (clay: 42 %, silt: 49 %, sand: 9 %) whereas the channelbed sediment (sandy loam) contains less clay but more sand (clay: %, silt: 26-41%, sand: %). Thus the silt with the high P-content seems to be of specific 5

(b) Azohía cross section: The sampling sites along the cross section of Azohía show great variability as well as the first cross section.

6 origin. In the channelbed sediments there is no clear gradient of phosphorus concentrations visible concerning the depth up to 20 cm). Depth: 0-2 cm 2-5 cm 5-10 cm cm Figure 5: Cross section sampling at the Albujón channel. Total phosphorus concentrations are given in [mg kg -1 ] at different depth. (b) Azohía cross section: The sampling sites along the cross section of Azohía show great variability as well as the first cross section. Total phosphorus content in the topsoil near the river Azohía is less concentrated ( mg kg -1 ) in comparison with the Albujón cross section. Occasionally the dust of the field path (926 mg kg -1 ) contains more P total than the topsoil (836 mg kg -1 ). There seems to exist a soil transport from the crop field on the right side to cm the channelbed, Figure because 6: there Cross has been section built sampling up a colluvial at the Azohía deposit channel. at the Total right phosphorus edge of the concentrations channelbed with are given a grain in [mg kg -1 ] at different depth. 6 Depth: 0-2 cm 2-5 cm 5-10 cm

size distribution very similar to the field soil (clay: 18-24 %, silt: 45-46 % and sand: 32-35 %).

7 size distribution very similar to the field soil (clay: %, silt: % and sand: %). The P-concentration in the colluvial deposit is lower than in the field soil, but it is comparative high regarding the other sites of the cross section. Within the channel the phosphorus content in sediment is decreasing with distance to the crop field ( mg kg -1 in the colluvial deposit versus 280 mg kg -1 in the middle part of the stream bed). There is no clear P-gradient visible in the channelbed concerning to the different depth up to 0-20 cm. (c) Crop field survey: Phosphorus concentration in the topsoil (0-10 cm and cm) of the horticulture field is increasing in downhill direction (table 1 and figure 7). Especially the silting soil crust at the field margin shows clearly an accumulation process of phosphorus by soil erosion. Increasing P Figure 7: Crop field survey. The field is strongly affected by erosion. Bank erosion was mapped with a GPS in February P-content is increasing with downslope direction. The annual erosion in this area is estimated at a rate of tonnes ha -1 yr -1. The input parameters for the soil erosion modeling were rainfall, soil crusting and erodibility as well as land use and elevation (KIRKBY M., verbal information). At the investigated field with a surface area of 5.74 ha the assumed annual soil loss of this field is round about tonnes. Assuming a P- concentration of 900 mg kg -1 the erosion loss on this field of 5.74 ha surface area generates a phosphorus-transfer of kg P yr -1 (= kg ha -1 yr -1 ). Rill erosion and a surplus of irrigation water caused heavy bank erosion between the investigated field and the Albujón river channel during last winter. This bank erosion was mapped with GPS (Figure 7). The measured erosion loss had a volume of 43.5 m³. With a presumed average bulk density of 1.4 kg dm -3 the lost soil had a mass of 60.9 tonnes along the 200 m field length. 7

8 Assuming an average P-concentration of 300 mg kg -1 this bank erosion contributed ~18 kg total phosphorus to the river channel along a stream bank of 200 meters. (The real P-content of this stream bank material has not yet been measured, but on the basis of other stream bank measurements not reported in this paper- 300 mg kg -1 seems to be adequate). 5) Discussion As P is adsorbed by soil material, erosion is an essential factor of P movement in landscapes (SHARPLEY et al. 1993). Sources of particulate phosphorus in streams include eroded surface soil, plant material, stream banks and channel beds. As shown by the cross section survey at the Albujón and Azohía there exist a stock of easy removable matter (topsoil and dust) with high phosphorus concentrations. During forthcoming rainstorms this material will be washed away into the channel by surface runoff. But the instream channel sediments have less P-concentrations than the topsoil and the dust. It is still uncertain what is happening to the eroded material and why the concentrations of P in sediments are less. One possible answer could be that eroded and P-enriched material is mixed with lower concentrated sediment of upper stream parts (there are for example a lot of quarries, which generate loose and unpolluted sediment). Another more probable- possibility is that most of the eroded soil material (especially clay and silt) is washed away completely and leaving behind the coarser gravel and sand-fractions. In this case there should be some basins in the river course, where fine sediment is settling and particle-bound phosphorus is accumulating, like the hot spot at the Albujon cross section. There exist a lot of settling basins within the Albujon channel that have to be examined more closely. The eroding topsoil of the surveyed crop field contributes only low amounts ( kg ha -1 yr -1 ) to the P-loss. Some values of other authors reveal a wide range of P-loss in surface runoff, due to land use and fertilizer use, etc. ( kg ha -1 yr -1 summarized in SHARPLEY et al. 1993). This first example of calculating the P-loss in surface runoff in the Albujon catchment is a very raw estimation and seems to be underestimated and not representative, because there are other regions in the Albujón catchment with higher annual erosion (up to 10 t ha -1 yr -1 ). In addition the crop field survey has shown that there occur great amounts of stream bank erosion at the Albujón channel. Stream bank material is often of lower P-concentration, similar to subsoils, but nevertheless the P-masses, that derived from Albujón stream banks are very high (18 kg P along a stream bank of 200 meters) due to the large quantity of soil loss. The stream bank P-contribution seems to be of higher importance than the P-loss of the horticulture field. The downstream area of the Albujón catchment is dominated by channel straightening and agricultural land use (Campo de Cartagena). The natural geomorphology of the river system has completely changed due to human activities. Crop fields are bordering the artificial channel without any riparian vegetation. Field paths, located between field and stream bank, are sloping 8

