Influence of seabird guano and camelid dung fertilization on the nitrogen isotopic composition of field-grown maize (Zea mays)

Organic fertilizers have the capacity to alter the nitrogen isotopic composition of plants. Camelid dung and seabird guano are two potentially important fertilizers in the agricultural systems of western South America, particularly Peru and Chile. This paper presents isotopic data (δ¹³C and δ¹⁵N) from field grown plants (maize, Zea mays) fertilized with the following four treatments: CO (control, no fertilizer applied), AS (ammonium sulfate, a chemical fertilizer), DU (camelid dung), and SG (seabird guano). Plants were grown in experimental plots in the Virú Valley, northern Peru. Plants fertilized with the chemical fertilizer presented very similar isotopic compositions compared to the control. Conversely, the camelid dung fertilized plants were characterized by higher δ¹⁵N values compared to the control plants (by 1.8 to 4.2‰ depending on the plant part). The seabird guano fertilized plants were greatly enriched in ¹⁵N in comparison to the control plants (by 11.3 to 20.0‰). The results of this study have important implications for the reconstruction of human diet using isotopic data derived from bone collagen and related tissues, particularly in the prehispanic Andes, but also in Europe and North America during the 19th century, when Peruvian seabird guano was used extensively. Specifically, the interpretation of the relative contributions of plant and animal protein to the diet on the basis of bulk isotopic compositions of bone collagen (or similar tissues) may be confounded by camelid dung fertilization if the carbon isotopic compositions of the two sources are similar. Likewise, the interpretation of the relative contributions of maize and marine protein may be confounded by seabird guano fertilization.     

Salt weathering of sandstone at the Angkor monuments,Cambodia: identification of the origins of salts using sulfur and strontium isotopes

The Angkor monuments in northwestern Cambodia, which are primarily made of sandstone, are suffering from deterioration due to salt weathering. In order to elucidate the sources of the salts and salt weathering process, this paper analyzed bulk chemical compositions and S (sulfur) and Sr (strontium) isotopic ratios for the salts and surrounding environmental materials. At places where bats inhabit the structures, various kinds of sulfate and phosphate salts are formed on the surface of the sandstone. The results of the analysis demonstrate that the S and P (phosphorus) components in the salts are primarily derived from bat guano. Moreover, Ca (calcium), which is the major element in the salts, is suggested to be derived from both bat guano and the sandstone. The isotopic data strongly suggests that bat guano is related to salt weathering. Removal of these animal excrements is essential for future conservation of these monuments. On the other hand, exfoliation of sandstone commonly occurs due to crystallization of calcite (CaCO₃) on platform surfaces of pyramid-type monuments. A large amount of Ca in calcite is suggested to be derived from calcite cement of the building sandstone.     

Chemical Alteration of Lithic Artefacts: an Experimental Case Study on the effect of Guano on Stone Flakes and Its Contextualization in the Archaeological Assemblage of Azokh Cave (Southern Caucasus)

Chemical weathering of archaeological material is well known; however, while there have been a number of experimental studies demonstrating different types and degrees of chemical alteration on faunal remains, little attention has been paid to stone tools, and the few studies that exist relate mainly to siliceous materials and water‐induced chemical alteration. Azokh Cave, located in the South Caucasus, contains a Middle Pleistocene to Holocene infill, and detailed macro‐ and microscopic examination of the lithic assemblages recovered there indicates potential chemical weathering of the stone artefacts. The cave is also currently home to one of the largest bat colonies in the region, and their guano forms a significant component of the infill of the inner galleries. Based on these two factors, an experimental pilot study was set up to artificially chemically alter a range of stone flakes produced specifically for the task, in order to determine the nature and likely cause of weathering. The experimental flakes, produced from different raw materials, were buried in fresh bat guano for up to two years. The results reported herein demonstrate that in a relatively short time, the highly acidic composition of bat guano strongly affects calcium‐bearing rocks (e.g., limestone, basalt) altering their entire surface. Similar comparisons may be made with chemical alteration evident on archaeological lithics from Azokh Cave, suggesting that bat guano has played a significant role in diagenetic alteration.