Changing Biogeochemical Flows

Coral Reef BleachingBiogeochemical cycles are the pathways by which elements like carbon, phosphorus, nitrogen and sulfur, or compounds like water, flow between living organisms and the environment. Human activities can alter these cycles be producing or consuming in different quantities. For example, agricultural fertilizer and soil erosion have substantially increased levels of biologically available nitrogen and phosphorous in natural systems. Human production of biologically available nitrogen, primarily driven by the synthetic production of nitrogen fertilizer, is now greater than all forms of natural production combined. Flow of phosphorous into the oceans, primarily driven by the use of fertilizer from mines and livestock manure, is roughly three times the preindustrial level. Excess nitrogen decreases plant diversity in terrestrial ecosystems, and the combination of excess nitrogen and phosphorous in water bodies leads to algal blooms and eutrophication.

Learning Objectives

  • L1: Summarize each of the major biogeochemical cycles.
  • L2: Identify areas for intervention in each of the biogeochemical cycles whereby human intervention could mitigate downstream impacts.
  • L3: Relate specific changes in each biogeochemical cycle with the corresponding human health impacts.

Resources

Singh N, Kaur M, Katnoria JK. Analysis on bioaccumulation of metals in aquatic environment of Beas River Basin: A case study from Kanjli wetland. GeoHealth [Internet]. 2017. Publisher's VersionAbstract

Wetlands, the biological filters of the Earth, play an important role in biochemical transformation of various pollutants. Wetland plants, in this direction, help in accumulating various contaminants from aquatic bodies. Considering this, the present study was planned to estimate different metals (Cd, Cu, Cr, Co, Fe, Pb, Zn, and Mn) in water, sediment, soil, and plant (4 aquatic and 12 terrestrial) samples of Kanjli wetland, Kapurthala, Punjab (India), and a Ramsar site. It was observed that the contents of Cd and Pb in water samples were higher than limits prescribed by Bureau of Indian standards. Bioaccumulation and translocation factors for various metals were also calculated. Although all the plant species were found to be hyperaccumulator for one or the other metal studied, maximum six metals (Cd, Co, Fe, Mn, Pb, and Zn) were bioaccumulated in Panicum antidotale among aquatic plant species while (Cd, Cu, Fe, Mn, Pb, and Zn) in Lantana camara and Ageratum conyzoids among terrestrial plants species. It is evident that all these plants have potential to phytoremediate various inorganic pollutants and can act as bioindicators. The physicochemical characteristics revealed high biochemical oxygen demand (BOD) and nitrate (NO3) contents and low dissolved oxygen (DO) in water samples while the high content of phosphates in soil and sediment samples.

Galvani AP, Bauch CT, Anand M, Singer BH, Levin SA. Human–environment interactions in population and ecosystem health. PNAS [Internet]. 2016;113 (51) :14502–14506. Publisher's VersionAbstract

As the global human population continues to grow, so too does our impact on the environment. The ingenuity with which our species has harnessed natural resources to fulfill our needs is dazzling. Even as we tighten our grip on the environment, however, the escalating extent of anthropogenic actions destabilizes long-standing ecological balances (12). The dangers of mining, refining, and fossil fuel consumption now extend beyond occupational or proximate risks to global climate change (3). Among a plethora of environmental problems, extreme climate events are intensifying (45). Storms, droughts, and floods cause direct destruction, but also have pervasive repercussions on food security, infectious disease transmission, and economic stability that take their toll for many years. For example, within weeks of the catastrophic wind and flood damage from the 2016 Hurricane Matthew in Haiti, there was a dramatic surge in cholera, among other devastating repercussions (67). In a world where 1% of the population possesses 50% of the wealth (8), those worst affected by extreme climatic events and the aftermath are also the least able to rebound.

Hunter DJ, Frumkin H, Jha A. Preventive Medicine for the Planet and Its Peoples. The New England Journal of Medicine [Internet]. 2017. Publisher's VersionAbstract

“Health is the human face of climate change” was the motivating idea behind the Climate and Health conference held at the Carter Center in Atlanta on Thursday, February 16, 2017. Originally scheduled by the Centers for Disease Control and Prevention (CDC), which then postponed it indefinitely, the meeting was resurrected by a coalition of nongovernmental organizations and universities and convened by former Vice President Al Gore. More than 300 attendees and a worldwide audience watching the live stream listened to more than 25 speakers addressing the health effects of climate change, the role of health professionals in adapting to these effects and communicating with the public and policymakers, and the health benefits of climate-change mitigation.