9 towards the river. The practices of ploughing downhill and overirrigation occurs on some fields in the study catchment. Altogether it generates an increased surface runoff and soil erosion loss. An improved management that minimizes surface runoff and erosion will reduce P transport from agricultural land to surface waters (SHARPLEY et al. 1993). Soil erosion is only one potential source of sediment and eutrophication. There are further sources of pollution in the artificial landscape of the Albujón catchment: Several stone quarries within river courses of El Albujón and its tributaries deliver high quantities of coarse sediment. Some basins with liquid manure are located nearby the channels; hence there exist high pollution risks by leachate. Drought, high wind velocity and sparse vegetation generate wind erosion. It is obviously an important factor for this agricultural landscape. Waste water treatment plants discharge into the lower part of El Albujón. Due to the N- and P-point source there is an increase growth and accumulation of biomass and biological transformation processes within the sediment. During dry periods sediment environment and processes are changing, but its impact to water quality during first flush events is hardly known. The above mentioned points are a description of pollution-hot spots that means sites of high potential for water pollution. In the same way important is the knowledge about the hot moments that means the moment of rainstorm that generates the first flush event with extreme concentration of pollution. 6) Conclusion As the investigation has shown the stream bank erosion can contribute a great amount of phosphorus and sediment to the river channel. Stream bank erosion is widespread along the Albujón river channel thus it is important to investigate more detailed and more representative the amounts of stream bank erosion. In terms of landscape and water protection the stream bank erosion has to be limited by erosion control activities. Furthermore it has to be examined more closely the behavior of the sediments and what is the retention capacity of sedimentation basins in the stream network. More attention has to be given to the development of strategies that minimise nonpoint P-sources. The implementation of the EU Water Framework Directive (WFD) requires the quantification of real pollutant loads and the derivation of management options. For the Albujón catchment this quantification is difficult due to several human impacted factors as described above. The current study is a first approach to solve this problem. Nevertheless the landscape and water management 9

10 has to be improved completely, in order to protect the sensitive lagoonal ecosystem and in order to realise the EU-WFD. Acknowledgement The research for this paper was carried out as part of the tempqsim project ( It is supported by EC (contract-number EVK-CT ) and this is gratefully acknowledged. References ALONSO-ZARZA A.M., SILVA P.G., GOY J.L. and ZAZO C., 1998: Fan-surface dynamics and biogenic calcrete development: Interactions during ultimate phases of fan evolution in the semiarid SE Spain (Murcia). Geomorphology 24, pp CNIG (CENTRO NACIONAL DE INFORMACIÓN GEOGRÁFICA) 1992: Atlas Nacional De España. Sección II, Grupo 7, Edafología. Instituto Geográfico Nacional, Madrid. ISBN HOFRICHTER R. (Hrsg.), 2002: Das Mittelmeer: Fauna, Flora, Ökologie. Bd.1.Allgemeiner Teil. Spektrum Akademischer Verlag Heidelberg, Berlin. ISBN SCHINNER F., ÖHLINGER R., KENDELER E. AND MARGESIN R., 1996: Methods in Soil Biology. Springer Verlag Berlin. ISBN SHARPLEY A.N., DANIEL T.C., EDWARDS D.R., 1993: Phosphorus Movement in the Landscape. J. Prod. Agric. Vol. 6, no. 4, pp

Which map shows the stream drainage pattern that most likely formed on the surface of this volcano? A) B)

Which map shows the stream drainage pattern that most likely formed on the surface of this volcano? A) B) 1. When snow cover on the land melts, the water will most likely become surface runoff if the land surface is A) frozen B) porous C) grass covered D) unconsolidated gravel Base your answers to questions