Guano

Guano (via Spanish from Quechua: wanu) is the accumulated excrement of seabirds and bats. As a manure, guano is a highly effective fertilizer due to its exceptionally high content of nitrogen, phosphate and potassium: nutrients essential for plant growth. Guano was also, to a lesser extent, sought for the production of gunpowder and other explosive materials. The 19th-century guano trade played a pivotal role in the development of modern input-intensive farming, but its demand began to decline after the discovery of the Haber–Bosch process of nitrogen fixing led to the production of synthetic fertilizers. The demand for guano spurred the human colonization of remote bird islands in many parts of the world, resulting in some of the first examples of U.S. colonialism and the expansion of the British Empire. The guano mining process resulted in ecological degradation through the loss of millions of seabirds. Unsustainable guano mining in caves alters cave shape, causing bats to abandon the roost. Guano mining also involved the poor treatment and enslavement of workers such as Chinese immigrants, Native Hawaiians, and African diaspora. Guano plays important ecological roles due to its role in dispersing nutrients. Cave ecosystems, in particular, are often wholly dependent on bats to provide nutrients via their guano, which supports bacteria, fungi, invertebrates, and vertebrates. The loss of bats from a cave can result in the extinction of species that rely on their guano. Guano also has a role in shaping caves, as its high acidity results in erosion. Bird guano may react with the rocky substrate of islands like basalt to form authigenic, phosphatic minerals including taranakite and leucophosphite. It has high levels of nutrients like nitrate and ammonium. By mass, it is 8–21% nitrogen; the nitrogen content is about 80% uric acid, 10% protein, 7% ammonia, and 0.5% nitrate. Some of bird guano's most common chemical elements are phosphorus, calcium, and magnesium. When freshly excreted, the guano of insectivorous bats consists of fine particles of insect exoskeleton, which are largely composed of chitin. Elements found in large concentrations include carbon, nitrogen, sulfur, and phosphorus. Through the action of bacteria and fungi, the fresh guano decays rapidly, usually losing its organic matter the fastest. Organic matter usually does not persist in a cave guano deposit at depths greater than a few centimeters. Fresh guano contains about 2.4–7 times as much carbon as nitrogen; the carbon-to-nitrogen ratio drops or remains similar when sampling older guano. Fresh guano has a pH of 5.1–7.3, making it neutral or somewhat acidic. However, as it ages, the guano becomes strongly acidic, reaching pH levels of 2.7–4.1. Similar to bird guano, the acidic properties of the guano and limestone of the cave can interact to create phosphatic minerals such as whitlockite, taranakite, variscite, spheniscidite, montgomeryite, and leucophosphite. Other minerals found in guano include quartz, graphite, gypsum, bassanite, and mica. Guano composition varies among bat species with different diets, however. In comparing guano from insectivores (Mexican free-tailed bats), frugivores (Rodrigues flying foxes), and sanguivores (common vampire bats), a 2007 study found that the three did not differ significantly in proportions of organic matter or percentage of carbon in dry matter. They did differ significantly in percentage of carbon in organic matter, with the sanguivore's value greater than the frugivore's. The sanguivore and insectivore had a greater percentage of nitrogen in both organic matter and dry matter than the frugivore. In terms of phosphorus, however, the insectivore and frugivore had higher values than the sanguivore. The frugivore had the greatest carbon-to-nitrogen ratio due to its very low nitrogen content. The sanguivore had both the greatest nitrogen-to-phosphorus ratio and carbon-to-phosphorus ratio. The word 'guano' originates from the Andean indigenous language Quechua, which refers to any form of dung used as an agricultural fertilizer. Archaeological evidence suggests that Andean people have collected guano from small islands and points located off the desert coast of Peru for use as a soil amendment for well over 1,500 years and perhaps as long as 5,000 years. Spanish colonial documents suggest that the rulers of the Inca Empire assigned great value to guano, restricted access to it, and punished any disturbance of the birds with death. The Guanay cormorant has historically been the most abundant and important producer of guano. Other important guano producing species off the coast of Peru are the Peruvian pelican and the Peruvian booby. In November 1802, Alexander von Humboldt first encountered guano and began investigating its fertilizing properties at Callao in Peru, and his subsequent writings on this topic made the subject well known in Europe. Though Europeans were aware of its fertilizing properties, guano was not widely used before this time. Cornish Chemist Humphry Davy delivered a series of lectures which he compiled into a bestselling book about the role of nitrogenous manure as a fertilizer. In them, he highlighted the special efficacy of Peruvian guano, noting that it made the 'sterile plains' of Peru fruitful. Though Europe had marine seabird colonies and thus, guano, it was of poorer quality because its potency was leached by high levels of rainfall and humidity. The arrival of commercial whaling on the Pacific coast of South America contributed to scaling of its guano industry. Whaling vessels carried consumer goods to Peru such as textiles, flour, and lard; unequal trade meant that ships returning north were often half empty, leaving entrepreneurs in search of profitable goods that could be exported. In 1840, Francisco Quirós y Ampudia negotiated a deal to commercialize guano export among a merchant house in Liverpool, a group of French businessmen, and the Peruvian government. This agreement resulted in the abolition of all preexisting claims to Peruvian guano; thereafter, it was the exclusive resource of the State. By nationalizing its guano resources, the Peruvian government was able to collect royalties on its sale, becoming the country's largest source of revenue. Some of this income was used by the State to free its more than 25,000 black slaves. Peru also used guano revenue to abolish the head tax on its indigenous citizens. This export of guano from Peru to Europe has been suggested as the vehicle that brought a virulent strain of potato blight from the Andean highlands that began the Irish Potato Famine.