Putnam AE, Broecker WS. Human-induced changes in the distribution of rainfall. Science Advances [Internet]. 2017;3 (5). Publisher's VersionAbstract

A likely consequence of global warming will be the redistribution of Earth’s rain belts, affecting water availability for many of Earth’s inhabitants. We consider three ways in which planetary warming might influence the global distribution of precipitation. The first possibility is that rainfall in the tropics will increase and that the subtropics and mid-latitudes will become more arid. A second possibility is that Earth’s thermal equator, around which the planet’s rain belts and dry zones are organized, will migrate northward. This northward shift will be a consequence of the Northern Hemisphere, with its large continental area, warming faster than the Southern Hemisphere, with its large oceanic area. A third possibility is that both of these scenarios will play out simultaneously. We review paleoclimate evidence suggesting that (i) the middle latitudes were wetter during the last glacial maximum, (ii) a northward shift of the thermal equator attended the abrupt Bølling-Allerød climatic transition ~14.6 thousand years ago, and (iii) a southward shift occurred during the more recent Little Ice Age. We also inspect trends in seasonal surface heating between the hemispheres over the past several decades. From these clues, we predict that there will be a seasonally dependent response in rainfall patterns to global warming. During boreal summer, in which the rate of recent warming has been relatively uniform between the hemispheres, wet areas will get wetter and dry regions will become drier. During boreal winter, rain belts and drylands will expand northward in response to differential heating between the hemispheres.

Almada AA, Golden CD, Osofsky SA, Myers SS. A case for Planetary Health/Geohealth. GeoHealth [Internet]. 2017;1 (2) :75-78. Publisher's VersionAbstract

Concern has been spreading across scientific disciplines that the pervasive human transformation of Earth's natural systems is an urgent threat to human health. The simultaneous emergence of “GeoHealth” and “Planetary Health” signals recognition that developing a new relationship between humanity and our natural systems is becoming an urgent global health priority—if we are to prevent a backsliding from the past century's great public health gains. Achieving meaningful progress will require collaboration across a broad swath of scientific disciplines as well as with policy makers, natural resource managers, members of faith communities, and movement builders around the world in order to build a rigorous evidence base of scientific understanding as the foundation for more robust policy and resource management decisions that incorporate both environmental and human health outcomes.

Sokolow SH, Jones IJ, Merlijn J, La D, Cords O, Knight A, Lund A, Wood CL, Lafferty KD, Hoover CM, et al. Nearly 400 million people are at higher risk of schistosomiasis because dams block the migration of snail-eating river prawns. Philosophical Transactions of the Royal Society B [Internet]. 2017;372 (1722). Publisher's VersionAbstract

 

Dams have long been associated with elevated burdens of human schistosomiasis, but how dams increase disease is not always clear, in part because dams have many ecological and socio-economic effects. A recent hypothesis argues that dams block reproduction of the migratory river prawns that eat the snail hosts of schistosomiasis. In the Senegal River Basin, there is evidence that prawn populations declined and schistosomiasis increased after completion of the Diama Dam. Restoring prawns to a water-access site upstream of the dam reduced snail density and reinfection rates in people. However, whether a similar cascade of effects (from dams to prawns to snails to human schistosomiasis) occurs elsewhere is unknown. Here, we examine large dams worldwide and identify where their catchments intersect with endemic schistosomiasis and the historical habitat ranges of large, migratory Macrobrachium spp. prawns. River prawn habitats are widespread, and we estimate that 277–385 million people live within schistosomiasis-endemic regions where river prawns are or were present (out of the 800 million people who are at risk of schistosomiasis). Using a published repository of schistosomiasis studies in sub-Saharan Africa, we compared infection before and after the construction of 14 large dams for people living in: (i) upstream catchments within historical habitats of native prawns, (ii) comparable undammed watersheds, and (iii) dammed catchments beyond the historical reach of migratory prawns. Damming was followed by greater increases in schistosomiasis within prawn habitats than outside prawn habitats. We estimate that one third to one half of the global population-at-risk of schistosomiasis could benefit from restoration of native prawns. Because dams block prawn migrations, our results suggest that prawn extirpation contributes to the sharp increase of schistosomiasis after damming, and points to prawn restoration as an ecological solution for reducing human disease.

This article is part of the themed issue ‘Conservation, biodiversity and infectious disease: scientific evidence and policy implications’.

 

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